LOCALIZATION OF ALPHA(2C)-ADRENERGIC RECEPTOR IMMUNOREACTIVITY IN CATECHOLAMINERGIC NEURONS IN THE RAT CENTRAL-NERVOUS-SYSTEM

Given the importance of alpha(2)-adrenergic receptors in the regulatio n of catecholaminergic transmission, we analysed the distribution of i mmunoreactivity corresponding to the C-subtype of alpha(2)-adrenergic receptor in central catecholaminergic neurons using double-label immun ohistochemistry with antibodies directed against alpha(2C)-adrenergic receptors and tyrosine hydroxylase. Cells exhibiting both alpha(2C)-ad renergic receptor and tyrosine hydroxylase immunoreactivity were found in most areas containing catecholaminergic cell groups. However, the percentage of double-labelled cells varied in a region-specific manner . In the medulla, alpha(2C)-adrenergic receptor immunoreactivity was c haracteristic of only a minority of cells exhibiting tyrosine hydroxyl ase immunoreactivity (40-43% in area Al/Cl, 27-36% in area A2/C2, 35% in area C3) while a larger percentage of double-labelled cells was obs erved in the pens (65% in A5, 92% in locus coeruleus, 68% in A7). In t he midbrain, alpha(2C)-adrenegic receptor immunoreactivity was detecte d in most tyrosine hydroxylase-immunoreactive cells in dopaminergic re gions (63% in the retrorubral field, 77-83% in substantia nigra, 67% i n ventral tegmental area). These results suggest that alpha(2C)-adrene rgic receptors may act as autoreceptors on some central adrenergic and noradrenergic neurons. In addition, the colocalization of alpha(2C)-a drenergic receptor and tyrosine hydroxylase immunoreactivity in dopami nergic cell groups suggests that reported effects of alpha(2)-adrenerg ic receptor agonists in these areas may be mediated by the C-subtype. (C) 1998 IBRO. Published by Elsevier Science Ltd.