Response of moist-air receptor on antenna of the stick insect, Carausius morosus, to step changes in temperature

Abstract

The moist-air sensory cell in the antennal mound-shaped sensillum of Carausius responds to changes in relative humidity brought about by changing either the temperature (T) of the air or the partial pressure of water vapor (Pw) (Figs. 1, 5). When changes in either parameter cause relative humidity (Hr) to rise between roughly 5% and 55%, the same Hr-changes elicit very close to the same responses, no matter how Hr is changed (Figs. 2, 3). Even the resolving power for upward Hr-steps produced by lowering T is very close to that produced by raising Pw: 7.4% vs. 6.3%. Thus upward transients in impulse frequency (F) may be read off directly as quantitative rises in Hr. Whether the rise in Hr as signalled by the moist-air cell is the result of a rise in Pw or of a drop in T could well be indicated by the simultaneous reactions of the cold and dry-air cells (Figs. 1, 5). The moist-air cell also reacts to downward step changes in Hr, but very differently, depending on how they are brought about. Upward steps in T have a much larger effect on F than corresponding downward steps in Pw (Fig. 4). This result demonstrates that changes in relative humidity do not suffice to explain the changes in the activity of the moist-air cell. The receptor may be better construed as bimodal, reacting to changes in T and Pw with independent sensitivities and well matched to relative humidity when changes in either lead to increases in this parameter. The moistair cell's responses to T-steps at Pw = 0 (Figs. 1, 5) offer some support for this interpretation.