Neuroscience letters
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Neuroscience letters · Sep 2000
Antiallodynic effects produced by stimulation of the periaqueductal gray matter in a rat model of neuropathic pain.
It has been well documented that there is opioid resistance in neuropathic pain. This indicates that the endogenous opioid system may not be involved effectively in modulating neuropathic pain. The present study sought to determine if activation of the descending pain inhibition system might produce analgesia in the animal neuropathic model we developed. ⋯ Mechanical allodynia and cold allodynia were reduced by PAG stimulation. Naloxone reversed the antiallodynic effects of ventral PAG stimulation. These results suggest that activation of the descending pain inhibition system including the ventral PAG reduces neuropathic pain syndrome and that opiates are involved in this system.
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Neuroscience letters · Aug 2000
Mediation of spinal nerve injury induced tactile allodynia by descending facilitatory pathways in the dorsolateral funiculus in rats.
Evidence exists to indicate that tactile allodynia arising from peripheral nerve injury is integrated predominately at supraspinal, rather than spinal, sites. In the present experiments, the possibility that disruption of descending pathways through the dorsolateral funiculus (DLF) might alter expression of nerve-injury induced tactile allodynia was explored. Male, Sprague-Dawley rats received L(5)/L(6) spinal nerve ligation (SNL). ⋯ DLF lesions made ipsilateral to SNL completely blocked tactile allodynia in SNL rats. Contralateral DLF lesions and sham surgery did not have any effect on SNL-induced allodynia. These results indicate that tactile allodynia after peripheral nerve injury is dependent upon tonic activation of net descending facilitation from supraspinal sites and support the hypothesis of tonic activation of descending facilitation as a basis for chronic pain.
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Neuroscience letters · Aug 2000
Morphine and gabapentin decrease mechanical hyperalgesia and escape/avoidance behavior in a rat model of neuropathic pain.
A behavioral test paradigm that measures the aversive quality of stimulus-evoked pain in an animal model of neuropathic pain (L5 ligation) was tested for sensitivity to (1) different forces (476 and 202 mN) and frequencies (once every 15 or 30 s) of mechanical stimulation to the hyperalgesic paw and (2) different doses of the common antinociceptive compounds morphine (1 and 10 mg/kg) and gabapentin (30 and 90 mg/kg). Compared to non-ligated controls, the greater force (476 mN) and frequency (every 15 s) of mechanical stimulation of the hyperalgesic paw was associated with the greatest degree of escape/avoidance behavior. ⋯ The antinociceptive and antiaversive effects were found at doses that did not produce evidence of decreased motor activity. It is concluded that the behavioral test paradigm used to measure the aversiveness of stimulus-evoked nociceptive behavior is sensitive to different degrees of evoked pain and traditional analgesic compounds.
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Neuroscience letters · Aug 2000
Inhibition of the central heme oxygenase-carbon monoxide pathway increases 2-deoxy-D-glucose-induced hypothermia in rats.
The present study was designed to test the hypothesis that carbon monoxide (CO) plays a role in 2-deoxy-D-glucose (2-DG)-induced hypothermia. The body temperature (T(b)) of awake, unrestrained rats was measured before and after systemic administration of 2-DG (50 mg/kg) and intracerebroventricular administration of zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG, a heme-oxygenase inhibitor, 200 nmol/4 microl). ⋯ When the two treatments were combined, 2-DG-induced hypothermia was significantly increased. The data indicate that heme oxygenase-carbon monoxide pathway plays a key role in 2-DG-induced hypothermia, inhibiting 2-DG-induced hypothermia.
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Neuroscience letters · Jul 2000
gamma-aminobutyric acid- and glycine-immunoreactive neurons postsynaptic to substance P-immunoreactive axon terminals in the superficial layers of the rat medullary dorsal horn.
gamma-Aminobutyric acid (GABA)ergic and glycinergic neurons were examined light- and electron-microscopically in laminae I and II of the medullary dorsal horn (MDH, i.e. spinal trigeminal nucleus caudalis in the rat). The majority of GABA- and glycine (Gly)-immunoreactive (-ir) neurons showed both GABA- and Gly-immunoreactivities (-IRs). ⋯ GABA- and Gly-ir neuronal profiles were postsynaptic to substance P-ir axon terminals. These results suggest that nociceptive information being carried by primary afferent SP-fibers may be relayed directly to GABAergic and glycinergic neurons in laminae I and II of the MDH.