Electrophysiological identification of cold receptors on the antennae of the ground beetle Pterostichus aethiops

Abstract.  In single-sensillum extracellular electrophysiological recordings, terminal campaniform sensilla at the tip of antennae of the ground beetle Pterostichus aethiops (Pz., 1797) show action potentials of three sensory cells, A-, B- and C-cells, distinguished by differences in their spike amplitudes. Only the A-cell, with the largest spike amplitude, is highly sensitive to temperature fluctuations, showing remarkable changes in its firing rate induced by changes in temperature of 0.1 °C. The firing rate of A-cells at 23 °C varies from 15–52 Hz among different beetles. Mean impulse frequency of A-cells is found to be a function of steady temperature, the firing rate decreasing with temperature increase. A-cells respond to a rapid temperature drop with a strong phasic-tonic reaction; larger decreases in temperature evoke higher peak frequency values. Maximum peak frequencies, varying from 380–630 Hz in different beetles, are induced by temperature decreases of 3–10 °C, whereas temperature rise strongly inhibits impulse activity of the A-cell. The first manifestation of rapid warming in the nerve impulse sequence is a very long interspike period, followed by diminished activity. Both the length of the long interspike period and the rate of following impulse activity are functions of temperature change; hence, A-cells respond to temperature changes as typical cold receptors, similar to coeloconic and short hair-like sensilla in other insects.