Pain
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Comparative Study
Involvement of local cholecystokinin in the tolerance induced by morphine microinjections into the periaqueductal gray of rats.
The ventrolateral periaqueductal gray (PAG) is a key structure for the development of opioid tolerance. An increased activity of 'anti-opioids' like cholecystokinin (CCK) has been proposed as a possible mechanism for opioid tolerance. The present study evaluates the role of PAG-located CCK in the opioid tolerance induced by repeated microinjections of morphine (MOR) into PAG. ⋯ These results show that CCK has anti-opioid activity in PAG and that tolerance to MOR in PAG can be prevented or reversed if CCK receptors are blocked with PRO. Finally, opioid tolerance induced by repeated systemic MOR injections (5mg/kg intraperitoneal ) was reversed by a single microinjection of PRO into PAG. This emphasizes the central importance of PAG in the MOR/CCK interactions that lead to opioid tolerance.
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Comparative Study
'CatWalk' automated quantitative gait analysis as a novel method to assess mechanical allodynia in the rat; a comparison with von Frey testing.
A characteristic symptom of neuropathic pain is mechanical allodynia. In animal models of neuropathic pain, mechanical allodynia is often assessed using von Frey filaments. Although the forces applied with these filaments are highly reproducible, there are various disadvantages of using this method. ⋯ We demonstrate that these rats minimise contact with the affected paw during locomotion, as demonstrated by a reduction in stance phase and pressure applied during stance. Moreover, these parameters show a high degree of correlation with mechanical withdrawal thresholds as determined by von Frey filaments. We therefore suggest that the CatWalk method might serve as an additional tool in the investigation of mechanical allodynia.
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Comparative Study
Anti-allodynic effect of NW-1029, a novel Na(+) channel blocker, in experimental animal models of inflammatory and neuropathic pain.
NW-1029, a benzylamino propanamide derivative, was selected among several molecules of this chemical class on the basis of its affinity for the [(3)H]batracotoxin ligand displacement of the Na(+) channel complex and also on the basis of its voltage and use-dependent inhibitory action on the Na(+) currents of the rat DRG (dorsal root ganglia) sensory neuron. This study evaluated the analgesic activity of NW-1029 in animal models of inflammatory and neuropathic pain (formalin test in mice, complete Freund's adjuvant and chronic constriction injury in rats) as well as in acute pain test (hot-plate and tail-flick in rats). Orally administered NW-1029 dose-dependently reduced cumulative licking time in the early and late phase of the formalin test (ED(50)=10.1 mg/kg in the late phase). ⋯ No effects were observed in the hot-plate and tail-flick tests up to 30 mg/kg p.o. The compound orally administered (0.1-10 mg/kg) was well tolerated, without signs of neurological impairment up to high doses (ED(50)=470 and 245 mg/kg in rat and mice Rotarod test, respectively). These results indicate that NW-1029 has anti-nociceptive properties in models of inflammatory and neuropathic pain.
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The present study examined the effect of peripheral administration of the excitatory amino acid (EAA) glutamate on the intensity of perceived pain and pressure pain thresholds (PPTs) in healthy young women (n=17) and men (n=18). Two injections separated by 25 min of 0.2 ml, 1.0M glutamate into the masseter muscle produced significantly higher scores of pain on 0-10 cm visual analogue scales (VAS) in women than in men (analysis of variance, ANOVA: P<0.001). There was no significant difference between the VAS scores for the first and the second injections in either men or women. ⋯ The reduction of PPTs in the masseter muscle following administration of glutamate in a concentration of 1.0M may reflect allodynia to mechanical stimuli. This process of sensitization was not gender-dependent. The present results suggest that injection of 1.0M glutamate into the masseter muscle may provide a useful experimental method to test sensitization and efficacy of peripheral EAA receptor antagonists in human subjects.
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Comparative Study
The pain vigilance and awareness questionnaire (PVAQ): further psychometric evaluation in fibromyalgia and other chronic pain syndromes.
In chronic pain patients, preoccupation with or attention to pain is associated with pain-related fear and perceived pain severity. The current study investigated psychometric properties of the pain vigilance and awareness questionnaire (PVAQ). An exploratory factor analysis on Dutch fibromyalgia patients indicated that a two-factor solution was most suitable. ⋯ The uniqueness of the attention to changes in pain subscale was also supported by an exploratory factor analysis on all items of the PVAQ, PCS, PASS, and TSK which showed that all items from that scale loaded on one separate factor. Overall, the PVAQ showed good internal consistency. Implications for future research and treatment interventions are discussed.