Lack of circadian variation in the responsiveness of alpha 2-heteroreceptors regulating serotonin release.
We have previously shown that the circadian variation in 5-HT release is not the consequence of a variation in the activity of terminal 5-HT1B autoreceptors. However, recently identified alpha 2-adrenoceptors located on 5-HT nerve terminals may be important in regulating the release of 5-HT from serotonergic neurons. The sensitivity of hippocampal alpha 2-heteroreceptors to both agonist and antagonist was determined at different time points in the light:dark cycle of the rat. No significant circadian differences were evident in either the apparent pD2 values calculated for noradrenaline to inhibit potassium-evoked tritium efflux or in the apparent pA2 values calculated for phentolamine to antagonize the effect of noradrenaline. The corollary of the lack of a circadian rhythm in sensitivity to the alpha 2-heteroreceptor is that this receptor population will accurately reflect any circadian variation in noradrenaline release and in the available concentration of noradrenaline at the receptor sites.
Singh
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A
Pharmacology Group, School of Pharmacy and Pharmacology, University of Bath, Avon, England.
Redfern
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P
D000704:Analysis of Variance; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D002940:Circadian Rhythm; D003624:Darkness; D004305:Dose-Response Relationship, Drug; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010293:Pargyline / Q000494:pharmacology; D017374:Paroxetine / Q000494:pharmacology; D010646:Phentolamine / Q000031:analogs & derivatives / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000378:metabolism*; D014316:Tritium
D018341:Receptors, Adrenergic, alpha-2; D014316:Tritium; D012701:Serotonin; D017374:Paroxetine; D010293:Pargyline; D011188:Potassium; D009638:Norepinephrine; D010646:Phentolamine