Sympathetic neural regulation of olfactory bulb blood flow in adult and aged rats.

Sympathetic adrenergic nerves originating in the superior cervical ganglia innervate cerebral blood vessels. The present study aimed to characterize olfactory bulb blood flow changes in response to cervical sympathetic trunk (CST) stimulation. Further, we compared the sympathetic control of olfactory bulb blood flow in adult (4-6 mo) and aged (18-21 mo) Wistar rats. Under urethane anesthesia, trains of electrical stimuli were applied to the CST for periods of 1 min while olfactory bulb blood flow was measured with laser Doppler flowmetry. In adult rats, stimulation at 5-30 Hz produced frequency-dependent decreases in CBF of as much as 31+/-4% (at 30 Hz). In aged rats, blood flow decreases occurred in response to stimulus trains ranging from 10-30 Hz, but the largest average decreases were 15+/-2% (at 20 Hz). Blood flow was significantly decreased from pre-stimulus flow in both adult and aged rats, and the stimulus-induced changes in flow were larger in adult compared with aged rats. Blood flow responses were abolished by i.v. administration of the alpha-adrenergic blocker phenoxybenzamine, in both age groups. These results indicate that blood vessels in the rat olfactory bulb are constricted by sympathetic nerve fibers via activation of alpha-adrenergic receptors, and the effectiveness of this regulation declines in aged rats.