Many species express endogenous cycles in physiology and behavior that allow anticipation of the seasons. The anatomical cellular bases these circannual rhythms have not been defined. Here, we provide strong evidence using an vivo Soay sheep model regulation prolactin secretion, its associated biology, derive from a pituitary-based timing mechanism. Circannual rhythm generation is seen as product interaction between melatonin-regulated timer cells adjacent prolactin-secreting cells, which...

The 24-h expression of seven clock genes (Bmal1, Clock, Per1, Per2, Cry1, Cry2, and CK1 epsilon ) was assayed by in situ hybridization the suprachiasmatic nucleus (SCN) pars tuberalis (PT) pituitary gland, collected every 4 h throughout 24 h, from female Soay sheep kept under long (16-h light/8-h dark) or short (8-h light/16-h photoperiods. Locomotor activity diurnal, inversely related to melatonin secretion, prolactin levels were increased days. All expressed ovine SCN PT. In SCN, there a...

Photoperiodic responses enable animals to adapt their physiology predictable patterns of seasonal environmental change. In mammals, this depends on pineal melatonin secretion and effects in the hypothalamus, but cellular molecular substrates its action are poorly understood. The recent identification a mammalian orthologue avian gonadotrophin‐inhibitory hormone gene has led interest possible involvement breeding. long‐day breeding Syrian hamsters, hypothalamic RFamide‐related peptide (RFRP)...

Abstract Previous studies demonstrated that the clock gene Per1 and transcription factor ICER are expressed rhythmically in suprachiasmatic nucleus (SCN) pars tuberalis (PT). In Syrian hamster duration of photoperiod affects amplitude expression PT, melatonin administered before lights‐on suppressed peak Per1/ICER expression; these effects were not seen SCN. It was speculated inefficacy due to low density receptors SCN this species. The aim present study determine whether phenomenon also...

In photoperiodic mammals, seasonal cycles of growth and reproduction are cued by changes in the duration nocturnal profile secretion pineal hormone melatonin. To investigate likely mode action this on target tissues, effect prolonged treatment with melatonin sensitivity adenylate cyclase (AC) system was examined primary cultures ovine pars tuberalis (PT) cells. When cells were exposed to (100 pM or 1 microM) for 16 h, then removed a series washes, basal production cAMP elevated over that...

cAMP-dependent protein kinase induction of PPARgamma coactivator-1alpha (PGC-1alpha) and uncoupling 1 (UCP1) expression is an essential step in the commitment preadipocytes to brown adipose tissue (BAT) lineage. We studied molecular mechanisms responsible for differential PGC-1alpha HIB1B 3T3-L1 white (WAT) precursor cell lines. In cells UCP1 cAMP-inducible, but cells, reduced cAMP-insensitive. A proximal 264-bp reporter construct was cAMP-inducible only suppressed by site-directed...

At temperate latitudes, increases in day length the spring promote summer phenotype. In mammals, this long-day response is mediated by decreasing nightly duration of melatonin secretion pineal gland. This affects adenylate cyclase signal transduction and clock gene expression melatonin-responsive cells pars tuberalis pituitary, which control seasonal prolactin secretion. To define photoperiodic limits mammalian long response, we transferred short (8 h light per 24 h) acclimated Soay sheep to...

Epidemiological and experimental evidence correlates adverse intrauterine conditions with the onset of disease later in life. For a fetus to achieve successful transition extrauterine life, myriad temporally integrated humoral/biophysical signals must be accurately provided by mother. We others have shown existence daily rhythms fetus, peripheral clocks being entrained maternal cues, such as transplacental melatonin signaling. Among developing tissues, fetal hippocampus is key structure for...

At temperate latitudes, many mammals and birds show internally timed, long‐term changes in seasonal physiology, synchronised to the seasons by changing day length (photoperiod). Photoperiodic control of thyroid hormone levels hypothalamus dictates timing. This is effected through reciprocal regulation deiodinase gene expression. The local synthesis type 2 ( D io2) promotes triiodothyronine T 3) production summer biology, whereas 3 io3) degradation winter biology. In present study, we...

In mammals, maternal photoperiodic programming (MPP) provides a means whereby juvenile development can be matched to forthcoming seasonal environmental conditions.

The purpose of this study was to determine whether the cells ovine pars tuberalis (PT) secrete a factor(s) that can influence activity in distalis (PD). By Northern blotting total RNA isolated from PD had been stimulated presence cycloheximide (10 micrograms/ml), PT cell-conditioned medium shown induce significant increase expression early response gene, c-fos, above both and nonconditioned control levels (P < 0.05). Although forskolin (5 microM) induced weak c-fos cells, effect conditioned...

In mammals, changing day length modulates endocrine rhythms via nocturnal melatonin secretion. Studies of the pituitary pars tuberalis (PT) suggest that melatonin-regulated clock gene expression is critical to this process. Here, we considered whether continue in PT absence and effects on these genes are temporally gated. Soay sheep acclimated long photoperiod (LP) were transferred constant light for 24 h, suppressing endogenous Animals infused with at 4-h intervals across final killed 3 h...

Abstract In seasonal animals, prolonged exposure to constant photoperiod induces photorefractoriness, causing spontaneous reversion in physiology that of the previous photoperiodic state. This study tested hypothesis onset photorefractoriness is correlated with a change circadian expression clock genes suprachiasmatic nucleus (circadian pacemaker) and pars tuberalis (PT, melatonin target tissue). Soay sheep were exposed summer (16-h light) for either 6 or 30 wk produce photostimulated...

Melatonin secretion by the pineal gland transduces photoperiod into a neuroendocrine signal. In pars tuberalis (PT), we have shown that modifies amplitude of clock gene Per1. The aim this study was to test whether endogenous melatonin signal is required for rhythmic expression Per1 in PT. Male Syrian hamsters housed long days (LD, 16:8h light:dark) were pinealectomized and mRNA studied situ hybridization. Pinealectomy abolished rhythm PT, but had no effect on suprachiasmatic nucleus (SCN),...

Abstract Photoperiod regulates the seasonal physiology of many mammals living in temperate latitudes. Photoperiodic information is decoded by master circadian clock suprachiasmatic nuclei (SCN) hypothalamus and then transduced via pineal melatonin secretion. This neurochemical signal interpreted tissues expressing receptors (e.g. pituitary pars tuberalis, PT) to drive physiological changes. In this study we analysed photoperiodic regulation clockwork SCN PT Siberian hamster. Female hamsters...