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
The role of capsaicin-sensitive afferent fibers in the lower urinary tract dysfunction induced by chronic spinal cord injury in rats.
The role of capsaicin-sensitive afferents in neurogenic voiding dysfunction was studied in chronic spinal cord injured rats (SCI). Cystometry and external urethral sphincter (EUS) electromyography were performed on 2 consecutive days after induction of urethane anesthesia in SCI rats 6-8 weeks after spinal cord injury. SCI rats exhibited voiding abnormalities including: non-voiding contractions (NVCs) before micturition, increased volume threshold (VT) for initiating voiding, increased amplitude and duration of voiding contractions, decreased voiding efficiency, increased residual urine, and changes in the pattern of the EUS-EMG. ⋯ Capsaicin treatment increased the percentage of animals (from 55% to 80%) that voided on day 1. The results indicate that capsaicin-sensitive C-fiber bladder afferents are not essential for reflex micturition in SCI rats. However, these afferents do contribute to overactivity of the bladder and detrusor sphincter dyssynergia in deeply anesthetized SCI rats.