HETEROGENEITY OF NEUROGENIC RESPONSES IN INTRAMENINGEAL AND EXTRAMENINGEAL ARTERIES OF DOGS

1 Neurogenic responses to transmural electrical stimulation were exami ned in endothelium-denuded extrameningeal (vertebral and carotid) and intrameningeal (spinal, basilar and middle cerebral) arteries isolated from dogs. 2 In the extrameningeal arteries, transmural electrical st imulation produced a phasic contraction. This contraction was abolishe d by tetrodotoxin, prazosin and guanethidine. However, alpha,beta-meth ylene ATP and N-G-nitro-L-arginine (L-NOARG) had no significant effect on the contractile responses. 3 In the intrameningeal arteries, the n eurogenic responses to electrical stimulation were composed of a trans ient contraction and relaxation. The transient contraction was selecti vely inhibited by guanethidine or after desensitization of P-2X-purino ceptors with alpha,beta-methylene ATP. L-NOARG abolished the relaxatio n but not the contraction induced by electrical stimulation. Prazosin had no effect on either neurogenic response. 4 Noradrenaline produced a large contraction in the extrameningeal arteries which was selective ly inhibited by prazosin. alpha,beta-Methylene ATP produced neither co ntraction nor inhibition of the response to noradrenaline in the extra meningeal arteries. 5 In the intrameningeal arteries, alpha,beta-methy lene ATP produced a greater contraction than noradrenaline. The respon se to alpha,beta-methylene ATP was selectively abolished by desensitiz ation of P-2X-purinoceptors with alpha,beta-methylene ATP itself. The contractile response to noradrenaline was inhibited by rauwolscine but not by prazosin. 6 ATP produced endothelium-dependent relaxations in the extrameningeal and intrameningeal arteries, which were attenuated by endothelium removal. 7 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 trac es were observed in the vasa vasorum. 8 The present findings indicate that the neurogenic responses of intrameningeal arteries of dogs are c omposed of NO-ergic and sympathetic purinergic components, while the e xtrameningeal arteries tested produced only sympathetic adrenergic res ponses, suggesting that regional heterogeneity may be associated with a sudden transition in innervation and receptor expression at the meni nx.