The role of inner retinal inhibitory circuits in tuning off retinal ganglion cell output

Retinal ganglion cells (RGCs) encode key visual features, yet the synaptic mechanisms shaping their responses remain incompletely understood. This study examines light‑evoked inputs to OFF brisk‑sustained (OFF‑BS) RGCs in rabbit retina, focusing on the contributions of NMDA, AMPA, and inhibitory pathways. We show that NMDA and AMPA receptors provide distinct excitatory synaptic inputs, differing in contrast adaptation and sensitivity to GABAergic blockade. NMDA receptors preferentially enhance responses at low contrasts, while AMPA inputs dominate at higher contrasts. Additionally, a glycinergic disinhibitory input from the ON pathway boosts contrast sensitivity at high temporal frequencies. Together, these findings identify two synaptic circuits that fine‑tune contrast and temporal processing in OFF‑BS RGCs.