Population Of GABAergic Neurons Research Articles

Populations of GABAergic neurons and axons in layer I of rat auditory cortex

Neurons and axon terminals (puncta) immunostained by an antibody against glutamic acid decarboxylase were studied in layer I of adult rats in architectonically identified area 41 of auditory cortex. The borders of area 41 and the laminar subdivisions of cortex were established in normal material and in other studies of cortical connections. Vibratomed or frozen sections were immunostained. The objectives of the study were to classify the types of (i) glutamic acid decarboxylase-positive neurons and (ii) puncta, and (iii) to examine their spatial distribution within layer I. Control sections were devoid of specific immunostaining. More than 90% of layer I cells are glutamic acid decarboxylase-positive. Four types of neuron were identified in Golgi material, including small neurons with stellate dendritic fields, horizontal cells with laterally projecting arbors, medium-sized neurons with stellate, widely ramifying dendritic fields, and large neurons with broad dendritic fields spanning the depth of layer I or branching laterally. In the glutamic acid decarboxylase material, examples with a somatodendritic shape matching each of these types were found. The average somatic diameter of glutamic acid decarboxylase-positive neurons ( X¯= 59μm 2, S.D. = 21μm 2) suggests that the small and medium-sized neurons predominate. Glutamic acid decarboxylase-positive neurons occur throughout the depth of layer I, but are far more numerous in the deeper half (68% in layer Ib) than in the superficial part (32% in layer Ia). Glutamic acid decarboxylase-positive neurons form small clusters of three to five cells across the cortical surface, with a range of 0–9/100 μm across the cortex. Most glutamic acid decarboxylase-positive neuronal perikarya were intensely immunostained, and the dendrites of the medium-sized and large neurons were traced as far as 50–75 μm beyond their initial branching point. Glutamic acid decarboxylase-positive puncta also had variable shapes. Both small, fine puncta (< 0.5 μm in diameter) and larger, coarser ones (>1.5 μm in diameter) were present, though the former were much more common. In traverses from the pia to the layer II border, the puncta average about 40/100 μm 2 (range: 20–80), and the shape of individual pia-layer II traverses is multipeaked, often with a slight trough at −80μm depth, then rising slowly in number toward layer II. These anatomical arrangements may have physiological consequences for cortical functional organization: (i) the GABAergic influences of layer I cells are directed laterally, toward other layer I neurons, or at the apical dendritic arbors of deep-lying commissural or corticofugal neurons, whose activity might be modulated by GABAergic layer I influences; (ii) the axons of layer II glutamic acid decarboxylase-positive neurons or of corticocortical interneurons may affect layer I. While many different transmitter molecules have been identified in layer I, it is probable that their activity influences a largely GABAergic neuronal population.

Further evidence that preoptic anterior hypothalamic GABAergic neurons are part of the GnRH pulse and surge generator.

The in vivo release rates of GABA from the preoptic/anterior hypothalamic area (PO/AH) of ovariectomized rats were assessed by means of a focal perfusion cannula system. Seven days after surgery all animals received a sc silastic capsule implant containing either estradiol-17 beta (E2) or corn oil, and they were perfused 3 days later. Perfusate fractions were sampled at 5-min intervals and blood was collected every 10 min over a period of 5 h. In ovariectomized animals PO/AH GABA release was pulsatile without any diurnal rhythm. Prior to frequency analysis by means of the pulsar-programme, LH and GABA values were z-transformed. Significant LH peaks of all examined ovariectomized rats were superimposed and GABA data were arranged accordingly. It became evident that LH episodes are preceded by a significant reduction of preoptic anterior hypothalamic GABA release. The secretion patterns of GABA and LH were profoundly affected by E2 replacement. During early noon when LH levels were low, constantly elevated hypothalamic GABA release rates were observed in E2-substituted rats in comparison to ovariectomized rats. GABA release rates fell significantly during the E2-induced LH surge. Our previous demonstration of the existence of a large number of estrogen-respective GABAergic neurons in the PO/AH is suggestive of these neurons changing their activity in response to estrogen treatment. We conclude that these estrogen-respective GABAergic neurons are involved in the generation of GnRH pulses as well as in the generation of the so-called positive feedback effect of E2 on LH release.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of GABAergic neurons and axon terminals in the macaque striate cortex.

Antisera to glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid (GABA) have been used to characterize the morphology and distribution of presumed GABAergic neurons and axon terminals within the macaque striate cortex. Despite some differences in the relative sensitivity of these antisera for detecting cell bodies and terminals, the overall patterns of labeling appear quite similar. GABAergic axon terminals are particularly prominent in zones known to receive the bulk of the projections from the lateral geniculate nucleus; laminae 4C, 4A, and the cytochrome-rich patches of lamina 3. In lamina 4A, GABAergic terminals are distributed in a honeycomb pattern which appears to match closely the spatial pattern of geniculate terminations in this region. Quantitative analysis of axon terminals that contain flat vesicles and form symmetric synaptic contacts (FS terminals) in lamina 4C beta and in lamina 5 suggest that the prominence of GAD and GABA axon terminal labeling in the geniculate recipient zones is due, at least in part, to the presence of larger GABAergic axon terminals in these regions. GABAergic cell bodies and their initial dendritic segments display morphological features characteristic of nonpyramidal neurons and are found in all layers of striate cortex. The density of GAD and GABA immunoreactive neurons is greatest in laminae 2-3A, 4A, and 4C beta. The distribution of GABAergic neurons within lamina 3 does not appear to be correlated with the patchy distribution of cytochrome oxidase in this region; i.e., there is no significant difference in the density of GAD and GABA immunoreactive neurons in cytochrome-rich and cytochrome-poor regions of lamina 3. Counts of labeled and unlabeled neurons indicate that GABA immunoreactive neurons make up at least 15% of the neurons in striate cortex. Layer 1 is distinct from the other cortical layers by virtue of its high percentage (77-81%) of GABAergic neurons. Among the other layers, the proportion of GABAergic neurons varies from roughly 20% in laminae 2-3A to 12% in laminae 5 and 6. Finally, there are conspicuous laminar differences in the size and dendritic arrangement of GAD and GABA immunoreactive neurons. Lamina 4C alpha and lamina 6 are distinguished from the other layers by the presence of populations of large GABAergic neurons, some of which have horizontally spreading dendritic processes. GABAergic neurons within the superficial layers are significantly smaller and the majority appear to have vertically oriented dendritic processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Hippocampus of the seizure-sensitive gerbil is a specific site for anatomical changes in the GABAergic system.

The brains of seizure-sensitive (SS) and seizure-resistant (SR) gerbils were studied with an immunocytochemical method to localize glutamic acid decarboxylase (GAD) to determine whether a defect existed in the inhibitory GABAergic system similar to that which has been reported in animal models of focal epilepsy in which GABAergic cell bodies and terminals are decreased in number. A major difference between the two strains of gerbils was found in the number of GABAergic neurons in the hippocampal formation. Specifically, a paradoxical increase occurred in the number of glutamate decarboxylase GAD-immunoreactive neurons: there were approximately 65% more GABAergic cells within the dentate gyrus and the CA3 region of the hippocampus in the SS gerbils. Furthermore, the density of GAD-immunoreactive puncta, the light microscopic correlates of synaptic boutons, was greater in the SS animals. Other histological methods were used to determine if the difference between SS and SR gerbils was specific for the GABAergic system. Nissl-stained preparations showed that the number of granule cells in the dentate gyrus was 20% greater in SS gerbils than in SR gerbils. An examination of some hippocampal afferents, efferents, and intrinsic connections with acetylcholinesterase histochemistry and the Timm's stain for heavy metals demonstrated no differences between the two strains. In addition, Golgi-stained preparations of the dentate gyrus indicated that the morphology of basket cells did not differ between the two strains nor between the gerbil and the rat. Several brain regions in addition to the hippocampus were studied to determine whether or not the increased number of GAD-immunoreactive neurons was specific for the hippocampal formation. These regions included the substantia nigra, motor cortex, and nucleus reticularis thalami and were selected because they contain large populations of GABAergic neurons and have been implicated in seizure activity. No differences between the two strains were detected in any of these regions. Therefore, a major morphological difference between the brains of SS and SR gerbils exists in the hippocampal formation of SS gerbils in which an increase occurs in the number of GABAergic neurons and granule cells. If these additional inhibitory neurons act mainly to inhibit other inhibitory neurons, the net effect would be increased disinhibition of the principal excitatory neurons of the hippocampal formation. This could lead to seizure activity within the hippocampal formation and at distant sites through multiple synaptic connections.

Postnatal Appearance of Glycoconjugate with Terminal N-Acetylgalactosamine on the Surface of Selected Neurons in Mouse Brain

Selected neurons in the cortex and other regions of the brain of adult mice stain with Vicia villosa agglutinin (VVA) conjugated to horseradish peroxidase (HRP). This staining demonstrates glycoconjugate with terminal N-acetylgalactosamine (GalNAc) in periodic foci on the neuronal surface. However, brains from mice at 1 week of age lacked neurons with surface reactivity for VVA-HRP but showed neurons with faint cytoplasmic staining. Two weeks postnatally, infrequent cortical neurons located mostly in layer IV disclosed light surface affinity for VVA-HRP. The deep cerebellar nucleus at 2 weeks revealed VVA-positive neurons that were less abundant than in adults but exceeded in number the stained neurons in the cortex of 2-week-old mice. By 3 weeks of age the prevalence of positive neurons in cortical layers II-VI and the deep cerebellar nucleus and the intensity of the surface staining approximated that observed in adult mice. No staining of fiber tracts was observed 1 week postnatally. However, certain tracts exemplified by decussating fibers in the basal pontine region showed strong VVA-HRP reactivity in brains of 2-week-old mice as in adults. Acquisition of VVA surface affinity 3 weeks postnatally coincided with the appearance of cytosolic immunostaining for glutamic acid decarboxylase in a population of GABAergic neurons in the cortex. These findings demonstrate the postnatal development of GalNAc-containing glycoconjugate associated with selected neurons and the variable acquisition of the glycoconjugate among these neurons possibly related to onset of function.

GABAergic neurons of rodent brain correspond partially with those staining for glycoconjugate with terminalN-acetylgalactosamine

Sections of fixed, paraffin-embedded brain from mice and rats were stained with agglutinin from Vicia villosa conjugated to horseradish peroxidase (VVA-HRP) to localize glycoconjugate containing terminal N-acetylgalactosamine (GalNAc). VVA-HRP binding sites were localized in periodic foci at the surface of a selective population of non-pyramidal interneurons in layers II through IV of the rodent cerebral cortex. These multipolar interneurons were shown to utilize gamma-aminobutyric acid (GABA) as a transmitter and thus to be GABAergic by their immunostaining for glutamic acid decarboxylase (GAD) throughout the cytoplasm in serial sections. Pyramidal and other non-pyramidal cortical neurons received GABAergic input as evidenced by punctate immunostaining for GAD on their soma and proximal dendritic arborizations, but these cells failed to show VVA affinity or cytosolic GAD reactivity. Most neurons in the thalamic reticular nucleus stained for the presence of glycoconjugate with terminal GalNAc on their surface and for GAD in the cytosol. In contrast, cerebellar Purkinje cells showed strong cytosolic reactivity with anti-GAD but lacked surface staining with VVA-HRP. These observations show that some but not other populations of GABAergic neurons possess binding capacity for VVA on their surface. The surface of neurons in the deep cerebellar nucleus stained heavily with VVA but failed to show clear cytosolic reactivity for GAD. Some neurons with surface glycoconjugate containing terminal GalNAc are therefore not GABAergic.

Neurotransmitter-related markers in the normal and experimentally lesioned telencephalon of the goldfish

The telencephalon of teleost fish shows high affinity uptake for d-[ 3H]aspartate, intermediate levels of GABAergic markers and low levels of cholinergic enzymes. Experimental results (resection of the olfactory or unilateral kainic acid administration in the telencephalon) suggest that: (1) the projection from the olffactory bulbs to telencephalic targets is mediated by aspartate and/or glutamate; and (2) a population of GABAergic neurons is present in a telecephalic area which is considered homologous to part of the striatal complex of land vertebrates. From the present results, it appears that the neurochemical approach can be used, in conjunction with neuroanatomical methods, to study evolutionary problems of telencephalic function.

In vivo release of [ 3H]GABA in cat caudate nucleus and substantia nigra. I. Bilateral changes induced by a unilateral nigral application of muscimol

Push-pull cannulae were implanted in both caudate nuclei and both substantiae nigrae (SN) of halothane-anesthetized cats and the release of [ 3H]GABA, continuously synthesized from [ 3H]glutamine, was measured in these structures during 4 h of superfusion. In some experiments, multi-unit neuronal activity was recorded at the tip of the nigral push-pull cannulae, using a bipolar electrode. Two hours after the onset of superfusion with [ 3H]glutamine, 10 −6M of muscimol was added (for 1 h) in the superfusion medium delivered to one SN. This treatment increased locally the release of [ 3H]GABA and enhanced the neuronal activity of the nigral cells in the zona reticulata. An increased release of [ 3H]GABA was also observed in the contralateral SN, in association with an inhibition of the activity of the zona reticulata cells. The unilateral nigral application of muscimol also induced asymmetric changes in the release of [ 3H]GABA in both caudate nuclei, since [ 3H]GABA release was increased ipsilaterally and reduced on the contralateral side. The present findings are considered in relation to possible GABAergic neuronal populations affected by this local pharmacological treatment.

GABA and the enteric nervous system. A neurotransmitter function?

GABA and GABA-related properties in the enteric nervous system of the gastrointestinal tract, the third and most complex division of the vertebrate autonomic nervous system, have been the subject of relatively few studies. This chapter aims at being a comprehensive review of these investigations. With respect to GABA the enteric nervous system shows in some respects similarities with, and in others, notable differences from other parts of the peripheral nervous system. Like the cell bodies of other autonomic and sensory neurons, the cell bodies of enteric neurons possess bicuculline and picrotoxin sensitive GABA receptors, the activation of which leads to depolarization, probably mediated by increase in Cl- conductance. Further, in common with other peripheral glia, the cell membrane of the enteric glial cells appears to contain beta-alanine sensitive high affinity transport sites by which they can accumulate exogenous GABA. However, the present evidence, although not completely conclusive, suggests that unlike other parts of the peripheral nervous system, the enteric ganglia may contain a population of GABA-ergic neurons; in vertebrates such neurons have hitherto been thought to be present in the brain and spinal cord only. At present the mst important single strand of evidence for this notion is the demonstration of a population of enteric neurons possessing high affinity transport sites for GABA, while it is supported by studies of GAD and GABA content, the effects of GABA receptors blockade on gut motility and GABA release.

Organization and plasticity of GABAergic neurons in some extrapyramidal nuclei of the rat

The organization of GABAergic neurons in the extrapyramidal system has been investigated in the rat. Striatal hemitransections or electrolytic lesions anterior to the rostral pole of the globus pallidus (GP) decreased glutamic acid decarboxylase (GAD) activity in the GP and entopeduncular nucleus (EP), but did not significantly affect the activity of the enzyme in the substantia nigra (SN). Electrolytic lesions of the tail of the striatum produced only a small decrease in nigral GAD activity. Selective but extensive kainic acid lesions of the GP did not significantly affect the activity of GAD in the SN. These results indicate: (1) that different populations of striatal GABA-ergic neurons innervate the GP and the SN, the former being mainly precommissural and the latter mainly postcommissural; (2) that the pallidonigral projection is not GABAergic; and (3) that the source of the striatonigral GABAergic projection is a group of neurons situated immediately lateral, rostral and perhaps dorsal to the GP. In addition to striato-GP and striato-EP GABAergic projections, evidence is reviewed that demonstrates that the GP and EP send GABAergic efferents to the subthalamic and lateral habenular nuclei respectively. Similarly, the SN contains GABA-ergic perikarya some of which may innervate the tectum and certain thalamic nuclei. 6-Hydroxydopamine lesions of the ascending dopaminergic projections resulted in significant increases in GAD activities in the striatum, nucleus accumbens and GP, but not in the SN. Kinetic analyses indicated that the striatal increase was due to an increased number of enzyme molecules (V max) and not to enzyme activation (K m). These results raise the possibility that striatal GABAergic terminals “sprout” in response to a lesion of the dopaminergic terminals. The increase in striatal GAD activity is opposite to the decrease that has consistently been observed in Parkinson's disease. These results suggest that in addition to the documented pathology of dopaminergic neurons, Parkinson's disease is also characterized by significant degeneration of striatal GABAergic neurons.

HYPOTHALAMIC REGULATION OF SLEEP IN RATS. AN EXPERIMENTAL STUDY

The essential role of the nervous system in the regulation of the sleep-waking rhythm of higher animals is now widely recognized. No less a person than von Economo, however, drew attention to the fact that the phenomenon of sleep cannot be accounted for by a mere functional change of the central nervous system from its condition during the waking state. It is indeed an important fact that the function of sleep, instead of being characteristic of higher animals, is also observed in organisms which do not possess a central nervous system, and even in several vegetable species. It is therefore impossible to attribute this mysterious function to any special organ. Since all experimental work on sleep has hitherto been confined to mammals, chiefly to cats and monkeys, practically no data concerning the comparative physiology of this phenomenon are available. Nevertheless, it seems probable that during the phylogenetic development the function of sleep, together with many other mechanisms, was progressively centralized into the nervous system from which organ all changes, characteristic of sleep, were ultimately effected. This centralization proceeded so far that the alternation of wake and sleep seems to be governed in mammals by a circumscribed area of the central nervous system, capable of determining physical and psychical activities. The existence of this “centre” for the regulation of sleep is generally accepted by students of this subject.