Excitation-Contraction Coupling in Crayfish

High-sensitivity recording techniques demonstrate a continuousrelation between the onset and magnitude ot tension and themembrane depolarization that is induced by increasing K in thebathing medium or by intracellularly applied outward currents.This finding is not consistent with the mechanism of signallinge-c coupling by electrotonic spread of a "critical" depolarizationinward along the membrane of the transverse tubular system.It is in accord, however, with the channelled current mechanismthat is based on the known anion-permselectivity of the membranein the terminals of the TTS. The channelled-current model alsopredicts a direct role of Cl and a possible interaction betweenCa and CI in e-c coupling. The initiation and maintenance oftension as well as its magnitude, are in fact dependent uponthe concentrations of Ca and Cl in the medium. Thus, both thesignalling to, and the activation of, the contractile systemappear to be performed by a flow of current in the loop: cellmembrane – cell interior – TTS membrane –TTS channels – exterior, as is envisaged in the channelled-currentmodel of e-c coupling.     

Response of stream‐breeding salamander larvae to sediment deposition in southern Appalachian (U.S.A.) headwater streams

1. Increased fine sediment deposition is a prevalent threat to stream biodiversity and has been shown to impact stream‐breeding salamanders negatively. However, their complex life histories make it difficult to determine which stage is affected. 2. We conducted field experiments from 26 August to 11 September 2010 and 11 October to 11 November 2010 in two southern Appalachian headwater streams (U.S.A.) to examine the response of larval salamanders to increased fine sediment deposition. Fine sediment was increased in artificial stream channels by 0, 33 and 67%. The number of larvae observed at the end of the experiments was used to determine whether larval microhabitat selection was influenced by fine sediment deposition. A concurrent survey of aquatic larvae in three nearby streams complemented this experiment. Stream substratum composition at survey sites was quantified to examine the effects of fine sediment on larval salamander abundance. 3. Increases in fine sediment deposition failed to explain the number of larval salamanders detected in stream channels. Similarly, a negligible effect of fine sediment was observed on abundance estimates. 4. These results suggest that fine sediment deposition has a minimal impact on aquatic salamander larvae. Therefore, the effects of increased fine sediment loads on stream‐breeding salamanders may not be the result of deleterious effects on the aquatic larvae but instead may be the result of effects on other stages. Management efforts that consider these other stages are therefore needed to protect stream‐breeding salamander communities.     

Intraclonal Dimorphism of Caudal Cirri in Euplotes vannus: Cortical Determination*

SYNOPSIS. Intraclonal variation in number of right caudal cirri (RCC) occurs within some species of the hypotrichous genus Euplotes. Euplotes vannus, a marine species, may have either 2 or 3 RCC. A single clone always contains individuals of both types. The frequency of individuals of each type within a clone was found to be 0.5. This fact suggested that during division each parental cell gives rise to one daughter having 3 RCC and one having 2. Formation of RCC during division was studied in E. vannus and in E. plumipes, a fresh-water form which always has 2 RCC. The studies were made on living animals and on fixed animals stained with protargol or by the Chatton-Lwoff method. In both species, the new RCC first appear in the right dorsal kineties and later migrate to the ventral surface. The RCC for the proter develop near the parental equator while those for the opisthe form near the posterior end of the parent cell, both sets developing in close proximity to kinetosomes of the kineties. In both species the 2 dorsal kineties furthest to the right each give rise to 2 RCC, one for the proter and one for the opisthe. In E. vannus, however, the third-from-the-right dorsal kinety also produces one right caudal cirrus for the proter. Therefore, in E. vannus it is the proter which always receives 3 caudal cirri and the opisthe which gets only 2. The role of the cortex in determining these events is discussed. Two cases of abnormal caudal cirrus formation are also described. Other aspects of morphogenesis during division, not previously reported, are also presented and discussed.     

Phenotypic plasticity in the spawning traits of bigheaded carp (Hypophthalmichthys spp.) in novel ecosystems

1. Bigheaded carp, including both silver (Hypophthalmichthys molitrix) and bighead (H. nobilis) carp, are successful invasive fishes that threaten global freshwater biodiversity. High phenotypic plasticity probably contributes to their success in novel ecosystems, although evidence of plasticity in several spawning traits has hitherto been largely anecdotal or speculative. 2. We collected drifting eggs from a Midwestern U.S.A. river from June to September 2011 and from April to June 2012 to investigate the spawning traits of bigheaded carp in novel ecosystems. 3. Unlike reports from the native range, the presence of drifting bigheaded carp eggs was not related to changes in hydrological regime or mean daily water temperature. Bigheaded carp also exhibited protracted spawning, since we found drifting eggs throughout the summer and as late as 1 September 2011. Finally, we detected bigheaded carp eggs in a river reach where the channel is c. 30 m wide with a catchment area of 4579 km², the smallest stream in which spawning has yet been documented. 4. Taken with previous observations of spawning traits that depart from those observed within the native ranges of both bighead and silver carp, our findings provide direct evidence that bigheaded carp exhibit plastic spawning traits in novel ecosystems that may facilitate invasion and establishment in a wider range of river conditions than previously envisaged.     

Evaluation of the water fern Azolla microphylla for mosquito population management in the rice-land agro-ecosystem of south India

The floating water fern Azolla microphylla Kaulfess was evaluated as a biocontrol agent against mosquitoes breeding in rice fields in Tamil Nadu, South India. Anopheles subpictus Grassi, Culex pseudovishnui Colless and Culex tritaeniorhynchus Giles were the predominant species of mosquitoes, with peak densities of late instar larvae and pupae occurring during the second week after transplantation of rice seedlings of short-term (c. 80 days from transplantation to harvest) or medium-term (c. 95 days) varieties. Immature mosquito populations were reduced by mats of Azolla microphylla covering more than 80% of the water surface. However, since 80% coverage by Azolla was achieved only 13-14 days after rice transplantation, its usefulness for mosquito control was limited. Azolla may have a greater potential in an integrated control programme, or in areas where long-term varieties of rice are predominantly grown.     

The electrophysiology and pharmacology of lobster neuromuscular synapses

Effects of drugs on resting potential, membrane resistance, and excitatory and inhibitory postsynaptic potentials (e.p.s.p.'s and i.p.s.p.'s) of lobster muscle fibers were studied using intracellular microelectrodes Acetylcholine, d-tubocurarine, strychnine, and other drugs of respectively related actions on vertebrate synapses were without effects even in 1 per cent solutions (10^- w/v). Gamma-aminobutyric acid (GABA) acted powerfully and nearly maximally at 10^-7 to 10^-6 w/v. Membrane resistance fell two- to tenfold, the resting potential usually increasing slightly. This combination of effects, which indicates activation of inhibitory synaptic membrane, was also produced by other short chain ω-amino acids and related compounds that inactivate depolarizing axodendritic synapses of cat. The conductance change, involving increased permeability to Cl^-, by its clamping action on membrane potential shortened as well as decreased individual e.p.s.p.'s. Picrotoxin in low concentration (ca. 10^-7 w/v) and guanidine in higher (ca. 10^-3 w/v) specifically inactivate inhibitory synapses. GABA and picrotoxin are competitive antagonists. The longer chain ω-amino acids which inactivate hyperpolarizing axodendritic synapses of cat are without effect on lobster neuromuscular synapse. However, one member of this group, carnitine (β-OH-GABA betaine), activated the excitatory synapses, a decreased membrane resistance being associated with depolarzation. The pharmacological properties of lobster neuromuscular synapses and probably also of other crustacean inhibitory synapses appear to stand in a doubly inverted relation to axodendritic synapses of cat.     

Development of combined use of neem (Azadirachta indica) and water management for the control of culicine mosquitoes in rice fields

Abstract. Crude neem products have earlier shown considerable promise for control of culicine mosquito vectors in rice fields as a by-product of their agricultural use as fertilizers, but suffer from disadvantages of bulkiness and lack of stability in storage. Relatively stable lipid-rich fractions of neem were shown to be as effective as good-quality crude neem products in control of breeding of culicine vectors of Japanese encephalitis, and also produced a slight but significant reduction in populations of anopheline pupae. Neem-based formulations coated over urea significantly increased grain yield, but used alone did not, whereas combining the use of neem-coated urea and water management by intermittent irrigation had a greater effect on grain yield than that of water management alone. The neem fractions were relatively cost-effective, and the combined water management and neem-coated urea strategy is acceptable to farmers, who are already aware of the benefits of the use of neem-coated urea, and of water management. This technology therefore has considerable promise as an environmentally benign method of rice-field mosquito control that could be sustainably implemented by farmers.     

Platelet Requirement in the Interaction of the Complement and Clotting Systems

THE study of immunological reactions in rabbits genetically deficient in the sixth component of complement (C6) can provide information about the biological role of the complement system. Since their discovery¹, these rabbits have been found to produce no C6 protein and they can form antibody against it (ref. 2 and review in ref. 3). Furthermore, although the plasma and serum of these rabbits contain the normal coagulation factors, the whole blood clotting time is longer than normal⁴.     

Induction of Long Term Lymphocyte Lines from Delayed Hypersensitive Human Donors using Specific Antigen plus Epstein–Barr Virus

THE availability of homogeneous populations of human and murine myeloma cells has provided a unique opportunity for investigating the mechanism of immunoglobulin formation¹. Continuous lines of cultured lymphoid cells producing specific antibody or manifesting delayed hypersensitivity would be even more useful in studying the molecular events of the immune response. Human lymphoid cell lines have been established in long term culture using Epstein–Barr virus (EBV)^{2, 3} or phyto-haemagglutinin⁴ but antigen alone has not been effective⁵. The purpose of the work reported here was selectively to establish antigen-sensitive cells in culture by stimulating peripheral white cells from delayed hypersensitive donors with antigen in vitro and then exposing the cells to EBV. This combination of antigen and virus was chosen because of the following considerations: (1) some RNA and DNA viruses do not replicate in resting lymphocytes but can infect antigen-sensitive lymphocytes which have been stimulated in vitro with mitogens or specific antigen^{6, 7}; (2) polyoma virus transforms cells in the G₂ phase of the cell cycle more effectively than in G₁ (ref. 8). These observations suggested that combined exposure to antigen and EBV might result in the establishment of cell lines enriched for antigen-sensitive or antibody-forming cells.