Showing papers on "Dentate gyrus published in 1984"

Different populations of GABAergic neurons in the visual cortex and hippocampus of cat contain somatostatin- or cholecystokinin- immunoreactive material

Abstract: The coexistence of gamma-aminobutyric acid (GABA), glutamate decarboxylase (GAD), and cholecystokinin (CCK)- or somatostatin- immunoreactive material in the same neurons was studied in the hippocampus and visual cortex of the cat. One-micrometer-thick serial sections of the same neuron were reacted to reveal different antigens by the unlabeled antibody enzyme method. All CCK- and somatostatin- immunoreactive neurons in the cortex and all CCK-immunoreactive and the majority of somatostatin-immunoreactive neurons in the hippocampus that could be examined in serial sections were also immunoreactive for GABA. In neurons that were immunoreactive for GAD it was often possible to demonstrate immunoreactivity for one of the peptides as well as for GABA. GABA-immunoreactive neurons, as revealed by an antiserum to GABA, were present in all layers of the cortex and hippocampus, and their shape, size, and distribution were similar to GAD-immunoreactive neurons. All GAD-immunoreactive neurons were also positive for GABA, but the latter staining revealed additional neurons. CCK/GABA- and somatostatin/GABA-immunoreactive neurons were present mainly in layers II and upper III and in layers V and VI in the visual cortex. CCK/GABA- immunoreactive neurons were most frequently present in the strata oriens, pyramidale, and moleculare of the hippocampus and in the polymorph cell layer of the dentate gyrus. Somatostatin/GABA- immunoreactive neurons were localized mainly in the stratum oriens and in the hilus of the fascia dentata. The two peptides could not be found in the same neuron. The majority of neurons that were GABA immunoreactive did not stain for either peptide. The presence of CCK- and somatostatin-immunoreactive material in GABAergic cortical neurons raises the possibility that neuroactive peptides affect GABAergic neurotransmission.

Mitotic neuroblasts in the 9-day-old and 11-month-old rodent hippocampus.

Abstract: Ultrastructural identification of mitotic neuronal precursors beneath the basal hippocampal granule cell layer was made using electron micrographs of [3H]thymidine-labeled cells. Ultrathin sections were obtained by a method that allows serial thin sectioning of reembedded sections previously prepared for light microscopic radioautography. The electron microscopic observations reported in this study reveal: (1) that a steady rate of granule cell neurogenesis occurs during the first year of a rodent's life; (2) that newly formed granule neurons in the dentate gyrus of the newborn mouse and adult rat are a result of neuroblast division; and (3) two distinct classes of mitotic cells can be identified during the peak period of postnatal neurogenesis--those with synapses on their cell bodies and processes and those with no synapses or processes.

The distribution of hypoglycemic brain damage.

Abstract: Rats were exposed to insulin-induced hypoglycemia resulting in periods of cerebral isoelectricity ranging from 10 to 60 min. After recovery with glucose, they were allowed to wake up and survive for 1 week. Control rats were recovered at the stage of EEG slowing. After sub-serial sectioning, the number and distribution of dying neurons was assessed in each brain region. Acid fuchsin was found to stain moribund neurons a brilliant red. Brains from control rats showed no dying neurons. From 10 to 60 min of cerebral isoelectricity, the number of dying neurons per brain correlated positively with the number of minutes of cerebral isoelectricity up to the maximum examined period of 60 min. Neuronal necrosis was found in the major brain regions vulnerable to several different insults. However, within each region the damage was not distributed as observed in ischemia. A superficial to deep gradient in the density of neuronal necrosis was seen in the cerebral cortex. More severe damage revealed a gradient in relation to the subjacent white matter as well. The caudatoputamen was involved more heavily near the white matter, and in more severely affected animals near the angle of the lateral ventricle. The hippocampus showed dense neuronal necrosis at the crest of the dentate gyrus and a gradient of increasing selective neuronal necrosis medially in CA1. The CA3 zone, while relatively resistant, showed neuronal necrosis in relation to the lateral ventricle in animals with hydrocephalus. Sharp demarcations between normal and damaged neuropil were found in the hippocampus. The periventricular amygdaloid nuclei showed damage closest to the lateral ventricles. The cerebellum was affected first near the foramina of Luschka, with damage occurring over the hemispheres in more severely affected animals. Purkinje cells were affected first, but basket cells were damaged as well. Rare necrotic neurons were seen in brain stem nuclei. The spinal cord showed necrosis of neurons in all areas of the gray matter. Infarction was not seen in this study. The possibility is discussed that a neurotoxic substance borne in the tissue fluid and cerebrospinal fluid (CSF) contributes to the pathogenesis of neuronal necrosis in hypoglycemic brain damage.

On the role of hippocampal connections in the performance of place and cue tasks: comparisons with damage to hippocampus.

Abstract: Behavioral changes following interruption of the main connections of hippocampus and closely related areas (entorhinal cortex, mammillary bodies, dentate gyrus) were determined and compared with findings of previous research that involved direct damage to hippocampus. By a within-subjects design, rats were trained to run in a radial maze with a procedure that involved two kinds of learning (place and cue) and two memory functions (working and reference memory). Rats with fimbria-fornix and entorhinal cortex lesions were impaired on both the place and the cue task. Specifically, the animals suffered a general impairment in working memory on both tasks but were impaired in reference memory only on the place task. Animals with lesions of the dentate gyrus and mammillary bodies were able to perform the complex place and cue tasks with minimal problems. In previous research it was found that direct damage to hippocampus (including all cell fields, alveus, fimbria) resulted in impaired performance only on the place task (Jarrard, 1983). Taken together, these findings indicate that interruption of hippocampal input/output pathways and/or damaging some closely related structures has a greater effect on the behaviors studied than does direct damage to hippocampus.

Regional changes in brain glucose metabolism reflect cognitive impairments in aged rats.

Abstract: Aged rats (22 to 24 months) and young control rats (3 months) were tested in a battery of behavioral tests which included tests of learning, place navigation, sensorimotor integration, motor coordination, activity, and exploration. Following testing all animals were analyzed in an unanesthetized state for their local glucose utilization. Significant differences in glucose utilization were found between the aged and young groups on some behaviors and in some brain regions. There was considerable variability in the aged group in both their behavioral performance and their glucose utilization scores; thus, attempts were made to determine whether the variability in the degree of impairment within any particular behavioral test was correlated to the regional glucose utilization scores in any of the 45 brain regions analyzed. In two of the behavioral tests employed (i.e., one for learning and one for place navigation), the decline in performance correlated significantly with the decrement in regional glucose utilization. Moreover, the performance in these two tests showed significant correlation with glucose use in only five regions (dentate gyrus, medial septum-diagonal band area, hippocampal CA1, hippocampal CA3, and prefrontal cortex). These results show that the learning impairments in the aged rats are related to the extent of decrease in glucose utilization in restricted areas of the limbic system. In addition, the results show that the individual rats within an aged rat population develop cognitive impairments to a variable degree and that the aged rats with the most pronounced learning impairments are the ones exhibiting the most severe functional decrements, in terms of glucose utilization, in the septohippocampal system and the prefrontal cortex. This suggests that aging rats may be interesting not only for the study of the normal aging process, but also as a model of dementia.

Cellular and connective organization of slice cultures of the rat hippocampus and fascia dentata

Abstract: This study examined the cellular and connective organization of hippocampal tissue taken from 6–8-day-old rats and cultured by the roller tube technique for 3–6 weeks. In the cultures containing the fascia dentata and the hippocampus proper (CA1, CA3, CA4) the main cell and neuropil layers were organotypically organized when observed in ordinary cell stains. The normal distribution of smaller cell populations of AChE-positive neurons and somatostatin-reactive neurons was demonstrated by histochemical and immunohistochemical methods. Both cell types were mainly confined to str. oriens of CA3 and CA1 and the dentate hilus (CA4). Individual dentate granule fells and hippocampal pyramidal cells were injected with lucifer yellow and HRP, revealing great stability of the dendritic patterns of these cells in the culture condition. The same was found for the axonal branching and termination of HRP-filled mossy fibers arising from an HRP-injected granule cell. The preservation of organotypic afferent patterns in the cultures was also shown by Timm staining of the terminal distribution of the mossy fiber system. Mossy fiber terminals, with characteristic ultrastructural features verified in the electron microscope, were thus found in the hilus (CA4) and along the CAS pyramidal cell layer onto the CA3-CA1 transition. Depending on the amount of dentate tissue relative to CA3 the terminals could stop before reaching CA1 (small fascia dentata) or take up additional intra and infrapyramidal locations along CA3 (small CA3). In cultures with a gap in the CA3 pyramidal cell layer some mossy fiber terminals were found in contact with the CA3 pyramidal cells beyond the gap. In all cultures there was an aberrant projection of supragranular mossy fibers. This projection is analogous to the one known from lesion and transplant studies to form in the absence of the entorhinal perforant path input to the dentate molecular layer. Also, in accordance with these studies the Timm staining pattern of the outer parts of the dentate molecular layer and the entire molecular layer of the hippocampus was altered corresponding to the spread of afferents normally confined to the inner zone of the dentate and str. radiatum of CA3 and CA1. Possibly as a consequence of the lack of normal targets for projections from CA1, this subfield contained an unusually dense Timm staining suggestive of autoinnervation. In the analysis of the cellular and connective organization of hippocampal slice cultures both normal and additional traits were found. The normal traits demonstrated the stability of the intrinsic structure once it survives in vitro. The additional traits had formed according to the principles for reorganization of nerve connections known from lesion and transplant studies of hippocampal and dentate tissue.

Radial organization of the hippocampal dentate gyrus: A Golgi ultrastructural, and immunocytochemical analysis in the developing rhesus monkey

Abstract: The cytoarchitectonic organization of the dentate gyrus was analyzed in the rhesus monkey at various embryonic (E) and postnatal (P) ages with the rapid Golgi method, transmission electron microscopy (EM), and immunocytochemical localization of glial fibrillary acidic protein (GFAP). From the earliest ages (stage I, E38-E83), immature granule cells were arranged radially along elongated fibers that extend from the ventricular zone to the pial surface. The glial nature of these radial fibers was confirmed by the presence of GFAP antigen in their cytoplasm detected clearly by E70. EM analysis at this age showed that granule cells situated within the dentate plate, as well as many neurons still migrating from the ventricular zone, were closely apposed to fascicles of radial glial fibers. The radial organization of the dentate plate was even more evident during stage II (E83-E165). Thus, in E97 and E125 specimens, radially oriented immunoreactive glial processes emerged from somas situated either in the ventricular or subgranular zones, penetrated between columns of neurons in the granular layer, branched upon entering the molecular layer, and finally terminated at the pial surface. Palisades of glial processes delineated ontogenetic radial units which consisted of stacks of granule cell bodies in different stages of maturation. In a given radial unit, more mature cells were located superficially (closer to the pial surface) and less mature cells were located at progressively deeper levels. This radial organization of the dentate gyrus was maintained during stage III (P0-P60) and stage IV (2 months-adult). Furthermore, the number of GFAP-positive proliferating cells in the subgranular zone increased from 1 to 5 months. In the mature brain, the radial organization of the dentate gyrus was less apparent although many glial fibers still penetrated the granule cell layer. The present results indicate that the developing dentate gyrus in primates consists of a series of ontogenetic radial units that resemble those described in the fetal neocortex (Rakic, '72). They further suggest that the development and maintenance of this radial columnar organization may be imposed by the orientation of glial scaffolding during development.

The commissural connections of the monkey hippocampal formation.

Abstract: The commissural connections of the hippocampal formation have been analyzed in the monkey (Macaca fascicularis) using both anterograde and retrograde labeling techniques. We have observed a number of striking differences between the organization of the commissural projections in the monkey and that observed in the rodent brain. In particular, only the rostral (or uncal) part of Ammon's horn (or hippocampus proper) and the associated part of the dentate gyrus have been found to be connected by commissural fibers. This is in marked contrast to the organization of the crossed connections in the rodent brain where both major fields of the hippocampus (i.e., the regio superior and the region inferior) receive a strong, topographically organized, projection throughout their rostrocaudal extent from the regio inferior of the opposite side, while the inner third of the molecular layer of the entire dentate gyrus receives a topographically organized input from calls in the hilar region of the contralateral dentate gyrus. The subicular complex of the monkey gives rise to a substantially greater number of commissurally directed fibers. The subiculum itself projects to the postserior portion of the contralateral medial entorhinal cortex and receives a less substantial reciprocal projection from this same area; the subiculum does not appear to be homotopically interconnected. The presubiculum gives rise to the major commissural projection of the monkey hippocampal formation. From all rostrocaudal levels of the presubiculum there is a robust projection to the contralateral medial entorhinal cortex. This projection seems to be topographically organized and terminates most heavily in layers III and IV of the entorhinal cortex. This crossed presubiculo-entorhinal projection is paralleled in its organization by an associational projection from the presubiculum to the ipsilateral entorhinal cortex, but, interestingly, the presubiculum does not seem to project to the presubiculum of the opposite side. The parasubiculum projects to neither the contralateral entorhinal cortex nor the contralateral parasubiculum. However, the subicular complex as a whole appears to be in receipt of a minor input from the contralateral parahippocampal gyrus (fields TF of and TH of Bonin and Bailey). Cells primarily in layer III of the medial entorhinal cortex (area 28a) project homotopically to the contralateral entorhinal cortex where they terminate in layer III. The medial entorhinal cortex also gives rise to a minor projection the contralateral parasubiculum and to the region superior of the contralateral hippocampus and the caudalmost part of the outer molecular layer of the dentate gyrus. This crossed temporo-ammonic projection appears to arise only from the caudal part of the medial entorhinal cortex. The lateral entorhinal cortex (area 28b) has no commissural projection to the corresponding field on the opposite side, but it does receive a minor projection from the contralateral perirhinal cortex (area 35). Both divisions of the entorhinal cortex receive a light projection from the contralateral parahippocampal gyrus.

The projection of the supramammillary nucleus to the hippocampal formation: an immunohistochemical and anterograde transport study with the lectin PHA-L in the rat.

Abstract: The organization and possible neurotransmitter specificity of a projection from the lateral supramammillary nucleus to the hippocampal formation has been examined with immunohistochemical and axonal transport methods in the adult male rat. Experiments with the retrograde tracer true blue indicate that neurons throughout the rostrocaudal extent of the nucleus are labeled after injections in either dorsal parts of the dentate gyms and Ammon's horn, or the entorhinal area, although cells labeled by the entorhinal injections tended to occupy more ventral parts of the nucleus. Combined immunohistochemical-retrograde transport studies showed that a small number (<5%) of cholecystokinin-immunoreactive neurons in the caudal tip of the supramammillary nucleus project to, the hippocampal formation, as do some (5–10%) vasoactive intestinal polypeptide (VIP)-immunoreactive neurons throughout the nucleus. Anterograde transport studies with the lectin phaseolus vulgaris leucoagglutinin (PHA-L) indicate that fibers from the supramammillary nucleus innervate all parts of the hippocampal formation. Many varicose fibers with terminal boutons were observed in the granular and molecular layers of the dentate gyrus, throughout the molecular layer of field CA3 of Ammon's horn, and in the pyramidal layer and stratum oriens of subfield CA3a. Only scattered fibers were found in fields CA1 and CA2. Apparent terminal fields were also observed in superficial parts of the molecular layer, and deep parts of the pyramidal layer, of the subiculum, in the deepest layer of the presubiculum and parasubiculum, and in all layers of the entorhinal area.

Electrophysiology of dentate gyrus granule cells

Abstract: The orthodromic synaptic responses, membrane properties, and responses of dentate gyrus granule cells (DGCs) to several convulsant agents were studied in the in vitro hippocampal slice preparation....

A diffuse alpha MSH-immunoreactive projection to the hippocampus and spinal cord from individual neurons in the lateral hypothalamic area and zona incerta.

Abstract: The course, distribution, and possible neurotransmitter specificity of a projection from the lateral hypothalamic area (LHA) and zona incerta to the hippocampal formation (dentate gyrus, Ammon's horn, subicular region, and entorhinal area) and spinal cord were examined anatomically in the adult rat. First, small injections of the fluorescent tracer fast blue were made into either the septal part of the dentate gyrus and Ammon's horn or the entorhinal area, and the distribution of retrogradely labeled cells was plotted. In each experiment many cells were labeled in the LHA and zona incerta, and little evidence for a topographically organized projection to different parts of the hippocampal formation was found. Second, a combined retrograde transport-immunofluorescence method was used to show that some 95% of the fast blue-labeled neurons in the LHA and zona incerta were also stained with an antiserum to the opiate peptide alpha-melanocyte-stimulating hormone (alpha MSH), but not an antiserum to adrenocorticotropin (ACTH)1-24. It was also found that small numbers of retrogradely labeled neurons were stained with antisera to somatostatin 14 and 28, dynorphin (1-17), and angiotensin II. Third, the distribution of alpha MSH-immunoreactive fibers was plotted, and they were found to form a diffusely organized plexus throughout all of the subfields of the hippocampal formation. These fibers were virtually eliminated after transections of the fimbria and the region between the entorhinal area and the caudal amygdala. Forth, the course of fibers from the LHA and zona incerta was examined with the anterogradely transported lectin Phaseolus Vulgaris Leucoagglutinin (PHAL). Such fibers reach the hippocampal formation by a dorsal route through the septal region and fimbria, and by a ventral route through the amygdala. And fifth, double retrograde transport and immunohistochemical methods were used to show that at least some alpha MSH-stained neurons in the LHA and zona incerta give rise to collaterals that innervate both the hippocampal formation and the spinal cord. Alpha MSH-stained fibers in the spinal cord also form a widely scattered plexus with no obvious circumscribed terminal fields. It is suggested that the diffusely organized projection from the LHA to the cerebral cortex and spinal cord may play a role in the general arousal associated with a variety of motivated behaviors.

Direct commissural connections to the basket cells of the hippocampal dentate gyrus: anatomical evidence for feed-forward inhibition

Abstract: After lesions were placed in the hippocampal commissures, degenerating terminals could be localized above, inside and beneath the granule cell layer of the contralateral dentate gyrus. The terminals formed asymmetric synapses with spines, dendritic shafts and somata of granule cells. Degenerating terminals also formed synapses with dendrites and somata of basket cells identified by the Golgi-electron microscope technique. These basket cells were located either at the hilar border of the granule cell layer or in the molecular layer and each formed an axonal plexus around the somata and proximal dendrites of granule cells. These observations provide an anatomical basis for the recently described feed-forward inhibition in this brain region.

The distribution of acetylcholinesterase in the hippocampal formation of the monkey.

Abstract: In order to study the distribution of acetylcholinesterase (AChE) in the primate hippocampal formation, we have stained serial sections through the brains of nine macaque monkeys for AChE by two variants of the Koelle acetyl-thiocholine method. We have found a distinctive pattern of staining in the hippocampal formation which varies in intensity both from region to region, and along rostrocaudal and radial gradients within each region. In the dentate gyrus, there is intense staining of the inner one-third of the molecular layer with much lighter staining in the rest of the molecular layer except for a moderately stained band at its outer edge. In the caudal half of the dentate gyrus, the inner portion of the molecular layer is less intensely stained though there is a distinctly denser band of staining just above, and partly within, the superficial margin of the granule cell layer. The granule cells are unstained but there are AChE-positive fibers which run through the granule cell layer to the molecular layer. The hilar region of the dentate gyrus has a narrow band of heavy staining (which corresponds to an acellular layer in Nissl-stained sections) just subjacent to the granule cell layer; the remainder of the hilus, where most of the hilar cells reside, is less intensely stained and at caudal levels is almost entirely unstained. In the regio inferior of the hippocampus, there is intense staining of the stratum oriens which extends into the pyramidal cell layer; the stratum radiatum and the stratum lacunosum-moleculare are also stained and here the staining pattern shows some degree of stratification. By contrast, most of the alveus, the pyramidal cell somata, and the layer of mossy fibers (stratum lucidum) are unstained. The border region between regio inferior and regio superior of the hippocampus (field CA2 of Lorente de No, ′34) is especially heavily stained. This contrasts markedly with regio superior, which is more lightly stained than regio inferior. Stratum oriens and stratum radiatum of regio superior have a more evenly distributed pattern of staining, though the intensity of staining increases sharply at the border with the subiculum. Stratum lacunosum-moleculare is only lightly stained throughout much of the transverse extent of regio superior but there is also a conspicuous and constant patch of heavier staining at the border with the subiculum. The pyramidal cell layer of the subiculum is entirely unstained but there is a thin band of staining just above the pyramidal cell layer in the molecular layer of the subiculum which is most noticeable at about the middle of its rostrocaudal extent. The most distinctive layer of the subiculum in acetylcholinesterase preparations is the deep or polymorphic layer which, throughout its rostrocaudal extent, contains numerous stained fibers and cell bodies. The deep portion of the outer, cell dense layer of the presubiculum contains a thin plexus of AChE-positive fibers as well as lightly stained capillary profiles. The superficial portion of the principal cell layer is relatively unstained and contrasts with the fairly heavy staining of the molecular layer, which is especially pronounced in the medial half of the presubiculum. The superficial, or primary, cell layer of the parasubiculum can be divided into three subdivisions on the basis of cytoarchitectonic appearance and on acetylcholinesterase staining characteristics. The lateral and dorsal divisions of this layer stain darkly for acetylcholinesterase while the medial division is less intensely stained. The rostral portion of the entorhinal cortex, which has cytoarchitectonic features characteristic of the lateral entorhinal cortex in nonprimates, is diffusely stained with the greatest density of precipitate observed in layers III and V and the lateral half of layer I. The pattern of staining is more laminar at more caudal levels (medial entorhinal cortex) where layers I, III, IV, and V are distinctly labeled. In the lateral entorhinal cortex, the distribution of acetylcholinesterase-positive fibers in layer III takes on a patchy appearance and this pattern appears to be most closely associated with the irregular patches of cells in this layer rather than the acellular interstices. In the caudal portion of the medial entorhinal cortex, there are distinctive spheres of acetylcholinesterase-positive fibers which straddle layers I and II, and which have tightly packed clusters of layer II cells at their cores. Interestingly, these cells are distinct in appearance from the more common layer II stellate cells.

Evidence for a ventral septal projection to the hippocampal formation of the rat

Abstract: In a series of experiments in which the known projections of the septal complex to the hippocampal formation have been transected, we have used both anterograde and retrograde tracing techniques in an attempt to demonstrate a ventral septo-hippocampal pathway. In cases where transections of the fimbria, dorsal fornix and supracallosal stria were complete, injections of the retrograde tracers wheat germ agglutinin-conjugated horseradish peroxidase or Fast blue, resulted in labeled cells in the ipsilateral septal complex, primarily in the nucleus of the diagonal band. The number of cells labeled in these experiments was approximately 5–10% of that seen in experiments in animals with intact dorsal pathways who had received similar injections. The presence of a ventral pathway was confirmed in anterograde labeling experiments in which injections of 3H-amino acids were made into the septal complex. The autoradiogfaphs demonstrated that the projection terminates most heavily in the entorhinal cortex and to a lesser extent in the ventral subicular complex; there may be an additional minor projection to the temporal half of the hippocampus and dentate gyrus. Finally, using double labeling procedures, we were able to demonstrate that at least a portion of the cell population that gives rise to the ventral pathway demonstrates choline acetyltransferase immunoreactivity and is presumably cholinergic.

The distribution of Timm's stain in the nonsulphide‐perfused human hippocampal formation

Abstract: A detailed description is given of the distribution of Timm's staining in the human hippocampal formation. In sections cut transverse to the long axis of the hippocampal formation the same pattern of staining is seen throughout almost all of the structure, i.e., through all the main body except the most caudal region and, following the medial bend made by the long axis, through most of the pes hippocampi. The staining typically filled almost the whole of the hilus of the dentate gyrus and the whole depth of the adjacent stratum pyramidale and stratum lucidum of subfield CA3. Rostrally, staining was traced into the tip of the uncus. Caudally, staining was traced to the inferior surface of the splenium at the apex of the caudal taper of the hippocampus. No staining was found in the gyrus fasciolaris, indusium griseum, or anterior hippocampal rudiment. Except in the medial part of the pes hippocampi, the Timm's staining did not reach the proximal border of the subfield CA1. In some sections of the main body of the hippocampus a narrow, infragranular stain-free zone was observed in the hilus. In the dentate gyrus of three older subjects, but not in those of three younger subjects, supragranular staining was found. It is argued that the Timm's staining described in this study is specific to the hippocampal mossy fibres. The distribution of the staining is discussed in relation to the boundaries of subfields CA3 and CA2 as delineated by other authors.

Neuropeptides and astroglia in intracerebral hippocampal transplants: an immunohistochemical study in the rat.

Abstract: The rat hippocampus and fascia dentata contain neurons and terminal fields that react immunohistochemically with antisera raised against the peptides somatostatin, cholecystokinin (CCK), and enkephalin. Neurons with overlapping distribution synthesize acetylcholinesterase (AChE) as shown histochemically after systemic administration of diisopropylfluorophosphate (DFP). We used these techniques to examine the organization of peptidergic neurons and fibers and AChE-positve neurons in transplants of late embryonic and early postnatal rat hippocampi inserted into the brain of immature and adult rats. The astroglial organization was examined using an antibody raised against the astroglial marker, glial fibrillary acidic protein (GFAP). Eighty percent of the transplants were recovered. Within the transplants the peptidergic neurons, and the AChE-producing neurons retained their characteristic distributions. An organotypical astroglial pattern was also retained with some indication of a higher than normal density of cells and processes. The transplant neuropil displayed characteristic patterns of terminal field-like staining with the enkephalin and CCK antibodies. An enkephalin-like reactivity characteristic of the large mossy fiber terminals was found in the normal mossy fiber zones. A similar staining, but of smaller particle size, was found in and above the granule cell layer. It corresponded to the aberrant, supragranular mossy fiber projection, known to form after denervation of the dentate molecular layer. Also the CCK-like reactivity of the transplant neuropil was distributed in laminar patterns characteristic of the different subfields. Deviations from the normal patterns again followed known principles for lesion-induced aberrant nerve growth. Normalization of the enkephalin and CCK staining patterns in the dentate molecular layer was observed in transplants with intimate contact with the host dentate molecular layer or entorhinal cortex, but only in immature recipients, and not in every case. The staining was typically of the enkephalin-reacting lateral perforant path and the CCK-reacting medial perforant path and distributed in normal, mutually exclusive laminae in the dentate molecular layer. An invasion of the transplant dentate molecular layer by heterologous, host enkephalin- and CCK-like reacting afferents in transplants located in the host basal ganglia was limited at most. Outgrowth of CCK and enkephalin reacting transplant fibers into the host brains was not observed in this study. We conclude (1) that peptidergic and AChE-producing hippocampal and dentate neurons can survive intracerebral transplantation and that an organotypic, astroglial pattern of the tissue was retained after transplantation, (2) that the enkephalin- and CCK-reacting afferents have a growth capacity similar to most other hippocampal afferents and participate in the intrinsic connective reorganizations like these afferents, and (3) that enkephalin- and CCK-reacting host afferents, presumably of entorhinal origin, can innervate the transplant dentate molecular layer in a homotypic, laminar fashion, in immature recipients with close contact between the transplant and the host dentate or entorhinal area.

The reversal potential of excitatory amino acid action on granule cells of the rat dentate gyrus.

Abstract: The responses of granule cells to glutamate, aspartate, N-methyl-D-aspartate (NMDA), quisqualate and kainate applied by ionophoresis on to their dendrites in the middle molecular layer of the dentate gyrus were studied with intracellular electrodes using an in vitro hippocampal slice preparation. On passive depolarization 75% of the granule cells displayed anomalous rectification, which persisted in the presence of TTX and TEA but was eliminated by Co2+ or the intracellular injection of Cs+. Short ionophoretic applications of all the excitatory amino acids evoked dose-dependent depolarizations that were highly localized: movement of the ionophoretic electrode by as little as 10 microns could substantially change the size of the response. The depolarizations evoked by glutamate, asparatate, quisqualate and kainate were unaffected by TTX and Co2+. The depolarization evoked by NMDA was unaffected by TTX but markedly reduced by Co2+. Following intracellular injection of Cs+, neurones could be depolarized to +30 mV and the depolarizations produced by glutamate, quisqualate, NMDA and kainate reversed. The reversal potentials (E) were Eglutamate: -5.6 +/- 0.4 mV; ENMDA: 1.8 +/- 1.9 mV; Equisqualate: -3.9 +/- 1.9 mV; Ekainate: -4.6 +/- 2.0 mV. The excitatory post-synaptic potential (e.p.s.p.) evoked by stimulation of the medial perforant path could also be reversed and Ee.p.s.p. was -5.5 +/- 1.1 mV. The 6 mV difference between ENMDA and the equilibrium potential for the other exogenously applied excitatory amino acids and the statistically significant difference between ENMDA and Ee.p.s.p. (P less than 0.005; d.f.: 7) is consistent with our earlier hypothesis that both the transmitter released by the medial perforant path and exogenously applied glutamate are unlikely to interact with NMDA receptors.