A NEW CEREBRAL FACTOR STIMULATES IP3 LEVELS IN THE PROTHORACIC GLANDSOF 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 wa s 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 fi rst day of the pupal stage, except day 0 of the 5th instar. This cereb ral factor is different from Bombyx big prothoracicotropic hormone and bombyxin, because neither of these neuropeptides could stimulate glan dular IP3 levels. The nonhydrolysable GTP analogue GTP gamma S could s timulate 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 combin ed results suggest that a cerebral factor enhances IP3 levels in the P Gs of Bombyx mori probably by interacting with a G protein-mediated ph ospholipase C. (C) 1998 Elsevier Science Ltd. All rights reserved.