A new cerebral factor stimulates IP3 levels in the prothoracic glands of Bombyx mori

A new cerebral factor was found to stimulate intracellular inositol 1,4,5-trisphosphate (IP3) levels in the prothoracic glands (PGs) of the silkworm, Bombyx mori. Maximal stimulation of IP3 levels in the PGs was observed after 10 min incubation of PGs with crude brain extracts of Bombyx mori. This stimulatory effect was dose dependent. Enhancement of IP3 levels in PGs was observed throughout the 5th instar and the first day of the pupal stage, except day 0 of the 5th instar. This cerebral factor is different from Bombyx big prothoracicotropic hormone and bombyxin, because neither of these neuropeptides could stimulate glandular IP3 levels. The nonhydrolysable GTP analogue GTP gamma S could stimulate glandular IP3 levels. Moreover, the phospholipase C inhibitor 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate could block the ability of this cerebral factor to stimulate glandular IP3 levels. The combined results suggest that a cerebral factor enhances IP3 levels in the PGs of Bombyx mori probably by interacting with a G protein-mediated phospholipase C. (C) 1998 Elsevier Science Ltd. All rights reserved.