Data from: Distinct BOLD fMRI responses of capsaicin-induced thermal sensation reveal pain-related brain activation in nonhuman primates

Background: Approximately 20% of the adult population suffer from chronic
pain that is not adequately treated by current therapies, highlighting a
great need for improved treatment options. To develop effective
analgesics, experimental human and animal models of pain are critical.
Topically/intra-dermally applied capsaicin induces hyperalgesia and
allodynia to thermal and tactile stimuli that mimics chronic pain and is a
useful translation from preclinical research to clinical investigation.
Many behavioral and self-report studies of pain have exploited the use of
the capsaicin pain model, but objective biomarker correlates of the
capsaicin augmented nociceptive response in nonhuman primates remains to
be explored. Methodology: Here we establish an aversive capsaicin-induced
fMRI model using non-noxious heat stimuli in Cynomolgus monkeys (n = 8).
BOLD fMRI data were collected during thermal challenge (ON:20 s/42°C;
OFF:40 s/35°C, 4-cycle) at baseline and 30 min post-capsaicin (0.1 mg,
topical, forearm) application. Tail withdrawal behavioral studies were
also conducted in the same animals using 42°C or 48°C water bath pre- and
post- capsaicin application (0.1 mg, subcutaneous, tail). Principal
Findings: Group comparisons between pre- and post-capsaicin application
revealed significant BOLD signal increases in brain regions associated
with the ‘pain matrix’, including somatosensory, frontal, and cingulate
cortices, as well as the cerebellum (paired t-test, p<0.02, n = 8),
while no significant change was found after the vehicle application. The
tail withdrawal behavioral study demonstrated a significant main effect of
temperature and a trend towards capsaicin induced reduction of latency at
both temperatures. Conclusions: These findings provide insights into the
specific brain regions involved with aversive, ‘pain-like’, responses in a
nonhuman primate model. Future studies may employ both behavioral and fMRI
measures as translational biomarkers to gain deeper understanding of pain
processing and evaluate the preclinical efficacy of novel analgesics.