Connections of the anterior ectosylvian visual area (AEV)

Summary We have previously described a visual area situated in the cortex surrounding the deep infolding of the anterior ectosylvian sulcus of the cat (Mucke et al. 1982). Using orthograde and retrograde transport methods we now report anatomical evidence that this anterior ectosylvian visual area (AEV) is connected with a substantial number of both cortical and subcortical regions. The connections between AEV and other cortical areas are reciprocal and, at least in part, topographically organized: the rostral AEV is connected with the bottom region of the presylvian sulcus, the lower bank of the cruciate sulcus, the rostral part of the ventral bank of the splenial sulcus, the rostral portion of the lateral suprasylvian visual area (LS) and the lateral bank of the posterior rhinal sulcus; the caudal AEV is connected with the bottom region of the presylvian sulcus, the caudal part of LS, the ventral part of area 20 and the lateral bank of the posterior rhinal sulcus. Subcortically, AEV has reciprocal connections with the ventral medial thalamic nucleus (VM), with the medial part of the lateralis posterior nucleus (LPm), as well as with the lateralis medialis-suprageniculate nuclear (LM-Sg) complex. These connections are also topographically organized with more rostral parts of AEV being related to more ventral portions of the LPm and LM-Sg complex. AEV also projects to the caudate nucleus, the putamen, the lateral amygdaloid nucleus, the superior colliculus, and the pontine nuclei. It is concluded that AEV is a visual association area which functionally relates the visual with both the motor and the limbic system and that it might play a role in the animal's orienting and alerting behavior.Abbreviations Ac aqueductus cerebri - AEs anterior ectosylvian sulcus - ALLS anterolateral lateral suprasylvian area - AMLS anteromedial lateral suprasylvian area - ASs anterior suprasylvian sulcus - Cd caudate nucleus - CL central lateral nucleus - Cl claustrum - Cos coronal sulcus - Crs cruciate sulcus - DLS dorsal lateral suprasylvian area - GI stratum griseum intermediale - GP stratum griseum profundum - IC inferior colliculus - LAm lateral amygdaloid nucleus - LGNd dorsal nucleus of lateral geniculate body - LGNv ventral nucleus of lateral geniculate body - Llc nucleus lateralis intermedius, pars caudalis - LM nucleus lateralis medialis - LPl nucleus lateralis posterior, pars lateralis - LPm nucleus lateralis posterior, pars medialis - Ls lateral sulcus - MD nucleus mediodorsalis - MG medial geniculate body - MSs middle suprasylvian sulcus - Ndl nucleus dorsolateralis pontis - Nl nucleus lateralis pontis - Np nucleus peduncularis pontis - Npm nucleus paramedianus pontis - Nrt nucleus reticularis tegmenti pontis - Nv nucleus ventralis pontis - Ped cerebral peduncle - PEs posterior ectosylvian sulcus - Pg periaqueductal gray - PLLS posterolateral lateral suprasylvian area - PMLS posteromedial lateral suprasylvian area - PSs presylvian sulcus - Pul pulvinar - Put putamen - R red nucleus - Sg suprageniculate nucleus - SN substantia nigra - Sps splenial sulcus - Syls sylvian sulcus - T trapezoid body - VA ventral anterior nucleus - VL ventral lateral nucleus - VLS ventral lateral suprasylvian area - VM ventral medial nucleus - VPL ventral posterolateral nucleus - VPM ventral posteromedial nucleus Sponsored by Max-Planck-Society during part of the studySponsored by Thyssen FoundationSponsored by Alexander von Humboldt-Foundation     

GABAergic projections from the thalamic reticular nucleus to the anteroventral and anterodorsal thalamic nuclei of the rat

We have studied GABAergic projections from the thalamic reticular nucleus to the anterior thalamic nuclei of the rat by combining retrograde labelling with horseradish peroxidase and GABA-immunohistochentistry. Small iontophoretic injections of the tracer into subnuclei of the anterior thalamic nuclear complex resulted in retrograde labelling of cells in the rostrodorsal pole of the ipsilateral thalamic reticular nucleus. All of these cells were also GABA-positive. The projections were topographically organized. Neurons located in the most dorsal part of the rostral reticular nucleus projected to the dorsal half of both the posterior subdivision and the medial subdivision of the anteroventral thalamic nucleus, and to the rostral portion of the anterodorsal thalamic nucleus. Immediately ventral to this group of neurons, but still within the dorsal portion of the reticular nucleus, a second group of neurons, extending from the dorsolateral to the dorsomedial edge of the nucleus, projected to the ventral parts of the posterior and medial subdivisions of the anteroventral nucleus. Following injection of tracer into the dorsal part of the rostral anteroventral nucleus, retrograde labelled GABA-containing cell bodies were also found in the ipsilateral anterodorsal nucleus.     

The cingulate bridge between allocortex,isocortex and thalamus

The Fink-Heimer silver impregnation and the autoradiographic methods were used to study the fiber projections of the cingulate cortex in the squirrel monkey. It was found that this cortex provides inputs to the striatum, thalamus and several areas of isocortex. Evidence was found for a number of fiber projections (1) Fibers from the anterior limbic area were traced to the central part of the head of the caudate nucleus, putamen, septum, dorsomedial nucleus of the thalamus, anterior hypothalamus and lateral basal nucleus of the amygdala. (2) Projections from the cingulate area were traced to the lateral part of the head of the caudate nucleus, putamen, and to the centromedian, anterior, lateral dorsal, and lateral ventral thalamic nuclei and to medial nuclei of the base of the pons. (3) There were projections from the retrosplenial area of the anterior, lateral dorsal, dorsomedial, and posterior thalamic nuclei and lateral nuclei of the pons. These results indicate that most of the cingulate gyrus is an intermediate structure between the thalamus and overlying cortex. The anterior limbic area forms a bridge between the thalamus and other areas of the cingulate gyrus and the frontal cortex. (4) The retrosplenial area and the posterior part of the cingulate area bridge the adjacent visual sensory association cortex and pelvic areas of the sensory motor cortex, respectively. These areas of the cingulate gyrus project directly to the striatum as well as to the thalamus, structurally providing limbic system input to subcortical motor structures.     

The cingulate bridge between allocortex, isocortex and thalamus.

The Fink-Heimer silver impregnation and the autoradiographic methods were used to study the fiber projections of the cingulate cortex in the squirrel monkey. It was found that this cortex provides inputs to the straitum, thalamus and several areas of isocortex. Evidence was found for a number of fiber projections (1) Fibers from the anterior limbic area were traced to the central part of the head of the caudate nucleus, putamen, septum, dorsomedial nucleus of the thalamus, anterior hypothalamus and lateral basal nucleus of the amygdala. (2) Projections from the cingulate area were traced to the lateral part of the head of the caudate nucleus, putamen, and to the centromedian, anterior, lateral dorsal, and lateral ventral thalamic nuclei and to medial nuclei of the base of the pons. (3) There were porjections from the retrosplenial area of the anterior, lateral dorsal, dorsomedial, and posterior thalamic nuclei and lateral nuclei of the pons. These results indicate that most of the cingulate gyrus is an intermediate structure between the thalamus and overlying cortex. The anterior limbic area forms a bridge between the thalamus and other areas of the cingulate gyrus and the frontal cortex. (4) the retrosplenial area and the posterior part of the cingulate area bridge the adjacent visual snesory association cortex and pelvic areas of the snesory motor cortex, respectively. These areas of the cingulate gyrus project directly to the striatum as well as to the thalamus, structurally providing limbic system input to subcortical motor structures.     

Topographic organization and collateralization of the projections of the anterior and laterodorsal thalamic nuclei to cingulate areas 24 and 29 in the rat

Fast blue and Rhodamine microspheres were used to analyze the topography and collateralization of the limbic nuclei of the thalamus to 4 defined areas of the cingulate gyrus (anterior 24, posterior 24, anterior 29, and posterior 29). The anterodorsal nucleus and the anteroventral nucleus project to posterior area 24 and all of area 29. The anteromedial nucleus projects generally to both areas 24 and 29, but principally to anterior area 24. The laterodorsal nucleus projects only to area 29. The anterior and posterior portions of the thalamic nuclei topographically project to the anterior and posterior regions of the cingulate gyrus, respectively. Neurons in the medial region of the anterior nuclei project to the anterior area of the cingulate gyrus while neurons located in the lateral region project to posterior areas. Collaterals (9-13%) from the anteromedial nucleus project diffusely to areas 24 and 29, while collaterals from other nuclei project primarily to areas adjacent to each other. Modulation of limbic system functions probably occurs via these projection fibers. Furthermore, the idea appears to be reinforced that at least a dual and coupled function exists for these direct thalamocingulate connections.     

Differential projection from the motor and limbic cortical regions to the mediodorsal thalamic nucleus in the dog

The cortical afferents to the mediodorsal thalamic nucleus in the dog were studied by using horseradish peroxidase. Small injections allowed to establish two specific projection zones connected separately with the lateral and medial segments of the nucleus. The lateral segment received the major projection from the dorsal half of the hemisphere. It included premotor and part of the motor cortices in the anterior sigmoid gyrus and precruciate areas as well as the presylvian cortex. The medial segment of the nucleus was innervated by the limbic areas of the ventral half of the hemisphere. These areas included the medioventrally located genual, subcallosal and piriform cortices, as well as the cortex of the ventral bank of the anterior rhinal sulcus and the caudal part of the orbital gyrus. The cortical fields situated between these two main cortical zones, both on the lateral and medial surfaces (rhinal and sylvian sulci and anterior cingular gyrus, respectively) sent projections to both medial and lateral segments of the nucleus. These results indicate that in the mediodorsal thalamic nucleus may take place the integration of information from two functionally defined systems, the motor and limbic ones.     

Interconnections of the auditory cortical fields of the cat with the cingulate and parahippocampal cortices

Summary The interconnections of the auditory cortex with the parahippocampal and cingulate cortices were studied in the cat. Injections of the anterograde and retrograde tracer WGA-HRP were performed, in different cats (n = 9), in electrophysiologically identified auditory cortical fields. Injections in the posterior zone of the auditory cortex (PAF or at the PAF/AI border) labeled neurons and axonal terminal fields in the cingulate gyrus, mainly in the ventral bank of the splenial sulcus (a region that can be considered as an extension of the cytoarchitectonic area Cg), and posteriorly in the retrosplenial area. Labeling was also present in area 35 of the perirhinal cortex, but it was sparser than in the cingulate gyrus. Following WGA-HRP injection in All, no labeling was found in the cingulate gyrus, but a few neurons and terminals were labeled in area 35. In contrast, no or very sparse labeling was observed in the cingulate and perirhinal cortices after WGA-HRP injections in the anterior zone of the auditory cortex (AI or AAF). A WGA-HRP injection in the cingulate gyrus labeled neurons in the posterior zone of the auditory cortex, between the posterior ectosylvian and the posterior suprasylvian sulci, but none was found more anteriorly in regions corresponding to AI, AAF and AII. The present data indicate the existence of preferential interconnections between the posterior auditory cortex and the limbic system (cingulate and parahippocampal cortices). This specialization of posterior auditory cortical areas can be related to previous observations indicating that the anterior and posterior regions of the auditory cortex differ from each other by their response properties to sounds and their pattern of connectivity with the auditory thalamus and the claustrum.Abbreviations AAF anterior auditory cortical field - aes anterior ectosylvian sulcus - AI primary auditory cortical field - AII secondary auditory cortical field - ALLS anterior-lateral lateral suprasylvian visual area - BF best frequency - C cerebral cortex - CC corpus callosum - CIN cingulate cortex - CL claustrum - DLS dorsal lateral suprasylvian visual area - DP dorsoposterior auditory area - E entorhinal cortex - IC inferior colliculus - LGN lateral geniculate nucleus - LV pars lateralis of the ventral division of the MGB - LVe lateral ventricule - MGB medial geniculate body - OT optic tract - OV pars ovoidea of the ventral division of the MGB - PAF posterior auditory cortical field - pes posterior ectosylvian sulcus - PLLS posterior-lateral lateral suprasylvian visual area - PS posterior suprasylvian visual area - PU putamen - RE reticular complex of thalamus - rs rhinal sulcus - SC superior colliculus - SS suprasylvian sulcus - T temporal auditory cortical field - TMB tetramethylbenzidine - VBX ventrobasal complex of thalamus, external nucleus - VL pars ventrolateralis of the ventral division of the MGB - VLS ventrolateral suprasylvian visual area - VPAF ventroposterior auditory cortical field - WGA-HRP wheat germ agglutinin labeled with horseradish peroxidase - wm white matter     

Segregation of lemniscal inputs and motor cortex outputs in cat ventral thalamic nuclei: application of a novel technique

Summary A double labeling method that permits accurate delineation of the terminals of medial lemniscal fibers was used to determine whether thalamic neurons projecting to motor cortex in the cat are in a position to be contacted by such terminals. Thalamic neurons in the VL nucleus were retrogradely labeled by injections of fluorogold placed in the cytoarchitectonically defined area 4, while lemniscal axons and their terminal boutons were anterogradely labeled, in a Golgi-like manner, from injections of Fast Blue placed under physiological control in different parts of the contralateral dorsal column nuclei. In additional experiments, spinothalamic fibers were similarly labeled by injections of Fast Blue in the spinal cord. The results reveal that there is no significant overlap in the distributions of lemniscal terminals and motor cortex-projecting neurons and that no somata or proximal dendrites of motor cortex-projecting neurons are in a position to receive lemniscal terminals. Spinothalamic terminals, on the other hand, end in clusters around motor cortex-projecting neurons in the VL nucleus as well as in other nuclei and are a more likely route for short latency somatosensory inputs to the motor cortex.Abbreviations AD anterodorsal nucleus - AM anteromedial nucleus - AP area postrema - AV anteroventral nucleus - C cuneate nucleus - CeM central medial nucleus - CL central lateral nucleus - CM centre médian nucleus - EC external cuneate nucleus - G gracile nucleus - L limitans nucleus - LD lateral dorsal nucleus - LP lateral posterior nucleus - MGM magnocellular medial geniculate nucleus - MD mediodorsal nucleus - MTT mamillothalamic tract - MV medioventral nucleus - Pc paracentral nucleus - Pf parafascicular nucleus - Po posterior nuclei - R reticular nucleus - RF fasciculus retroflexus - S solitary nucleus - SG suprageniculate nucleus - T spinal trigeminal nucleus - VA ventral anterior nucleus - VIN vestibular nuclei - VL ventral lateral nucleus - VMb basal ventral medial nucleus - VMp principal ventral medial nucleus - VPL ventral posterior lateral nucleus - VPM ventral posterior medial nucleus - ZI zona incerta - 1,2,3a,3b,4 fields of cerebral cortex - C4, C5, C6 spinal cord segments - 5SP,5ST spinal trigeminal nucleus and tract - 10, 12 vagal and hypoglossal nuclei     

Subcortical projections to the prefrontal cortex in the rat as revealed by the horseradish peroxidase technique

The sources and distribution of subcortical afferents to the anterior neocortex were investigated in the rat using the horseradish peroxidase technique. Injections into the prefrontal cortex labelled, in addition to the mediodorsal thalamic nucleus, neurons in a total of fifteen subcortical nuclei, distributed in the basal telencephalon, claustrum, amygdala, thalamus, subthalamus, hypothalamus, mesencephalon and pons. Of these, the projections from the zona incerta, the lateroposterior thalamic nucleus, and the parabrachial region of the caudal mesencephalon to the prefrontal cortex have not previously been described.Different parts of the mediodorsal thalamic nucleus project to different areas of the frontal cortex. Thus, horseradish peroxidase injections in the most ventral pregenual part of the medial cortex labelled predominantly neurons in the medial anterior and dorsomedial posterior parts of the mediodorsal nucleus; injections into the more dorsal pregenual area labelled only neurons in the lateral and ventral parts of the nucleus; injections placed supragenually labelled neurons in the dorsolateral posterior part of the nucleus; and injections into the dorsal bank of the anterior rhinal sulcus labelled neurons in the centromedial part of the nucleus.Several other subcortical nuclei had projections overlapping with that of the mediodorsal thalamic nucleus. Five different types of such overlap were distinguished: (1) cell groups labelled after horseradish peroxidase injections into one of the subfields of the projection area of the mediodorsal nucleus (defined as the prefrontal cortex), but not outside this area (parataenial nucleus of the thalamus); (2) cell groups labelled both after injection into a subfield of the projection area of the mediodorsal nucleus and after injections in a restricted area outside this area (anteromedial, ventral and laterposterior thalamic nuclei); (3) cell groups labelled after injections into all subfields of the mediodorsal nucleus projection area, but not outside this area (ventral tegmental area, basolateral nucleus of amygdala); (4) cell groups labelled after injections into any area of the anterior neocortex, including the mediodorsal nucleus projection area (parabrachial neurons of the posterior mesencephalon); (5) cell groups labelled after all neocortical injections investigated (claustrum, magnocellular nuclei of the basal forebrain, lateral hypothalamus, zona incerta, intralaminar thalamic nuclei, nuclei raphe dorsalis and centralis superior, and locus coeruleus).We can draw the following conclusions from these and related findings. First, because of the apparent overlap of projections of the mediodorsal, the anteromedial and ventral thalamic nuclei in the rat, parts of the prefrontal cortex can also be called ‘cingulate’ and ‘premotor’. Second, on the basis of projections from parts of the mediodorsal nucleus, the prefrontal cortex of the rat can be subdivided into areas corresponding to those in other species. Third, the neocortex receives afferents from a large number of subcortical cell groups outside the thalamus, distributed from the telencephalon to the pons; however, the prefrontal cortex seems to be the only neocortical area innervated by the ventral tegmental area and amygdala. Finally, neither the prefrontal cortex nor the mediodorsal thalamic nucleus receives afferents from regions directly involved in sensory and motor functions.     

Topographic arrangement of the projection from the anterior thalamic nuclei to the cingulate cortex in the cat

After injection of HRP into the cingulate and its adjacent cortical areas, neuronal cells were retrogradely labeled ipsilaterally in the anterior, lateral, ventral, intralaminar and midline thalamic nuclei. Most of them occurred in the anterior nuclei, and a topographic correlation was revealed in the projections from the anterior thalamic nuclei to the cingulate gyrus: the rostral part of the cingulate gyrus receives fibers predominantly from the lateral part of the AM and additionally from the caudomedial part of the AV. The caudal part of the cingulate gyrus receives fibers from the medial part of the anteromedial nucleus (AM) and the rostromedial part of the anteroventral nucleus (AV). The intermediate part of the cingulate gyrus receives fibers from the intermediate part of the AM and the caudal half of the AV.     

The distribution and topographical organization in the thalamus of anterogradely-transported horseradish peroxidase after spinal injections in cat and raccoon

Summary The distribution of anterogradely-transported horseradish peroxidase (HRP) was examined in the rostral mesencephalon and thalamus of cats and raccoons that had received injections of HRP in the cervical and/or lumbosacral enlargements of the spinal cord. Labeling was consistently observed in a large number of loci. All regions previously identified as targets of spinomesencephalic or spinothalamic fibers were included. Evidence of topographical organization was obtained in several regions. Adjacent fields of labeling were often separable on the basis of the distribution, appearance and topographical organization of the labeling. Subject to the methodological constraints imposed by the possibilities of transneuronal and/or collateral labeling, we conclude that a wide variety of loci in the thalamus receive direct spinal input. The organization of these projections suggests that each terminal region may be associated with different aspects of spinal cord function.Abbreviations A anterior pretectal nucleus - AD anterodorsal n. - AM anteromedial n. - AV anteroventral n. - CeM centromedial n. - CD centrodorsal n. (raccoon) - CL centrolateral n. - CM centre median - H habenula - L n.a limitans - LD laterodorsal n. - LG lateral geniculate - LGv lateral geniculate, ventral subnucleus - LP lateral posterior n. - LPvi lateral posterior n., ventral intermediate part - M medial pretectal n. - mc medial geniculate, magnocellular subnucleus - MD mediodorsal n. - MG medial geniculate - ML medial lemniscus - N pretectal nucleus of the optic tract - nBIC n. of the brachium of the inferior colliculus - O olivary pretectal n. - OT optic tract - P posterior nucleus of Rioch - Pc paracentral n. - Pf parafascicular n. - PO posterior group of thalamus - PP posterior pretectal n. - Pt parataenial n. - Pul pulvinar - Pv paraventricular n. of thalamus - R reticular n. - Re n. reuniens - Rh rhomboid n. - RN red nucleus - SG suprageniculate n. - Sm n. submedius - SN substantia nigra - Spf subparafascicular n. - Tg mesencephalic tegmentum - VA ventroanterior n. - VP ventroposterior thalamus (i.e. VPM, VPI, and VPL) - VL ventrolateral n. - VM ventromedial n. - VMb ventromedial n., basal part - VPI ventroposteroinferior n. - VPL1a ventroposterolateral n., lateral part - VPLm ventroposterolateral n., medial part - VPM ventroposteromedial n. - ZI zona incerta     

Organization of serotoninergic projections from the raphé nuclei to the anterior thalamic nuclei in the rat: a combined retrograde tracing and 5-HT immunohistochemical study

We combined retrograde transport of horseradish peroxidase (HRP) with 5-hydroxytryptamine (5-HT) immunohistochemistry to study serotoninergic projections to the anterior thalamic nuclei (ATN) of the rat. Small iontophoretic injections of HRP into the anterodorsal thalamic nucleus resulted in double-labelled neurons predominantly in the ventromedial and also in the ventrolateral part of the ipsilateral dorsal raphé (DR). A smaller number of double-labelled neurons was also found in the dorsomedial part of the nucleus, predominantly ipsilaterally, and in the median raphé nucleus (MnR), close to the midline. After injection into the medial subdivision of the anteroventral thalamic nucleus, the pattern of labelling in DR and MnR was similar to that detected following injections into the anterodorsal thalamic nucleus. However, injection into the posterior subdivision of the anteroventral thalamic nucleus resulted in bilateral retrograde labelling of a few 5-HT-containing neurons in the dorsolateral part of the DR. Labelling in the ventromedial, ventrolateral and dorsomedial regions of DR and MnR was similar to that detected after injections into the medial subdivision of the anteroventral thalamic nucleus. After all injections into the ATN, double-labelled cells were found throughout the rostrocaudal extent of MnR and throughout the rostral two-thirds of DR. The caudal extension of DR was devoid of double-labelled cells. Although double-labelled cells were observed bilaterally in the dorsolateral part of the DR, the projection from DR to ATN was predominantly ipsilateral. These results show that there is an internal organization within DR such that subnuclei of the DR can be defined on the basis of their efferent projections to specific subdivisions of the ATN.     

Projections of cholinergic and non-cholinergic neurons of the brainstem core to relay and associational thalamic nuclei in the cat and macaque monkey

The projections of brainstem core neurons to relay and associational thalamic nuclei were studied in the cat and macaque monkey by combining the retrograde transport of wheat germ agglutinin conjugated with horseradish peroxidase with choline acetyltransferase immunohistochemistry. All major sensory (medial geniculate, lateral geniculate, ventrobasal), motor (ventroanterior, ventrolateral, ventromedial), associational (mediodorsal, pulvinar, lateral posterior) and limbic (anteromedial, anteroventral) thalamic nuclei of the cat were found to receive projections from cholinergic neurons located in the peribrachial area of the pedunculopontine nucleus and in the laterodorsal tegmental nucleus as well as from non-cholinergic neurons in the rostral (perirubral) part of the central tegmental mesencephalic field. Specific relay nuclei receive less than 10% of their brainstem afferents from non-cholinergic neurons located at rostral midbrain levels and receive 85-96% of their brainstem innervation from a region at midbrain-pontine junction where the cholinergic peribrachial area and laterodorsal tegmental nucleus are maximally developed. Of the total number of horseradish peroxidase-positive brainstem neurons seen after injections in various specific relay nuclei, the double-labeled (horseradish peroxidase + choline acetyltransferase) neurons represent approximately 70-85%. Three to eight times more numerous horseradish peroxidase-labeled brainstem cells were found after injections in associational (mediodorsal and pulvinar-lateral posterior complex) and diffusely cortically-projecting (ventromedial) thalamic nuclei of cat than after injections in specific relay nuclei. The striking retrograde cell labeling observed after injections in nuclei with associative functions and widespread cortical projections was due to massive afferentation from non-cholinergic parts of the midbrain and pontine reticular formation, on both ipsi- and contralateral sides. After wheat germ agglutinin-horseradish peroxidase injections in the associative pulvinar-lateral posterior complex and mediodorsal nucleus of Macaca sylvana, 45-50% of horseradish peroxidase-positive brainstem peribrachial neurons were also choline acetyltransferase-positive. While cells in the medial part of the cholinergic peribrachial area were found to project especially towards the pulvinar-lateral posterior nuclear complex in monkey, the retrograde cell labeling seen after the mediodorsal injection was mostly confined to the lateral part of both dorsal and ventral aspects of the peribrachial area.(ABSTRACT TRUNCATED AT 400 WORDS)     

The bed nucleus of the stria terminalis in the Syrian hamster: subnuclei and connections of the posterior division

The bed nucleus of the stria terminalis is a key part of a ring of cells extending between the centromedial amygdala and bed nucleus of the stria terminalis referred to as the extended amygdala. The present study describes the architecture of the bed nucleus of the stria terminalis and the connections of subnuclei in posterior bed nucleus of the stria terminalis. The hamster bed nucleus of the stria terminalis is readily allotted to anterior and posterior divisions separated by the fibers of the body of the anterior commissure. The anterior division has four subnuclei: anteromedial, anterointermediate, anterolateral, and anteroventral. Within the posterior division, there are three distinct regions: posteromedial, posterointermediate, and posterolateral. In hamsters, the posterior bed nucleus of the stria terminalis contributes to male sexual behavior, particularly chemoinvestigation. Moreover, the posterior bed nucleus of the stria terminalis is part of a neural circuit essential for mating, including the medial amygdaloid nucleus and medial preoptic area. The connections of bed nucleus of the stria terminalis, posteromedial part, bed nucleus of the stria terminalis, posterointermediate part and bed nucleus of the stria terminalis, posterolateral part were visualized by co-injection of anterograde (Phaseolus vulgaris leucoagglutinin) and retrograde (cholera toxin B) tract tracers. The bed nucleus of the stria terminalis, posterointermediate part and bed nucleus of the stria terminalis, posteromedial part have dense bidirectional connections with medial amygdaloid nucleus and cortical amygdala via the stria terminalis and ventral amygdalofugal pathway. These subnuclei also maintain bidirectional connections with steroid-concentrating areas including lateral septum, medial preoptic area, hypothalamus, and periaqueductal gray. The bed nucleus of the stria terminalis, posterointermediate part and bed nucleus of the stria terminalis, posteromedial part receive projections from the subiculum and send projections to deep mesencephalic nuclei. By contrast, the bed nucleus of the stria terminalis, posterolateral part is connected with the central amygdala, lateral hypothalamus, subthalamic nucleus, nucleus accumbens, substantia innominata, substantia nigra and thalamus. Thus, the bed nucleus of the stria terminalis, posterointermediate part and bed nucleus of the stria terminalis, posteromedial part have similar connections with areas involved in social behaviors. The bed nucleus of the stria terminalis, posterolateral part maintains connections with areas involved in motivational circuits. This supports the concept of distinct circuits within the extended amygdala which differentially link the centromedial amygdala and bed nucleus of the stria terminalis.     

Physiologic and anatomic investigation of a visual cortical area situated in the ventral bank of the anterior ectosylvian sulcus of the cat

Summary In this paper a cortical area is described that covers approximately the posterior two-thirds of the ventral bank of the anterior ectosylvian sulcus of the cat and is called anterior ectosylvian visual area (AEV).In cats anesthetized with a combination of N₂O and barbiturate we explored this area by recording extracellularly the responses of AEV neurons to visual and electric stimulation as well as by injecting HRP into physiologically verified points. AEV neurons were found to be highly sensitive to small light stimuli moving rapidly in a particular direction through their large receptive fields. The properties of 74 neurons were quantitatively analyzed. Increasing the length of the stimulus within the receptive field to more than 2 deg strongly inhibited the responses, whereas increasing the speed of the stimulus movement up to 72–120 deg/s enhanced the neuronal responsiveness. Although the majority of neurons responded to a wide range of possible directions, one clearly preferred direction could usually be found for each neuron. There was a predominance of preferred directions toward the contralateral hemifield. Anatomic and electrophysiologic connectivity studies showed that AEV receives its main afferent inputs from the lateral suprasylvian visual area (LS) and from the tecto-recipient zone of the nucleus lateralis posterior (LP)-pulvinar complex.Although these studies suggested some topographical organization within the projection from LS to AEV, the large receptive fields in AEV, the great majority of which included the central area, did not reveal a clear retinotopic order. It is concluded that AEV is a specific visual area and that functionally the extrageniculate inputs predominate.Abbreviations AEs anterior ectosylvian sulcus - ALLS anterolateral lateral suprasylvian area - AMLS anteromedial lateral suprasylvian area; - Cl Claustrum - DLS dorsal lateral suprasylvian area - LGNd dorsal nucleus of lateral geniculate body - LGNv ventral nucleus of lateral geniculate body - LM nucleus lateralis medialis - LP1a nucleus lateralis posterior, pars lateralis - LPm nucleus lateralis posterior, pars medialis - Ls lateral sulcus - MGmc magnocellular division of medial geniculate body - MGpc parvocellular division of medial geniculate body - MSs middle suprasylvian sulcus - NP nucleus posterior of Rioch - PLLS postero-lateral lateral suprasylvian area - PLs posterolateral sulcus - PMLS posteromedial lateral suprasylvian area - Pu putamen - Pul pulvinar - Sg suprageniculate nucleus - VLS ventral lateral suprasylvian area Sponsored by Max-Planck-Gesellschaft and IBRODept. of Anatomy, School of Medicine, Iwate Medical University, Morioka 020, JapanSponsored by Alexander von Humboldt-FoundationDept. of Physiology, University Medical School, Szeged, Hungary     

Restricted cortical termination fields of the midline and intralaminar thalamic nuclei in the rat.

The projections from the midline and intralaminar thalamic nuclei to the cerebral cortex were studied in the rat by means of anterograde tracing with Phaseolus vulgaris-leucoagglutinin. The midline and intralaminar nuclear complex taken as a whole projects to widespread, predominantly frontal, cortical areas. Each of the constituent thalamic nuclei has a restricted cortical projection field that overlaps only slightly with the projection fields of adjacent midline and intralaminar nuclei. The projections of the intralaminar nuclei cover a larger cortical area than those of the midline nuclei. The laminar distributions of fibres from individual midline and intralaminar thalamic nuclei are different and include both deep and superficial cortical layers. The parataenial, paraventricular and intermediodorsal midline nuclei each project to circumscribed parts of the prefrontal cortex and the hippocampal and parahippocampal regions. In the prefrontal cortex, the projections are restricted to the medial orbital, infralimbic, ventral prelimbic and agranular insular fields, and the rostral part of the ventral anterior cingular cortex. In contrast to the other midline nuclei, the rhomboid nucleus projects to widespread cortical areas. The rostral intralaminar nuclei innervate dorsal parts of the prefrontal cortex, i.e. the dorsal parts of the prelimbic, anterior cingular and dorsal agranular insular cortical fields, the lateral and ventrolateral orbital areas, and the caudal part of the ventral anterior cingular cortex. Additional projections are aimed at the agranular fields of the motor cortex and the caudal part of the parietal cortex. The lateral part of the parafascicular nucleus sends fibres predominantly to the lateral agranular field of the motor cortex and the rostral part of the parietal cortex. The medial part of the parafascicular nucleus projects rather sparsely to the dorsal part of the prelimbic cortex, the anterior cingular cortex and the medial agranular field of the motor cortex. Individual midline and intralaminar thalamic nuclei are thus in a position to directly influence circumscribed areas of the cerebral cortex. In combination with previously reported data on the organization of the midline and intralaminar thalamostriatal projections and the prefrontal corticostriatal projections the present results suggest a high degree of differentiation in the convergence of thalamic and cortical afferent fibres in the striatum. Each of the recently described parallel basal ganglia-thalamocortical circuits can thus be expanded to include projections at both the cortical and striatal levels from a specific part of the midline and intralaminar nuclear complex. The distinctive laminar distributions of the fibres originating from the different nuclei emphasize the specificity of the midline and intralaminar thalamocortical projections.     

Afferent connections of dorsal and ventral agranular insular cortex in the hamsterMesocricetus auratus

The agranular insular cortex is transitional in location and structure between the ventrally adjacent olfactory allocortex primutivus and dorsally adjacent sensory-motor isocortex. Its ventral anterior division receives major afferent projections from olfactory areas of the limbic system (posterior primary olfactory cortex, posterolateral cortical amygdaloid nucleus and lateral entorhinal cortex) while its dorsal anterior division does so from non-olfactory limbic areas (lateral and basolateral amygdaloid nuclei).The medial segment of the mediodorsal thalamic nucleus projects to both the ventral and dorsal divisions of the agranular insular cortex, to the former from its anterior portion and to the latter from its posterior portion. Other thalamic inputs to the two divisions arise from the gelatinosus, central medial, rhomboid and parafascicular nuclei. The dorsal division, but not the ventral division, receives input from neurons in the lateral hypothalamus and posterior hypothalamus.The medial frontal cortex projects topographically and bilaterally upon both ventral and dorsal anterior insular cortex, to the former from the ventrally located medial orbital and infralimbic areas, to the latter from the dorsally-located anterior cingulate and medial precentral areas, and to both from the intermediately located prelimbic area. Similarly, the ipsilateral posterior agranular insular cortex and perirhinal cortex project in a topographic manner upon the two divisions of the agranular insular cortex.Commissural input to both divisions originates from pyramidal neurons in the respective contralateral homotopical cortical area. In each case, pyramidal neurons in layer V contribute 90% of this projection and 10% arises from layer III pyramidals.In the brainstem, the dorsal raphe nucleus projects to the ventral and dorsal divisions of the agranular insular cortex and the parabrachial nucleus projects to the dorsal division.Based on their cytoarchitecture, pattern of afferent connections and known functional properties, we consider the ventral and dorsal divisions of the agranular insular cortex to be, respectively, periallocortical and proisocortical portions of the limbic cortex.     

Distribution of GABA-immunoreactive neurons in the thalamus of the squirrel monkey (Saimiri sciureus)

A light microscopic study of the cellular localization of GABA in the thalamus of the squirrel monkey (Saimiri sciureus) was undertaken by means of the indirect peroxidase-antiperoxidase method using a highly purified antiserum directed against GABA-glutaraldehyde-lysyl-protein conjugate. GABA-immunoreactive cell bodies and axon terminals were visualized in all thalamic nuclei in the squirrel monkey but their relative density varied from one nucleus to the other. At the level of the anterior nuclear group, GABA-positive cells and terminals abounded in the anterodorsal nucleus but were much less numerous in the anteromedial and anteroventral nuclei. In the nuclei of the ventral group, GABA-immunoreactive cells were found to be smaller and less numerous than nonimmunoreactive neurons. In the ventral anterior nucleus, GABA-positive neuronal profiles formed typical clusters, whereas they were more uniformly distributed in the posterior nuclei of the ventral group. In the intralaminar nuclei, GABA-immunoreactive cells and terminals abounded in the dorsal portion of the paracentral and centrolateral nuclei, whereas more caudally, GABA-positive terminals pervaded the entire parafascicular nucleus. In the mediodorsal nucleus, GABA-positive cell bodies and axon terminals formed typical clusters of various sizes scattered within the lateral parvocellular portion of the nucleus, while GABA-immunoreactive neuronal profiles were less numerous and more uniformly distributed in the medial portion of this structure. In the nuclei of the posterior group, GABA-immunoreactive neuronal profiles were uniformly distributed except in the pulvinar where they abounded in the inferior and oral parts but were scarce in the medial part. In the dorsal lateral geniculate nucleus, the magnocellular layers received the most massive GABA-positive innervation and contained the largest number of GABA-immunoreactive cell bodies. In the ventral lateral geniculate nucleus, GABA-positive cells occurred only ventrolaterally while GABA-immunoreactive terminals pervaded the entire structure. In the medial geniculate nucleus, GABA-immunoreactive cell bodies and terminals abounded particularly within the ventromedial third of the structure. In the habenula, a few GABA-immunoreactive cell bodies and numerous GABA-positive terminals were scattered throughout the lateral habenular nucleus, whereas only a few GABA-immunoreactive terminals surrounded the closely packed unreactive cells in the medial habenular nucleus. In contrast to other thalamic nuclei all neurons in the reticular nucleus displayed GABA immunoreactivity.(ABSTRACT TRUNCATED AT 400 WORDS)     

Efferent connections of the medial prefrontal cortex in the rabbit

The different cytoarchitectonic regions of the medial prefrontal cortex (mPFC) have recently been shown to play divergent roles in associative learning in rabbits. To determine if these subareas of the mPFC, including areas 24 (anterior cingulate cortex), 25 (infralimbic cortex), and 32 (prelimbic cortex) have differential efferent connections with other cortical and subcortical areas in the rabbit, anterograde and retrograde tracing experiments were performed using the Phaseolus vulgaris leukoagglutinin (PHA-L), and horseradish peroxidase (HRP) techniques. All three areas showed local dorsal-ventral projections into each of the other areas, and a contralateral projection to the homologous area on the other side of the brain. All three also revealed a trajectory through the striatum, resulting in heavy innervation of the caudate nucleus, the claustrum, and a lighter projection to the agranular insular cortex. The thalamic projections of areas 24 and 32 were similar, but not identical, with projections to the mediodorsal nucleus (MD) and all of the midline nuclei. However, the primary thalamic projections from area 25 were to the intralaminar and midline nuclei. All three areas also projected to the ventromedial and to a lesser extent to the ventral posterior thalamic nuclei. Projections were also observed in the lateral hypothalamus, in an area just lateral to the descending limb of the fornix. Amygdala projections from areas 32 and 24 were primarily to the lateral, basolateral and basomedial nuclei, but area 25 also projected to the central nucleus. All three areas also showed projections to the midbrain periaqueductal central gray, median raphe nucleus, ventral tegmental area, substantia nigra, locus coeruleus and pontine nuclei. However, only areas 24 and the more dorsal portions of area 32 projected to the superior colliculus. Area 25 and the ventral portions of area 32 also showed a bilateral projection to the parabrachial nuclei and dorsal and ventral medulla. The dorsal portions of area 32, and all of area 24 were, however, devoid of these projections. It is suggested that these differential projections are responsible for the diverse roles that the cytoarchitectonic subfields of the mPFC have been demonstrated to play in associative learning.Abbreviations ACC anterior cingullate cortex - ACN amygdaloid central nucleus - AD anterodorsal nucleus of thalamus - AIC, Iag agranular insular cortex - AM anteromedial nucleus of thalamus - AMG amygdala - AV anteroventral nucleus of thalamus - BL basolateral nucleus of amygdala - BM basomedial nucleus of amygdala - CdN, CD caudate nucleus - CL claustrum - CN centromedian nucleus of thalamus - D MV, DVM dorsal motor nucleus of vagus - IC internal capsule - L lateral nucleus of amygdala - LC locus coeruleus - LH lateral hypothalamus - MB mammillary bodies - MDN mediodorsal nucleus of thalamus - mPFC medial prefrontal cortex - MRN, R median raphe nucleus - MV medioventral nucleus of thalamus - NA nucleus ambiguus - NTS nucleus of solitary tract - PAG periaqueductal central gray - PAV, PV para ventricular nucleus of thalamus - PC paracentral nucleus of thalamus - PF parafascicular nucleus of thalamus - PN,LP pontine nuclei - PS posterior subiculum - PS CG posterior cingulate cortex - PT paratenial nucleus of thalamus - Put putamen - ReN nucleus reuniens of thalamus - RF reticular formation - RN reticular nucleus of thalamus - RhN rhomboid nucleus of thalamus - RS CX retrosplenial cortex - S septum - SC superior colliculus - SN substantia nigra - tt tenia tecta - VL ventrolateral nucleus of thalamus - VM ventromedial nucleus of thalamus - VP ventroposterior nucleus of thalamus - VTA ventral tegmental area     

Auditory corticocortical interconnections in the cat: evidence for parallel and hierarchical arrangement of the auditory cortical areas

Summary The origin and laminar arrangement of the homolateral and callosal projections to the anterior (AAF), primary (AI), posterior (PAF) and secondary (AII) auditory cortical areas were studied in the cat by means of electrophysiological recording and WGA-HRP tracing techniques. The transcallosal projections to AAF, AI, PAF and AII were principally homotypic since the major source of input was their corresponding area in the contralateral cortex. Heterotypic transcallosal projections to AAF and AI were seen, originating from the contralateral AI and AAF, respectively. PAF received heterotypic commissural projections from the opposite ventroposterior auditory cortical field (VPAF). Heterotypic callosal inputs to AII were rare, originating from AAF and AI. The neurons of origin of the transcallosal connections were located mainly in layers II and III (70–92%), and less frequently in deep layers (V and VI, 8–30%). Single unit recordings provided evidence that both homotypic and heterotypic transcallosal projections connect corresponding frequency regions of the two hemispheres. The regional distribution of the anterogradely labeled terminals indicated that the homotypic and heterotypic auditory transcallosal projections are reciprocal. The present data suggest that the transcallosal auditory interconnections are segregated in 3 major parallel components (AAF-AI, PAF-VPAF and AII), maintaining a segregation between parallel functional channels already established for the thalamocortical auditory interconnections. For the intrahemispheric connections, the analysis of the retrograde tracing data revealed that AAF and AI receive projections from the homolateral cortical areas PAF, VPAF and AII, whose neurons of origin were located mainly in their deep (V and VI) cortical layers. The reciprocal interconnections between the homolateral AAF and AI did not show a preferential laminar arrangement since the neurons of origin were distributed almost evenly in both superficial (II and III) and deep (V and VI) cortical layers. On the contrary, PAF received inputs from the homolateral cortical fields AAF, AI, AII and VPAF, originating predominantly from their superficial (II and III) layers. The homolateral projections reaching AII originated mainly from the superficial layers of AAF and AI, but from the deep layers of VPAF and PAF. The laminar distribution of anterogradely labeled terminal fields, when they were dense enough for a confident identification, was systematically related to the laminar arrangement of neurons of origin of the reciprocal projection: a projection originating from deep layers was associated with a reciprocal projection terminating mainly in layer IV, whereas a projection originating from superficial layers was associated with a reciprocal projection terminating predominantly outside layer IV. This laminar distribution indicates that the homolateral auditory cortical interconnections have a feed-forward/feed-back organization, corresponding to a hierarchical arrangement of the auditory cortical areas, according to criteria previously established in the visual system of primates. The principal auditory cortical areas could be ranked into 4 distinct hierarchical levels. The tonotopically organized areas AAF and AI represent the lowest level. The second level corresponds to the non-tonotopically organized area AII. Higher, the tonotopically organized areas VPAF and PAF occupy the third and fourth hierarchical levels, respectively.Abbreviations AAF anterior auditory cortical area - AI primary auditory cortical area - AII secondary auditory cortical area - BF best frequency - C cerebral cortex - CA caudate nucleus - CL claustrum - D dorsal nucleus of the dorsal division of the MGB - ea anterior ectosylvian sulcus - ep posterior ectosylviansulcus - IC internal capsule - LGN lateral geniculate nucleus - LV pars lateralis of the ventral division of the MGB - LVe lateral ventricule - M pars magnocellularis of the medial division of the MGB - MGB medial geniculate body - MGBv ventral division of the MGB - OT optic tract - OV pars ovoidea of the ventral division of the MGB - PAF posterior auditory cortical area - PH parahippocampal cortex - PO lateral part of the posterior group of thalamic nuclei - PU putamen - RE reticular complex of thalamus - rs rhinal sulcus - SG suprageniculate nucleus of the dorsal division of the MGB - ss suprasylvian sulcus - TMB tetrametylbenzidine - VBX ventrobasal complex - VLa ventrolateral complex - VL ventro-lateral nucleus of the ventral division of the MGB - WGA-HRP wheat germ agglutinin conjugated to horse-radish peroxidase - WM white matter - VPAF ventro-posterior auditory cortical area