Effect of 20-hydroxyecdysone on neurosecretory cell activity in female Hyalomma dromedarii synganglion (Acari: Ixodidae).

Twenty micrograms of 20-hydroxyecdysone (20-HE) were applied topically to nymphal Hyalomma dromedarii Koch on the day of detachment. In emerging adult females, some neurosecrtory cells (NSC) in certain synganglion centers exhibited changes in size and/or neurosecretory material (NSM) shape, distribution and/or quantity. These changes were compared with those normally occurring in untreated unfed, semifed virgin and mated, and engorged females. 20-HE effects included (a) accelerating the changes induced by mating and/or feeding in certain NSC, (b) reducing, to various extents, NSC response to mating and feeding, and (c) inducing changes in some NSC which do not normally exhibit any changes in untreated females. The results suggest that (a) most female NSC respond more or less similarly to indigenous 20-HE, (b) 20-HE may have a role as a positive feedback regulator for NSM synthesis and/or release by certain NSC, (c) the response to 20-HE may be primarily a function of NSC location in the synganglion, and/or (d) NSC considered to be of one type may actually belong to different cell types.