An autoradiographic analysis of ascending projections from the medullary reticular formation in the rat

Ascending projections from the several nuclei of the medullary reticular formation were examined using the autoradiographic method. The majority of fibers labeled after injections of [3H]leucine into nucleus gigantocellularis ascended within Forel's tractus fasciculorum tegmenti which is located ventrolateral to the medial longitudinal fasciculus. Nucleus gigantocellularis injections produced heavy labeling in the pontomesencephalic reticular formation, the intermediate layers of the superior colliculus, the pontine and midbrain central gray, the anterior pretectal nucleus, the ventral midbrain tegmentum including the retrorubral area, the centromedian-parafascicular complex, the fields of Forel/zona incerta, the rostral intralaminar nuclei and the lateral hypothalamic area. Nucleus gigantocellularis projections to the rostral forebrain were sparse. Labeled fibers from nucleus reticularis ventralis, like those from nucleus gigantocellularis, ascended largely in the tracts of Forel and distributed to the pontomedullary reticular core, the facial and trigeminal motor nuclei, the pontine nuclei and the dorsolateral pontine tegmentum including the locus coeruleus and the parabrachial complex. Although projections from nucleus reticularis ventralis diminished significantly rostral to the pons, labeling was still demonstrable in several mesodiencephalic nuclei including the cuneiform-pedunculopontine area, the mesencephalic gray, the superior colliculus, the anterior pretectal nucleus, the zona incerta and the paraventricular and intralaminar thalamic nuclei. The main bundle of fibers labeled by nucleus gigantocellularis-pars alpha injections ascended ventromedially through the brainstem, just dorsal to the pyramidal tracts, and joined Forel's tegmental tract in the midbrain. With the brainstem, labeled fibers distributed to the pontomedullary reticular formation, the locus coeruleus, the raphe pontis, the pontine nuclei, and the dorsolateral tegmental nucleus and adjacent regions of the pontine gray. At mesodiencephalic levels, labeling was present in the rostral raphe nuclei (dorsal, median and linearis), the mesencephalic gray, the deep and intermediate layers of the superior colliculus, the medial and anterior pretectal nuclei, the ventral tegmental area, zona incerta as well as the mediodorsal and reticular nuclei of the thalamus. Injections of the parvocellular reticular nucleus labeled axons which coursed through the lateral medullary tegmentum to heavily innervate lateral regions of the medullary and caudal pontine reticular formation, cranial motor nuclei (hypoglossal, facial and trigeminal) and the parabrachial complex.(ABSTRACT TRUNCATED AT 400 WORDS)     

A lectin horseradish peroxidase study of the origin of ascending fibers in the medial forebrain bundle of the rat. The upper brainstem

The origins of projections within the medial forebrain bundle from the upper brainstem were examined with the horseradish peroxidase technique. Labeled cells were found in approximately 15 upper brainstem nuclei following injections of a conjugate of horseradish peroxidase and wheat germ agglutinin at various levels of the medial forebrain bundle. Labeled nuclei included (from caudal to rostral): dorsal and ventral parabrachial nuclei; Kolliker-Fuse nucleus; dorsolateral tegmental nucleus; A7 (lateral pontine tegmentum medial to lateral lemniscus); median and dorsal raphe nuclei; distinct group of cells oriented mediolaterally in the dorsal pontine tegmentum below the central gray; B9 (ventral midbrain tegmentum dorsal to medial lemniscus); retrorubral nucleus; nucleus of Darkschewitsch, interfascicular nucleus; rostral and caudal linear nuclei; ventral tegmental area; medial part of substantia nigra, pars compacta; and the supramammillary nucleus. With the exception of the ventral parabrachial nucleus, Kolliker-Fuse, A7, B9 and substantia nigra, pars compacta, each of the nuclei mentioned above sent strong projections along the medial forebrain bundle to the rostral forebrain. Sparse labeling was observed throughout the pontine and midbrain reticular formation. With the exception of the dorsal raphe nucleus, projections to the most anterior regions of the medial forebrain bundle (level of the anterior commissure) essentially only arose from presumed dopamine-containing nuclei-retrorubral nucleus (A8 area), interfascicular nucleus, rostral and caudal linear nuclei, substantia nigra pars compacta, and ventral tegmental area. Evidence was reviewed indicating that major forebrain sites of termination for these dopaminergic nuclei are structures that have been collectively referred to as the 'ventral striatum'. It is concluded from the present findings that several pontine and mesencephalic cell groups are in a position to exert a strong, direct effect on structures in the anterior forebrain and that the medial forebrain bundle is the main communication route between the upper brainstem and the forebrain.     

The cells of origin of the incertofugal projections to the tectum,thalamus, tegmentum and spinal cord in the rat: A study using the autoradiographic and horseradish peroxidase methods

Efferent projections of the zona incerta were examined in the rat using the autoradiographic and horseradish peroxidase methods, with special reference to the cytoarchitectonic structure of the zona incerta.Autoradiographic experiments showed that the incertofugal fiber systems reach ipsilaterally to the thalamus (lateral dorsal, central lateral, ventral lateral geniculate, parafascicular, subparafascicular and reuniens nuclei, and posterior nuclear complex), to the hypothalamus (dorsal, lateral and posterior hypothalamic areas), to the tectum (medial pretectal area, deep pretectal and pretectal nuclei, superior colliculus and periaqueductal gray) and to the midbrain tegmentum, pons and medulla oblongata (subcuneiform, cuneiform and red nuclei, nuclei of the posterior commissure and Darkschewitsch, interstitial nucleus of Cajal, pedunculopontine tegmental nucleus, oral and caudal pontine reticular nuclei, nucleus raphe magnus, gigantocellular reticular nucleus, pontine gray and inferior olivary complex). Contralaterally, incertal efferent fibers reach to the zona incerta.Cells of origin of the incertofugal fiber systems to the tectum, thalamus, tegmentum and spinal cord were examined using the retrograde horseradish peroxidase method. Cells of origin of the incertotectal pathway are located mainly in the ventral and caudal parts of the zona incerta and partly in the antero-polar, dorsal and postero-polar parts. Cells projecting to the thalamus (at least to the lateral dorsal and central lateral nuclei) are situated in the ventral and caudal parts of the zona incerta, but they are rare in the other incertal structures. Cells of origin of the incertotegmental system are located mainly in the dorsal, magnocellular and caudal parts and partly in the antero- and postero-polar parts, but they are not situated in the ventral part. Cells of the magnocellular part project more caudally to the medulla oblongata and spinal cord than those of the other parts of the zona incerta. Forel's field contains many cells projecting to the tegmentum.The results provide good evidence that the cells of origin of efferent projections are topographically organized and are related to cytoarchitectonic areas within the zona incerta.     

A study of subcortical afferents to the hippocampal formation in the rat.

The distribution of neurons in diencephalon and brainstem which project upon the hippocampal formation has been analyzed in adult rats by the injection of horseradish peroxidase into different parts of the hippocampus and dentate gyrus and the related retrohippocampal structures, including the subicular complex and the entorhinal cortex. Any large injection of horseradish peroxidase inlo the hippocampal region results in the retrograde labeling of some neurons in each of the following structures: in the thalamus—the nucleus reuniens, the parataenial and paraventricular nuclei, the anterodorsal and antermedial nuclei, and the laterodorsal and lateral posterior nuclei; in the hypothalamus, septum and preoptic region—the medial septal nucleus and the diagonal band of Broca, the substantia innominata, the lateral preoptic area, the magnocellular preoptic nucleus, and the anterior amygdaloid area, the dorsomedial hypothalamic nucleus, the lateral and posterior hypothalamic areas, the ventral premammillary nucleus, the supramammillary region, and parts of the tuberomammillary and lateral and medial mammillary nuclei: in the brainstem: the ventral tegmental area, the substantia nigra, the interpeduncular and interfascicular nuclei, the dorsal and median nuclei of the raphe, the dorsal and laterodorsal tegmental nuclei, the locus coeruleus, the central gray, and certain of the tegmental reticular fields.It is clear that these afferents to the hippocampal formation do not comprise a single, homogeneous system, and that their terminations within the hippocampal region are not restricted to a particular topographic level (i.e. septal, intermediate or temporal).     

Substance P-containing neurons in the pontomesencephalic tegmentum of the human brain.

We have employed immunohistochemical and computerized morphometric procedures to study substance P-containing neurons in the tegmentum of adult humans. An estimated 192,500 +/- 40,500 substance P-containing neurons were found in three main cytoarchitectural regions: the mesencephalic reticular formation, the central gray, and the pontine reticular formation. The morphology of the immunoreactive neurons varied according to the region in which they were found. On the basis of size alone two types of substance P-containing neurons, large and small, were readily distinguishable by eye and measurement. Within each of the three main regions it was possible to distinguish distinct subgroups using cell size, morphology and position. Large neurons were concentrated in the caudal midbrain (pedunculopontine tegmental nuclei), in the oral pontine reticular nucleus and in the lateral dorsal tegmental nucleus. In contrast, small neurons were concentrated in the rostral mesencephalic reticular formation (cuniform nuclei). Both small and large neurons were found in the midbrain and pontine raphe nuclei. In addition, small neurons were concentrated in discrete midline regions (the periaqueductal gray, the tegmental nuclei of the pontine central gray, and the interpeduncular nucleus). The findings suggest that the majority of neurons in the brainstem tegmental nuclei previously identified as cholinergic also contain substance P in humans.     

Distribution of premotor neurons for orbicularis oculi motoneurons in the cat, with particular reference to possible pathways for blink reflex

After injecting horseradish peroxidase into the facial nucleus regions containing orbicularis oculi motoneurons, labeled neuronal cell bodies were found in the lateral medullary reticular formation, pretectal olivary nucleus, sensory trigeminal nuclei, lateral and medial parabrachial nuclei, ventromedial reticular formation medial to the facial nucleus, red nucleus and its surroundings, anterior horn of the upper cervical cord, medullary raphe nuclei, oculomotor nucleus and its surroundings, nuclei of Darkschewitsch, Cajal and Edinger-Westphal, ventral part of the midbrain central gray, pontine tegmentum, lateral vestibular nucleus and deep layers of the superior colliculus.     

Projections from the intracerebellar nuclei to the ventral midbrain tegmentum in the rat

The present study was undertaken to provide anatomical evidence, in the rat, for a direct projection from the cerebellum towards structures, other than the red nucleus, which belong to the ventral midbrain tegmentum, by using the retrograde as well as the anterograde horseradish peroxidase transport method. Following unilateral injection in the ventral midbrain tegmentum of horseradish peroxidase, free or conjugated to wheat germ agglutinin, sparing the red nucleus, retrogradely labeled neurons were found in the contralateral cerebellar lateral nucleus and, at lower density, in the interpositus nucleus. No labeled neurons were found in the fastigial nucleus of either side. Anterogradely labeled axons from lectin coupled horseradish peroxidase injection sites in the lateral and interpositus nuclei reached the contralateral ventral midbrain tegmentum. Terminal labeling was observed in the entire red nucleus as well as in the lateral division of the ventral tegmental area of Tsai, in the dorsal region of the substantia nigra pars compacta, and in the medial part of the retrorubral field. No terminal labeling was found in the caudal linear nucleus, interfascicular nucleus, peripeduncular nucleus, rostral linear nucleus of the raphe, substantia nigra pars lateralis and the substantia nigra pars reticulata. Terminal labeling was also not observed in the ventral midbrain tegmentum following horseradish peroxidase injection in lateral and interpositus nuclei of rats pretreated with kainic acid. In conclusion, it is noteworthy that, besides the red nucleus, the sole structures of ventral midbrain tegmentum receiving cerebellar efferents are those with a higher density of dopaminergic cells.     

大鼠终纹床核卵圆核及其邻近区域的传出纤维联系——WGA-HRP顺行追踪法研究

本实验选用150～260g的雄性Sprague-Dawley大鼠13只,把WGA-HRP/HRP混合水溶液加压注入一侧终纹床核群前外侧区的卵圆核区域,冰冻切片,TMB法呈色后,在中枢看到顺行标记终末最密集的部位是:下丘脑后部外侧区、中央杏仁核、中脑中央灰质、臂旁核、三叉神经中脑核、蓝斑;比较多的部位是视前区、下丘脑室周区、弓状核、丘脑中线核群、内侧纽核、腹侧背盖核、脚桥背盖核、中脑网状结构、中缝背核以及迷走神经复合体;在线形中缝核、中央上核、腹侧背盖区、黑质,以及延髓中介核,也看到少量标记终末。本工作对卵圆核的传出纤维联系,进行了较全面的观察。     

The organization of afferent projections to the midbrain periaqueductal gray of the rat

The retrograde transport technique was utilized in the present study to investigate the afferent projections to the periaqueductal gray of the rat. Iontophoretic injections of horseradish peroxidase were made into the periaqueductal gray of 22 experimental animals and into regions adjacent to the periaqueductal gray in 6 control animals. Utilization of the retrograde transport method permitted a quantitative analysis of the afferent projections not only to the entire periaqueductal gray, but also to each of its four intrinsic subdivisions. The largest cortical input to this midbrain region arises from areas 24 and 32 in the medial prefrontal cortex. The basal forebrain provides a significant input to the periaqueductal gray and this arises predominantly from the ipsilateral lateral and medial preoptic areas and from the horizontal limb of the diagonal band of Broca. The hypothalamus was found to provide the largest descending input to the central gray. Numerous labeled cells occurred in the ventromedial hypothalamic nucleus, the lateral hypothalamic area, the posterior hypothalamic area, the anterior hypothalamic area, the perifornical nucleus and the area of the tuber cinereum. The largest mesencephalic input to the periaqueductal gray arises from the nucleus cuneiformis and the substantia nigra. The periaqueductal gray was found to have numerous intrinsic connections and contained a significant number of labeled cells both above and below the injection site in each case. Other structures containing significant label in the midbrain and isthmus region included the nucleus subcuneiformis, the ventral tegmental area, the locus coeruleus and the parabrachial nuclei. The medullary and pontine reticular formation provide the largest input to the periaqueductal gray from the lower brain stem. The midline raphe magnus and superior central nucleus also supply a significant fiber projection to the central gray. Both the trigeminal complex and the spinal cord provide a minor input to this region of the midbrain.The sources of afferent projections to the periaqueductal gray are extensive and allow this midbrain region to be influenced by motor, sensory and limbic structures. In addition, evidence is provided which indicates that the four subdivisions of the central gray receive differential projections from the brain stem as well as from higher brain structures.     

Retrograde labeling of neurons in the brain stem following injections of [3H]choline into the forebrain of the rat

Summary In an attempt to identify cholinergic neurons of the brain stem which project to the forebrain, retrograde labeling of neurons in the brain stem was examined by autoradiography following injections of 20 Ci [³H]choline into the thalamus, hypothalamus, basal forebrain and frontal cortex. After injections into the thalamus, retrogradely labeled neurons were evident within the lateral caudal mesencephalic and dorsolateral oral pontine tegmentum (particularly in the laterodorsal and pedunculopontine tegmental nuclei) and in smaller number within the latero-medial caudal pontine (Reticularis pontis caudalis, Rpc) and medullary (Reticularis gigantocellularis, Rgc) reticular formation. Following [³H]choline injections into the lateral hypothalamus and into the basal forebrain, retrogradely labeled neurons were localized in the dorsolateral caudal midbrain and oral pontine tegmentum and in smaller number in the medial medullary reticular formation (Rgc), as well as in the midbrain, pontine and medullary raphe nuclei. After injections into the anterior medial frontal cortex, a small number of retrogradely labeled cells were found in the brain stem within the laterodorsal tegmental nucleus and the dorsal raphe nucleus. In a parallel immunohistochemical study, choline acetyltransferase (ChAT)-positive neurons were found to be located in most of the regions of the reticular formation where cells were retrogradely labeled from the forebrain following [³H]choline injections. These results suggest that multiple cholinergic neurons within the lateral caudal midbrain and dorsolateral oral pontine tegmentum and a few within the caudal pontine and medullary reticular formation project to the thalamus, hypothalamus and basal forebrain and that a limited number of pontine cholinergic neurons project to the frontal cortex.Abbreviations of Neuroanatomical Terms 3 oculomotor nuc - 4 trochlear nuc - 4V fourth ventricle - 6 abducens nuc - 7 facial nuc - 7n facial nerve - 8n vestibulocochlear nerve - 10 dorsal motor nuc vagus - 12 hypoglossal nuc - 12n hypoglossal nerve - Amb ambiguus nuc - Aq cerebral aqueduct - bic brachium inf colliculus - CB cerebellum - CG central gray - CLi caudal linear nuc raphe - Cnf cuneiform nuc - cp cerebral peduncle - Cu cuneate nuc - D nuc Darkschewitsch - DCo dorsal cochlear nuc - DLL dorsal nuc lateral lemniscus - DPB dorsal parabrachial nuc - DR dorsal raphe nuc - dsc dorsal spinocerebellar tract - DTg dorsal tegmental nuc - dtgx dorsal tegmental decussation - ECu external cuneate nuc - Fl flocculus - IC inferior colliculus - icp inferior cerebellar peduncle - IF interfascicular nuc - InC interstitial nuc Cajal - IO inferior olive - IP interpeduncular nuc - KF Kolliker-Fuse nuc - LC locus coeruleus - Ldt laterodorsal tegmental nuc - Ifp longitudinal fasciculus pons - ll lateral lemniscus - LRt lateral reticular nuc - LRtS5 lateral reticular nucsubtrigeminal - LSO lateral superior olive - LTz lateral nuctrapezoid body - LVe lateral vestibular nuc - mcp middle cerebellar peduncle - Me5 mesencephalic trigeminal nuc - MGD medial geniculate nuc, dorsal - ml medial lemniscus - mlf medial longitudinal fasciculus - MnR median raphe nuc - Mo5 motor trigeminal nuc - MSO medial superior olive - MTz medial nuc trapezoid bbody - MVe medial vestibular nuc - PBg parabigeminal nuc - Pgl nuc paragigantocellularis lateralis - Pn pontine nuc - PPTg pedunculopontine tegmental nuc - Pr5 principal sensory trigeminal - PrH prepositive hypoglossal nuc - py pyramidal tract - Rgc reticularis gigantocellularis - Rgca reticularis gigantocellularis pars alpha - Rmes reticularis mesencephali - RMg raphe magnus nuc - RN red nuc - Ro nuc Roller - ROb raphe obscurus nuc - Rp reticularis parvicellularis - RPa raphe pallidus nuc - Rpc reticularis ponds caudalis - RPn raphe pontis nuc - Rpo reticularis pontis oralis - RR retrorubral nuc - rs rubrospinal tract - RtTg reticulotegmental nuc pons - s5 sensory root trigeminal nerve - SC superior colliculus - SCD superior colliculus,deep layer - SCI superior colliculus, intermediate layer - scp superior cerebellar peduncle - SCS superior colliculus, superficial layer - SGe suprageniculate nuc pons - SNC substantia nigra compact - SNL substantia nigra,lateral - SNR substantia nigra, reticular - SolL solitary tract nuc,lateral - SolM solitary tract nuc, medial - sp5 spinal tract trigeminal nerve - sp5I spinal trigeminal nuc, interpositus - Sp5O spinal trigeminal nuc, oral - spth spinothalamic tract - SpVe spinal vestibular nuc - SuVe superior vestibular nuc - tp tectopontine - ts tectospinal tract - tz trapezoid body - VCo ventral cochlear nuc - VLL ventral nuc lateral lemniscus - VPB ventral parabrachial nuc - vsc ventral spinocerebellar tract - VTA ventral tegmental area - VTg ventral tegmental nuc - vtgx ventral tegmental decussation - xscp decussation superior cerebellar peduncle This investigation was supported by grants from the Medical Research Council (MRC) of Canada (MT-6464: BEJ and MT 7376: AB). B.E. Jones holds a Chercheur Boursier Senior Award from the Fonds de la Recherche en Santé du Quebec (FRSQ), and A. Beaudet a Scientist Award from MRC     

Somatostatin-like immunoreactivity in the brain of an electric fish (Apteronotus leptorhynchus) identified with monoclonal antibodies.

The immunohistochemical localization of somatostatin-like immunoreactive (SSir) cells and fibers in the brain of the gymnotiform teleost (Apteronotus leptorhynchus) was investigated using well-characterized monoclonal antibodies directed against somatostatin-14 and -28. Large populations of SSir neurons occur in the basal forebrain, diencephalon and rhombencephalon and a dense distribution of fibers and terminal fields is found in the ventral, dorsomedial and dorsolateral telencephalon, hypothalamus, centralis posterior thalamus, subtrigeminal nucleus, the motor nucleus of vagus and in the ventrolateral medulla. Immunoreactive neurons in the forebrain are concentrated mainly in the ventral telencephalic areas, the region of the anterior commissure and entopeduncular nucleus. In a fashion similar to the large basal telencephalic cells of other species, the cells of the rostral nucleus entopeduncularis have a significant projection to the dorsal telencephalon. The preoptic region and the peri- and paraventricular hypothalamic nuclei are richly endowed with SSir cells; some of these cells contribute fibres to the pituitary stalk and gland. In the thalamus, only the n. centralis posterior stands out for the density of SSir cells and terminals; these cells appear to project to the prepacemaker nucleus, thus suggesting an SS influence on electrocommunication. In the mesencephalon most SSir cells occur in the optic tectum, torus semicircularis and interpeduncular nucleus. The rhombencephalic SSir cells have a wider distribution (central gray, raphe, sensory nuclei, reticular formation, electrosensory lateral line lobe and surrounding the central canal). The results of this study show the presence of SS in various sensory systems, electromotor system and specific hypothalamic nuclei, suggesting a modulatory role in the processing of sensory information, electrocommunication, endocrine and motor activities.     

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 thePhaseolus 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.     

Afferents to the periaqueductal gray in the rat. A horseradish peroxidase study

Afferent projections to the periaqueductal gray matter in the rat have been studied by use of the retrograde axonal transport of horseradish peroxidase. Iontophoretic injections of horseradish peroxidase were made in dorsal, lateral and medial areas of the periaqueductal gray, primarily at intercollicular levels. The pattern of projections was similar in all of the injections restricted to the periaqueductal gray. Within the brainstem, numerous reticular formation nuclei were labeled, including nucleus reticularis lateralis, nucleus raphe magnus, pallidus and obscurus, the nucleus reticularis pontis oralis and caudalis, the paralemniscal nucleus and the dorsal and ventral parabrachial nuclei. At diencephalic levels, dense projections were seen from the parafascicular nucleus, dorsal premamillary nucleus, zona incerta, dorsomedial and ventromedial nuclei of the hypothalamus and the retrochiasmatic area, in the ventral portion of the anterior hypothalamus. At forebrain levels, occasional cells were seen in the medial preoptic area, lateral septum and the anterior cingulate cortex. Control injections of horseradish peroxidase into structures adjacent to the periaqueductal gray matter included three well localized deposits in the dorsal raphe. Retrogradely-labeled cells were found in lateral reticular nucleus of the medulla, nucleus raphe magnus, nucleus reticularis pontis caudalis, locus ceruleus, dorsal and ventral parabrachial nuclei, substantia nigra and the lateral hypothalamus. No labeled cells were found in the habenular nuclei. It is suggested that many of the descending hypothalamic and forebrain afferents may be relay centers for descending hippocampal formation efferents. Many of the periaqueductal gray afferent systems receive a direct projection from the hippocampal formation and could therefore coordinate influences from this limbic center with information on homeostatic mechanisms controlled by the hypothalamus. The numerous brainstem afferents to the periaqueductal gray could be involved in relay of ascending sensory information important for initiating any of several behavioral responses known to be controlled by the periaqueductal gray. In addition, certain raphe afferents might play a part in a feedback loop of the pain suppression circuit of which the periaqueductal gray is an important component.     

Amygdaloid projections to the mesencephalon,pons and medulla oblongata in the cat

Summary Amygdalotegmental projections were studied in 26 cats after injections of horseradish peroxidase (HRP) in the diencephalon, midbrain and lower brain stem and in 6 cats after injection of ³H-leucine in the amygdala. Following HRP injections in the posterior hypothalamus, periaqueductal gray (PAG) and tegmentum many retrogradely labeled neurons were present in the central nucleus (CE) of the amygdala, primarily ipsilaterally. Injections of HRP in the posterior hypothalamus and mesencephalon also resulted in the labeling of neurons in the basal nucleus, pars magnocellularis.Following ³H-leucine injections in CE and adjacent structures autoradiographically labeled fibers were present in the stria terminalis and ventral amygdalofugal pathways. In the mesencephalon heavily labeled fiber bundles were located lateral to the red nucleus. Labeled fibers and terminals were distributed to the mesencephalic reticular formation, substantia nigra, ventral tegmental area and PAG. In the pontine and medullary tegmentum the bulk of passing fibers was located laterally in the reticular formation. Many labeled fibers and terminals were distributed to the parabrachial nuclei, locus coeruleus, nucleus subcoeruleus and lateral tegmental fields. Many terminals were also present in the solitary nucleus and dorsal motor nucleus of the vagus nerve.The location of the cells of origin and the distribution of the terminals of the amygdalotegmental projection suggest that this pathway plays an important role in the integration of somatic and autonomic responses associated with affective defense.Abbreviations A nucleus ambiguus - AL lateral amygdaloid nucleus - AQ cerebral aqueduct - BC brachium conjunctivum - BL basal amygdaloid nucleus, pars magnocellularis - BM basal amygdaloid nucleus, pars parvocellularis - BP brachium pontis - CE central amygdaloid nucleus - CI internal capsule - CN cochlear nucleus - CO cortical amygdaloid nucleus - CP cerebral peduncle - DCN dorsal column nuclei - DMV dorsal motor nucleus of the vagus nerve - E entopeduncular nucleus - F fornix - FLA longitudinal association bundle - GP globus pallidus - H hippocampal formation - 1C inferior colliculus - INJ injection site - LC locus coeruleus - IO inferior olive - LG lateral geniculate nucleus - LRN lateral reticular nucleus - LT lateral tegmental field - M medial amygdaloid nucleus - MB mammilary body - MG medial geniculate nucleus - ML medial lemniscus - MT medial tegmental field - MV motor nucleus of the trigeminus - OC optic chiasm - OT optic tract - P putamen - PAG periaqueductal gray - PB parabrachial nuclei - PC posterior commissure - PH posterior hypothalamus - PT pyramidal tract - PV principal sensory nucleus of the trigeminus - PYR pyriform cortex - R red nucleus - RF reticular formation - S solitary nucleus - SC nucleus subcoeruleus - SN substantia nigra - SO superior olive - SOL solitary nucleus - SPV spinal trigeminal complex - ST stria terminalis - VC vestibular complex - VTA ventral tegmental area - VII facial nucleus - XII hypoglossal nucleus     

Distribution of somatostatinlike immunoreactivity in the brain of the little brown bat (Myotis lucifugus)

The distribution of somatostatinlike immunoreactive (SLI) perikarya, axons, and terminals was mapped in subcortical areas of the brain of the little brown bat, Myotis lucifugus, using light microscopic immunocytochemistry. A preponderance of immunoreactivity was localized in reticular, limbic, and hypothalamic areas including: (1) in the forebrain: the bed nucleus of the stria terminalis; lateral preoptic, dorsal, anterior, lateral and posterior hypothalamic areas; amygdaloid, periventricular, arcuate, supraoptic, suprachiasmatic, ventromedial, dorsomedial, paraventricular, lateral and medial mammillary, and lateral septal nuclei; the nucleus of the diagonal band of Broca and nucleus accilmbens septi; (2) in the midbrain: the periaqueductal gray, interpeduncular, dorsal and ventral tegmental, pretectal, and Edinger-Westphal nuclei; and (3) in the hindbrain: the superior central and parabrachial nuclei, nucleus incertus, locus coeruJeus, and nucleus reticularis gigantocellularis. Other areas containing SLI included the striatum (caudate nucleus and putamen), zona incerta, infundibulum, supramammiilary and premammillary nuclei, medial and dorsal lateral geniculate nuclei, entopeduncular nucleus, lateral habenular nucleus, central medial thalamic nucleus, central tegmental field, linear and dorsal raphe nuclei, nucleus of Darkschewitsch, superior and inferior colliculi, nucleus ruber, substantia nigra, mesencephalic nucleus of V, inferior olivary nucleus, inferior central nucleus, nucleus prepositus, and deep cerebellar nuclei. While these results were similar in some respects to those previously reported in rodents, they also provided interesting contrasts.     

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.     

Origin of projections from the midbrain raphe nuclei to the hypothalamic paraventricular nucleus in the rat: A combined retrograde and anterograde tracing study

A number of neuronal functions governed by the hypothalamic paraventricular nucleus are influenced by serotonin, and it is generally believed that the moderate density of serotonin-immunoreactive fibres and terminals within the paraventricular nucleus originates from the midbrain dorsal and median raphe nuclei. To further evaluate the intricate anatomy of projections from brain stem raphe nuclei of the rat, a combination of retrograde and anterograde tracing experiments were conducted to determine the medullary raphe nuclei projection to the paraventricular nucleus. Rhodamine-labelled latex microspheres, Cholera toxin subunit B and FluoroGold we used as retrograde tracers. Intracerebroventricular injections into the third ventricle of all retrograde tracers labelled a distinct population of neurons in the dorsal raphe situated in the subependymal stratum adjacent to the cerebral aqueduct indicating that these cells take up the tracer from the cerebrospinal fluid. Very few retrogradely labelled neurons were seen in the median raphe after i.c.v. administration of the tracers. Retrograde tracers delivered into the medial part of the paraventricular nucleus labelled no further cells in the midbrain dorsal and median raphe nuclei, whereas a substantial number of retrogradely labelled cells emerged in the pontine raphe magnus. However, when the retrograde tracers were delivered into the lateral part of the paraventricular nucleus, avoiding leakage of the tracer into the ventricle, very few labelled neurons were seen in the dorsal and median raphe, whereas the prominent labelling of raphe magnus neurons persisted. The anatomical organization of nerve fibres terminating in the area of paraventricular nucleus originating from midbrain raphe nuclei was studied in a series of anterograde tracing experiments using the plant lectin Phaseolus vulgaris leucoagglutinin. Injections delivered into the dorsal raphe or median raphe labelled but a few fibres in the paraventricular nucleus proper. A high number of fine calibered nerve fibres overlying the ependyma adjacent to the paraventricular nucleus was, however, seen after the injections into the subependymal rostral part of the dorsal raphe. Injections delivered into the raphe magnus gave rise to a dense plexus of terminating fibres in the parvicellular parts of the paraventricular nucleus and moderately innervated the posterior magnocellular part of the paraventricular nucleus as well as the magnocellular supraoptic nucleus. Concomitant visualization of serotonin-immunoreactive neurons and retrograde FluoroGold-tracing from the paraventricular nucleus revealed that none of the serotonergic neurons of the raphe magnus projects to this nucleus, while a few of the neurons putatively projecting to the paraventricular nucleus from the median raphe are serotonergic.

The current observations suggest that the raphe magnus constitute by far the largest raphe input to the paraventricular nucleus and strongly questions the earlier held view that most raphe fibres innervating the paraventricular nucleus are derived from the midbrain dorsal and median raphe. However, the source of serotonergic innervation of the paraventricular nucleus remains elusive.