Involvement of postsynaptic α1- and α2-adrenoceptors in the flexor reflex activity in the spinal Rats

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Abstract
Clonidine (0.2 mg/kg i.v.) and St 587 (1 mg/kg i.v.), selective agonsists ofα 2- andα 1-adrenoceptors, respectively, increased the flexor reflex amplitude in the spinal rat. Yohimbine and rauwolscine,α 2-adrenoceptor antagonists, inhibited dose-dependently the effect of clonidine but not of St 587. However, prazosin and clozapine,α 1-adrenoceptor antagonists, diminished the action of both agonists in a dose-dependent manner. After central chemosympathectomy caused by 6-OH-DA or DSP-4 the response to clonidine did not differ from that in the sham-operated animals. In 6-OH-DA treated rats yohimbine (1 mg/kg i.v.) antagonized the effect of clonidine to the same extent as it did in unlesioned animals. It is concluded that the results are functional evidence thatα 1- andα 2-adrenoceptors are present in the rat spinal cord, and stimulation of each receptor increases flexor reflex activity.