Brainstem nicotinic receptor subtypes that influence intragastric and arterial blood pressures

The purpose of this study was to investigate the effect of microinjection o f nicotine and nicotinic receptor antagonists into the dorsal motor nucleus of the vagus (DMV) or medial subnucleus of the tractus solitarius (mNTS) o n intragastric (IGP) and arterial blood pressures (BP) in anesthetized rats . Nicotine microinjected into the DMV (10-300 pmol) produced dose-related i ncreases in IGP (ED50 = 89 pmol); no significant changes were noted for BP. Ipsilateral vagotomy abolished nicotine-induced increases in IGP. Nicotine microinjected into the mNTS in a dose range of 0.1 to 300 pmol produced do se-related decreases in IGP (ED50 = 0.6 pmol) and BP (ED50 = 5.4 pmol). Bil ateral vagotomy abolished nicotine-induced decreases in IGP while having no effect on BP. In rats treated with daily s.c. injections of nicotine (0.8 mg/kg of base) for 10 days, microinjections of nicotine into the DMV produc ed similar increases in IGP. BP responses from the mNTS were not affected b y chronic treatment. However, nicotine microinjections into the mNTS no lon ger produced a decrease in IGP in these chronically treated animals. alpha- Bungarotoxin (100 pmol) significantly blocked nicotine-evoked increases in IGP from the DMV while having no effect on nicotine-induced responses elici ted from the mNTS. Hexamethonium (10 and 100 pmol) microinjected into the m NTS dose-dependently blocked nicotine-induced effects but did not interfere with the action of nicotine at the DMV. Our data indicate that nicotine-in duced changes in IGP result from nicotine acting at two sites, the DMV and mNTS; and that at least three different nicotinic receptors in the dorsal m edulla oblongata can influence gastrointestinal and cardiovascular function .