Endocrine Abstracts

For many animals anticipation of future changes in environmental conditions is a critical adaptation for survival. Seasonal changes in reproductive activity, body weight and adiposity, metabolism and coat condition are examples of such adaptive physiology. Clearly each of these involves neuroendocrine control. The environmental cue that triggers these changes is photoperiod, which is translated into the hormonal signal, melatonin, a product of the pineal gland. A considerable body of work has been reported on the mode of action of melatonin at the cellular level, but it is still unclear how melatonin programmes the anticipatory cycles in physiology through the neuroendocrine system. Through radioligand binding and in situ hybridisation studies the sites of action of melatonin within the hypothalamus have been defined. Studies measuring the expression of early response genes such as the clock gene Per1 and the transcription factor ICER have been instrumental in showing how daylength is decoded within the neuroendocrine system. To try and explore the molecular basis of the neuroendocrine regulation of body weight in seasonal mammals, more recent studies have focused upon the identification of gene expression changes using subtractive hybridisation and cDNA microarray approaches. These studies are beginning to explore the interface between the temporal timing system underlying the biological clock and the regulation of physiological outputs.