Effects of inhibitory and excitatory drugs on the metabolic rhythm of the hamster suprachiasmatic nucleus in vitro

In order to elucidate the role of excitatory and inhibitory transmitters within the suprachiasmatic nucleus (SCN) in the circadian change of 2-deoxyglucose (2-DG) uptake in this nucleus, the effects of 8-hydroxy-2-(di-n-propylamino) tetralin hydrobromide (8-OH-DPAT), muscimol, flurazepam, pentobarbital and glutamate on uptake of 2-DG by hamster SCN were examined in hypothalamic slice preparations. 2-DG uptake in the SCN was high during the subjective day and low during the subjective night. The high uptake of 2-DG in the SCN during the daytime was inhibited by the superfusion of 8-OH-DPAT, muscimol, flurazepam and pentobarbital in a dose-dependent manner, but the low uptake of 2-DG during the night was unaffected. The low uptake during the night was significantly increased by treatment with glutamate, whereas 2-DG uptake during the day was unaffected. In contrast to the above results, 20 mM KCl and 1 μM tetrodotoxin increased and decreased 2-DG uptake during both the day and night, respectively. The present results strongly suggest that agonists of 5-HT_1A receptors and GABA_A-benzoadiazepine-barbiturate complex receptors regulate the function of the SCN through their inhibitory action on 2-DG uptake during the day, and that glutamate also regulates SCN function through it stimulatory action on 2-DG uptake during the night.