RELATIONSHIP BETWEEN MUSCARINIC RECEPTOR SUBTYPES AND CYCLIC-NUCLEOTIDES IN PONS-MEDULLA OBLONGATA

AIM: To study the relationship between muscarinic receptor (M-R) subty pes and cyclic nucleotides in pons-medulla oblongata (MeOb). METHODS: The contents of cGMP and cAMP in Sprague-Dawley rat pons-MeOb, cerebel lum and cerebral cortex were assayed by radioimmunoassay and competiti ve protein-binding assay, respectively, after ip injections of drugs. Control rats were given ip normal saline. RESULTS: M(1)-R agonist pilo carpine (6, 15 mg kg(-1), ip) increased the content of cGMP in the pon s-MeOb and cerebral cortex, but did not bring about any noticeable cha nge in the cAMP content. The increase of cGMP was antagonized by ip pi renzepine or scopolamine. On the other hand, ip M(2)-R agonist 6 beta- acetoxy nortropane (6 beta-AN) 25 mu g kg(-1) reduced not only cAMP co ntents in the pons-MeOb and cerebellum but also cGMP contents in the p ons-MeOb and cerebral cortex, while 6 beta-AN 12 mu g kg(-1) only lowe red cAMP content. The decreases of cGMP and cAMP induced by 6 beta-AN were antagonized by ip AF-DX 116 or atropine, respectively. CONCLUSION : Stimulation of M(1)-R causes the increase of cGMP and that of M(2)-R induces the decreases of both cGMP and cAMP in the pons-MeOb.