Doxylamine, a first-generation histamine H1 receptor antagonist widely used as an over-the-counter sedative, has poorly-characterized long-term neurobiological effects. This study investigated the impact of chronic doxylamine exposure on cognitive behavior, oxidative status, cholinergic signaling, and neuroinflammatory responses in the hippocampus and prefrontal cortex (PFC) of male and female Wistar rats. Adult rats were administered oral doses of doxylamine 2 mg/kg, 4 mg/kg and phosphate-buffered saline daily for 28 days. Behavioral performance was assessed using the Y-maze, Open field test, and Morris water maze. Biochemical assays evaluated antioxidant enzyme activity, lipid peroxidation, cholinergic markers, and bioenergetic indices, while histological and immunohistochemical analyses examined cytoarchitecture and the expression of Glial Fibrillary Acidic Protein (GFAP), Ionized Calcium-Binding Adapter Molecule 1 (IBA-1), Bcl-2–Associated X protein (BAX), and Nuclear factor erythroid 2–related factor 2 (NRF2).
Chronic doxylamine exposure resulted in dose-dependent increases in body weight and significant alterations in brain weight. Behavioral findings demonstrated impaired spatial learning and memory, alongside increased anxiety-like behavior, without significant changes in locomotor activity. These deficits were accompanied by oxidative imbalance, elevated lipid peroxidation, disrupted cholinergic signaling, and altered energy metabolism in both brain regions. Furthermore, doxylamine administration induced marked astrocytic and microglial activation, enhanced pro-apoptotic signaling, and pronounced neuroinflammatory responses, particularly at the higher dose.
In conclusion, prolonged doxylamine exposure induces dose-dependent cognitive impairment mediated by oxidative stress, cholinergic dysfunction, and neuroinflammation in brain regions critical for memory and executive function. These findings suggest potential neurobiological risks associated with chronic doxylamine use.
