Circadian variation in the activity of the 5‐HT 1B autoreceptor in the region of the suprachiasmatic nucleus, measured by microdialysis in the conscious freely‐moving rat

Intracerebral microdialysis was used to examine the function of the terminal 5‐hydroxytryptamine 1B (5‐HT 1B ) autoreceptor in the region of the suprachiasmatic nuclei (SCN) of freely moving conscious rats at six time points or zeitgeber times (ZTs) across the light:dark cycle. Infusion of the 5‐HT 1A/1B agonist 5‐methoxy‐3‐(1,2,3,6‐tetrahydro‐4‐pyridyl)‐1H‐indole (RU24969) (1 μ M ) via the microdialysis probe produced a decrease in 5‐HT output when applied at ZTs 3, 6, 15 and 21 (69.8±11.9, 59±11.7, 43.9±17.2 and 45.7±17.0% respectively). At ZTs 9 and 18 RU24969 (1 μm) failed to affect the 5‐HT output significantly (28.0±11 and 32.8±24.6% decrease respectively). The profile of inhibition of 5‐HT output following infusion of RU24969 (1 μ M ) at ZT 6 was unaffected by concurrent infusion of the specific 5‐HT 1A antagonist N‐[2‐[4‐(2‐methoxyphenyl)‐1‐piperazinyl]ethyl]‐N‐(2‐pyridinyl)cyclohexanecarboxamide trihydrochloride (WAY100635) (1 μ M ) (52.48±17.5% decrease). The data demonstrate a circadian rhythm in the activity of the 5‐HT 1B autoreceptor in the region of the SCN.British Journal of Pharmacology (2000) 131 , 1569–1576; doi: 10.1038/sj.bjp.0703753