EVIDENCE FOR OPIOID INVOLVEMENT IN THE REGULATION OF OVARIAN MATURATION OF THE FIDDLER-CRAB, UCA PUGILATOR

The potential involvement of an endogenous opioid system in the regula tion of ovarian development in the fiddler crab, Uca pugilator, was in vestigated in vivo. Injection of the opioid, methionine enkephalin, in to female crabs significantly slowed ovarian maturation in a dose-depe ndent manner. In contrast, injection of the opioid antagonist, naloxon e, produced dose-dependent ovarian maturation. These results provide t he first evidence that an opioid system is involved in the control of reproduction in a crustacean. It is hypothesized that the opioid (a) s timulates release of the gonad-inhibiting hormone, (b) inhibits releas e of the gonad-stimulating hormone or (c) does both (a) and (b).