Role of Neurokinins in Referred Visceral Pain and Hyperalgesia

The tachykinin family of peptide neurotransmitters are involved both in the control of intestinal motility and secretion, and in the pain and hyperalgesia (80). One of the most ubiquitous tachykinins, substance P, is present in a very high proportion of visceral afferent neurons ( > 80%) (81) and is thought to play a very significant role in visceral pain and hyperalgesia. For instance, mice with a deletion of the substance P receptor (NK1) show profound alterations in the visceral pain and hyperalgesia normally evoked by sensitizing noxious stimuli like those applied to the viscera (55).

The role of tachykinin NK1 receptors in the responses of spinal neurons to the stimulation of colon afferents after the induction of acute colonic inflammation in rats has been studied using selective tachykinin NK1 receptor antagonists (58). It was shown that NK1 receptors are involved in the enhanced responses of viscerosomatic neurons following colo-nic inflammation (82), implicating central NK1 receptors in the expression of referred hyperalgesia. The role of tachykinin NK2 receptors in the responses of spinal neurons to the stimulation of colon afferents in normal rats, and after the induction of acute colonic inflammation has also been examined (74). The effect of cumulative doses of a selective NK2 receptor antagonist on responses to these stimuli was tested in control conditions and 45 minutes after intracolonic instillation of acetic acid. After colonic inflammation, neuronal responses to colorectal distension and pelvic nerve stimulation were significantly greater and the NK2 antagonist dose-dependently inhibited the enhanced responses to colorectal distension after inflammation (74). These observations are consistent with previous behavioral and reflex studies in rats showing that NK2 receptor antagonists inhibit the enhanced responses to gut distension evoked by inflammation induced by trinitrobenzenesulphonic acid or nematode infestation (83,84).

Baby Sleeping

Baby Sleeping

Everything You Need To Know About Baby Sleeping. Your baby is going to be sleeping a lot. During the first few months, your baby will sleep for most of theday. You may not get any real interaction, or reactions other than sleep and crying.

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