Effects of raphe lesions on circadian ACTH, corticosterone and motor activity rhythms in free-running blinded rats.

Blinded female rats underwent additional midbrain raphe lesions, in order to explore the role of the raphe in the organization of endogenous circadian rhythms for ACTH, corticosterone (B) and motor activity (MA). Amplitudes and mean levels of rhythms were depressed for ACTH and MA, with persistent free-running circadian periodicity for MA and, in several rats, for ACTH and B as well. Other rats exhibited split circadian and ultradian rhythmicity for ACTH and B, whereas other again displayed no detectable ACTH rhythmicity. These results are discussed in the light of the structure of circadian pacemaker systems.