Abstract
The regulation of extracellular noradrenaline levels in the cingulate cortex by somatodendritic α 2-adrenoceptors located in the locus coeruleus was evaluated in the rat by using dual-probe microdialysis. The concentration of noradrenaline in the cingulate cortex was decreased (37%–40%) by administration into the locus coeruleus (1 μM) of the agonists clonidine and UK14304 (bromoxidine), whereas it was increased by similar administration of the nonselective antagonist RX821002 (2-methoxyidazoxan) (+103%) and the selective α 2A-adrenoceptor antagonist BRL44408 (2-[2 H-(1-methyl-1,3-dihydroisoindole)methyl]-4,5-dihydroimidazole) (+148%). The selective α 2B/C-adrenoceptor antagonist ARC239 (2-[2[4-( o-methoxyphenyl)piperazin-1-yl]ethyl]-4,4-dimethyl-1,3-(2 H,4 H)-isoquinolinedione) did not induce changes. In the presence of BRL44408, the effects of clonidine and UK14304 were abolished, but they were not modified in the presence of ARC239. The data demonstrate that noradrenaline release in terminal areas is tonically modulated by somatodendritic α 2A-adrenoceptors.
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