海马体神经元内源性大麻素 I 型受体与小清蛋白共表达的研究

内源性大麻素系统广泛分布于哺乳动物的中枢神经系统中,参与调节多种生理过程和行为反应。其中,大麻素 I 型受体(Cannabinoid Receptor 1,CB1R)大量分布在表达生长激素抑制素、胆囊收缩素、多巴胺、5-羟色胺等神经递质受体的神经元末梢上。CB1R 激活可抑制突触前膜神经递质的释放,逆行调控神经元的兴奋性。然而,对于中枢神经系统中另一类具有重要抑制性作用的小清蛋白(Parvalbumin,PV)阳性的 γ-氨基丁酸能中间神经元是否表达 CB1R,却鲜有报道。该文利用免疫荧光染色和激光共聚焦成像技术发现,小鼠海马体少量神经元存在 PV 与 CB1R 共表达,且 PV/CB1R 阳性神经元在海马体中的分布无雌雄差异。该结果能为进一步阐明 PV 与 CB1R 在功能上的相互作用提供一定参考价值,也将有助于更全面地了解内源性大麻素系统的调控作用。     

基于边界增强损失的海马体分割算法

快速准确地获得脑部核磁共振图像中海马体的体积变化情况,对阿尔兹海默症等疾病的诊断具有重要意义。海马体在大脑中占比很小且与周边结构的边界不明显,使得基于深度学习的核磁共振影像海马体分割具有一定难度。针对上述问题本文提出一种利用边界增强损失训练含注意力机制网络的海马体分割算法,主要贡献在于:1)设计了一种含注意力机制的U形三维卷积神经网络;2)提出一种边界增强的损失函数。在解决海马体与背景因为尺寸相差过大而带来的类不平衡问题的同时,使网络在训练时更注重对海马体边界的学习。在欧洲阿尔兹海默病协会和阿兹海默症神经影像学倡议数据集上,分析讨论了本文提出的损失函数和网络结构的性能。与目前几种先进的基于深度学习的三维分割算法进行了对比分析,实验结果表明本文提出的算法性能更优,达到了89.41%的Dice精度与人工分割精度相近。     

Stereological length estimation using spherical probes

Lineal structures in biological tissue support a wide variety of physiological functions, including membrane stabilization, vascular perfusion, and cell‐to‐cell communication. In 1953, Smith and Guttman demonstrated a stereological method to estimate the total length density (L_v) of linear objects based on random intersections with a two‐dimensional sampling probe. Several methods have been developed to ensure the required isotropy of object–probe intersections, including isotropic‐uniform‐random (IUR) sections, vertical‐uniform‐random (VUR) slices, and isotropic virtual planes. The disadvantages of these methods are the requirements for inconvenient section orientations (IUR, VUR) or complex counting rules at multiple focal planes (isotropic virtual planes). To overcome these limitations we report a convenient and straightforward approach to estimate L_v and total length, L, for linear objects on tissue sections cut at any arbitrary orientation. The approach presented here uses spherical probes that are inherently isotropic, combined with unbiased fractionator sampling, to demonstrate total L estimation for thin nerve fibres in dorsal hippocampus of the mouse brain.     

Spared discrimination and impaired reversal eyeblink conditioning in patients with temporal lobe amnesia.

The effect of medial temporal lobe damage on a 2-tone delay discrimination and reversal paradigm was examined in human classical eyeblink conditioning. Eight medial temporal lobe amnesic patients and their demographically matched controls were compared. Amnesic patients were able to distinguish between 2 tones during the initial discrimination phase of the experiment almost as well as control participants. Amnesic patients were not able to reverse the previously acquired 2-tone discrimination. In contrast, the control participants showed improved discrimination performance after the reversal of the tones. These findings support the hypothesis that the hippocampus and associated temporal lobe regions play a role in eyeblink conditioning that becomes essential in more complex versions of the task, such as the reversal of an acquired 2-tone discrimination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A model of hippocampal activity in trace conditioning: Where's the trace?

The hippocampus is generally thought to play a modulating role in the timing of conditioned responses in classical trace conditioning. One hypothesis is that the hippocampus stores a memory trace of the conditioned stimulus (CS) during the stimulus-free period. Cellular recordings, however, do not show any obvious CS storage. This article examines this issue by using a biologically plausible model of the CA3 region of the hippocampus. Simulations of the model reproduce both behavioral and physiological experimental data. On the basis of neural codes that develop in the model, the authors hypothesize that the hippocampus functions as a time-indexed encoding device for the CS and not as a CS storage buffer. Specifically, the CS initiates a sequence of neural activity during the trace interval that only indirectly represents the CS. The model yields 2 predictions: Some cells will increase in activity only during the trace interval, and some unconditioned stimulus (US)-coding cells will shift in time and fire before US onset. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of aging on the neural correlates of successful item and source memory encoding.

To investigate the neural basis of age-related source memory (SM) deficits, young and older adults were scanned with fMRI while encoding faces, scenes, and face-scene pairs. Successful encoding activity was identified by comparing encoding activity for subsequently remembered versus forgotten items or pairs. Age deficits in successful encoding activity in hippocampal and prefrontal regions were more pronounced for SM (pairs) as compared with item memory (faces and scenes). Age-related reductions were also found in regions specialized in processing faces (fusiform face area) and scenes (parahippocampal place area), but these reductions were similar for item and SM. Functional connectivity between the hippocampus and the rest of the brain was also affected by aging; whereas connections with posterior cortices were weaker in older adults, connections with anterior cortices, including prefrontal regions, were stronger in older adults. Taken together, the results provide a link between SM deficits in older adults and reduced recruitment of hippocampal and prefrontal regions during encoding. The functional connectivity findings are consistent with a posterior-anterior shift with aging previously reported in several cognitive domains and linked to functional compensation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modulation of the Impairment of Hippocampectomized Rats on the Radial-Arm Maze Cue Task by Visual Characteristics and Subicular Damage.

Rats with N-methyl-D-aspartate lesions of the hippocampus that partially damaged the subiculum and controls were trained on 2 versions of the radial-arm maze cue task, with either proximal or distal visual stimuli. In Experiment 1, the relative positions of the stimuli varied across trials. Lesioned rats were impaired when trained on the distal version, as opposed to transiently slowed down when trained on the proximal version. In Experiment 2, the relative positions of the stimuli were fixed throughout training. Lesioned rats were impaired when trained on the distal or the proximal version. Further analyses showed that combined damage to the hippocampus and the subiculum was required to impair performance in the proximal, but not the distal, version. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Performance on spatial working memory tasks after dorsal or ventral hippocampal lesions and adjacent damage to the subiculum.

Rats with excitotoxic lesions of the dorsal or ventral hippocampus and control rats were trained on 2 spatial working memory tasks: the standard version of the radial maze with 8 baited arms and the nonmatching-to-place procedure in the T maze. Dorsal lesions produced deficits in both tasks, whereas ventral lesions did not affect learning in either of them. A volumetric analysis of subicular damage showed that dorsal hippocampal lesions caused a deficit in the nonmatching-to-place only when accompanied by damage to the dorsal subiculum; on the other hand, lesions to the dorsal hippocampus impaired performance in the radial-arm maze regardless of the extent of subicular damage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

基于改进水平集的人脑海马图像分割方法

人脑MR图像中的海马结构存在低对比度、边界模糊等缺点,给海马的轮廓分割带来较大干扰.为解决水平集分割海马时边界容易停留在非目标区域梯度极值处的问题,提出一种改进的水平集方法.从图像全局出发考虑方差信息,在水平集函数的外部能量泛函中增加波动能量项,驱动零水平集曲线向灰度波动较小的区域运动.实验结果表明,该方法可提取出MR图像中的海马轮廓,分割效果较好,演化速度有所提高.