EEG Power Spectrum Profile In Morphine Rats And The Roles Of Hippocampal- Prefrontal Cortical Circuits In Morphine Addictive Memory

Drug addiction is a kind of global health and society problem.Drug addiction belongs to the nervous system diseases.Addictive drugs lead to adaptational changes of the morphology and function of the neural systerm.The forms of expression drug addiction include compulsive drug seeking,craving and relapse.It is hard to refuse if one was addicted.Recently,the mechanism of addiction has become more and more clear.Many reports indicated that addiction pathological usurp some brain regions and neural mechanisms of normal learning and memory.Addiction shares many neurocircuits with normal learning and memory.Therefore,it is considered that drug addiction,esp.the psychological addiction,should be a form of learning and memory.So it is also called addictive memory.The hippocampus(HP)and the prefrontal cortex(PFC)are two important brain regions in learning and memory,which are also proved being engaged in drug addiction.The PFC is related to reward effect,drugseeking and relapse.And the HP plays a more important role in addictive memory.There are densly anatomical projections and functional interactions between the two brain areas.Considering the key roles of the HP-PFC circuits in spatial memory,we want to know whether the circuits are involved in addictive memory.It is just the main aim of present dissertation.The experimental reseach included two parts.Most of drug addiction related EEG recording were from skull surface recoding.Few of data were from deeply intercranial recording.In Chapter 2,we investigated the effects of naloxone(Nx)antagonism of the opiate receptor on the local EEG power spectrum componants in the HP and the infralimbic cortex(ILC)of the PFC.Firstly,we established a morphine(Mf)addiction model in rats by injection contant dosage of morphine(10 mg / kg / 48 h,s.c.)for consecutive 8 d.Then the addictive effects were conformed by withdrawal test and conditioned place preference(CPP)test.Then the EEG signals were recorded from the dorsal HP(DH)and the ILC in anaesthetized CPP rats before and after Nx injection.The EEG power componants were analyzed after EEG recording.Results show that,the DH power of ? and ? reversibly decreased after Nx injection(P < 0.05).However,the ILC power of ?(P < 0.01)and ?(P < 0.05),and percentage in total power of ?(P < 0.05)increased after Nx injection.This part of results proved that Nx antagonism of opiate receptor could change the DH and ILC EEG power spectrum componants in Mf addicted rats.The HP and PFC play important roles in different phases of drug addiction.But it is unknown whether the HP-PFC circuits are key circuits in addictive memory.In Chapter 3,we investigated the effect of permanent lesion of the HP,medial PFC(mPFC)and the HP-PFC circuits in learning and memory,esp.in Mf addictive memory.At first,kainic acid(KA)was injected into the bilateral DH(DH group),bilateral ventral HP(VH group),bilateral mPFC(PFC group),unilateral DH with collateral mPFC(DH-PFC group),or unilateral DH with contralateral mPFC(DH/PFC group),unilateral VH with collateral mPFC(VH-PFC group),unilateral DH with contralateral mPFC(VH/PFC group)of Wistar rats.Then these rats were trained in CPP task,Morris water maze(MWM)task and passive avoidance(PA)task.The results show that,in CPP test,DH-PFC group and VH-PFC group looked like Mf sham group,can establish CPP nomally(all P < 0.05,vs.baseline;P>0.05,vs Mf sham group),but DH group,VH group,PFC group,DH/PFC group and VH/PFC group,looked like saline sham group,could not establish CPP.In MWM task,all groups showed normal motor and vision performance by swimming speed and visible platform test(all P > 0.05).In PA task,PFC group,along with saline sham group and Mf sham group,show powerful retention latency in test phase(P < 0.01,vs baseline),but all the other groups showed shorter but also significant retention latencies(all P <0.05,vs baseline and vs saline/Mf sham group).Present results firstly found that Mf addictive CPP memory dependent on the intact of HP-PFC circuits,so both of the VH-PFC circuit and the DH-PFC circuit are the key circuits for Mf addictive memory;and the HP would be the common node of the key circuits for spatial memory,passive avoidance memory and Mf addictive memory.