| ObjectivePrenatal cocaine exposure(PCE)may alter the the reward characteristics and motivation of offspring,such as changes in addiction susceptibility.Previous animal experiments have shown that cocaine exposure in the middle and late stages of embryo may reduce or affect the ability of offspring to form conditional place preference(CPP)induced by cocaine,but its mechanism has not been clarified.Drug addiction is considered to be an abnormal learning process.According to Morris water maze or Barnes maze experiments,spatial learning and memory abilities of offspring rats prenatally exposed to cocaine are damaged.Moreover,radioactive arm maze test also shows that prenatal cocaine exposure may weaken the working and memory abilities of offspring.Therefore,we speculate that PCE impairs the spatial memory,spatial location and navigation abilities of offspring animals,which leads to the inability of PCE offspring to establish the relationship between the conditions for cocaine administration and the corresponding spatial location in CPP experiments.This may be the mechanism by which PCE reduces the ability of offspring to form cocaine-induced CPP.The hippocampus is generally considered to be an important neural structure basis for learning and memory,especially the dorsal hippocampus,which is closely related to spatial memory and working memory.We guess that the decrease in spatial learning and memory abilities of offspring arisen from prenatal cocaine exposure may be due to the damage of dorsal hippocampal function,and the changes in dorsal hippocampal function may lead to changes in neuronal electrical activity.In addition,the ventral hippocampus also shows a close two-way connection with medial prefrontal cortex(mPFC),mPFC is an important component of the reward loop,and increased desires for drugs in drug addiction often leads to increased excitability of neurons in the reward loop.Furthermore,previous experiments have shown that PCE can enhance the excitability of mPFC pyramidal neurons,thereby facilitating the production of long-term potentiation(LTP)of mPFC pyramidal neurons.Therefore,we infer that the excitability changes of mPFC caused by PCE will affect the excitability of ventral hippocampal neurons,leading to the increase of overall activity of PCE offspring after cocaine induction training in CPP experiment,which also reflects the increase of desire for cocaine in animals.It has proved in previous experiments that PCE can lead to damage of spatial learning and memory abilities in offspring,and synaptic plasticity is considered as the neurobiological basis for animals and humans to form learning and memory.In addition,an important manifestation of neuronal excitability is the change of post-synaptic electrical activity of neurons,which often reflects the change of synaptic junction itself in function and/or structure,and its basis depends largely on the change of synaptic plasticity.Therefore,we will reveal the effect of PCE on the spatial learning and memory abilities of offspring and focus the neurobiological mechanism of increased activity of PCE offspring in CPP experiment on the changes of synaptic plasticity,and specifically study the possible changes of synaptic plasticity in function and structure.To verify the above hypothesis,this study intends to expound the mechanism of PCE-induced spatial learning and memory impairment and the specific molecular mechanism of synaptic plasticity changes from the perspective of PCE-induced changes in postsynaptic electrical activity and synaptic plasticity of neurons in CA1 region of dorsal and ventral hippocampus.These findings will provide new ideas and evidence for revealing the cellular mechanism of PCE induced neural developmental and cognitive changes in offspring.Methods 1.The effect of cocaine exposure during embryonic period on the ability of offspring rats to form cocaine-induced CPP is validated by the conditional place preference experiment using the holistic behavioral approach,so as to determine whether the changes of CPP caused by PCE are related to the impairment of spatial learning and memory abilities,and to analyze the changes of overall activity of PCE offspring before and after cocaine induction training in CPP experiment.2.The mini excitatory postsynaptic current(mEPSC)of CA1 pyramidal neurons in dorsal and ventral hippocampus of offspring rats in PCE group and normal saline control group are recorded by neuroelectrophysiological experimental methods,and the changes of mEPSC of CA1 pyramidal neurons in dorsal and ventral hippocampus of offspring rats in PCE group and control group after acute cocaine exposure are recorded,acute cocaine exposure is used to simulate the process of cocaine training in CPP experiments,so as to study the relationship between animal behavior and excitability of hippocampal neurons after training.3.Whole-cell patch clamp is used to record the AMPA/NMDA postsynaptic current ratio(AN ratio)of CA1 pyramidal neurons in dorsal and ventral hippocampus of offspring rats in PCE group and control group,so as to analyze the changes in postsynaptic plasticity of CA1 pyramidal neurons in offspring rats induced by PCE,and record the changes of the AN ratio of CA1 pyramidal neurons in dorsal and ventral hippocampus of offspring rats in PCE group and control group after acute cocaine exposure.4.Paired stimulus ratio(PPR)of CA1 pyramidal neurons in dorsal and ventral hippocampus of offspring rats in PCE group and control group is recorded to analyze the changes in presynaptic plasticity induced by PCE on hippocampal CA1 pyramidal neurons in offspring rats,and the changes of PPR in ventral and dorsal hippocampal CA1 pyramidal neurons in PCE group and control group are recorded and analyzed after acute cocaine exposure.5.Golgi staining method is adopted to study the effect of PCE on dendritic spine density of CA1 pyramidal neurons in dorsal and ventral hippocampus of offspring rats,and compare the dendritic spine density of CA1 pyramidal neurons in dorsal and ventral hippocampus between the animals after acute cocaine exposure and the same pretreatment animals that do not receive acute cocaine exposure.Results 1.CPP experimental results show: cocaine exposure during embryonic period significantly prolongs the time of offspring rats to form cocaine-induced CPP,but it does not affect the increase of total exercise time and distance of offspring after cocaine induction training,and it reduces the total exercise time and distance of offspring rats in pretest.2.mEPSC results show: cocaine exposure during embryonic period does not affect mEPSC of the offspring hippocampal CA1 pyramidal neurons,but PCE can the change of mEPSC amplitude of dorsal hippocampal CA1 pyramidal neurons in offspring rats after acute cocaine administration,and PCE has no significant effect on the amplitude and frequency of mEPSC of ventral hippocampal CA1 pyramidal neurons in offspring rats after acute cocaine exposure.3.AN ratio results show: cocaine exposure during embryonic period does not affect the AN ratio of CA1 pyramidal neurons in the dorsal and ventral hippocampus of offspring rats under basic state,but the AN ratio of CA1 pyramidal neurons in the dorsal hippocampus of offspring rats in PCE group is lower than that in control group after acute cocaine rekindling,and the AN ratio of CA1 pyramidal neurons in dorsal hippocampus of offspring rats induced by PCE's inhibition of acute cocaine exposure increases.4.PPR results show: cocaine exposure during embryonic period does not affect the PPR of CA1 pyramidal neurons in dorsal and ventral hippocampus of offspring rats.After acute cocaine exposure,the PPR of CA1 pyramidal neurons in ventral hippocampus of offspring rats in both PCE group and naive group increases,and there is no significant difference in amplitude.5.Dendritic spine density results show: cocaine exposure during embryonic period may reduce dendritic spine density of pyramidal neurons in CA1 region of dorsal hippocampus,and acute cocaine exposure reduces dendritic spine density of pyramidal neurons in CA1 region of dorsal hippocampus in offspring of PCE group and naive group,but PCE group does not reduce as much as naive group.Although cocaine exposure during embryonic period may reduce dendritic spine density of pyramidal neurons in CA1 area of ventral hippocampus,the dendritic spine density of ventral hippocampal CA1 pyramidal neurons in PCE offspring rats only changes significantly 4 weeks after birth after acute cocaine exposure,while offspring rats in naive group and PCE group that is 7 weeks after birth have no significant changes compared with the same pretreatment group without acute cocaine exposure.Conclusions 1.The behavioral experiment has proved that cocaine exposure in utero indeed weakens the ability of offspring rats to form cocaine-induced CPP,and significantly prolongs the time of offspring rats to form CPP.Moreover,PCE does not affect the desire of offspring for cocaine.2.It expounds that the impairment of spatial memory in offspring rats induced by prenatal cocaine exposure is an important reason that PCE hinders offspring rats from forming cocaine-induced CPP.Indeed,PCE inhibits the increase of mEPSC amplitude of CA1 pyramidal neurons in dorsal hippocampus of offspring rats after acute cocaine exposure,and decreases dendritic spine density of them.3.It is first found that the effect of PCE on synaptic plasticity of CA1 pyramidal neurons in the dorsal hippocampus of offspring rats mainly occurs on the postsynaptic membrane,which has no significant effect on presynaptic membrane.PCE inhibits the AN ratio of CA1 pyramidal neurons in dorsal hippocampus of offspring rats after acute cocaine exposure,but has no significant effect on PPR.4.It is found that the PPR of the ventral hippocampal CA1 pyramidal neurons increases significantly in both naive group and PCE group after acute cocaine exposure,and there is no difference in amplitude. |
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