Brain stem sites mediating adrenergic and non-adrenergic vasodilatation in the dog's nose and tongue

Abstract

The brain stem of anesthetized, immobilized and artificially ventilated dogs was probed with concentric bipolar electrodes, and those points were determined from which vasodilatation or vasoconstriction of the nose and tongue could be elicited by electrical stimulation of the brain stem (ESB). Blood flow was measured with electromagnetic flowprobes in the lingual (LA) and the infraorbital (IA) arteries. Arterial blood pressure, heart rate and temperatures of the ear and hindlimb were measured. The following results were obtained: (1) vasodilatation by ESB in the LA and/or IA could be induced from an area extending parasagittally through the ventral part of the brain stem from the hypothalamus to the upper pontine region. The most potent area was in the supraoptic area of the anterior hypothalamus, but no representation was found in the dorsolateral part of the central gray matter, one of the most excitable mesencephalic vasodilatator areas in the defence reaction. Sites in which ESB was followed by vasoconstriction in LA and IA were distributed in regions closely related to the dilatator sites within the brain stem; (2) the vasodilatation in LA and IA was not correlated with changes in skin temperatures of the ear and hindlimb; (3) blood pressure and heart rate decreased, in general, during ESB; (4) the additional analysis revealed that vasodilatation by ESB; (a) was not altered by atropine; (b) was abolished by transection of the cervical vagosympathetic trunk only in IA; (c) was abolished by spinal cord transection at C 2 only in IA; and (d) was abolished only in IA by either preceding catecholamine depletion with reserpine or by blockade of alpha-adrenergic receptors with phenoxybenzamine, and disappeared in both LA and IA after ganglionic blockade with hexamethonium; (5) the results demonstrate circumscribed vasoconstrictor as well as vasodilator sites in the brain stem influencing nose and tongue blood flow. The centrally elecited atropine resistant vasomotor responses of the nose are mediated by adrenergic fibres, which are conducted in the cervical sympathetic trunk. In contrast, the centrally elecited vasodilatation of the tongue is due to non-adrenergic, non-cholinergic efferents with pre- and postganglionic synapses running apart from the cervical sympathetic trunk. The anatomical origin of these efferents suggests that they belong to the parasympathetic section of the autonomic nervous system.