... rodents andungulates. In contrast to rodents , the nocturnal rise of melatonin arylalkylamine N-acetyltransferase (AA-NAT) in sheep is not accompanied by a si milar rise in A A-NAT mRNA expression ... in the SCN of the mammalian hypothalamus.Keywords: melatonin pineal, cortisol, horse, circadian, jet lag, rhythm, extended darkness Background In mammals, the suprachiasmatic nucleus (SCN) of ... Circadian Rhythms 2011, 9:3http://www.jcircadianrhythms.com/content/9/1/3Page 4 of 8 RESEARCH Open AccessAbsence of a serum melatonin rhythm under acutely extended darkness in the horseBarbara...