ADENOSINE-A1-RECEPTOR AGONIST ATTENUATES THE LIGHT-INDUCED PHASE-SHIFTS AND FOS EXPRESSION IN-VIVO AND OPTIC-NERVE STIMULATION-EVOKED FIELDPOTENTIALS IN THE SUPRACHIASMATIC NUCLEUS IN-VITRO

Adenosine is widely accepted to act as an inhibitory neuromodulator in the mammalian central nervous system. In the present study, we examin ed whether adenosine receptor agonist modifies the photic entraining r esponses in the rat suprachiasmatic nucleus both in vivo and in vitro. Light (200 lux, 15 min)-induced phase shifts of hamster wheel-running rhythms was attenuated by a systemic administration of AI-adenosine r eceptor agonist N-6-cyclohexyladenosine (N-CHA) in a dose-dependent ma nner; 0.5 mg/kg N-CHA caused 60% inhibition of light-induced phase shi fts. On the other hand, A2-adenosine receptor agonist imethoxyphenyl)- 2-(2-methylphenyl)-ethyl]adenosine (DPMA) failed to inhibit light-indu ced phase shifts. Systemic administration of N-CHA but not of DPMA inh ibited light (300 lux, 1 h)-induced Fos expression in the suprachiasma tic nucleus in a dose-dependent manner; 1 mg/kg N-CHA caused 73% inhib ition of light-induced Fos expression. Bath application of N-CHA but n ot of DPMA inhibited optic nerve stimulation-evoked field potentials i n rat suprachiasmatic nucleus slices. The present results suggest that activation of adenosine Al-receptor attenuates the photic input throu gh the inhibition of retinohypotalamic pathway to the SCN.