Daily changes of cytochrome oxidase activity within the suprachiasmatic nucleus of the Syrian hamster

Cytochrome oxidase (CO) activity was studied over a 24-h period in the Syri an hamster suprachiasmatic nucleus (SCN) (site of the biological clock), an terior hypothalamic area (AHA), and motor cortex. The SCN CO activity was h ighest at the middle of the day (Zeitgeber time (ZT) 05), decreased at the end of the light period (ZT 10) and continued at a low level during the nig ht (ZT 13, 16, 21.5 and 24). AHA and motor cortex showed a similar profile of CO activity and no changes of CO activity were found in animals maintain ed under darkness (DD). We propose that photic input plays a role in the SC N neuronal activity that modulates metabolic activity on this area. (C) 200 0 Published by Elsevier Science Ireland Ltd. All rights reserved.