Anatomical evidence for medial pulvinar connections with the posterior cingulate cortex, the retrosplenial area, and the posterior parahippocampal gyrus in monkeys

Reciprocal connections between the medial pulvinar and the limbic neocortex in monkeys were demonstrated by means of tritiated amino acid injections in the medial pulvinar and the cingulate cortex, and HRP injections in the medial pulvinar. It appears that the medial nucleus of the pulvinar sends projection fibres to the posterior cingulate gyrus (area 23), the retrosplenial area, and the posterior parahippocampal gyrus (areas TH and TF). The labeled terminals were concentrated in two bands, one in the deeper part of layer III and in layer IV, and the other in layer I. These projections were observed to be reciprocal, and the cortical afferent fibers to the medial pulvinar were found to originate from the deep layers of the cortex. The medial nucleus of the pulvinar was already known to be connected with the prefrontal cortex and with the inferior parietal lobule. Since this nucleus is now demonstrated to be connected with the posterior limbic neocortex, it is envisaged as being the thalamic counterpart of a cortical triad (prefrontal, parietal, and limbic) involved in modulating directed attention.     

Macaque monkey retrosplenial cortex: III. Cortical efferents

We have investigated the cortical efferent projections of the macaque monkey retrosplenial and posterior cingulate cortices by using (3)H-amino acids as anterograde tracers. All the injections produced extensive local connections to other portions of this region. There were also a number of extrinsic efferent cortical connections, many of which have not hitherto been reported. Major projections from the retrosplenial cortex were directed to the frontal lobe, with heaviest terminations in areas 46, 9, 10, and 11. There were also very substantial projections to the entorhinal cortex, presubiculum, and parasubiculum of the hippocampal formation, as well as to areas TH and TF of the parahippocampal cortex. Some injections led to labeling of area V4, the dorsal bank of the superior temporal sulcus, and area 7a of the parietal cortex. Projections from the posterior cingulate cortex innervated all these same regions, although the density of termination was different from the retrosplenial projections. The posterior cingulate cortex gave rise to additional projections to parietal area DP and to the cortex along the convexity of the superior temporal gyrus. The ventral portion of the posterior cingulate cortex (area 23v) gave rise to much denser efferent projections to the hippocampal formation than the dorsal portions (areas 23e and i). These connections are discussed in relation to the clinical syndromes of retrosplenial amnesia and topographic disorientation in humans commonly caused by lesions in the caudoventral portions of the retrosplenial and posterior cingulate cortices.     

Parahippocampal and retrosplenial connections of rat posterior parietal cortex

The posterior parietal cortex has been implicated in spatial functions, including navigation. The hippocampal and parahippocampal region and the retrosplenial cortex are crucially involved in navigational processes and connections between the parahippocampal/retrosplenial domain and the posterior parietal cortex have been described. However, an integrated account of the organization of these connections is lacking. Here, we investigated parahippocampal connections of each posterior parietal subdivision and the neighboring secondary visual cortex using conventional retrograde and anterograde tracers as well as transsynaptic retrograde tracing with a modified rabies virus. The results show that posterior parietal as well as secondary visual cortex entertain overall sparse connections with the parahippocampal region but not with the hippocampal formation. The medial and lateral dorsal subdivisions of posterior parietal cortex receive sparse input from deep layers of all parahippocampal areas. Conversely, all posterior parietal subdivisions project moderately to dorsal presubiculum, whereas rostral perirhinal cortex, postrhinal cortex, caudal entorhinal cortex and parasubiculum all receive sparse posterior parietal input. This indicated that the presubiculum might be a major liaison between parietal and parahippocampal domains. In view of the close association of the presubiculum with the retrosplenial cortex, we included the latter in our analysis. Our data indicate that posterior parietal cortex is moderately connected with the retrosplenial cortex, particularly with rostral area 30. The relative sparseness of the connectivity with the parahippocampal and retrosplenial domains suggests that posterior parietal cortex is only a modest actor in forming spatial representations underlying navigation and spatial memory in parahippocampal and retrosplenial cortex. © 2017 Wiley Periodicals, Inc.     

Macaque monkey retrosplenial cortex: I. three-dimensional and cytoarchitectonic organization

This is the first in a series of reports on the neuroanatomic organization and connectivity of the macaque monkey retrosplenial cortex, i.e., areas 29 and 30. To elucidate the topographic configuration of the retrosplenial cortex and adjacent structures, we have made three-dimensional computer reconstructions of the posterior cingulate region that includes the retrosplenial cortex. The largest portion of the posterior cingulate gyrus is located dorsal to the corpus callosum. At the caudal limit of the corpus callosum, the gyrus curves around the splenium, turns laterally and forms a region called the isthmus that links the cingulate and parahippocampal gyri. The isthmus contains the caudomedial lobule, which is a rostrally oriented bulge that is made up, in part, of portions of the retrosplenial cortex. To delineate the subdivisions of the retrosplenial and adjacent cortices, we conducted a cytoarchitectonic analysis by using cerebral hemispheres that were cut at oblique angles and stained with a variety of techniques, including immunohistochemistry for nonphosphorylated neurofilament protein. The dorsal bank of the callosal sulcus and the rostral surface of the isthmus are covered by the retrosplenial cortical areas 29l, 29m, and 30, whereas most of the medial surface of the posterior cingulate gyrus and the ventral bank of the posterior cingulate sulcus consist of areas 23i and 23e. The most caudoventral portion of the cingulate gyrus is composed of an area (area 23v) that resembles the retrosplenial and posterior cingulate cortices but has a much more prominent layer IV. On the dorsal bank of the calcarine sulcus, we also defined a transitional zone, area 30v, located between the retrosplenial cortex and the prestriate visual cortex.     

Thalamic connections with limbic cortex. I. Thalamocortical projections

The thalamocortical projections to limbic cortex in the cat have been studied with retrograde and anterograde axonal transport techniques. Five limbic cortical areas were identified on the basis of cytoarchitecture. The five areas are the anterior limbic area, the cingular area, the dorsal and ventral retrosplenial areas, and the presubiculum. Each of these cortical areas received small injections of horseradish peroxidase, and the afferent thalamic nuclei were identified by retrograde labelling of cells. The cortical projection of each of the anterior thalamic nuclei and the lateral dorsal nucleus was determined autoradiographically. Each of the anterior thalamic nuclei and the lateral dorsal nucleus projects to limbic cortex by two pathways. One group of fibers leaves the rostral thalamus by the fornix, pierces the corpus callosum, and joins the cingulate fasciculus to reach limbic cortex. The other group travels through the lateral thalamic peduncle and internal capsule. The anterior ventral nucleus projects primarily to the dorsal retroslenial area, particularly to layer I, the deep portion of layer II, and superficial portion of layer III. Sparse projections also exist to the ventral retrosplenial area, the cingular area, and the presubiculum. Very sparse projections to the anterior limbic area are seen. The anterior dorsal nucleus projects primarily to the ventral retrosplenial area, particularly layers I, the deep portion of layer II, and superficial layer III. Sparse projections exist to the dorsal retrosplenial area and presubiculum, but apparently no projections exist to the cingular or anterior limbic area. The anterior medial nucleus projects primarily to layers I and superficial III of the ventral retrosplenial area. Sparse projections exist to each of the other limbic cortical areas. The lateral dorsal nucleus projects extensively onto limbic cortex. Prominent projections occur to layer I, the external granular layer and lamina dessicans of the presubiculum, layers I and III-IV of the dorsal retrosplenial area, and layers I, III, and IV of the cingular area. Sparse projections occur to the ventral retrosplenial area and the anterior limbic areas. Thalamocortical projections also originate in the midline and intralaminar nuclei including the central medial reuniens, rhomboid, paracentral, central lateral, and central dorsal nuclei. These data indicate that the anterior thalamic nuclei project upon limbic cortex in a complex manner. Further, the projections to limbic cortex from the anterior nuclei overlap with projections from the lateral dorsal nucleus. This overlap of thalamic projections onto limbic cortex suggests a convergence of information from nonprimary sensory systems with information from the classical limbic system.     

Architecture and connections of retrosplenial area 30 in the rhesus monkey (Macaca mulatta).

Because of the sharp curvature of the retrosplenial region around the splenium of the corpus callosum, standard coronal sections are not appropriate for architectonic analysis of its posteroventral part. In the present study, examination of the posteroventral retrosplenial region of the rhesus monkey in sections that were orthogonal to its axis of curvature (and therefore appropriate for architectonic analysis) has permitted definition of its architecture and precise extent. This analysis demonstrated that areas 29 and 30 of the retrosplenial cortex, as well as adjacent area 23 of the posterior cingulate cortex, extend together as an arch around the splenium of the corpus callosum and maintain their topographical relationship with one another throughout their entire course. Injections of anterograde and retrograde tracers confined to retrosplenial area 30 revealed that this area has reciprocal connections with adjacent areas 23, 19 and PGm, with the mid-dorsolateral part of the prefrontal cortex (areas 9, 9/46 and 46), with multimodal area TPO in the superior temporal sulcus, as well as the posterior parahippocampal cortex, the presubiculum and the entorhinal cortex. There are also bidirectional connections with the lateroposterior thalamic nucleus, as well as the laterodorsal and the anteroventral limbic thalamic nuclei. The connectivity of area 30 suggests that it may play a role in working memory processes subserved by the mid-dorsolateral frontal cortex in interaction with the hippocampal system.     

Macaque monkey retrosplenial cortex: II. Cortical afferents

We investigated the cortical afferents of the retrosplenial cortex and the adjacent posterior cingulate cortex (area 23) in the macaque monkey by using the retrograde tracers Fast blue and Diamidino yellow. We quantitatively analyzed the distribution of labeled neurons throughout the cortical mantle. Injections involving the retrosplenial cortex resulted in labeled neurons within the retrosplenial cortex and in areas 23 and 31 (approximately 78% of the total labeled cells). In the remainder of the cortex, the heaviest projections originated in the hippocampal formation, including the entorhinal cortex, subiculum, presubiculum, and parasubiculum. The parahippocampal and perirhinal cortices also contained many labeled neurons, as did the prefrontal cortex, mainly in areas 46, 9, 10, and 11, and the occipital cortex, mainly area V2. Injections in area 23 also resulted in numerous labeled cells in the posterior cingulate and retrosplenial regions (approximately 67% of total labeled cells). As in the retrosplenial cortex, injections of area 23 led to many labeled neurons in the frontal cortex, although most of these cells were in areas 9 and 46. Larger numbers of retrogradely labeled cells were also distributed more widely in the posterior parietal cortex, including areas 7a, 7m, LIP, and DP. There were some labeled cells in the parahippocampal cortex. These connections are consistent with the retrosplenial cortex acting as an interface between the working memory functions in the prefrontal areas and the long-term memory encoding in the medial temporal lobe. The posterior cingulate cortex, in contrast, may be more highly associated with visuospatial functions.     

Organization of subcortical pathways for sensory projections to the limbic cortex. I. Subcortical projections to the medial limbic cortex in the rat

Subcortical afferent projections to the medial limbic cortex were examined in the rat by the use of retrograde axonal transport of horseradish peroxidase. Small iontophoretic injections of horseradish peroxidase were placed at various locations within the dorsal and ventral cingulate areas, the dorsal agranular and ventral granular divisions of the retrosplenial cortex and the presubiculum. Somata of afferent neurons in the thalamus and basal forebrain were identified by retrograde labeling. Each of the anterior thalamic nuclei was found to project to several limbic cortical areas, although not with equal density. The anterior dorsal nucleus projects primarily to the presubiculum and ventral retrosplenial cortex; the anterior ventral nucleus projects to the retrosplenial cortex and the presubiculum with apparently similar densities; and the anterior medial nucleus projects primarily to the cingulate areas. The projections from the lateral dorsal nucleus to these limbic cortical areas are organized in a loose topographic fashion. The projection to the presubiculum originates in the most dorsal portion of the lateral dorsal nucleus. The projection to the ventral retrosplenial cortex originates in rostral and medial portions of the nucleus, whereas afferents to the dorsal retrosplenial cortex originate in caudal portions of the lateral dorsal nucleus. The projection to the cingulate originates in the ventral portion of the lateral dorsal nucleus. Other projections from the thalamus originate in the intralaminar and midline nuclei, including the central lateral, central dorsal, central medial, paracentral, reuniens, and paraventricular nuclei, and the ventral medial and ventral anterior nuclei. In addition, projections to the medial limbic cortex from the basal forebrain originate in cells of the nucleus of the diagonal band. Projections to the presubiculum also originate in the medial septum. These results are discussed in regard to convergence of sensory and nonsensory information projecting to the limbic cortex and the types of visual and other sensory information that may be relayed to the limbic cortex by these projections.     

Forebrain connectivity of the prefrontal cortex in the marmoset monkey (Callithrix jacchus): an anterograde and retrograde tract-tracing study

The cortical and subcortical forebrain connections of the marmoset prefrontal cortex (PFC) were examined by injecting the retrograde tracer, choleratoxin, and the anterograde tracer, biotin dextran amine, into four sites within the PFC. Two of the sites, the lateral and orbital regions, had previously been shown to provide functionally dissociable contributions to distinct forms of behavioral flexibility, attentional set-shifting and discrimination reversal learning, respectively. The dysgranular and agranular regions lying on the orbital and medial surfaces of the frontal lobes were most closely connected with limbic structures including cingulate cortex, amygdala, parahippocampal cortex, subiculum, hippocampus, hypothalamus, medial caudate nucleus, and nucleus accumbens as well as the magnocellular division of the mediodorsal nucleus of the thalamus and midline thalamic nuclei, consistent with findings in the rhesus monkey. In contrast, the granular region on the dorsal surface closely resembled area 8Ad in macaques and had connections restricted to posterior parietal cortex primarily associated with visuospatial functions. However, it also had connections with limbic cortex, including retrosplenial and caudal cingulate cortex as well as auditory processing regions in the superior temporal cortex. The granular region on the lateral convexity had the most extensive connections. Based on its architectonics and functionality, it resembled areas 12/45 in macaques. It had connections with high-order visual processing regions in the inferotemporal cortex and posterior parietal cortex, higher-order auditory and polymodal processing regions in the superior temporal cortex. In addition it had extensive connections with limbic regions including the amygdala, parahippocampal cortex, cingulate, and retrosplenial cortex.     

Afferents to the cortical larynx area in the monkey

In 3 squirrel monkeys (Saimiri sciureus) horseradish peroxidase was injected into the cortical larynx area within the lower sensorimotor face cortex. Retrogradely labeled cells were found in a continuous band extending all along the upper bank of the Sylvian fissure from Broca's area rostrally to the parietal associationcortex (area 7) caudally. In addition, labeled cells were found in the ventrolateral prefrontal cortex, orbital cortex, anterior cingulate gyrus, supplementary motor area, insula and inferior temporal gyrus. Subcortically, labeled neurons were situated in the substantia innominata, basolateral amygdaloid nucleus, lateral and posterior hypothalamus, the thalamic nuclei ventralis lateralis, ventralis posteromedialis, medialis dorsalis, centralis lateralis, centralis inferior, parafascicularis and pulvinaris, the periventricular gray, reticular formation, nucl. annularis, nucl. centralis superior (Bechterew) and locus coeruleus. Many of these structures are connected with the cortical larynx area reciprocally. The possible phonatory role of some of them is discussed.     

Common cortical and subcortical targets of the dorsolateral prefrontal and posterior parietal cortices in the rhesus monkey: evidence for a distributed neural network subserving spatially guided behavior

Common efferent projections of the dorsolateral prefrontal cortex and posterior parietal cortex were examined in 3 rhesus monkeys by placing injections of tritiated amino acids and HRP in frontal and parietal cortices, respectively, of the same hemisphere. Terminal labeling originating from both frontal and parietal injection sites was found to be in apposition in 15 ipsilateral cortical areas: the supplementary motor cortex, the dorsal premotor cortex, the ventral premotor cortex, the anterior arcuate cortex (including the frontal eye fields), the orbitofrontal cortex, the anterior and posterior cingulate cortices, the frontoparietal operculum, the insular cortex, the medial parietal cortex, the superior temporal cortex, the parahippocampal gyrus, the presubiculum, the caudomedial lobule, and the medial prestriate cortex. Convergent terminal labeling was observed in the contralateral hemisphere as well, most prominently in the principal sulcal cortex, the superior arcuate cortex, and the superior temporal cortex. In certain common target areas, as for example the cingulate cortices, frontal and parietal efferents terminate in an array of interdigitating columns, an arrangement much like that observed for callosal and associational projections to the principal sulcus (Goldman-Rakic and Schwartz, 1982). In other areas, frontal and parietal terminals exhibit a laminar complementarity: in the depths of the superior temporal sulcus, prefrontal terminals are densely distributed within laminae I, III, and V, whereas parietal terminals occupy mainly laminae IV and VI directly below the prefrontal bands. Subcortical structures also receive apposing or overlapping projections from both prefrontal and parietal cortices. The dorsolateral prefrontal and posterior parietal cortices project to adjacent, longitudinal domains of the neostriatum, as has been described previously (Selemon and Goldman-Rakic, 1985); these projections are also found in close apposition in the claustrum, the amygdala, the caudomedial lobule, and throughout the anterior medial, medial dorsal, lateral dorsal, and medial pulvinar nuclei of the thalamus. In the brain stem, both areas of association cortex project to the intermediate layers of the superior colliculus and to the midline reticular formation of the pons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Corticothalamic connections of paralimbic regions in the rhesus monkey

This study addressed the issue of whether paralimbic regions of the cerebral cortex share common thalamic projections. The corticothalamic connections of the paralimbic regions of the orbital frontal, medial prefrontal, cingulate, parahippocampal, and temporal polar cortices were studied with the autoradiographic method in the rhesus monkey. The results revealed that the orbital frontal, medial prefrontal, and temporal polar proisocortices have substantial projections to both the dorsomedial and medial pulvinar nuclei, whereas the anterior cingulate proisocortex (area 24) projects exclusively to the dorsomedial nucleus. These proisocortical areas also have thalamic connections with the intralaminar and midline nuclei. The cortical areas between the proisocortical regions on the one hand and the isocortical areas on the other, that is, the posterior cingulate region (area 23) and the posterior parahippocampal gyrus (areas TF and TH), project predominantly to the dorsal portion of the medial pulvinar nucleus, the anterior nuclear group (AV, AM), and the lateral dorsal (LD) nucleus. Additionally, the posterior cingulate and medial parahippocampal gyri (area TH) have projections to the lateral posterior (LP) nucleus. Thus, it appears that the proisocortical areas, which are characterized by a predominance of infragranular layers and an absence of layer IV, have common thalamic relationships. Likewise, the intermediate paralimbic areas between the proisocortex and isocortical regions, which also have a predominance of infragranular layers but in addition have evidence of a fourth layer, project to the medial pulvinar and to the so-called limbic nuclei, AV, AM, LD, as well as a modality-specific nucleus, LP.     

Medial temporal lobe projections to the retrosplenial cortex of the macaque monkey

The projections to the retrosplenial cortex (areas 29 and 30) from the hippocampal formation, the entorhinal cortex, perirhinal cortex, and amygdala were examined in two species of macaque monkey by tracking the anterograde transport of amino acids. Hippocampal projections arose from the subiculum and presubiculum to terminate principally in area 29. Label was found in layer I and layer III(IV), the former seemingly reflecting both fibers of passage and termination. While the rostral subiculum mainly projects to the ventral retrosplenial cortex, mid and caudal levels of the subiculum have denser projections to both the caudal and dorsal retrosplenial cortex. Appreciable projections to dorsal area 30 [layer III(IV)] were only seen following an extensive injection involving both the caudal subiculum and presubiculum. This same case provided the only example of a light projection from the hippocampal formation to posterior cingulate area 23 (layer III). Anterograde label from the entorhinal cortex injections was typically concentrated in layer I of 29a–c, though the very caudal entorhinal cortex appeared to provide more widespread retrosplenial projections. In this study, neither the amygdala nor the perirhinal cortex were found to have appreciable projections to the retrosplenial cortex, although injections in either medial temporal region revealed efferent fibers that pass very close or even within this cortical area. Finally, light projections to area 30V, which is adjacent to the calcarine sulcus, were seen in those cases with rostral subiculum and entorhinal injections. The results reveal a particular affinity between the hippocampal formation and the retrosplenial cortex, and so distinguish areas 29 and 30 from area 23 within the posterior cingulate region. The findings also suggest further functional differences within retrosplenial subregions as area 29 received the large majority of efferents from the subiculum. © 2012 Wiley Periodicals, Inc.     

Thalamic connections with limbic cortex. II. Corticothalamic projections

The corticothalamic projections from the cat limbic cortex have been investigated with anterograde and retrograde axonal transport techniques. Five limbic cortical areas—the anterior limbic area, the cingular area, the granular and dysgranular retrosplenial areas, and the presubiculum—were identified on the basis of their cytoarchitecture. Emphasis was placed on determining the laminar distribution of the cells of origin of the efferent projections, the projection pathways, and the sites of termination within the thalamus. Projections to the thalamus originate in layers V and VI of limbic cortex. In the cingular region the cells of origin are predominantly in layer V and to a lesser extent in layer VI, while the majority of cells projecting from the more caudal retrosplenial areas and presubiculum are in layer VI. There are two fiber pathways from each cortical area to the thalamus. One system of fibers passes through the internal capsule and lateral thalamic peduncle, and a second system travels in the cingulate fasciculus before piercing the corpus callosum to join the postcommissural fornix. The lateral dorsal nucleus and the anterior nuclear group, including the anterior dorsal, anterior ventral, and anterior medial nuclei, are the major thalamic recipients of projections from limbic cortex. Corticothalamic projections also terminate sparsely in the midline and intralaminar nuclear complex, including the central lateral, central dorsal, paracentral, central medial, rhomboid, and reuniens nuclei. Projections from the anterior limbic area project predominantly to the anterior medial, centrall lateral, and paracentral nuclei. The anterior ventral nucleus, anterior medial nucleus, and lateral dorsal nucleus are the major thalamic recipients of projections from the cingular area, the granular and dysgranular retro-splenial areas, and the presubiculum. It appears that the anterior dorsal nucleus receives afferents only from the dysgranular retrosplenial area. Bilateral corticothalamic projections were found in the anterior medial, dorsal medial, central lateral, central medial, paracentral, and reuniens nuclei.     

Changes in Fos expression in the rat brain after unilateral lesions of the anterior thalamic nuclei

Activity of the immediate early gene c-fos was compared across hemispheres in rats with unilateral anterior thalamic lesions. Fos protein was quantified after rats performed a spatial working memory test in the radial-arm maze, a task that is sensitive to bilateral lesions of the anterior thalamic nuclei. Unilateral anterior thalamic lesions produced evidence of a widespread hippocampal hypoactivity, as there were significant reductions in Fos counts in a range of regions within the ipsilateral hippocampal formation (rostral CA1, rostral dentate gyrus, 'dorsal' hippocampus, presubiculum and postsubiculum). A decrease in Fos levels was also found in the rostral and caudal retrosplenial cortex but not in the parahippocampal cortices or anterior cingulate cortices. The Fos changes seem most closely linked to sites that are also required for successful task performance, supporting the notion that the anterior thalamus, retrosplenial cortex and hippocampus form key components of an interdependent neuronal network involved in spatial mnemonic processing.     

The postsubicular cortex in the rat: characterization of the fourth region of the subicular cortex and its connections.

The hippocampal formation contributes importantly to many cognitive functions, and therefore has been a focus of intense anatomical and physiological research. Most of this research has focused on the hippocampus proper and the fascia dentata, and much less attention has been given to the subicular cortex, the origin of most extrinsic projections from the hippocampal formation. The present experiments demonstrate that the postsubiculum is a distinct area of the subicular cortex. The major projections to the postsubiculum originate in the hippocampal formation, the cingulate cortex, and the thalamus (primarily from the anterodorsal (AD) nucleus and to a lesser extent from the anteroventral (AV) and lateral dorsal (LD) nuclei). These projections differ from the thalamic projections to presubiculum and parasubiculum. Efferent projections from the postsubiculum terminate in both cortical and subcortical areas. The cortical projections terminate in the subicular and retrosplenial cortices and in the caudal lateral entorhinal and perirhinal cortices. Subcortical projections primarily end in the AD and the LD nuclei of the thalamus. These thalamic projections end in areas that are distinct from those to which the presubiculum and parasubiculum project. For instance, the postsubiculum has a dense terminal field in the AD nucleus, but presubicular axons terminate predominantly in the AV nucleus. The cortical projections also distinguish postsubiculum. All subicular areas project to the entorhinal cortex, but the postsubicular projection ends in the deep layers (i.e. IV-VI), whereas presubiculum projects to layers I and III, and parasubiculum projects to layer II. Postsubiculum projects to retrosplenial granular b cortex and only incidentally to retrosplenial granular a cortex. In contrast presubiculum projects to the retrosplenial granular a cortex but not to the retrosplenial granular b cortex. These differences clearly mark the postsubiculum, the presubiculum, and the parasubiculum as distinct regions within the subicular cortex and suggest that they subserve different roles in the processing and integration of limbic system information.     

Afferent and efferent connections of the dorsolateral precentral gyrus (area 4, hand/arm region) in the macaque monkey, with comparisons to area 8

The afferent and efferent connections of the dorsolateral precentral gyrus, the primary motor cortex for control of the upper extremity, were studied by using the retrograde and anterograde capabilities of the horseradish peroxidase (HRP) technique in three adult macaque monkeys that had received HRP gel implants in this cortical region. Reciprocal corticocortical connections were observed primarily with the supplementary motor area (SMA) in medial premotor area 6 and dorsal bank of the cingulate sulcus, postarcuate area 6 cortex, dorsal cingulate cortex (area 24), superior parietal lobule (area 5, PE/PEa), and inferior parietal lobule (area 7b, PF/PFop, including the secondary somatosensory SII region). In these heavily labeled regions, the associational intrahemispheric afferents originated primarily from small and medium sized pyramidal cells in layer III, but also from layer V. The SMA projections were columnar in organization. Intrahemispheric afferents from contralateral homologous and nonhomologous frontal and cingulate cortices also originated predominantly from layer III, but the connections from contralateral area 4 were almost exclusively from layer III. The bilateral connections with premotor frontal area 6 and cingulate cortices were not observed with parietal regions; i.e., only ipsilateral intrahemispheric parietal corticocortical connections were observed. There were no significant connections with prearcuate area 8 or the granular frontal (prefrontal) cortex. Subcortical afferents originated primarily from the nucleus basalis of Meynert, dorsal claustrum, ventral lateral (VLo and VLc), area X, ventral posterolateral pars oralis (VPLo), central lateral and centromedian thalamic nuclei, lateral hypothalamus, pedunculopontine nucleus, locus ceruleus and subceruleus, and superior central and dorsal raphe nuclei. Lesser numbers of retrogradely labeled neurons were observed in the nucleus of the diagonal band, mediodorsal (MD), paracentral, and central superior lateral thalamic nuclei, nucleus limitans, nucleus annularis, and the mesencephalic and pontine reticular formation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Projection from the nucleus reuniens thalami to the hippocampal region: light and electron microscopic tracing study in the rat with the anterograde tracer Phaseolus vulgaris-leucoagglutinin

In order to study the morphological substrate of possible thalamic influence on the cells of origin and area of termination of the projection from the entorhinal cortex to the hippocampal formation, we examined the pathways, terminal distribution, and ultrastructure of the innervation of the hippocampal formation and parahippocampal region by the nucleus reuniens of the thalamus (NRT). We employed anterograde tracing with Phaseolus vulgaris-leucoagglutinin (PHA-L). Injections of PHA-L in the NRT produce fiber and terminal labeling in the stratum lacunosum-moleculare of field CA1 of the hippocampus, the molecular layer of the subiculum, layers I and III/IV of the dorsal subdivision of the lateral entorhinal area (DLEA), and layers I and III-VI of the ventral lateral (VLEA) and medial (MEA) divisions of the entorhinal cortex. Terminal labeling is most dense in the stratum lacunosum-moleculare of field CA1, the molecular layer of the ventral part of the subiculum, MEA, and layer I of the perirhinal cortex. In layer I of the caudal part of DLEA and in MEA, terminal labeling is present in clusters. Injections in the rostral half of the NRT produce the same distribution in the hippocampal region as those in the caudal half of the NRT, although the projections from the rostral half of the NRT are much stronger. A topographical organization is present in the projections from the head of the NRT, so that the dorsal part projects predominantly to dorsal parts of field CA1 and the subiculum and to lateral parts of the entorhinal cortex, whereas the ventral part projects in greatest volume to ventral parts of field CA1 and the subiculum and to medial parts of the entorhinal cortex. The distribution of the reuniens fibers coursing in the cingulate bundle was determined by comparing cases with and without transections of this bundle. The fibers carried by the cingulate bundle exclusively innervate field CA1 of the hippocampus, the dorsal part of the subiculum, and the presubiculum and parasubiculum. They participate in the innervation of the ventral part of the subiculum and MEA. Electron microscopy was used to visualize the axon terminals of PHA-L-labeled reuniens fibers. These terminals possess spherical synaptic vesicles and form asymmetric synaptic contacts with dendritic spines or with thin shafts of spinous dendrites.(ABSTRACT TRUNCATED AT 400 WORDS)     

'Non-specific' cholinesterase-containing neurons of the dorsal thalamus project to medial limbic cortex

Thalamocortical neurons that contain 'non-specific' cholinesterase (ChE) were studied with cholinesterase histochemistry and experimental axonal tracing techniques in adult rats. In addition to the presence of ChE that is ubiquitous in capillary endothelium, neurons that contain ChE are found in 3 distinct regions of the dorsal thalamus, the thalamic reuniens nucleus (Re), the anterior dorsal nucleus (AD) and a region that includes the lateral part of the central lateral nucleus (CL) and the ventral portion of the lateral dorsal nucleus (LD). ChE activity appears light in cerebral cortex in general but histochemical staining is slightly greater in neuropil of the cingulate gyrus. Anterograde transport techniques with autoradiography demonstrated that neurons in the LD-CL region project to anterior cingulate cortex and the dorsal retrosplenial area. Anterograde degeneration techniques demonstrated that AD projects primarily to ventral retrosplenial cortex. Injections of horseradish peroxidase (HRP) in the anterior cingulate cortex resulted in double labeled cells (cells containing both ChE and HRP reaction products) primarily in LD and CL. HRP injections into ventral retrosplenial cortex resulted in double labeled cells in AD and Re. HRP injections in the subiculum resulted in double labeled cells in Re. Lesions placed in the region of thalamocortical projections resulted in a loss of ChE in the ipsilateral cingulate gyrus, as measured both histochemically and enzymatically. The finding that neurons containing ChE project to medial limbic cortex suggests that the ChE may be involved in the function of the thalamocortical component of the limbic system.     

Efferent connections of the orbitofrontal cortex in the marmoset(Saguinus oedipus)

Unilateral partial ablations were made in the orbitofrontal cortex of 4 adult marmosets(Saguinus oedipus) and fiber degeneration was traced using the Nauta-Gygax and Fink-Heimer selective silver impregnation techniques. Corticocortical projections were found to the ipsilateral convexity and medial aspect of the frontal lobe and to the homologous orbitofrontal areas of the contralateral hemisphere. Fiber degeneration was followed through the uncinate fascicle to the temporal and insular cortices, and caudally into the rostrolateral entorhinal cortex. Other fibers joined the cingulum bundle and terminated throughout the cingulate cortex.Subcortical projections were observed to the lateral and basal amygdaloid nuclei, caudate head, ventrolateral putamen and ventral claustrum. The lateral preoptic and hypothalamic areas received a small number of fibers, as did the intralaminar and reticular thalamic nuclei. The dorsomedial nucleus of the thalamus was recipient of a large group of fibers which followed the ventral internal capsule and joined the inferior thalamic peduncle to terminate there. Preterminal debris appeared heaviest in the dorsomedial thalamic nucleus, pars magnocellularis (MDmc) in more caudal orbital lesions. A subthalamic projection to field H of Forel was observed. A small number of fibers terminated in the lateral midbrain tegmentum, but no appreciable fiber degeneration was observed more caudally than the midbrain. These results are compared in some areas to findings in the rhesus monkey. The possibility of a topical organization in the orbital cortical and thalamic projections is discussed.