Fig. 8.
Different cellular loci of PEI and recurrent inhibition. A, Diagram of experimental setup: voltage measurements were made at the base of the main dendrite, near the spike-initiating zone of the LG axon. Vprox was produced by Iprox. VAis generated by synapses in relatively distal LG dendrites (Lee and Krasne, 1993). The locus of action of recurrent inhibition is thought to be near the main dendrite and our recording site (Roberts, 1968; Vu et al., 1993). The presumptive locus of PEI, on distal dendrites, is indicated. B, Mean reduction by recurrent inhibition ofVA (filled circles) and ofVprox (solid curve) at various time points, for one animal. Recurrent inhibition was evoked by an action potential in the MG (Roberts, 1968). C, Comparison of the reduction of VA (open bars) and Vprox (filled bars) by recurrent inhibition and PEI. Each bar represents the mean value obtained from one preparation (at 8.0 msec after root stimulation for PEI and at 10 msec after MG stimulation for recurrent inhibition). D, Mean reduction ofVprox across animals as a fraction of the mean reduction of VA, calculated from data inC. Recur. Inhib., Recurrent inhibition;Excit. Input, excitatory input.