The Effects Of Morphine On The Firing Pattern Of Ventral Pallidal Neurons In The Addictive Rats

ABSTRACT The effects of morphine on the firing pattern of ventral pallidal neurons in the addictive rats The mesocorticolimbic dopamine system has long been the focus of research about drug dependence for its involvement in psychological dependence. It was well known that the nucleus accumbens might play an important role in this process. However, ventral pallidum, as an important relaying or projecting target of the nucleus accumbens, has still received little attention for its role in this process as far. Objective: In order to elucidate the pivotal roles played by ventral pallidum in the addiction mechanism, the present study was designed to examine the electrophysiological properties of ventral pallidal neurons in the addictive rats with the presence of morphine or morphine as well as naloxone. Method: The rats received graded morphine each day intraperitanealy. Then we evaluated their abstinence behavior in order to make sure they were addictive indeed. The firing series, frequencies, and spikes intervals of ventral pallidal neurons in the normal rats that received different doses of morphine were recorded and analysed respectively with the help of extracellular single-unit recording technique. The firing series, frequencies, and spikes intervals of ventral pallidal neurons in normal or addictive rats were recorded and analysed respectively with the presence of morphine or morphine as well as naloxone. Result: 1. The addictive rat model was established successfully according to the evaluation with their abstinence behavior. 2. The firing of ventral pallidal neurons was inhibited by morphine significantly in normal rats. 3. The firing of ventral pallidal neurons was enhanced prominently in addictive rats, and it could be reversed by naloxone completely. Conclusion: 1. The firing of ventral pallidal neurons could be inhibited by morphine significantly in normal rats, however, enhanced prominently in addictive rats. 2. The effects of morphine on the ventral pallidal neurons changed into excitation from inhibition in the addictive animals. 3. Ventral pallidum might play an important role in the drug addiction process.