Regulation of α 2A-adrenoceptor expression by chronic stress in neurons of the brain stem

Abstract

α 2-Adrenoceptors are supposed to be important regulatory elements in responses to stress. Previous receptor binding studies in male tree shrews have shown that chronic psychosocial stress down-regulates binding sites for α 2-adrenergic ligands in several brain stem nuclei. The aim of the present study was to quantify effects of chronic subordination stress on expression of the α 2-adrenoceptor subtype A gene in identified neurons of the brain stem. We partially cloned the α 2A-adrenoceptor cDNA of the tree shrew (1.22 kb) and localized receptor RNA expression in brain stem neurons by in situ hybridization using a 35S-labeled cRNA probe (1.06 kb). To identify neurons expressing receptor mRNA, brain sections were first immunocytochemically stained with antibodies against tyrosine hydroxylase, phenylethanolamine- N-methyltransferase, or glutamate, and then processed for in situ hybridization. Furthermore, expression of receptor-specific RNA was quantified in single neurons of animals which had been psychosocially stressed during 4 weeks and in unstressed controls. We found strong in situ hybridization in the noradrenergic neurons of the locus coeruleus, but only weak labeling of A2 neurons in the solitary tract nucleus and no labeling of A1 neurons in the caudal ventrolateral medulla. Adrenergic neurons in the solitary tract nucleus (group C2) did not express the α 2A-adrenoceptor, and C1 neurons in the rostral ventrolateral medulla showed only a minor labeling by the in situ probe. In contrast, large glutamatergic neurons in the lateral reticular nucleus were strongly labeled by the probe. Chronic psychosocial stress reduced α 2A-adrenoceptor RNA expression in locus coeruleus neurons (−24.0%), in solitary tract neurons (−31.0%), and in neurons of the lateral reticular nucleus (−18.8%). These findings show that stress not only decreases the expression of the α 2A-adrenergic autoreceptor in the locus coeruleus but also of α 2A-heteroreceptors in glutamatergic neurons.