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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)
 
 
 
 
 

Facilitation and inhibition by capsaicin of cholinergic neurotransmission in the guinea-pig small intestine.

The effects of capsaicin on [(3)H]acetylcholine release and muscle contraction were studied on the myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum preincubated with [(3)H]choline. Capsaicin concentration-dependently increased both basal [(3)H]acetylcholine release (pEC(50) 7.0) and muscle tone (pEC(50) 6.1). The facilitatory effects of capsaicin were antagonized by 1 muM capsazepine (pK (B) 7.0 and 7.6), and by the combined blockade of NK(1) and NK(3) tachykinin receptors with the antagonists CP99994 plus SR142801 (each 0.1 muM). This suggests that stimulation by capsaicin of TRPV1 receptors on primary afferent fibres causes a release of tachykinins which, in turn, mediate via NK(1) and NK(3) receptors an increase in acetylcholine release. The capsaicin-induced acetylcholine release was significantly enhanced by the NO synthase inhibitor L-N(G)-nitroarginine (100 muM). This indicates that tachykinins released from sensory neurons also stimulate nitrergic neurons and thus lead, via NO release, to inhibition of acetylcholine release. Capsaicin concentration-dependently reduced the electrically-evoked [(3)H]acetylcholine release (pEC(50) 6.4) and twitch contractions (pEC(50) 5.9). The inhibitory effects were not affected by either capsazepine, NK(1) and NK(3) receptor antagonists, the cannabinoid CB(1) antagonist SR141716A or by L-N(G)-nitroarginine. Desensitization of TRPV1 receptors by a short exposure to 3 muM capsaicin abolished the facilitatory responses to a subsequent administration, but did not modify the inhibitory effects. In summary, capsaicin has a dual effect on cholinergic neurotransmission. The facilitatory effect is indirect and involves tachykinin release and excitation of NK(1) and NK(3) receptors on cholinergic neurons. The inhibition of acetylcholine release may be due to a decrease of Ca(2+) influx into cholinergic neurons.[1]

References

  1. Facilitation and inhibition by capsaicin of cholinergic neurotransmission in the guinea-pig small intestine. Geber, C., Mang, C.F., Kilbinger, H. Naunyn Schmiedebergs Arch. Pharmacol. (2006) [Pubmed]
 
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