Showing papers in "Proceedings of The Royal Society B: Biological Sciences in 1973"
TL;DR: Calcium ions injected into the presynaptic nerve terminal in the giant synapse of the squid, evoked transmitter release while similar doses of Mg and Mn were ineffective.
Abstract: Calcium ions injected into the presynaptic nerve terminal in the giant synapse of the squid, evoked transmitter release while similar doses of Mg and Mn were ineffective The transmitter release induced by intracellular application was still observed when Ca was replaced in the external fluid by Mn, in spite of the fact that this abolished transmitter release in response to presynaptic depolarization
431 citations
TL;DR: Examination of the behaviour of pollen on the style of Raphanus, following compatible and incompatible intraspecific pollinations, has revealed the self-incompatibility system in this species to be composed of at least three stages.
Abstract: Examination of the behaviour of pollen on the style of Raphanus, following compatible and incompatible intraspecific pollinations, has revealed the self-incompatibility system in this species to be composed of at least three stages. The first, on which no information has been obtained in this study, involves the germination of the grain. The second stage concerns the ability of the pollen tube to penetrate the cuticle of the stigmatic papilla. It is possible that cutinase is deficient in incompatible pollen tubes but, in most instances, the outer layers of the stigmatic wall are penetrated. The third stage involves the interaction of substances secreted by the pollen tube with products of the stigmatic cytoplasm. The interaction is swiftly followed by the deposition, in the stigma, of a layered callosic body. This is formed immediately under the point of penetration and takes about 6 h to develop fully. Development of the pollen tube ceases as the first layers of callose are laid down. It is possible that the substances in the pollen responsible for the initiation of the second two stages are held in the tapetally synthesized tryphine, thus accounting for the sporophytic control of pollen compatibility in this species. The mature stigma contains large numbers of crystalline protein bodies, but it is not known whether they play any role in the self-incompatibility system.
172 citations
TL;DR: It is proposed that, in Raphanus, substances responsible for the initiation of at least two stages in the self-incompatibility system are held in the tryphine.
Abstract: The tryphine that coats the pollen grains of Raphanus is tapetally synthesized and is composed of a fibro-granular and a lipidic component. The fibro-granular material is proteinaceous and is secreted by cisternae of the endoplasmic reticulum. The lipidic component is derived, mainly, from degraded elaioplasts. The fibro-granular material is applied to the pollen exine first, followed by the lipidic mass. The tryphine condenses during the final stages of pollen maturation and dries down to form a thick, highly viscous coating. The major part of the condensation appears to result from dehydration. The tryphine, extracted from the pollen by a centrifugal method and mounted in a membrane, appears to be capable of penetrating the outer layers of a stigma of the same species and, if the pollen from which it was derived is incompatible with respect to the stigma, the stimulation of the production of the callosic reaction body in a manner similar to an incompatible pollen tube. It is proposed that, in Raphanus, substances responsible for the initiation of at least two stages in the self-incompatibility system are held in the tryphine.
142 citations
TL;DR: The growth of Microcystis aeruginosa in a small, shallow eutrophic lake was studied during three consecutive seasons; the alga was shown to be continuously present in the plankton throughout the period, and had an effective light-dependent buoyancy control mechanism.
Abstract: The growth of Microcystis aeruginosa in a small, shallow eutrophic lake was studied during three consecutive seasons The alga was shown to be continuously present in the plankton throughout the period Exponential increase in the population was confined to a 5 to 8-week period, following the onset of thermal stratification Populations appeared to originate near the bottom of the euphotic zone The possession of an effective light-dependent buoyancy control mechanism enabled the alga to maintain station, though progressive deterioration of the photic conditions forced populations to rise and become dissipated within the epilimnion Buoyancy increased after the cessation of growth; surface blooms often led to the physical removal of a majority of colonies to lee shores Surviving colonies became generally less buoyant after the lake destratified in autumn
137 citations
TL;DR: Cold shock and homogenization release from spermatozoa a substance, presumably a lipid, which provides the substrate for peroxidation, which is probably linked with the decline in motility and respiratory activity, and the structural damage to sperm membranes, which characterize ageing or degenerating spermutozoa.
Abstract: Ram spermatozoa produce aerobically an organic peroxide which can be determined quantitatively by the thiobarbituric acid reaction. The reaction is more intense in spermatozoa that have been stored at 5°C. Cold shock and homogenization release from spermatozoa a substance, presumably a lipid, which provides the substrate for peroxidation. Lipid peroxidation is probably linked with the decline in motility and respiratory activity, and the structural damage to sperm membranes, which characterize ageing or degenerating spermatozoa.
132 citations
TL;DR: It was found that, contrary to previous observations reported in the literature, both fish and zooplankton were able to digest and assimilate blue-green algae.
Abstract: The fauna of Lake George is dominated by herbivores, in particular the fish Tilapia nilotica and Haplochromis nigripinnis, and the cyclopoid copepod Thermocyclops hyalinus Digestion, and the assimilation of carbon from algae, by these herbivores were studied in detail It was found that, contrary to previous observations reported in the literature, both fish and zooplankton were able to digest and assimilate blue-green algae The diurnal feeding patterns of the herbivores were examined, and methods devised for assessing, in terms of carbon, the daily ingestion of algae Hence, using biomass data, the total amount grazed by the herbivores was calculated Estimates of carbon requirements at other trophic levels were made, as was an assessment of the required level of net production by the algae for comparison with figures for standing crop and net algal production measured by other means Food selection by secondary and tertiary producers is discussed, and in several species age correlated changes in selectivity were examined Both the major herbivorous species of fish adopt phytoplankton feeding after a period of carnivorous or omnivorous feeding as fry Thermocyclops hyalinus is herbivorous all its life, but the size of particle taken changes with age There are more species of carnivorous than herbivorous fish and these exploit a wider variety of food sources; the few species studied also show changes in food preference with age
113 citations
TL;DR: The specific composition of the open water community is described and shown to be dominated by blue-green algae and three herbivores which utilize them as a food source: one cyclopoid copepod and two fish.
Abstract: Ninety-five per cent of the total biomass in the open water of Lake George, a shallow equatorial lake, is phytoplankton. The biomass of this and the other major groups of organisms are given and compared with some figures from other lakes. Apart from the phytoplankton, standing crop levels in Lake George are not high and may be exceeded, although only for short periods, by organisms in temperate waters. Levels in Lake George, in contrast, fluctuate little throughout the year. The specific composition of the open water community is described and shown to be dominated by blue-green algae and three herbivores which utilize them as a food source: one cyclopoid copepod and two fish. The reasons why these and other species make up the open water community in Lake George are discussed and also possible factors which may limit some of the animal populations to the levels observed. Both the phytoplankton and the zooplankton exhibit a concentric pattern of distribution across the lake. Concentrations are highest in the centre and this may be attributable to the circular movements of the water mass which result from the shape of the basin and the wind regime. It might also be correlated with grazing effects since the fish population, which also shows a concentric distribution of biomass, has its highest concentrations in the inshore regions and its lowest in the centre. The distribution and species composition of the benthos is determined primarily by the nature of the substrate. In the open water area the bottom consists of soft, unstable, deoxygenated mud which contains few species. Inshore the substrate is firmer and more varied and carries a greater density and variety of animals. These are preyed upon by a greater variety of fish, particularly species of the cichlid genus Haplochromis, than are found in the mid-lake area. The inshore region is short, due to the regular shape of the lake basin, and narrow, but provides a variety of habitats in contrast to the homogeneity of the mid-lake area. The lake is fringed in many places by papyrus swamp, the Nile cabbage floats on the surface of the water but there is no submerged aquatic vegetation.
111 citations
TL;DR: The cerebral influx rates of fifteen amino acids were measured directly in living rats by means of a new technique which makes it possible to maintain a constant specific activity of a radioactively labelled amino acid in the bloodstream, consistent with the theory that amino acids enter the brain mainly by carrier mediated transport processes with high degree of specificity.
Abstract: The cerebral influx rates of fifteen amino acids were measured directly in living rats by means of a new technique which makes it possible to maintain a constant specific activity of a radioactively labelled amino acid in the bloodstream. A wide variation in the influx rates of the amino acids was found. These rates differed from those found by other workers using in vitro preparations, but are consistent with the theory that amino acids enter the brain mainly by carrier mediated transport processes with a high degree of specificity. There are a number of important differences between the behaviour of the transport processes in vivo and in vitro. The influx rates of the various amino acids were directly proportional to their concentrations in blood plasma (over the range of concentrations studied). All the nutritionally essential amino acids had relatively high influx rates as did other amino acids which the brain does not seem to be able to synthesize. On the other hand, amino acids that the brain can readily synthesize and two amino acids which are not normally found in mammalian tissues had low influx rates.
106 citations
TL;DR: In this paper, a mathematical model of the phytoplankton community in Lake George is presented, which interrelates the variables, photosynthesis, respiration, biomass and the underwater light climate.
Abstract: The ecological stability of Lake George is illustrated by the relatively small biomass fluctuations that occur in the fauna and flora of the lake. For the phytoplankton it is shown that the gradient of these oscillations is within the range depicted by a specific rate of population increase of +0.05 to -0.05 day$^{-1}$. The relative stability of the phytoplankton community is discussed in the terms of a mathematical model (Talling 1957, 1971) which interrelates the variables, photosynthesis, respiration, biomass and the underwater light climate. Examples of the interrelationship, and the extreme susceptibility of either a positive or a negative increase rate to diurnal environmental changes, are drawn from both long and short term measurements in Lake George. The optical characteristics of the water column are shown to be very dependent upon the mixing regime sustained over the previous 24 h. The occurrence of negative or positive increase rates is dependent not only upon the incident radiation but also upon the wind induced turbulence. It is shown that, given measurements of the rates of photosynthesis and respiration and the other variables included in Talling's model, the biomass at which the Lake George phytoplankton will stabilize is predictable. Although light is likely to limit photosynthesis under all circumstances in Lake George, it is demonstrated that a more favourable photosynthetic response to the light climate may be induced by nutrient enrichment of the nutrient-poor phytoplankton. Because nutrient enrichment can induce increased photosynthetic capacity values, the rates of nutrient supply are thought to be major factors in controlling the ecological stability of the phytoplankton. The mixing regime of the lake is of paramount importance in the decomposition of the sediments and the rate of nutrient release from them. The importance of the nutrient recycling via zooplankton excretion is compared with the total input of nitrogen and phosphorus to the lake. That the ecological stability of the lake is a delicately balanced equilibrium between climate and biota is illustrated by calculations on the oxygen budget of the water column, and by the occurrence of fish-kills. The general characteristics of the lake are discussed in the context of the problems associated with eutrophication.
104 citations
TL;DR: Chloroplasts in Elysia, unlike those in Codium, were not able to incorporate 14C from CO2 or other precursors into chlorophyll, suggesting that complete biosynthesis ofchlorophyll depends upon DNA in both the plant nucleus and the chloroplast.
Abstract: When Codium fragile chloroplasts in cells of Elysia viridis were examined by electron microscopy, no structural damage or alteration was observed beyond a general change in shape from ellipsoid in the plant to more oval in the animal; outer chloroplast envelopes were always intact. Some chloroplasts in animal cells were enclosed by a membrane external to the envelope but others were not; the origin of this membrane is unclear. Neither the mechanism of entry nor the ultimate fate of chloroplasts in animal cells is fully understood. Rates of photosynthetic carbon fixation by chloroplasts in Elysia and Codium were of a similar order. The pathways of photosynthetic $^{14}$C fixation in Elysia were not restricted compared to isolated chloroplasts. In Codium, incorporation of $^{14}$C into sucrose occurs outside the chloroplast, as does incorporation into galactose in Elysia. Substantial incorporation into galactose in Elysia does not begin until about 20 to 30 min after the start of $^{14}$C fixation, although a certain amount of $^{14}$C galactose is detectable after 5 to 8 mins, indicating rapid release from chloroplasts. Chloroplasts isolated from Codium release only 2% of their fixed $^{14}$C to the medium, mainly as glycolic acid. In animal homogenates, release of fixed $^{14}$C from chloroplasts rises to 40%, mostly composed of glucose with some glycolic acid. In intact animals, at least 36% of the fixed carbon is released from the chloroplasts. Chloroplasts in Elysia, unlike those in Codium, were not able to incorporate $^{14}$C from CO$_{2}$ or other precursors into chlorophyll. In Codium, incorporation from CO$_{2}$ ceased in the presence of cycloheximide or choramphenicol, suggesting that complete biosynthesis of chlorophyll depends upon DNA in both the plant nucleus and the chloroplast. Incorporation from CO$_{2}$ into glycolipids and sulpholipids could not be detected in Elysia. Chloroplasts in Elysia are unlikely to be completely autonomous.
94 citations
TL;DR: By comparing influx and net cerebral uptake rates it appears that efflux of glucose from the brain occurs, particularly in hyperglycaemic states.
Abstract: A new method, devised to maintain a steady concentration of glucose in the bloodstream, was used to study its influx into the brain of the living rat under sodium pentobarbitone or ether anaesthesia. The findings suggested that glucose entered the brain by a saturable carrier-mediated mechanism with a K$_{m}$ of 7.2 $\mu $mol ml$^{-1}$ and a maximum influx rate of 1.13 $\mu $mol min$^{-1}$ g$^{-1}$ brain. This mechanism was not affected by the type of anaesthetic used. We did not detect any appreciable passive diffusion of glucose into the brain. There was no movement of glucose between the red cells and the plasma during passage of the blood through the brain. By comparing influx and net cerebral uptake rates it appears that efflux of glucose from the brain occurs, particularly in hyperglycaemic states.
TL;DR: Severe depletion of thymus-derived lymphocytes does not reduce, and may significantly increase, the resistance of mice to syngeneic tumours, although it grossly impairs their ability to reject allotransplants, and appears to lend support to the hypothesis that the antitumour effect of C. parvum depends primarily on macrophage stimulation.
Abstract: Severe depletion of thymus-derived lymphocytes does not reduce, and may significantly increase, the resistance of mice to syngeneic tumours, although it grossly impairs their ability to reject allotransplants. Injection of killed C. parvum causes further inhibition of tumour growth in T-cell deprived mice to an extent comparable to that resulting from the same dose of C.parvum in normal mice. This appears to lend support to the hypothesis that the antitumour effect of C. parvum depends primarily on macrophage stimulation.
TL;DR: It has been widely assumed that the rate-limiting step in actomyosin ATPase activity during contraction is a single-stage attachment of the myosin head to a site on the thin filament, which leads to a rate of energy liberation that increases monotonically with speed of shortening.
Abstract: It has been widely assumed that the rate-limiting step in actomyosin ATPase activity during contraction is a single-stage attachment of the myosin head to a site on the thin filament. This assumption leads to a rate of energy liberation that increases monotonically with speed of shortening, in agreement with pre-war estimates of the output of work and heat; it does not explain the fall in energy release at high speeds that has been found more recently. This fall can be explained by assuming that the attachment is a two-stage process.
TL;DR: Comparison of the cross-striation in the paracrystals with that in the thin filament assembly of the myofibril supports the conclusion that filaments resembling the natural ones have been synthesized from actin, tropomyosin and the troponin complex.
Abstract: When purified F-actin is precipitated by Mg$^{2+}$, it forms paracrystals consisting of regularly packed filaments that retain the double-helical structure characteristic of actin polymers. In negatively stained preparations the only axial periodicity observed is that of the actin polymers. In sections, the polymer structure is not resolved and the paracrystals do not appear cross-striated. The paracrystals formed from unpurified actin preparations likewise contain regularly packed filaments in which the F-actin structure is observed but, in addition, the assembly of filaments is crossed at fairly regular intervals (approximately 37 nm) by bands of unstained amorphous material. Sections of these paracrystals show a corresponding cross-striation (mean spacing 38 nm). Other proteins known to be present in unpurified preparations of actin were prepared separately and added in solution to purified F-actin; paracrystals were formed on Mg$^{2+}$ precipitation. The cross-striation was reproduced when a mixture of tropomyosin and troponin had been added to the actin. The addition of purified tropomyosin alone resulted in paracrystals that lacked the cross-striation. Comparison of the cross-striation in the paracrystals with that in the thin filament assembly of the myofibril (as seen in sections and in negatively stained I-segments) supports the conclusion that filaments resembling the natural ones have been synthesized from actin, tropomyosin and the troponin complex. It follows that the cross-striation in the thin myofilaments can be attributed to the location of part or all of the troponin complex at sites spaced at regular intervals along the filaments.
TL;DR: Comparisons between the stages of male and female development within individual florets in Triticum aestivum, Hordeum vulgare and Secale cereale allowed the estimation of the time and duration of female meiosis fairly accurately, and nuclear DNA content and ploidy level are known to play an important role in controlling the duration of male meiosis.
Abstract: Few recent investigations have been made of female meiosis in cereals, and almost nothing is known about the duration of female meiosis in higher plants. Consequently, the time and duration of female meiosis in Triticum aestivum , Hordeum vulgare and Secale cereale have been studied. The appearance of the embryo sac mother cell (e. m. c.) and of the meiotic nuclei during female meiosis in Hordeum vulgare is described and illustrated. In the species studied, each floret contains only one ovary with a single e. m. c., and meiosis is almost synchronous in the pollen mother cells from all three anthers. Consequently, it is possible to make precise comparisons between the stages of male and female development within individual florets. Data from these comparisons, together with knowledge previously determined of the duration of male meiosis in these species, allowed the estimation of the time and duration of female meiosis fairly accurately for T. aestivum and H. vulgare and approximately for S. cereale . The results showed that for H. vulgar and T. aestivum grown at 20°C, the duration of female meiosis was very similar to the duration of male meiosis. Furthermore, on average male and female meiosis occurred almost synchronously. In S. cereale however, male meiosis preceeded female meiosis by about 15 h. Growing T. aestivum under environmental stress induced asynchrony between male and female development at meiosis. Synchrony was not re-established after a long period under normal conditions. Nuclear DNA content and ploidy level are known to be important factors determining or affecting the duration of male meiosis. These factors appear to play an important role in controlling the duration of female meiosis also.
TL;DR: The particulate secretion from the calyx cells of Nemeritis, which is thought to confer protection on the parasitoid, has been examined in detail ultrastructurally, using sectioned and negatively-stained material and enzyme-digest techniques.
Abstract: The particulate secretion from the calyx cells of Nemeritis, which is thought to confer protection on the parasitoid, has been examined in detail ultrastructurally, using sectioned and negatively-stained material and enzyme-digest techniques. These membrane-bounded particles are produced in large numbers within the nuclei of the calyx cells and are found in vast numbers in the lumen of the calyx. Only a few have been seen in the cytoplasm of the cells, and it may be inferred that they pass quickly through the cells. They appear in the microvilli of the luminal surface, and are released when the tips of microvilli enclosing particles become pinched off. As shown in the preceding paper, they become attached to the outer layer of the chorion of eggs passing through the calyx. The first signs of particles appear to be the presence of empty membranes found in the nuclei of 17-day-old individuals, and their development has been traced through to the adult stage of the parasitoid. The unique nature of the particulate secretion is discussed.
TL;DR: The egg of Nemeritis has been studied with both light and electron microscopes, with particular attention to the way in which the parasite becomes protected from the defence reactions of the host.
Abstract: The egg of Nemeritis has been studied with both light and electron microscopes, with particular attention to the way in which the parasite becomes protected from the defence reactions of the host. Because the protective property seemed to be associated with the surface of the egg, the formation and structure of the oocyte membranes - the vitelline membrane, inner and outer layers of the chorion - were investigated with the electron microscope. The lastformed, the outer layer of the chorion, is the surface which forms the interface between parasite and host. It is composed of long projections, perpendicular to the chorion, in which numerous particles produced in the calyx become embedded. The particles persist on the oocyte as it passes down the oviduct, and after it is laid, and they are also found on the surface of first-instar larvae. Attempts to confer protection artificially on to other objects were unsuccessful, and it is clear that the peculiar outer layer of the chorion is essential for the attachment of the protective substance.
TL;DR: The equatorial location of Lake George as discussed by the authors gives to Lake George (surface area 250 km$^{2}$) a climatic regime which makes for an exceptionally unvaried physico-chemical environment within the water mass throughout the year.
Abstract: The equatorial location gives to Lake George (surface area 250 km$^{2}$) a climatic regime which makes for an exceptionally unvaried physico-chemical environment within the water mass throughout the year. This is enhanced by peculiarities of the local geomorphometry and the morphometry of the lake. Incident solar energy, according to 10-day running means, varies during the year only $\pm $ 13% of the daily mean of 1970 J cm$^{-2}$. The mean air temperature of 23 degrees C is always equable (mean daily temperature = 29.5 $\pm $ 1.5 degrees C, mean nightly, 16.5 $\pm $ 1.5 degrees C), and is in equilibrium with the minimum water temperature of the bottom layers of the lake, the surface temperatures of which are usually about 30 degrees C. The effect of two, approximately equal, dry seasons is offset by the presence of mountainous catchment areas which have a high runoff and thus permit a continuous flow through the lake, which amounts to a mean flushing rate of 2.8 times the mean lake volume per year, so sustaining the supply of primary nutrients. These features promote a continuous productivity, although the allochthonous supplies of nutrients are not thought to be important compared to the total flux of nutrients within the lake. The wind regime, which is strongly influenced by local convectional rather than continental forces, assists convection currents in the water in effecting a nocturnal turbulence which provides an efficient recirculation of nutrients within the shallow water column (2.4 m). This turbulence, alternating with diurnal stratification, against the background of the relative constancy of the climate, means that the lake is dominated by a 24 h physiological cycle rather than the seasonal succession of other latitudes. Some evidence indicates that the concentric distribution of plankton in the lake is established by wind initiated rotary currents. Wave movements at the sediment/water interface are thought to disturb the majority of the sediment surface area possibly down to between 5 and 14 cm in depth, with a mean frequency of an order of magnitude of once every 3 weeks. Progressive organic enrichment has existed throughout the lake's history (3600 $\pm $ 90 years), but during the last approximately 700 years an equilibrium appears to have been reached as shown by a retarded rate of change of organic deposition.
TL;DR: It is suggested that the ‘robustness’ of chloroplasts from siphonaceous algae may be an important factor in their ability to enter and continue functioning inside animal cells.
Abstract: Chloroplasts of Codium fragile fix carbon photosynthetically at rates comparable to or higher than those of the intact plant for several hours after isolation. When stored in the dark at 5°C in a simple mineral medium containing mannitol as an osmoticum and no added cofactors, the chloroplasts continued to fix carbon photosynthetically for at least 5 days after isolation, although at a progressively declining rate; they retained the ‘halo’ characteristic of an intact outer envelope for the entire period. Patterns of 14 C fixation by isolated chloroplasts and intact Codium were generally similar, except that no incorporation of 14 C into sucrose could be detected in isolated chloroplasts, and incorporation into glycolic acid was higher. Only 2% of the photosynthetically fixed 14 C was released to the medium by isolated chloroplasts. Their Hill reaction was relatively weak, but this may have been due to the impermeability of the outer envelope which could not be ruptured even by the severe osmotic shock of transfer from the suspension medium (osmotic pressure greater than 14 atm) to distilled water. It is suggested that the ‘robustness’ of chloroplasts from siphonaceous algae may be an important factor in their ability to enter and continue functioning inside animal cells.
TL;DR: It appears that the main difference between the regions studied is in the mean duration of G1, that is, the average delay a newborn cell experiences before it begins to synthesize DNA.
Abstract: A pulse labelling experiment was used to study the mitotic cell cycle of proliferating cells throughout the root meristem of Zea mays. Seventeen different regions were identified within the area of proliferative activity, extending from the initial cells of the cap columella up to the stele, cortex and epidermis 1000 $\mu $m from the cap-quiescent centre junction, and the data were analysed for each region separately. The analyses were made in terms of a mathematical model for cell proliferation and yield statistically efficient estimates of the cell-cycle parameters. The validity of the model is discussed in some detail. It appears that the main difference between the regions studied is in the mean duration of G$_{1}$, that is, the average delay a newborn cell experiences before it begins to synthesize DNA. The mean durations of S and G$_{2}$, the DNA-synthetic and post-DNA-synthetic phases of the mitotic cycle, are relatively constant. The one exception to this pattern is the quiescent centre; this region includes a relatively high proportion of slowly dividing and non-proliferating cells.
TL;DR: Atropine modifies the elementary depolarization produced by the impact of acetylcholine molecules; it reduces the voltage amplitude and shortens the underlying ionic current pulse.
Abstract: The action of atropine at the motor end plate was studied by measuring its effect on acetylcholine-induced fluctuations of membrane potential (‘acetylcholine noise’). Atropine, in contrast to curare, modifies the elementary depolarization produced by the impact of acetylcholine molecules; it reduces the voltage amplitude and shortens the underlying ionic current pulse.
TL;DR: It is concluded that guinea-pig cerebellar slices, incubated under specified conditions, may provide a suitable means for quantitative correlation of neurochemical data with data obtained by electrophysiological techniques in tissue incubation under similar conditions and also for quantitative assessment of the effects of amino acids on Cerebellar electrical activity.
Abstract: The effects of incubation conditions on the frequency of spontaneous action potentials exhibited by guinea-pig cerebellar slices, and recorded with an extracellular microelectrode, have been investigated. Various incubation conditions that lead to tetrodotoxin-sensitive uptakes of water and of sodium ions by the incubated cerebellar slices lead to enhanced frequencies of the spontaneous action potentials, e. g. the presence of protoveratrine or of ouabain, the absence of glucose or the onset of anoxia. The frequency of the spikes is also enhanced by acetylcholine (in presence of neostigmine) or by the presence of excitatory amino acids, such as L-glutamate, D-glutamate or L-aspartate. It is suppressed by tetrodotoxin, or by the inhibitory amino acids, e. g. γ -aminobutyrate, glycine or taurine, or by ammonium ions or by pentobarbital. It is concluded that guinea-pig cerebellar slices, incubated under specified conditions, may provide a suitable means for quantitative correlation of neurochemical data with data obtained by electrophysiological techniques in tissue incubated under similar conditions and also for quantitative assessment of the effects of amino acids on cerebellar electrical activity.
TL;DR: It is now clear that the digestive diverticula of Nucula serve an absorptive and digestive function, however, that only fluid and particles of macromolecular dimensions resulting from extracellular digestion in the gastric cavity are able to enter the Diverticula.
Abstract: The digestive diverticula of Nucula sulcata consist of non-ciliated main ducts, ciliated secondary ducts and blind ending tubules. The cells lining the main ducts are of one type characterized by well-developed microvilli, iron-containing pigment spheres and, in animals fixed soon after collection, considerable amounts of lipid. The cells undergo a process of apocrine secretion and it is possible that they are involved in the absorption and metabolism of lipids. The ciliated cells lining the secondary ducts exhibit features similar to those lining the main ducts. The epithelium lining the tubules consists of two cell types, pyramid-shaped, basiphilic cells and columnar, digestive cells. The basiphilic cells possess a single flagellum and a well-developed rough endoplasmic reticulum and Golgi apparatus; they appear to secrete a proteinaceous product. There is no evidence that they serve to replace the digestive cells. The digestive cells, as in other bivalves, are filled with membrane-bound vesicles and possess distinct Golgi elements characterized by the presence of intracisternal membranes. Feeding experiments using ferritin show that the membrane-bound vesicles constitute a lysosomal system within which exogenous material is digested. The morphological features and the histochemical properties of the pinosomes, heterophagosomes, heterolysosomes and residual bodies are described. Contrary to the results obtained from earlier work it is now clear that the digestive diverticula of Nucula serve an absorptive and digestive function. The mode of functioning of the diverticula is such, however, that only fluid and particles of macromolecular dimensions resulting from extracellular digestion in the gastric cavity are able to enter the diverticula. Peroxisomes occur in the basal regions of all the cell types; the appearance of the contained nucleoids differs in each cell type.
TL;DR: Determinations of cyclic AMP represent a sensitive indicator of the onset of senescence changes in spermatozoa and both motility and synthesis are abolished by fluoride, but both are restored after removal of fluoride by washing.
Abstract: Spermatozoa of the ram, bull, boar, stallion and cock contain 37 to 177 pmol cyclic AMP/10$^{9}$ cells. Slow cooling of spermatozoa followed by storage causes only a minor decrease but cold shock leads to a rapid and nearly total loss of cyclic AMP, some of which passes into the external medium. Fructose prevents the loss of cyclic AMP in anaerobically incubated spermatozoa. Motility and synthesis of cyclic AMP are abolished by fluoride, but both are restored after removal of fluoride by washing. Determinations of cyclic AMP represent a sensitive indicator of the onset of senescence changes in spermatozoa.
TL;DR: The predilection shown by several Ctenuchids, and the related Arctiids, for foodplants containing cardiac glycosides or pyrrolizidine alkaloids is discussed.
Abstract: Syntomeida epilais sequesters and stores several cardiac glycosides from its food plant Nerium oleander L. Unlike the other insects previously examined which feed on oleander, this moth stores oleandrin in its body tissues. Amata phegea, feeding on non-poisonous plants, contains a histamine-like substance which increases capillary permeability in rats. Both species are repellent to many avian predators. The predilection shown by several Ctenuchids, and the related Arctiids, for foodplants containing cardiac glycosides or pyrrolizidine alkaloids is discussed.
TL;DR: The respiratory tract seems to be the major avenue for dissipating excess heat in dik-dik exposed to thermal stress and the low-water exchange and an efficient kidney helps explain the ability of this small antelope to inhabit hot arid areas.
Abstract: 1. In controlled laboratory experiments, rectal temperature, cutaneous moisture evaporation, and respiratory rate were studied in the dik-dik. The water balance of the dik-dik was investigated when the antelope were either fully hydrated or dehydrated at the environmental temperature of 22 °C or at temperatures alternating between 22 °C and 40 °C at 12 h intervals. 2. Faecal, urinary and evaporative water losses were all reduced by varying degrees during dehydration at 22 °C and 22 to 40 °C. The highest urine osmolality recorded was 4318 ± 105 mosmol/kg H 2 O which occurred when the antelopes were severely dehydrated. 3. At the high air temperatures (40 to 45 °C) cutaneous evaporation measured with a non-ventilated sweat capsule was 19 g H 2 O m -2 h -1 and the respiratory rate over 360/min. Thus the respiratory tract seems to be the major avenue for dissipating excess heat in dik-dik exposed to thermal stress. Injection of adrenaline, intravenously, stimulated sweat discharges similar to those observed in the small gazelles, and sheep and goats. 4. The low-water exchange and an efficient kidney helps explain the ability of this small antelope to inhabit hot arid areas.
TL;DR: In enrichment experiments, ammonia-nitrogen and phosphate-phosphorus were added to freshly sampled mixed populations of phytoplankton, implying a reserve of photosynthate unused for growth purposes and patterns of response to enrichment which were similar although quantitatively they were different.
Abstract: Observations suggested that nitrogen and probably phosphorus were major elements limiting the growth of phytoplankton in tropical Lake George (lat. equator, long. 30 degrees 20$^{\prime}$ E). To test this hypothesis enrichment experiments were carried out, in which ammonia-nitrogen and phosphate-phosphorus were added to freshly sampled mixed populations of phytoplankton. Nitrogen starvation has been inferred from the very high uptake rate of ammonia in the light and also substantial uptake in the dark, implying a reserve of photosynthate unused for growth purposes. Phosphate enhanced these responses. The addition of both ammonia and phosphate increased the respiratory rate of the algae, but not the photosynthetic rate until after a period when growth of the phytoplankton must have occurred. There is some evidence that such growth did not occur until after the second day of experimentation and that responses before this time reflected the demands of the algae in the lake at the time of sampling. Repeated experiments over a period of 6 months showed similar patterns of response to enrichment although quantitatively they were different. A number of ecological implications of the results are discussed.
TL;DR: The egg of the ichneumon wasp Nemeritis canescens is shown to be resistant to the defence reactions of its usual host, Ephestia kuehniella, by virtue of a coating on its surface, and the possibility that substances chemically similar to the particles of Nemersitis might inhibit cell adhesion and aggregation in vertebrates is briefly discussed.
Abstract: The egg of the ichneumon wasp Nemeritis canescens is known to be resistant to the defence reactions of its usual host, Ephestia kuehniella, by virtue of a coating on its surface. The coating is here shown also to endow Nemeritis with resistance to the defence reactions of Achroia grisella and, by implication, several other species of hosts. Three ways in which the coating might act are: (1) passively, by mimicking the lining of the haemocoele; (2) indirectly, by preventing the modification of substances in the haemolymph; (3) directly, by inhibiting the adhesion of blood cells. Mimicry of the host's internal lining is ruled out by experiments showing that the blood cells of Ephestia react to the internal lining of Achroia, and vice versa, although neither host reacts to Nemeritis. The idea that the coating might prevent modification of substances in the plasma, and so indirectly inhibit encapsulation, is not completely eliminated; but several experiments provide no evidence for it, and several observations favour a hypothesis of direct action by the particles on the blood cells. The nature of that direct action is inconclusively examined. Preliminary experiments suggest that the particles dissociate the cells of young capsules of Ephestia and may, therefore, act to inhibit the adhesion of cells to form capsules. Cells of capsules formed in Tenebrio molitor, which always encapsulates Nemeritis, were not dissociated; which indicates that this mode of action has the required element of specificity. The possibility that substances chemically similar to the particles of Nemeritis might inhibit cell adhesion and aggregation in vertebrates is briefly discussed.
TL;DR: The propodite-dactylopodite (PD) proprioceptor of Cancer pagurus consists of a receptor strand in which are embedded the dendrites of up to 80 bipolar nerve cells.
Abstract: The propodite-dactylopodite (PD) proprioceptor of Cancer pagurus consists of a receptor strand in which are embedded the dendrites of up to 80 bipolar nerve cells. The strand is composed of numerous cells and collagen and is surrounded by a thin layer of amorphous connective tissue. Beneath the latter there are often haemocoelic lacunae and individual haemocytes are found surrounded by strand tissue. The sensory cells can be divided into a proximal group with large cell bodies (movement sensitive cells) and a distal row with smaller cell bodies (position sensitive cells). The former can be further divided on the basis of the insertion of their dendrites into the strand. Thus elongation sensitive movement cells (e. s. m. cs) insert into the anterior surface and run in the ventral region of the receptor strand, while relaxation sensitive movement cells (r. s. m. cs) insert into the dorsal surface and run dorsally through the strand. The dendrites run in pairs, the members of each pair being either e. s. m. cs or r. s. m. cs. Each pair is surrounded distally by a scolopidium, consisting of a scolopale cell, two enveloping cells, a tube of extracellular material and, in e. s. m. cs, a canal cell. The scolopale cell contains a scolopale consisting of electron dense material laid down around a matrix of longitudinally oriented microtubules. In e. s. m. cs the enveloping cells also contain aggregations of a similar material. The dendrites make desmosome contacts with the scolopale cell and the corresponding thickenings of the scolopale cell membrane are juxtaposed by scolopale material. Beyond the scolopale the dendrites enter and terminate within a tube of extracellular material. In e. s. m. cs the scolopidium is surrounded mainly by strand cells, but in r. s. m. cs it is surrounded by collagen fibres. Where the collagen fibres meet the sheathing cells there are often contact zones. Other differences between e. s. m. cs and r. s. m. cs occur in the fine structure of the dendrites and these are described. It is suggested that in e. s. m. cs, since the scolopale is apposed by strand cells, stretching of the strand will lead to elongation of the scolopale and hence of the dendritic terminals. In contrast, in r. s. m. cs, it is possible that the scolopidium is not stretched during elongation of the strand, since there is little cellular contact between the two, but that during strand relaxation the energy stored in the collagen fibres forces the proximal end of the scolopale away from the more distal regions and hence stretches the dendritic terminations. Previous theories are discussed and compared with this idea. Also the relative merits of mechanical and physiological explanations for the phasic nature of these units are discussed.
TL;DR: The results agree well, over a wide range of concentration, with an extended version of the Manning (1969) theory of polyelectrolyte solutions, and dextran sulphate is considered to be a suitable model for connective tissue proteoglycan.
Abstract: 1 The use of gel osmometry for osmotic pressure measurements on polyelectrolyte solutions is discussed, with special reference to the effect of interaction of low molecular weight supporting electrolyte with the gel, and to the effect of penetration of the gel phase by a small multivalent fraction of a polydisperse polyelectrolyte 2 Measurements are reported of sodium chloride activity and of osmotic pressure for the system sodium dextran sulphate+sodium chloride+water 3 The results agree well, over a wide range of concentration, with an extended version (Wells 1973) of the Manning (1969) theory of polyelectrolyte solutions 4 Dextran sulphate is considered to be a suitable model for connective tissue proteoglycan The colloid osmotic pressures for proteoglycan solutions under physiological conditions are calculated in order to obtain an estimate of the internal osmotic pressure of cartilage The effects of variations in the composition of the proteoglycan, and hence of its charge density, are examined