Inhibitory interneurons, oxidative stress, and schizophrenia

Translational studies are becoming more common in schizophrenia research. The past couple of decades witnessed the emergence of novel ideas regarding schizophrenia pathophysiology that originated from both human and animal studies. The findings that glutamate and gamma-aminobutyric acid transmission are affected in the disease led to the hypothesis of altered inhibitory neurotransmission as critical for cognitive deficits and to an exploration of novel therapeutic approaches aimed at restoring excitation-inhibition balance. Much is to be done yet to elucidate the ultimate mechanisms by which excitation and inhibition are affected in this disorder; a comprehensive translational effort is necessary to address what may cause altered GABA function, for example. Here, we present an overview of the excitation-inhibition imbalance hypothesis in schizophrenia and discuss ongoing efforts aimed at determining whether cortical inhibitory interneurons are affected by oxidative stress during development.     

Immunocytochemical distribution of the cannabinoid CB1 receptor in the primate neocortex: a regional and laminar analysis

Delta-9-tetrahydrocannabinol (⁹-THC) has profound effects onhigher cognitive functions, and exposure to ⁹-THC has been associatedwith the appearance or exacerbation of the clinical featuresof schizophrenia. These actions appear to be mediated via theCB₁ receptor, the principal cannabinoid receptor expressed inthe brain. However, the distribution of the CB₁ receptor inneocortical regions of the primate brain that mediate cognitivefunctions is not known. We therefore investigated the immunocytochemicallocalization of the CB₁ receptor in the brains of macaque monkeysand humans using antibodies that specifically recognize theN- or C-terminus of the CB₁ receptor. In monkeys, intense CB₁immunoreactivity was observed primarily in axons and boutons.Across neocortical regions of the monkey brain, CB₁-immunoreactive(IR) axons exhibited considerable heterogeneity in density andlaminar distribution. Neocortical association regions, suchas the prefrontal and cingulate cortices, demonstrated a higherdensity, and exhibited a unique laminar pattern of CB₁-IR axons,compared with primary sensory and motor cortices. Similar regionaland laminar distributions of CB₁-IR axons were also presentin the human neocortex. CB₁-IR axons had more prominent varicositiesin human tissue, but this difference appeared to represent apostmortem effect as similar morphological features increasedin unperfused monkey tissue as a function of postmortem interval.In electron microscopy studies of perfused monkey prefrontalcortex, CB₁ immunoreactivity was predominantly found in axonterminals that exclusively formed symmetric synapses. The highdensity, distinctive laminar distribution, and localizationto inhibitory terminals of CB₁ receptors in primate higher-orderassociation regions suggests that the CB₁ receptor may playa critical role in the circuitry that subserves cognitive functionssuch as those that are disturbed in schizophrenia.     

GABAergic and pyramidal neurons of deep cortical layers directly receive and differently integrate callosal input

We studied the involvement of deep cortical layer neurons in processing callosal information in the rat. We observed with electron microscopy that both parvalbumin (PV)-labeled profiles and unlabeled dendritic spines of deep cortical layer neurons receive synapses from the contralateral hemisphere. Stimulation of callosal fibers elicited monosynaptic excitatory postsynaptic currents in both layer VI pyramidal neurons and gamma-aminobutyric acidergic (GABAergic) interneurons immunopositive for the vesicular GABA transporter and PV. Pyramidal cells had intrinsic electrophysiological properties and synaptic responses with slow kinetics and a robust N-metyhl-D-aspartate (NMDA) component. In contrast, GABAergic interneurons had intrinsic membrane properties and synaptic responses with faster kinetics and a less pronounced NMDA component. Consistent with these results, the temporal integration of callosal input was effective over a significantly longer time window in pyramidal neurons compared with GABAergic interneurons. Interestingly, callosal stimulation did not evoke feedforward inhibition in all GABAergic interneurons and in the majority of pyramidal neurons tested. Furthermore, retrogradely labeled layer VI pyramidal neurons of the contralateral cortex responded monosynaptically to callosal stimulation, suggesting interconnectivity between callosally projecting neurons. The data show that pyramidal neurons and GABAergic interneurons of deep cortical layers receive interhemispheric information directly and have properties supporting their distinct roles.     

Activation of phenotypically distinct neuronal subpopulations in the anterior subdivision of the rat basolateral amygdala following acute and repeated stress

The effects of acute and repeated stress on expression of the early immediate gene c-fos in the basolateral amygdala have previously been reported; however, characterization of which neuronal subpopulations are activated by these stimuli has not been investigated. This question is of considerable relevance, insofar as the basolateral amygdala houses a heterogeneous population of neurons, including those of gamma-aminobutyric acid (GABA)-ergic and glutamatergic phenotypes that may be subcategorized based on their expression of various calcium-binding proteins, including parvalbumin, calbindin, calretinin, and the calcium-sensitive enzyme calcium/calmodulin-dependent kinase II. Characterization of these subpopulations has revealed unique differences in their physiology, synaptology, and morphology, suggesting that each distinct phenotype may have profound effects on the local circuitry of the amygdala. Therefore, we examined the effects of acute and repeated restraint stress on expression of the immediate early gene c-fos in neurons containing parvalbumin, calbindin, calretinin, or calcium/calmodulin-dependent kinase II in the basolateral amygdala. Double-label immunohistochemistry revealed that acute restraint stress activated a proportion of parvalbumin-, calbindin-, or calcium/calmodulin-dependent kinase II-positive neurons. Prior exposure to repeated restraint stress markedly attenuated acute-stress mediated activation of these neuronal populations, although not equally. Expression of c-Fos protein was not detected in calretinin-positive neurons in any experimental group. These results demonstrate that distinct neuronal phenotypes in the basolateral amygdala are activated by acute restraint stress and that prior repeated restraint stress differentially affects this response.     

慢性吗啡处理及戒断后大鼠前额皮质、海马和杏仁核中Parvalbumin的表达变化

为了观察慢性吗啡处理及戒断后大鼠前额皮质、海马和杏仁核中parvalbumin(PV)的表达变化,为其功能的研究提供形态学依据,本实验将30只雄性SD大鼠随机分为吗啡依赖组和生理盐水对照组。吗啡依赖组大鼠腹膜腔注射吗啡,2次/d,起始剂量为5mg/kg,逐日递增5mg,至第10d为50mg/kg;对照组注射同体积的生理盐水。于末次注射后动物分别存活3h、3d和14d。用免疫组化方法和相对平均灰度值检测前额皮质、海马和杏仁核内PV的表达。结果显示:在生理盐水处理组各存活时间点,前额皮质、海马和杏仁核内PV的表达相同。和生理盐水对照组相比,3h时海马和杏仁核内PV的表达明显增加(P<0.05),但前额皮质内PV的表达减少。第3d时,海马CA1、CA3、CA4、齿状回和杏仁核内PV的表达减少,但CA2区PV表达继续增加,而前额皮质的表达开始恢复。至第14d时,CA2区PV的表达开始恢复,但CA1、CA4和杏仁核内PV的表达又开始增加,明显高于第3d组(P<0.05)。以上结果提示慢性吗啡处理及戒断后PV的表达具有区域特异性和时相特异性;这种变化在戒断早期可能主要与躯体依赖相关,而戒断晚期主要与精神依赖相关。     

小鼠纹状体尾部和听皮层PV神经元的电生理性质比较

目的 研究小白蛋白（PV）神经元在听皮层（AC）及其下行听觉投射脑区纹状体尾部（TS）的电生理性质异同。方法 以PVCre-Ai14小鼠为研究对象,运用离体膜片钳技术记录PV神经元对步进电流的刺激响应,并通过Clampfit和MATLAB软件分析PV神经元动作电位（AP）的发放特性和波形特性。AP的发放特性包括延时、阈值、平均放电率、F/I斜率以及动作电位频率自适应性(SFA);波形特性包括峰电位特性和后电位特性。实验结束后统计共使用PV-Cre-Ai14小鼠5只,共记录到29个TS-PV神经元和22个AC-PV神经元。结果 TS和AC的PV神经元存在显著不同的电生理特性。从峰电位特性上看,TS的PV神经元具有更小的半峰宽（P<0.001）和更大的幅值（P<0.01）,AP的最大上升斜率（P<0.01）和最大下降斜率（P<0.05）也更大;从后电位特性上看,TS的PV神经元后超极化程度更大（P<0.01）,恢复到静息电位的时间更短（P<0.01）;从发放特性上看,TS的PV神经元有更高的AP发放阈值（P<0.01）、更大的F/I斜率（P<...     

GAD67-GFP基因敲入小鼠5-羟色胺样和P物质样阳性终末与三叉神经中脑核神经元的联系

本研究应用免疫荧光组织化学三重标记技术,在激光共聚焦显微镜下观察了GAD67-GFP基因敲入小鼠三叉神经中脑核(Vme)内5-HT样和P物质(substanceP,SP)样阳性终末分别与小白蛋白(parvalbumin,PV)样和GFP阳性神经元之间的联系。结果显示:(1)Vme内有较多的PV样阳性神经元,这些神经元绝大多数为大、中型的假单极神经元,直径约为18～40μm;也可观察到少量的GFP阳性神经元,多为小的多极神经元,直径约为8～15μm;(2)5-HT样阳性终末广泛分布于Vme内,其中有部分阳性终末分别聚集在PV样或GFP阳性的Vme神经元的胞体周围,计数结果表明:大约有77.7%和22.3%的5-HT样阳性终末分别与PV样或GFP阳性胞体相接触;(3)SP样阳性终末也广泛分布于Vme内,并分别与PV样或GFP阳性神经元的胞体形成密切接触,其中有78.2%和21.8%的阳性终末分别与PV样或GFP阳性胞体相接触。以上结果提示,在口面部本体感觉信息向更高一级中枢传递过程中,5-HT能和SP能神经终末不仅对初级传入发挥直接的调控作用,还可能通过影响Vme内的GABA能神经元的活动,从而间接对该信息的传递发挥调控作用。