and Frédérique Scamps. Axotomy-induced expression of calciumactivated chloride current in subpopulations of mouse dorsal root ganglion neurons. J Neurophysiol 90: 3764 -3773, 2003. First published August 27, 2003 10.1152/jn.00449.2003. Whole cell patchclamp recordings of calcium-activated chloride current [I Cl(Ca) ] were made from adult sensory neurons of naive and axotomized mouse L 4 -L 6 lumbar dorsal root ganglia after 1 day of culture in vitro. A basal I Cl(Ca) was specifically expressed in a subset of naive mediumdiameter neurons (30 -40 m). Prior nerve injury, induced by sciatic nerve transection 5 days before experiments, increased both I Cl(Ca) amplitude and its expression in medium-diameter neurons. Moreover, nerve injury also induced I Cl(Ca) expression in a new subpopulation of neurons, the large-diameter neurons (40 -50 m). Small-diameter neurons (inferior to 30 m) never expressed I Cl(Ca) . Regulated I Cl(Ca) expression was strongly correlated with injury-induced regenerative growth of sensory neurons in vitro and nerve regeneration in vivo. Cell culture on a substrate not permissive for growth, D,L-polyornithine, prevented both elongation growth and I Cl(Ca) expression in axotomized neurons. Regenerative growth and the induction of I Cl(Ca) expression take place 2 days after injury, peak after 5 days of conditioning in vivo, slowly declining thereafter to control values. The selective expression of I Cl(Ca) within medium-and large-diameter neurons conditioned for rapid, efficient growth suggests that these channels play a specific role in postinjury behavior of sensory neuron subpopulations such as neuropathic pain and/or axonal regeneration.

Medium sized dorsal root ganglion neurones are involved in tactile sensation and responsible for allodynia following nerve injury. We examined the effects of sciatic nerve injury on the expression of low and high voltage-gated calcium currents in medium sized neurones isolated from lumbar dorsal root ganglia of adult mice. Based on the relative expression of these calcium channel types, three populations of medium sized neurones were identified in controls. Type I, II and III populations were characterised respectively by small, predominant and no low voltage-gated current compared to the high voltage-gated current. Five days after nerve injury, calcium current expression was differentially affected by axotomy in these three subsets of medium neurones. Altogether, these results suggest that calcium channels are heterogeneously distributed among the medium sized neurones. This heterogeneity should provide specificity not only to sensory functions but also to sensory responses following nerve injury.