Synaptic plasticity of neurons in nucleus accumbens, hippocampal CAl in chronic morphine treated rats

Objective: To explore the morphine - induced synaptic plasticity by measuring synaptic interface structural parameters of neurons in Nucleus accumbens (NAc) and hippocampus CA1 (HIPCA1) of chronic morphine - treated rats. Methods: Ten male Sprague - Dawley rats were randomly assigned into morphine group (injected intraperitoneally morphine twice a day for 10 days in ascending dosage schedule) or control group (injected physical saline of the same volume). Rats were killed on 6 day following the last injection. NAc and HIPCAlwere removed and prepared for electron microscope specimen. The synaptic interface structural parameters of neurons in NAc and HIPCAlwere measured. Results: The length of synaptic active zone (226.46 ± 21. 10nm) and post synaptic density (43. 5 ± 5.44nm) in NAc neurons of morphine - treated rats were significantly lower than that of control [(319.30 ± 13.40nm), (58. 7 ± 4. 95nm) ,P0. 01], but not the curvature of synaptic interface and the width of synaptic cleft. No significant difference was found in the synaptic interface structure parameters in HIPCA1 neurons between two groups. Conclusion: The synaptic plasticity in NAc neurons may occur following the chronic morphine treatment.