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

Halimat Amin Abdulrahim,1,2 Noah Adavize Omeiza,3,4 Ganiu Jimoh Akorede,5 Oluwadamilare Iyapo,6 John Olabode Fatoki,1,7 Ben-Azu Benneth,8 Emmanuel Bukoye Oyewo,1 Aboyeji Lukuman Oyewole,9 Abdullateef Isiaka Alagbonsi,10 Adeniran Sanmi Adekunle1 1Department of Biochemistry, Faculty of Basic Medical Sciences, College of Health Sciences, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria; 2Department of Medical Biochemistry, Faculty of Basic Medical Sciences, College of Health Sciences, University of Ilorin, Ilorin, Kwara State, Nigeria; 3Department of Pharmacology and Therapeutics, Faculty of Basic Clinical Sciences, University of Medical Sciences, Ondo, Ondo State, Nigeria; 4Department of Pharmacology and Therapeutics, College of Medicine, University of Ibadan, Ibadan, Oyo State, Nigeria; 5Department of Veterinary Pharmacology and Toxicology, Faculty of Veterinary Medicine, University of Ilorin, Ilorin, Kwara State, Nigeria; 6Department of Morbid Anatomy, Eko University of Medicine and Health Sciences, Ijanikin, Lagos State, Nigeria; 7Department of Medical Biochemistry, Faculty of Basic Medical Sciences, College of Health Sciences, Osun State University, Osogbo, Nigeria; 8DELSU Joint Canada-Israel Neuroscience and Biopsychiatry Laboratory, Department of Pharmacology, Faculty of Basic Medical Sciences, Delta State University, Abraka, Delta State, Nigeria; 9Department of Physiology, Faculty of Basic Medical Sciences, College of Health Sciences, University of Ilorin, Ilorin, Kwara State, Nigeria; 10Department of Physiology, School of Medicine and Pharmacy, College of Medicine and Health Sciences, University of Rwanda, Huye, Southern Province, RwandaCorrespondence: Abdullateef Isiaka Alagbonsi, Department of Physiology, School of Medicine and Pharmacy, College of Medicine and Health Sciences, University of Rwanda, Huye, Southern Province, Rwanda, Tel +250786092444, Email [email protected]: 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. Keywords: cognitive dysfunction, glutamatergic pathway, hippocampus, levonorgestrel, memory, neuropsychological tests