A factor in the haemolymph of the stick insect that depresses the activity of extraganglionic neurosecretory cells

Abstract

Action potentials from extraganglionic neurosecretory neurons of the stick insectCarausius morosus have been recorded from low-activity preparations taken from animals in the light phase and from high-activity preparations taken from animals in the dark phase of a diel cycle. Wood'sCarausius saline, which has a K+ concentration of 18 mmol/1, was found to cause an increase in discharge frequency in all cells. Saline with a concentration of 12 mmol/1 K+ depressed activity. A ‘neutral’ concentration lies between 12 and 15 mmol/1. Light phase haemolymph contains an inhibitory factor which is independent of K+ concentration of the medium. Spectrophotometric studies show that the K+ level does not differ significantly at the times in the photophase that coincide with maximum and minimum electrical activity of the cells. Light phase haemolymph can be diluted to at least 20% with 18 mmol/1 K+ saline and still produce depression of activity in dark phase cells.