Somatostatin- and neuropeptide Y-like immunoreactivity in the dentate area, hippocampus, and subiculum of the domestic pig.

With the principal aim of providing baseline observations for future experimental studies, the distribution of somatostatin-like and neuropeptide Y-like immunoreactivities is described in the dentate area, hippocampus, and subiculum of the domestic pig (Sus scrofa domesticus) and compared with the distribution described in other mammals. Intensely stained somatostatin-like immunoreactive nerve cell bodies were present throughout the region, with highest densities in the dentate hilus, stratum radiatum and stratum oriens of the hippocampal regio inferior, stratum oriens of the hippocampal regio superior, and in the subicular cell layer. Somatostatin-like immunoreactive terminals were represented by both stained fibers and stained puncta. Scattered somatostatin-like immunoreactive nerve fibers were seen in most areas, but regular fiber plexuses were present in the dentate molecular layer and dentate hilus, stratum moleculare of the hippocampus, and in the subicular plexiform layer. Somatostatin-like immunoreactive puncta were seen in the dentate molecular layer, stratum moleculare of the hippocampus, and in the subicular plexiform layer. Neuropeptide Y-like immunoreactive nerve cell bodies were less numerous than somatostatin-like immunoreactive ones. They were mainly seen in the dentate granule cell layer and dentate hilus, stratum radiatum and stratum oriens of the hippocampus, and in the subicular cell layer. Intensely stained neuropeptide Y-like immunoreactive fibers were numerous, and present in all areas examined. They formed fiber plexuses in the dentate molecular layer and dentate hilus, stratum moleculare of the hippocampal regio superior, and in the subicular plexiform layer. Neuropeptide Y-like immunoreactive puncta were present in the dentate molecular layer, stratum moleculare of the hippocampus, and in the subicular plexiform layer. Consistent and very characteristic variation in the distribution of somatostatin-like and neuropeptide Y-like immunoreactivity was found along the septotemporal axis of the hippocampus. The distribution of somatostatin-like and neuropeptide Y-like neurons and terminals in the domestic pig displayed striking similarities with the basic pattern of organization of these neuropeptides in other species, although more subtle species-specific characteristics were also observed in the pig.     

Ultrastructural characterization and GAD co-localization of somatostatin-like immunoreactive neurons in CA1 of rabbit hippocampus

Immunocytochemical techniques have been used to identify a striking interneuronal population which is immunoreactive for the peptide, somatostatin. The cell population, which is seen most densely in stratum oriens and at the oriens/alveus border of the CA1 region of rabbit hippocampus, was characterized in light and electron microscopic observations. The cells have dendrites which extend parallel to and into the alveus, with occasional processes ascending through stratum pyramidale toward the hippocampal fissure. The dendrites receive numerous synaptic contacts directly onto aspinous dendritic shafts. Axon collaterals ramify profusely within the pyramidale region, and among the proximal apical and basal pyramidal cell dendrites in areas of stratum radiatum and stratum oriens. Somatostatin-like immunoreactive terminals make synaptic contact, primarily of the symmetric type, with the somata and proximal dendrites of pyramidal neurons. Somatostatin-like neurons are found at approximately equal density in the hippocampus of immature (8 days postnatal) and mature (30 days postnatal) rabbit. Double-labelling techniques, to identify both somatostatin-like and glutamic acid decarboxylase (GAD) immunoreactive neurons, demonstrated that a large proportion of the somatostatin neurons were also GABAergic.     

Somatostatin-containing neurons in rat organotypic hippocampal slice cultures: Light and electron microscopic immunocytochemistry

Light and electron microscopic immunocytochemical techniques were used to study the interneuron population staining for somatostain (SRIF) in cultured slices of rat hippocampus. The SRIF immunoreactive somata were most dense in stratum oriens of areas CA1 and CA3, and in the dentate hilus. Somatostain immunoreactive cells in areas CA1 and CA3 were characteristically fusiform in shape, with dendrites that extended both parallel to and into the alveus. The axonal plexus in areas CA1 and CA3 was most dense in stratum lacunosum-moleculare and in stratum pyramidale. Electron microscopic analysis of this area revealed that the largest number of symmetric synaptic contacts from SRIF immunoreactive axons were onto pyramidal cell somata and onto dendrites in stratum lacunosum-moleculare. In the dentate gyrus, SRIF somata and dendrites were localized in the hilus. Hilar SRIF immunoreactive neurons were fusiform in shape and similar in size to those seen in CA1 and CA3. Axon collaterals coursed throughout the hilus, projected between the granule cells and into the outer molecular layer. The highest number of SRIF synaptic contacts in the dentate gyrus were seen on granule cell dendrites in the outer molecular layer. Synaptic contacts were also observed on hilar neurons and granule cell somata. SRIF synaptic profiles were seen on somata and dendrites of interneurons in all regions. The morphology and synaptic connectivity of SRIF neurons in hippocampal slice cultures appeared generally similar to intact hippocampus. © 1994 Wiley-Liss, Inc.     

A novel population of calretinin-positive neurons comprises reelin-positive Cajal-Retzius cells in the hippocampal formation of the adult domestic pig

Calretinin-containing neurons in the hippocampal formation, including the subiculum, presubiculum, parasubiculum, and entorhinal cortex, were visualized with immunocytochemistry. Calretinin immunoreactivity was present exclusively in non-principal cells. The largest immunoreactive cell population was found in the outer half of the molecular layer of the dentate gyrus and in the stratum lacunosum-moleculare of Ammon's horn. A proportion of these cells were also immunoreactive for reelin, a Cajal-Retzius cell marker. Similar calretinin-positive cells were found in the molecular layer of the subicular complex and entorhinal cortex. In the parasubiculum, a few immunoreactive bipolar and multipolar cells could be observed in the superficial and deep pyramidal cell layers. In the entorhinal cortex, bipolar and multipolar calretinin-positive cells were frequent in layer II, and large numbers of multipolar cells in layer V were immunoreactive. Electron microscopic analysis showed that somata of calretinin-positive cells contained either round nuclei with smooth nuclear envelopes or nuclei with multiple deep infoldings. Immunoreactive dendrites were smooth varicose, and the apposing axon terminals formed both symmetric and asymmetric synapses. Zonula adherentia were observed between calretinin-positive dendrites. Calretinin-positive axon terminals formed two types of synapses. Axon terminals with asymmetric synapses were found close to the hippocampal fissure, whereas axon terminals forming symmetric synapses innervated spiny dendrites in both the molecular layer of the dentate gyrus and in stratum lacunosum-moleculare of Ammon's horn. Calretinin-positive axon terminals formed both symmetric and asymmetric synapses with calretinin-positive dendrites. In conclusion, calretinin-positive neurons form two major subpopulations in the adult domestic pig hippocampus: (1) a gamma-aminobutyric acid (GABA)ergic subpopulation of local circuit neurons that innervates distal dendrites of principal cells in both the dentate gyrus and in Ammon's horn; and (2) Cajal-Retzius type cells close to the hippocampal fissure, as well as in the molecular layer of the subicular complex and entorhinal cortex.     

The distribution of somatostatin-like immunoreactivity in the monkey hippocampal formation

The distribution of somatostatin-like immunoreactivity was studied in the hippocampal formation of the Old World (Macaca fascicularis) and New World (Saimiri sciureus) monkeys. Series of coronal sections were processed by the unlabeled second antiserum method using primary antisera which recognize somatostatin-28 (S309) or somatostatin-28(1-12) (S320). Neuronal cell bodies were more readily stained with antiserum S309 and were observed throughout the hippocampal formation. The most prominent accumulations of stained neurons occur in the hilar region of the dentate gyrus, in strata oriens and pyramidale of regio inferior of the hippocampus, and in the deep layers of the entorhinal cortex. Both antisera demonstrated extensive fiber systems which varied in density regionally in the hippocampal formation. Stained fibers were most prominent in the outer two-thirds of the molecular layer of the dentate gyrus, in stratum lacunosum-moleculare of the hippocampus, in layer I of the presubiculum and in layers I, III, and V of the entorhinal cortex.     

GABAergic neurons containing the Ca2+-binding protein parvalbumin in the rat hippocampus and dentate gyrus

The distribution of Ca2+-binding protein, parvalbumin (PV), containing neurons and their colocalization with glutamic acid decarboxylase (GAD) were studied in the rat hippocampus and dentate gyrus using immunohistochemistry. PV immunoreactive (PV-I) perikarya were concentrated in the granule cell layer and hilus in the dentate gyrus and in the stratum pyramidale and stratum oriens in the CA3 and CA1 regions of the hippocampus. They were rare in the molecular layer of the dentate gyrus, in the stratum radiatum and in the stratum lacunosum-moleculare of the hippocampus. PV-I axon terminals were restricted to the granule cell layer, the stratum pyramidale and the immediately adjoining zones of these layers. Almost all PV-I neurons were also GAD immunoreactive (GAD-I), whereas only about 20% of GAD-I neurons also contained PV. The percentages of GAD-I neurons which were also immunoreactive for PV were dependent on the layer in which they were found; i.e. 40-50% in the stratum pyramidale, 20-30% in the dentate granule cell layer and in the stratum oriens of the CA3 and CA1 regions, 15-20% in the hilus and in the stratum lucidum of CA3 region and only 1-4% in the dentate molecular layer and in the stratum radiatum and the stratum lacunosum-moleculare of the CA3 and CA1 regions. PV-I neurons are a particular subpopulation of GABAergic neurons in the hippocampal formation. Based on their morphology and laminar distribution, they probably include basket cells and axo-axonic cells.     

Ultrastructural description of taurine-like immunoreactive cells and processes in the rat hippocampus

A monoclonal antibody against taurine conjugated to KLH was used to identify and describe taurine-like immunoreactive processes in the rat hippocampus. Tissue from perfused rats was processed for immunohistochemical visualization of taurine and embedded for electron microscopy. Representative tissue samples from three regions, the dentate gyrus, CA3, and CA1, were sectioned, examined, and photographed. In the dentate gyrus, both granule cells and pyramidal basket cells were taurine-like immunoreactive. Some axon terminals in the dentate gyrus molecular layer as well as some mossy fiber boutons in the hilus were also taurine-like immunoreactive. In the CA3 region both pyramidal neurons and glial cells were taurine-like immunoreactive A few small-diameter axon terminals in stratum radiatum and some mossy fiber boutons in stratum lucidum were taurine-like immunoreactive. In CA1, pyramidal neurons and some glia were intensely taurine-like immunoreactive. A few immunoreactive axon terminals were seen in stratum radiatum and stratum oriens. In all regions, dendritic staining predominated. Our results support the hypothesis that while taurine may act as a neurotransmitter in a small portion of hippocampal terminals, its main function is probably as a neuromodulator or ionic regulator.     

Nerve growth factor-like immunoreactive profiles in the primate basal forebrain and hippocampal formation

The distribution of nerve growth factor (NGF), the prototypic neurotrophin, within the basal forebrain and hippocampal formation of young adult monkeys and aged humans was characterized with and affinity purified polyclonal β-NGF antibody raised against mouse β-NGF. In the basal forebrain of both primates, a granular NGF-like immunoreactive (ir) reaction product was observed within neurons of the medial septum, nucleus of the diagonal band, and nucleus basalis of Meynert. NGF-like immunoreactivity exclusively colocalized within p75 NGF receptor (NGFR) containing basal forebrain neurons. The intensity of NGF immunolabeling varied between cell bodies. Many NGF-ir perikarya were highly immunoreactive. In other basal forebrain neurons, NGF-like immunoreactivity was either undetectable or minimally expressed. In the hippocampus of both species, NGF-like immunoreactivity was mainly localized within the hilus of the dentate gyrus and within CA3 and CA2 hippocampal subfields. A marked diminution in NGF-like staining was seen in CA1. Within the hippocampal formation, NGF-like immunoreactivity was heaviest within the neuropil of stratum radiatum, intermediate in stratum oriens, and lightest in stratum pyramidal. NGF-like immunoreactivity was not found within the granule or pyramidal cells of the dentate gyrus and hippocampal formation, respectively. These findings demonstratre the presence of an NGF-like antigen in association with monkey and human magnocellular basal forebrain neurons and within their hippocampal target sites. This lends support to the hypothesis that NGF is internalized from sources located within target regions of the primate cholinergic basal forebrain neurons and is retrogradely transported to these cell bodies where the NGF trophic effect likely occurs.     

Localization of enkephalin-like immunoreactivity to identified axonal and neuronal populations of the rat hippocampus

The distribution of enkephalin-like immunoreactivity in the hippocampal formation of the rat was analyzed. Two specific projection systems are described. The first emerges from the hilus of the dentate gyrus and appears to terminate with notably large boutons on the proximal apical and, to a lesser extent, basal dendrites of hippocampal regio inferior pyramidal cells. This projection corresponds in source, position, and character to the hippocampal mossy fiber system. The second axonal population enters the temporal hippocampal formation from the medial wall of the subicular complex and follows the hippocampal fissure to occupy stratum lacunosum-moleculare of the hippocampus proper and the distal third of the dentate gyrus molecular layer; this pattern corresponds to the distribution of afferent input from the lateral entorhinal cortex and/or perirhinal area. Lesions of the hilus or retrohippocampal area caused a selective depletion of immunoreactivity in the mossy fiber fields and molecular layers of the dentate gyrus, respectively. Enkephalin-like immunoreactivity was found within the somata of three types of hippocampal neurons: (1) granule cells of the dentate gyrus, (2) occasional pyramidal shaped cells of field CA1 stratum pyramidale, and (3) varied scattered interneurons. Of this last group, two types of interneurons were consistently seen. The first occupy the border between stratum radiatum and stratum lacunosum-moleculare and extend processes at right angles to the long axis of the pyramidal cell dendrites, whereas the second lie within stratum radiatum of field CA1 and extend processes in alignment with the long axis of the pyramidal cell dendrites. Cells containing enkephalin-like immunoreacactivity were also observed in the subiculum and retrohippocampal region, most notably including layers II and III of the lateral entorhinal cortex-perirhinal area—the probable source of extrinsic immunoreactive input to the hippocampal formation. Intraventricular colchicine treatment intensified the immunoreactive staining of some hippocampal neurons but did not reveal any cell types not seen to be labeled in untreated rats.     

Catecholaminergic innervation of the hippocampus in the cynomolgus monkey

We studied the immunocytochemical distribution of catecholaminergic fibers in the hippocampal formation from two cynomolgus monkeys by using phenylethanolamine-N-methyltransferase, dopamine-beta-hydroxylase, and tyrosine-hydroxylase antibodies. There were no phenylethanolamine-N-methyltransferase immunoreactive fibers suggesting the lack of epinephrine containing fibers. In order to compare the distributions of tyrosine-hydroxylase and dopamine-beta-hydroxylase immunoreactive fibers, we counted fibers in four hippocampal regions, the dentate gyrus, CA3, CA1, and the subiculum at three different rostrocaudal levels. The distributions of dopamine-beta-hydroxylase and tyrosine-hydroxylase immunoreactive fibers were overlapping but clearly different, suggesting that the hippocampus receives both noradrenergic and dopaminergic inputs in primates. Dopamine-beta-hydroxylase-immunoreactive fibers were present in moderate density and roughly evenly distributed throughout the hippocampus. Tyrosine-hydroxylase immunoreactive fibers were found in high density in the dentate gyrus, in the stratum lacunosum-moleculare, and in the molecular layer of the subiculum. There were only minor side-side and rostrocaudal differences in the distribution of tyrosine-hydroxylase and dopamine-beta-hydroxylase immunoreactive fibers. The identification of a putative dopaminergic projection to primate hippocampus, which is more dense and widely distributed than in the rodent, parallels similar increases in dopaminergic projections reported for primate cerebral neocortex.     

Gap junction protein in rat hippocampus: light microscope immunohistochemical localization

An affinity-purified antibody against a 27-kD rat liver gap-junctional protein (GJP) was used to determine the distribution of GJP immunoreactivity in sections of rat hippocampus. Four heterogeneously distributed GJP-immunostaining patterns were observed. The two most common were punctate immunoreactive elements ranging in size from 0.3 to 0.7 microns and networks of immunoreactive varicose fibers coursing in a variety of directions within the various hippocampal layers and ranging in length from a few microns up to 200 microns. The density of punctate immunostaining was highest within a portion of the stratum pyramidale, at the border between the stratum pyramidale and stratum oriens, and at the border between the molecular and granule cell layers of the dentate gyrus. Moderate to low densities were observed in other hippocampal areas. Immunoreactive fibers were most concentrated within the border portions of the stratum pyramidale and oriens, moderately distributed in the stratum radiatum and the remaining part of the stratum oriens, and sparse in the alveus. In the dentate gyrus, fiber networks were most evident at the border between the granule cell and molecular layers and very unevenly distributed in the molecular layer. The two other patterns observed included intense filamentous immunostaining within a small number of neuronal perikarya located mainly in the stratum pyramidale of areas CA2 and CA3, but rarely in area CA1 or the dentate gyrus, and diffuse immunostaining of small cell bodies dispersed throughout the hippocampus but most numerous in the vicinity of the stratum pyramidale and in the alveus. All of these immunostaining patterns were seen at all rostrocaudal hippocampal levels. These results suggest that if GJP-immunoreactive fibers and neurons observed in the hippocampus have the capacity to form gap junctions, then electrotonic transmission may constitute an important means of information processing within this structure.     

Intravesicular localization of zinc in rat telencephalic boutons. A histochemical study

A transition metal (presumably zinc) has been localized inside the synaptic vesicles of rat telencephalic boutons which make asymmetric synaptic contacts (Gray type I). A modification of Timm's sulphide-silver method for electron microscopy was applied to different areas of the rat forebrain: olfactory bulb, septum, caudate-putamen, amygdaloid complex, neocortex, entorhinal cortex and different parts of the hippocampal formation, viz. subiculum, stratum radiatum and oriens of both regio superior (CA1) and regio inferior hippocampi (CA3), the mossy fibre zone and the hilus fascia dentata and stratum moleculare in the gyrus dentatus. It was observed that the Timm staining in all these areas was located in synaptic boutons. Labelled boutons displayed a population of round clear vesicles and few dense core vesicles and made asymmetric synaptic contacts on dendritic spines. Silver granules in these boutons were confined to only a minor fraction of the round clear vesicles (approximately 10%). Labelled boutons occasionally showed silver granules in the synaptic clefts. The possible involvement of vesicular zinc in synaptic transmission is discussed.     

The distribution of neurons containing delta sleep-inducing peptide in the hippocampal formation

The distribution of neurons containing immunoreactive delta sleep-inducing peptide (IDSIP) in the hippocampal formation was investigated by immunocytochemistry. For this study, thirteen antisera to the peptide were used. Three antisera were found suitable for immunocytochemistry; the remainder gave only non-specific background staining. Neurons containing IDSIP were demonstrable in the subicular cortex immediately adjacent to CA1. No specific staining was found in other parts of the hippocampal formation including the pyramidal layer of Ammon's Horn and the dentate gyrus. These three antisera also stained cells in the cerebral cortex-primarily temporal, parietal and frontal regions--as well as in the ventral forebrain, although the number of cells in each area varied somewhat with the different antisera. The presence of IDSIP in neurons which constitute the major efferent pathway of the hippocampus, as well as in areas known to be functionally related to the hippocampus, i.e., the adjacent isocortices and ventral forebrain, suggests a possible role for the peptide in the regulation of behavior.     

Direct synaptic contacts of medial septal efferents with somatostatin immunoreactive neurons in the rat hippocampus

Anterogradely labeled projections from the medial septum to hippocampal somatostatin immunoreactive (SOM-i) neurons were studied with double-label immunocytochemistry under light (LM) and electron microscopic (EM) conditions. Medial septal projections were identified after injecting the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) followed by immunohistochemical visualization of PHA-L presynaptic terminal labeling and concurrent immunocytochemical staining of SOM in hippocampal target cell bodies. This double-label procedure yielded blue-black nickel enhanced DAB stained, PHA-L-immunoreactive terminals on light brown SOM-i neurons that were investigated by correlative LM and EM observations. PHA-L-labeled terminal contacts with often basket-like appearance were localized with highest densities on soma and proximal dendrites of SOM-i neurons in stratum oriens of Ammon's horn and hilus of dentate gyrus, and some minor projections to stratum pyramidale and radiatum. Most double-labeled contacts could be identified as symmetric type synapses equally divided over soma and proximal dendrites of several forms of SOM-i neurons. These data indicate monosynaptic regulation of the hippocampal intrinsic SOM system by septal input, which probably represents a peptidergic subpopulation of the hippocampal GABAergic system.     

The distribution of substance P in the cerebral cortex and hippocampal formation: an immunohistochemical study in the monkey and rat

The distribution of substance P-containing fibers in the cerebral cortex and the hippocampal formation of the Japanese monkey (Macaca fuscata fuscata) was studied by immunohistochemistry using a monoclonal antibody raised against substance P. The results were compared with the distribution in homologous regions of the rat brain. Substance P-containing fibers and cell bodies were observed in all regions of the cerebral cortex. In deep layers of the neocortex (IV-VI), substance P-immunoreactive fibers formed arrays that ran perpendicular to the surface. These immunoreactive fibers tended to branch as they approached the cortical surface in layers II and III, at which point they were oriented in many directions. The molecular layer (I) of the monkey neocortex contained many granular, substance P-immunoreactive structures, resembling terminal boutons. In contrast to the monkey, rat cortical areas contained substantially fewer substance P-containing fibers. The immunoreactive profiles, mostly fine dot-like structures, were seen uniformly in layers II and IV of the rat neocortex, although in the medial prefrontal cortex many thick, varicose fibers were also observed. Substance P-containing fibers were seen throughout the hippocampal formation of the monkey, including the subiculum and the parahippocampal regions. The regional distribution of immunoreactive fibers was most dense in the molecular layers of dentate gyrus, in the stratum moleculare of the CA1 region, and in the stratum pyramidalis of the CA2 region. In the rat, the hippocampus and dentate gyrus contained fewer immunoreactive fibers. Moderate densities were observed in the rat subiculum and entorhinal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)     

An immunocytochemical study of choline acetyltransferase-containing neurons and axon terminals in normal and partially deafferented hippocampal formation

Monoclonal antibodies to the acetylcholine synthesizing enzyme, choline acetyltransferase (ChAT), have been used to study putative cholinergic structures in immunocytochemical preparations of normal rat hippocampal formation and of hippocampal formation deprived of its septal innervation. Small numbers of ChAT-positive (ChAT+) neuronal somata were observed scattered throughout the septotemporal extent of the normal hippocampal formation. They were most common in stratum lacunosum-moleculare of regio superior, but were also found in various layers of the dentate gyrus and occasionally in the remaining hippocampal laminae. In addition, light microscopy demonstrated that ChAT+ terminal fields in normal hippocampal formation were organized in discrete bands and laminae. Pronounced dense bands were observed: immediately superficial to stratum granulosum; deep to stratum pyramidale; and at the border between stratum radiatum and stratum lacunosum-moleculare. In the dentate gyrus, ChAT+ staining was pronounced in the hilus at temporal levels, but only moderate staining occurred in the anterior hilus and throughout the molecular layer. A close correspondence was observed in the density and distribution of ChAT+ immunoreactivity and acetylcholinesterase staining. Electrolytic lesions of the medial septal nucleus/diagonal band complex had no effect on the occurrence of ChAT+ somata, but virtually abolished the ChAT+ laminar staining pattern and eliminated all but occasional small patches of ChAT+ terminals. These results confirm that the vast majority of hippocampal cholinergic terminals originate either from neurons of the medial septum/diagonal band complex or from fibers of passage. The newly observed intrinsic hippocampal neurons can account for at least some of the ChAT activity remaining after septal lesions, and they apparently contribute to the cholinergic innervation of the hippocampal formation.     

GABA plasma membrane transporters,GAT-1 and GAT-3, display different distributions in the rat hippocampus

This study evaluates the distribution of two high affinity gamma-aminobutyric acid (GABA) transporters (GAT-1 and GAT-3) in the rat hippocampus using immunocytochemistry and affinity purified antibodies. GAT-1 immunoreactivity was prominent in punctate structures and axons in all layers of the dentate gyrus. In Ammon's horn, immunoreactive processes were concentrated around the somata of pyramidal cells, particularly at their basal regions. The apical and basal dendritic fields of pyramidal cells also displayed numerous GAT-1 immunoreactive punctate structures and axons. The zone of termination of the mossy fibers that includes both the hilus of the dentate gyrus and stratum lucidum of the CA3 area was the lightest immunolabeled region of the hippocampal complex. Electron microscopic preparations demonstrated that GAT-1 immunoreactive axon terminals form symmetric synapses with somata, axon initial segments, and dendrites of granule and pyramidal cells in the dentate gyrus and Ammon's horn, respectively. Immunoreactivity was localized to the plasma membrane and the cytoplasm of axon terminals. The somata of previously described local circuit neurons in the dentate gyrus and Ammon's horn contained GAT-1 immunoreactivity associated with the Golgi complex. Light, diffuse GAT-3 immunoreactivity was present throughout the hippocampal formation. Thin, astrocytic glial processes displayed GAT-1 and GAT-3 immunoreactivity. This localization of GAT-1 and GAT-3 indicates that they are involved in the uptake of GABA from the extracellular space into GABAergic axon terminals and astrocytes. © 1996 Wiley-Liss, Inc.     

Radioautographic study of the rat brain after injection of [1,2-3H]corticosterone.

Cryostat sections of the central nervous system of adrenalectomized male rats injected with [3H]corticosterone were examined by radioautography. One hour after the injection, radioactivity was found to be selectively concentrated in specific neurons of the septum, the hippocampal complex (precommissural hippocampus, cornu Ammonis, gyrus dentatus, subiculum), the indusium griseum, the amygdala and in certain areas of the cortex. In the hippocampus, the pyramidal neurons in fields CA1 and CA2 of the cornu Ammonis and the granule neurons of the gyrus dentatus contained more radioactivity than did other regions of the brain. Most of the silver grains were localized in the nuclei of labeled cells. The topographic distribution of corticosterone-concentrating neurons shows that the hormonal target sites in the central nervous system are mainly extrahypothalamic.     

The fine structures of the VIP-Like immunoreactive neurons in the cat hypothalamus

The fine structures of the VIP-like immunoreactive neurons in the suprachiasmatic nucleus (SCN) and the arcuate nucleus ( ARN ) of the cat hypothalamus were investigated by electron microscopic immunocytochemistry. The VIP-like immunoreactive soma and fibers could be successfully visualized by a modified PAP method. VIP-like immunoreactive neurons in both nuclei contained immunoreactive rER, Golgi complexes and many immunoreactive granules, as well as well developed mitochondria. VIP-like immunoreactive synaptic endings with synaptic membrane specialization of Gray's type I and II were found in the SCN. Moreover VIP-like immunoreactive preterminal elements that made synaptic contact with VIP-like immunoreactive neuronal soma were also detected. On the other hand, it was difficult to detect typical preterminal endings with immunoreactivity in the ARN ; however, VIP-like immunoreactive processes in contact with the basement membrane of the capillaries were observed. These observations indicate that VIP-like immunoreactive neurons in the SCN act as intrinsic neurons and are involved in neuroendocrine function in ARN .     

Distribution,morphological features,and synaptic connections of parvalbumin- and calbindin D28k-immunoreactive neurons in the human hippocampal formation

Calcium binding proteins calbindin D_28k (CaBP) and parvalbumin (PV) are known to form distinct subpopulations of gamma-aminobutyric acid (GABA)ergic neurons in the rodent hippocampal formation. Light and electron microscopic morphology and connections of these protein-containing neurons are only partly known in the primate hippocampus. In this study, CaBP and PV were localized in neurons of the human hippocampal formation including the subicular complex (prosubiculum, subiculum, and presubiculum) in order to explore to what extent these subpopulations of hippocampal neurons differ in phylogenetically distant species. CaBP immunoreactivity was present in virtually all granule cells of the dentate gyrus and in a proportion of pyramidal neurons in the CA1 and CA2 regions. A distinct population of CaBP-positive local circuit neurons was found in all layers of the dentate gyrus and Ammon's horn. Most frequently they were located in the molecular layer of the dentate gyrus and the pyramidal layer of Ammon's horn. In the subicular complex pyramidal neurons were not immunoreactive for CaBP. In the prosubiculum and subiculum immunoreactive nonpyramidal neurons were equally distributed in all layers, whereas in the presubiculum they occurred mainly in the superficial layers. Electron microscopy showed typical somatic and dendritic features of the granule, pyramidal, and local circuit neurons. CaBP-positive mossy fiber terminals in the hilus of the dentate gyrus and terminals of presumed pyramidal neurons of Ammon's horn formed asymmetric synapses with dendrites and spines. CaBP-positive terminals of nonprincipal neurons formed symmetric synapses with dendrites and dendritic spines, but never with somata or axon initial segments. PV was exclusively present in local circuit neurons in both the hippocampal formation and subicular complex. Most of the PV-positive cell bodies were located among or close to the principal cell layers. However, large numbers of immunoreactive neurons were also found in the molecular layer of the dentate gyrus and in strata oriens of Ammon's horn. PV-positive cells were equally distributed in all layers of the subicular complex. Electron microscopy showed the characteristic somatic and dendritic features of local circuit neurons. PV-positive axon terminals formed exclusively symmetric synapses with somata, axon initial segments and dendritic shafts, and in a few cases with dendritic spines. The CaBP- and PV-containing neurons formed similar subpopulations in rodents, monkeys, and humans, although the human hippocampus displayed the largest variability of these immunoreactive neurons in their morphology and location. Calcium binding protein-containing neurons frequently occurred in the molecular layer of the human dentate gyrus and in the stratum lacunosum-moleculare of Ammon's horn. The corresponding areas of the rat or monkey hippocampus were devoid of such neurons. In both rodents and primates similar populations of principal neurons contained CaBP. In addition, CaBP and PV were localized in distinct and nonoverlapping populations of nonprincipal cells. Their target selectivity did not change during phylogeny (e.g., PV-positive cells mainly innervate the perisomatic region and CaBP-positive cells the distal dendritic region of principal cells). © 1993 Wiley-Liss,Inc.