ON retinal bipolar cell

An ON retinal bipolar cell is a retinal bipolar cell whose central receptive response shows depolarization when illumination increases appropriately. At the input synapse, this reverses the response sign of a photoreceptor, which undergoes hyperpolarization in response to light and releases less glutamate.^[ref]

The postsynaptic glutamate-sensing receptor mGluR6 controls a current requiring TRPM1. In a 2009 study, TRPM1-deficient mice retained the rod-related electroretinogram a-wave but lacked the b-wave; direct recordings of bipolar responses provided evidence for a postsynaptic signaling defect.^[ref]

A local sign model makes the circuit transformation visible. If a small light increment $\delta L$ changes glutamate release by $\delta G=-a\delta L$ and the ON response obeys $\delta V=-b\delta G$, with $a,b>0$, then $\delta V=ab\delta L>0$. These are illustrative gains, not fitted measurements. The label describes response polarity under specified stimulation, not continuous firing or identical behaviour in every ON subtype.