Fig. 10. Electrical coupling between sint1 and the synergistic sint2. (A,B) Simultaneous recordings from Rsint1 (upper traces) and Rsint2 (lower traces) in a quiescent whole animal preparation. Hyperpolarizing current pulses were applied to one of the cells via the recording electrode while membrane voltage was recorded in the other. Bridge balance was checked using short hyperpolarizing pulses of the same amplitude before and after the recording. (Ai) A current pulse applied to Rsint1 causes hyperpolarization of Rsint2 due to current flow across the electrical junction. (Aii) The reciprocal connection. (Bi) The electrically coupled epsp in Rsint2 (lower trace; recorded at higher gain) in response to driven action potentials in Rsint1 (eight superimposed traces, stimulus rate one per second). (Bii) The strongly attenuated electrically coupled epsp recorded in Rsint1 (upper trace; recorded at higher gain) in response to single action potentials driven in Rsint2 (seven superimposed traces, stimulus rate one per second). (C) Bode plot showing conduction of sinusoidal currents across the electrical junction in both directions. Rsint1 and Rsint2 were stimulated, one at a time, with subthreshold currents of fixed amplitude but varying frequencies while recording the coupled sine wave in the other cell. The electrical junction passes current symmetrically in both directions and has the characteristics of a low-pass filter with a corner frequency of 1.5 Hz and final slope of 6 dB per octave in frequency. These results were confirmed in each of six separate whole animal preparations.