The long form of the leptin receptor (OB-Rb) is widely expressed in the human brain

Leptin exerts important effects on the regulation of food intake and energy expenditure by acting in the brain. Leptin action is mediated by the inter action with a receptor that is alternatively spliced, resulting in at least five different isoforms. The long form (OB-Rb) has a long intracellular do main that is essential for intracellular signal transduction. The specific aim of this study was to further investigate the role that the brain may pl ay in the pathogenesis of obesity in humans. We studied the expression of O B-R mRNA (both short or common and long isoforms) in the brains of obese, l ean and diabetic subjects, by in situ hybridization, semiquantitative RT-PC R and Northern blots analysis. We used two alternative probes: one that rec ognizes all known splice variants (OB-Ra) and a second that recognizes only the long form, OB-Rb. Several brain regions, including hypothalamus, cereb ellum, neocortex, entorrhinal cortex, amygdala, and rostral medulla, were e valuated. In situ hybridization studies revealed that both OB-Ra and OB-Rb mRNAs are widely distributed in the human brain. The specific hybridization signal with both probes was detected exclusively in the cytoplasm of the c ell body, dendrites and proximal axons of neurons. Hypothalamic nuclei, Pur kinje cells and dentate nuclei of the cerebellum, inferior olivary and cran ial nerves nuclei in the medulla, amygdala and neurons from both neocortex and entorrhinal cortex demonstrated positive signals. The hybridization sig nal obtained in ependyma was lower than that in neurons and no specific hyb ridization was detected in glial cells. No significant differences were ide ntified among the regions or among the three groups studied. These results match those previously obtained by us [Couce et al.: Neuroendocrinology 199 7;66:145] in which the distribution of the OB-R protein in the human brain was first described. RT-PCR indicated that the OB-Rb was highly expressed i n the hypothalamus and cerebellum. No significant differences of OB-Ra or O B-Rb mRNA expression were identified in lean or obese individuals in these two cerebral regions. The levels of OB-Rb were significantly higher in cere bellum compared to hypothalamus in lean and obese individuals. The original hypothesis that OB-Rb is present only in the hypothalamus needs to be reco nsidered. This OB-Rb isoform seems to be widely expressed in the human brai n with highest levels in the cerebellum. Obesity and hyperleptinemia appear s not to be associated with down-regulation of the OB-Rb in the human brain . Copyright (C) 2000 S. Karger AG, Basel.