Serotonin Modulates the Action Potential in Growth Cone Precursors of Sensory Neuron Terminals in Aplysia

Abstract

Serotonin (5-HT) closes a specific class of K⁺ channels in the sensory neurons of Aplysia, resulting in a slow EPSP, an increase in action potential duration (APD), and presynaptic facilitation of transmitter release (Klein and Kandel 1978, 1980; Kandel and Schwartz 1982; Siegelbaum et al. 1982). Because of the small size and inaccessibility of the sensory neuron terminals, previous studies have been limited to readings from the cell body of the sensory neurons. To explore whether K⁺ channel closure also occurs in presynaptic terminals, we have used the patch clamp technique and studied the action of 5-HT on both intact and isolated growth cones (g.c.), the precursors to the mature synaptic terminal of Aplysia sensory neurons in culture.