All indoleamine-accumulating cells in the rabbit retina contain GABA.
The indoleamine-accumulating amacrine cells of the rabbit retina are wide-field and numerous. They form a dense plexus in sublamina 5 of the inner plexiform layer where they make reciprocal synapses with rod bipolar cells. To provide a quantitative test for the colocalization of serotonin (5-HT) and gamma-aminobutyric acid (GABA) in the rabbit retina, we designed two parallel double-label experiments. In the first series, the indoleamine-accumulating cells were labeled with 5,7-dihydroxytryptamine (5,7-DHT), which was subsequently visualized by photooxidation in the presence of diaminobenzidine. This was combined with autoradiography for 3H-muscimol. In the second and complementary series, 3H-5-HT uptake was combined with postembedding GABA immunocytochemistry. These two experiments provided essentially identical results: over 98% of the indoleamine-accumulating amacrine cells were double-labeled. This means that, within the limit of experimental error, all the indoleamine-accumulating amacrine cells are GABAergic. The indoleamine-accumulating amacrine cells account for 15-20% of a large diverse group of GABA amacrine cells. In addition, the rare type 3 indoleamine-accumulating cells and fine processes running in the optic fiber layer were double-labeled. If there is insufficient 5-HT to support a transmitter role in the rabbit retina, our results suggest that the indoleamine-accumulating cells may use GABA as a neurotransmitter. Thus, rod bipolar cells, in common with other bipolar cell types, receive extensive negative feedback at GABA-mediated reciprocal synapses.
Massey
S C
SC
Sensory Sciences Center, Graduate School of Biomedical Sciences, University of Texas Health Science Center, Houston 77030.
Mills
S L
SL
Marc
R E
RE
D015116:5,7-Dihydroxytryptamine / Q000378:metabolism; D000818:Animals; D001345:Autoradiography; D015306:Biogenic Monoamines / Q000378:metabolism*; D005260:Female; D007150:Immunohistochemistry; D007211:Indoles / Q000378:metabolism*; D008297:Male; D009118:Muscimol / Q000378:metabolism; D010084:Oxidation-Reduction; D010777:Photochemistry; D010786:Photoreceptor Cells / Q000166:cytology; D011817:Rabbits; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D015306:Biogenic Monoamines; D007211:Indoles; D009118:Muscimol; D015116:5,7-Dihydroxytryptamine; D005680:gamma-Aminobutyric Acid