A Simple Generalized Excitability Model Mimicking Salient Features of Neuron Dynamics

A generalization of the FitzHugh—Nagumo model for excitability is provided to account for salient features of Inferior Olive neurons. The base state is a limit cycle and excitability appears as spiking over peaks of the oscillations. The response of the model to various types of external stimulus is also presented. In particular, we show the relevance of an appropriate balance between amplitude and duration of the stimulus.     

基于抑制性突触可塑性的反馈神经回路兴奋性与抑制性动态平衡

大脑皮层的兴奋性与抑制性平衡是维持正常脑功能的前提, 而其失衡会诱发癫痫、帕金森、抑郁症等多种神经疾病, 因此兴奋性与抑制性平衡的研究是脑科学领域的核心科学问题. 反馈神经回路是脑皮层网络的典型连接模式, 抑制性突触可塑性在兴奋性与抑制性平衡中扮演关键角色. 本文首先构建具有抑制性突触可塑性的反馈神经回路模型; 然后通过计算模拟研究揭示在抑制性突触可塑性的调控下反馈神经回路的兴奋性与抑制性可取得较高程度的动态平衡, 并且二者的平衡对输入扰动具有较强的鲁棒性; 其次给出了基于抑制性突触可塑性的反馈神经回路兴奋性与抑制性平衡机理的解释; 最后发现反馈回路神经元数目有利于提高兴奋性与抑制性平衡的程度, 这在一定程度上解释了为何神经元之间会存在较多的连接. 本文的研究对于理解脑皮层的兴奋性与抑制性动态平衡机理具有重要的参考价值.     

Hopf‐pitchfork bifurcation in a two‐neuron system with discrete and distributed delays

Both discrete and distributed delays are considered in a two‐neuron system. We analyze the influence of interaction coefficient and time delay on the Hopf‐pitchfork bifurcation. First, we obtain the codimension‐2 unfolding with original parameters for Hopf‐pitchfork bifurcation by using the center manifold reduction and the normal form method. Next, through analyzing the unfolding structure, we give complete bifurcation diagrams and phase portraits, in which multistability and other dynamical behaviors of the original system are found, such as a stable periodic orbit, the coexistence of two stable nontrivial equilibria, and the coexistence of a stable periodic orbit and two stable equilibria. In addition, the obtained theoretical results are verified by numerical simulations. Finally, we perform the comparisons of the obtained results of Hopf‐pitchfork bifurcation with other Hopf‐fold bifurcation results in some biological neural systems and give the obtained mathematical results corresponding to the physical states of neurons. Copyright © 2015 JohnWiley & Sons, Ltd.     

Regulation of charged groups and laminin patterns for selective neuronal adhesion

Primary neuronal cultures on substrates patterned with extracellular matrix proteins such as laminin have yielded much information regarding the physiological characteristics of neuronal cells in vitro. Surface charge also influences neuronal adherence, and a positive charge can have stimulatory effects. The attraction between laminin patterns and polycation films are of interest in the study of neuronal adhesion. We cultured primary hippocampal neurons on poly(ethylenimine) (PEI) films with laminin grids and evaluated their viability and morphology by means of fluorescent microscopy after 5–7 days. The results showed that the neurons did not form networks on the laminin grids. It is inferred that the PEI films were more favourable for neuronal adhesion than the laminin grid.     

Laser-induced photodynamic effects of chlorinse 6 andp 6 on an isolated neuron

Photodynamic effects of chlorins e₆ and p₆ on an isolated mechanoreceptor neuron of a fluvial crayfish are investigated. A He−Ne laser (632.8 nm, 0.3 W/cm²) was used as an excitation source. The impulsive activity of neurons was found to be extremely sensitive to the photodynamic effect of low concentrations of chlorins e₆ and p₆ (0.005–6.000 and 0.05–0.50 μM, respectively). Cell reactions consisted of several phases of acceleration and inhibition of pulsations followed by an irreversible cancellation of nervous pulse generation. The type of reaction depended on the photosensitizer form and concentration. It is supposed that the phases of acceleration of impulsive activity are connected with the photodynamic damage of the cell membrane, and the inhibition phases are connected with the photodynamic effect on intracell organells. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 250–255, March–April, 1999.     

Toward a charge-transfer model of neuromolecular computing

A computational model of charge transfer through an associated polyenic system is presented. This model is based on proposed transient alignment of adjacent ethylenes of phospholipid diacyls in the neural membrane. Influx of anions and cations into the cytosol at ∼10⁸ ions/s at ligand-gated channels hypothetically establishes the conditions for charge transfer through adjacent diacyl ethylenes. It is suggested that this process produces interactions between phospholipid potential energy hypersurfaces. These interactions operating in many-dimensional (Hilbert) space represent a form of massively parallel computation. Basic theoretical principles of quantum computing relevant to the present model are briefly discussed. A preliminary computational model of charge transfer through stacked ethylenes is then presented. In this model molecules were aligned with planes parallel and perpendicular. Singly charged counterions were positioned at the ends of the stacks and ab initio Hartree–Fock calculations at the 6-31+G(d, p) level were carried out. Degree of charge transfer between counterions was monitored by Mulliken population analysis from which atomic charges and dipole moments were calculated. The results of these calculations are interpreted in a larger neurobiological context. Models are proposed which relate the charge-transfer process to ion channel dynamics (open/closed), changes in membrane potential, and macroscopic memory systems. A hypothetical feedback circuitry which could regulate membrane potential and prevent recurrent excitation or hyperpolarization is described. Potential tests of the model utilizing photoinduced charge transfer through a polyenic molecular wire are proposed. It is concluded that this research could lead to a better understanding of computational processes in neurophysiology and cognition. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 3–10, 1998     

Glutathione in Brain Disorders and Aging

Glutathione is a remarkably functional molecule with diverse features, which include being an antioxidant, a regulator of DNA synthesis and repair, a protector of thiol groups in proteins, a stabilizer of cell membranes, and a detoxifier of xenobiotics. Glutathione exists in two states—oxidized and reduced. Under normal physiological conditions of cellular homeostasis, glutathione remains primarily in its reduced form. However, many metabolic pathways involve oxidization of glutathione, resulting in an imbalance in cellular homeostasis. Impairment of glutathione function in the brain is linked to loss of neurons during the aging process or as the result of neurological diseases such as Huntington’s disease, Parkinson’s disease, stroke, and Alzheimer’s disease. The exact mechanisms through which glutathione regulates brain metabolism are not well understood. In this review, we will highlight the common signaling cascades that regulate glutathione in neurons and glia, its functions as a neuronal regulator in homeostasis and metabolism, and finally a mechanistic recapitulation of glutathione signaling. Together, these will put glutathione’s role in normal aging and neurological disorders development into perspective.     

Reduction of Deuterium Level Supports Resistance of Neurons to Glucose Deprivation and Hypoxia: Study in Cultures of Neurons and on Animals

The effect of a reduced deuterium (D) content in the incubation medium on the survival of cultured neurons in vitro and under glucose deprivation was studied. In addition, we studied the effect of a decrease in the deuterium content in the rat brain on oxidative processes in the nervous tissue, its antioxidant protection, and training of rats in the T-shaped maze test under hypoxic conditions. For experiments with cultures of neurons, 7–8-day cultures of cerebellar neurons were used. Determination of the rate of neuronal death in cultures was carried out using propidium iodide. Acute hypoxia with hypercapnia was simulated in rats by placing them in sealed vessels with a capacity of 1 L. The effect on oxidative processes in brain tissues was assessed by changes in the level of free radical oxidation and malondialdehyde. The effect on the antioxidant system of the brain was assessed by the activity of catalase. The study in the T-maze was carried out in accordance with the generally accepted methodology, the skill of alternating right-sided and left-sided loops on positive reinforcement was developed. This work has shown that a decrease in the deuterium content in the incubation medium to a level of −357‰ has a neuroprotective effect, increasing the survival rate of cultured neurons under glucose deprivation. When exposed to hypoxia, a preliminary decrease in the deuterium content in the rat brain to −261‰ prevents the development of oxidative stress in their nervous tissue and preserves the learning ability of animals in the T-shaped maze test at the level of the control group. A similar protective effect during the modification of the ²H/¹H internal environment of the body by the consumption of DDW can potentially be used for the prevention of pathological conditions associated with the development of oxidative stress with damage to the central nervous system.     

脉动型神经元网络的联想记忆与分割

以广泛讨论的Hodgk in-Hux ley神经元节点组成脉动神经元网络,从神经系统空时模式编码理论研究网络的记忆(或模式)存储与时间分割问题。给定一个输入模式,它是几种模式的叠加,网络能够以一部分神经元同步发放的形式一个接一个地在时间域分割出每一种模式。如果输入的模式是缺损的,系统能够把它们恢复成完好的原型,即神经网络的联想记忆功能。     

生物神经网络系统动力学与功能研究

生物神经系统是由数量极其巨大的神经元相互联结的信息网络系统,在生物体的感觉、认知和运动控制中发挥关键性的作用.首先介绍神经元、大脑和一些生物神经网络的生理结构和理论模型,然后分别介绍其放电活动和网络动态特性的一些重要问题,包括神经元的复杂放电模式、耦合神经元网络系统的同步活动和时空动力学、大脑联合皮层神经微回路的网络结构特征,以及工作记忆和抉择过程的动力学机制等. 最后对今后研究给出一些展望.