Figure 3. NMDARs contribute to rapid temporal modulation in OFF Alpha cells.

A, synaptic currents recorded from an OFF Alpha cell in response to 1 Hz temporal contrast modulation at two of eight V_holds (top). The response to one cycle was averaged over the last 2 s (bottom, left). For an excitatory response window (grey box), an I–V relationship is shown (bottom, right) with a basis-function fit (continuous line). The response depends strongly on an NMDAR-mediated conductance, as indicated by the J-shaped I–V relationship. B, as for A for 10 Hz modulation. Data from the last 2 s were averaged to generate the I–V plot. As in A, the response depended strongly on an NMDAR-mediated conductance, as indicated by the J-shaped I–V relationship. C, fitted conductances are shown for responses at five temporal frequencies. Both AMPAR- and NMDAR-mediated conductances were present at all frequencies. Error bars indicate ±SEM across cells (with number of cells in parentheses above the data points). The NMDAR- mediated conductances here and below (F) were scaled to their value at V_M = −62 mV (i.e. near the resting potential) and reflect 8.1% of the maximal conductance (Manookin et al. 2010). D, average cycles and I–V plots for responses to 1 Hz temporal stimulation with inhibition and ON pathway input suppressed (l-AP4, gabazine, strychnine). The I–V relationship remained J-shaped (compare to A). E, as in D, for 10 Hz modulation. The I–V relationship remained J-shaped (compare to B). F, as in C, but with inhibition suppressed. NMDAR-mediated conductance is present at both 1 and 10 Hz.