In this regard, our in vitro readout would be a useful experimental
platform to help delineate the precise cell death pathways and
signaling cascades engaged (which could then be experimentally
manipulated). Such studies should consider that plasticity may
evolve over time. The loss of IB41 central terminals is transient
following crush and has even been observed to reverse at longer
timepoints following SNItrans.36 These observations, in conjunction
with ours of loss of neurons, raise the intriguing question of the
source of such central reinnervation.
4.4. Study limitations
Our efforts focused on traumatic nerve injury paradigms owing to
previous contrasting results using these robust and reproducible
experimental models. We did not extend our studies to systemic
neuropathy models, such as chemotherapy or diabetic neurop-
athy. A recent postmortem analysis reported a neuronal loss in
the DRG from patients with painful diabetic peripheral neurop-
athy.19 Transcriptional responses vary substantially across
different nerve insults, 44 so it would be of interest to test whether
neuronal loss and the subpopulation vulnerability reported in this
study are common features across different types of insults.
Using multiple approaches, we assess the na ¨ıve mouse L4
DRG to contain approximately 8000 neurons, consistent with
a previous estimate,67 and observed a frank loss of small-
diameter neurons following injury. However, the extent of loss
observed using our semiautomated approach was less than that
observed using manual techniques.67 Two major limitations in
this study may explain this discrepancy: First, owing to technical
issues, the cleared DRG dataset is unpaired ipsilateral–contra-
lateral which adds larger variability. Second, the analysis method
is prone to undercounting deep nuclei. The signal-to-noise is
better for superficial nuclei and smaller tissue volumes. Given the
reduction in DRG volume after SNI trans, nuclei in larger
contralateral DRG may be undercounted.
While we made efforts to profile the loss of several molecularly
discrete sensory neuron populations, we acknowledge that not all
subtypes were profiled. Furthermore, recent single-cell RNA
sequencing has given us a more granular appreciation of the
heterogeneity of sensory neurons. 42 Future studies could
leverage our experimental approach and new transgenic lines
to characterize the loss of neurons in more detail. Such
experiments may be pertinent before embarking on molecular
or functional profiling of populations post–nerve injury.
4.5. Conclusions
In sum, we have provided data from multiple complementary
experimental approaches to support the hypothesis that DRG
neurons are lost following nerve injury in mice. We describe
a substantial loss, which is biased towards specific subpopula-
tions and particularly present in small-diameter nonpeptidergic
nociceptive neurons.
Conflict of interest statement
D.L.B. has acted as a consultant in the last 2 years for AditumBio,
Biogen, Biointervene, Combigene, LatigoBio, GSK, Ionis, Lexicon
therapeutics, Neuvati, Olipass, Orion, Replay, SC Health Manag-
ers, Theranexus, Third Rock Ventures, and Vida Ventures on behalf
of Oxford University Innovation. D.L.B. has received research
funding from Lilly and Astra Zeneca, and G.A.W. has received
research funding from Ono Pharmaceutical. D.L.B. has received
2874 A.H. Cooper et al. ·165 (2024) 2863–2876 PAIN®