An investigation of a sympathetic innervation of the vertebral artery in primates: is there a neurogenic substrate for vasoconstriction?

Vasoconstriction of the vertebral artery may be neurogenic in origin. Although the existence of a perivascular sympathetic plexus of the vertebral artery is not in doubt, no method used to date has conclusively demonstrated a direct sympathetic innervation of the vascular smooth muscle cells and, hence, vasomotor function. It was the aim of this study, therefore, to visualise and localise noradrenergic fibres in the wall of the vertebral artery. Intracranial vertebral artery specimens (10 vervet monkeys and 10 baboon vessels) were sectioned (40 mm serial sections) and treated with anti-tyrosine hydroxylase, anti-dopamine b-hydroxylase, and anti-chromogranin-A antibodies. Some evidence of catecholaminergic fibres in the tunica adventitia but not penetrating the external elastic lamina or tunica media of the vertebral artery wall was seen. These findings were confirmed by electron microscopy. It was concluded that although a perivascular sympathetic plexus exists, the vertebral artery of primates was not shown to have a direct sympathetic innervation and a neurogenic vasoconstrictor function is unlikely.