Molecular Hydrogen Reverses Nociplastic Pain and Depressive-like Behaviors via Region- and Sex-Dependent Central Mechanisms

Fibromyalgia is a chronic nociplastic pain condition frequently accompanied by affective disturbances, particularly depression, for which effective treatments remain limited. Increasing evidence implicates central oxidative stress, maladaptive synaptic plasticity, and neuroinflammatory alterations in its pathophysiology. This study investigated the therapeutic effects of molecular hydrogen (H2) in a reserpine-induced murine model of fibromyalgia, with emphasis on sex-dependent and region-specific mechanisms. Male and female C57BL/6 mice received repeated reserpine injections to induce fibromyalgia-like symptoms. Mechanical allodynia, thermal hyperalgesia, cold allodynia, and depressive-like behaviors were assessed, followed by molecular analyses in the spinal cord and amygdala. Reserpine induced persistent nociceptive hypersensitivity and depressive-like behaviors in both sexes, with earlier cold allodynia in females. Hydrogen-rich water (HRW) progressively reversed mechanical and thermal hypersensitivity and rapidly abolished cold allodynia, showing greater efficacy in females. HRW also normalized depressive-like behaviors in both sexes. At the molecular level, HRW reduced spinal oxidative stress and ERK-dependent plasticity without altering spinal NLRP3 expression, whereas it fully reversed NLRP3 upregulation and HO-1 downregulation in the amygdala. HRW additionally engaged sex-dependent antioxidant pathways in the spinal cord. These findings indicate that H2 alleviates sensory and affective alterations through region- and sex-dependent central mechanisms, supporting HRW as a promising therapeutic strategy for nociplastic pain and its affective comorbidities.