Neuroscience letters
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Neuroscience letters · Dec 2005
Differential expression of NMDA receptor subunits between neurons containing and not containing enkephalin in the mouse embryo spinal cord.
We transfected cultures of mouse spinal cord slices with the enhanced green fluorescent protein (GFP) gene driven by the promoter for preproenkephalin, using the particle-mediated gene transfer system adapted for small neurons in the superficial dorsal horn, and observations were made after 4-6 days in vitro. A considerable number of cells in the superficial dorsal horn were observed to express GFP fluorescence, reminiscent of the previously reported distribution of enkephalinergic neurons in the spinal cord. ⋯ These observations suggest that expression of NMDA receptor subunits is controlled differentially in distinct populations of neurochemically identified neurons in the spinal cord. Biolistic particle-mediated gene transfection seems useful for identifying neuronal phenotypes in organotypic cultures of the spinal cord.
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Neuroscience letters · Dec 2005
Comparative StudyEffect of metabotropic glutamate receptor subtype 5 antagonist, 2-methyl-6-(phenylethynyl)-pyridine on mechanosensory afferents innervating rat hind paw following inflammation.
We investigated whether the metabotropic glutamate receptor subtype 5 (mGluR5) selective antagonist, 2-methyl-6-(phenylethynyl)-pyridine (MPEP) has direct effects on primary afferent fiber responses to noxious mechanical stimulation following inflammation. Mechanosensory primary afferent fibers innervating the hind paw were recorded in naïve and complete Freunds adjuvant (CFA) inflamed rats. Following intraplantar injection of CFA, afferent fibers showed property changes including expanded receptive fields, burst firing with fast adaptive mechanical responses and a higher incidence of cold and/or heat sensitivities compared to naïve rats. ⋯ The mean ID50 value of MPEP was 6.49+/-0.43 mg/kg. In contrast to its inhibitory action in the CFA model, i.v. administration of MPEP produced only a mild reduction of mechanical responses in 3 fibers out of 11 in naïve rats. These results provide direct functional evidence that blockade of peripheral mGluR5 receptors inhibits nociceptive transmission and support previous studies demonstrating a peripheral site of action associated with the antinociceptive effect of MPEP following inflammation.
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Neuroscience letters · Dec 2005
The modulation effects of BmK I, an alpha-like scorpion neurotoxin, on voltage-gated Na(+) currents in rat dorsal root ganglion neurons.
The present study investigated the effects of BmK I, a Na(+) channel receptor site 3 modulator purified from the Buthus martensi Karsch (BmK) venom, on the voltage-gated sodium currents in dorsal root ganglion (DRG) neurons. Whole-cell patch-clamping was used to record the tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) components of voltage-gated Na(+) currents in small DRG neurons. ⋯ The results suggested that the inhibitory effect of BmK I on open-state inactivation might contribute to the increase of peak TTX-S and TTX-R currents, and the enhancing effect of BmK I on time-dependent activation might also contribute to the increase of peak TTX-S currents. It was further suggested that a combined effect of BmK I including inhibiting the inactivation of TTX-S and TTX-R channels, accelerating activation and decreasing the activation threshold of TTX-S channels, might produce a hyperexcitability of small DRG neurons, and thus contribute to the BmK I-induced hyperalgesia.
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Neuroscience letters · Dec 2005
Changes in nociceptive sensory innervation in the epidermis of the rat lower lip skin in a model of neuropathic pain.
The epidermis is innervated by fine nerve endings that are important in the perception of nociceptive stimuli. However, their role in neuropathic pain is controversial. In this paper, changes in the innervation patterns of epidermal sensory afferent fibres in the rat lower lip have been studied following bilateral chronic constriction injury (CCI) of the mental nerve-a purely sensory branch of the trigeminal nerve. ⋯ At 8 weeks post-CCI, the fibre lengths of both populations did not differ significantly from shams. This transient hyper-innervation of the epidermis by one subpopulation of nociceptive fibres coincided with the occurrence of spontaneous pain or dysesthetic sensations which we detected in a previous study in the same animal model. Therefore, we speculate that this transient hyper-innervation of the epidermis following injury could play a role in nociception in these animals.
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Neuroscience letters · Dec 2005
Functional alteration of inhibitory influences on spinal motor output in painful diabetic neuropathy in rats.
Diabetes is frequently accompanied by painful polyneuropathies that are mediated by enhanced neuronal excitability in the spinal cord, partly because of decrease in spinal intrinsic inhibitory influences. Changes in spinal excitatory-inhibitory balance may alter spinal segmental motor output. In the study presented here, the mono- and disynaptic (the fastest polysynaptic) reflexes (MSR and DSR, respectively) were recorded from L5 ventral roots in response to stimulation of the ipsilateral L5 dorsal root in spinalized streptozotocin (STZ)-induced diabetic rats with a reduced withdrawal threshold to mechanical stimuli. ⋯ The recurrent inhibition of the MSR and DSR elicited by preceding antidromic conditioning stimulation delivered to the recorded L5 ventral root was markedly suppressed in diabetic rats. By contrast, the presynaptic inhibition of the MSR and DSR elicited by preceding conditioning stimulation to the ipsilateral L4 dorsal root was not impaired. Thus, in diabetic painful neuropathy, reduced spinal intrinsic inhibition in the ventral horn contributes to an enhanced spinal segmental motor output.