An in vivo tethered toxin approach for the cell-autonomous inactivation of voltage-gated sodium channel currents in nociceptors

Understanding information flow in sensory pathways requires cell-selective approaches to manipulate the activity of defined neurones. Primary afferent nociceptors, which detect painful stimuli, are enriched in specific voltage-gated sodium channel (VGSC) subtypes. Toxins derived from venomous animals can be used to dissect the contributions of particular ion currents to cell physiology. Here we have used a transgenic approach to target a membrane-tethered isoform of the conotoxin MrVIa (t-MrVIa) only to nociceptive neurones in mice. t-MrVIa transgenic mice show a 44 +/- 7 % reduction of tetrodotoxin resistant (TTX-R) VGSC current densities. This inhibition is permanent, reversible and does not result in functional upregulation of TTX-sensitive (TTX-S) VGSC, voltage-gated calcium currents (VGCC) or transient receptor potential (TRP) channels present in nociceptive neurones. As a consequence of the reduction of VGSC currents, t-MrVIa transgenic mice display decreased inflammatory mechanical hyperalgesia, cold pain insensitivity and reduced firing of cutaneous C-fibres sensitive to noxious cold temperatures. These data validate the use of genetically encoded t-toxins as a powerful tool to manipulate VGSC in specific cell types within the mammalian nervous system. This novel genetic methodology can be used for circuit mapping and has the key advantage that it enables to dissect the contribution of specific ionic currents to neuronal function and to behaviour