Excitability of A? sensory neurons is altered in an animal model of peripheral neuropathy.

By London Spine
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Excitability of Aβ sensory neurons is altered in an animal model of peripheral neuropathy.

BMC Neurosci. 2012;13:15

Authors: Zhu YF, Henry JL

Abstract
BACKGROUND: Causes of neuropathic pain following nerve injury remain unclear, limiting the development of mechanism-based therapeutic approaches. Animal models have provided some directions, but little is known about the specific sensory neurons that undergo changes in such a way as to induce and maintain activation of sensory pain pathways. Our previous studies implicated changes in the Aβ, normally non-nociceptive neurons in activating spinal nociceptive neurons in a cuff-induced animal model of neuropathic pain and the present study was directed specifically at determining any change in excitability of these neurons. Thus, the present study aimed at recording intracellularly from Aβ-fiber dorsal root ganglion (DRG) neurons and determining excitability of the peripheral receptive field, of the cell body and of the dorsal roots.
METHODS: A peripheral neuropathy was induced in Sprague Dawley rats by inserting two thin polyethylene cuffs around the right sciatic nerve. All animals were confirmed to exhibit tactile hypersensitivity to von Frey filaments three weeks later, before the acute electrophysiological experiments. Under stable intracellular recording conditions neurons were classified functionally on the basis of their response to natural activation of their peripheral receptive field. In addition, conduction velocity of the dorsal roots, configuration of the action potential and rate of adaptation to stimulation were also criteria for classification. Excitability was measured as the threshold to activation of the peripheral receptive field, the response to intracellular injection of depolarizing current into the soma and the response to electrical stimulation of the dorsal roots.
RESULTS: In control animals mechanical thresholds of all neurons were within normal ranges. Aβ DRG neurons in neuropathic rats demonstrated a mean mechanical threshold to receptive field stimulation that were significantly lower than in control rats, a prolonged discharge following this stimulation, a decreased activation threshold and a greater response to depolarizing current injection into the soma, as well as a longer refractory interval and delayed response to paired pulse electrical stimulation of the dorsal roots.
CONCLUSIONS: The present study has demonstrated changes in functionally classified Aβ low threshold and high threshold DRG neurons in a nerve intact animal model of peripheral neuropathy that demonstrates nociceptive responses to normally innocuous cutaneous stimuli, much the same as is observed in humans with neuropathic pain. We demonstrate further that the peripheral receptive fields of these neurons are more excitable, as are the somata. However, the dorsal roots exhibit a decrease in excitability. Thus, if these neurons participate in neuropathic pain this differential change in excitability may have implications in the peripheral drive that induces central sensitization, at least in animal models of peripheral neuropathic pain, and Aβ sensory neurons may thus contribute to allodynia and spontaneous pain following peripheral nerve injury in humans.

PMID: 22289651 [PubMed – indexed for MEDLINE]

Acute motor-sensory axonal neuropathy after cervical spine surgery.

By London Spine
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Acute motor-sensory axonal neuropathy after cervical spine surgery.

J Neurosurg Spine. 2012 Jul;17(1):82-5

Authors: Miscusi M, Currà A, Della Rocca C, Missori P, Petrozza V

Abstract
The authors report the case of a 55-year-old man who presented with acute motor-sensory axonal neuropathy (AMSAN), a variant of Guillain-Barré syndrome with a poor prognosis, immediately after surgery for resection of a cervical chondroma. A misdiagnosis of spinal cord shock due to an acute surgical or vascular postoperative complication was initially made in this patient. Nevertheless, there was continuous transient improvement that was followed by progressive worsening, and further investigation was necessary. The diagnosis of AMSAN, associated with acute colitis caused by Helicobacter pylori, was made based on neurophysiological examinations and colonoscopy. Interestingly, the patient also developed nephrotic syndrome, which was thought to be a further complication of the autoimmune reaction. Delayed administration of immunoglobulins (400 mg/kg/day), mesalazine (800 mg 3×/day), and meropenem (3 g/day) was used to treat the Helicobacter infection and the autoimmune reaction, leading to restoration of renal function and slight neurological improvement. The patient’s general condition and neurological status improved slightly, but he remained seriously disabled (Frankel Grade C). This case demonstrates that a new onset of neurological symptoms in the early postoperative period after spine surgery could be related to causes other than iatrogenic myelopathy, and that an early diagnosis can reduce neurological sequelae, leading to a better outcome.

PMID: 22559275 [PubMed – indexed for MEDLINE]

Does sensory stimulation threshold affect lumbar facet radiofrequency denervation outcomes? A prospective clinical correlational study.

By London Spine
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Does sensory stimulation threshold affect lumbar facet radiofrequency denervation outcomes? A prospective clinical correlational study.

Anesth Analg. 2011 Nov;113(5):1233-41

Authors: Cohen SP, Strassels SA, Kurihara C, Lesnick IK, Hanling SR, Griffith SR, Buckenmaier CC, Nguyen C

Abstract
BACKGROUND: Radiofrequency facet denervation is one of the most frequently performed procedures for chronic low back pain. Although sensory stimulation is generally used as a surrogate measure to denote sufficient proximity of the electrode to the nerve, no study has examined whether stimulation threshold influences outcome.
METHODS: We prospectively recorded data in 61 consecutive patients undergoing lumbar facet radiofrequency denervation who experienced significant pain relief after medial branch blocks. For each nerve lesioned, multiple attempts were made to maximize sensory stimulation threshold (SST). Mean SST was calculated on the basis of the lowest stimulation perceived at 0.1-V increments for each medial branch. A positive outcome was defined as a ≥50% reduction in back pain coupled with a positive satisfaction score lasting ≥3 months. The relationship between mean SST and denervation outcomes was evaluated via a receiver’s operating characteristic (ROC) curve, and stratifying outcomes on the basis of various cutoff values.
RESULTS: No correlation was noted between mean SST and pain relief at rest (Pearson’s r=-0.01, 95% confidence interval [CI]: -0.24 to 0.23, P=0.97), with activity (r=-0.17, 95% CI: -0.40 to 0.07, P=0.20), or a successful outcome. No optimal SST could be identified.
CONCLUSIONS: There is no significant relationship between mean SST during lumbar facet radiofrequency denervation and treatment outcome, which may be due to differences in general sensory perception. Because stimulation threshold was optimized for each patient, these data cannot be interpreted to suggest that sensory testing should not be performed, or that high sensory stimulation thresholds obtained on the first attempt should be deemed acceptable.

PMID: 21918166 [PubMed – indexed for MEDLINE]

Sensory and Motor Behavior Evidences Supporting the Usefulness of Conditioned Medium from Dental Pulp-Derived Stem Cells in Spinal Cord Injury in Rats.

By London Spine

Related Articles Sensory and Motor Behavior Evidences Supporting the Usefulness of Conditioned Medium from Dental Pulp-Derived Stem Cells in Spinal Cord Injury in Rats. Asian Spine J. 2018 Oct;12(5):785-793 Authors: Asadi-Golshan R, Razban V, Mirzaei E, Rahmanian A, Khajeh S, Mostafavi-Pour Z, Dehghani F Abstract STUDY DESIGN: Experimental animal study. PURPOSE: This study aimed to…