Responses of rat spinal neurons to distension of inflamed colon: role of tachykinin NK2 receptors.

Tachykinin NK2 receptors are implicated in nociception and the control of intestinal motility. Here we examined their involvement in responses of spinal lumbosacral neurons with colon input to distension of normal or inflamed colon in anesthetized rats. The responses of single neurons to colorectal distension (5-80 mmHg), to electrical stimulation of the pelvic nerve (bypassing sensory receptors) and to somatic stimulation were characterized. The effect of cumulative doses of an NK2 receptor antagonist, MEN 11420 (10-1000 microg kg(-1) IV), on responses to these stimuli was tested in control conditions (n=6), or 45 min after intracolonic instillation of acetic acid (n=6). After colonic inflammation, neuronal responses to colorectal distension and pelvic nerve stimulation were significantly greater. MEN 11420 dose-dependently inhibited the enhanced responses to colorectal distension after inflammation (ID50=402+/-14 microg kg(-1)), but had no significant effect on responses to pelvic nerve stimulation or distension of the normal colon, suggesting a peripheral action selective for the inflamed colon. We conclude that MEN 11420 possesses peripheral anti-hyperalgesic effects on neuronal responses to colorectal distension. These results provide a neurophysiological basis for a possible use of tachykinin NK2 receptor antagonists in treating abdominal pain in irritable bowel syndrome patients.

Deficits in visceral pain and hyperalgesia of mice with a disruption of the tachykinin NK1 receptor gene.

Studies in mice lacking genes encoding for substance P or its receptor (NK1), or with NK1 antagonists, have shown that this system contributes to nociception, but the data are complex. Here, we have further examined the role of NK1 receptors in pain and hyperalgesia by comparing nociceptive responses to mechanical and chemical stimulation of viscera and the resulting hyperalgesia and inflammation in NK1 knockout (-/-) and wild-type (+/+) mice. We concentrated on visceral nociception because substance P is expressed by a much greater proportion of visceral than cutaneous afferents. NK1 -/- mice showed normal responses to visceral mechanical stimuli, measured as behavioural responses to intraperitoneal acetylcholine or hypertonic saline or reflex responses to colon distension in anaesthetized mice, although -/- mice failed to encode the intensity of noxious colon distensions. In contrast, NK1 -/- mice showed profound deficits in spontaneous behavioural reactions to an acute visceral chemical stimulus (intracolonic capsaicin) and failed to develop referred hyperalgesia or tissue oedema. However, in an identical procedure, intracolonic mustard oil evoked normal spontaneous behaviour, referred hyperalgesia and oedema in -/- mice. The inflammatory effects of capsaicin were abolished by denervation of the extrinsic innervation of the colon in rats, whereas those of mustard oil were unchanged, showing that intracolonic capsaicin evokes neurogenic inflammation, but mustard oil does not. Tests of other neurogenic inflammatory stimuli in NK1 -/- mice revealed impaired behavioural responses to cyclophosphamide cystitis and no acute reflex responses or primary hyperalgesia to intracolonic acetic acid. We conclude that NK1 receptors have an essential role mediating central nociceptive and peripheral inflammatory responses to noxious stimuli that evoke neurogenic inflammation, and modulating responses to noxious mechanical stimuli. We propose that two separate hyperalgesia pathways exist, one of which is NK1 receptor dependent, whereas the other does not require intact substance P/NK1 signalling.

Responses of rat spinal neurones to natural and electrical stimulation of colonic afferents: effect of inflammation.

Single unit electrical activity has been recorded from 107 neurones excited by electrical stimulation of the pelvic nerve in or around lamina X of the L6-S1 spinal cord in anaesthetised rats. Responses to colorectal distension (CRD; 30 s, 5-80 mmHg) and to somatic electrical and mechanical stimulation were characterised. Of 107 neurones excited by pelvic nerve stimulation, 58 (54%) were affected by CRD: 46 neurones were excited (39 with a sustained response and 7 with an on-off response) and 12 neurones were inhibited. The vast majority of the neurones affected by CRD (54/58) had nociceptive somatic receptive fields. Neurones excited by CRD showed graded stimulus response functions in the noxious range (20-80 mmHg), except for two neurones which only encoded stimulus intensity below 20 mmHg. Neurones inhibited by CRD had significantly larger somatic receptive fields, and more superficial recording sites than those excited by CRD. A group of 12 neurones with sustained excitatory responses to CRD were characterised before and 45 min after intracolonic instillation of 1 ml 0.6% acetic acid. Colon inflammation provoked a significant increase in responses to CRD and to pelvic nerve stimulation (n=12), but no significant change in responses to pinch of their somatic receptive field (n=10). We conclude that of these neurones, the population with excitatory sustained responses to CRD are those likely responsible for processing information leading to acute pain sensations from the colon, and also show central sensitisation after colon inflammation, suggesting they play an important role in development of colonic hyperalgesia.

Neurogenic vasodilation in rabbit basilar isolated artery: involvement of calcitonin-gene related peptide.

Neurogenic vasodilation in cranial arteries may be an important mechanism in the pathogenesis of migraine headache. We describe a novel, in vitro assay to characterise neurogenic vasodilator responses in endothelium-denuded segments of rabbit isolated basilar artery, with particular focus on calcitonin-gene related peptide (CGRP). In arterial segments precontracted with prostaglandin F(2alpha), relaxations evoked by exogenously applied alphaCGRP (EC(50)=2.9 nM) were inhibited by alphaCGRP-(8-37) (pA(2)=6.49) or by desensitisation resulting from prior exposure to alphaCGRP. Relaxations evoked by exogenously applied vasoactive intestinal polypeptide (VIP) (EC(50)=2.5 nM) were inhibited by VIP-(7-28) 1 microM. The 5-HT(1) receptor agonists L-771,331 ((3S)-3[N-(S)-alpha-methylbenzyl]aminomethyl-(S)-1-[2-(5-(2-oxo-1, 3-oxazolidin-4-ylmethyl)-1H-indol-3-yl)ethyl]pyrrolidine) and sumatriptan exerted contractile effects (EC(50)=293 and 95 nM, respectively). In neurogenic experiments, vasodilation evoked by electrical field stimulation was markedly attenuated by pre-treatment with capsaicin (10 microM) or by prior CGRP receptor desensitisation and to a lesser extent by pre-treatment with VIP-(7-28) 1 microM. L-771,331 (100 nM) exerted a weak inhibitory effect, marked only by a short reduction in the recovery time (post-electrical stimulation) and sumatriptan (30 nM) had no effect. The neurogenic response was potentiated by alphaCGRP-(8-37) 1 microM (reversible on wash-out). Short application (5-10 min) of capsaicin (10 microM) produced vasodilation that was inhibited by alphaCGRP-(8-37) 1 microM. These data suggest that electrically evoked neurogenic vasodilation in rabbit basilar artery has a large component resulting from the release of sensory neuropeptides in particular CGRP and a smaller component involving the release of VIP.

Antinociceptive activity of metamizol in rats with experimental ureteric calculosis: central and peripheral components.

OBJECTIVE AND DESIGN: To study the antinociceptive effects of metamizol in a rat model of ureteric calculosis. SUBJECTS: Adult female Wistar rats (n = 40). TREATMENT: Metamizol was given i.p. 50-100 mg/kg, 3 times daily for 4 days for behavioural testing, and 25-100 mg/kg i.v. whilst recording peristalsis or dorsal horn neurons. METHODS: An artificial stone was induced in one ureter. In 3 separate groups of stone-implanted rats, behaviour was recorded continuously on video tape, ureteric peristalsis or the electrical activity of single nociceptive dorsal horn neurons with ureteric input was recorded under anaesthesia. Data were compared with analysis of variance. RESULTS: Metamizol inhibited the behavioural visceral crises, the abnormal ureteric peristalsis and the activity of nociceptive dorsal horn neurons. CONCLUSIONS: Metamizol has central antinociceptive effects on the pain produced by a ureteric stone, and an additional spasmolytic effect on the hyperperistalsis produced by the stone.

Cyclophosphamide cystitis in mice: behavioural characterisation and correlation with bladder inflammation.

The generation of transgenic 'knock-out' mice which lack genes relevant to pain is becoming increasing common. However, only one visceral pain model, the writhing test, is available in mice. The aim of this study was to adapt cyclophosphamide cystitis, a model of inflammatory visceral pain described in rats, for use in mice, and to characterise its behavioural effects. The toxic metabolites of systemically-administered cyclophosphamide are excreted in the urine, and induce bladder inflammation. We compared the effects of cyclophosphamide (100 and 300 mg/kg i.p., 4 h survival period) and vehicle (saline) in male mice on spontaneous behaviour (4 h continuous video-tape, and a 5-min Open Field test after 4 h). Involvement of the urinary bladder and other abdominal tissues was assessed by macroscopic examination and measurement of Evan's Blue plasma extravasation. Cyclophosphamide (300 mg/kg) produced significant changes in behaviour, including 22 +/- 6 min of 'crises' of visceral pain-related behaviour and a 53% reduction in activity, and also induced haemorrhage and substantial plasma extravasation in the bladder, but no change in other abdominal tissues. We conclude that cyclophosphamide cystitis has many advantages as a model of sub-acute, inflammatory visceral pain in mice. It does not require surgery or intubation, and we have found it to produce consistent, reproducible and quantifiable behavioural changes, which are significantly correlated with the degree of bladder inflammation in the absence of inflammation of other abdominal tissues. Copyright 1999 European Federation of Chapters of the International Association for the Study of Pain.