Regulation Of TNF-α And GDNF Proteins In Hippocampal CA₁ Of Rats Chronically Treated With Morphine And After Naloxone Precipitated Withdrawal

OBJECTIVES: Recent evidence has suggested that various neurotrophic factors and cytokines are involved in the effects of psychomotor stimulants, suggesting that these factors play a role in drug addiction. In the present study we used immunohistochemistry methodology to analyze the expression of tumor necrosis factor[alpha] (TNF-α) and glial cell line-derived neurotrophic factor (GDNF) proteins in the rat hippocampal CA1 chronically treated with morphine and after naloxone precipitated withdrawal. In order to understand the molecular mechanisms underlying such plasticity during drug addiction,METHODS: Twenty four male Sprague-Dawley rats were divided randomly into three groups : the control group(A group), morphine-dependent group(B group), and naloxone-precipitated withdrawal group (which were divided again randomly into 1h and 3h group, i.e C and D group), There are 6 rats in each group. Except A group, All of the rats were treated with ascending doses of morphine (10-50 mg/kg twice daily, subcutaneous, s.c.) for 6 days, then withdrawal withnaloxone (5 mg/kg, s.c.) or saline 6h after the final morphine injection. The rats all in four groups were perfused transcardially and their brains were removed and processed for immunohistochemistry. The expression of TNF-a and GDNF in the rat hippocampal CAl was studied with immunohistochemistry and the average light-density and quantity of postive cells were analyzed by an image processing system. One-way ANOVA and Bonferroni was used to analyze the data. RESULTS: We found that both B group and C, D group significantly increased the level of TNF-a and GDNF proteins in the rat hippocampal CAl region (P < 0.01). There was a persistently increased level of GDNF proteins in morphine-dependent rats and withdrawal rats while at the same time a slightly attenuated level of TNF-a proteins in D group compared to that of C group. The colour of the immunohistochemical staining of TNF-a and GDNF in B, C and D group was darker than that of A group (P < 0.01). Comparison of average light-density of TNF-a and GDNF shows that there was no difference in the groups between B and D, and C and D group, respectively, this result was also obtained in the groups between B and D group when contrasted quantity of TNF-a postive cells (P > 0.05). The form of the positive cells that are mainly glial cells and neuron was changed in each group. In addtion, the modelof morphine-dependent rats was established successfully. CONCLUSION: These results suggest that the activation of theTNF-a and GDNF proteins in rat hippocampal CAl contributes to morphine dependence and naloxone-precipitated withdrawal. The neurotrophic factors and cytokines participate in morphinedependence by acute and chronic morphine adminstration which are mediated by neurotoxicity, immunosuppression and inflammation or insult. These may be associated with adaptive changes in gene expression in the brain, in which GDNF acts as protective effective and TNF-a may have both deleterious and beneficial effects. Understanding these changes and neuroadaptive process can lead to the development of strategies that may potentially enable therapeutic interventions to offset or reverse the neurobehavioral defects.