Inhibition by locally applied alpha-adrenoreceptor blocking drugs of the depressor response to stimulation of the anterior hypothalamus.

Cats were anaesthetized with pentobarbital sodium and the anterior hypothalamus was superfused with artificial cerebrospinal fluid through a push-pull cannula. Electrical stimulation of the superfused area with the tip of the cannula elicited a fall of the arterial blood pressure which was dependent on frequency and voltage. Maximal depressor response was obtained at 60 Hz with 2-4V; further increase of the voltage often led to a rise of the arterial blood pressure. Superfusion of the anterior hypothalamus with the alpha-adrenoreceptor blocking drugs tolazoline, piperoxan, yohimbine or phentolamine caused a dose-dependent inhibition of the depressor response to hypothalamic stimulation. Tolazoline was less effective than the other drugs. Superfusion of the anterior hypothalamus with the alpha-sympathomimetic drug phenylephrine prior to and during superfusion with phentolamine abolished the inhibitory action of the latter drug. It is concluded that alphaadrenoreceptors are present in the anterior hypothalamus and involved in the depressor response to electrical stimulation of this hypothalamic area.