The Regulatory Mechanism Of MP-10against Morphine Induced Conditioned Place Preference And Withdrawal Symptom

BackgroundDrug abuse is regarded as a kind of pertinacious encephalopathy with a high recurrence rate. Response of brain to addictive drug includes the adaptive of neuron and plasticity of synaptic. These changes are due to the effects of addictive drug on nucleus accumbens (NAc), prefrontal cortex (PFC), amygdale, and hippocampus of reward circuit in the brain. The effects will then give rise to the activation of some transcription factor such as CREB, ERK, and AFosB, regulating the transcription of genes participating synapse plasticity. Conditional place preference (CPP) is a kind of commonly used animal model to study drug abuse because it can simulate the psychological dependence of human on animal, and naloxone can precipitate physical dependence of human on animal which was chronically administrated with morphine. MP-10, a kind of novel phosphodiesterase (PDE) inhibitor characterized as specificity to the PDE10A isoform which is localized in medium spine neuron (MSN) of striatum, can hydrolyze cAMP and cGMP to influence signal transduction of MSN. Striatum, with90%-97%MSN cells, is principal projection target of dopaminergic neuron correlative to withdrawal symptoms. At the same time, the ventral striatum is the nucleus mediating addictive effect of abuse. So it is supposed the physiologic function of striatum would be influenced after administration of MP-10through affecting signal transduction of MSN.AimTo investigate the effect of MP-10on the acquisition, expression, extinction, relapse of morphine-induced CPP and on naloxone precipitated morphine withdrawal symptom.To clarify the mechanism of MP-10through investigating the activation of pCREB, pERK, and△FosB in NAc, dorsal striatum, PFC, amygdale, and hippocampus of reward circuit. MethodIn CPP experiment, rats were randomly divided into saline group, morphine group, MP-10/1.25mg/kg group, MP-10/2.5mg/kg group, MP-10/5.0mg/kg group and MP-10/10.0mg/kg group to observe the effect of each dose of MP-10on morphine-induced CPP. A separate experiment was carried out with MP-10/2.5mg/kg, MP-10/5.0mg/kg, and MP-10/10.0mg/kg administrated alone respectively to examine whether MP-10can induce CPP. After we determined that MP-10/2.5mg/kg inhibited the acquisition of morphine-induced CPP and did not induce CPP when administrated alone, then we examined whether MP-10/2.5mg/kg can affect the locomotion, inhibit the expression of CPP, accelerate the extinction of CPP, and inhibit the relapse of CPP.We established morphine dependence model with subcutaneous injection of increasing doses of morphine. The doses were10,20,40,60,80,100mg/kg in6days. Naloxone (2.0mg/kg) was i.p. injected to precipitate withdrawal symptom. Different dose of MP-10was s.c. injected30min before naloxone administration to observe the effect of MP-10on withdrawal symptom.After acquisition of morphine-induced CPP, rats were perfused with4%paraformaldehyde through left ventricle. The brains were taken and sliced in freezing microtome. The sections were taken according to rats’ brain mapping of Paxinos and Watson (2004,5th):anterior cingutate cortex (bregma+2.16), caudate putamen (bregma+1.56), NAc (bregma+1.56), amygdale (bregma-2.16). The sections were incubated with antibodies of pCREB and△FosB, and then observed with laser confocal microscopy.After the test section of CPP acquisition and observation of withdrawal symptom, rats were anesthetized and decapitated. Caudate putamen (CPu), NAc, hippocampus, and prefrontal cortex were taken. Total protein were extracted with lysing buffer and separated with SDS-PAGE gel electrophoresis and blotted to PVDF film. Then the film was blocked and incubated with primary and second antibody of pERK and total ERK in sequence. The protein was colored with ECL and photographed. The relative expression of protein was calculated with image analysis system.ResultsMP-10/2.5mg/kg s.c. injection can not induce CPP, but it significantly inhibited the acquisition of morphine-induced CPP. Furthermore, it can not inhibit the expression of CPP, but it can accelerate the extinction of morphine-induced CPP. MP-10/0.5mg/kg and MP-10/1.0mg/kg s.c. injection significantly decrease the score of naloxone precipitated morphine withdrawal symptom accompanied by obvious sedative effect.MP-10/2.5mg/kg s.c. injection can not increase the pCREB in dorsomedial striatum, shell of NAc, anterior cingutate cortex (ACC), and basolateral amygdale, but it inhibited morphine induced pCREB upregulation in these areas.MP-10/2.5mg/kg s.c. injection increased the△FosB in dorsomedial striatum, shell of NAc, and ACC, but it inhibited morphine induced increase of△FosB in shell of NAc, ACC, and basolateral amygdale when it was administration30min before morphine.MP-10/2.5mg/kg s.c. injection lightly increase pERK in NAc and hippocampus, but it significantly inhibit morphine induced increase of pERK in PFC, NAc, and hippocampus.ConclusionMP-10/2.5mg/kg administration inhibits morphine induced conditional place preference through inhibiting morphine induced increasing of pCREB and AFosB in dorsomedial striatum. shell of nucleus accumbens, anterior cingutate cortex, basolateral amygdale and increasing of pERK upregulation in prefrontal cortex, nucleus accumbens, and hippocampus. MP-10/0.5mg/kg and MP-10/1.0mg/kg s.c. injection significantly decrease the score of naloxone precipitated morphine withdrawal symptom accompanied by obvious sedative effect.Our results strongly support that MP-10can inhibit morphine induced CPP and withdrawal symptom, and thus it might have therapeutic potential in the treatment of opioid abuse.