Trigeminal neuralgia (TN) is a type of
neuropathic pain characterized by intense
pain; although
anticonvulsants are used as an option to relieve
pain, adverse side effects can decrease patient adherence. In this context, a low dose of
naltrexone is effective in relieving
pain in other
pain conditions. Thus, the objective of the present study was to evaluate the
analgesic effect of low-dose
naltrexone on facial
mechanical allodynia in a rat model of TN, as well as its effect(s) on
biomarkers in the
central nervous system (tumor necrosis factor-
alpha, brain-derived
neurotrophic factor [
BDNF],
interleukin [IL]-10, and
toll-like receptor-4). Fifty-nine adult male Wistar rats (CEUA-HCPA#2017-0575) were allocated to following groups: control;
sham-pain + vehicle;
sham-pain + carbamazepine (100 mg/kg);
sham-pain + naltrexone (0.5 mg/kg); pain + vehicle; pain + carbamazepine; and pain + naltrexone. TN was induced using chronic constriction of the infraorbital nerve. Facial
allodynia was assessed using von Frey test. Drugs were administered by gavage 14 days after surgery for 10 days. At baseline, the mechanical threshold was similar between groups (P > 0.05; generalized estimating equation). Seven days after surgery, facial
allodynia was observed in
sham-TN and
pain-TN groups (P < 0.05). Fourteen days after surgery, only
pain-TN groups exhibited facial
allodynia. The first dose of low-dose
naltrexone or
carbamazepine partially reversed facial
allodynia. After 10 days of treatment, both drugs completely reversed it. Spinal cord levels of
BDNF and
IL-10 were modulated by low-dose
naltrexone. Thus, low-dose
naltrexone may be suitable to relieve TN; however, the exact mechanisms need to be clarified.