Fig. 5. Post-serotonin enhancement of the depolarizing postsynaptic potentials of a nonspiking interneurone (ns int) that showed a serotonin-mediated depolarization during sensory stimulation. Bath application of 100 µmol l^-1 serotonin for 3 min mediated a depolarization of the membrane potential of the nonspiking interneurone and decreased the tonic spike discharge of the reductor motor neurone (red mn). After serotonin perfusion, the amplitude of depolarizing postsynaptic potentials of the interneurone in response to the sensory stimulation at 20 Hz of 11 stimuli (indicated by arrows) initially decreased slightly in association with serotonin-mediated depolarization. The depolarizing postsynaptic potentials then increased in amplitude, although the membrane potential was still depolarized. The time indicated on each trace (A—D) shows the elapsed time after serotonin application. The dashed line indicates the resting membrane potential level.

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