Distribution of the alpha 1 subunit of the GABA(A) receptor on midget and parasol ganglion cells in the retina of the common marmoset Callithrix jacchus

The inhibitory neurotransmitter gamma aminobutyric acid (GABA) has been sho wn to influence the responses of ganglion cells in the mammalian retina. Co nsistently, GABA(A) receptor subunits have been localized to different gang lion cell types. In this study, the distribution of the alpha 1 subunit of the GABA(A) receptor on the dendrites of midget and parasol ganglion cells was investigated quantitatively in the retina of a New World monkey, the ma rmoset. Ganglion cells were injected with Neurobiotin in a live in vitro re tinal whole-mount preparation. Retinal pieces were then processed with an a ntibody against the alpha 1 subunit of the GABA(A) receptor. Strong punctat e immunoreactivity indicative of synaptic localization is present in the ON and OFF sublamina of the inner plexiform layer. Many of the immunoreactive puncta coincide with the dendrites of both midget and parasol ganglion cel ls. Immunoreactive puncta are present on distal and proximal dendrites of O N and OFF cells of both ganglion cell types. On average, parasol cells show a slight increase in the spatial density of immunoreactive puncta with dis tance from the soma, whereas the density of immunoreactive puncta on midget cells stays even. Parasol ganglion cells show a slightly higher average de nsity of immunoreactive puncta (0.083 puncta/mu m dendrite) than midget cel ls (0.054 punta/mu m dendrite).