Ferguson, S.Kennaway, D.2006-06-242006-06-241999American Journal of Physiology. Regulatory Integrative and Comparative Physiology, 1999; 277(4 46-4):R1171-R11780363-61192163-5773http://hdl.handle.net/2440/7928Mammalian circadian rhythms are controlled by the suprachiasmatic nuclei (SCN) in concert with light information. Several neurotransmitters and neural pathways modulate light effects on SCN timing. This study used a line of rat with an upregulated cholinergic system to investigate the role of acetylcholine in rhythmicity. With the use of a selective breeding program based on the thermic response to a cholinergic agonist, we developed a supersensitive (S(ox)) and subsensitive (R(ox)) rat line. The S(ox) rats showed an earlier onset time of melatonin rhythm under a 12:12-h light-dark photoperiod from generation 3 (3 +/- 0.5 h after dark) compared with R(ox) rats (4.5 +/- 0.1 h) and an earlier morning decline in temperature (0.9 +/- 0.3 h before lights on) compared with R(ox) animals (0.1 +/- 0.1 h). Furthermore, the S(ox) animals displayed a significantly shorter free-running period of temperature rhythm than R(ox) rats (23.9 +/- 0.04 and 24.3 +/- 0.1 h, respectively, P < 0.05). The results suggest that the altered circadian timing of the S(ox) rats may be related to the cholinergic supersensitivity, intimating a role for acetylcholine in the circadian timing system.enSuprachiasmatic NucleusAnimalsRatsAcetylcholineOxotremorineMelatoninProto-Oncogene Proteins c-fosCholinergic AgentsMuscarinic AgonistsBody TemperatureCircadian RhythmDrug ResistanceLightDarknessJournal article0030005346001999050410.1152/ajpregu.1999.277.4.r11710000839197000312-s2.0-003272562969352Kennaway, D. [0000-0002-5864-3514]