Circadian expression of Period 1, Period 2, and arylalkylamine N-acetyltransferase rnRNA in the rat pineal gland under different light conditions

Period 1 (Per1), 2 (Per2) and arylalkylamine N-acetyltransferase (AA-NAT) m RNA levels were determined by semiquantitative in situ hybridization in rat pineal glands. In agreement with previous reports, AA-NAT mRNA levels were rhythmic in light:dark (LD) cycles and the rhythm persisted in constant di m light (DLL). Per1 and Per2 mRNA also showed significant variations both i n LD and DLL. AA-NAT and Per1 mRNA levels showed very similar patterns of v ariations in LD and DLL to one another, whereas Per2 showed a different pat tern of expression from AA-NAT and Per1. Exposure to 30 min of light did no t affect the expression of the th ree genes, while exposure to a longer lig ht pulse (1 or 2 h) decreased AA-NAT and Per1 mRNA levels; Per2 mRNA levels were also decreased but only temporarily. Our results demonstrate that Per 1 and Per2 expression in the rat pineal is under circadian control, and sug gest Per1 may be regulated by the same mechanism which controls the express ion of AA-NAT gene. Per2 seem to be controlled by a different mechanism. (C ) 2000 Elsevier Science Ireland Ltd. All rights reserved.