title: A cholinergic receptor 12-hour interval-timer displaying "circa" periodicities.
abstract: The finding of brief pulses of receptor escape from atropine blocking of acetylcholine paralleling moonset and moonset-plus-12-hr led to a search for similar pulses paralleling sunset. Pulses occurring in the hour before sunset as well as in the hour before sunset-plus-12-hr were found. The pulses of receptor escape associated with sunset and sunset-plus-12-hr were in the opposite direction from those associated with moonset and moonset-plus-12-hr. The direction of receptor escape in all cases reversed with the winter solstice. These findings appear to provide evidence for an endogenous 12-hr interval-timer responding to external 24- and 24.8-hr oscillating systems which interact to yield a family of frequencies including those designated "circa".
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D002940:Circadian Rhythm; D003058:Cockroaches / Q000502:physiology*; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D008297:Male; D010526:Periplaneta / Q000502:physiology*; D011950:Receptors, Cholinergic / Q000187:drug effects / Q000502:physiology*; D012621:Seasons
chemical_list: D011950:Receptors, Cholinergic; D001285:Atropine; D000109:Acetylcholine