MODULATION OF CRAYFISH RETINAL FUNCTION BY RED PIGMENT CONCENTRATING HORMONE

The role of the crustacean octapeptide red pigment concentrating hormo ne (RPCH) in the control of crayfish retinal activity was explored. RP CH injection into intact animals resulted, after a latency of 10-30 mi n, in a dose-dependent enhancement of electroretinogram (ERG) amplitud e lasting 60-120 min, RPCH was able to potentiate ERG amplitude in bot h light-adapted and dark-adapted animals. Following light-adaptation, responsiveness to RPCH was five times higher than following dark-adapt ation. In conjunction with ERG enhancement, in light-adapted animals, RPCH injection elicited a dose-dependent retraction of distal retinal pigment, but did not affect proximal retinal pigment position, The eff ects of RPCH were blocked by a polyclonal antibody raised against a ty rosinated form of RPCH (A-tyr-RPCH). The antibody was also capable of partially blocking the nocturnal phase of the circadian rhythm of ERG amplitude and the darkness-induced retraction of distal retinal pigmen t, These results suggest that RPCH acts both on the retinal photorecep tors and on the distal pigment cells, playing a physiological role as a mediator of the effects induced by darkness and by the nocturnal pha se of the circadian rhythm.