Title: Effects of (‐)bicuculline and gamma‐aminobutyric acid on the NiCl2 mediated stimulation of the ERG b‐wave amplitude from the isolated superfused vertebrate retina
Abstract: Abstract Purpose: NiCl2 (15 μM) stimulates the b‐wave amplitude of vertebrate retina, up to 1.5‐fold through its blocking of E/R‐type voltage‐gated Ca2+ channels. Assuming that these channels may trigger the release of the inhibitory neurotransmitter GABA, we tested the effect of (‐)bicuculline and GABA itself. Methods: We have used a superfused vertebrate retina assay, testing retina from bovine (Lüke et al., 2005: Brain Res Brain Res Protoc 16 : 27‐36). The retina was separated from the underlying pigment epithelium and mounted on a mesh occupying the center of the perfusing chamber. The electroretinogram was recorded in the surrounding nutrient medium via two silver/silver‐chloride electrodes on either side of the retina. The recording chamber containing a piece of retina was placed in an electrically and optically insulated air thermostat. The retina was dark‐adapted and the electroretinogram was elicited at intervals of five min using a single white flash for stimulation. Results: (‐)Bicuculline increased the b‐wave amplitude to a similar extent as observed in parallel recordings for low NiCl2 (15 μM). The GABA effect was biphasic, and let to a transient stimulation after NiCl2 application. Those retina segments which did not respond to NiCl2 (15 μM), also could not be stimulated by bicuculline and vice versa. Conclusions: The stimulatory effect of NiCl2 on the ERG b‐wave amplitude is mediated by a NiCl2‐sensitive, probably Cav2.3 / voltage‐gated Ca2+‐channel triggered GABA‐release, and GABA itself may act on at least two different receptors.