Alzheimer’s Disease: Soluble Oligomeric Aβ(1–40) Peptide in Membrane Mimic Environment from Solution NMR and Circular Dichroism Studies

Amyloid beta peptide (A) is a small peptide present in normal cells and aggregated A is the main constituent of the extracellular amyloid plaques found in Alzheimers disease (AD) brain. Recent studies suggest that soluble A oligomers are neurotoxic rather than amyloid fibrils found in amyloid plaques. This study using multidimensional NMR spectroscopy and circular dichroism (CD) provides the first direct evidence that alterations in membrane structure can trigger the conversion of soluble -helical monomeric A into oligomeric A in a -sheet conformation.     

Role of βγ-Dimers of GTP-Binding Proteins in Processes of Hormonal Signal Transduction

This review summarizes and analyzes data on structural and functional peculiarities of - and -subunits of heterotrimeric G proteins and their participation in -dimer in processes of hormonal signal transduction to the cell. The molecular mechanisms are discussed, which are responsible for formation of the -dimer complex and its interaction with the wide spectrum of signal and structural proteins, such as G protein -subunit, serpentine type receptors, kinases of G protein-coupled receptors, adenylyl cyclase, phospholipase C2, phosphatidyl-inositol-3-kinase, Raf-kinase, potassium and calcium channels, microtubular and RGS-proteins. The characteristics of - and -subunits are given for living organisms of different phylogenetic levels (lower eukaryotes, fungi, plants, vertebrates, and invertebrates). It is concluded that the -dimer is the most important regulatory link in various signal systems to carry out switch from one signal cascade to another and thereby to determine the final cellular response to the signal impulse.     

Structural analyses of new tri- and tetrasaccharides produced from disaccharides by transglycosylation of purified Trichoderma viride β-glucosidase

A new -glucosidase was partially purified from Trichoderma viride cellulase. This -glucosidase catalyzed a transglycosylation reaction of cellobiose to give -D-Glc-(16)--D-Glc-(14)-D-Glc (1, yield: 18.8%) and -D-Glc-(16)--D-Glc-(16)--D-Glc-(14)-D-Glc (2, 3.7%), regioselectively. Furthermore, the enzyme regioselectively converted laminaribiose and gentiobiose into -D-Glc-(16)--D-Glc-(13)-D-Glc (3, 15.3%) and -D-Glc-(16)--D-Glc-(16)-D-Glc (4, 20.2%), respectively. The structures (1–4) of the products were determined by ¹H and ¹³C NMR spectroscopies. This high regio- and stereoselectively of the -glucosidase could be applied for oligosaccharide synthesis.     

Holling's “hungry mantid” model for the invertebrate functional response considered as a Markov process. Part II: Negligible handling time

In this paper we analyse a stochastic model for invertebrate predation taking account of the predator's satiation. This model approximates Holling's hungry mantid model when handling time is negligible (see Part I). For this model we derive equations from which we can calculate the functional response and the variance of the total catch. Moreover we study a number of approximations which can be used to calculate these quantities in practical cases in a relatively simple manner.List of Notation a rate constant of digestion - b maximum of rate constant of prey encounter in the mantid - c satiation threshold for search - c satiation threshold for pursuit in the mantid - c _i (w^1/2(N- N)ⁱ) - expectation operator - f rate of change of satiation during search - F functional response: mean number of prey eaten per unit of time - g rate constant of prey capture - h probability generating function of N conditional on S = s times p - H probability generating function of N - m_i ¹ - n, N number of prey caught - p probability density of S - p_n simultaneous probability (density) of N and S - q probability of strike success - r dummy variable in generating function - s, S satiation - T _s search time - T _d digestion time - v asymptotic rate of increase of var v - V asymptotic rate of increase of var N - w weight of edible part of prey - W standard Wiener process - x prey density - z (N{S = s}-N)p - rate constant of prey escape time maximum pursuit time - (v{S = + w ^1/2}-v) - present time as a fraction of the time from the start to the end of the experiment - hazard rate of T _s - mean time between (downward) passages of S through c - v w_–1/2(N-) - edible prey biomass density - probability density of , number pi - parameter of Weibull distribution of T _s = (1/2acx(-g(c)))_1/2 - w_–1/2(S -) - satiation in the guzzler approximation: solution to d/dt = f() + g(), (0)=S(0). - biomass functional response: wF - total biomass catch in the guzzler approximation: solution to d/dt = g(), (0) = 0     

The checkerboard score and species distributions

Summary There has been an ongoing controversy over how to decide whether the distribution of species is random — i.e., whether it is not greatly different from what it would be if species did not interact. We recently showed (Roberts and Stone (1990)) that in the case of the Vanuatu (formerly New Hebrides) avifauna, the number of islands shared by species pairs was incompatible with a random null hypothesis. However, it was difficult to determine the causes or direction of the community's exceptionality. In this paper, the latter problem is examined further. We use Diamond's (1975) notion of checkerboard distributions (originally developed as an indicator of competition) and construct a C-score statistic which quantifies checkerboardedness. This statistic is based on the way two species might colonise a pair of islands; whenever each species colonises a different island this adds 1 to the C-score. Following Connor and Simberloff (1979) we generate a control group of random colonisation patterns (matrices), and use the C-score to determine their checkerboard characteristics. As an alternative mode of enquiry, we make slight alterations to the observed data, repeating this process many times so as to obtain another control group. In both cases, when we compare the observed data for the Vanuatu avifauna and the Antillean bat communities with that given by their respective control group, we find that these communities have significantly large checkerboard distributions, making implausible the hypothesis that their species distributions are a product of random colonisation.     

Das organische Gerüstwerk der Kalkschale des Schwanen-Eies

Zusammenfassung Kegel und Säulen der Schwanen-Eischale hinterlassen am Querschliff nach Entkalkung mit EDTA organisches (mucoproteides) Material als ein zusammenhängendes Gerüst, das sich mit Thionin metachromatisch färbt; ohne Demineralisierung oder wenigstens Anätzung bleibt Thionin an Schliffen und Bruchkanten der Schale wirkungslos. Das Lichtmikroskop zeigt an Schliffen nichts von dem organischen Material, es wurde während des Kristallwachstums fein zerteilt in Gitterlücken des Schalencalcits eingeschlossen. Es findet sich am stärksten angehäuft an den äueren und inneren Oberflächen der Kristall-individuen. In den Kegeln ist das Gerüst radial ausgebildet als die Loculi der Keile, und konzentrisch geschichtet, entsprechend den Lagen der Globularinklusionen, um deren jede herum Verdichtung der organischen Substanz statthat. In den inneren Säulen folgt das organische Gerüst dem Rhombenmuster; die äueren Säulen sind arm an organischer Substanz, hier verbleibt nach der Entkalkung eine dünne laterale Oberflächenschicht.

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Summary The cones and columns of the swans egg shell leave behind after decalcification with EDTA an organic (mucoproteid) material in form of a continuous frame work stainable metachromatically with thionine. Without demineralisation or at least etching, thionine proves ineffectual in ground sections or breaking edges of the shell. In ground sections the light microscope demonstrates nothing of the organic material: it was inclosed during the crystal growth in submicroscopical lattice gaps of the calcite individuals. The organic material is chiefly accumulated in the outer and inner surfaces of the crystals. In the cones the organic frame work is developed radially as the loculi of the wedges and concentrically layered corresponding with the globular inclusions, concentrated in the circumference of each. In the inner columns the organic material follows to the rhomb pattern. The outer columns after decalcification only leave behind a thin lateral organic sheath.

     

Modulation of cytokine responses of murine CD8+ αβ intestinal intraepithelial lymphocytes by IL-4 and IL-12

The immune responses of the intestine mucosa feature the noninflammatory type, such as IgA production and oral tolerance. Th2 type cytokines have been implicated in the induction of these noninflammatory responses. In the present study, cytokine responses of CD8+ and CD4+ TCR+ intestinal intraepithelial lymphocyte ( iIEL) subsets to TCR stimulation under the influence of IL-12, IL-4, or CD28 costimulation were examined. IL-12 enhanced production of IL-10 and IFN- by the CD8+ iIEL significantly but only marginally affected the CD8+ subset, whereas IL-4 induced IL-4, IL-5, and IL-10 production and augmented TGF- production by both subsets. CD28 costimulation induced production of Th2 cytokines by CD4+ iIEL in the absence of exogenous IL-4. Unlike lymph node CD4+ cells, the CD28 costimulation-induced Th2 differentiation of CD4+ iIEL was not inhibited by IFN-. These results demonstrate active cytokine production by CD4+, CD8+, as well as CD8+ iIEL. The Th2-skewed cytokine profile of CD8+ iIEL and the IFN--resistance of Th2 differentiation of the CD4+ iIEL suggest that both iIEL subsets contribute to the induction of noninflammatory mucosal immune responses.     

Carbohydrate antigen expression in murine embryonic stem cells and embryos. II. Sialylated antigens and glycolipid analysis

Summary A mouse embryonic stem (ES) cell line E14 and early mouse embryos were stained with a panel of 15 monoclonal antibodies recognizing sialylated or potentially sialylated carbohydrate determinants, Sialyl Le-x and sialyl Le-a were detected on the pre-implantation embryo from the 8-cell stage, and sialyl Le-a weakly on undifferentiated ES cells. Changes in cell surface carbohydrates occurred after induction of ES cell differentiation with retinoic acid (RA) and dibutyryl cAMP. Qualitative analysis of the neutral glycolipids of untreated and RA-treated ES cells using high-performance thin-layer chromatography (HPTLC) revealed few differences between the two types of culture. The major gangliosides in both cultures were indicative of an active a ganglioside synthesis pathway. GD₃, a precursor of the b synthesis pathway, previously reported to be characteristic of embryonal carcinoma (EC) cells, was absent. RA-induced differentiation caused a shift in the spectrum to more complex gangliosides. Application of fast atom bombardment mass spectrometry (FAB-MS) to permethylated derivatives of individual bands permitted partial characterization of an unusual sialylated glycolipid and a rare ganglioside with the suggested structure of GalNAc-GD1a.Abbreviations NeuAc N-acetylneuraminic acid - Cer ceramide - CMH monohexosylceramide - CDH lactosylceramide (Gal1-4Glc1-Cer) - CTH ceramide trihexoside (Gal1-4Gal1-4Glc1-Cer) - globoside (GalNAc1-3 Gal1-4Gal1-4Glc1-Cer) - Forssman antigen (GalNAc1-3GalNAc1-3Gal1-4Gal1-4Glc1-Cer) - GM₃ (NeuAc2-3Gal1-4Glc1-Cer) - GD₃ (NeuAc2-8NeuAc2-3Gal1-4Glc1-Cer) - GM1 (Gal1-3GalNAc1-4[NeuAca2-3]Gal1-4Glc1-Cer) - GD1a (NeuAc2-3Gal1-3GalNAc1-4[NeuAc2-3]Gal1-4Glc1-Cer) - GT1b (Neu5Ac2-3Gal1-3GalNAc1-4[Neu5Ac2-8Neu5Ac2-3]Gal1-4Glc1-Cer) The glycolipids are named according to Svennerholm (1963) and the recommendations of the IUPAC-IUB Commission on Biochemical Nomenclature (1978).     

Allotype distribution of human T cell receptor β and γ chain genes in Caucasians,Asians and Australian Aborigines: Relevance to chronic hepatitis B

Summary RFLPs of TCR and genes have been analyzed in chronic HBV carriers of three different ethnic populations to determine if there is an association of TCR allotypes with the development of chronic hepatitis B. The RFLPs of TCR and genes were defined respectively by BglII and PvuII genomic fragments on Southern blots. These methods allow allotype assignment. The distribution of TCR alleles showed ethnic variation, with one allele significantly decreased in Australian Aborigines, but there was no association with chronic hepatitits B. The distribution of TCR alleles did not show ethnic variation. However, a significant frequency decrease of one allele occurred in Aboriginal HBV carriers, suggesting the possibility of involvement of TCR allotypes in the development of the chronic HBV carrier state in Australian Aborigines.     

Triggering and predisposing factors in the “Red” decline syndrome of Norway spruce (Picea abies)

Summary Analysis of 62 mature Norway spruce (Picea abies provenance Viborg) trees growing in a Danish plantation was undertaken along with analysis of their nutrient contents (N, P, K, Ca, Mg, Fe, Mn, Cu, Zn, B and Na), in each of the three youngest needle age classes, from branches of four exposure directions near the tree top. The aim was to investigate if one among the studied possible predisposing factors was also a triggering factor in the 1989 outbreak of the Red Norway spruce decline in Denmark. Neither nutrient imbalance or deficiency, nor excessive N-deposition or salt-stress were indicated as triggering factors in 1989. The Red syndrome, noticeable for the bright red colour of the current-year needles, was found to be an extension of the European type Novel Decline. Red syndrome is similar to previously reported phenomena of top-dying and sub top-dying, in that it had fewer needle age classes and significantly higher contents of mobile cations (and Ca) in the younger needle classes. Tree ring analysis suggested that the Red syndrome was initiated in the early 1980s, when the trees experienced adverse climatic conditions. Because of this long-term development of the Red Norway spruce decline syndrome, it is concluded that a triggering factor is of minor importance relative to the multitude of predisposing factors.     

The cytology of phytophthora infestans

Summary Phytophthora infestans has three kinds of somatic nuclei: an oval shaped nucleus (approx. 3.1×2.7 ) which stains diffusely except for a crescent shaped Feulgen positive cap which stains intensely; a granular nucleus whose contents are organized into a fairly constant number of stained bodies, and, a deeply staining condensed nucleus. The capped nucleus is thought to be metabolic or resting and the granular nucleus is thought to be dividing as it is most commonly found in hyphal tips. Attenuated forms of all three kinds of nuclei are found.Nuclear division is mitotic and intranuclear. Eight—ten chromosomes are seen at metaphase.Sporangia have a mean of 6.3 nuclei which is constant for age and strain of culture. Sporangia become multinucleate as a result of nuclear migration and not by division in the developing sporangium. Zoospores are usually uninucleate.The nuclear cap is persistent throughout nuclear division when it also divides. It is associated with flagella production and nuclear migration and has some of the properties of a blepharoplast.     

Enrichment and efficient screening of ES cells containing a targeted mutation: the use of DT‐A gene with the polyadenylation signal as a negative selection maker

Gene targeting in embryonic stem (ES) cells via homologous recombination can occur at very low frequency. In order to enrich homologous recombinants before screening, a negative selection marker, such as thymidine kinase (TK) and diphtheria toxin A fragment (DTA), has been commonly used. In this study, we developed a negative selection marker using DTA gene with polyadenylation signal and it was designated DTApA. To determine the difference in targeting efficiency of the negative selections, we constructed three different targeting vectors for each negative selection (first, TK at the 3 end, second, TK at both the 5 and 3 ends <2 X TK>, and third, DTApA at the 5 end of the homologous sequences). Gene targeting experiments using these constructs clearly showed that negative selection using DTApA was more efficient than that using TK for homologous recombination and that negative selection using DTApA was as efficient as that using 2 X TK. Considering the fact that the use of DTApA is more convenient for construction of targeting vectors than that of 2 X TK, DTApA is an efficient negative selection marker.In addition, we examined long and accurate PCR (LAPCR) for screening gene targeted clones. The use of LAPCR with genomic DNAs from ES cell clones facilitated simple detection of homologous recombinants, suggesting that the screening with LAPCR is compatible with the use of longer homologous sequences of both arms in vector design. Our results indicate that the use of DTApA for negative selection together with the application of LAPCR for screening ensures efficient and timesaving screening for homologous recombinants.     

Retinoic acid receptor isoform RARγ 1: an antagonist of the transactivation of the RARβ RARE in epithelial cell lines and normal human keratinocytes

The diversity of isoforms of retinoic acid (RA) receptors (RARs) and of DNA sequences of retinoic acid-responsive elements (RAREs) suggests the existence of selectivities in the RAR/RARE recognition or in the subsequent gene modulation. Such selectivities might be particularly important for RAREs involved in positive feedback, eg. the RAR RARE. In the present work we found that in several epithelial cell lines, reporter constructs containing the RAR RARE linked to the HSV-tk promoter were transactivated in the presence of RA by endogenous RARs and co-transfected RAR₁ and RAR₂ isoforms, but not by RAR₁. On the contrary, this latter isoform behaved towards the RAR RARE as an inhibitor of the transactivation produced by endogenous RARs and by cotransfected RAR₁ and RAR₂. RAR₁ also behaved as an antagonist of the transactivation produced by cotransfected RXR. The natural RAR gene promoter or RAR RARE tk constructs were not activated by the endogenous receptors of normal human keratinocytes (NHK), which are known to contain predominantly RAR₁. It was, however, possible to activate to a certain extent RAR RARE-reporter constructs in NHK by co-transfecting RAR₁, RAR₂ or RXR. The antagonist behavior of RAR₁ towards the RAR RARE may explain why in certain cell types such as keratinocytes, RAR is neither expressed nor induced by RA.Abbreviations DMEM Dulbecco's modified Eagle medium - DMSO dimethyl sulfoxide - FCS fetal calf serum - MEM minimal Eagle medium - NHK normal human keratinocyte - RA retinoic acid - RAR retinoic acid receptor - RARE retinoic acid responsive element - TRE thyroid responsive element - VDRE vitamin D response element - RXR retinoid X receptor     

Possible indirect interactions between transient and resident killer whales: implications for the evolution of foraging specializations in the genus Orcinus

Summary Two distinct forms of killer whale (Orcinus orca) occur off the coast of British Columbia, Alaska and Washington State. These have different diets, and may be reproductively isolated. Because the primary food of transient whales (pinnipeds) is a potential competitor for the primary food of resident whales (salmon), or for the smaller fishes on which salmon feed, there should be an indirect interaction between the two forms of killer whale. We use simple mathematical models to show that this interaction will be either of a plus-minus type, or a plus-plus type (indirect mutualism), depending on whether or not pinnipeds and residents are on the same trophic level. In the case of the plus-minus interaction, increasing the population density or improving the environmental conditions of transients will increase the population density of residents, while increasing resident populations will reduce the equilibrium population size of transients. In the case of the plus-plus interaction, increasing the population density or improving the environmental conditions of transients will increase the population density of residents, while increasing resident populations will reduce the equilibrium population size of transients. In the case of the plus-plus interaction, increasing the population density or improving the environmental conditions of transients will increase the population density of residents, and vice versa. Such effects may not be currently manifest due to reduced populations at most levels in the food web. Regardless, considering such indirect interactions may be important for the management of many of the species involved, and can also provide a valuable framework for examining the evolution of the two forms of killer whales. Frequency-dependent indirect interactions, acting in concert with density-dependence within populations and disruptive selection on prey-type specific foraging characteristics, may have favoured reproductive isolation of the two forms of killer whales. We suggest that these two forms of whale are in the process of speciating, i.e., the two forms are incipient species.     

Synthesis of Galβ1-4GlcNAcβ- and Galβ1-3GalNAcα-O-L-serine Derivatives employing glycosidases

A new approach for the highly specific preparation of L-serine conjugates of lactosamine and Gal1-3GalNAc is described. Thus, the L-serine derivative of lactosamine Gal1-4GlcNAc-O-(N-Z)-Ser-OEt, was obtained from lactose, employing GlcNAc-O-(N-Z)-Ser-OEt as acceptor and a yeast -galactosidase as catalyst Galp 1-3GalNAc-O-(N-Alloc)-Ser-OMe was obtained from lactose, employing GalNAc-O-(N-Alloc)-Ser-OMe as acceptor and -galactosidase from bovine testes as catalyst.     

Utilization and degradation of lindane by soil microorganisms

Of 147 microorganisms isolated from a loamy sand, 71 showed good growth with lindane (-1,2,3,4,5,6-hexachlorocyclohexane) and produced chloride in an aqueous medium. Thirteen soil microorganisms were selected to study the utilization of lindane. Lindane was metabolized by the microbes to -2,3,4,5,6-pentachloro-1-cyclohexene (-PCCH), -3,4,5,6-tetrachloro-1-cyclohexene (-TCCH), -3,4,5,6-tetrachloro-1-cyclohexene (-TCCH), -3,4,5,6-tetrachloro-1-cyclohexene (-TCCH), and pentachlorobenzene (PCB). Cells of Pseudomonas sp. No. 62 grown on lindane simultaneously adapted to -PCCH, -TCCH, -TCCH, -TCCH, PCB, 1,2,3,4-tetrachlorobenzene (1,2,3,4-TCB) and 1,2,4,5-tetrachlorobenzene (1,2,4,5-TCB). The bacteria degraded each of these chemicals at least partially as indicated by an increased rate of oxygen consumption.Abbreviations Lindane -1,2,3,4,5,6-hexachlorocyclohexane - -PCCH -2,3,4,5,6-pentachloro-1-cyclohexene - -TCCH -3,4,5,6-tetrachloro-1-cyclohexene - -TCCH -3,4,5,6-tetrachloro-1-cyclohexene - -TCCH -3,4,5,6-tetrachloro-1-cyclohexene - PCB pentachlorobenzene - 1,2,3,4-TCB 1,2,3,4-tetrachlorobenzene - 1,2,3,5-TCB 1,2,3,5-tetrachlorobenzene - 1,2,4,5-TCB 1,2,4,5-tetrachlorobenzene - 1,2,3-tCB 1,2,3-trichlorobenzene - 1,2,4-tCB 1,2,4-trichlorobenzene - 1,3,5-tCB 1,3,5-trichlorobenzene - 1,2-DCB 1,2-dichlorobenzene - 1,3-DCB 1,3-dichlorobenzene - 1,4-DCB 1,4-dichlorobenzene - MCB monochlorobenzene Contribution No. 631, Research Institute, Agriculture Canada, University Sub Post Office, London, Ontario N6A 5B7     

Stereospecificity and electrogenicity of amino acid transport in Riccia fluitans

In the aquatic liverwort Riccia fluitans, membrane depolarization (_m), change in membrane conductance (g_m), and current-voltage (I-V) characteristics in the presence of different amino acids as well as the uptake of ¹⁴C-labeled amino acids were measured. L-isomers of the tested amino acids generate larger electrical effects (_m, g_m) than D-isomers, and the I-V characteristics show that the positive electrical inward-current of 20 mA m^-2 generated by 0.5 mM D-serine is only about 50% of the current generated by adding 0.5 mM L-serine. Whereas - and -amino acids rapidly depolarize the membrane to the same extend, with -aminobutyric acid (-AB) and dipeptides no significant electrical effects have been measured. The uptake kinetics of ¹⁴C-labeled amino acids display three components: (I) A saturable high-affinity component with K_s-values of 48 M D-alanine, 12 M -aminoisobutyric acid (AIB), 9 M L-alanine, 8 M L-proline, and 6 M L-serine, respectively; (2) an apparently linear low-affinity component, and (3) an also linear but unspecific component at concentrations >20 times the given K_s-value. Uptake of ¹⁴C-labeled AIB can be inhibited competitively by all tested neutral amino acids, the L-isomers being more effective than the D-isomers, as well as by ammonium or methylamine. Vice versa, AIB competitively inhibits uptake of L-serine and L-alanine. It is concluded that an uncharged stereospecific carrier for the investigated amino acids exists in the plasmalemma of Riccia fluitans. Accumulation ratios of about 50 suggest secondary active transport driven by a transmembrane electro-chemical gradient (mainly _m) which is generated by the electrogenic proton pump. It is suggested that this carrier binds to the amino group forming either a charged binary complex with positively charged amines (Felle 1980), or an uncharged complex with -AB or dipeptides, whereas electrogenic transport of - and -amino acids is mediated by a ternary carrier complex, probably charged by a proton.Symbols and Abbreviations _m membrane potential (mV) - E_co equilibrium potential (mV) of the transport system - g_m membrane (slope) conductance (Sm^-2) - g_m change in g_m - I-V curve current-voltage curve - AIB -aminoisobutytric acid - -AB -aminobutyric acid     

Plasma α- and γ-tocopherol have different pattern during normal human pregnancy

Plasma - and -tocopherol were monitored in pregnant women throughout healthy gestational periods and after delivery and were compared with that of non pregnant women. The mean plasma -tocopherol and -tocopherol concentrations in non pregnant Saudi women (15.2 ± 1.3 and 1.8 ± 0.2 ol/l respectively) were found within normal range. The maternal plasma -tocopherol level steadily increased reaching maximum level (19.1 ± 1.6 mol/l) at late gestation and then gradually decreased after delivery. On the contrary, the optimum level of -tocopherol (2.1 ± 0.2 mol/l) was at mid gestation, followed by a progressive decrease until one month after delivery (1.5 ± 0.1 ol/l). This study shows that the maternal plasma - and -tocopherol have different profiles that may be attributed to their different responses to the changes in maternal lipids during pregnancy.     

The nature of the coupling between segmental oscillators of the lamprey spinal generator for locomotion: A mathematical model

We present a theoretical model which is used to explain the intersegmental coordination of the neural networks responsible for generating locomotion in the isolated spinal cord of lamprey.A simplified mathematical model of a limit cycle oscillator is presented which consists of only a single dependent variable, the phase (t). By coupling N such oscillators together we are able to generate stable phase locked motions which correspond to traveling waves in the spinal cord, thus simulating fictive swimming. We are also able to generate irregular drifting motions which are compared to the experimental data obtained from cords with selective surgical lesions.