Abstract
Previous studies in our laboratory have shown that electrical stimulation of both cervical sympathetic trunks (CSTs) produces an initial-increase and a late-decrease of regional cerebral blood flow (rCBF) in the neocortex, by an activation of β- and α-adrenergic receptors, respectively. The responses reached about 10% in both adult and aged rats. Neurodegenerative disorders such as Alzheimer's disease are known to involve early olfactory deficits and typical histopathological lesions in the olfactory bulb. Thus, it seems important to determine nature and aging of the sympathetic neural regulation of rCBF in the olfactory bulb. In the present study, the effects of repetitive electrical stimulation of CSTs for 1 min at various frequencies and supramaximum intensity on rCBF in the olfactory bulb were studied using laser Doppler flowmetry in adult (4-6 mo) and aged (18-21 mo) male Wistar rats anesthetized with urethane. In adult rats, stimulation at 0.5-30 Hz produced frequency-dependent decreases in rCBF, by up to 31±4% of the prestimulus control flow. In aged rats, the decreased response was produced at 10-30 Hz, by up to 14±2%. The responses were abolished by an i.v. administration of the α-adrenergic blocker phenoxybenzamine, in both age groups. These results indicate that, in the olfactory bulb, blood vessels are constricted by sympathetic nerve fibers via activation of α-adrenergic receptors; the effectiveness of this regulation declines with age. [J Physiol Sci. 2008;58 Suppl:S154]
