Articles: hyperalgesia.
-
Devices designed for mechanical pain threshold studies are often difficult to implement. The purpose of this study was to investigate a simple tool based on calibrated forceps to induce quantifiable mechanical stimulation in the rat on a linear scale. The most suitable protocol was tested by determining the effects of 3 repetitive measurements on both hind paws, respectively, during long-term (9 days), mid-term (1 day), and short-term (2 hours). Only threshold increase related to weight gain over long-term was observed, suggesting that moderate rat training can be used. The capacity of the device to reveal hyperalgesia was tested in a model of carrageenan-induced inflammation in the hind paw. The hyperalgesia was maximal 6 hours after carrageenan injection and progressively decreased. Similar, although more variable, responses were observed with von Frey filaments. Morphine-induced analgesia resulted in a dose-dependent increase of paw threshold. Tolerance to morphine administrated on a once daily schedule (10 mg/kg) during 5 days was revealed by a significant decrease in analgesia by day 3. Taken together, these results demonstrated accuracy of this device for easy, fast, and reproducible measure of mechanical pain threshold on rat limbs. Moreover, it allows the performance of rat testing with minimal constraint, which reduces data variability. ⋯ The calibrated forceps is an easy to use device well-suited to rapidly test mechanical pain threshold with accuracy. It is well-designed for preclinical behavioral screening of noxious or analgesic properties of molecules.
-
Promising recent developments in the therapeutic value of neuropeptide antagonists have generated renewed importance in understanding the functional role of neuropeptides in nociception and inflammation. To explore this relationship we examined behavioral changes and primary afferent neuronal plasticity following deep tissue inflammation. One hour following craniofacial muscle inflammation ipsilateral as well as contralateral head withdrawal thresholds and ipsi- and contralateral hindpaw withdrawal thresholds were lowered and remained reduced for 28 days. ⋯ Local injection of CGRP antagonist directly into the masseter muscle prior to CFA produced similar, but less pronounced, effects. These findings indicate that unilateral craniofacial muscle inflammation produces mechanical allodynia at distant sites and upregulates CGRP and SP in primary afferent neurons innervating deep tissues. These data further implicate CGRP and SP in deep tissue nociceptive mechanisms and suggest that peptide antagonists may have therapeutic potential for musculoskeletal pain.
-
Administration of the neurotrophin nerve growth factor (NGF) to rats and humans has been shown to induce both thermal and mechanical hyperalgesia and is used as a model of inflammatory pain. Here we describe a mouse model of secondary hyperalgesia after NGF application. NGF was injected into the biceps femoris muscle unilaterally, and at various intervals afterwards the electromyographic (EMG) activity from the same muscle was recorded in response to mechanical von Frey hair stimulation of the plantar surface of the hind paw in isoflurane-anesthetized mice. Secondary cutaneous hyperalgesia in the hind paw reached a peak 60 minutes after injection and returned to baseline levels after an additional 60 minutes. This was followed by a second increase in EMG magnitude at 24 hours after injection that was still present after 5 days. The effects of NGF were dose-dependent, and a dose of 2 microg/g NGF had the maximal observed effect. No increase in EMG magnitude occurred on the untreated side. This study describes a quantitative mouse model of prolonged secondary cutaneous hyperalgesia after NGF-induced muscle inflammation that can be used for genetic manipulations of putative central molecular pathways that underlie secondary hyperalgesia. ⋯ This study describes the development of a novel model of NGF-induced secondary hyperalgesia. The development of this model will allow further investigations into the processes that underlie the development of secondary hyperalgesia and pain associated with the musculature.
-
Controlled Clinical Trial
Retrospenial cortical deactivation during painful stimulation of fibromyalgic patients.
To study fibromyalgic pain this article contrasts positron emission tomographic measures of regional cerebral blood flow (rCBF) during externally induced acute pain and rest in eight fibromyalgia syndrome patients. An expected pattern of frontal and parietal cortical activation during acute pain as compared to rest was observed. However, reduced rCBF was additionally found in the retrosplenial cortex during acute pain as compared to rest. This may reflect that externally induced pain inhibits fibromyalgic pain and syndrome-related evaluative processes located in the retrosplenial cortex, and that fibromyalgic pain results from exaggerated attention to sub-noxious pain signaling, that is, secondary hyperalgesia.
-
J Manipulative Physiol Ther · Jan 2006
Spinal manipulation reduces pain and hyperalgesia after lumbar intervertebral foramen inflammation in the rat.
To document potential mediating effects of the Activator-assisted spinal manipulative therapy (ASMT) on pain and hyperalgesia after acute intervertebral foramen (IVF) inflammation. ⋯ These studies show that ASMT can significantly reduce the severity and shorten the duration of pain and hyperalgesia caused by lumbar IVF inflammation. This effect may result from ASMT-induced faster elimination of the inflammation and recovery of excitability of the inflamed DRG neurons by improving blood and nutrition supplement to the DRG within the affected IVF. Manipulation of a specific spinal segment may play an important role in optimizing recovery from lesions involving IVF inflammation.