INHIBITION BY LOCALLY APPLIED ALPHA-ADRENORECEPTOR BLOCKING-DRUGS OF DEPRESSOR RESPONSE TO STIMULATION OF ANTERIOR HYPOTHALAMUS

Cats were anesthetized with pentobarbital sodium and the anterior hypothalamus was superfused with artificial CSF 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 2-4 V; 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. .alpha.-Adrenoreceptors are present in the anterior hypothalamus and involved in the depressor response to electrical stimulation of this hypothalamic area.