DIFFERENTIAL TROPHIC EFFECTS OF ORG-2766, AN ACTH(4-9) MSH(4-9) ANALOG, ON PEPTIDERGIC NEURONS AND GLIAL-CELLS IN THE SNAIL LYMNAEA-STAGNALIS/

Cerebral ganglia of the pond snail Lymnaea stagnalis were incubated in vitro in 10(-6) M ORG 2766 for 10 and 20 h, with or without regular r efreshment of the medium. Quantitative ultrastructural study of cross sections of the cerebral commissure showed that the number of microtub ules in large axons of all ORG 2766-treated groups had increased after 10 h by approximately 40%. In a separate experiment, central nervous systems were incubated in ORG 2766 for only 15 min and then kept in Ri nger's for 9 h and 45 min. Maximal stimulation (40% increase of microt ubules) in these specimens was also observed. The results would seem t o support the hypothesis that ORG 2766 binds to a receptor and initiat es a long-lasting effect. It is argued that ORG 2766 stimulates novel synthesis of tubulin rather than being involved in the assembly of mic rotubules. Also, glial cells were found to be activated by ORG 2766. T his was concluded from the fact that the number of heterochromatin clu mps and the size of the clumps in these cells had decreased and the am ount of glial tissue surrounding the axons had increased (approximatel y 50%). In contrast to the activating effects of ORG 2766 on glial tis sue, this drug did not affect nucleoli, number, and size of the hetero chromatin clumps and the Golgi apparatus in the neuropeptidergic caudo dorsal cells. The data indicate that ORG 2766 exerts differential trop hic effects.