Gastroenterology

Gastroenterology

Volume 130, Issue 6, May 2006, Pages 1729-1742
Gastroenterology

Basic–alimentary tract
The Role of Neurokinin 1 Receptors in the Maintenance of Visceral Hyperalgesia Induced by Repeated Stress in Rats

Presented in part at the 2005 annual meeting of the American Gastroenterological Association in abstract form (Gastroenterology 2005;128:A-494).
https://doi.org/10.1053/j.gastro.2006.01.037Get rights and content

Background & Aims: The neurokinin 1 receptors (NK1Rs) and substance P (SP) have been implicated in the stress and/or pain pathways involved in chronic pain conditions. Here we examined the participation of NK1Rs in sustained visceral hyperalgesia observed in rats exposed to chronic psychological stress. Methods: Male Wistar rats were exposed to daily 1-hour water avoidance stress (WA) or sham WA for 10 consecutive days. We tested intraperitoneal or intrathecal injection of the NK1R antagonist SR140333 on the visceromotor reflex to colorectal distention in both groups at day 11. Real-time reverse-transcription polymerase chain reaction, Western blot, and immunohistochemistry were used to assess the expression of NK1Rs and/or SP in samples of colon, spinal cord, and dorsal root ganglia. Results: Both intraperitoneal and intrathecal SR140333 injection diminished the enhanced visceromotor reflex to colorectal distention at day 11 in stressed rats but did not affect the response in control animals. Real-time polymerase chain reaction and Western blotting demonstrated stress-induced up-regulation of spinal NK1Rs. Immunohistochemistry showed an increased number of NK1R-expressing neurons in the laminae I of the dorsal horn in stressed rats. The expression of NK1Rs was decreased in colon from stressed rats compared with control. The expression of SP gene precursor in dorsal root ganglia was unchanged in stressed rats compared with controls. Conclusions: Stress-induced increased NK1R expression on spinal neurons and the inhibitory effect of intrathecal NK1R antagonist on visceral hyperalgesia support the key contribution of spinal NK1Rs in the molecular pathways involved in the maintenance of visceral hyperalgesia observed after chronic WA.

Section snippets

Animals

Adult male Wistar rats (250–275 g) were purchased from Harlan (Indianapolis, IN). Animals were maintained on a normal light-dark cycle, housed in pairs or singly when equipped with a chronic intrathecal catheter. They were provided with food and water ad libitum. All protocols were approved by the Institutional Animal Care and Use Committee at the VA Greater Los Angeles Healthcare System (Los Angeles, CA).

Implantation of electromyographic electrodes

Adult male rats were deeply anesthetized with pentobarbital sodium (45 mg/kg, Nembutal;

IP injection of the NK1R antagonist SR140333

There was a significant increase of the VMR following repeated exposure to WA stress at day 11 (CRD#2) compared with baseline (CRD#1). The increase was significant for the pressures of 40 and 60 mm Hg (P < .05, repeated-measures ANOVA followed by Bonferroni posttest). One hour later, the effect of systemic application of the NK1R antagonist SR140333 (at the previously established dose of 1 mg/kg27) or vehicle was tested on the VMR to CRD#3. As shown in Figure 1A, SR140333 abolished the

Discussion

The present study expands on previous observations that repeated psychological stress in male Wistar rats results in a phenotype characterized by increased autonomic responsiveness, anxiety-like behavior, and sustained visceral hyperalgesia, consistent with stress sensitization.35 Our results point to a major role for the SP/NK1R signaling system in mediating the visceral hyperalgesia component of this model, because the stress-induced exaggerated VMR to CRD was abolished by intrathecal

Summary and Conclusions

The findings from the present study show an up-regulation of NK1R on spinal neurons in a model of chronic WA stress associated with sustained visceral hyperalgesia. The pharmacologic efficacy of a spinal treatment with an NK1R antagonist to abolish the enhanced visceral response in this model suggests an important contribution of the spinal NK1R-expressing neurons in visceral hyperalgesia. The lack of enhanced SP gene expression in DRG or enhanced SP spinal release suggests that increased

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  • Cited by (0)

    Supported by National Institutes of Health grants P50 DK64539 (to E.A.M.), R24 AT00281 (to E.A.M.), DK47343 (to C.P.), DK41301 Morphology and Imaging Core (to C.S.) and Antibody Core (to G.O.), R01 DK57037 (to C.S.), and DK54155 (to C.S.); a Fellowship Award from the Crohn’s and Colitis Foundation (to S.S.); GlaxoSmithKline (Neurology and GI Centre of Excellence for Drug Discovery, Harlow, England); and R21 DK071767-01 (to S.B.).

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