Distribution of galanin immunoreactivity in the sheep diencephalon

Although the physiological role of galanin has been demonstrated in several endocrine regulations in sheep, the anatomical characteristics of this neu ronal system has never been studied. The distribution of galanin-containing neurones was described by immunohistochemistry using galanin antiserum in the diencephalon of adult awes, both ovariectomized or treated with colchic ine. Galanin-immunoreactivity was found throughout the diencephalon. In the ovar iectomized ewes, galanin-immunoreactive neurones were mainly observed in th e medial preoptic area and the infundibular nucleus. The highest density of immunoreactive fibres was found in the external layer of the median eminen ce. Numerous galanin-immunoreactive fibres were also observed in the preopt ic area, the mediobasal hypothalamus, the periphery of the supraoptic and t he paraventricular nuclei. With colchicine treatment, the number of labelle d neurones increased, and additional galanin-immunoreactive perikarya were observed in the bed nucleus of the stria terminalis, the lateral septum, th e supraoptic. the paraventricular and the periventricular nuclei and the pa raventricular nucleus of the thalamus. In the caudal part of the diencephal on. the density of labelled neurones was lower in both groups of animals th an in other species studied. Regardless of treatment, labelling was not see n in the suprachiasmatic nucleus and only rarely in the ventromedial nucleu s. These results describe, for the first time. the distribution of galanin-imm unoreactive neurones in the sheep diencephalon. Compared to other species s tudied, distribution in the sheep diencephalon has several distinct differe nces. In ovariectomized animals, the medial preoptic area presents more lab elled neurones in sheep than in monkeys, whereas in the supraoptic nucleus the density of labelled neurones is lower in sheep than in humans or opossu ms. After colchicine treatment only very few differences were observed betw een sheep and rats, but in contrast to other species, the suprachiasmatic n ucleus of the sheep does not contain labelled neurones. (C) 1999 Elsevier S cience B.V. All rights reserved.