Electrophysiological evidence of GABA_A and GABA_C receptors on zebrafish retinal bipolar cells

Abstract

To refine inhibitory circuitry models for ON and OFF pathways in zebrafish retina, GABAergic properties of zebrafish bipolar cells were studied with two techniques: whole cell patch responses to GABA puffs in retinal slice, and voltage probe responses in isolated cells. Retinal slices documented predominantly axon terminal responses; isolated cells revealed mainly soma-dendritic responses. In the slice, GABA elicited a conductance increase, GABA responses were more robust at axon terminals than dendrites, and E rev varied with [Cl − ] in . Axon terminals of ON-and OFFtype cells were similarly sensitive to GABA (30-40pA peak current); axotomized cells were unresponsive. Bicuculline-sensitive, picrotoxin-sensitive, and picrotoxin-insensitive components were identified. Muscimol was as effective as GABA; baclofen was ineffective. Isolated bipolar cells were either intact or axotomized. Even in cells without an axon, GABA or muscimol (but not baclofen) hyperpolarized dendritic and somatic regions, suggesting significant distal expression. Median fluorescence change for GABA was −0.22 log units (~−16mV); median half-amplitude dose was 0.4μM. Reduced [Cl − ] out blocked GABA responses. GABA hyperpolarized isolated ONbipolar cells, OFF-cells were either unresponsive or depolarized. Hyperpolarizing GABA responses in isolated cells were bicuculline and TPMPA insensitive, but blocked or partially blocked by picrotoxin or zinc. In summary, axon terminals contain bicuculline-sensitive GABA A

Immunocytochemical evidence for SNARE protein‐dependent transmitter release from guinea pig horizontal cells

“…Studies in non‐mammalian retinas have argued for GABA uptake and release occurring via a Na + ‐dependent and Ca 2+ ‐independent transport process in these horizontal cells due to the presence of a plasmalemmal GABA transporter (Schwartz, 1982, 1987; Yazulla et al. , 1985; Ayoub & Lam, 1987; O’Malley & Masland, 1989; Connaughton et al. , 2008; Nelson et al.…”

A spectral model for signal elements isolated from zebrafish photopic electroretinogram

“…On this argument the delayed peak-time of the CNQX-treated b-wave, which leads to the b1/b2 distinction, is not likely caused by CNQX-hyperpolarized horizontal cells, though the b2 amplitude increase might be. CNQX blocks amacrine responses with attendant loss of GABAergic and glycinergic inhibition of bipolar cells (Connaughton et al , 2008). These actions are not expected to be fast enough to alter the rising phase of the ON-bipolar-cell response.…”

Genetic approaches to retinal research in zebrafish

“…However, the limited number of publications on recordings in retinal slices shows one of the limitations of the zebrafish model to study retinal physiology (Connaughton et al 2008).…”