左归降糖解郁方对糖尿病并发抑郁症大鼠海马胰岛素抵抗的影响

目的研究左归降糖解郁方对糖尿病并发抑郁症大鼠海马胰岛素抵抗的调节作用。方法建立糖尿病并发抑郁症大鼠模型,并随机分为4组,模型组,阳性药组(二甲双胍0.18 g/kg+氟西汀1.8 mg/kg),左归降糖解郁方高、低剂量组(20.52、10.26g/kg),另设健康大鼠为对照组。各组大鼠ig给药28 d后,采用血糖仪及ELISA法检测空腹血糖及外周胰岛素抵抗程度。采用旷野实验和强迫游泳实验检测大鼠抑郁样行为。采用免疫荧光法和Western blotting法检测大鼠海马胰岛素受体磷酸化蛋白(p-IR)、磷酸化的胰岛素受体底物-1(p-IRS-1)的表达,采用Westernblotting法检测海马磷酸化的磷脂酰肌醇3-激酶(p-PI3K)、磷酸化蛋白激酶B(p-Akt)蛋白的表达。结果与对照组比较,模型组大鼠血糖显著升高并伴随明显的外周胰岛素抵抗,其在旷野实验中的活动次数显著降低、在强迫游泳实验中的不动时间显著延长;蛋白检测结果表明大鼠脑内p-IR、p-IRS-1、p-PI3K、p-Akt表达水平均显著降低。与模型组比较,左归降糖解郁方高剂量组大鼠血糖水平显著降低,外周胰岛素抵抗水平减轻,其在旷野实验中的活动次数显著增加、在强迫游泳实验中的不动时间显著缩短,而海马内p-IR、p-IRS-1、p-PI3K、p-Akt表达显著升高。结论左归降糖解郁方可有效调节糖尿病并发抑郁症大鼠海马胰岛素信号通路,从而改善动物脑内的胰岛素抵抗状态。     

Inhibitory neuronal changes following a mixed diffuse-focal model of traumatic brain injury

Traumatic brain injury (TBI) can result in excitation: inhibition imbalance, as well as a range of chronic neurological deficits. However, how TBI affects different interneurons, and how this relates to behavioral abnormalities, remains poorly understood. This study examined the effects of a mixed diffuse-focal model of TBI, the lateral fluid percussion injury (LFPI), on interneurons, 8 weeks post-TBI in rats. Brains were labeled with antibodies against calbindin, parvalbumin, calretinin, neuropeptide Y, and somatostatin, and the number of interneurons were assessed in the cortex and hippocampus following LFPI. LFPI caused a reduction in the numbers of interneurons mediating both perisomatic and dendritic inhibition in the somatosensory cortex. In hippocampus, there were heterogenous changes in the number of interneurons while motor cortex, showed no obvious loss in any of the subsets of interneurons after TBI. In parallel to the investigations of changes in the number of interneurons, we also investigated the long-term behavioral consequences of LFPI. Behaviorally, rats given an LFPI displayed transient reduction in performance in motor tasks and were significantly impaired in reversal learning in the water maze task post-TBI. We also report here progressive neurodegeneration in cortex and hippocampus indicated by Fluoro-Jade C in the different brain areas examined after injury. Our findings suggest differential vulnerability of inhibitory neurons to LFPI in the different brain areas examined after injury. These data will aid in evaluation of new treatments for TBI and help target specific neuronal subtypes as a function of injury time and type.     

Why considering sexual differences is necessary when studying encephalopathy of prematurity through rodent models

Preterm birth is a high‐risk factor for the development of gray and white matter abnormalities, referred to as “encephalopathy of prematurity,” that may lead to life‐long motor, cognitive, and behavioral impairments. The prevalence and clinical outcomes of encephalopathy of prematurity differ between sexes, and elucidating the underlying biological basis has become a high‐priority challenge. Human studies are often limited to assessment of brain region volumes by MRI, which does not provide much information about the underlying mechanisms of lesions related to very preterm birth. However, models using KO mice or pharmacological manipulations in rodents allow relevant observations to help clarify the mechanisms of injury sustaining sex‐differential vulnerability. This review focuses on data obtained from mice aged P1–P5 or rats aged P3 when submitted to cerebral damage such as hypoxia‐ischemia, as their brain lesions share similarities with lesion patterns occurring in very preterm human brain, before 32 gestational weeks. We first report data on the mechanisms underlying the development of sexual brain dimorphism in rodent, focusing on the hippocampus. In the second part, we describe sex specificities of rodent models of encephalopathy of prematurity (RMEP), focusing on mechanisms underlying differences in hippocampal vulnerability. Finally, we discuss the relevance of these RMEP. Together, this review highlights the need to systematically search for potential effects of sex when studying the mechanisms underlying deficits in RMEP in order to design effective sex‐specific medical interventions in human preterms.     

Sex differences in the performance of cognitive tasks in a murine model of metabolic syndrome

The metabolic syndrome includes changes in blood glucose levels, arterial hypertension, triglycerides, dyslipidemia and central obesity. Countless reports have described the correlation between the metabolic syndrome and cognitive impairment. However, only a few reports have assessed cognitive impairment associated with the metabolic syndrome in animals of both sexes. For this purpose, Sprague‐Dawley male and female rats were fed either with a hypercaloric diet as model of the metabolic syndrome or with a standard chow diet as controls. Subsequently, spatial learning and memory (Morris water maze) as well as short‐ and long‐term memory (passive avoidance task) were evaluated. Body weight, blood pressure, triglycerides, and total cholesterol significantly increased (F(1, 36) = 94.89, p < .001) in rats fed with hypercaloric diet compared to control rats. Furthermore, cognitive impairment was observed in spatial learning and spatial memory on male rats but not on female rats fed with hypercaloric diet. In addition, a long‐term memory impairment was observed in both groups fed with hypercaloric diet in comparison to their respective control group (F(1, 32) = 10.61, p = .0027). Immunohistochemistry results showed no changes in the number of positive cells for NeuN, GFAP and Ox‐42. In males fed with a hypercaloric diet, a decrease in testosterone levels was observed, whereas estradiol levels decreased in females when compared with their respective control group (p < .0001). In this MetS animal model, metabolic and cognitive differences were observed in males and females, which demonstrates that sex hormones play a significant role in metabolic regulation and neuroprotection related to the CA1 region of the hippocampus.     

Increased activation of the fear neurocircuitry in children exposed to violence

Most studies investigating the effect of childhood trauma on the brain are retrospective and mainly focus on maltreatment, whereas different types of trauma exposure such as growing up in a violent neighborhood, as well as developmental stage, could have differential effects on brain structure and function. The current magnetic resonance imaging study assessed the effect of trauma exposure broadly and violence exposure more specifically, as well as developmental stage on the fear neurocircuitry in 8‐ to 14‐year‐old children and adolescents (N = 69). We observed reduced hippocampal and increased amygdala volume with increasing levels of trauma exposure. Second, higher levels of violence exposure were associated with increased activation in the amygdala, hippocampus, and ventromedial prefrontal cortex during emotional response inhibition. This association was specifically observed in children younger than 10 years. Finally, increased functional connectivity between the amygdala and brainstem was associated with higher levels of violence exposure. Based on the current findings, it could be hypothesized that trauma exposure during childhood results in structural changes that are associated with later risk for psychiatric disorders. At the same time, it could be postulated that growing up in an unsafe environment leads the brain to functionally adapt to this situation in a way that promotes survival, where the long‐term costs or consequences of these adaptations are largely unknown and an area for future investigations.     

Hippocampal and medial prefrontal cortical volume is associated with overnight declarative memory consolidation independent of specific sleep oscillations

The current study was designed to further clarify the influence of brain morphology, sleep oscillatory activity and age on memory consolidation. Specifically, we hypothesized, that a smaller volume of hippocampus, parahippocampal and medial prefrontal cortex negatively impacts declarative, but not procedural, memory consolidation. Explorative analyses were conducted to demonstrate whether a decrease in slow‐wave activity negatively impacts declarative memory consolidation, and whether these factors mediate age effects on memory consolidation. Thirty‐eight healthy participants underwent an acquisition session in the evening and a retrieval session in the morning after night‐time sleep with polysomnographic monitoring. Declarative memory was assessed with the paired‐associate word list task, while procedural memory was tested using the mirror‐tracing task. All participants underwent high‐resolution magnetic resonance imaging. Participants with smaller hippocampal, parahippocampal and medial prefrontal cortex volumes displayed a reduced overnight declarative, but not procedural memory consolidation. Mediation analyses showed significant age effects on overnight declarative memory consolidation, but no significant mediation effects of brain morphology on this association. Further mediation analyses showed that the effects of age and brain morphology on overnight declarative memory consolidation were not mediated by polysomnographic variables or sleep electroencephalogram spectral power variables. Thus, the results suggest that the association between age, specific brain area volume and overnight memory consolidation is highly relevant, but does not necessarily depend on slow‐wave sleep as previously conceptualized.     

Early signal from the hippocampus for memory encoding

The mediotemporal lobe (MTL), including the hippocampus, is involved in all stages of episodic memory including memory encoding, consolidation, and retrieval. However, the exact timing of the hippocampus' involvement immediately after stimulus encounter remains unclear. In this study, we used high‐density 156‐channel electroencephalography to study the processing of entirely new stimuli, which had to be encoded, in comparison to highly overlearned stimuli. Sixteen healthy subjects performed a continuous recognition task with meaningful pictures repeated up to four consecutive times. Waveform and topographic cluster analyses of event‐related potentials revealed that new items, in comparison to repetitions, were processed significantly differently at 220–300 ms. Source estimation localized activation for processing new stimuli in the right MTL. Our study demonstrates the occurrence of a transient signal from the MTL in response to new information already at 200–300 ms poststimulus onset, which presumably reflects encoding as an initial step toward memory consolidation.     

Differential development of relational memory and pattern separation

Researchers have taken a number of different approaches in their exploration of hippocampal function. One approach seeks to describe hippocampal function by probing the memory representations that the hippocampus supports. Another approach focuses on the role of the hippocampus in pattern separation and completion. Each of these approaches to understanding hippocampal function utilizes a distinct set of specialized tasks, and both of these task sets are known to be sensitive to changes in hippocampal function with age and disease status. But the question remains whether the tasks utilized in these two approaches tap into the same aspects of hippocampal function. We explored this question in the context of hippocampal development. Preadolescent children (N = 73) and young adults (N = 41) completed an identical battery of cognitive tasks consisting of a spatial reconstruction relational memory task, the mnemonic similarity task (MST)—an object‐based pattern separation task, and a novel hybrid task—the Object Discrimination and Distribution (ODD) Task—designed to integrate and simultaneously tax pattern separation and spatial relational memory. Children did not demonstrate impairments in lure discrimination relative to young adults on either the object‐based pattern separation task or for aspects of the ODD task that required pattern separation in the absence of relational memory demands but performed more poorly across aspects of tasks that required relational binding.     

Hippocampal‐striatal functional connectivity supports processing of temporal expectations from associative memory

The hippocampus and dorsal striatum are both associated with temporal processing, but they are thought to play distinct roles. The hippocampus has been reported to contribute to storing temporal structure of events in memory, whereas the striatum contributes to temporal motor preparation and reward anticipation. Here, we asked whether the striatum cooperates with the hippocampus in processing the temporal context of memorized visual associations. In our task, participants were trained to implicitly form temporal expectations for one of two possible time intervals associated to specific cue‐target associations, and subsequently were scanned using ultra‐high‐field 7T functional magnetic resonance imaging. During scanning, learned temporal expectations could be violated when the pairs were presented at either the associated or not‐associated time intervals. When temporal expectations were met during testing trials, activity in left and right hippocampal subfields and right putamen decreased, compared to when temporal expectations were not met. Further, psycho‐physiological interactions showed that functional connectivity between left hippocampal subfields and caudate decreased when temporal expectations were not met. Our results indicate that the hippocampus and striatum cooperate to process implicit temporal expectation from mnemonic associations. Our findings provide further support for a hippocampal‐striatal network in temporal associative processing.