Effects of muscarinic receptor agonists and antagonists on qadrenoceptors in rat brain

The specific binding of [ 3 Hlclonidine to a,-adrenoceptors on neural membranes isolated from six brain areas was determined with rats treated for various periods of time with the muscarinic agonists, oxotremorine or pilocarpine, or with the muscarinic antagonists atropine, atropine methyl nitrate, scopolamine and scopolamine methyl bromide. Administration of pilocarpine, 10 mg/kg, twice daily i.p. for 1 and 14 days increased markedly the number of a,-adrenoceptors on neural membranes from all six brain areas. In contrast, oxotremorine, 0.3 mg/kg, twice daily i.p., for 7 days decreased the number of a,-adrenoceptors on membranes from all brain areas except the brainstem and caudate nucleus. Both atropine and scopolamine increased the density of a,-adrenoceptors in specific brain areas. Neither atropine methyl nitrate nor scopolamine methyl bromide had an appreciable effect upon the specific binding of [ 3 Hlclonidine to neural membranes from most brain areas.