Gap junction modulation of hippocampal formation theta and local cell discharges in anesthetized rats

During the past decade experimental evidence has accumulated demonstrating that the electrical communication between neurons through gap junctions (GJs) is a necessary neural mechanism underlying oscillations and synchrony. Here we extended our earlier observations concerning the involvement of GJs in hippocampal theta production. Using trimethylamine, a GJ opener, we demonstrated a reversible increase in theta amplitude and power and an increase in the duration of theta epochs. This effect was accompanied by a decrease in the percentage of recorded theta-off cells, an increase in the percentage of recorded theta-on phasic cells, and an increase in the number of rhythmic cell discharges per theta wave. We suggest that all these findings result from an enhanced level of interneuronal excitation, mediated by an increase in the efficacy of local GJ coupling.