[Circadian variations in the incorporation of gamma-aminobutyric acid (GABA) and tritiated taurine into the pineal body of CD mice].

Pineal uptake of two putative neurotransmitters, gamma-aminobutyric acid (GABA) and taurine, was investigated during the 24 h-cycle in mice kept in long (14L/10D) or short (10L/14D) photoperiods. Tritiated mediators were intraperitoneally injected and their concentration both in pineal gland and cerebellum were measured at several times along the nycthemere. A circadian rhythm of exogenous GABA uptake was observed in mice kept in long photoperiods: GABA uptake was high during the night, when the gland was active and low during the day. It corresponded to the pineal cycle of indoleamine synthesis. It was particularly sensitive to sudden changes of lighting. In short photoperiods, a similar cycle was observed but the result was not significant because of individual variations. Taurine uptake did not show such a circadian rhythm either in long or in short photoperiods: it was constant and rather low with large variations from one animal to another.