Nerve injury increases native CaV2.2 trafficking in dorsal root ganglion mechanoreceptors

Neuronal N-type (Ca(V)2.2) voltage-gated calcium channels are essential for neurotransmission from primary afferent terminals in the dorsal horn. In this study, we have used a knockin mouse containing Ca(V)2.2 with an inserted extracellular hemagglutinin tag (Ca(V)2.2_HA), to visualise the pattern of expression of endogenous Ca(V)2.2 in dorsal root ganglion (DRG) neurons and their primary afferents in the dorsal horn. We examined the effect of partial sciatic nerve ligation (PSNL) and found an increase in Ca(V)2.2_HA only in large and medium dorsal root ganglion neurons and also in deep dorsal horn synaptic terminals. Furthermore, there is a parallel increase in coexpression with GFRa1, present in a population of low threshold mechanoreceptors, both in large DRG neurons and in their terminals. The increased expression of Ca(V)2.2_HA in these DRG neurons and their terminals is dependent on the presence of the auxiliary subunit a(2)d-1, which is required for channel trafficking to the cell surface and to synaptic terminals, and it likely contributes to enhanced synaptic transmission at these synapses following PSNL. By contrast, the increase in GFRa1 is not altered in a(2)d-1-knockout mice. We also found that following PSNL, there is patchy loss of glomerular synapses immunoreactive for Ca(V)2.2_HA and CGRP or IB4, restricted to the superficial layers of the dorsal horn. This reduction is not dependent on a(2)d-1 and likely reflects partial deafferentation of C-nociceptor presynaptic terminals. Therefore, in this pain model, we can distinguish 2 different events affecting specific DRG terminals, with opposite consequences for Ca(V)2.2_HA expression and function in the dorsal horn.

Automated summary

In this study, the expression pattern of Ca(V)2.2, a voltage-gated calcium channel, in primary afferent terminals in the dorsal horn was visualized using a knockin mouse model. The increase in Ca(V)2.2 expression following partial sciatic nerve ligation (PSNL) was observed in large and medium dorsal root ganglion (DRG) neurons as well as their synaptic terminals. The upregulation of Ca(V)2.2 expression was dependent on the auxiliary subunit a(2)d-1 and was associated with enhanced synaptic transmission.