Lack of circadian variation in the sensitivity of rat terminal 5-HT1B autoreceptors.
The sensitivity of terminal 5-HT1B autoreceptors in the cerebral cortex and hippocampus to both agonist and antagonist was determined at four different time points in the light:dark cycle of the rat to evaluate whether changes in their responsiveness underlie the circadian rhythm in 5-hydroxytryptamine (5-HT) release. No significant circadian differences were evident in the apparent pIC50 values calculated for 5-HT to inhibit K(+)-evoked tritium efflux or in the apparent pA2 values calculated for methiothepin to antagonize the effect of 5-HT, at the different time points, in either brain region. These findings suggest that the sensitivity of terminal 5-HT1B autoreceptors in rat cerebral cortex and hippocampus does not change in a circadian pattern, during the light:dark cycle, and argues against such a change influencing the circadian variation in 5-HT release.
Singh
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A
Pharmacology Group, School of Pharmacy and Pharmacology, University of Bath, Avon, UK.
Redfern
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P
D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D002940:Circadian Rhythm; D004305:Dose-Response Relationship, Drug; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism; D008027:Light; D008297:Male; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000378:metabolism; D012702:Serotonin Antagonists / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*
D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D011188:Potassium