| Background: Repeated morphine exposure can induce behavioral sensitization. Thereare evidences have shown that central gamma-aminobutyric acid (GABA) system is involvedin morphine dependence. However, the effect of GABABreceptor agonist baclofen onmorphine-induced behavioral sensitization in rats is unclear. Methods: we used morphine-induced behavioral sensitization model in rat to investigate the effects of baclofen onbehavioral sensitization. Moreover, dopamine release in the shell of the nucleus accumbenswas evaluated using microdialysis assay in vivo. Results: The present study demonstrated thatmorphine challenge (3mg/kg, s.c.) obviously enhanced the locomotor activity following4-day consecutive morphine administration and3-day withdrawal period, which indicated theexpression of morphine sensitization. In addition, chronic treatment with baclofen (2.5,5mg/kg) significantly inhibited the development of morphine sensitization. It was also foundthat morphine challenge3days after repeated morphine administration produced a significantincrease of extracellular dopamine release in nucleus accubens. Furthermore, chronictreatment with baclofen decreased the dopamine release induced by morphine challenge.Conclusions: Our results indicated that gamma-aminobutyric acid system plays an importantrole in the morphine sensitization in rat and suggested that behavioral sensitization is apromising model to study the mechanism underlying drug abuse.
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