Local administration of EAA antagonists blocks light-induced phase shifts and c-fos expression in hamster SCN
Rea, M.A.; Buckley, B.; Lutton, L.M.
American Journal of Physiology 265(5 Pt 2): R1191-R1198
1993
ISSN/ISBN: 0002-9513 PMID: 7902017 Document Number: 406025
Syrian hamsters were fitted with guide cannulas stereotaxically aimed at the suprachiasmatic nuclei (SCN) and housed in constant darkness in cages equipped with running wheels. Animals received 300-nl injections of either vehicle, CNQX, or MK-801 into the region of the SCN 5 min before a brief (10 min at 20 lx) light exposure. Local administration of either 1 nM CNQX or 1 mM MK-801 at circadian time (CT) 18 significantly inhibited light-induced phase advances (vehicle = 52 +- 9 min; CNQX = 12 +- 7 min; MK-801 = 12 +- 5 min; P lt 0.05 relative to vehicle + light group). The effects of both drugs were reversible and dose related. Injection of 1 mM MK-801 at CT13.5 resulted in a 71% inhibition of light-induced phase delays (vehicle = -51 +- 6 min; MK-801 = -15 +- 5 min; P lt 0.05), while CNQX failed to significantly inhibit light-induced phase delays (-39 +- 10 min). Local administration of either 1 mM CNQX or MK-801 into the SCN region reduced the number of Fos-immunoreactive cells relative to vehicle-injected controls by apprx 32 and 44%, respectively (vehicle = 951 +- 79; CNQX = 643 +- 135, P lt 0.05; MK-801 = 533 +- 143, P lt 0.05). These results demonstrate that both N-methyl-D-aspartic acid (NMDA) and non-NMDA receptors located in the SCN region mediate light-induced phase shifts and Fos expression in the SCN.