Changes in aromatase activity in the neuroendocrine tissues of red grouse (Lagopus lagopus scoticus) in relation to the development of long-day refractoriness.

Changes in aromatase activity in the neuroendocrine tissues of captive male and female red grouse (Lagopus lagopus scoticus) were measured during a photo-induced breeding cycle. The gonads enlarged and subsequently regressed, as a consequence of the development of long-day refractoriness, within 84 days of transferring photoinsensitive birds from a non-stimulatory to a stimulatory daylength. The object of the study was to determine whether long-day refractoriness is related to an increase in aromatase activity in the neuroendocrine tissues which might result in a greater inhibitory action of locally produced oestrogens on the release of LH-releasing hormone. Aromatase activity was measured and found to be present in the anterior pituitary gland, the anterior/preoptic hypothalamus, the posterior hypothalamus and the hyperstriatum dorsale. It was higher in the hypothalamus than in the hyperstriatum dorsale and higher in the posterior than in the anterior/preoptic hypothalamus. Aromatase activity in the posterior hypothalamus was higher in males than in females in short-day photosensitive and reproductively active birds, but not in long-day refractory birds. A similar sex difference was also observed in the anterior/preoptic hypothalamus in reproductively active birds. Hypothalamic aromatase activity in both sexes was directly related to gonadal function, being highest in reproductively active birds and lowest in long-day refractory birds. It is concluded that the development of long-day refractoriness is not related to an increase in aromatase activity in the neuroendocrine tissues. The decrease in aromatase activity in the neuroendocrine tissues in long-day refractory birds parallels a decrease in aggressive and territorial behaviour.