The effects of current treatments for
neuropathic pain are limited.
Oxytocin is a novel candidate substance to relieve
neuropathic pain, as demonstrated in various animal models with nerve injury.
Low-level laser therapy (
LLLT) is another option for the treatment of
neuropathic pain. In this study, we quantified the effects of
oxytocin or
LLLT alone and the combination of
oxytocin and
LLLT on cortical excitation induced by electrical stimulation of the dental pulp using optical imaging with a voltage-sensitive
dye in the
neuropathic pain model with partial
ligation of the infraorbital nerve (pl-ION). We applied
oxytocin (OXT, 0.5 μmol) to the rat once on the day of pl-ION locally to the injured nerve.
LLLT using a
diode laser (810 nm, 0.1 W, 500 s, continuous mode) was performed daily via the skin to the injured nerve from the day of pl-ION to 2 days after pl-ION. Cortical responses to electrical stimulation of the mandibular molar pulp under
urethane anesthesia were recorded 3 days after pl-ION. Both the amplitude and area of excitation in the primary and secondary somatosensory and insular cortices in pl-ION rats were larger than those in
sham rats. The larger amplitude of cortical excitation caused by pl-ION was suppressed by OXT or
LLLT. The expanded area of cortical excitation caused by pl-ION was suppressed by OXT with
LLLT but not by OXT or
LLLT alone. These results suggest that the combined application of OXT and
LLLT is effective in relieving the
neuropathic pain induced by
trigeminal nerve injury.