Neurogenic sympathetic vasoconstriction of the rabbit basilar artery

When examined by fluorescence microscopy the rabbit basilar artery contains a rich adrenergic-like plexus at the adventitiomedial junction. The fluorescence disappears upon chronic reserpinization and bilateral superior cervical ganglionectomy. Transmural stimulation of intramural nerves a results in a response which is predominantly constrictor but also contains a small, inconstant dilator component. The constrictor response is abolished by chronic reserpinization, bilateral superior cervical ganglionectomy, and cold storage of the preparation. The constriction is prevented by the adrenergic neuron blocking agents guanethidine and bretylium but not by such alpha-adrenergic receptor blocking agents as phenoxybenzamine (PBZ), phentolamine, and tolazoline. Our results show that doses of the three latter agents sufficient to abolish contractions to norepinephrine (NE) in concentrations of up to 10(-2) M only potentiate and prolong the contractile response to nerve stimulation. The beta-adrenergic receptor blocking agent, propranolol, and inhibitors of NE neuronal uptake, such as desipramine (desmethylimipramine, DMI) and cocaine, do not influence the size of the neurogenic response. These results suggest that the vasoconstrictor component of the rabbit basilar artery response to transmural nerve stimulation (TNS) is mediated via sympathetic adrenergic-like neurons, but at the same time also raise the question whether the transmission process is typical of classic adrenergic neuroeffector mechanisms.