Leptin receptor immunoreactivity is present in ascending serotonergic and catecholaminergic neurons of the rat

Using double-labelling immunohistochemistry we have studied the localisatio n of leptin receptor proteins including both long and short forms and their possible presence in serotonergic (5-HT) and catecholaminergic neurons in the rat brain. Leptin receptor immunoreactivity was found to be widely dist ributed in the central nervous system including cortical areas, amygdala, s everal hypothalamic and thalamic nuclei, the raphe system, pontine nuclei, locus coeruleus, parabrachial nucleus, tractus solitarus and the medullary reticular formation. Serotoner gic cell groups were identified by 5-HT immu nocytochemistry and classified according to standard nomenclature. High deg rees of co-existence of leptin receptor immunoreactivity with serotonin in the raphe system were observed in B1, B5, B6, B7, B8 and B9. In B3 and B2 l ess than 50% of the 5-HT cells colocalised leptin receptor immunoreactivity . Brainstem and diencephalic (catecholaminergic) neurons were identified by tyrosine hydroxylase immunocytochemistry and classified according to stand ard nomenclature. Within the periventricular hypothalamic dopaminergic nucl ei A14 and A12, the metencephalic noradrenergic A6, A7, A2, A1, and the adr energic C3, C2 and C1 cell groups, nearly all tyrosine hydroxylase-positive cells colocalised with leptin receptor immunoreactivity. In contrast, co-e xistence of tyrosine hydroxylase and leptin receptor immunoreactivities in the dopaminergic A13, A11, A10, A9 and A8 cell was practically non-existent . Thus leptin, the adipose tissue-derived ligand of the leptin receptor, ma y in some brain areas directly influence serotonergic, dopaminergic, adrene rgic and noradrenergic inputs to the periventricular and medial hypothalami c nuclei. Copyright (C) 2001 S. Karger AG, Basel.