L-Lactate Administration Improved Synaptic Plasticity and Cognition in Early 3xTg-AD Mice.

Synaptic plasticity impairment and behavioral deficits constitute classical pathological hallmarks in early-stage Alzheimer's disease (AD). Emerging evidence suggests these synaptic dysfunctions may stem from metabolic dysregulation, particularly impaired aerobic glycolysis. As a key product of astrocyte-mediated aerobic glycolysis, lactate serves dual roles as both an energy substrate and a signaling molecule, playing a critical regulatory role in synaptic plasticity and long-term memory formation. This study investigated whether exogenous L-lactate supplementation could ameliorate synaptic dysfunction and cognitive deficits in early-stage AD models. Our findings reveal significant reductions in hippocampal lactate levels in experimental AD mice. Systemic administration of L-lactate (200 mg/kg) effectively restored physiological lactate concentrations in both hippocampal tissue and cerebrospinal fluid (CSF). Chronic L-lactate treatment significantly improved spatial learning and memory performance in behavioral assessments. Electrophysiological recordings demonstrated that either acute bath application of L-lactate (2 mM) to hippocampal slices or chronic intraperitoneal administration enhanced high-frequency stimulation (HFS)-induced long-term potentiation (LTP) magnitude in 3xTg-AD mice. Ultrastructural analysis revealed that L-lactate treatment enhanced synaptic density and improved morphological features of hippocampal synapses. At the molecular level, L-lactate administration upregulated synaptic marker synaptophysin (SYP) expression while downregulating activity-regulated cytoskeletal-associated protein (ARC) levels in AD mice. These multimodal findings demonstrate that exogenous L-lactate supplementation effectively restores synaptic plasticity and cognitive function in early-stage 3xTg-AD mice through concurrent improvements at behavioral, structural, and molecular levels.