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Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The reorganization of the GABAergic system was studied by means of immunohistochemistry after the symmetrical and asymmetrical (unilateral) extirpation of the brain of the annelid Eisenia fetida. GABA-immunoreactive neurons were first observed in the wound tissue on the 3rd postoperative day. Thereafter the number of labelled cells gradually increased, and by postoperative days 76-80 all GABA-immunoreactive cells (approx. 140 neurons) could be found in their final positions in the symmetrically regenerated brain. After asymmetrical brain extirpation, nearly all cells (70-75) could be detected in the regenerating hemisphere by postoperative days 50-56. In the early stages of the asymmetrical regeneration of the brain, more GABAergic cells were concentrated dorsally and laterally in the preganglion than during the symmetrical type of regeneration. In both types of regeneration, the immunoreactive neurons in the regenerated brain originated in part from undifferentiated neuroblasts situated in different parts of the body, and in part from dividing neurons localized mainly in the pharyngeal nerve plexus. Both exogenous GABA and picrotoxin, applied during the early stages (days 10- 12) of brain regeneration, inhibited the development of the wound tissue and the migration of the neuroblasts and the enteric neurons. At the same time, exogenous GABA application accelerated the proliferation of the pharyngeal neurons. No effect on the process of regeneration could be demonstrated when exogenous GABA and picrotoxin were given together.
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PMID:Reorganization of the GABAergic system following brain extirpation in the earthworm (Eisenia fetida, Annelida, Oligochaeta). 1206 78

Pre-embedding immunoperoxidase (for serotonin) and postembedding immunogold (for gamma-aminobutyric acid; GABA) labelling were combined at light and electron microscopic levels to demonstrate the neuronal targets of serotonin (5-HT) afferents in the ventral posterior lateral nucleus (VPL) of the cat thalamus. 5-HT-immunoreactive fibres and terminal varicosities were found in close proximity to GABA-immunoreactive interneurons and non-GABAergic relay neurons. Ultrastructurally, the vast majority of 5-HT terminals made close membrane contacts without overt membrane specializations with GABAergic axon terminals, GABAergic presynaptic dendrites and GABAergic somata. A very small number of 5-HT terminals formed typical asymmetrical synapses with GABAergic presynaptic dendrites and with dendritic shafts of relay cells. Some 5-HT terminals participated with the presynaptic dendrites in triadic synaptic arrangements. These findings suggest a dual innervation pattern by 5-HT afferents in VPL and the release of 5-HT in large part at sites not associated with morphologically detectable synapses.
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PMID:Simultaneous Demonstration of Serotonin-immunoreactive Terminals and GABAergic Neurons in the VPL Nucleus of the Cat Thalamus. 1210 12

Continuous current source densities were calculated in two dimensions (proximo-distal vs. medio-lateral) from slices of hippocampal field CA1 placed on a 64-electrode array in the presence of GABA blockers. The synaptic sink generated by stimulation of the Schaffer-commissural fibers spread across the extent of field CA1 within the same sublamina of the stratum radiatum as the stimulation electrode. The size and shape of the current sink varied according to the proximo-distal position of the stimulation site. Sinks generated by stimulation close to the cell body layer were more compact when compared to those produced by stimulation near the top of stratum radiatum which were broad and skewed in the proximal direction. These distributions were obtained with stimulation at either the CA3 or the subicular border of CA1. Induction of LTP increased the intensity of the current field but did not notably affect its distribution. It is concluded that (1) axons remain at the same proximo-distal level as they traverse stratum radiatum of CA1 and (2) generate proximally directed collaterals. Because of this, fibers that enter CA1 stratum radiatum immediately above the pyramidal cell bodies form compact synaptic fields while those entering CA1 at the top of the lamina form much broader and asymmetrical distributed fields.
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PMID:Asymmetrical distribution of the Schaffer projections within the apical dendrites of hippocampal field CA1. 1223 Dec 54

The synaptic organizations of gamma-aminobutyric acid-immunoreactive (GABA-IR, GABAergic) and non-GABA-IR (non-IR, glutamatergic) bipolar cells in salamander retina were compared by postembedding immunoelectron microscopy. A total of 238 presynaptic bipolar cell synapses were studied; 61 were GABA-IR and 177 were non-IR. Both groups were similar in that (1). they made asymmetrical ribbon synapses as well as asymmetrical non-ribbon synapses; (2). they made ribbon synapses at dyads, triads, and monads; and (3). the vast majority of ribbon synapses ( approximately 90%) were with dyads. The differences were that synapses of GABA-IR bipolar cells had a higher proportion of (1). direct contact with ganglion cells, (2). non-ribbon synapses, (3). output to GABA-IR amacrine cells, and (4). output in sublamina a. Overall, the output of GABA-IR ribbons was equally split between amacrine and ganglion cell processes, whereas for non-IR ribbons, it was approximately 2:1 in favor of amacrine cells. The ribbon:non-ribbon synapse ratio was approximately 1.2:1 (33:28) for GABA-IR but approximately 2:1 (118:59) for non-IR terminals. Thus, GABA-IR bipolar cells made more direct contacts with ganglion cells and used a higher proportion of non-ribbon synapses. GABA-IR dyads were more likely to contact GABA-IR amacrine profiles (52% vs. 38%). Finally, GABA-IR ribbon synapses were more common in sublamina a than sublamina b (2:1), whereas non-IR synapses were equally present in sublaminas a and b. This differential targeting of ganglion cells and amacrine cells in the OFF vs. ON layers indicates a difference in the role of bipolar cells in the generation of receptive field properties, depending on whether or not they use GABA as well as glutamate for their transmitter.
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PMID:Differential synaptic organization of GABAergic bipolar cells and non-GABAergic (glutamatergic) bipolar cells in the tiger salamander retina. 1245 84

In the thalamus of the rat the reversal potential of GABA-induced anion currents is more negative in relay cells than in neurones of the reticular nucleus (nRt) due to different chloride extrusion mechanisms operating in these cells. The distribution of KCl cotransporter type 2 (KCC2), the major neuronal chloride transporter that may underlie this effect, is unknown in the thalamus. In this study the precise regional and ultrastructural localization of KCC2 was examined in the thalamus using immunocytochemical methods. The neuropil of all relay nuclei was found to display intense KCC2 immunostaining to varying degrees. In sharp contrast, the majority of the nRt was negative for KCC2. In the anterior and dorsal part of the nRt, however, KCC2 immunostaining was similar to relay nuclei and parvalbumin and calretinin were found to colocalize with KCC2. At the ultrastructural level, KCC2 immunoreactivity was mainly located in the extrasynaptic membranes of thick and thin dendrites and the somata of relay cells but was also found in close association with asymmetrical synapses formed by cortical afferents. Quantitative evaluation of KCC2 distribution at the electron microscopic level demonstrated that the density of KCC2 did not correlate with dendritic diameter or synaptic coverage but is 1.7 times higher on perisynaptic membrane surfaces than on extrasynaptic membranes. Our data demonstrate that the regional distribution of KCC2 is compatible with the difference in GABA-A reversal potential between relay and reticular nuclei. At the ultrastructural level, abundant extrasynaptic KCC2 expression will probably play a role in the regulation of extrasynaptic GABA-A receptor-mediated inhibition.
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PMID:Differential distribution of the KCl cotransporter KCC2 in thalamic relay and reticular nuclei. 1530 65

Metabotropic gamma-aminobutyric acid receptors (GABAB) play modulatory roles in central synaptic transmission and are involved in controlling neuronal migration during development. We used immunohistochemical methods to elucidate the expression pattern as well as the cellular and the precise subcellular localization of the GABA(B1a/b) and GABAB2 subunits in the rat hippocampus during prenatal and postnatal development. At the light microscopic level, both GABA(B1a/b) and GABAB2 were expressed in the hippocampal primordium from embryonic day E14. During postnatal development, immunoreactivity for GABA(B1a/b) and GABAB2 was distributed mainly in pyramidal cells, with discrete GABA(B1a/b)-immunopositive cell bodies of interneurons present throughout the hippocampus. Using double immunofluorescence, we demonstrated that during the second week of postnatal development, GABA(B1a/b) but not GABAB2 was expressed in glial cells throughout the hippocampal formation. At the electron microscopic level, GABA(B1a/b) and GABAB2 showed a similar distribution pattern during postnatal development. Thus, at all ages the two receptor subunits were located postsynaptically in dendritic spines and shafts at extrasynaptic and perisynaptic sites in both pyramidal and nonpyramidal cells. We further demonstrated that the two subunits were localized presynaptically along the extrasynaptic plasma membrane of axon terminals and along the presynaptic active zone in both asymmetrical and, to a lesser extent, symmetrical synapses. These results suggest that GABAB receptors are widely expressed in the hippocampus throughout development and that GABA(B1a/b) and GABAB2 form both pre- and postsynaptic receptors.
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PMID:Distribution of metabotropic GABA receptor subunits GABAB1a/b and GABAB2 in the rat hippocampus during prenatal and postnatal development. 1538 54

In the present study the terminals of retinal fibres and those of internal layer cells in ventral geniculate nucleus of chicks were labelled with the anterograde tracer biotinylated dextran amine. The tracer showed the connections from the internal cell layers of ventral geniculate nucleus to the medial part of the dorsal lateral geniculate nucleus. The labelled retinal terminals were located exactly in the lateral part of nucleus. The labelled terminals in the two parts of the nucleus were analysed with the electron microscope and showed a different synaptic organisation in the two parts of the dorsal lateral geniculate nucleus. In the lateral part, two kinds of synaptic glomeruli were found mostly in the vicinity of large dendrites, which are proximal dendrites of projection neurons. One type is a simple glomerulus containing a large dendrite, a large optic terminal and a large and/or series of asymmetrical synapses surrounded by glial processes. The other type is a complex synaptic unit with several pre- and postsynaptic components, among them synapses of GABA-positive axon terminals and/or dendraxons. No glomeruli were found in the medial part of the nucleus. In the medial part of the lateral geniculate nucleus, the terminals of internal layer cell axons established asymmetrical synapses with dendrites. Often, a large terminals and large dendritic profiles established serial asymmetrical synapses. GABA-positive myelinated fibres entered and ramified in both parts of the dorsal lateral geniculate nucleus, and GABA-positive terminals were seen to form synapses on the same dendrite near to the asymmetrical contacts. To our knowledge, this is the first report of the connection from ventral geniculate internal layer cells to the dorsal lateral geniculate nucleus in the chick.
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PMID:Anterograde tracer study on the nucleus geniculatus dorsalis and its internal synaptic structure in chick brain. 1581 49

Kainic acid-induced neuron loss in the hippocampal dentate gyrus may cause epileptogenic hyperexcitability by triggering the formation of recurrent excitatory connections among normally unconnected granule cells. We tested this hypothesis by assessing granule cell excitability repeatedly within the same awake rats at different stages of the synaptic reorganization process initiated by kainate-induced status epilepticus (SE). Granule cells were maximally hyperexcitable to afferent stimulation immediately after SE and became gradually less excitable during the first month post-SE. The chronic epileptic state was characterized by granule cell hyper-inhibition, i.e., abnormally increased paired-pulse suppression and an abnormally high resistance to generating epileptiform discharges in response to afferent stimulation. Focal application of the gamma-aminobutyric acid type A (GABA(A)) receptor antagonist bicuculline methiodide within the dentate gyrus abolished the abnormally increased paired-pulse suppression recorded in chronically hyper-inhibited rats. Combined Timm staining and parvalbumin immunocytochemistry revealed dense innervation of dentate inhibitory interneurons by newly formed, Timm-positive, mossy fiber terminals. Ultrastructural analysis by conventional and postembedding GABA immunocytochemical electron microscopy confirmed that abnormal mossy fiber terminals of the dentate inner molecular layer formed frequent asymmetrical synapses with inhibitory interneurons and with GABA-immunopositive dendrites as well as with GABA-immunonegative dendrites of presumed granule cells. These results in chronically epileptic rats demonstrate that dentate granule cells are maximally hyperexcitable immediately after SE, prior to mossy fiber sprouting, and that synaptic reorganization following kainate-induced injury is temporally associated with GABA(A) receptor-dependent granule cell hyper-inhibition rather than a hypothesized progressive hyperexcitability. The anatomical data provide evidence of a possible anatomical substrate for the chronically hyper-inhibited state.
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PMID:Kainic acid-induced recurrent mossy fiber innervation of dentate gyrus inhibitory interneurons: possible anatomical substrate of granule cell hyper-inhibition in chronically epileptic rats. 1638 88

Starburst amacrine cells in the mammalian retina respond asymmetrically to movement along their dendrites; centrifugal movement elicits stronger responses in each dendrite than centripetal movement. It has been suggested that the asymmetrical response can be attributed to intrinsic properties of the processes themselves. But starburst cells are known to release and have receptors for both GABA and acetylcholine. We tested whether interactions within the starburst cell network can contribute to their directional response properties. In a computational model of interacting starburst amacrine cells, we simulated the response of individual dendrites to moving light stimuli. By setting the model parameters for "synaptic connection strength" (cs) to positive or negative values, overlapping starburst dendrites could either excite or inhibit each other. For some values of cs, we observed a very robust inward/outward asymmetry of the starburst dendrites consistent with the reported physiological findings. This is the case, for example, if a starburst cell receives inhibition from other starburst cells located in its surround. For other values of cs, individual dendrites can respond best either to inward movement or respond symmetrically. A properly wired network of starburst cells can therefore account for the experimentally observed asymmetry of their response to movement, independent of any internal biophysical or biochemical properties of starburst cell dendrites.
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PMID:Symmetric interactions within a homogeneous starburst cell network can lead to robust asymmetries in dendrites of starburst amacrine cells. 1659 66

The nucleus rotundus of the turtles Emys orbicularis and Testudo horsfieldi was analysed by axonal tracing methods and post-embedding GABA immunocytochemistry. After injections of horseradish peroxidase or biotinylated dextran amine into the optic tectum, electron microscopic observations showed that the vast majority of ipsilateral tectorotundal axon terminals were small in size, had smooth contours and contained small, round, densely packed synaptic vesicles. These terminals were GABA-immunonegative, often gathered in clusters, and established asymmetrical synaptic contacts with either small- or medium-sized GABA-negative dendritic profiles and with GABA-immunoreactive (GABA-ir) dendrites, which did not contain synaptic vesicles. Occasional GABA-ir-labelled axon terminals were observed; these may arise from the rare GABAergic neurons in the central tectal layer, or from neurons in the ventral pretectal nucleus, which projects both to the optic tectum and nucleus rotundus. In addition to tracer-labelled axon terminals, we observed both GABA-negative and GABA-ir cell bodies and dendrites also labelled by the tracer. No GABA-ir presynaptic dendritic profiles containing synaptic vesicles were observed. The existence in reptiles of reciprocal connections between the nucleus rotundus and the optic tectum as a phylogenetically ancient feedback system is discussed.
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PMID:Tectorotundal connections in turtles: an electron microscopic tracing and GABA-immunocytochemical study. 1799 57


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