Pain
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We tested both pain thresholds and pain tolerance in patients with Alzheimer's disease (AD) by means of phasic and tonic noxious stimuli. In the first case, electrical stimulation was used, whereas in the second case arm ischemia was studied. By comparing AD patients with normal subjects of the same age, we found no differences in stimulus detection and pain thresholds, whereas a clearcut increase in pain tolerance was present in AD patients. ⋯ In addition, analysis of the EEG power spectra indicated that patients with low alpha and high delta peaks showed an increase in pain tolerance to both electrical stimulation and ischemia. These findings show that, whereas the sensory-discriminative component of pain is maintained in AD patients, pain tolerance is altered and depends on cognitive and affective factors. Thus, pain tolerance is tightly related to the severity of the disease according to the rule, 'the more severe the MMSE and EEG changes, the higher the tolerance to pain'.
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The right hemisphere is assumed to play a unique role for pain sensitivity and negative affect. Pressure pain thresholds were assessed daily in eight right-handed participants over a 6-week period in order to obtain reliable measures of pain sensitivity unaffected by situational influences. In an additional session, cerebral laterality was assessed with behavioral and an EEG measures. ⋯ In addition, a significant positive correlation between a relatively increased right frontal brain activity and depression was found. Correlations between pain thresholds and 'non-emotional' laterality measures (central or parietal EEG asymmetry, dichotic consonant-vocal-recall test) were not significant. We conclude that a right frontal brain hyperactivity might be a biological marker for enhanced pain sensitivity and negative affect.
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Opioids used topically may exercise several useful clinical effects. Opioids may cause immediate local analgesia and also may work indirectly through decreasing the inflammation process. ⋯ The side effects of topical opioids were none or minimal. Possible mechanisms of topical analgesia are discussed.
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Comparative Study
The effectiveness of spinal and systemic morphine on rat dorsal horn neuronal responses in the spinal nerve ligation model of neuropathic pain.
The treatment of pain arising from nerve injury can be difficult and the opioid sensitivity of neuropathic pain remains debatable. Clinical and animal studies report a wide range in the effectiveness of morphine, ranging from inadequate to potent analgesia. In this electrophysiological study we compare the effectiveness of spinal versus systemic administration of morphine on the natural and electrically evoked responses of spinal neurones of rats with a selective spinal nerve (L5/6) ligation. ⋯ This was especially clear for the C-fibre evoked and noxious natural stimuli evoked responses (mechanical and thermal) of spine nerve ligated rats. Our results suggest that the effectiveness of morphine may be partly related to the timing of the treatment relative to the duration of the neuropathy, the route of administration and also the neuropathic symptom. Spinal opioids may be a useful approach to pain control in neuropathic pain states where systemic routes produce inadequate analgesia.
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The long-term changes in Fos like-immunoreactivity (Fos-LI) in the dorsal horn of the spinal cord following various peripheral nerve lesions remain controversial. This study considers such an approach with chronic constriction injury rats (CCI: loose ligations of the sciatic nerve), at 2 weeks after the surgery, when changes in spontaneous and evoked behaviour were clearly described. All rats used for Fos studies displayed allodynia to mechanical stimulation (decrease of 32% of the vocalization threshold to paw pressure). ⋯ In contrast, stroking of the nerve-injured paw induced a significant expression of Fos-LI in the superficial laminae (I-II) of the dorsal horn of CCI rats (19.5 +/- 3/sections, P = 0.027) which was greater than that observed in sham-operated (6.5 +/- 3/sections) or in normal rats (3.5 +/- 2/section). These modifications may reflect mechanical allodynia observed in behavioural studies and could be related to A beta fibers, which are known to be severely affected after the constriction of the nerve. These results suggest that this approach could be useful to study, at the cellular level, in freely moving rats, some pharmacological aspects of neuropathic pain.