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Research Express@NCKU - Articles DigestFIG 5. Exchange energy 8J vs d D .To identify the possible long-range magnetic ordering in these systems, the Heisenberg type of spincoupling is employed to model the interaction J between the nearest-neighbour magnetic moments dueto defects (FIG.5). There are only two systems, i.e. O N and V B , which have large enough exchangeenergies to be identified numerically as magnetically ordered systems. Within the framework of theHeisenberg model, it is possible to estimate the Curie temperature (T C ) while the estimated values(T MF C ) from the present treatment are expected as the upper bound. For O N systems with a defectconcentration of 3.125%, the T MF C can reach up to 72K. In summary, we have demonstrated that all thestudied defect systems with partially filled defect bands exhibited a definite preference for finitemagnetic moments. The magnetic properties can depend on the defect concentrations and a long-rangemagnetic order is likely to occur in the systems of high defect concentration like O N and V B whose defectbands are extended in nature.5 of 5
Research Express@NCKU - Articles DigestResearch Express@NCKU Volume 6 Issue 2 - October 17, 2008[ http://research.ncku.edu.tw/re/articles/e/20081017/5.html ]Repeated cocaine exposure impairs theinduction of long-term depression in ratmedial prefrontal cortexChiung-Chun Huang 1 , Ping-Chun Yang 1 , Hsiao-Ju Lin 1 , and Kuei-SenHsu 1,2,*1 Department of Pharmacology, College of Medicine, and 2 Center for Gene Regulation and SignalTransduction Research, National Cheng Kung University, Tainan 701, Taiwanrichard@mail.ncku.edu.twThe Journal of Neuroscience (2007) 27: 2958-2968.IntroductionRepeated exposure to psychostimulants, such as cocaine andamphetamine, produces a progressive and enduring increasein their locomotor stimulatory effects. This enhancedbehavioral response is generally referred to as behavioralsensitization and is postulated to contribute to drug cravingand relapse to addiction. Many recent studies on theneurobiological basis of behavioral sensitization havefocused on the mesolimbic dopaminergic system becausecocaine and amphetamine act to block the reuptake orstimulate the release, respectively, of dopamine within this system. The mesolimbic system consists ofdopamine perikarya located in the ventral tegmental area (VTA) that project to numerous limbic areasincluding nucleus accumbens (NAc). Furthermore, cumulative evidence suggests that adaptive changeswithin the VTA appear to mediate the induction of behavioral sensitization, whereas adaptations in theNAc are involved in its long-term maintenance. Besides the mesolimbic system, recent studies haveimplicated an important role for the mesocortical system, in particular the medial prefrontal cortex(mPFC), in the development of behavioral sensitization. For example, direct electrical stimulation of thePFC leads to rewarding effects and sensitization to cocaine, whereas lesion of the PFC or impairment ofmesocorticolimbic glutamatergic transmission prevents the development of cocaine-induced behavioralsensitization. Furthermore, evidence is accumulating that the alterations of multiple mPFCneurotransmitter systems, including dopamine, serotonin, glutamate, noradrenalin, acetylcholine,GABA and peptides, and signaling by receptors activated by these neurotransmitters may also contributeto the development of cocaine sensitization and addiction.Accumulating evidence indicates that drug-induced synaptic plasticity may contribute to thereorganization of neural circuitry that underlies behavioral sensitization to drugs of abuse and thus thedevelopment of addiction. It has been shown that a single or repeated exposure in vivo to addictivedrugs induces alterations of synaptic transmission and/or long-term synaptic plasticity at excitatorysynapses in in vitro slice preparations of the VTA, NAc, periaqueductal gray, hippocampus, andstriatum. Less work has been done on the impact of in vivo exposures to drugs of abuse on excitatorysynaptic transmission in the mPFC. Our laboratory has recently demonstrated that repeated cocaine1 of 5
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