Vasodilator innervation of small cerebral arteries of guinea pigs.

The neuronal influence on the resistance of cerebral arteries was analyzed in middle cerebral arteries of guinea pigs. Calcitonin gene-related peptide- and vasoactive intestinal peptide-immunoreactive nerves and NADPH-diaphorase-positive nerves were present in the distal portion of the middle cerebral artery. Isolated middle cerebral arteries were cannulated and perfused at a constant flow rate (1 ml/min) and the perfusion pressure was monitored. Prostaglandin F2 alpha (PGF2 alpha) and K+ (50 mM) elicited a sustained increase of the perfusion pressure (vasoconstriction), while noradrenaline and 5-hydroxytryptamine caused only a slight constriction. Electrical field stimulation (FS) at 8 Hz did not elicit a contractile response. In tissues precontracted with PGF2 alpha, FS induced a tetrodotoxin-sensitive vasodilator response. Endothelium-denudation and removal of the effect of sensory nerves by capsaicin-treatment did not affect the FS-induced vasodilation. In contrast, nitro-L-arginine, an inhibitor of NO formation, attenuated the FS-induced vasodilatation. These results show that the resistance of the cerebral vessels of guinea pigs is under the influence of vasodilator nerves and that the neurogenic vasodilator mechanism involves NO synthesis.