Ultradian and circadian changes in the cAMP concentration in the preoptic region of the rat.

The concentration of adenosine 3',5'-cyclic monophosphate was measured, during the wake-sleep cycle, in the preoptic region and the cerebral cortex of rats kept in normal laboratory conditions (ambient temperature 22 +/- 0.5 degrees C, 12 h:12 h light-dark cycle) and, during wakefulness, in the preoptic region of rats exposed to extended light and dark periods (i.e. dark in the light hours of the normal photoperiod, and light in the dark hours of the normal photoperiod). The results show that the concentration of cAMP in the preoptic region changes according to the ultradian wake-sleep cyclic, decreasing from wakefulness, through synchronized sleep and to desynchronized sleep. This pattern of change was found to occur both in light and dark hours, however, in the dark hours the levels of preoptic cAMP are higher than those observed in the light hours. In contrast, no significant modification in cAMP concentration was found in the cerebral cortex. In the extended light and dark periods preoptic cAMP concentration increases above the levels found during wakefulness in normal photoperiods. These results show that preoptic cAMP concentration is influenced by ultradian and circadian factors which also appear to be related to sleep processes.