SEROTONIN-INDUCED CHANGES IN THE EXCITABILITY OF CULTURED ANTENNAL LOBE NEURONS OF THE SPHINX MOTH MANDUCA-SEXTA

The modulatory actions of 5-hydroxytryptamine (5HT or serotonin) on a morphologically identifiable class of neurons dissociated from antenna l lobes of Manduca sexta at stages 9-15 of the 18 stages of metamorphi c adult development were examined in vitro with whole-cell patch-clamp recording techniques. Action potentials could be elicited from approx imately 20% of the cells. These cells were used to examine effects of 5HT (5 x 10(-6) to 5 x 10(-4) M) on cell excitability and action-poten tial waveform. 5HT increased the number of spikes elicited by a consta nt depolarizing current pulse and reduced the latency of responses. 5H T also led to broadening of action potentials in these neurons and inc reased cell input resistance. Modulation of potassium channels by 5HT is likely to contribute to these responses. 5HT causes reversible redu ction of at least 3 distinct potassium currents, one of which is descr ibed for the first time in this study. Because effects of 5HT on anten nal-lobe neurons in culture mimic those observed in situ in the brain of the adult moth, in vitro analysis should contribute to elucidation of the cellular mechanisms that underlie the modulatory effects of 5HT on central olfactory neurons in the moth.