To demonstrate the characterization calretinin-immunoreactive displaced amacrine cells in the ganglion cell layer using immunohistochemistry and electron microscopy.

For immunohistochemistry, sections from guinea pig retina were incubated with mouse monoclonal antibody directed against calretinin. For double label studies, sections were incuated in mixture of mouse monoclonal anti-calretinin or rabbit polyclonal anti-calretinin with following antibodies : goat polyclonal anti-ChAT, rabbit polyclonal anti-GABA, mouse monoclonal anti-GABA_A receptor α1, β2/3. Sections were analyzed using Bio-rad Radiance Plus confocal scanning microscope. Stained sections from three guinea pig were observed with transmission electron microscope.

Calretinin immunoreactivity was present in displaced amacrine cells and ganglion cells gaving rise to processes ramified in the inner part of the inner plexiform layer in stratum 4. The same stratum was also occupied by the dendrites of ON-cholinergic amacrine cells. Double-labeling demonstrated that dendrites and cell bodies of displaced amacrine cells colocalized with ON-cholinergic amacrine cells and dendrites of ganglion cells directly overlapped with dendrites of ON-cholinergic amacrine cells. The synaptic connectivity was identified by electron microscopy. Ganglion cell dendrites received synaptic input from ON-cholinergic amacrine cell. GABA_A receptor β2/3 subunit bands cofaciculates the dendrites of displaced amacrine cell and ganglion cell that are juxtapose to the α1 subunit of GABA_A receptor.

These results indicate that ON-cholinergic amacrine cells modulate calretinin-labeled ganglion cell via GABA_A receptor β2/3 in the guinea pig retina.