Experimental neurology
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Experimental neurology · Jul 2004
Differential effect of anterior cingulate cortex lesion on mechanical hypersensitivity and escape/avoidance behavior in an animal model of neuropathic pain.
Various limbic system structures have been implicated in processing noxious information. One such structure is the anterior cingulate cortex (ACC), a region that is thought to modulate higher order processing of noxious input related to the affective/motivational component of pain. The present experiment examined the involvement of the ACC in higher order pain processing by measuring paw withdrawal threshold and escape/avoidance responses in the L5 spinal nerve ligation model of neuropathic pain before and following electrolytic lesion of the ACC. ⋯ ACC lesion in animals with L5 ligation did not alter mechanical hypersensitivity, but did significantly decrease escape/avoidance behavior. Anxiety, as measured using the light-enhanced startle paradigm, was not altered by ACC lesion. These results highlight the utility of novel behavioral test paradigms and provide additional support for the role of the ACC in higher order processing of noxious information, suggesting that ACC lesions selectively decrease negative affect associated with neuropathy-induced hypersensitivity.
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Experimental neurology · Jul 2004
MRI of peripheral nerve degeneration and regeneration: correlation with electrophysiology and histology.
Acute axonal nerve lesions cause a hyperintense signal on T2-weighted (T2-w) magnetic resonance imaging (MRI) at the nerve lesion site and distal to it. The aim of this experimental study was to investigate the spatiotemporal evolution and resolution of MR nerve signal changes following denervation and reinnervation, and to relate these findings to electrophysiology and histology. The proximal sciatic nerve of adult rats was ligated by a tight suture that was removed 1 week later to induce complete axotomy and nerve regeneration upon release. ⋯ MR signal alterations occur as early as 24 h after an axonal nerve lesion and correlate with nerve fiber degeneration and later with nerve oedema on histology. MR findings in denervation and reinnervation parallel the electrophysiological changes. Thus, MRI is a promising diagnostic tool for the early detection of acute axonal nerve lesions and monitoring of nerve regeneration.
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Experimental neurology · Jun 2004
Concentrations of glutamate released following spinal cord injury kill oligodendrocytes in the spinal cord.
We investigated in vivo in rats whether sufficient glutamate is released following spinal cord injury (SCI) to kill oligodendrocytes. Microdialysis sampling was used to establish the level of glutamate released (550 +/- 80 microM) in the white matter during SCI. This glutamate concentration was administered into the spinal cords of other rats and the densities of oligodendrocytes remaining 24 and 72 h later determined by counting cells immunostained with the oligodendrocyte marker CC-1. ⋯ Oligodendrocyte densities near the fiber track were not significantly different at 72 h from 24 h post-exposure, so most glutamate-induced oligodendrocyte death occurs within 24 h after exposure. Injecting the AMPA/kainate receptor blocker NBQX into the spinal cord during glutamate administration reduced the glutamate-induced decrease in oligodendrocyte density, evidence for AMPA/kainate receptor involvement in glutamate-induced oligodendrocyte death. This work directly demonstrates in vivo that following SCI glutamate reaches concentrations toxic to white matter and that AMPA/kainate receptors mediate this glutamate toxicity to oligodendrocytes.
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Experimental neurology · Jun 2004
Co-treatment with riluzole and GDNF is necessary for functional recovery after ventral root avulsion injury.
Unilateral avulsion of lumbar ventral roots kills approximately 50% of injured motoneurons within 2 weeks of surgery. Immediate treatment involving surgical reimplantation of the ventral root (VRI) or intrathecal glial cell line-derived neurotrophic factor (GDNF) delivery or intraperitoneal injection of riluzole for 2 weeks ameliorates motoneuron death to 80% of control but combining the different treatment paradigms did not further enhance survival except when GDNF was combined with VRI. At 3 months, all combined treatments provided a neuroprotective effect compared to avulsion only, but the neuroprotective effect of surgical reimplantation alone was not maintained unless combined with riluzole and GDNF treatment. ⋯ However, when functional motor recovery was assessed using the BBB locomotor score and rotarod tests, only VRI animals treated with riluzole and GDNF application showed significantly improved locomotor function in both tests. Our results show that functional recovery appears related to a combination of enhanced dendrite formation, increased motoneuron survival and the neurotrophic actions of GDNF. Thus, combination treatment may offer a new therapeutic strategy for treating patients with avulsion injury.