Cell responses to acoustic stimuli in the pterothoracic ganglion of two noctuoid moths.

The spike activity of various types of cell responses in the pterothoracic ganglion of Ascalapha odorata (Noctuidae) and Empyreuma pugione (Arctiidae) was studied. Pure tones (16 kHz for A. odorata and 20 kHz for E. pugione, 45 ms pulses) were presented at a 1 Hz rate over 9 s and at intensities ranging from 25 to 95 dB SPL. The values of the latency period and the interspike intervals allowed us to describe the intensity-latency and intensity-response functions as well as the spike distribution during the responses, the latter being given by the 'instantaneous frequency', i.e., as the inverse value of the mean of the nine measurements of each interspike interval during the response time. 'Repeater' (RA1 and RA2) is a type of cell response that shows a phasic-tonic spike distribution similar to that of the receptor cells (A1 and A2), but that differs from the latter in a longer (ca. 1.0 ms) latency period, a lower number of spikes per pulse, and a lower instantaneous frequency during the response time. Another repeater type of cell response (RA) differs from the receptors and the other two repeaters in the form of its intensity-latency function, having the widest dynamic range (from 40 to 50 dB), and exhibiting the highest maximal number of spikes per pulse of all the response types recorded. We recorded also strictly phasic responses (1 or 2 spikes per pulse), which are considered as pulse markers. Of these, one (PM1) has a shorter latency period (ca. 10 ms) and higher sensitivity than the other (PM2). Two other types of cell responses showed significant differences in their latency period and the number of spikes per pulse under binaural and monoaural stimulation and are assumed to be the consequence of binaural summation, one by inhibition (BSI) and the other by excitation (BSE); they also differ in the spike distribution during the response. For the other types of cell responses recorded we used names that reflect the form of their spike distribution: chopper, build, On-S, tonic, and suppression. The spike distributions during the response time recorded in the pterothoracic ganglion of these two noctuoid moths are compared with the temporal patterns of discharge described in the auditory neurons of the first relay stations of birds and mammals.(ABSTRACT TRUNCATED AT 400 WORDS)