ALPHA(2A) SUBTYPE OF PRESYNAPTIC ALPHA(2)-ADRENOCEPTORS MODULATES THERELEASE OF [H-3] NORADRENALINE FROM RAT SPINAL-CORD

The modulation of noradrenaline (NA) release from rat spinal cord slic es was investigated and the subtype of presynaptic alpha(2)-adrenocept ors involved in the negative feedback modulation was characterized usi ng in vitro perfusion experiments, Rat spinal cord slices were loaded with [H-3]NA and the release of radioactivity at rest and in response to field stimulation was determined, The alpha(2)-adrenoceptor agonist s, clonidine and dexmedetomidine inhibited the stimulation-evoked rele ase of NA from spinal cord slices, whereas alpha(2)-adrenoceptor antag onists yohimbine and CH-38083 (7,8-(methylenedioxy)-14-alpha-hydroxyal loberbane HCl), enhanced it, ARC 239, a selective alpha(2B)-antagonist , had no effect on the release, In contrast, BRL 44408 a selective alp ha(2A)-antagonist increased the release of NA. Our results indicate th at the negative feedback modulation of NA release from noradrenergic f ibres in the spinal cord is mediated via alpha(2A) subtype of alpha(2) -adrenoceptors. Copyright (C) 1997 Elsevier Science Inc.