GABA-like Immunoreactivity Research Articles

Visualization of taurine, GABA and glutamate in developing feline cerebellum by immunohistochemistry

The localization of taurine, GABA and glutamate in developing feline cerebellum was performed using antibodies raised against the amino acids conjugated to bovine serum albumin with glutaraldehyde. Distinct patterns of immunostaining were observed for each of the amino acids. Taurine-like immunoreactivity reached a peak at 4 weeks after birth, as did GABA-like immunoreactivity, whereas glutamate-like immunoreactivity was greatest in the mature cerebellum. Purkinje cells are all taurine-positive in cerebellum from neonatal animals, whereas in the mature cerebellum they appear to contain only GABA and glutamate, with virtually no taurine, in contrast to observations reported with rodent cerebellum. Ultrastructural studies and immunogold labelling visualized by electron microscopy show that the band of taurine-like immunoreactivity observed in newborn feline cerebellum is localized within dendrites, axons and glial processes. Granule cells migrating through this region also show prominent taurine-like immunoreactivity.

Distribution of GABA-like immunoreactivity during post-metamorphic development and regeneration of the central nervous system in the ascidian Ciona intestinalis

During regeneration of the neural ganglion in Ciona intestinalis, the pattern of reappearance of some peptidergic cells is similar to the ontogenetic patterns exhibited by these cell types during normal post-metamorphic development. Using a specific antiserum to gamma-aminobutyric acid (GABA), we describe here the appearance of GABA-ergic cells in Ciona during both post-metamorphic development and regeneration of the neural ganglion following total ablation. Post-metamorphic animals were divided into the categories: 1, 3–5, 6–10, 11–15 and 23–27 mm in body length. Regeneration was monitored at 12, 15, 18, 21, 28 and 56 days post ablation. The first appearance of GABA-like immunoreactive cells during normal development were at the 3 to 5-mm stage where they were seen as discrete cells, without processes, evenly distributed in the cortical region throughout the ganglion. Fibres were first seen at the 6 to 10-mm stage. As development proceeded, GABA-like immunoreactive cells became more concentrated near the nerve root exits and along the dorsal rind of the ganglion. In regenerating ganglia, GABA was first detected at 18–21 days post ablation, in cells that lacked any obvious processes and that were distributed in all regions of the ganglion. At 28 days post ablation, processes could be detected in the neuropile, and after 56 days GABA cells were found predominantly in the same regions as in the normally developing adult ganglion. Although the overall pattern reflects that in a normal adult, a few differences were detectable. For example, rather more GABAergic cells were concentrated ventrally in the ganglion close to the neural gland.

Spinal cord neuron classes in embryos of the smooth newt Triturus vulgaris: a horseradish peroxidase and immunocytochemical study.

Spinal cord neurons were investigated in embryos of Triturus vulgaris, the smooth newt, just prior to hatching. These embryos can swim if freed from their egg membranes. Horseradish peroxidase (HRP) labelling, together with GABA and glycine immunocytochemistry (ICC), revealed nine distinct anatomical classes of neuron. 1. Ventrolateral motoneurons with mainly dorsal dendrites, sometimes a descending central axon and peripheral axon innervating the trunk muscles. 2. Dorsal primary sensory Rohon-Beard neurons innervating skin and with dorsal ascending and descending axons in spinal cord. 3. Commissural interneurons with mid-cord unipolar soma, glycine-like immunoreactivity, dendrites on initial segment of ventral axon which crosses cord to ascend or branch. 4. Dorsolateral commissural interneurons with multipolar soma in dorsolateral position with dorsal dendrites and ventral axon which crosses and ascends or branches. 5. Giant dorsolateral commissural interneurons with large dorsolateral somata widely spaced (130-250 microns spacing) with process projecting dorsally to other side, dorsolateral dendrites and ventral axon which crosses to ascend and branch. 6. Dorsolateral ascending interneurons in dorsolateral position with multipolar soma and ascending axon on same side. 7. Ascending interneurons with unipolar soma, GABA-like immunoreactivity and ascending axon on same side. 8. Descending interneurons with bi- or multi-polar soma, extensive dorsal and ventral dendrites, and descending axon on same side. They may also have ascending axons. 9. Kolmer-Agduhr cerebrospinal fluid contacting neurons with cilia and microvilli in lateral corners of neural canal. GABA-like immunoreactivity, no dendrites and ascending axon. Eight of the nine cells classes were found to bear a marked resemblance to neurons previously described in zebrafish and Xenopus embryos in terms of their anatomy, distribution and immunoreactivity to GABA and glycine. Homologies and possible functions are discussed. Giant dorsolateral commissural neurons, were not found in Xenopus or teleosts but were present in Ambystoma mexicanum and Neoceratodus. The regular, possibly segmental longitudinal distribution pattern of these cells within the cord is unusual among amphibian spinal neurons.

Neurotransmitters and neuromodulators of the mammalian cochlea.

Major topics addressed in this review on neurotransmitters and neuromodulators of the mammalian cochlea are ; 2) neuronal circuity of the organ of Corti ; 2) hair cell neurotransmitter(s) ; efferent neurotransmitters and neuromodulators (acetylcholine, γ-aminobutyric acid, dopamine, enkephalins, dynorphins, calcitonin gene-related peptide, excitatory amino acids ; and 3) other neuroactive substances in the cochlea (adenosine, ATP, taurine, auditory nerve-activating substance, histamine)

Immunocytochemistry of GABA and glutamic acid decarboxylase in the thoracic ganglion of the crab Eriphia spinifrons

We have used specific antisera against protein-conjugated γ-aminobutyric acid (GABA) and rat-brain glutamic acid decarboxylase (GAD) in immunocytochemical preparations to study the distribution of putatively GABAergic neurons in the fused thoracic ganglion of the crab Eriphia spinifrons. In the thoracic neuromeres, about 2000 neurons with somata arranged in clusters or located singly in the cell cortex exhibited both GABA-like and GAD-like immunoreactivity. In addition, more than a hundred cells showed only GABA-like immunoreactivity. Fibrous immunoreactive staining to GAD and GABA was distributed throughout the neuropil of the thoracic ganglion, and several fiber tracts contained immunoreactive processes. Sets of serially homologous neurons exhibited GABA-like and GAD-like immunoreactivity in the thoracic neuromeres. Especially prominent were one medial and four ventro-lateral clusters of somata, together with thirteen individually recognized cells in each neuromere. Six of these cells in the ventro-medial cell cortex may be the somata of inhibitory motoneurons. The leg nerves contained three immunoreactive fibers, corresponding to the previously described common inhibitory motoneuron and the two specific inhibitors. The results present further evidence for GABA being the neurotransmitter of all inhibitory leg motorneurons, and suggest its presence and role as a neurotransmitter in a considerable number of interneurons in the thoracic ganglion of the crab.

Immunocytochemical study of somatostatin, neurotensin, GABA, and glycine in rat spinal dorsal horn

In order to determine whether somatostatin coexists with GABA or glycine in neurones in rat spinal dorsal horn, a combined pre- and post-embedding immunocytochemical study was carried out. One hundred six somatostatin-immunoreactive neurones located in lamina II and the dorsal half of lamina III were tested with antiserum or monoclonal antibody to GABA and none of these cells showed GABA-like immunoreactivity. However, 8 out of 13 somatostatin-immunoreactive neurones located deeper in the dorsal horn (ventral lamina III and lamina IV) showed glycine-like immunoreactivity, and 6 of these were also GABA-immunoreactive. We have previously shown that neurotensin-immunoreactive neurones in laminae II and III are also not immunoreactive when tested with GABA antiserum (Todd et al.: Neuroscience 47:685-691, 1992), and a double-labelling fluorescence method was therefore used to compare the distribution of somatostatin and neurotensin within the superficial dorsal horn. The two types of peptide-immunoreactivity were never found in the same profile. These results suggest that somatostatin and neurotensin are present in different populations of non-GABAergic neurones in rat superficial dorsal horn, but that some somatostatin-containing neurones in the deeper part of the dorsal horn contain glycine, with or without GABA.

Presumptive GABAergic centrifugal input to the lamprey retina: a double-labeling study with axonal tracing and GABA immunocytochemistry

The distribution of GABA-like immunoreactivity (GABA-LI) was performed in the lamprey retinopetal system which was previously identified by either anterograde or retrograde axonal tracing methods. This study was carried out at the ultrastructural level for the retina and under both the light and electron microscope for the mesencephalic retinopetal centers (M5 and RMA). The GABA-LI was distributed in about 40% of anterogradely HRP-labeled axon terminals in the inner retina. These made synaptic contacts upon either HRP-labeled ganglion cell dendrites or mostly on GABA-LI or on immunonegative amacrine cell dendrites and somata. The other immunonegative HRP-labeled axon terminals also established synaptic contacts on amacrine cell dendrites and somata. The mesencephalic retinopetal neurons, retrogradely labeled with HRP or [ 3H]proline, were GABA-LI in 65% of M5 somata and only in 15% of RMA neurons. M5 and RMA retinopetal neurons and dendrites, either GABA-LI or immunonegative, were contacted: (1) asymmetrically by HRP-labeled or unlabeled axon terminals containing rounded synaptic vesicles, always immunonegative and (2) symmetrically by HRP-unlabeled axon terminals containing pleiomorphic synaptic vesicles, which were either GABA-LI or immunonegative. The role of GABA as a putative neurotransmitter in the centrifugal visual system is discussed.

GABA-like immunoreactivity in the gustatory zone of the nucleus of the solitary tract in the hamster: Light and electron microscopic studies

The distribution of GABA-like immunoreactive (GABA-LI) somata was studied in the gustatory zone of the nucleus of the solitary tract (NST) in the hamster in order to identify putative inhibitory circuitry in gustatory processing. Immunoreactive somata were located throughout the gustatory NST, in accordance to the distribution of large and small types of neurons as determined in previous morphometric studies. Consequently, GABA-LI somata were mostly found in the dorsal two-thirds of the gustatory zone. Such somata were mostly ovoid in shape and possessed somal areas that averaged 85.5 ± 2.8 μm 2 (12.7 × 8.4 μm). A narrow range of somal areas (50–125 μm 2) suggested a single functional group. At the electron microscopic level, 18% of the neurons encountered were immunoreactive and their nuclei always possessed deeply invaginated boundaries. This morphological feature indicated that GABA-LI neurons are smaller members of the most common class of neurons within the gustatory NST. Because GABA is often implicated as the neurotransmitter of small inhibitory local circuit neurons, these findings indicate a possible inhibitory aspect to the processing of taste information at the level of the first relay in the brainstem.

Localization of GABA-like immunoreactivity in the monkey amygdala

Neurons exhibiting GABA-like immunoreactivity were identified in the monkey amygdala using an avidin-biotin immunohistochemical technique. The pattern of GABA immunoreactivity was very similar in the basolateral and superficial amygdaloid nuclei. In these regions GABA-positive cells were nonpyramidal neurons that were often arranged in clusters or curvilinear rows. These GABA-positive nonpyramidal neurons constituted about 25% of the total neuronal population of the basolateral and superficial amygdaloid nuclei. Numerous GABA-positive puncta resembling axon terminals were observed both in the neuropil and encapsulating the perikarya of GABA-negative pyramidal cells. The pattern of GABA-like immunoreactivity was different in the central and medial amygdaloid nuclei. These regions contained a very dense array of GABA-positive puncta. There were numerous GABA-positive neurons in the lateral subdivision of the central nucleus and fewer cells in the medial nucleus and medial subdivision of the central nucleus. Many immunoreactive puncta were observed contacting the perikarya and dendrites of GABA-positive cells in these regions. The intercalated nuclei consisted of numerous, small, GABA-positive neurons and a few, larger, GABA-negative cells. Both cell types were contacted by GABA-positive puncta. This study indicates that neuronal subpopulations in each of the amygdaloid nuclei of the monkey are GABAergic. The pattern of immunoreactivity varies in different amygdaloid regions and is very similar to that described in the rat. Certain aspects of the functional organization of this rich GABAergic circuitry can be elucidated by correlating the findings of the present investigation with previous anatomical, physiological, and pharmacological studies of the amygdala.

Quantitative analysis of neurons and glial cells in the rat somatosensory cortex, with special reference to GABAergic neurons and parvalbumin-containing neurons.

The number of neuronal and glial cells in the rat somatosensory cortex (barrel area) has been estimated by a stereological method, the disector, using pairs of toluidine blue-stained, plastic-embedded 0.5-microns-thick sections, 1.5 microns distant from each other. Chemical properties of those disector-counted cells were further analyzed by postembedding immunocytochemical methods on adjacent semithin sections. Thus we were able to analyze quantitatively number, distribution, and proportion of five cell types: (1) gamma-aminobutyric acid-(GABA)-negative neurons; (2) GABA-like immunoreactive (GABA-LIR) neurons; (3) a specific calcium-binding protein parvalbumin-immunoreactive (PV-IR) neurons, a subpopulation of GABA-LIR neurons; (4) S-100 beta-LIR glial cells (astrocytes); and (5) S-100 beta-negative glial cells (oligodendrocytes and microglia). The densities of total cells, glial cells, and neurons in the rat somatosensory cortex were 85.4 +/- 10(3)/mm3, 30.5 x 10(3)/mm3, and 54.9 x 10(3)/mm3, respectively. Of all neurons 25% and 14% were GABA-LIR and PV-IR, respectively; all PV-IR neurons are GABA-LIR, and thus about 54% of GABA-LIR neurons are PV-positive. The number of total cells under a unit surface area of 1 mm2 through the thickness of the somatosensory cortex was 171.6 x 10(3); the number of neurons and glial cells were 110.2 x 10(3) and 61.4 x 10(3), respectively. There were 27.7 x 10(3) GABA-LIR neurons and 15.0 x 10(3) and 12.7 x 10(3) PV-IR neurons and PV-negative GABA-LIR neurons, respectively. The laminar distribution of each group of cells shows prominent differences, indicating that the cellular composition was different from layer to layer. The density of GABA-LIR neurons was highest in layer IV. The numerical density of PV-IR neurons was 2-4 times higher in layer IV than in layers II/III, V, and VI, whereas that of PV-negative GABA-LIR neurons was almost constant throughout the layers.

A double-label analysis demonstrating the non-coexistence of tyrosine hydroxylase-like and GABA-like immunoreactivities in amacrine cells of the larval tiger salamander retina

Previous studies have localized tyrosine hydroxylase, the rate-limiting enzyme for the production of dopamine, and γ-aminobutyric acid (GABA) to amacrine cell populations in the larval tiger salamander retina. Double-label immunocytochemistry was used to examine if tyrosine hydroxylase-like and GABA-like immunoreactivities colocalize in tiger salamander amacrine cells. A total of 2,162 tyrosine hydroxylase-like immunoreactive amacrine cells were observed in double-labelled sections. None of these cells were observed to express GABA-like immunoreactivity. Therefore, the present study demonstrates that dopamine and GABA are localized to distinct neuronal populations in the larval tiger salamander retina.

Colocalization of enkephalin-, glucagon-, and corticotropin-releasing factor-like immunoreactivity in GABAergic amacrine cells in turtle retina

The large number of amacrine cells which contain γ-aminobutyric acid (GABA) in the turtle retina makes it difficult to examine specific GABAergic cell types. In order to seletively label subpopulations of GABAergic neurons, we have used fluorescent double-labeling immunocytochemical techniques to examine the localization of GABA-like immunoreactivity (LI) in amacrine cells which contain antigens resembling the neuropeptides glucagon (GLUC), corticotropin-releasing factor (CRF) or enkephalin (ENK). GABA-LI was found in 41% of the cells with GLUC-, 100% of the cells with CRF-, and 69% of the cells with ENK-LI. There were regional differences in the presence of GABA-LI in amacrine cell populations with ENK-LI. GABA-LI was present in about 80% of the cells with ENK-LI outside of the visual streak, while only 37% of the cells within the streak had GABA-LI. Based on the distinct morphologies and regional distributions of these peptidergic amacrine cells, we conclude that they represent different subpopulations of GABAergic amacrine cells in the turtle retina. Future studies can now utilize existing information regarding the synaptic connectivity of these peptidergic amacrine cells to help delineate the functions of GABAergic amacrine cells in the turtle retina.

An atlas of glycine- and GABA-like immunoreactivity and colocalization in the cochlear nuclear complex of the guinea pig.

The distribution and colocalization of gamma-aminobutyric acid (GABA)- and glycine-like immunoreactivity in the cochlear nuclear complex of the guinea pig have been studied to produce a light microscopic atlas. The method used was based on post-embedding immunocytochemistry in pairs of 0.5-micron-thick plastic sections treated with polyclonal antibodies against conjugated GABA and glycine respectively. Immunoreactive cells, presumably short axon neurones, predominated in the dorsal cochlear nucleus, with mostly single-GABA-labelled cells in the superficial layer, double-labelled in the middle, and single-glycine-labelled in the deep layers. A few large single-glycine-labelled cells, interpreted as commissural neurons, occurred in the ventral nucleus. Scattered double-labelled cells, probably Golgi cells, were seen in the granule cell domain. Immunolabeled puncta of all three staining categories occurred in large numbers throughout the complex, apposed to somata and in the neuropil, showing a differential distribution onto different types of neuron. Three immunolabeled tracts were noted: the tuberculoventral tract, the commissural acoustic stria, and the trapezoidal descending fibres. Most of the fibres in these tracts were single-labelled for glycine, although in the last mentioned tract single-GABA- and double-labelled fibres were also found. Some of the immunolabeled cell types described here are proposed as the origins of the similarly labelled puncta and fibres on the basis of known intrinsic connections.

Spatial density and immunoreactivity of bipolar cells in the macaque monkey retina.

The anatomical substrates of spatial and color vision in the primate retina are investigated by measuring the immunoreactivity and spatial density of bipolar, amacrine and horizontal cells in the inner nuclear layer of the macaque monkey retina. Bipolar cells can be distinguished from amacrine and horizontal cells by their differential immunoreactivity to antisera against glutamate, glycine, GABA, parvalbumin, calbindin (CaBP D-28K), and the L7 protein from mouse cerebellum. The spatial density of bipolar cells is compared to the densities of photoreceptors and ganglion cells at different retinal eccentricities. In the centralmost 2 mm, cone bipolar cells outnumber ganglion cells by about 1.4:1. The density of cone bipolar cells is thus high enough to allow for input to different (parasol and midget) ganglion cell classes by different (diffuse and midget) bipolar cell classes. The density gradient of cone bipolar cells follows closely that of ganglion cells in central retina but falls less steeply in peripheral retina. This suggests that the convergence of cone signals to the receptive fields of ganglion cells in the peripheral retina occurs in the inner plexiform layer. The density of cone bipolar cells is 2.5-4 times that of cones at all eccentricities studied, implying that cone connectivity to bipolar cells remains constant throughout the retina. Different subgroups of bipolar cells are distinguished by their relative immunoreactivity to the different antisera. All rod and cone bipolar cells show moderate to strong glutamate-like immunoreactivity. The bipolar cells that show weak to moderate GABA-like immunoreactivity are also labeled with the antiserum to the L7 protein and are thus identified as rod bipolar cells. Nearly half of all cone bipolar cells showed glycine-like immunoreactivity. The results suggest that the inhibitory neurotransmitter candidates GABA and glycine are segregated respectively in rod and cone bipolar cell pathways. A diffuse, cone bipolar cell type can be identified by the anti-parvalbumin and the anti-calbindin antisera. All horizontal cells show parvalbumin-like immunoreactivity. Nearly all amacrine cells show GABA-like or glycine-like immunoreactivity; a variety of subpopulations also show immunoreactivity to one or more of the other markers used.

Immunocytochemical evidence for an afferent GABAergic neurotransmission in the guinea pig vestibular system

To implicate γ-aminobutyric acid (GABA) as an afferent neurotransmitter (AN), the localization of GABA synthesizing and degradation enzymes; l-glutamate decarboxylase (GAD) and GABA transminase (GABA-T) was investigated by light and electron microscopy immunocytochemistry in guinea pig vestibular cristae and ganglion cells (GC). GAD-like immunoreactivity was exclusively confined to the sensory hair cell (HC) cytoplasm, suggesting that GAD synthesizes GABA in the HC. GABA-like immunoreactivity was found within HC, nerve calyces, nerve fibers, and GC, suggesting its participation in terminating transmitter action. These results demonstrate the existence of a GABAergic system in the guinea pig vestibule and strongly support GABA as a vestibular AN.

Termination pattern and fine structural characteristics of GABA- and [Met]enkephalin-containing nerve fibers and synapses in the superior cervical ganglion of adult rat

Morphological features of nerve fibers and synapses containing GABA and [Met]enkephalin were studied at the light and electron microscopic levels in the superior cervical ganglia of rats by preand postembedding immunohistochemistry. Both GABA and [Met]enkephalin immunoreactivities were found in varicose nerve fibers, forming diffuse networks which were denser in the rostral than in the caudal part of each ganglion. For both antigens rich and basket-like innervation was observed around some of the principal neurons. The GABA-immunoreactive fibers were evenly stained, while in case of [Met]enkephalin-positive nerve fibers the varicosities showed intensive immunopositivity only. Postembedding immunochemistry revealed that both inhibitory substances were located in axon varicosities which established asymmetric synapses of Gray I type. Fine structural investigation revealed that GABA-like immunoreactivity was confined in the nerve endings to the clear synaptic vesicles of 40 nm diameter, whereas the immunogold particles, indicating the occurrence of [Met]enkephalin, were located over the large dense-cored vesicles of 120 nm diameter. The clear and dense-cored vesicles were, however, mixed in the nerve endings labeled by either neurotransmitter substance. Interestingly, the [Met]enkephalin-immunopositive axon terminals were found, consequently, in synaptic contacts with dendrites containing dense bodies in a row underlying the postsynaptic membrane thickening. Since nerve terminals with GABA-like immunoreactivity established synapses of Gray I type without such subjunctional bodies, one can reasonably assume that, in spite of similarities in termination pattern, there is no co-existence of GABA and enkephalin in the axons in the superior cervical ganglion.

Immunocytochemical evidence for in vitro release of glutamate and GABA from separate nerve terminal populations in the rat pontine nuclei.

A quantitative electron microscopic immunocytochemical method was used to study the synaptic handling of glutamate and GABA in slice preparations from the rat pontine nuclei. Slices were subjected to a depolarizing stimulus (55 mM K+, 20 min) in the presence of a physiological or low Ca(2+)-concentration. Depolarization at physiological [Ca2+] evoked a depletion of glutamate-like immunoreactivity from nerve terminals that contain round vesicles and establish asymmetric synaptic contacts. When depolarization was induced in the presence of only 0.1 mM Ca2+ (10 mM Mg2+ added), the loss of glutamate was significantly reduced or abolished, indicative of a Ca(2+)-dependent component of glutamate release. By means of a double-labeling immunocytochemical method we could identify a population of nerve terminals that displayed strong GABA-like immunoreactivity, and a level of glutamate-like immunoreactivity that was low but yet clearly above background level. This type of terminal contains elongated or pleomorphic vesicles and establishes symmetric synaptic contacts. In these terminals, depolarization evoked a Ca(2+)-dependent depletion of GABA-like immunoreactivity, but failed to change the level of glutamate-like immunoreactivity. The present study demonstrates that two different types of nerve terminal in the rat pontine nuclei contain releasable pools of glutamate and GABA, respectively, and that the GABA-releasing terminals also contain a non-releasable pool of glutamate. The glutamate of the latter pool could act as precursor of GABA.

A double-label study demonstrating that all serotonin-like immunoreactive amacrine cells in the larval tiger salamander retina express GABA-like immunoreactivity

A previous study localized serotonin-like immunoreactivity to amacrine cell populations in the larval tiger salamander retina. The present double-label immunocytochemical analysis of the tiger salamander retina was performed to determine if gamma-aminobutyric acid (GABA)-like immunoreactivity is expressed by serotonin-immunoreactive amacrine cells. More than 3,000 serotonin-amacrine cells were observed in double-label preparations, and all were found to express GABA-like immunoreactivity. This finding extends previous studies of serotonin-GABA coexistence in the retina by providing the first report of the co-localization of endogenous serotonin and GABA-like compounds in a retinal neuron.

Immunocytochemical evidence that GABA and neurotensin exist in different neurons in laminae II and III of rat spinal dorsal horn

Pre-embedding immunocytochemistry with antiserum to neurotensin was combined with post-embedding immunocytochemistry with GABA antiserum, in order to identify neurotensin- and GABA-containing neurons in laminae I-III of rat spinal dorsal horn. The distribution of cell bodies containing these two compounds was similar to that which has been described previously. None of the 88 neurotensin-immunoreactive neurons which were tested showed GABA-like immunoreactivity, which suggests that GABA and neurotensin exist in different cells in this region. Since both compounds are thought to be present in islet cells, it is likely that there are two neurochemically distinct populations of islet cells in lamina II of rat spinal cord.

Neuroactive amino acids in organotypic slice cultures of the rat hippocampus: An immunocytochemical study of the distribution of GABA, glutamate, glutamine and taurine

Antisera raised against protein-glutaratdehyde-amino acid conjugates were used to study the light and electron microscopic distribution of GABA, glutamate, glutamine and taurine in organotypic slice cultures of rat hippocampi. In the stratum oriens and radiatum, glutamate-like immunoreactivity was particularly concentrated in nerve endings establishing asymmetric junctions with dendritic spines. Mossy fiber terminals in CA3 and the dentate hilus were also strongly labeled. A quantitative immunogold analysis of the glutamate-immunolabelled profiles showed a pattern that was highly reminiscent of that previously observed in perfusion-fixed hippocampi, including a correspondingly sparse labeling of glial processes and of presynaptic elements in symmetric synapses. GABA-like immunoreactivity was localized predominantly in interneurons and in presynaptic terminals contacting dendritic shafts and neuronal cell bodies, while immunoreactivities for glutamine and taurine were found mainly in astroglial cells and pyramidal cells, respectively. Our data indicate that the major intrinsic fiber systems of the cultured hippocampi have retained their normal transmitter phenotypes.