Perineuronal nets and cocaine-associated memories

 描述（由申请人提供）：治疗人类成瘾的一种策略是靶向成瘾行为背后的记忆过程。反复使用毒品会建立与毒品有关的记忆。当这些与药物相关的记忆被回忆起来时，当生物体重新暴露于与药物相关的线索、背景或药物本身时，这些记忆会被重新巩固，以维持或加强它们。内侧前额叶皮层（mPFC）是人类可卡因寻求行为复发和啮齿动物恢复行为的关键因素。从mPFC锥体神经元到延髓核（NAc）的兴奋性输出增加被认为是复发的基础。在啮齿类动物中，这种增加的输出在5次可卡因注射后和可卡因自我给药后45天戒断后被发现，这暗示了mPFC在维持可卡因相关记忆中的关键作用。然而，我们不知道mPFC对这些记忆表达的作用机制。来自mPFC的输出由小清蛋白（PV）-快速尖峰GABA能中间神经元有力地调节，其中大多数被形成神经元周网（PNN）的特化细胞外基质结构包围。PNN在发育过程中包裹某些神经元，似乎稳定突触，降低成年期神经元的可塑性。然而，PNN可以在成年期被移除以重建可塑性或通过其他强加的刺激来修改可塑性。我们已经发现，大鼠前边缘mPFC（PL mPFC）内的PNN的去除减少可卡因相关的记忆的再巩固与条件性位置偏好（CPP;以下称为“可卡因CPP记忆”）的测试。重复可卡因暴露具有相反的效果：它增加PNN强度，并且该强度与行为正相关，表明PL mPFC中的PNN强度可以作为可卡因诱导的行为的预测因子。我们的实验的总体布局如下：建立可卡因CPP记忆→重新激活可卡因CPP记忆± PNNs→重新巩固可卡因CPP记忆→随后测试可卡因CPP记忆的恢复，看看它是维持还是减少。我们建议，从PL mPFC的PNNs的去除防止可卡因CPP记忆通过减少记忆再巩固的维护。然而，我们不知道PNN去除减少记忆再巩固的机制。我们推测，PL mPFC内的PNNs的去除修改可卡因诱导的可塑性可卡因CPP记忆的再巩固过程中。我们进一步假设，通过改变PL mPFC中抑制性中间神经元和锥体神经元的活性，PNNs介导了再巩固。我们将在存在和不存在PNN的情况下训练大鼠进行可卡因诱导的CPP，并确定PL mPFC中PNN包围的神经元的动态变化：1）记忆重新激活之前和之后; 2）可卡因诱导的恢复之前和之后。我们将使用行为，电生理，形态，共聚焦和电子显微镜的方法来测试我们的假设。PNNs是一个非常新颖的目标，解剖可卡因诱导的可塑性和可卡因相关记忆的维持至关重要的事件。我们的研究结果将对理解已经形成的可卡因记忆如何通过靶向mPFC内PNN周围的神经元来破坏产生潜在的深远影响。

 DESCRIPTION (provided by applicant): One strategy for treating human addiction is to target memory processes that underlie addictive behaviors. Repeated drug use establishes drug-related memories. When these drug-related memories are recalled, as occurs when the organism is re-exposed to drug-associated cues, context, or the drug itself, those memories are reconsolidated to maintain or strengthen them. The medial prefrontal cortex (mPFC) is a key contributor to relapse to cocaine-seeking behavior in humans and reinstatement behavior in rodents. Increased excitatory output from mPFC pyramidal neurons to the nucleus accumbens (NAc) is thought to underlie relapse. In rodents, this increased output is found after 5 cocaine injections and after 45 days of withdrawal from cocaine self-administration, implicating a key role for the mPFC in the maintenance of cocaine-associated memories. However, we do not know the mechanisms by which the mPFC contributes to the expression of these memories. Output from the mPFC is powerfully regulated by parvalbumin (PV)-fast-spiking GABAergic interneurons, the majority of which are surrounded by specialized extracellular matrix structures that form perineuronal nets (PNNs). PNNs envelope certain neurons during development and appear to stabilize synapses, reducing plasticity in neurons during adulthood. However, PNNs can be removed during adulthood to re-establish plasticity or to modify plasticity by other imposing stimuli. We have discovered that removal of PNNs within the rat prelimbic mPFC (PL mPFC) decreases the reconsolidation of cocaine-associated memories as tested with conditioned place preference (CPP; hereafter called "cocaine CPP memory"). Repeated cocaine exposure has the opposite effect: it increases PNN intensity, and this intensity is positively correlated with behavior, suggesting that PNN intensity in the PL mPFC may serve as a predictor of cocaine- induced behavior. A general layout of our experiments is as follows: Establish cocaine CPP memory→ reactivate cocaine CPP memory ± PNNs→ reconsolidate cocaine CPP memory→ subsequent test for reinstatement of cocaine CPP memory to see if it is maintained or diminished. We propose that removal of PNNs from the PL mPFC prevents the maintenance of cocaine CPP memory via diminished memory reconsolidation. However, we do not know the mechanisms by which PNN removal decreases memory reconsolidation. We hypothesize that removal of PNNs within the PL mPFC modifies cocaine-induced plasticity during the reconsolidation of a cocaine CPP memory. We further hypothesize that reconsolidation is mediated by PNNs through altered activity of inhibitory interneurons and pyramidal neurons in the PL mPFC. We will train rats for cocaine-induced CPP in the presence and absence of PNNs and define the dynamic changes in PNN-surrounded neurons in the PL mPFC 1) just prior to and after memory reactivation; and 2) just prior to and after cocaine-induced reinstatement. We will use behavioral, electrophysiological, morphological, and confocal and electron microscopic approaches to test our hypotheses. PNNs are a highly novel target for dissecting events critical for cocaine-induced plasticity and the maintenance of cocaine-associated memories. Our findings will have potentially far-reaching consequences for understanding how already-formed cocaine memories can be disrupted by targeting PNN-surrounded neurons within the mPFC.