Heterogeneity of neurogenic responses in intra‐ and extrameningeal arteries of dogs

Abstract

. Neurogenic responses to transmural electrical stimulation were examined in endothelium‐denuded extrameningeal (vertebral and carotid) and intrameningeal (spinal, basilar and middle cerebral) arteries isolated from dogs. . In the extrameningeal arteries, transmural electrical stimulation produced a phasic contraction. This contraction was abolished by tetrodotoxin, prazosin and guanethidine. However, α,β‐methylene ATP and NG‐nitro‐L‐arginine (1‐NOARG) had no significant effect on the contractile responses. . In the intrameningeal arteries, the neurogenic responses to electrical stimulation were composed of a transient contraction and relaxation. The transient contraction was selectively inhibited by guanethidine or after desensitization of P2x‐purinoceptors with α,β‐methylene ATP. L‐NOARG abolished the relaxation but not the contraction induced by electrical stimulation. Prazosin had no effect on either neurogenic response. . Noradrenaline produced a large contraction in the extrameningeal arteries which was selectively inhibited by prazosin. α,β‐Methylene ATP produced neither contraction nor inhibition of the response to noradrenaline in the extrameningeal arteries. . In the intrameningeal arteries, α,β‐methylene ATP produced a greater contraction than noradrenaline. The response to α,β‐methylene ATP was selectively abolished by desensitization of P2X‐purinoceptors with α,β‐methylene ATP itself. The contractile response to noradrenaline was inhibited by rauwolscine but not by prazosin. . ATP produced endothelium‐dependent relaxations in the extrameningeal and intrameningeal arteries, which were attenuated by endothelium removal. . NADPH diaphorase‐positive fibres were dense in the middle cerebral and basilar arteries but rare or absent in the spinal artery. In the extrameningeal arteries diaphorase‐positive traces were observed in the vasa vasorum. . The present findings indicate that the neurogenic responses of intrameningeal arteries of dogs are composed of NO‐ergic and sympathetic purinergic components, while the extrameningeal arteries tested produced only sympathetic adrenergic responses, suggesting that regional heterogeneity may be associated with a sudden transition in innervation and receptor expression at the meninx. 1995 British Pharmacological Society