Calbindin D28k-like immunoreactivity during the formation of the enamel-free area in the rat molar teeth

Previous studies have demonstrated the presence of calbindin D28k in the ameloblasts derived from the inner enamel epithelium. The occlusal surfaces of the rodent molars partly lack the enamel covering, which is referred to as enamel-free area (EFA). In the present study, we compared the immunohistochemical localization of calbindin D28k-like immunoreactivity (CB-LI) in the cells at the EFA (EFA cells) and ameloblasts of the rat molar teeth at the light microscopic level. CB-LI was strong in the ameloblasts of the presecretory through the protective stages, while it was faint at the late secretory to transitional stages. However, some mature ameloblasts lacked the immunoreactivity. On the other hand, the majority of EFA cells showed distinct polarization and elongation that were absent in few cells at the early stage of EFA formation. At all stages, the EFA cells adjacent to the ameloblasts showed CB-LI, however, some cells adjacent to the mature ameloblasts lacked the reaction. Intensive CB-LI was demonstrated in EFA cells at the reduced enamel epithelium. These immunohistochemical findings suggest EFA cells have cytochemical properties similar to those of ameloblasts.     

Calbindin D28k and parvalbumin immunoreactivity in the rabbit superior colliculus: an anatomical study

The expression pattern of two calcium binding proteins (CaBP), calbindin D28k (CB) and parvalbumin (PV), in the superior colliculus (SC) of the adult rabbit, as well as the morphology of the immunoreactive cells were examined. The study was performed on 12 rabbits. Coronal sections from postmortem SC were analyzed by light microscopy, and drawings of CaBP-labeled cells were obtained using a drawing tube. No previous information is available on either the CB/PV expression or the morphology of CB/PV positive cells in the SC of the adult rabbit. Therefore, in this study we show that CB neurons and neuropil form three main tiers: the first located within the stratum zonale (SZ) and the upper part of the stratum griseum superficiale (SGS), the second located within the stratum griseum intermedium (SGI), and the third, located within the medial and central areas of the stratum griseum profundum (SGP). In contrast to this layer labeling, almost no CB-positivity is found within the other collicular layers. On the other hand, the densest concentration of PV labeled cells and terminals is found within a single dense tier that spanned the ventral part of the startum griseum superficiale (SGS) and the dorsal part of the stratum opticum (SO). Anti-PV neurons are also scattered through the deeper layers below the dense tier. In contrast, almost no anti-PV labeled neurons or neuropil are found within the stratum zonale (SZ) and upper SGS. This distribution represents a new pattern of sublamination in the SC of this species. All the previously described cell types in other mammals are observed in the rabbit SC: marginal cells, horizontal cells, pyriform cells, narrow-field vertical cells, wide-field vertical cells, and stellate/multipolar cells. Detailed drawings of all these cellular types are represented to show their complete morphology. The results of this study indicate that both CB and PV are present in a variety of neurons, which present a number of homologies between mammals, but have a different location and/or distribution, according to the different species. These findings are thus relevant to better understand the organisation of the SC in mammals.     

Decrease in GABA immunoreactivity and alteration of GABA metabolism after kindling in the rat hippocampus

Summary The kindling model of epilepsy, induced by tetanic stimulation of Schaffer collateral/commissural fibers, was studied in the rat hippocampus. Gamma-aminobutyric acid immunoreactivity was used to quantify the number of GABA-immunoreactive somata per mm² in CA1 region, 28 days after the last generalized seizure. Comparison of the numbers obtained from kindled animals with those from controls, showed a significant decrease (18%) on the ipsilateral stimulated side but none on the contralateral side. In control rats injection of the GABA-transaminase inhibitor, amino oxyacetic acid (AOAA), led to a 46% increase in the number of cell somata immunoreactive for GABA. This probably results from an accumulation of GABA, reflecting GABA synthesis by glutamate decarboxylase (GAD) activity, in somata of interneurons that had initially a GABA content below the immunocytochemical detection threshold. In kindled rats, 31 days after the last seizure, the number of GABA-immunoreactive cells that could be observed after AOAA-treatment was significantly lower (35% ipsilateral and 25% contralateral) when compared to AOAA-treated controls. This suggests that in kindled animals a GAD dependent increase in GABA content did not take place in a subpopulation of interneurons. The observations for kindled rats are interpreted as a long-term decrease in GABA content and as an alteration in GABA turnover in a subpopulation of interneuron somata, the latter possibly due to a decrease in GAD activity. The long-term enhanced seizure sensitivity, characteristic for kindled animals, may be due to a decreased GABAergic inhibitory control of the neuronal circuitry in the CA1 region of the hippocampus.     

Brain stem afferents to the rat medial septum.

1. Activity of neurones in the medial septal nucleus and the diagonal band was recorded from urethane anaesthesized rats. Responses of the cells to electrical stimulation of the raphe nuclei and nucleus locus coeruleus (LC) were measured. 2. LC stimulation caused a long latency, 30-100 msec, and long duration, 100-300 msec cessation of spontaneous activity of most recorded neurones. When bursting-type neurones were recorded, the stimulation occasionally caused a synchronized repetitive bursting firing pattern. 3. Pre-treatment with drugs which interfere with catecholamine neurotransmission, i.e. reserpine and 6OHDA, prevented the appearance of cellular responses to LC stimulation. 4. Stimulation of the dorsal or the median raphe nuclei generated more complex and less clear-cut responses. These included several types of long (20-50 msec) and short (2-5 msec) latency responses. These responses were also accompanied in some cells by synchronized repetitive bursting. 5. Interference with serotonin neurotransmission with PPCA or reserpine reduced the detection of long latency responses. 6. Short latency responses accompanied by evoked field potentials were recorded also after stimulation of dorsal tegmental nucleus. 7. Rates of spontaneous firing cells were augmented after monoamine neurotransmission interruption whereas after fornix lesion, when there is supposedly an increased monoamine innervation of the septum, cells fire at lower rates than normal. 8. It is suggested that noradrenaline and serotonin may serve as neurotransmitters in the medial-septum-diagonal band areas.     

Long-term changes in calbindin D(28K) immunoreactivity in the rat hippocampus after cardiac arrest

Calbindin D(28K) (CB) expression was analyzed in the rat hippocampus following 10-min-cardiac arrest-induced ischemia within a year after reperfusion. In rats examined 3 days after ischemia, CB immunoreactivity disappeared completely from CA1 pyramidal neurons and from most CA2 pyramids. In the stratum granulosum of the dentate gyrus, mossy fibers, and hippocampal interneurons, CB immunoreactivity was preserved, although staining was somewhat paler than that in control rats. A similar pattern of CB immunoreactivity was found in rats sacrificed 14 days and 1 month after cardiac arrest. From the 14th postischemic day, neuronal loss in the stratum pyramidale of CA1 but not in that of CA2 became apparent. The reappearance of CB immunoreactivity in CA1 and CA2 pyramidal neurons was noticed 6 months after ischemia, and the pattern was identical to that observed in animals sacrificed 12 months after the ictus. The prolonged loss and delayed reappearance of CB immunoreactivity in the hippocampus demonstrate that ischemia may induce long-term disturbances of protein expression, which may in turn result in impairment of hippocampal functioning.     

Cellular localization of nerve growth factor-like immunoreactivity in hippocampus and septum of adult rat brain.

The cellular localization of the nerve growth factor-like immunoreactivity (NGF-LIR) has been studied in the intact adult rat brain at the level of the hippocampus and the septum. Immunolabelling for NGF combined with counterstaining with cresyl violet and double immunostaining technique, which allowed simultaneous localization of NGF-LIR and that of astroglial marker -GFAP, were used. The data indicate neuronal localization of NGF-like immunoreactivity and a lack of colocalization of NGF-LIR with the immunoreactivity of GFAP in the hippocampus. These data are consistent with in situ hybridization results for NGF and immunocytochemical results for pro-NGF localization obtained by others. At the septal level, apart from neuronal localization of NGF-LIR, single NGF-like immunoreactive astrocytes have been observed. This suggests that, although to a very small extent, in vivo intact brain astrocytes may, just as astrocytes growing in vitro, synthesize NGF-like molecules. This finding may be of importance in better understanding the trophic support for NGF responsive cholinergic neurones in the brain.     

Calbindin D28k‐like immunoreactivity during the formation of the enamel‐free area in the rat molar teeth

Previous studies have demonstrated the presence of calbindin D28k in the ameloblasts derived from the inner enamel epithelium. The occlusal surfaces of the rodent molars partly lack the enamel covering, which is referred to as enamel‐free area (EFA). In the present study, we compared the immunohistochemical localization of calbindin D28k‐like immunoreactivity (CB‐LI) in the cells at the EFA (EFA cells) and ameloblasts of the rat molar teeth at the light microscopic level. CB‐LI was strong in the ameloblasts of the presecretory through the protective stages, while it was faint at the late secretory to transitional stages. However, some mature ameloblasts lacked the immunoreactivity. On the other hand, the majority of EFA cells showed distinct polarization and elongation that were absent in few cells at the early stage of EFA formation. At all stages, the EFA cells adjacent to the ameloblasts showed CB‐LI, however, some cells adjacent to the mature ameloblasts lacked the reaction. Intensive CB‐LI was demonstrated in EFA cells at the reduced enamel epithelium. These immunohistochemical findings suggest EFA cells have cytochemical properties similar to those of ameloblasts. Anat Rec 258:384–390, 2000. © 2000 Wiley‐Liss, Inc.     

Calbindin D28K and parvalbumin gene expression in rat embryonic ventral forebrain grafts

The present study characterizes expression of calbindin D28 K (CB-D28 K) and parvalbumin (PV) in ventral forebrain (VFB) grafts placed in the neocortex of adult rats bearing quisqualic acid lesions to the nucleus basalis magnocellularis. Three to nine months after transplantation surgery, rats were killed for in situ hybridization with probes to CB-D28K or PV and for immunohistochemistry with antibodies to CB-D28K or PV. In addition, an antibody to choline acetyltransferase (ChAT) was used to characterize the cholinergic component in the graft and an antibody to tyrosine hydroxylase (TH) to explore catecholaminergic innervation of the graft. Quantitative analysis of CB-D28K and PV messenger ribonucleic acid (mRNA) was based on counts of silver grains generated by emulsion autoradiography. Cells expressing CB-D28K mRNA were significantly larger than such cells in the adult VFB and the mean number of silver grains per cell was significantly greater than to such cells in the adult VFB. The level of CB-D28K mRNA expression as calculated by ratio of silver grains per unit area was also significantly increased. Quantification of PV mRNA showed no significant differences between the cells in the graft and in the adult VFB. In order to begin to interpret these findings, a comparison was made with such cells in the VFB of developing rats. Brain sections were sampled from embryonic day 17 and postnatal days 1, 5, 12, 19 and adult (6–12 months of age). Cells expressing CB-D28K mRNA were detected in ventral forebrain from postnatal day 5 and cells expressing PV mRNA were detected in ventral forebrain from postnatal day 19. In the course of normal development of the ventral forebrain, no CB-D28K cells were found that were as large or expressed such high levels of CB-D28K mRNA as observed in the grafts. We conclude that changes in grafted cells expressing CB-D28K do not reflect an arrest of developmental processes. TH immunohistochemistry revealed lack of catecholaminergic innervation of the graft, whereas adult mediolateral septal cells that express CB-D28K receive such innervation in addition to other neurotransmitter inputs. Imbalance in neurotransmitter inputs to grafted cells expressing CB-D28K is discussed as a possible factor in their increased size and gene expression. Received: 4 June 1996 / Accepted: 11 June 1997     

Calbindin D-28k and parvalbumin in the rat nervous system

This paper describes the distribution of structures stained with mono- and polyclonal antibodies to the calcium-binding proteins calbindin D-28k and parvalbumin in the nervous system of adult rats. As a general characterization it can be stated that calbindin antibodies mainly label cells with thin, unmyelinated axons projecting in a diffuse manner. On the other hand, parvalbumin mostly occurs in cells with thick, myelinated axons and restricted, focused projection fields. The distinctive staining with antibodies against these two proteins can be observed throughout the nervous system. Calbindin D-28k is primarily associated with long-axon neurons (Golgi type I cells) exemplified by thalamic projection neurons, strionigral neurons, nucleus basalis Meynert neurons, cerebellar Purkinje cells, large spinal-, retinal-, cochlear- and vestibular ganglion cells. Calbindin D-28k occurs in all major pathways of the limbic system with the exception of the fornix. Calbindin D-28k is, however, also found in some short-axon cells (Golgi type II), represented by spinal cord interneurons in layer II and interneurons of the cerebral cortex. It is also detectable in some ependymal cells and abundantly occurs in vegetative centres of the hypothalamus. The "paracrine core" of the nervous system and its adjunct (1985, Nieuwenhuys, Chemoarchitecture of the Brain. Springer, Berlin) is very rich in calbindin D-28k. The distribution of calbindin D-28k-positive neurons is very similar to that of the dihydroperydine subtype of calcium channels. Most of the cells containing calbindin D-28k are vulnerable to neurodegenerative processes. Parvalbumin-immunoreactive neurons have a different, and mostly complementary distribution compared with those which react with calbindin D-28k antisera, but in a few cases (Purkinje cells of the cerebellum, spinal ganglion neurons), both calcium-binding proteins co-exist in the same neuron. Many parvalbumin-immunoreactive cells in the central nervous system are interneurons (Golgi type II) and, to a lesser extent, long-axon cells (Golgi type I), whereas conditions are vice versa in the peripheral nervous system. Intrinsic parvalbuminic neurons are prominent in the cerebral cortex, hippocampus, cerebellar cortex and spinal cord. Long-axon parvalbumin-immunoreactive neurons are, for example, the Purkinje cells, neurons of the thalamic reticular nucleus, globus pallidus, substantia nigra (pars reticulata) and a subpopulation among large spinal-, retinal-, cochlear- and vestibular ganglion cells. Parvalbumin is rich in cranial nerve nuclei related to eye movements. In addition to nervous elements, parvalbumin immunoreactivity occurs in a few ependymal cells and in some pillar cells of the organ of Corti.(ABSTRACT TRUNCATED AT 400 WORDS)     

An electrophysiological study of neurones in the rat median raphe and their projections to septum and hippocampus

Extracellular single unit recordings were made in the median raphe nucleus from rats anaesthetized with urethane. Spontaneous firing as well as orthodromic and antidromic responses to stimulation of the fornix and the medial septum were studied. One hundred and twelve units (out of a total of 355) with a regular spontaneous firing rate of 0.2-3 spikes/s were classified as serotonin-containing neurons. Fifty nine of them were antidromically invaded from either the fornix or the medial septum (conduction velocity, 0.8 m/s) and 7 additional neurones from both the fornix and the medial septum. Antidromic action potentials were followed by a period of decreased probability of firing, that was already present below threshold for antidromic invasion, were proportional to the stimulation intensity and had a latency similar to orthodromic inhibition. No preferential topographical distribution within the median raphe nucleus was observed for the serotonin neurones, even those invaded antidromically. Twenty six neurones with a clear-cut anatomical location around the borders of the median raphe nucleus showed a spontaneous rhythmic activity (4-20 spikes/s) characterized by the presence of extremely prolonged silent periods (up to 5 min). Only one of these neurones was invaded antidromically from the medial septum and none from the fornix. Of the remaining non-serotonin neurones, 28 showed a very low firing rate consisting of single action potentials every 10-60 s while 189 had a spontaneous activity of 6-30 spikes/s. Regardless of their firing rate they were all antidromically invaded from the fornix and/or the medial septum and had a conduction velocity of 5 m/s. These experiments demonstrate the electrophysiological heterogeneity of the neuronal population of the median raphe nucleus, the presence of strong projections of both putative serotonin and non-serotonin neurones to the medial septum and, via the fornix, to the hippocampus, and the existence of axonal branching in both types of neurones.     

5-HT1A receptor mRNA and immunoreactivity in the rat medial septum/diagonal band of Broca-relationships to GABAergic and cholinergic neurons

Activation of 5-HT1A receptors results in a variety of physiological responses, depending on their localization on neurons with different phenotypes in the brain. This study investigated the localization of 5-HT1A receptor mRNA and 5-HT1A receptor immunoreactivity in cell bodies of the rat septal complex using in situ hybridization and immunohistochemistry. In adjacent sections of the medial septum/diagonal band of Broca (MSDB), the distribution of cell bodies expressing 5-HT1A receptor mRNA was closely related to cells labeled with oligonucleotide probes to GAD (glutamic acid decarboxylase), VAChT (vesicular acetylcholine transporter) or parvalbumin mRNA. Using antiserum to GAD and antibodies to GABA, 5-HT1A receptor immunoreactivity was demonstrated in a majority of GABAergic cells in the MSDB. 5-HT1A receptor-immunoreactive GABAergic cells in the MSDB were also demonstrated to contain the calcium-binding protein parvalbumin, a marker for septohippocampal projecting GABAergic neurons. In the lateral septum, 5-HT1A receptor immunoreactivity was colocalized with the calcium-binding protein calbindin D-28k, a marker for septal GABAergic somatospiny neurons. 5-HT1A receptor immunoreactivity was also detected in a subpopulation of VAChT-containing cholinergic neurons of the MSDB. In MSDB neurons, colocalization of 5-HT1A and 5-HT2A receptor immunoreactivities was demonstrated. These observations suggest that serotonin via 5-HT1A receptors may represent an important modulator of hippocampal transmission important for cognitive and emotional functions through actions on both GABAergic and cholinergic neurons of the rat septal complex. In addition, 5-HT may exert its effects in the MSDB via cells expressing both 5-HT1A and 5-HT2A receptors.     

Somatostatin immunoreactivity in the entopeduncular projection to the lateral habenula in the rat

Many neurons within the ipsilateral entopeduncular nucleus were retrogradely labelled following the stereotaxic injection of the fluorescent tracer True Blue into the lateral habenula of the rat. These neurons also displayed somatostatin immunoreactivity when examined with a monoclonal antibody to cyclic somatostatin. Excitotoxic lesions of the entopeduncular nucleus resulted in a loss of the dense somatostatin terminal field normally present in the lateral habenula. These results indicate that the neuropeptide somatostatin is present in the projection from the entopeduncular nucleus to the lateral habenula.     

Early postnatal corticosterone administration regulates neurotrophins and their receptors in septum and hippocampus of the rat

The principal glucocorticoid in rats, corticosterone, interacts with neurons in the limbic system and leads to morphological and behavioral changes. Putative corticosterone-triggered mediators are neurotrophins. In the present study we investigated the effects of early postnatal corticosterone treatment in rats on neurotrophic factors of the nerve growth factor (NGF) family and their receptors. Newborn rats were treated with corticosterone-containing polymers until postnatal day 12. The mRNA and protein levels of the neurotrophins of the NGF family (NGF, BDNF, NT-3 and NT-4/5) and their receptors (trkA, trkB, trkC and p75) were quantified in septum and hippocampus using RT-PCR. In the septal region, we found an unchanged mRNA expression after corticosterone treatment, whereas in the hippocampus there was a general increase in mRNA. Particularly, the gene expression of NGF, NT-3, and the high affinity receptors trkA, trkB and trkC increased significantly. Quantification of the neurotrophin protein levels using an ELISA revealed significant treatment effects for NGF and NT-4/5 in the hippocampus. The present study of corticosterone treatment in young rats demonstrates interactions of steroid hormones with neurotrophic factors and their receptors in the septo-hippocampal system during the first two postnatal weeks.     

Calcium binding protein containing neurons in the gliotic mouse hippocampus with special reference to their afferents from the medial septum and the entorhinal cortex

In CA1 area and the hilus of the dentate gyrus of the mouse hippocampus, drastic reduction of NeuN, calbindin, calretinin, or parvalbumin immunopositive neurons was shown at 3, 7 and 60 days after pilocarpine-induced status epilepticus. In gliotic CA1 area at 60 days, few dendritic branches of calcium binding protein immunopositive neurons could be found suggesting reorganization of the afferents of surviving calcium binding protein immunopositive neurons. Calbindin, calretinin, or parvalbumin and 5-bromo-2′-deoxyuridine (BrdU) double labeling showed that calcium binding protein immunopositive neurons in gliotic CA1 area at 60 days were surviving instead of newly generated neurons. Iontophoretic injection of Phaseolus vulgaris leucoagglutinin into the medial septum and the nucleus of the diagonal band of Broca or the lateral entorhinal cortex showed contacts between Phaseolus vulgaris leucoagglutinin immunopositive en passant and terminal boutons and surviving calcium binding protein immunopositive neurons in the hippocampus. The presence in the gliotic hippocampus of enlarged and/or aggregated bouton-like structures 60 days after pilocarpine-induced status epilepticus is indicative for the reorganization of connections between the hippocampal afferents and surviving hippocampal neurons. This reconstruction could be a factor in the ongoing epileptic activity in this model of mesial temporal lobe epilepsy.     

Large retinal ganglion cells in the rat: their distribution and laterality of projection

Summary The distributions of the ipsilaterally and contralaterally projecting large ganglion cells in the retina of the rat were determined, using the retrograde transport of Horseradish peroxidase (HRP) following injections into one optic tract. Labelled large retinal ganglion cells occur throughout the contralateral retina and throughout the temporal crescent of the ipsilateral retina, but there is a noticeable decrease in their density in the contralateral retina's temporal crescent. This retinal region was identified in these same retinae by injecting a retrogradely transported flourescent tracer into the optic tract opposite that receiving the HRP. The density of large retinal ganglion cells increases in both the contralateral retina and the ipsilateral temporal crescent in the upper temporal periphery such that, together, these two populations of large cells combine to produce a peak density centred on the retinal representation of the visual field's vertical midline. This peak density of large retinal ganglion cells must therefore be further peripheral than the peak density for the total population of retinal ganglion cells, since all evidence indicates that the latter is positioned nasal to the vertical midline's representation. This was verified in one rat, in which the density distribution of the total population of retinal ganglion cells was determined and compared with the distribution of the large cell population. The results suggest that the rat possesses a specialized retinal focus of large ganglion cells for viewing the visual field directly in front of the animal.     

Calcium binding protein (calbindin D28k) immunoreactivity in the hamster superior colliculus: ultrastructure and lack of co-localization with GABA

Summary The expression of specific calcium binding proteins is being used increasingly as a potential neuroanatomical marker for neurons with similar functions. In this study, the distribution of calbindin D28k in the superior colliculus (SC) of adult hamsters was examined by light and electron microscopy. Calbindin immunoreactivity was prominent in specific regions and laminae of the SC throughout its rostrocaudal extent, and was found to label horizontal, vertical and stellate cell types. In addition, calbindin label highlighted bridges of neuronal processes in the intermediate layers. The most frequent calbindin-immunoreactive profiles seen in the electron microscope were dendrites, some of which were post-synaptic to apparent retinal ganglion cell axon terminals. Labelled axons and axon terminals were less frequently encountered. There was considerable overlap between the size distribution of calbindin D28k-immunoreactive neurons and that of GABA-immunoreactive or Nissl stained neurons in the SC. However, using a double fluorescent labelling technique, and examination of the tissue with confocal laser microscopy, no neurons were observed in the hamster SC that showed immunoreactivity for both calbindin and GABA. In this regard, the SC is similar to the mammalian lateral geniculate nucleus and the pretectum, but differs from the neocortex, where calbindin and GABA are colocalized. The demonstration in the SC, as well as other parts of the nervous system, of sub-populations of neurons that contain distinct calcium-binding proteins suggests that these neurons have different functional properties. Correlative studies may clarify the relevance of these cytoplasmic components as cell markers, as well as their different patterns of association with neurotransmitters and peptides.     

Changed vesicular GABA transporter immunoreactivity in the gerbil hippocampus following spontaneous seizure and vigabatrin administration

To identify the roles of vesicular gamma-aminobutyric acid (GABA) transporter (VGAT) in epileptogenesis and the recovery mechanisms in spontaneous seizure, we conducted a chronological and comparative analysis of VGAT expression. VGAT immunoreactivity was stronger in the seizure resistant group than that in the pre-seizure group of seizure sensitive (SS) gerbils. In 3 h postictal group, the density of VGAT immunoreactivity was significantly increased in the hippocampus, as compared to pre-seizure group. In 24 h postictal group, VGAT immunodensity had recovered to its pre-seizure level. In addition, VGAT immunoreactivity in the hippocampus was also increased by vigabatrin (GVG) administration. These results suggest that decreased VGAT expression in the SS gerbil hippocampus may affect epileptogenesis in this animal, and that the subsequent alteration in its expression induced by seizure and the administration of GVG may reflect a modulation of GABA release to alleviate seizure activity.     

Inhibition in postischemic rat hippocampus: GABA receptors,GABA release,and inhibitory postsynaptic potentials

Summary We have investigated the GABAergic system in rat hippocampus at 1 hour and up to 21 days following 20 min of global cerebral ischemia. Distribution of ³H-GABA (in excess of unlabeled baclofen) and ³H-Ro-15-1788 (benzodiazepine antagonist) binding sites in hippocampus was studied utilizing quantitative autoradiography. The ³H-GABA binding was unchanged (p> 0.01) after ischemia, whereas the ³H-Ro-15-1788 binding decreased significantly (p< 0.01) in all hippocampal subfields 1–21 days after ischemia. Using microdialysis in CA1, we found that K⁺-stimulated GABA release at 1 hour and 1 day after ischemia was unchanged (p> 0.01) in comparison to preischemic controls. Electrophysiological recordings were made from CA1 of hippocampal slices prepared from rats sacrificed 1 hour, 1 day and 2 days after ischemia. Field potentials evoked by stimulation of the Schaffer collaterals showed no differences (p > 0.01) from those taken from controls. Postischemic intracellular recordings from the CA1 pyramidal cells showed that fast and slow inhibitory postsynaptic potentials were readily evoked on orthodromic stimulation. Together with our previous morphological results, demonstrating survival of hippocampal interneurons following ischemia, we conclude that hippocampal GABAergic interneurons preserve their inhibitory potential in the period preceding delayed CA1 pyramidal cell death. This conclusion taken together with the observation that postischemic ³H-Ro-15-1788 binding in hippocampus declined, suggest that benzodiazepines (by increasing the receptor affinity), GABA analogs, and GABA uptake inhibitors may be usefull in the treatment of ischemic CA1 pyramidal cell death in the rat.