Fig. 1. Serotonin-mediated inhibition of the exopodite reductor motor neurone. (A) The relative change in spike frequency of the reductor motor neurone during bath application of serotonin plotted every 1 min (mean ± S.E.M.). The number of tonically occurring spikes of the motor neurone is expressed as an average rate relative to the initial 3 min period prior to serotonin (5-HT) perfusion. The thick bar indicates the period of serotonin application. , 10 µmol l^-1 (N=4); , 100 µmol l^-1 (N=6); [UNK], 1 mmol l^-1 (N=4) serotonin perfusion. (B) Input resistance of the reductor motor neurone (red mn) measured by a brief injection of 1 nA hyperpolarizing current was reduced during serotonin (5-HT; 1 mmol l^-1)-mediated membrane hyperpolarization. The dashed line indicates the resting membrane potential level.