Electrophysiological Studies on the Temporal Organ of the Japanese House Centipede, Thereuonema Hilgendorfi

Abstract

The response of the temporal organ (organ of Tömösváry) has been studied electrophysiologically in the Japanese house centipede (Thereuonema hilgendorfi : Chilopoda).Receptor cells of the temporal organ show spontaneous discharges (15–40 impulses s-1) which are depressed in a phasic-tonic manner by carbon dioxide stimuli. Perfusion of the presumed receptor site with a carbon dioxide-containing solution also changes the impulse frequency. The impulse frequency of a receptor cell decreases linearly with a logarithmic increase in carbon dioxide concentration ranging from 0·001 % to 0·1 % in the phasic state and from 0·05% to 5·0% in the tonic state. These results suggest that the temporal organ of the house centipede functions as a carbon dioxide receptor, though it responds to other stimuli as described below. Changing the pH of a carbon dioxide-containing solution changes the impulse frequency, probably by changing the molar fraction of CO2 molecules in the lymph surrounding the receptor site. pH also directly influences the impulse frequency of the receptor cell, but the effect is smaller than that of CO2 molecules. Receptor cells respond to humidity changes, but the response is smaller than that to carbon dioxide. When receptor cells are stimulated by moist air (100% relative humidity, RH) after adaptation to dry air (0% RH), the impulse frequency increases by a factor of 1·29 ±0·37 (mean ± S.D. measured for the first second, N = 29), and 1·16 ± 0·28 (measured after adaptation to moist air, N = 29). Air-borne chemicals also affect the impulse frequency of a receptor cell; it is increased by amines and decreased by fatty acids and aldehydes. Effects of these chemicals are discussed in relation to changing the pH of lymph bathing the receptor site.