This investigation was designed to study the role of muscarinic receptor subtypes in the cardiovascular responses elicited by microinjection of cholinergic agonists in the intermediate portion of the NTS, the VLPA and VLDA areas and the IML of the spinal cord. Microinjections of L-glutamate (1.77 nmol in 20 - 50 nl in 0.9% sodium chloride solution) were used to identify these areas. Bilateral microinjections (0.02 - 2 nmollsite) of a potent M, muscarinic receptor agonist, CD, but not those of a relatively selective M, receptor agonist (McNA343; 3 nmollsite), into the intermediate portion of NTS and the VLDA induced depressor and bradycardic responses. In the VLPA these agonists elicited pressor and tachycardic effects while in the IML at T, - T3 only increase in HR was observed. Previous microinjections of a selective competitive M2,receptor antagonist (AFDX- 116; 0.8 - 1.6 nmollsite), but not those of a potent selective M, receptor antagonist (PZ; 1.5 - 2.0 nmollsite), into these areas blocked the effects of CD. These results indicate that the muscarinic receptors of M2 type may play a part in the regulation of cardiovascular function in the abovementioned cardiovascular areas in a yet unidentified manner.
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