Cohen, Ethan D. Interactions of inhibition and excitation in the light-evoked currents of X type retinal ganglion cells. J. Neurophysiol. 80: 2975–2990, 1998. The excitatory and inhibitory conductances driving the light-evoked currents (LECs) of cat and ferret on- and off-center X ganglion cells were examined in sliced and isolated retina preparations using center spot stimulation in tetrodotoxin (TTX)-containing Ringer. on-center X ganglion cells showed an increase in an excitatory conductance reversed positive to +20 mV during the spot stimulus. At spot offset, a transient inhibitory conductance was activated on many cells that reversed near E Cl. off-center X ganglion cells showed increases in a sustained inhibitory conductance that reversed near E Cl during spot stimulation. At spot offset, an excitatory conductance was activated that reversed positive to +20 mV. The light-evoked current kinetics of on- and off-center X cells to spot stimulation did not significantly differ in form from their Y cell counterparts in TTX Ringer. When inhibition was blocked, current-voltage relations of the light-evoked excitatory postsynaptic currents (EPSCs) of both on- and off-X cells were L-shaped and reversed near 0 mV. The EPSCs averaged between 300 and 500 pA at −80 mV. The metabotropic glutamate receptor agonist 2-amino-4-phosphonobutyric acid (APB), was used to block on-center bipolar cell function. The LECs of on-X ganglion cells were totally blocked in APB at all holding potentials. APB caused prominent reductions in the dark holding current and synaptic noise of on-X cells. In contrast, the LECs of off-X ganglion cells remained in APB. An increase in the dark holding current was observed. The excitatory amino acid receptor antagonist combination of d-amino-5-phosphono-pentanoic acid (d-AP5) and 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo-(F)-quinoxalinedione (NBQX) was used to block ionotropic glutamate receptor retinal neurotransmission. The LECs of all on-X ganglion cells were totally blocked, and their holding currents were reduced similar to the actions of APB. For off-X ganglion cells, the antagonist combination always blocked the excitatory current at light-off; however, in many cells, the inhibitory current at light-on remained. on-center X ganglion cells receive active excitation during center illumination, and a transient inhibition at light-off. In contrast off-center X ganglion cells experience a sustained active inhibition during center illumination, and a shorter increase in excitation at light-offset. Cone bipolar cells provide a resting level of glutamate release on X ganglion cells on which their light-evoked currents are superimposed.
X-Cells Are Globally Distributed, Genetically Divergent Fish Parasites Related to Perkinsids and Dinoflagellates