title: Regulation of pineal rhythms in chickens: refractory period and nonvisual light perception.
abstract: Pineal serotonin N-acetyltransferase activity and melatonin content exhibit marked daily rhythms in chickens; peak values occur during the period of low locomotor activity which coincides with dark in a 24-h light-dark regime. We studied the regulation of these daily rhythms by measuring pineal serotonin N-acetyltransferase activity, hydroxyindole-O-methyltransferase (HIOMT) activity, and melatonin content in experiments in which birds were exposed to light-to-dark and dark-to-light transitions at atypical times. We observed that there is a refractory period for dark-initiation of the increase in pineal N-acetyltransferase activity and melatonin content. We also learned that a dark-to-light transition causes a rapid decrease in dark-elevated pineal N-acetyltransferase activity and melatonin content. The rapid decrease occurs in blinded chickens as well as sighted ones. HIOMT activity did not change consistently in any of the experimental treatments.
mesh_terms: D000123:Acetyltransferases / Q000378:metabolism*; D000818:Animals; D002645:Chickens / Q000502:physiology*; D002940:Circadian Rhythm; D003624:Darkness; D006897:Hydroxyindoleacetic Acid; D008027:Light; D008550:Melatonin / Q000096:biosynthesis*; D008780:Methyltransferases / Q000378:metabolism; D009799:Ocular Physiological Phenomena; D010870:Pineal Gland / Q000502:physiology*; D012701:Serotonin; D013997:Time Factors
chemical_list: D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D008780:Methyltransferases; D000123:Acetyltransferases; D008550:Melatonin