DYNAMIC EFFECTS OF SUBTHRESHOLD CONDUCTANCE GATING (GKLT AND GNA) AND OF INHIBITION ON COINCIDENCE DETECTION IN MSO NEURONS

Distinct biophysical properties including multiple voltage-dependent membrane conductances and well-timed transient inhibition contribute to the temporally precise processing characteristics of auditory neurons. We investigate the underlying mechanisms of coincidence detection through in vitro experiments (gerbil MSO) using dynamic clamp stimuli and with computational models of the Hodgkin-Huxley type. We focus particularly on what makes these neurons fire, i.e. on how they integrate subthreshold signals in the presence of a noisy synaptic (excitatory and inhibitory) background, as is typical in vivo. Consistent with previous reports, the partial blockade of low threshold potassium currents (IKLT) reduced coincidence detection (as well as reduced phase-locking and signal-to-noise ratio). We used analysis by spike triggered reverse correlation for injected current Irevcor to evaluate and interpret our results. Blockade of IKLT slowed the rise of Irevcor, indicating a less precise time window for integration. Presumably the faster rise, in control, is required to reach threshold before IKLT is activated. Also, spike generation was associated with a preceding (by a few msec) hyperpolarization (“dip”) in Irevcor, suggesting a drop in excitatory current or increase in inhibitory current t