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Photorefractoriness is the insensitivity of gonadal development to the stimulatory effects of long photoperiods in birds and to the inhibitory effects of short photoperiods in small mammals. Its molecular mechanism remains unknown. Recently, it has been shown that reciprocal expression of thyroid hormone-activating enzyme [type 2 deiodinase (Dio2)] and(More)
Reproduction of many temperate zone birds is under photoperiodic control. The Japanese quail is an excellent model for studying the mechanism of photoperiodic time measurement because of its distinct and marked response to changing photoperiods. Studies on this animal have suggested that the mediobasal hypothalamus (MBH) is an important centre controlling(More)
Local thyroid hormone catabolism within the mediobasal hypothalamus (MBH) by thyroid hormone-activating (DIO2) and -inactivating (DIO3) enzymes regulates seasonal reproduction in birds and mammals. Recent functional genomics analysis in birds has shown that long days induce thyroid-stimulating hormone production in the pars tuberalis (PT) of the pituitary(More)
The molecular mechanisms responsible for seasonal time measurement have yet to be fully described. Recently, we used differential analysis to identify that the type 2 iodothyronine deiodinase (Dio2) gene is responsible for the photoperiodic response of gonads in Japanese quail. It was found that expression of Dio2 in the mediobasal hypothalamus is induced(More)
The molecular mechanisms underlying photoperiodic time measurement are not well understood in any organism. Relatively recently, however, it has become clear that thyroid hormones play an important role in photoperiodism, and in a previous study we reported that long daylengths in Japanese quail increase hypothalamic levels of T(3) and of the thyroid(More)
In most animals that live in temperate regions, reproduction is under photoperiodic control. In long-day breeders such as Japanese quail and Djungarian hamsters, type 2 deiodinase (Dio2) plays an important role in the mediobasal hypothalamus, catalyzing the conversion of prohormone T4 to bioactive T3 to regulate the photoperiodic response of the gonads.(More)
In birds, the mediobasal hypothalamus (MBH) including the infundibular nucleus, inferior hypothalamic nucleus, and median eminence is considered to be an important center that controls the photoperiodic time measurement. Here we show expression patterns of circadian clock genes in the MBH, putative suprachiasmatic nucleus (SCN), and pineal gland, which(More)
The molecular basis of seasonal or nonseasonal breeding remains unknown. Although laboratory rats are generally regarded as photoperiod-insensitive species, the testicular weight of the Fischer 344 (F344) strain responds to photoperiod. Recently, it was clarified that photoperiodic regulation of type 2 iodothyronine deiodinase (Dio2) in the mediobasal(More)
Prolactin (PRL) secretion is regulated by photoperiod in mammals and birds. In mammals, the pars tuberalis (PT) in the pituitary is involved in the regulation of photoperiodic regulation of PRL secretion. In birds, however, hypothalamic vasoactive intestinal peptide is implicated in PRL secretion, and physiological roles of the avian PT remain unknown. In(More)
The molecular mechanism underlying photoperiodism is not well understood in any organism. Long-day-induced conversion of prohormone T(4) to bioactive T(3) within the mediobasal hypothalamus (MBH) is critical for the photoperiodic regulation of reproduction. However, because thyroidectomy does not completely block the photoperiodic response in some species,(More)