| Drug addiction is an important factor endangering social stability.Cocaine is one of the most inundant drugs.The most prominent characteristic of drug addiction is behavioral sensitization,i.e.excessive use of addictive drugs evokes significant increase in spontaneous activity.And behavioral sensitization has been reported pertinent to impulsive drug seeking and addictive craving.It is believed that behavioral sensitization is mediated through the pathway of the ventral tegmental area(VTA),nucleus accumbens(NAc)and prefrontal cortex(PFC).However,current investigations are mostly focused on VTA and NAc,few studies are made on PFC,especially the medial PFC(mPFC).To explore the effect of mPFC in cocaine-induced behavioral sensitization,this study was delved into the change of cocaine-induced behavioral sensitization and the pyramidal neuron firing activities in mPFC based on ethology of C57BL/6N mice.The results were as follows:1.A single injection of cocaine significantly increases the mouse spontaneous activity in an annular track;and the mice demonstrate a progressive increment in the spontaneous activity during a period of successive 5-day injections;and the spontaneous activity show further enhancement at cocaine injection after a subsequent 10-day withdrawal,exhibiting a credible outcome of behavioral sensitization.2.Electrophysiological results show that acute cocaine evokes decrease of firing frequency(both the spontaneous firing and the burst firing)in the pyramidal neurons in mPFC.Both repeated cocaine injections(for successive 5 days)and 10-day withdrawal after repeated cocaine injections induce more remarkable decrease in neuronal firings.In conclusion,our present results indicate that cocaine-induced inhibition in mPFC neuronal activity is involved in addictive behaviors.These findings uncover a new mechanism underlying drug addiction and may provide new thoughts on addiction intervention. |
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