Pain
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Several theories about musculoskeletal pain syndromes such as whiplash-associated disorder (WAD) suggest that pain and muscle activity interact and may contribute to the chronicity of symptoms. Studies using surface electromyography (sEMG) have demonstrated abnormal muscle activation patterns of the upper trapezius muscles in the chronic stage of WAD (grade II). There are, however, no studies that confirm that these muscle reactions are initiated in the acute stage of WAD, nor that these muscle reactions persist in the transition from acute neck pain to chronic neck pain disability. ⋯ Furthermore, follow-up assessments of the EMG level during these two tasks, did not show a time related change. In conclusion, in subjects with future disability, the acute stage is characterized by a reorganization of the muscular activation of neck and shoulder muscles, possibly aimed at minimizing the use of painful muscles. This change of motor control, is in accordance with both the (neurophysiological) 'pain adaptation model' and (cognitive behavioral) 'fear avoidance model'.
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Comparative Study
Affective associative learning modifies the sensory perception of nociceptive stimuli without participant's awareness.
The present experiment examined the possibility to change the sensory and/or the affective perception of thermal stimuli by an emotional associative learning procedure known to operate without participants' awareness (evaluative conditioning). In a mixed design, an aversive conditioning procedure was compared between subjects to an appetitive conditioning procedure. Both groups were also compared within-subject to a control condition (neutral conditioning). ⋯ This experiment shows that it is possible to modify the perception of intensity of thermal stimuli by a non-conscious learning procedure based on the transfer of the valence of the unconditioned stimuli (pleasant or unpleasant slides) towards the conditioned stimuli (non-painful and painful thermal stimuli). These results plead for a conception of pain as a conscious output of complex informational processes all of which are not accessible to participants' awareness. Mechanisms by which affective input may influence sensory experience and clinical implications of the present study are discussed.
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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.