Cocaine Addiction and the Role of Serotonin in Orbitofrontal Cortex Function

在脑切片中使用全细胞电生理学，我们发现，5-HT 1A和5-HT 2A受体激活的生理效应显着降低后，无论是可卡因自我管理（CSA）或轭可卡因管理（CYA）在锥体神经元（PyNs）的撤退。此外，这些减少5-HT在这些受体的影响持续了许多周后，可卡因戒断，这表明他们可能参与可卡因成瘾的长期方面，如药物渴望。 由于OFC中的5-HT与行为灵活性，学习和其他认知能力有关，我们的实验提供了关于5-HT在可卡因成瘾中所起作用的新信息，以及在可卡因成瘾和戒断期间所表现出的决策受损中所起的作用。 此外，由于5-HT与几种神经精神障碍，如抑郁症，焦虑症，痴呆症，冲动-攻击性障碍（IAD），强迫症（OCD）和创伤后应激障碍（PTSD），这些实验提供了有价值的信息，靶向5-HT系统在OFC作为潜在的治疗的临床效用。 我们最近在这个项目中的努力集中在开发一个转基因大鼠模型，这将使我们能够检查的作用，5-HT在一类重要的神经元在OFC的调节，被称为快速尖峰（FS），parvalbumin（PV），interneurons。 这些神经元在眶额皮层的总细胞群中占少数，但它们很重要，因为它们使用抑制性神经递质γ-氨基丁酸（GABA）通过广泛的突触连接来协调更大的锥体神经元群的活动。 因此，这些神经元对于正常OFC功能所必需的计算过程是不可或缺的，并且很可能涉及该大脑所贡献的精神病和成瘾性疾病。 为了研究这些神经元，我们的转基因核心和科学合作者开发了一种大鼠模型，其中PV基因启动子驱动cre重组酶的表达。 这允许选择性表达荧光蛋白和视蛋白，如channelrhodopsin-2（ChR 2），使我们能够研究这些神经元，并利用光操纵它们的活动。 我们最近的研究表明，5-HT信号，虽然存在于PV细胞的OFC，是没有改变后，从可卡因自我管理撤回。因此，可卡因暴露相关的5-HT功能的变化似乎几乎完全由眶额皮层锥体神经元介导。 此外，在后一项研究中，我们研究了雄性和雌性大鼠之间OFC小清蛋白细胞的变化。 我们发现，女性OFC parvalbumin细胞接受较弱的mammatergic突触输入比男性，这些突触电流减少后5周的退出可卡因自我管理，只有在男性。此外，雄性大鼠的小清蛋白细胞也在可卡因戒断后去极化。 药理学研究还表明，仅在雌性大鼠的神经元中，OFC中5-HT对小清蛋白神经元的兴奋可被5-HT 2A/C受体的非选择性拮抗剂（称为酮色林）阻断。为了进一步了解这是否表明男性和女性之间的小白蛋白神经元中5-HT 2A或5-HT 2C受体的不同功能表达，我们正在进行额外的研究，使用这些受体的更具选择性的拮抗剂，沿着5-HT 2受体选择性激动剂，称为DOI。 我们的数据表明，可卡因戒断后，OFC中小白蛋白神经元的功能特性存在性别相关差异，这些变化可以解释人类对可卡因成瘾和精神后遗症的差异脆弱性。 希望这些神经元在精神疾病和成瘾中的作用的鉴定将有助于开发用于人类治疗的新的靶向治疗方法。

Using whole-cell electrophysiology in brain slices, we find that physiological effects of 5-HT1A and 5-HT2A receptor activation were dramatically reduced following withdrawal of either cocaine self-administration (CSA) or yoked cocaine administration (CYA) in pyramidal neurons (PyNs). Moreover, these reduced effects of 5-HT at these receptors persisted for many weeks after cocaine withdrawal, suggesting they may be involved in long-term aspects of cocaine addiction, such as drug craving. As 5-HT in the OFC is implicated in behavioral flexibility, learning and other cognitive abilities, our experiments provide novel information as to the role that 5-HT plays in cocaine addiction, and in the impaired decision-making exhibited during cocaine addiction and withdrawal. In addition, since 5-HT is linked to several neuropsychiatric disorders, such as depression, anxiety, dementia, impulsive-aggression disorder (IAD), obsessive-compulsive disorder (OCD), and post-traumatic stress disorder (PTSD), these experiments provide valuable information as to the clinical utility of targeting the 5-HT system in the OFC as potential therapies. Our recent efforts in this project have focused on developing a transgenic rat model that will permit us to examine the role of 5-HT in the regulation of a class of important neurons in the OFC, known as fast-spiking (FS), parvalbumin (PV), interneurons. These neurons constitute a minority of the total cell population in the OFC, but are important because they use the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA), to coordinate the activity of the much larger population of pyramidal neurons, via extensive synaptic connections. Therefore, these neurons are integral to the computational processes that are necessary for normal OFC function, and are likely to be involved in psychiatric and addiction disorders in which this brain are contributes. To study these neurons our transgenic core and scientific collaborators have developed a rat model in which the PV gene promoter drives the expression of cre recombinase. This permits selective expression fluorescent proteins and opsins, such as channelrhodopsin-2 (ChR2), that allows us to study these neurons, and manipulate their activity with light. Our most recent studies indicate that 5-HT signaling, although present in PV cells in the OFC, is not altered after withdrawal from cocaine self-administration. Therefore, the changes in 5-HT function related to cocaine exposure appear to be mediated almost entirely by pyramidal neurons in the OFC. Moreover, in this latter study we examined changes in OFC parvalbumin cells between male and female rats. We found that female OFC parvalbumin cells receive weaker glutamatergic synaptic inputs than males and that these synaptic currents are reduced following 5 weeks of withdrawal from cocaine self-administration only in males. Additionally, parvalbumin cells from male rats were also depolarized after cocaine withdrawal. Pharmacological studies have also shown that the excitation of parvalbumin neurons by 5-HT in the OFC can be blocked by a non-selective antagonist of 5-HT2A/C receptors, known as ketanserin, only in neurons from female rats. To gain additional insight as to whether this indicates a distinct functional expression of 5-HT2A or 5HT2C receptors in parvalbumin neurons between males and females, we are conduction additional studies using more selective antagonists of these receptors, along with a a 5-HT2 receptor-selective agonist, known as DOI. Our data suggest that there are sex-linked differences in the functional properties of parvalbumin neurons in the OFC after cocaine withdrawal, and that these changes could explain differential vulnerabilities to cocaine addiction and psychiatric sequalae in humans. It is hoped that the identification of the roles of these neurons in psychiatric illness and addiction will aid in developing novel targeted therapeutic approaches for treatment in humans.