Effects of locus coeruleus stimulation on carotid vascular resistance in the cat

The locus coeruleus was stimulated in 62 cats in order to investigate the effect on cephalic blood flow and cephalic vascular resistance. Flow was measured by electromagnetic flow probes applied to the common carotid artery. Stimulation over a range of frequencies (0.2-200 s-1) produced a frequency-dependent fall in carotid vascular resistance, greater on the ipsilateral side. This response was not affected by either cervical sympathectomy or spinal cord section. The response was blocked by bilateral section of the facial nerve but was not abolished by classical cholinergic, histaminergic or adrenergic blocking agents. Stimulation of the locus coeruleus also resulted in a pressor response through spinal mechanisms in which coeruleo-hypothalamic projections were not involved. A post-stimulation constriction in the carotid vasculature followed the dilator response and was attributed to release of catecholamines from the adrenal medulla.