CIRCADIAN-RHYTHM OF CONTENT OF RED PIGMENT-CONCENTRATING HORMONE IN THE CRAYFISH EYESTALK

The content of red pigment-concentrating hormone (RPCH) was determined in the crayfish eyestalk at different times of day and various condit ions of illumination. Two types of preparations were used: (a) eyestal ks removed from otherwise intact animals; and (b) isolated eyestalks k ept in organ culture. The RPCH content was determined under (a) 12:12 hr light:dark cycles, (b) continuous darkness, and (c) continuous illu mination under 500 lx. In all three conditions, RPCH content varied in a 24-hr rhythm. Under LL and DD, the period deviated from 24 hr both in intact animals and in isolated eyestalks. The rhythm amplitude rang ed from 2 to 3 log units of RPCH content, depending on the experimenta l conditions, being highest in the intact animals under LD (1200 pg at night to 2 pg in daytime), and the lowest in the isolated eyestalks u nder DD (400 pg at night to 6 pg in daytime). These results suggest th at the isolated eyestalk is capable of generating a self-sustanining c ircadian rhythm of RPCH secretion, with similar properties to those in the intact animal.