Pineal glands (five glands each) were incubated in 1 ml of DMEM for 1 hr. After the glands were washed with MEM, NE (10 μm) (Exp. 1) or DBcAMP (1 mm) (Exp. 2) plus listed compounds (1 mm each, except MCCG at 2 mm) were added. After further incubation for 6 hr, the medium was carefully collected, and the melatonin content was determined. Simultaneously, the glands were homogenized, and NAT activity was assayed. For cAMP measurements, cultured cells were used. The results are presented as relative activity ± SEM (four independent experiments). In Experiment 1, 100% activities for melatonin synthesis was 0.55 nmol/ml, NAT activity was 2.2 nmol · min⁻¹ · mg⁻¹ protein, and cAMP content was 0.54 nmol/10⁶ cells. For Experiment 2, 100% activities for melatonin synthesis was 0.48 nmol/ml, and NAT activity was 1.4 nmol · min⁻¹ · mg⁻¹ protein. MCCG itself did not affect NE-dependent NAT activity, melatonin synthesis, and cAMP levels. Neither l-glutamate nor GluRs agonists affected the level of these activities in the absence of NE. NT, Not tested. (S)-3,5-Dihydroxyphenylglycine ((S)-3,5-DHPG) is an agonist for class I mGluRs (Sekiyama et al., 1996).