Circadian firing activities of neurosecretory cells releasing pheromonotropic neuropeptides in the silkmoth, Bombyx mori

Neurosecretory cells releasing the pheromone biosynthesis-activating neuropeptide (PBAN) in Bombyx mori exhibit diurnal firing activity. Diel changes in the firing activity of the PBAN producing cells persisted in both constant dark and constant dim light (0.1 lx) at mean periods of 23.0+/-1.6 hr and 22.6+/-0.8 hr, respectively, thereby suggesting that the neurosecretory cell system is under the control of a circadian pacemaker. The circadian firing rhythm was greatly modified by background illumination: (1) the period of free-running activity rhythm was significantly short (18.5+/-1.6 hr) under continuous illumination of a moderate intensity (100 lx) and (2) the duration of a firing period of cells elongated by 2.1+/-0.7 hr, when light intensity during a photophase was lowered to 0.01 lx. The suppressive effect of light on the firing activity may induce a nocturnal component of a daily activity pattern by releasing PBAN cells from suppression after termination of illumination.