Conotoxin contulakin-G engages a neurotensin receptor 2/R-type calcium channel (Cav2.3) pathway to mediate spinal antinociception

Intrathecal application of contulakin-G (CGX), a conotoxin peptide and a
neurotensin analogue, has been demonstrated to be safe and potentially
analgesic in humans. However, the mechanism of action for CGX analgesia is
unknown. We hypothesized that spinal application of CGX produces
antinociception through activation of the presynaptic neurotensin receptor
(NTSR)2. In this study, we assessed the mechanisms of CGX antinociception
in rodent models of inflammatory and neuropathic pain. Intrathecal
administration of CGX, dose dependently, inhibited thermal and mechanical
hypersensitivities in rodents of both sexes. Pharmacological and clustered
regularly interspaced short palindromic repeats/Cas9 editing of NTSR2
reversed CGX-induced antinociception without affecting morphine analgesia.
Electrophysiological and gene editing approaches demonstrated that CGX
inhibition was dependent on the R-type voltagegated calcium channel
(Cav2.3) in sensory neurons. Anatomical studies demonstrated coexpression
of NTSR2 and Cav2.3 in dorsal root ganglion neurons. Finally, synaptic
fractionation and slice electrophysiology recordings confirmed a
predominantly presynaptic effect. Together, these data reveal a nonopioid
pathway engaged by a human-tested drug to produce antinociception.