Pain
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NaV1.8 is a voltage-gated sodium channel expressed only in a subset of sensory neurons of which more than 85% are nociceptors. In order to delete genes in nociceptive neurons, we generated heterozygous transgenic mice expressing Cre recombinase under the control of the NaV1.8 promoter. Functional Cre recombinase expression replicated precisely the expression pattern of NaV1.8. ⋯ Sodium channel subtypes were normal in isolated DRG neurons. Pain behaviour in response to mechanical or thermal stimuli, and in acute, inflammatory and neuropathic pain was also normal. These data demonstrate that the heterozygous NaV1.8-Cre mouse line is a useful tool to analyse the effects of deleting floxed genes on pain behaviour.
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Comparative Study
Enhanced excitability of dissociated primary sensory neurons after chronic compression of the dorsal root ganglion in the rat.
A chronic compression of the dorsal root ganglion (CCD) produces ipsilateral cutaneous hyperalgesia and allodynia in rats. Intracellular electrophysiological recordings from formerly compressed neurons in the intact dorsal root ganglion (DRG) reveal lower than normal current thresholds (CTs) and abnormal spontaneous activity (SA) (Zhang JM, Song XJ, LaMotte RH. Enhanced excitability of sensory neurons in rats with cutaneous hyperalgesia produced by chronic compression of the dorsal root ganglion. ⋯ The overall incidence of SA was higher for CCD than for control neurons after 1d culture (10.3 vs. 1.8%) and similar to that obtained in the intact DRG. We conclude that the CCD-induced hyperexcitability of medium- and large-sized neurons remains after dissociation and is intrinsic to the soma. For small-sized neurons, the effects of CCD observed in the intact DRG are less apparent after dissociation possibly due to the hyperexcitability produced by the dissociation process itself.
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Cavernous hemangiomas (cavernomas) of the spinal cord are rare congenital malformations that comprise less than 5% of all intramedullary lesions. Despite this rarity, we describe the third case of central neuropathic itch associated with intramedullary cavernoma. Since fewer than 10 cases of central spinal itch from all causes have been published, this concurrence suggests the possibility of a specific association. ⋯ Such rats develop unilateral dermatomal hyperalgesia and self-injurious scratching and biting (autotomy). Although this pathological grooming is currently interpreted as a response to chronic pain, we propose that it more likely models scratching provoked by central neuropathic itch, as seen in our patient and others. Study of quisqualate-injected rats may provide leads towards new treatments for neuropathic itch.