Cardiovascular responses to intracisternal administration of nicotine in rats.

The administration of nicotine into the cisterna magna evoked a delayed depressor effect with an initial pressor effect in anaesthetized rats. The depressor response was accompanied by a bradycardia. The cardiovascular effects of nicotine were abolished after intracisternal administration of hexamethonium but not after atropine given via the same route. Intravenous administration of methylatropine abolished the bradycardic response to nicotine but did not affect the blood pressure responses. The pressor effect of nicotine was abolished by intravenous administration of phenoxybenzamine. The cardiovascular effects of nicotine injected intracisternally were abolished when the diffusion of nicotine onto an area around the area postrema was interrupted using a polyethylene tube. In contrast, nicotine applied to the area produced a marked pressor--depressor response. It is concluded that the cardiovascular responses to intracisternal administration of nicotine result from the activation of central nicotinic receptor sites that may be present around the area postrema.