Response characteristics and specificity of chemoreceptors inHemilepistus reaumuri (Crustacea, Isopoda)

Summary

• 1. Chemoreceptor units were investigated electrophysiologically in the apical sensory cone on the antenna of the desert isopod,Hemilepistus reaumuri. Activity of 141 single units was recorded from fibres in the antennal nerve.

• 2. The receptors responded to a variety of chemical substances with excitation up to 300 imp/s or with inhibition. They were classified into distinct physiological response types with non-overlapping response spectra (Table 1).

• 3. Two physiological response types were excited by airborne odour stimuli: (a) butyric acid cells were sensitive to short-chain fatty acids and aldehydes (Table 3); (b) amine cells responded to short-chain mono- and diamines (Table 5).

• 4. Four groups of gustatory cells were found: (c) sugar cells responded to several sugars and α-glucosides (Table 6); (d) calcium cells were excited by CaCl₂ which was inhibitory in most other cells; (e) amino acid cells were found in only two cases, responding to 1-asparagine and 1-methionine; (f) 29 cells responded only to an aqueous rinse of desert woodlice, and not to other stimuli tested.

• 5. Olfactory cells responded to n-fatty acids (namines, respectively) with phasic-tonic excitation at low concentrations, but with phasic excitation followed by an off-response at higher concentrations (Figs. 1, 3). Complete inhibition could be caused by applying still higher concentrations of the same substances.

• 6. Transition from phasic-tonic to phasic responses occurred at low initial impulse frequencies with some stimulus substances, but at high initial frequencies with other substances in the same receptor cell (Figs. 1, 3). Chain length of the stimulus molecule influenced phasic-tonic behaviour in a different manner in both olfactory cell groups (Tables 2, 4).

• 7. No influence of stimulus concentration on time course was found in sugar cells (Figs. 4a, b, 5). There were, however, remarkable differences in the poststimulatory frequency decay for different sugars (Fig. 4a, b).