It is well known that the synapses undergo some changes in the brain during the course of normal life and under certain pathological or experimental circumstances. One of the main goals of numerous researchers has been to find the reasons for these structural changes. In the present study, we investigated the effects of chronic morphine consumption on synaptic plasticity, postsynaptic density thickness, and synaptic curvatures of hippocampus CA1 area of rats. So for reaching these goals, 24 N-Mary male rats were randomly divided into three groups, morphine ( ), placebo ( ), and control ( ) groups. In the morphine group, complex of morphine (0.1, 0.2, 0.3, and 0.4) mg/mL and in the placebo (sucrose) group complex of sucrose (% 0.3) were used for 21 days. After the end of drug treatment the animals were scarified and perfused intracardinally and finally the CA1 hippocampal samples were taken for ultrastructural studies, and then the obtained data were analyzed by SPSS and one-way analysis of variance. Our data indicated that synaptic numbers per nm3 change significantly in morphine group compared to the other two groups (placebo and control) ( ) and also statistical analysis revealed a significant difference between groups in terms of thickness of postsynaptic density ( ) and synaptic curvature ( ). It seems that morphine dependence in rats plays a main role in the ultrastructural changes of hippocampus. 1. Introduction Today the opiates are the most addictive substance used in the world wide and they are considered as one of the greatest neuropsychological disorder reasons [1–4]. It has been shown that chronic consumption of opiates can significantly change the functions, structures, and morphology of neural systems [5, 6]. This kind of changes causes several different types of disorders such as drug addiction, carelessness, fluent speech disorders, memory and learning impairment, and psychological disorders [7–10]. According to the studies, drug addiction is an abnormal form of learning and an adaptation of the memory system in certain regions of the brain, such as the hippocampus [11]. The learning processes are defined as a modification in some synaptic functions (synaptic plasticity), changes in the pre- and postsynaptic ultrastructure, and the formation of new synapses [10, 12]. It is known that the synapses of hippocampus formation are more structurally affected by learning process [12–16]. There are previous researchers demonstrate that opiates have either direct or indirect effect on capacity of learning and memory, processes. Concerning the role
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