Populations of substance P, Met-enkephalin and serotonin immunoreactive neurons in the interpeduncular nucleus of cat: Cytoarchitectonics

The indirect antibody-peroxidase immunostaining method was used to study the distribution of substance P- (SPLI), Met-enkephalin- (MELI) and serotonin-like (5-HTLI) immunoreactivity within the interpeduncular nuclear complex (IPN) of the cat. Populations of immunoreactive cell bodies were found to have a distinct pattern of localization within the IPN. This distribution pattern is described as seen at 4 representative levels rostrocaudally through the IPN. SPLI cell bodies were mainly at rostral levels I, II and III especially in the median region and as a cluster of cells in the intermediate regions of the IPN. MELI cell bodies were seen at all 4 levels, being confined mainly to the median and intermediate regions at levels I and II and also in the lateral regions at levels III and IV. There were few 5-HTLI cell bodies at the rostral levels I and II where they were confined to the dorsal zone of the median region. whereas at levels III and IV there were numerous cell bodies located throughout the intermediate region of the IPN. The immunoreactive cell bodies in the IPN may belong to both intrinsic and projection neurons. The distinctive neurochemical cytoarchitectonics of the IPN suggest that this region of the brain which lies along the course of major limbic pathways, may be a center of complex integrative mechanisms of neuronal activity.     

Substance P in the interpeduncular nucleus of the rat: normal distribution and the effects of deafferentation

The interpeduncular nucleus (IPN) is a midbrain structure that receives its major afferents from the medial habenulae via the fasciculi retroflexi. Among the axons projecting to the IPN is a population of substance P (SP)-containing axons. The IPN has been subdivided into the central, dorsal, intermediate, rostral, and lateral subnuclei using cytoarchitectonic criteria. The distribution of SP among these subnuclei was determined by using Sternberger's ('79) peroxidase-antiperoxidase technique. In the normal IPN the rostral subnucleus can be subdivided into two sectors on the basis of SP content. The ventral sector contains a moderate amount of SP and scattered SP positive perikarya. The dorsal cap of the rostral subnucleus contains denser SP than the ventral sector and it is continuous with the SP found in the dorsal subnucleus. The lateral subnuclei contain the densest SP found in the IPN and appear as laterally placed columns that expand in size caudally. The central and intermediate subnuclei contain very sparse SP. The fasciculus retroflexus was destroyed in 30 animals unilaterally or bilaterally and animals were perfused 4 days to 3 months postoperatively. After unilateral fascicular lesion, the SP in the rostral part of the ipsilateral lateral subnucleus is almost abolished, but caudally the decrease is confined to its lateral aspect. There is no visible decrease contralateral to the lesion. SP in the rostral part of the cap of the rostral subnucleus is decreased ipsilaterally but no loss is seen contralaterally or caudally. Animals with bilateral lesions show a great decrease in staining in the dorsal cap of the rostral subnucleus and the lateral subnuclei, with no decrease seen in the central, dorsal, or intermediate subnuclei. These results confirm that the origin of most of the SP in the IPN is fasciculus retroflexus fibers, but some of the SP arises from intrinsic SP perikarya located in the ventral sector of the rostral subnucleus and some may also arise from other sources. The areas of the IPN that receive bilateral SP projections from the fasciculus retroflexus (parts of the lateral and rostral subnuclei) show evidence for replacement of SP after lesion. This replacement implies sprouting or an increase in production of SP by remaining systems.     

The subnuclear distribution of substance P,cholecystokinin, vasoactive intestinal peptide,somatostatin, leu-enkephalin,dopamine-β-hydroxylase,and serotonin in the rat interpeduncular nucleus

The distribution of immunofluorescent somata and processes within the interpeduncular nucleus (IPN) containing substance P (SP), cholecystokinin (CCK), vasoactive intestinal peptide (VIP), somatostatin (SST), leu-enkephalin (L-ENK), dopamine β hydroxylase (DBH), and serotonin (5HT) was examined in male rats treated with colchicine 48 hours prior to perfusion. Serial sections were examined for immunofluorescence and variations in the density of fluorescence rated 1+ (sparse) to 4+ (dense). The rostral subnucleus contained SP, SST, and L-ENK-positive somata and processes. Substance P and VIP processes were present throughout the rostral subnucleus but were concentrated in two ovoid areas located dorsally in the caudal region of this subnucleus. Cholecystokinin and L-ENK processes surrounded these ovoid areas. The entire width of the central subnucleus was crossed by SP and L-ENK processes oriented horizontally in narrow bands. Substance P processes were also aligned into vertical columns adjacent to the lateral margins of the central subnucleus. Leu-enkephalin and 5HT processes were distributed throughout this subnucleus, while VIP processes were present only caudally. Dopamine β hydroxylase processes were evenly distributed but were restricted from the vertical columns laterally. The intermediate subnuclei contained a sparse density of SP and 5HT processes that were present in proximity to the major blood vessels penetrating this subnucleus. Only DBH processes were evenly distributed. The lateral subnuclei contained a dense concentration of SP processes. The medial edges of this subnucleus were distinguished by VIP, CCK, L-ENK, and 5HT processes. The dorsal subnucleus contained 5HT, L-ENK, and SST-positive somata and processes. Substance P, VIP, CCK., and DBH processes were also present. Dorsal-lateral subnuclei contained SP, SST, L-ENK, and DBH processes. Interstitial subnuclei contained SP, CCK, L-ENK, 5HT, and DBH processes. This study demonstrates that perikarya and processes containing peptides and monoamines are distributed within subnuclei of IPN in a topographic and heterogeneous pattern. New features of IPN organization are revealed.     

Developmental profiles of cholinergic activity in the habenulae and interpeduncular nucleus of the rat

Choline acetyltransferase (ChAT) was measured in the habenula and in the interpeduncular nucleus of rats from 1 to 12 weeks of age. A remarkable degree of parallelism was shown by the developmental curves in the two nuclei. In both cases the highest level of enzyme activity was reached at 3 weeks of age and was followed by some decrease towards adult values. A statistically highly significant correlation was demonstrated between ChAT levels in the two nuclei at the various developmental stages. The rise of the cholinergic marker was slightly advanced in the habenula in comparison with the interpeduncular nucleus. The present data may be useful for studies focused on neonatal synaptogenesis, plasticity and synaptic neurochemistry of this relatively simple model of brain connections.     

The ultrastructure of enkephalin-immunoreactive neurons in the interpeduncular nucleus of the rat

The interpeduncular nucleus of the rat is a complex structure, displaying diverse immunocytochemical and ultrastructural features. This nucleus contains opiate receptors, enkephalin-positive cell bodies and enkephalin-positive fibers. The ultrastructure of rat interpeduncular enkephalinergic neurons has not been described, nor has the role that these neurons play in the internal organization of the interpeduncular nucleus been established. The purpose of the present study was to describe the ultrastructure of enkephalinlike-immunoreactive (ELI) cells with particular emphasis on the subnuclear organization of their dendritic and terminal fields. Enkephalinlike-immunoreactive (ELI) cell bodies are present in the rostral and apical subnuclei of the interpeduncular nucleus (IPN), but are absent from the other subnuclei of the IPN. The rostral subnucleus also contains immunoreactive dendrites that are postsynaptic to nonreactive terminal boutons. Numerous ELI axon terminals were observed in the central and intermediate subnuclei. The results of our study suggest that enkephalinergic interneurons link the rostral IPN with more caudal regions of this nucleus.     

Cytoarchitecture and efferent projections of the nucleus incertus of the rat

The nucleus incertus is located caudal to the dorsal raphe and medial to the dorsal tegmentum. It is composed of a pars compacta and a pars dissipata and contains acetylcholinesterase, glutamic acid decarboxylase, and cholecystokinin-positive somata. In the present study, anterograde tracer injections in the nucleus incertus resulted in terminal-like labeling in the perirhinal cortex and the dorsal endopyriform nucleus, the hippocampus, the medial septum diagonal band complex, lateral and triangular septum medial amygdala, the intralaminar thalamic nuclei, and the lateral habenula. The hypothalamus contained dense plexuses of fibers in the medial forebrain bundle that spread in nearly all nuclei. Labeling in the suprachiasmatic nucleus filled specifically the ventral half. In the midbrain, labeled fibers were observed in the interpeduncular nuclei, ventral tegmental area, periaqueductal gray, superior colliculus, pericentral inferior colliculus, pretectal area, the raphe nuclei, and the nucleus reticularis pontis oralis. Retrograde tracer injections were made in areas reached by anterogradely labeled fibers including the medial prefrontal cortex, hippocampus, amygdala, habenula, nucleus reuniens, superior colliculus, periaqueductal gray, and interpeduncular nuclei. All these injections gave rise to retrograde labeling in the nucleus incertus but not in the dorsal tegmental nucleus. These data led us to conclude that there is a system of ascending projections arising from the nucleus incertus to the median raphe, mammillary complex, hypothalamus, lateral habenula, nucleus reuniens, amygdala, entorhinal cortex, medial septum, and hippocampus. Many of the targets of the nucleus incertus were involved in arousal mechanisms including the synchronization and desynchronization of the theta rhythm.     

Interpeduncular nucleus organization in the rat: Cytoarchitecture and histochemical analysis

The organization of the interpeduncular nucleus (IPN) in the adult rat was analyzed using cytoarchitectonic, histochemical and immunohistochemical methods. Four paired and four unpaired subnuclei can be distinguished in the IPN on the basis of neuronal size, morphology, staining characteristics and packing density. The rostral portion of the IPN contains a rostral dorsal, a rostral ventral and paired rostral lateral and dorsal lateral nuclei. The dorsal lateral nuclei continue into the caudal IPN, which also contains a caudal dorsal, a caudal ventral and paired caudal lateral nuclei. The distribution of extrinsic afferents and of chemically identified intrinsic neuronal and fiber populations within subdivisions of the IPN was examined using immunohistochemistry, acetylcholinesterase histochemistry, catecholamine histofluorescence and the autoradiographic tracing method. Six immunohistochemically distinct neuronal groups are identified in the IPN. Perikarya and axons showing substance P-, leu-enkephalin-, somatostatin-, avian pancreatic polypeptide-, serotonin- and glutamic acid decarboxylase-like immunoreactivity are localized to specific IPN subnuclei. Acetylcholinesterase-positive staining, extrinsic norepinephrine-containing fibers and afferents from the dorsal tegmental nuclei are also distributed specifically to IPN subnuclei. These findings demonstrate a cytoarchitectonic and cytochemical complexity in the rat IPN that implies an important functional role for this poorly understood nuclear complex.     

Multiple neurotransmitters in the tuberomammillary nucleus: comparison of rat, mouse, and guinea pig.

Tuberomammillary neurons in the posterior hypothalamus are the sole source of neuronal histamine in adult mammalian brain. In the rat, these cells are reported to contain immunoreactivity for gamma-aminobutyric acid (GABA) and several neuropeptides. We compared the presence of these substances in the tuberomammillary cells of the rat, mouse, and guinea pig. In all three species, all histamine-immunoreactive neuronal cell bodies were positive for GABA. This suggests that GABAergic transmission may be important in tuberomammillary function. No cell bodies immunoreactive for thyrotropin releasing hormone (TRH) were found in the guinea pig or mouse tuberomammillary area. In contrast, about 14% of the histamine-immunoreactive tuberomammillary cells in the rat were TRH-positive. These cells were small or medium-sized and were located only in the medial part of the tuberomammillary complex. An antibody against porcine galanin stained about 45% of the tuberomammillary cell bodies in the rat and about 28% in the mouse, but none in the guinea pig. A large proportion of the cells in the rat and mouse, but none in the guinea pig, were positive for met-enkephalin-arg-phe. In contrast, all histamine-containing tuberomammillary cells in the guinea pig, but none in the rat or mouse, were immunoreactive for met-enkephalin. This may indicate a different expression of proenkephalin-derived peptides in the tuberomammillary neurons in these species. Some substance P-immunoreactive cell bodies were located in the tuberomammillary area in all three species. However, only 3% of the histamine-immunoreactive cell bodies in the rat and mouse but none in the guinea pig were substance P-positive. The neurochemical properties of the tuberomammillary nucleus that exhibited species commonality deserve to be studied neurochemically and electrophysiologically in order to determine the functional relevance of coexisting transmitters in this nucleus.     

Cytoarchitecture and fiber connections of the nucleus lateralis valvulae in the carp (Cyprinus carpio)

The cytoarchitecture and fiber connections of the nucleus lateralis valvulae of the carp (Cyprinus carpio) were studied by Nissl, Bodian, Golgi, and horseradish peroxidase methods. Chief cells composing the nucleus lateralis valvulae (NLV) are small and granular, and their axons terminate in the cerebellum. These neurons have no dendrite, and the cell body is enveloped in a single terminal of afferent fibers to the NLV. In order to observed local cell clustering, the NLV was three-dimensionally reconstructed with the aid of a computer image analysis system. Afferent sources to the NLV were the nucleus pretectalis superficialis pars magnocellularis (Northcutt and Braford, '84: Brain Res. 296:181-184), nucleus ventromedialis thalami (Ito et al., '86: J. Comp. Neurol 250:215-227), and the inferior lobe. The NLV projects to the inferior lobe and the cerebellum. In particular, the cerebellar projections were strong and topographically arranged. Some larger neurons lying just beneath the NLV, some of which were intermingled with the NLV neurons, projected to the torus longitudinalis. On the basis of the local cell clustering as well as NLV-cerebellar connections, three subdivisions of the NLV could be recognized, i.e., anterior, central, and posterior portions. The posterior portion was further subdivided into lateral and medial parts.     

Immunohistochemistry and spinal projections of the reticular formation in the northern leopard frog,Rana pipiens

Over 30 nuclei have been identified in the reticular formation of rats, but only a small number of distinct reticular nuclei have been recognized in frogs. We used immunohistochemistry, retrograde tracing, and cell morphology to identify nuclei within the brainstem of Rana pipiens. FluoroGold was injected into the spinal cord, and, in the same frogs, antibodies to enkephalin, substance P, somatostatin, and serotonin were localized in adjacent sections. We identified many previously unrecognized reticular nuclei. The rhombencephalic reticular formation contained reticularis (r.) dorsalis; r. ventralis, pars alpha and pars beta; r. magnocellularis; r. parvocellularis; r. gigantocellularis; r. paragigantocellularis lateralis and dorsalis; r. pontis caudalis, pars alpha and pars beta; nucleus visceralis secundarius; r. pontis oralis, pars medialis and pars lateralis; raphe obscurus; raphe pallidus; raphe magnus; and raphe pontis. The mesencephalic reticular formation contained locus coeruleus-subcoeruleus, r. cuneiformis, r. subcuneiformis, raphe dorsalis-raphe centralis superior, and raphe linearis. Thus, the reticular formation of frog, which is an anamniote, is organized complexly and is similar to the reticular formation in amniotes. Because many of these nuclei may be homologous to reticular nuclei in mammals, we used mammalian terminology for frog reticular nuclei. J. Comp. Neurol. 404:387–407, 1999. © 1999 Wiley-Liss, Inc.     

Distribution,parabrachial region projection,and coexistence of neuropeptide and catecholamine cells of the nucleus of the solitary tract in the pigeon

The chemical nature of the cells of the nucleus of the solitary tract (NTS) that project to the parabrachial nucleus (PB) was investigated in the pigeon by the use of fluorescent bead retrograde tracer and immunofluorescence for the detection of substance P (SP), leucineenkephalin (LENK), cholecystokinin (CCK), neurotensin (NT), somatostatin (SS), and tyrosine hydroxylase (TH). Cells immunoreactive for CCK were located in subnuclei lateralis dorsalis pars anterior (LDa) and medialis superficialis pars posterior, and caudal NTS (cNTS); 22–26.5% of these cells were double-labeled bilaterally. Immunoreactive SP cells were found in ventral NTS subnuclei; 24–25% of these cells were double-labeled bilaterally. Cells immunoreactive for LENK and NT were concentrated in the anterior NTS; 5.5–7.5% of the LENK cells were double-labeled bilaterally, while 11% (ipsilateral) and 21% (contralateral) of the NT immunoreactive cells were double-labeled. Many SS immunoreactive cells were found in peripherally located subnuclei; 5.5–6.5% of these cells were double-labeled bilaterally. Catecholamine cells were distributed in LDa, peripheral subnuclei, and cNTS; 23% of these cells were double-labeled ipsilaterally and 8.5% contralaterally. A two-color double-labeling immunofluorescence technique revealed many cells immunoreactive for both NT and LENK, only a rare cell immunoreactive for both SS and SP, and no cells immunoreactive for both TH and SP. Cells immunoreactive for SP, CCK, NT, and TH are major contributors to NTS projections to PB. The confinement of these substances to specific NTS subnuclei, which receive visceral sensory information from specific organs, may contribute to the chemical encoding of ascending visceral information. 1993 Wiley-Liss, Inc.     

Cytoarchitecture and cortical connections of the posterior cingulate and adjacent somatosensory fields in the rhesus monkey

The cytoarchitecture and connections of the caudal cingulate and medial somatosensory areas were investigated in the rhesus monkey. There is a stepwise laminar differentiation starting from retrosplenial area 30 towards the isocortical regions of the medial parietal cortex. This includes a gradational emphasis on supragranular laminar organization and general reduction of the infragranular neurons as one proceeds from area 30 toward the medial parietal regions, including areas 3, 1, 2, 5, 31, and the supplementary sensory area (SSA). This trend includes a progressive increase in layer IV neurons. Area 23c in the lower bank and transitional somatosensory area (TSA) in the upper bank of the cingulate sulcus appear as nodal points. From area 23c and TSA the architectonic progression can be traced in three directions: one culminates in areas 3a and 3b (core line), the second in areas 1, 2, and 5 (belt line), and the third in areas 31 and SSA (root line). These architectonic gradients are reflected in the connections of these regions. Thus, cingulate areas (30, 23a, and 23b) are connected with area 23c and TSA on the one hand and have widespread connections with parieto-temporal, frontal, and parahippocampal (limbic) regions on the other. Area 23c has connections with areas 30, 23a and b, and TSA as well as with medial somatosensory areas 3, 1, 2, 5, and SSA. Area 23c also has connections with parietotemporal, frontal, and limbic areas similar to areas 30, 23a, and 23b. Area TSA, like area 23c, has connections with areas 3, 1, 2, 5, and SSA. However, it has only limited connections with the parietotemporal and frontal regions and none with the parahippocampal gyrus. Medial area 3 is mainly connected to medial and dorsal sensory areas 3, 1, 2, 5, and SSA and to areas 4 and 6 as well as to supplementary (M2 or area 6m), rostral cingulate (M3 or areas 24c and d), and caudal cingulate (M4 or areas 23c and d) motor cortices. Thus, in parallel with the architectonic gradient of laminar differentiation, there is also a progressive shift in the pattern of corticocortical connections. Cingulate areas have widespread connections with limbic, parietotemporal, and frontal association areas, whereas parietal area 3 has more restricted connections with adjacent somatosensory and motor cortices. TSA is primarily related to the somatosensory-motor areas and has limited connections with the parietotemporal and frontal association cortices.     

Specific connections of the interpeduncular subnuclei reveal distinct components of the habenulopeduncular pathway

The habenulopeduncular pathway consists of the medial habenula (MHb), its output tract, the fasciculus retroflexus, and its principal target, the interpeduncular nucleus (IP). Several IP subnuclei have been described, but their specific projections and relationship to habenula inputs are not well understood. Here we have used viral, transgenic, and conventional anterograde and retrograde tract‐tracing methods to better define the relationship between the dorsal and ventral MHb, the IP, and the secondary efferent targets of this system. Although prior studies have reported that the IP has ascending projections to ventral forebrain structures, we find that these projections originate almost entirely in the apical subnucleus, which may be more appropriately described as part of the median raphe system. The laterodorsal tegmental nucleus receives inhibitory inputs from the contralateral dorsolateral IP, and mainly excitatory inputs from the ipsilateral rostrolateral IP subnucleus. The midline central gray of the pons and nucleus incertus receive input from the rostral IP, which contains a mix of inhibitory and excitatory neurons, and the dorsomedial IP, which is exclusively inhibitory. The lateral central gray of the pons receives bilateral input from the lateral IP, which in turn receives bilateral input from the dorsal MHb. Taken together with prior studies of IP projections to the raphe, these results form an emerging map of the habenulopeduncular system that has significant implications for the proposed function of the IP in a variety of behaviors, including models of mood disorders and behavioral responses to nicotine.     

Neuropeptide neuronal efferents from the bed nucleus of the stria terminalis and central amygdaloid nucleus to the dorsal vagal complex in the rat

The lateral bed nucleus of the stria terminalis (BSTL) and central nucleus of the amygdala (Ce) are amygdaloid nuclei that have similar afferent and efferent connections within the brain. Previous studies have demonstrated that both regions send axonal projections to the dorsal vagal complex (dorsal motor nucleus and nucleus tractus solitarii). The present study used the combined retrograde fluorescence-immunofluorescence method to examine whether cells contributing to this pathway contained any of the following neuropeptides: corticotropin-releasing factor, neurotensin, somatostatin, substance P, enkephalin, or galanin. The inputs to the dorsal vagal complex originated mainly from ventral BSTL and medial Ce, although a significant number of neurons within the dorsal BSTL and lateral Ce also contributed. Corticotropin-releasing factor, neurotensin, and somatostatin neurons mainly located within the dorsal BSTL and the lateral Ce contained retrograde tracer after injections into the vagal complex. Substance P neurons in the ventral BSTL and medial Ce provide a sparse input to the dorsal vagal complex. Enkephalin and galanin neurons within the BSTL and Ce did not appear to project to the dorsal vagal complex. Corticotropin-releasing factor and neurotensin neurons within the lateral hypothalamus also project to the dorsal vagal complex. Approximately 22% of the Ce and 15% of the BSTL retrogradely labeled neurons were peptide immunoreactive. Thus, it is concluded the Ce and BSTL are sources of a significant peptidergic pathway to the dorsal vagal complex. However, it is also apparent that the majority of putative transmitter types within the amygdaloid vagal projection still are unknown. The results suggest that the dorsal and ventral BSTL and the lateral and medial Ce, respectively, are homologous zones with regard to chemoarchitecture and connections. The data is discussed considering the possible function of peptides within descending amygdaloid pathways to the brainstem.     

Fibers from the basolateral nucleus of the amygdala selectively innervate striosomes in the caudate nucleus of the cat

The compartmental organization of the amygdalostriatal projection was studied in the cat by comparing staining patterns seen by cholinesterase enzyme histochemistry with the distribution of fibers labelled with a horseradish peroxidase-wheat germ agglutinin conjugate or by incorporation of 35S-methionine or 3H-leucine. Fibers from the basolateral nucleus of the amygdala were found to innervate selectively acetylcholinesterase-poor striosomes demonstrated in the caudate nucleus and butyrylcholinesterase-rich zones observed in the anterodorsal nucleus accumbens. In no case were the amygdalar fibers fully restricted to striosomes, but the nature and degree of labelling of the striatal matrix, as well as the range of the labelled fibers in dorsal striatum, varied with the positions of the injection sites.     

Ontogeny of bidirectional connections between the medial nucleus of the amygdala and the principal bed nucleus of the stria terminalis in the rat

Nuclei in the amygdala and bed nuclei of the stria terminalis (BST) form functionally organized units that are linked by topographically organized connections. The posterodorsal part of the medial nucleus of the amygdala (MEApd) and the principal nucleus of the BST (BSTpr) share strong birectional connections that project primarily through the stria terminalis. The presence of structural and neurochemical sexual dimorphisms in both the MEApd and BSTpr suggests that connections between the nuclei may develop during the postnatal critical period for sexual differentiation. In this study, 1,1'dioctadecyl-3,3,3'-tetramethylindocarbocyanine perchlorate (DiI) axonal labeling was used to define the ontogeny of this bidirectional pathway. Placement of DiI crystals into the MEApd of rats perfused on embryonic day (E) 20 resulted in DiI-labeled fibers with axonal morphology in the BSTpr, but similar labeling was not evident in the MEApd until after birth. However, as early as E14, tracer implants into the caudal MEA (the presumptive MEApd) labeled elongated cellular processes in the region of the stria terminalis that extended into the presumptive BSTpr. Based on the correspondence of these DiI-labeled processes with immunostaining for vimentin, these cellular processes are probably derived from glial cells. Implants of DiI into the posterior BST also labeled cellular processes that extended through the medial part of the stria terminalis, but they remained confined to the molecular layer of the MEApd from E14 through P1. Labeled axons derived from the BSTpr were not observed in the MEApd until P5, demonstrating that the bidirectional connections that exist between the MEApd and BSTpr in mature rats do not develop simultaneously. The density of connections between the BSTpr and MEApd increased during the postnatal period and was similar to that of adults by P15. These findings suggest that projections from the MEApd through the stria terminalis to the BSTpr may be specified initially by a glial substrate and that return projections to the amygdala from the BSTpr develop secondary to its innervation by the MEApd.     

An immuno-electronmicroscopical study comparing vasopressin, oxytocin, substance P and enkephalin containing nerve terminals in the nucleus of the solitary tract of the rat

Vasopressin, oxytocin, substance P and enkephalin fibers were demonstrated to terminate synaptically in the nucleus of the solitary tract. The detergent Triton X-100 proved to be indispensable for the demonstration of vasopressin and oxytocin while enkephalin and substance P could be visualized very well without it. The differences with respect to morphology between these 4 peptides disappeared when Triton X-100 was used in both groups.     

Afferent projections to the interpeduncular nucleus in the rat, as studied by retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase

We examined the afferent projections to the subnuclei of the interpeduncular nucleus (IPN) in the rat by means of retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). We observed locations of retrogradely labeled cells following injections of WGA-HRP into the IPN, and distributions of anterogradely labeled fibers and terminals within the IPN following injections into the areas that contain cells of origin of afferents. Results of the retrograde and anterograde experiments have clarified the detailed organization of the IPN afferents. A part of the nucleus incertus, located dorsomedial to the dorsal tegmental nucleus, projects to the contralateral half of the rostral subnucleus of the IPN; the pars caudalis of the dorsal tegmental nucleus projects sparsely to the rostral lateral, dorsal lateral, lateral, caudal, and apical subnuclei predominantly contralaterally; the laterodorsal tegmental nucleus, to most of the subnuclei predominantly contralaterally; the ventromedial central gray rostral to the dorsal tegmental nucleus and lateral to the dorsal raphe nucleus projects to the rostral lateral and dorsal lateral subnuclei predominantly contralaterally; the median raphe nucleus, substantially to all subnuclei; the medial habenular nucleus, in a topographic manner, to the rostral, central, and intermediate subnuclei, to the rostral lateral and lateral subnuclei predominantly ipsilaterally, and to the dorsal lateral subnucleus predominantly contralaterally; the supramammillary nucleus and areas around the origin of the mammillothalamic tract and near the third ventricle project sparsely to the ventral part of the rostral subnucleus and to the central, lateral, caudal and apical subnuclei; the nucleus of the diagonal band, sparsely to the rostral, central, dorsal lateral, caudal, and apical subnuclei. These differential projections of the afferents to the subnuclei of the IPN may reflect its complex functions within the limbic midbrain circuit.     

The ultrastructural localization of enkephalin and substance P immunoreactivities in the nucleus tractus solitarii of the cat

In the medial and commissural subdivisions of the nucleus tractus solitarii enkephalin and substance P immunoreactivities were localized within synaptic terminals, unmyelinated axons, and neuronal cell bodies. Both enkephalin and substance P immunoreactivities were contained within synaptic terminals which had a mixture of small clear vesicles and dense core vesicles. The presence of dense core vesicles within both the enkephalin- and substance P-immunoreactive terminals was a consistent feature, although they were not associated with the actual synaptic junction. While enkephalin- and substance P-immunoreactive terminals shared a similar morphology, their respective distributions along the dendritic tree were quite distinct. Enkephalin-immunoreactive terminals contacted mainly the cell body and proximal portions of the dendritic tree. In contrast, substance P-immunoreactive terminals synapsed predominantly with spines and shafts of small to medium-sized dendrites. Few substance P-immunoreactive terminals contacted proximal dendrites and they were never presynaptic to the neuronal cell body. This apparent segregation of synaptic terminals on neurons suggests that enkephalin synapses have a more pronounced effect than substance P terminals.