Fig. 2.

Example of combined chemical synaptic and gap junction connection between a pair of model interneurons. Top left, Schematic of the interactions. Cell 1 produces a sum of two GABA_A receptor-mediated IPSCs in the soma of cell 2 (peak conductance of 2 nS, decay time constant of 5 msec; and peak conductance of 0.2 nS, decay time constant of 50 msec; each with reversal potential −15 mV relative to resting potential). The cells are also connected by a nonrectifying gap junction in the proximal dendrites of each cell (85 μm from the soma, conductance of 0.7 nS).Bottom, Both cells were held with −0.05 nA tonic currents, whereas cell 1 was induced to fire (▴) with current pulses delivered every 50 msec, inducing rhythmic IPSPs in cell 2.Traces are superimposed for cases when the gap junction was either open or shut. (Data shown correspond to the fifth and sixth spikes in a train in cell 1.) The gap junction has two effects on the potential in cell 2; cell 2 is relatively hyperpolarized for most of the cycle (attributable to gap junctional communication of the afterhyperpolarization in cell 1), and cell 2 develops a ∼0.4 mV spikelet (coupling potential) in association with the spike of cell 1.Top right, Detail of the spikelet. Thick line, Gap junction closed. Thin line, Gap junction open. Compare Galarreta and Hestrin (1999) with Gibson et al. (1999).