Simulation and Parameter Estimation Study of a Simple Neuronal Model of Rhythm Generation: Role of NMDA and Non-NMDA Receptors

Simple neural network models of the Xenopus embryo swimming CPG, based on the one originally developed by Roberts and Tunstall (1990), were used to investigate the role of the voltage-dependent N-methyl-D-aspartate (NMDA) receptor channels, in conjunction with faster non-NMDA components of synaptic excitation, in rhythm generation. The voltage-dependent NMDA current "follows" the membrane potential, leading to a postinhibitory rebound that is more efficient than one without voltage dependency and allows neurons to fire more than one action potential per cycle. Furthermore, the model demonstrated limited rhythmic activity in the absence of synaptic inhibition, supporting the hypothesis that the NMDA channels provide a basic mechanism for rhythmicity. However, the rhythmic properties induced by the NMDA current were observed only when there was moderate activation of the non-NMDA synaptic channels, suggesting a modulatory role for this component. The simulations also show that the voltage dependency of the NMDA conductance, as well as the fast non-NMDA current, stabilizes the alternation pattern versus synchrony. To verify that these effects and their implications on the mechanism of swimming and transition to other types of activity take place in the real preparation, constraints on parameter values have to be specified. A method to estimate synaptic parameters was tested with generated data. It is shown that a global analysis, based on multiple iterations of the optimization process (Foster et al., 1993), gives a better understanding of the parameter subspace describing network activity than a standard fit with a sensitivity analysis for an individual solution.     

Rare hybridization and introgression in smooth and palmate newts (Salamandridae: Triturus vulgaris and T. helveticus)

This paper describes the occurrence of hybridization and introgression in two species of amphibians (the newts Triturus helveticus and Triturus vulgaris ) in mid-Wales, northern France and western France. A single aberrant adult male with intermediate phenotype was found. The multivariate analysis of 14 morphometric and two meristic characters supported its hybrid status. Electrophoretic analysis of 42 protein loci showed a genetic distance of 0.57 ± 0.14 Nei units between the species and revealed 15 diagnostic loci. The aberrant specimen was heterozygous at 11 of those and most likely to be a F₁ hybrid. Four marker loci appeared homozygous, suggesting the presence of enzymatically non-active ('null') alleles. The analysis of (maternally inherited) mitochondrial DNA showed the hybrid to be the offspring of a T. helveticus mother (and a T. vulgaris father). This observation does not conform to expectations based on the species composition in the pond from which the hybrid was collected. No F₁ hybrids were observed in a large sample (n > 5000) of larvae, recently metamorphosed newts and adults using two diagnostic protein loci. Occasionally alleles characteristic for one species were observed in the gene pool of the other species, suggesting the presence of bidirectional introgression. However, the frequency of alien genes was low (maximally 0.07%) which renders it difficult to rule out alternative explanations conclusively. The increase in total genetic variation in T. helveticus and T. vulgaris due to gene flow between them is negligible.     

Modelling spatial dynamics of fish

Our ability to model spatial distributions of fish populations is reviewed by describing the available modelling tools. Ultimate models of the individual's motivation for behavioural decisions are derived from evolutionary ecology. Mechanistic models for how fish sense and may respond to their surroundings are presented for vision, olfaction, hearing, the lateral line and other sensory organs. Models for learning and memory are presented, based both upon evolutionary optimization premises and upon neurological information processing and decision making. Functional tools for modelling behaviour and life histories can be categorized as belonging to an optimization or an adaptation approach. Among optimization tools, optimal foraging theory, life history theory, ideal free distribution, game theory and stochastic dynamic programming are presented. Among adaptation tools, genetic algorithms and the combination with artificial neural networks are described. The review advocates the combination of evolutionary and neurological approaches to modelling spatial dynamics of fish.     

Analysis of zinc binding sites in protein crystal structures

The geometrical properties of zinc binding sites in a dataset of high quality protein crystal structures deposited in the Protein Data Bank have been examined to identify important differences between zinc sites that are directly involved in catalysis and those that play a structural role. Coordination angles in the zinc primary coordination sphere are compared with ideal values for each coordination geometry, and zinc coordination distances are compared with those in small zinc complexes from the Cambridge Structural Database as a guide of expected trends. We find that distances and angles in the primary coordination sphere are in general close to the expected (or ideal) values. Deviations occur primarily for oxygen coordinating atoms and are found to be mainly due to H-bonding of the oxygen coordinating ligand to protein residues, bidentate binding arrangements, and multi-zinc sites. We find that H-bonding of oxygen containing residues (or water) to zinc bound histidines is almost universal in our dataset and defines the elec-His-Zn motif. Analysis of the stereochemistry shows that carboxyl elec-His-Zn motifs are geometrically rigid, while water elec-His-Zn motifs show the most geometrical variation. As catalytic motifs have a higher proportion of carboxyl elec atoms than structural motifs, they provide a more rigid framework for zinc binding. This is understood biologically, as a small distortion in the zinc position in an enzyme can have serious consequences on the enzymatic reaction. We also analyze the sequence pattern of the zinc ligands and residues that provide elecs, and identify conserved hydrophobic residues in the endopeptidases that also appear to contribute to stabilizing the catalytic zinc site. A zinc binding template in protein crystal structures is derived from these observations.     

华北平原及黄土高原啮齿动物物种丰富度的空间格局及其分异

在采用网格法对华北平原及黄土高原啮齿动物调查的基础上,分析了啮齿动物物种丰富度空间格局。华北平原物种丰富度最低,其次为晋、翼山地和汾、渭谷地,而南蒙高原和黄土高原的丰富度较高;物种丰富度纬向变化不明显,而经向变化显著,由东向西,物种丰富度呈递增趋势;丰富度在海拔上的变化并不存在相关的地理模式;丰富度与山地面积呈正相关,与平原面积呈负相关,而与丘陵面积相关不显著,丰富度与各地地貌类型面积的总和呈明显的正相关;丰富度与温度相关不明显,而与降雨量呈负相关。在华北平原及黄土高原,生境结构类型愈复杂的地区,啮齿动物物种丰富度愈高。     

银杏开发造园模式的探讨

根据银杏生物学特性和生产栽培目的的不同以及目前银杏的生产状况,阐述了银杏开发的重要意义,概述了叶材兼用银杏园、果叶兼用银杏园、果材兼用银杏园的立地选择、栽培密度和抚育管理等方面的技术要求,分析了各类园的利弊,并对低效的银杏园提出了改造的建议。     

“城-郊-乡”森林生态样带植被变化梯度分析

沿纽约市“市区－郊区－农区”１４０ｋｍ森林生态样带,对９个样地１９个样方的森林植被进行了研究。植被组成和结构沿样带变化明显,分异出城区森林、郊区森林和农区森林等不同类型,优势种替代明显,植物种类也形成了不同的生态类型。植被的梯度变化与人类活动密切相关,城市化对植被有重要影响。森林生态样带是研究人类活动对植被影响的好手段。     

The Use Of Methods For Injury Determination And Quantification From Natural Resource Damage Assessment In Ecological Risk Assessment

Several Federal statutes provide the government the authority to recover natural resource damages including the Clean Water Act Amendments (1977), the Outer Continental Shelf Act Amendments (1978), the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980, and the Oil Pollution Act of 1990 (OPA 90). CERCLA and OPA 90 are the principle Federal statutes which authorize trustees to assess damages for trust resources which are lost, injured, or destroyed as a result of the discharge of oil or the release of hazardous substances. The Department of the Interior was charged with developing natural resource damage assessment (NRDA) regulations and procedures from CERCLA and the Department of Commerce, National Oceanic and Atmospheric Administration (NOAA) was charged with developing regulations for OPA 90. NRDA is a process for making the public “whole” for direct injury to natural resources and/or the services of natural resources. The primary objectives of the NRDA process are to identify and quantify natural resource injury, determine the damages resulting from the injury, and develop and implement appropriate restoration actions. The goal is to be accomplished by implementing a plan for the restoration, rehabilitation, replacement, or acquisition of equivalent natural resources. NRDA is an after-the-fact process; however, the OPA 90 NRDA rules describe a pre-spill planning process. The models and formulae can be used in this pre-spill planning process to estimate damages (both ecological and economic). Some of those tools, in particular NRDAMCME, have uses in ranking risk from spills of petroleum products and hazardous substances. This information can be used to protect ecological resources and lower NRDA costs through pre spill planning and management of resources during a spill.