Oscillations of the transepithelial potential of moth olfactory sensilla are influenced by octopamine and serotonin

(T)he biogenic amine octopamine is known to enhance the sensitivity of male moths to their species-specific pheromones in flight-tunnel experiments. T his sensitization of pheromone-guided upwind flight is at least partly due to octopamine-dependent increases in the peak nerve impulse frequency of th e pheromone response of olfactory receptor neurons. It is not known, howeve r, whether octopamine exerts its effects directly on the electrical propert ies of the olfactory receptor neurons or indirectly, via modulation of the accessory cells of the sensillum. In extracellular tip recordings of pheromone-dependent trichoid sensilla on the antennae of male Manduca sexta moths, we investigated the effects of o ctopamine and serotonin on the transepithelial potential, which is generate d by the activity of V-ATPases in sensillar accessory cells. In addition, t he action potential activity of unstimulated olfactory receptor neurons was examined in the presence of biogenic amines. Under constant environmental conditions, the transepithelial potential oscillated regularly with periods of 2-8min and with a 1-25mV peak-to-peak amplitude over periods of several hours. These oscillatory intervals were interrupted by periods of relative ly stable transepithelial potential, correlated with flight activity by the moth. Octopamine reduced the amplitude of the transepithelial potential os cillation and decreased the resistance of the sensillum preparation in a do se-dependent manner. Serotonin altered the waveform of the transepithelial potential, but did not change the resistance of the preparation. Thus, both amines affect the accessory cells, but have different targets in the regul ation of the transepithelial potential. Neither amine significantly influen ced the spontaneous action potential activity of the olfactory receptor neu rons.