PSD-95-like membrane associated guanylate kinases (PSD-MAGUKs) and synaptic plasticity

Activity-dependent modification of excitatory synaptic transmission is a fundamental mechanism for developmental plasticity of the neural circuits and experience-dependent plasticity. Synaptic glutamatergic receptors including AMPA receptors and NMDA receptors (AMPARs and NMDARs) are embedded in the postsynaptic density, a highly organized protein network. Overwhelming data have shown that PSD-95-like membrane associated guanylate kinases (PSD-MAGUKs), a major family of scaffold proteins at glutamatergic synapses, regulate basal synaptic AMPAR function and trafficking. It is now clear that PSD-MAGUKs have multifaceted functions in regulating both basal synaptic transmission and synaptic plasticity. Here we discuss recent advancements in understanding the roles of PSD-95 and other family members of PSD-MAGUKs in synaptic plasticity, both as an anchoring protein for synaptic AMPARs and as a signaling scaffold for mediating the interaction of the signaling complex and NMDARs.National Institute of Mental Health (U.S.) (Grant MH080310

A Super Fast Algorithm for Estimating Sample Entropy

: Sample entropy, an approximation of the Kolmogorov entropy, was proposed to characterize complexity of a time series, which is essentially defined as − log(B/A), where B denotes the number of matched template pairs with length m and A denotes the number of matched template pairs with m + 1, for a predetermined positive integer m. It has been widely used to analyze physiological signals. As computing sample entropy is time consuming, the box-assisted, bucket-assisted, x-sort, assisted sliding box, and kd-tree-based algorithms were proposed to accelerate its computation. These algorithms require O(N2) or O(N2− 1/m+1 ) computational complexity, where N is the length of the time series analyzed. When N is big, the computational costs of these algorithms are large. We propose a super fast algorithm to estimate sample entropy based on Monte Carlo, with computational costs independent of N (the length of the time series) and the estimation converging to the exact sample entropy as the number of repeating experiments becomes large. The convergence rate of the algorithm is also established. Numerical experiments are performed for electrocardiogram time series, electroencephalogram time series, cardiac inter-beat time series, mechanical vibration signals (MVS), meteorological data (MD), and 1/ f noise. Numerical results show that the proposed algorithm can gain 100–1000 times speedup compared to the kd-tree and assisted sliding box algorithms while providing satisfactory approximate accuracy

Controllability and Observability of Fractional Linear Systems with Two Different Orders

This paper is concerned with the controllability and observability for a class of fractional linear systems with two different orders. The sufficient and necessary conditions for state controllability and state observability of such systems are established. The results obtained extend some existing results of controllability and observability for fractional dynamical systems

Alternative N-Terminal Domains of PSD-95 and SAP97 Govern Activity-Dependent Regulation of Synaptic AMPA Receptor Function

SummaryPSD-95 and SAP97 are scaffolding proteins that have been implicated in regulating AMPA receptor incorporation and function at synapses. Gain- and loss-of-function approaches, however, have generated conflicting results. To minimize adaptations during development and potential dominant-negative effects of overexpression, we have combined silencing of endogenous PSD-95 in mature neurons with heterologous expression of specific SAP97 or PSD-95 isoforms. We find that both PSD-95 and SAP97 contain alternative N termini expressing either double cysteines that normally are palmitoylated (α-isoforms) or an L27 domain (β-isoforms). Whereas α-isoforms of PSD-95 and SAP97 influence AMPA receptor-mediated synaptic strength independent of activity, the effects of β-isoforms are regulated by activity in a CaMKII-dependent manner. Importantly, the synaptic effects of the β-isoforms are masked by the endogenous α-isoform of PSD-95. These results demonstrate that the different N termini of the predominant endogenous forms of PSD-95 (α-isoform) and SAP97 (β-isoform) govern their role in regulating synaptic function