Figure 4.

A single spike in an LAI inhibits evoked EPSC in a neighboring LAI. A, An example of the lack of detectable direct interactions between two neighboring LAIs. The two LAIs were simultaneous recorded in current clamp and slightly hyperpolarized (at approximately −60 mV) to prevent spontaneous firing; one of them was then depolarized for 500 ms to elicit action potentials. B, Average effects of a single spike in an LAI on the evoked EPSC amplitude in a neighboring LAI. Data are from nine LAI–LAI pairs in which (1) significant effects were observed for some intervals and (2) at least three different intervals were tested. The EPSC amplitude (in percentage of control) is plotted as a function of the interval between the spike peak and the EPSC peak. C, Average effects of LAI spikes on neighboring LAI EPSC amplitude as a function of the interval, for all of the pairs in which significant effects were observed for at least one interval. D, A representative example of the experiments performed to investigate these effects. Top traces are individual current-clamp recordings from an LAI, in which spikes (when present) were elicited with brief current injections at different intervals before an EPSC was evoked in a neighboring LAI. Bottom traces are superimposed recordings from the second LAI (voltage clamp; V_h = −60 mV), showing the EPSCs evoked at different intervals after the spike in the other LAI. Gray bars represent the intervals between the LAI spike peak and the other LAI EPSC peak (∼10, 20, 30, and 40 ms).