EVIDENCE FOR ECDYSTEROID FEEDBACK ON RELEASE OF MOLT-INHIBITING HORMONE FROM CRAB EYESTALK GANGLIA

Abstract

The content and release of molt-inhibiting hormone activity (MIH) in isolated eyestalk ganglia of crabs (Cancer antennarius S.) were measured in vitro as a function of exposure in vivo to elevated or reduced hemolymph ecdysteroid levels. Ecdysteroid titers of intermolt crabs injected with 20-hydroxyecdysone (two 45 µg injections/24 h) rose 8- to 10-fold; MIH released from subsequently isolated ganglia was significantly less than that released from ganglia of saline-injected controls, while MIH content of ganglia from treated crabs was increased. The hemolymph ecdysteroid level of intermolt crabs was low (6 ng/ml) and was further reduced by 40% 6 days after Y-organectomy. MIH release from ganglia of both Y-organectomized and sham-operated control crabs was high, similar to that of unoperated controls, but MIH content of ganglia from both Y-organectomized and sham groups was significantly reduced relative to controls. The results indicate a negative feedback regulation of MIH release but not synthesis by ecdysteroids and are discussed in relation to the patterns of ecdysteroid titers observed in the normal crustacean molt cycle.