Circadian variation in behavioural responses to central 5-HT receptor stimulation in the mouse.
The intensity of the head-twitch response and the 5-hydroxytryptamine (5-HT) syndrome (tremor, fore-paw treading, head-weaving and hind-limb abduction) was measured in male CFLP mice following IP injection of 5 mg/kg 5-methoxy-N,N-dimethyltryptamine (5-MeODMT). The results of separate experiments carried out at 1.5-h intervals throughout the light-dark cycle showed a clear circadian variation in head-twitch, with highest scores mid-light. No circadian variation in the 5-HT syndrome, or in any individual element of it, was observed. Dose-response curves constructed for 5-MeODMT mid-light and mid-dark over the range 2-64 mg/kg IP confirmed the difference in head-twitch response, showing a parallel shift to the right for mid-dark compared to mid-light up to 32 mg/kg. Again, no difference was seen between the two curves for the 5-HT syndrome. Measurement of the time course of behavioural activity following 5-MeODMT failed to show any differences between mid-light and mid-dark, making it unlikely that pharmacokinetic differences account for the observed circadian variation. It is suggested that the demonstration of a circadian rhythm in the head-twitch response and the failure to show any comparable rhythm in the 5-HT syndrome provides further evidence that these behaviours are mediated by different 5-HT receptor subtypes.
D006916:5-Hydroxytryptophan / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001921:Brain / Q000187:drug effects* / Q000502:physiology; D002940:Circadian Rhythm; D008297:Male; D008732:Methoxydimethyltryptamines / Q000494:pharmacology*; D051379:Mice; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000502:physiology; D012701:Serotonin / Q000031:analogs & derivatives*
D008732:Methoxydimethyltryptamines; D011985:Receptors, Serotonin; D012701:Serotonin; D006916:5-Hydroxytryptophan