Temporal analysis of adaptation in moth (Trichoplusia ni) pheromone receptor neurons

The temporal pattern of response in chemoreceptor neurons reflects both the temporal distribution of stimuli and the timing of signal transduction, action potential generation and propagation. Here we analyze the temporal characteristics of the responses elicited in pheromone receptor neurons by computer-controlled rectangular pulses of odorant. Extracellular recordings from the HS sensilla trichodea on the antenna of male Trichoplusia ni reveal the activity of two neurons: the "A" neuron, which responds to the major component of the female pheromone blend, (Z)7-dodecenyl acetate and the "B" neuron, which responds to (Z)7-dodecenol. "B" neurons were divided into two classes (HR, LR), based on the magnitude and temporal pattern of their response to (Z)7-dodecenol. Most "A" and HR "B" neurons responded to rectangular pulses of various durations (0.1-40 s) with an initial phasic burst (approximately 100 ms), followed by a slowly declining tonic component. At moderate and elevated pheromone doses, prolonged stimulation resulted in significant reductions in the tonic response levels (adaptation); stimuli of increasing duration effected greater adaptation. Most LR "B" neurons lacked a phasic response component and showed virtually no adaptation with prolonged stimulation. Pheromone receptor neurons may differ in both their spectral and temporal response properties which may provide the animal with additional sensory information for blend discrimination and spatial orientation in complex natural pheromone plumes. The potential functional value of adaptation in the moth pheromone communication system is discussed.