Distribution of galanin messenger RNA-expressing cells in murine brain andtheir regulation by leptin in regions of the hypothalamus

Galanin is widely distributed throughout the mammalian brain and has been i mplicated in the regulation of food intake, metabolism and reproduction-fun ctions that are also thought to be under the control of leptin. To investig ate the possible role of galanin in mediating the physiological effects of leptin in the mouse, we had three experimental objectives: first, to map th e distribution of galanin messenger RNA-expressing cells in the brain of th e mouse; second, to assess the effects of leptin on galanin gene expression in areas of the brain thought to be involved in the regulation of body wei ght and reproduction; and third, to determine whether galanin neurons in th ese regions express leptin receptor messenger RNA. We found the pattern of galanin messenger RNA expression in the mouse brain to be similar, but not identical, to that in the rat. Leptin treatment (2 mug/g for six days) sign ificantly reduced cellular levels of galanin messenger RNA in the hypothala mic periventricular nucleus of leptin-deficient obese (ob/ob) mice (P < 0.0 1) by approximately 30%; however, leptin did not appear to influence the ex pression of galanin in the arcuate or dorsomedial nucleus of the hypothalam us. Galanin-producing neurons in the arcuate, dorsomedial and periventricul ar nuclei did not appear to express leptin receptor messenger RNA (P > 0.05 ). These results demonstrate that galanin distribution patterns in the mouse b rain are comparable to other species and, yet, possess unique features. In addition, galanin-expressing neurons in the hypothalamic periventricular nu cleus are targets for regulation by leptin; however, the effect of leptin o n galanin gene expression is likely to be mediated indirectly, perhaps thro ugh either proopiomelanocortin- or neuropeptide Y-expressing cells in the h ypothalamus. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights r eserved.