Cocaine Addiction and the Role of Serotonin in Orbitofrontal Cortex Function

在脑片上应用全细胞电生理学，我们发现在锥体神经元(PYN)中，5-HT1A和5-HT2A受体激活的生理效应在停用可卡因自给药(CsA)或交叉可卡因给药(CyA)后显著降低。此外，这些受体上5-羟色胺的减少效应在可卡因戒断后持续了数周，这表明它们可能与可卡因成瘾的长期方面有关，如对药物的渴望。由于OFC中的5-羟色胺与行为灵活性、学习和其他认知能力有关，我们的实验为5-羟色胺在可卡因成瘾中所起的作用以及在可卡因成瘾和戒断过程中表现出的决策障碍提供了新的信息。此外，由于5-羟色胺与几种神经精神障碍有关，如抑郁、焦虑、痴呆、冲动攻击障碍(IAD)、强迫症(OCD)和创伤后应激障碍(PTSD)，这些实验为将5-HT系统作为潜在治疗方法在OFC中的临床应用提供了有价值的信息。 我们最近在这个项目中的努力集中在开发转基因大鼠模型上，该模型将使我们能够研究5-羟色胺在OFC中一类重要神经元--快峰(FS)、小白蛋白(PV)、中间神经元的调节中的作用。这些神经元在OFC的细胞总数中只占少数，但它们很重要，因为它们使用抑制性神经递质伽马氨基丁酸(GABA)，通过广泛的突触连接来协调更大数量的锥体神经元的活动。因此，这些神经元是正常OFC功能所必需的计算过程的组成部分，并可能参与精神障碍和成瘾障碍，而这一大脑也参与其中。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个大鼠模型，其中PV基因启动子驱动cre重组酶的表达。这允许选择性地表达荧光蛋白和视蛋白，如通道视紫红质-2(ChR2)，使我们能够研究这些神经元，并利用光来操纵它们的活动。我们最新的研究表明，尽管5-羟色胺信号存在于OFC的PV细胞中，但在戒断可卡因自身给药后没有改变。因此，与可卡因暴露有关的5-羟色胺功能的改变似乎几乎完全是由OFC中的锥体神经元介导的。此外，在后一项研究中，我们检测了雄性和雌性大鼠之间OFC小白蛋白细胞的变化。我们发现，女性OFC小白蛋白细胞接受比男性更弱的谷氨酸能突触输入，这些突触电流在停用可卡因5周后减少，只有男性。此外，雄性大鼠的小白蛋白细胞在可卡因戒断后也被去极化。药理学研究还表明，5-羟色胺对OFC小白蛋白神经元的兴奋作用可被5-HT2A/C受体的非选择性拮抗剂酮丝氨酸阻断，这种拮抗剂仅在雌性大鼠的神经元中起作用。为了进一步了解这是否表明5-HT2A或5HT2C受体在男性和女性的小蛋白神经元中有不同的功能表达，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，以及一种被称为DOI的5-HT2受体选择性激动剂。我们的数据表明，在可卡因戒断后，OFC内小白蛋白神经元的功能特性存在性别联系的差异，这些变化可以解释人类对可卡因成瘾和精神后遗症的不同易感性。人们希望，确定这些神经元在精神疾病和成瘾中的作用将有助于开发针对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.