Posterior hypothalamic control of rabbit tracheal tension and involvement of central histaminergic neurons

The hypothalamus is involved in the control of the cardiovascular system, but airway tone is less well defined. In the posterior hypothalamus, histaminergic neuronal cell bodies are located. Effects of electrical stimulation in the posterior hypothalamus on tracheal tension and the cardiovascular system were examined in anesthetized, paralyzed and artificially ventilated rabbits. Tracheal tension was determined from pressure exerted on a balloon inserted in the trachea and measured by a pressure transducer. Electrical stimulation of the posterior hypothalamus caused tracheal tension to decrease, arterial blood pressure to increase, and mild tachycardia followed by bradycardia. The tracheal tension decrease induced by posterior hypothalamic stimulation was not affected by atropine nor by transection of either the superior laryngeal nerve or the vagus nerve, but was depressed by adrenoceptor blockade. Tracheal tension decrease was also reduced by pyrilamine, a histamine H1-receptor antagonist, administered into the fourth ventricle, but was not affected by cimetidine, a histamine H2-receptor antagonist. The stimulation sites where these effects were evoked were interspersed among the loci of histamine immunoreactive cell bodies previously reported. Results suggest that posterior hypothalamic neurons decrease tracheal tension through the sympathetic nervous system, and involve the histaminergic neurons in this route.