Compartmental localization of γ-aminobutyric acid type B receptors in the cholinergic circuitry of the rabbit retina (original) (raw)
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Cholinergic amacrine cells of the rat retina express the δ-subunit of the GABAA-receptor
Neuroscience Letters, 1993
Antibodies directed against the ~-subunit of the GABA~,-receptor were applied to cryostat sections of rat retinae. Two narrow bands of the inner plexiform layer were strongly immunoreactive. Some cell bodies in both the amacrine-and ganglion-cell layer were weakly immunoreactive. The position of the labelled bands and the distribution of the cell bodies was strongly reminiscent of the cholinergic amacrine cells. In order to show directly that cholinergic amacrine cells express the 6-subunit of the GABAA-receptor, double immunofluorescence with an antibody against choline acetyltransferase (CHAT) and with antibodies against the ~-subunit was performed on the same cryostat sections. This showed the labelled cells to be cholinergic amacrine cells.
Modes and models of GABA(A) receptor gating
The Journal of physiology, 2006
Upon activation by agonist, the type A gamma-aminobutyric acid receptor (GABAR) 'gates', allowing chloride ions to permeate membranes and produce fast inhibition of neurons. There is no consensus kinetic model for the GABAR gating mechanism. We expressed human alpha(1)beta(1)gamma(2S) GABARs in HEK 293 cells and recorded single channel currents in the cell-attached configuration using various GABA concentrations (50-5000 microm). Closed and open events occurred individually and in clusters that had at least three different modes that were distinguishable by open probability (P(O)): High (P(O)= 0.73), Mid (P(O)= 0.50), and Low (P(O)= 0.21). We used a critical time to isolate shorter bursts of openings and to thus eliminate long-lived, desensitized events. Bursts from all three modes contained three closed and three open components. We employed maximum likelihood fitting, autocorrelation analysis and macroscopic current simulation to distinguish kinetic schemes. The 'core&...
Frontiers in Cellular Neuroscience, 2015
is a major retinal neurotransmitter that modulates visual processing through a large repertoire of cholinergic receptors expressed on different retinal cell types. ACh is released from starburst amacrine cells (SACs) under scotopic conditions, but its effects on cells of the rod pathway have not been investigated. Using whole-cell patch clamp recordings in slices of rat retina, we found that ACh application triggers GABA release onto rod bipolar (RB) cells. GABA was released from A17 amacrine cells and activated postsynaptic GABA A and GABA C receptors in RB cells. The sensitivity of ACh-induced currents to nicotinic ACh receptor (nAChR) antagonists (TMPH ∼ mecamylamine > erysodine > DhβE > MLA) together with the differential potency of specific agonists to mimic ACh responses (cytisine >> RJR2403 ∼ choline), suggest that A17 cells express heteromeric nAChRs containing the β 4 subunit. Activation of nAChRs induced GABA release after Ca 2+ accumulation in A17 cell dendrites and varicosities mediated by L-type voltage-gated calcium channels (VGCCs) and intracellular Ca 2+ stores. Inhibition of acetylcholinesterase depolarized A17 cells and increased spontaneous inhibitory postsynaptic currents in RB cells, indicating that endogenous ACh enhances GABAergic inhibition of RB cells. Moreover, injection of neostigmine or cytisine reduced the b-wave of the scotopic flash electroretinogram (ERG), suggesting that cholinergic modulation of GABA release controls RB cell activity in vivo. These results describe a novel regulatory mechanism of RB cell inhibition and complement our understanding of the neuromodulatory control of retinal signal processing.
Immunocytochemical localization of GABAA receptors in goldfish and chicken retinas
The Journal of Comparative Neurology, 1989
A monoclonal antibody (mAb 62-3G1) to the GABAA receptor/benzodiazepine receptor/Cl- channel complex from bovine brain was used with light and electron microscopy in goldfish retina and light microscopy in chicken retina to localize GABAA receptor immunoreactivity (GABAr-IR). GABAr-IR was found in the outer plexiform layer (OPL) in both species, in three broad bands in the inner plexiform layer (IPL) of goldfish, and in seven major bands of the chicken IPL. A small percentage of amacrine cell bodies (composing at least three types) were stained in chicken. In goldfish OPL, GABAr-IR was localized intracellularly and along the plasma membrane of cone pedicles, whereas rod spherules were lightly stained, but always only intracellularly. In chicken, all three sublayers of the OPL were GABAr-IR. The presence of GABAr-IR on photoreceptor terminals is consistent with data indicating feedback from GABAergic horizontal cells to cones. In the goldfish IPL, GABAr-IR was localized to postsynaptic sites of amacrine cell synapses; intracellular staining of processes in the IPL also was observed in presumed "GABAergic" targets. A comparison of GABAr-IR with the distributions of 3H-muscimol uptake/binding, glutamate decarboxylase-IR, GABA-IR, and 3H-GABA uptake in the IPL showed either a reasonable correspondence or mismatch, depending on the marker, species, and lamina within the IPL. The distribution of GABAr-IR in the retina corresponded better with the 3H-muscimol than with 3H-benzodiazepine binding patterns yet overall was in excellent agreement with many other physiological and anatomical indicators of GABAergic function. We suggest that intracellular GABAr-IR represents the biosynthetic and/or degradative pathway of the receptor and we conclude that mAb 62-3G1 is a valid marker of GABAA receptors in these retinas and will serve as a useful probe with which to address the issue of mismatches between the localization of GABAA receptors and indicators of presynaptic GABAergic terminals.
Many neurons express a multiplicity of GABA A receptor subunit isoforms. Despite having only a single source of inhibitory input, the cerebellar granule cell displays, at various stages of development, more than 10 different GABA A subunit types. This subunit diversity would be expected to result in significant receptor heterogeneity, yet the functional consequences of such heterogeneity remain poorly understood. Here we have used single-channel properties to characterize GABA A receptor types in the synaptic and extrasynaptic membrane of granule cells. In the presence of high concentrations of GABA, which induced receptor desensitization, extrasynaptic receptors in outside-out patches from the soma entered long-lived closed states interrupted by infrequent clusters of openings. Each cluster of openings, which is assumed to result from the repeated activation of a single channel, was to one of three main conductance states (28, 17, or 12 pS), the relative frequency of which differed between patches. Such behavior indicates the presence of at least three different receptor types. This heterogeneity was not replicated by individual recombinant receptors (␣ 1  2 ␥ 2S or ␣ 1  3 ␥ 2S ), which gave rise to clusters of a single type only. By contrast, the conductance of synaptic receptors, determined by fluctuation analysis of the synaptic current or direct resolution of channel events, was remarkably uniform and similar to the highest conductance value seen in extrasynaptic patches. These results suggest that granule cells express multiple GABA A receptor types, but only those with a high conductance, most likely containing a ␥ subunit, are activated at the synapse.