Ultradian Firing Rhythm of Neurosecretory Cells Producing an Insulin-related Peptide in the Silkmoth Bombyx mori

Abstract

Abstract There are four pairs of neurosecretory cells producing bombyxin, an insulin-related peptide, in the brain of Bombyx mori. In the present study, electrical signals of the bombyxin-producing cells were identified and short- and long-term activity patterns of the cells throughout the pupal period were analyzed. Activity pattern of the cells was characterized by periodic discharges of a volley of action potentials. Periodicity of the electrical activity depended on the temperature and mean±SD of periods was 34.7±4.8 min at 26°C. Four cells in a brain hemisphere were functionally heterogeneous: individual cells had specific activity amplitudes and rhythms, thereby suggesting that an ultradian activity rhythm of a cell originates from its intrinsic pacemaker activity. There was no significant diel (circadian) oscillation in the electrical activity. Daily activity patterns had a maximum at an early stage (day-2 or 3) of pupal period. Periodic secretion of bombyxin, like insulin, seems to be an efficient...