100 Section - Photobiomodulation Therapy For Neuropathic Pain: Preclinical Evidence from Female Wistar Rats to Clinical Application

Neuropathic pain arises from somatosensory system injury and is marked by hyperalgesia and allodynia. Despite its higher prevalence in women, preclinical studies rarely address female-specific factors such as the estrous cycle, limiting translational value. Photobiomodulation Therapy (PBMT) is a non-invasive approach capable of modulating inflammation and tissue repair. This study investigated the effects of PBMT on pain-like behaviors, estrous cycle influences, and neuropathy-related muscle atrophy in female Wistar rats.

Design:

Twenty-five young female Wistar rats were used (CEUA/ICB-USP, 2017110820). Neuropathic pain was induced by unilateral chronic constriction injury (CCI) of the sciatic nerve. Animals were allocated into four groups (n = 5): CCI + PBMT; CCI; Sham + PBMT; and Sham. PBMT began 14 days after CCI using an 808 nm continuous laser applied at seven points (2–4 J/point). Behavioral tests included Randall–Selitto, von Frey, and Hargreaves. Estrous cycle phases were determined by vaginal cytology. Gastrocnemius muscles were collected for macroscopic and H&E histological analyses.

Results:

PBMT significantly reduced mechanical, thermal, and tactile hypersensitivity in CCI rats (p< 0.05) Metestrus animals showed slightly higher pain thresholds, indicating hormonal modulation (p< 0.05). CCI markedly reduced gastrocnemius mass, while PBMT partially restored it (p < 0.02). Histology confirmed reduced inflammatory infiltrate and better preservation of muscle fibers in PBMT-treated CCI rats. All data were analyzed using two-way ANOVA followed by Bonferroni post hoc tests.

Conclusion:

PBMT effectively reversed neuropathic pain-like behaviors in female rats and highlighted the relevance of considering estrous cycle influences. Its ability to attenuate CCI-induced muscle loss suggests protective neuromuscular effects, likely linked to anti-inflammatory and mitochondrial mechanisms. These results support PBMT as a promising dual-action therapy, reducing pain and preserving muscle structure, relevant for future rehabilitation strategies targeting neuropathy and nerve-injury–related atrophy