Does a Melatonin-Dependent Circadian Oscillator in the Pars Tuberalis Drive Prolactin Seasonal Rhythmicity?

• Published in: Journal of neuroendocrinology 2007-08, Vol.19 (8), p.657-666
• Main Author: Dardente, H.
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Biological Clocks - drug effects; Biological Clocks - physiology; Chronobiology; circadian; clock genes; cryptochromes; Fundamental and applied biological sciences. Psychology; Life Sciences; melatonin; Melatonin - pharmacology; Melatonin - physiology; Models, Biological; pars tuberalis; Periodicity; Photoperiod; Pituitary Gland, Anterior - drug effects; Pituitary Gland, Anterior - metabolism; prolactin; Prolactin - secretion; Receptors, Melatonin - physiology; Reproductive Biology; Seasons; Signal Transduction - drug effects; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Vertebrates: endocrinology
• ISSN: 0953-8194; 1365-2826
• DOI: 10.1111/j.1365-2826.2007.01564.x

The pars tuberalis (PT) of the adenohypophysis expresses a high density of melatonin receptors and is thought to be a crucial relay for the actions of melatonin on seasonal rhythmicity of prolactin secretion by the pars distalis (PD). In common with the suprachiasmatic nucleus of the hypothalamus and most other peripheral tissues, the PT rhythmically expresses a range of ‘clock genes’. Interestingly, this expression is highly dependent upon melatonin/photoperiod, with several aspects unique to the PT. These observations led to the establishment of a conceptual framework for the encoding of seasonal timing in this tissue. This review summarises current knowledge of the morphological, functional and molecular aspects of the PT and considers its role in seasonal timing. The strengths and weaknesses of current hypotheses that link melatonin action in the PT to its seasonal effect on lactotrophs of the PD are discussed and alternative working hypotheses are suggested.