ABSTRACT
Melatonin secretion by the pineal gland transduces photoperiod into a neuroendocrine signal. In the pars tuberalis (PT), we have shown that photoperiod modifies the amplitude of the clock gene Per1. The aim of this study was to test whether the endogenous melatonin signal is required for rhythmic expression of Per1 in the PT. Male Syrian hamsters housed in long days (LD, 16:8h light:dark) were pinealectomized and Per1 mRNA expression studied by in situ hybridization. Pinealectomy abolished the rhythm of Per1 expression in the PT, but had no effect on Per1 expression in the suprachiasmatic nucleus (SCN), or the ventromedial nucleus (VMH) of the hypothalamus. Interestingly, a single night-time injection of melatonin (25 microg), given to pinealectomized animals, failed to restore Per1 expression in the PT. These data demonstrate that Per1 expression in the PT is driven by melatonin, and that the features of the endogenous signal through which the Per1 expression is achieved cannot be reproduced by a single melatonin injection.
Subject(s)
Nuclear Proteins/genetics , Pineal Gland/surgery , Pituitary Gland, Anterior/physiology , Suprachiasmatic Nucleus/physiology , Animals , Antioxidants/pharmacology , CLOCK Proteins , Circadian Rhythm/physiology , Cricetinae , Gene Expression/drug effects , Gene Expression/physiology , Male , Melatonin/pharmacology , Mesocricetus , Pineal Gland/physiology , RNA, Messenger/analysis , Trans-Activators/geneticsABSTRACT
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 microM) 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 microm) 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 microM) 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)cyclohe xanecarboxamide trihydrochloride (WAY100635) (1 microM) (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.
