Repeated Levonorgestrel Administration Impairs Cognitive Function via Glutamatergic Transmission and CaMKII-PKA-BDNF Signaling in the Hippocampus of Female Wistar Rats.

Background: Levonorgestrel (LNG), a synthetic progestin widely used in emergency contraception, is increasingly taken frequently and often without medical supervision. With rising concerns that repeated exposure to such hormones may adversely affect brain function, this study investigated whether chronic LNG administration impairs cognitive-like behavior and alters key neurochemical pathways in female Wistar rats. Methods: Experimental rats were assigned to three groups receiving normal saline (control) or LNG (4 or 8 µg/kg) every alternate day for 60 days. Cognitive performance was assessed using the Morris water maze (MWM) and novel object recognition (NOR) tests. Hippocampal tissues were subsequently analyzed for glutamatergic markers and downstream signaling molecules involved in learning and memory. Results: Chronic LNG exposure (4 and 8 µg/kg) impaired both spatial and non-spatial memory, evidenced by prolonged escape latency and reduced path efficiency in the MWM, along with a decreased discrimination index in the NOR test. Neurochemically, LNG significantly reduced hippocampal levels of glutamate, N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor ligands, protein kinase A (PKA), calcium/calmodulin-dependent kinase II (CaMKII), and brain-derived neurotrophic factor (BDNF), with the 8 µg/kg dose exerting more pronounced effects. Conclusion: Repeated LNG administration leads to notable cognitive deficits, likely mediated by impairments in glutamatergic signaling and downstream molecular pathways essential for synaptic plasticity. These findings underscore potential neurocognitive risks associated with prolonged LNG exposure.