Role of the cholinergic muscarinic receptors of the CA1 area in the memory impairment induced by iron oxide nanoparticle in adult male rats

Objective(s): Nanoparticles of iron oxide (nFe2O3) are widely used in medicine and industry and could interfere with the brain processes associated with memory. The involvement of muscarinic cholinergic receptors in the process of memory formation has been confirmed. The present study aimed to investigate the possible interference of the cholinergic muscarinic receptors of the dorsal hippocampal CA1 area in the memory impairment induced by nFe2O3 in adult male rats. Materials and Methods: In this study, we examined the possible involvement of the cholinergic muscarinic receptors of the dorsal hippocampal CA1 area in the memory impairment induced by nFe2O3. In total, 70 male rats were divided into 10 groups of saline (1 μl/rat)+saline (1 ml/kg; intraperitoneal [IP]), saline (1 μl/ rat)+nFe2O3 (5 and 7.5 mg/kg; IP), pilocarpine (1 and 2 μg/rat)+saline (1 ml/kg), pilocarpine (1 and 2 μg/ rat)+nFe2O3 (7.5 mg/kg; IP), scopolamine (1 and 2 μg/rat)+saline (1 ml/kg), and scopolamine (1 μg/rat)+ nFe2O3 (5 mg/kg; IP). Results: Pilocarpine and scopolamine were injected intra-CA1 after training and before the IP administration of nFe2O3. The latency to enter the dark compartment in the step-through apparatus and locomotor activity was performed on the animals in an open field at 24 hours and seven days after training. The results indicated that nFe2O3 (7.5 mg/kg) decreased memory retrieval (P 0.01), while pilocarpine (1 and 2 μg/rat) significantly increased the step-through latency compared to the animals receiving nFe2O3 only (P 0.01). In addition, scopolamine (2 μg/rat) significantly decreased the step-through latency compared to the controls (P 0.05), while scopolamine (1 μg/rat) with nFe2O3 (5 mg/kg) reduced the step-through latency compared to the controls (P 0.01). Conclusion: According to the results, nFe2O3 could impair memory through decreasing the function of the cholinergic muscarinic receptors of the dorsal hippocampal CA1 area. It seems that the memory impairment caused by nFe2O3 might be due to the reduced activity of the cholinergic muscarinic receptors of the dorsal hippocampal CA1 area.