EVIDENCE FOR CIRCADIAN TIME-DEPENDENT VARIATIONS OF 2 COEXISTENT NEURONAL AGENTS (CCK, DOPAMINE) IN SUBSTANTIA-NIGRA AND STRIATUM OF RAT-BRAIN

Concerning the interaction between a classical transmitter and a neuro peptide there is no general accepted point of view. Moreover, circadia n time has not yet been considered as an important variable. In rats k ept under a light:dark cycle of 12:12 h the content of dopamine (DA) a s well as of cholecystokinin octapeptide (CCK) was measured in striatu m (STR) and substantia nigra (SN) every two hours during two days. CCK was determined by RIA, DA determination was done by HPLC and electroc hemical detection. Results obtained indicate a complex pattern of time dependent variation in DA and CCK content in both brain regions. The rhythms seem to be composed of ultradian (5-6, 10-12 h), circadian (20 -24 h) and infradian (7-10 days) rhythms. There are distinct phase rel ationships between CCK and DA between and within the brain regions. Th e nature of these relations (accidentally or due to a feed-back) remai ns to be elucidated. The results are of relevance for neurobiological investigations.