Resetting of the rat circadian clock after a shift in the light/dark cycle depends on the photoperiod.
Adjustment of the circadian clock to shifts in the light/dark (LD) cycle was assessed from the rat pineal N-acetyltransferase (NAT) rhythm which is controlled by a pacemaker in the suprachiasmatic nucleus of the hypothalamus. Re-entrainment to an 8-h delay in the LD cycle took more than 3 days in rats maintained under a regime with 18 h of light and 6 h of darkness per day (LD 18:6) whereas it was completed within 3 days in those maintained under LD 12:12. Re-entrainment to an advance in the LD cycle proceeded through a transient diminution or almost disappearance of the NAT rhythm amplitude following a 5-h, 3-h and even a mere 2-h advance shift under LD 18:6, whereas no such diminution occurred under LD 12:12 even after a 5-h advance shift. Altogether, the data indicate that resetting of the circadian clock after shifts in the LD cycle depends on the photoperiod.
Humlová
M
M
Institute of Physiology, Czechoslovak Academy of Sciences, Prague.
Illnerová
H
H
D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000378:metabolism*; D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D008027:Light; D008297:Male; D010870:Pineal Gland / Q000201:enzymology / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013493:Suprachiasmatic Nucleus / Q000502:physiology*; D013997:Time Factors
D001191:Arylamine N-Acetyltransferase