Effects of Feeding and Drinking on Acetylcholine Release in the Nucleus Accumbens, Striatum, and Hippocampus of Freely Behaving Rats

Extracellular levels of acetylcholine (ACh) were measured in the nucleus accumbens (NAC), striatum (STR), and hippocampus (HIPP) using microdialysis in 30-min intervals before, during, and after free-feeding in 20-h food-deprived rats. The effects on ACh in the NAC and STR were also observed in response to water intake in 20-h water-deprived animals. Neostigmine was used in the perfusate to improve ACh recovery. Basal ACh was sensitive to tetrodotoxin and low calcium, and therefore largely neuronal in origin. Feeding caused a 38% increase in extracellular ACh in the NAC and no change in the STR or HIPP. Dopamine was also increased in the NAC (48%) and to a lesser extent in the STR (21%) following feeding. Drinking caused 18-20% increases in ACh release in both the NAC and STR. In a separate experiment, ACh release in the NAC was monitored in 10-min intervals during free-feeding; ACh increased in the interval immediately following maximal food intake. These results suggest a site-specific increase in ACh release following feeding that cannot be solely attributed to the activation associated with this behavior.     

Influence of month and climatic factors on the period of birth,litter size,birth weight and preweaning mortality of sheep in Ghana

Relationships between month and clinatic factors-rainfall, ambient temperature, relative humidity (RH) and temperature-humidity index (THI)-with time of parturition, litter size, birth weight and preweaning mortality were studied in Djallonke and Dja lonke x Sahelian sheep. Births (4142) occurred all year round although there were significant differences in the number of births per month. Maximum litter size did not coincide with the maximum births. Peak conceptions occurred in the early parts of the major rainy season. There were also significant differences in birth weights and mortalities (%) per month. Maximum and minimum values (of birth weighs and mortalities) occurred in the latter part of the rainy seasons and dry periods respectively. There were significant positive correlations between litter size and cumulative rainfall in the 4th–6th months periods prior to lambing. Birth weights of both males and females were positively and significantly associated with minimum temperature and cumulative rain-fall in the 2- and 3-months period prior to lambing respectively. There were significant positive correlations between mortality and minimum and maximum RH and cumulative rainfall in the 3 months after lambing.     

Biological Control of the Bulb Mite, Rhizoglyphus robini , by the Predatory Mite, Hypoaspis aculeifer , on Lilies: Predator-Prey Dynamics in the Soil, under Greenhouse and Field Conditions

We tested the capacity of the soil-dwelling predatory mite, Hypoapsis aculeifer , to control mites attacking lily bulbs. Experiments in the greenhouse and in the field showed that in the absence of predatory mites populations of the bulb mite, Rhizoglyphus robini , on lily bulbs increased, whereas the release of predatory mites either slowed down the increase - as observed in the field - or caused the bulb mites populations to decrease - as observed in the greenhouse. In all cases the population of predatory mites increased as long as bulb mite densities were not too low. However, within the first week after predator release there was usually a sharp decline to 10-40% of the original number released. Greenhouse experiments on intact lily bulbs in pots, boxes and 1 m 2 plots with peat soil showed that when released in a ratio of 1 predator to 2 or 5 prey, the predatory mite, Hypoaspis aculeifer , suppressed populations of bulb mites to less than 10 individual per bulb within 6 weeks. Elimination of bulb mites was observed only when the predator-to-prey ratio at release was equal to 3:1. Field experiments in 2 m 2 plots with intact bulbs in rather compact sandy soil showed that when released in ratio of 1 predator to 1 or 2 prey, the predatory mite, H. aculeifer , did not cause the population of bulb mites to decrease, but it did reduce their population growth. The initial predator-to-prey ratios required to achieve suppression (ca 1:2) or elimination (3:1) in the soil environment are much higher than those required for bulb mite elimination when lily bulb scales were embedded in a medium of vermiculite (ca 1:20). Among the possible causes are: (1) the initial losses of predators in the greenhouse and even more so in the field due to mortality and/or emigration from the experimental plots; (2) the lower temperatures in the greenhouse and especially in the field, which slow down the growth and predation processes and thereby delay prey extinction; and (3) the spatial complexity of the soil environment which creates refuges for the bulb mites.     

Effect of Mutations of Arginine 94 on Proton Pumping,Electron Transfer,and Superoxide Anion Generation in Cytochrome b of the bc1 Complex from Rhodobacter sphaeroides

Proton transfer involving internal water molecules that provide hydrogen bonds and facilitate proton diffusion has been identified in some membrane proteins. Arg-94 in cytochrome b of the Rhodobacter sphaeroides bc₁ complex is fully conserved and is hydrogen-bonded to the heme propionate and a chain of water molecules. To further elucidate the role of Arg-94, we generated the mutations R94A, R94D, and R94N. The wild-type and mutant bc₁ complexes were purified and then characterized. The results show that substitution of Arg-94 decreased electron transfer activity and proton pumping capability and increased O₂^˙̄ production, suggesting the importance of Arg-94 in the catalytic mechanism of the bc₁ complex in R. sphaeroides. This also suggests that the transport of H⁺, O₂, and O₂^˙̄ in the bc₁ complex may occur by the same pathway.     

Influence of Temperature,Photoperiod and Trophic Conditions on the Seasonal Cycles of Phytoplankton and Zooplankton in Two Deep Subarctic Lakes of Northern Canada

The densities of phytoplankton and zooplankton were determined for 12 consecutive months (1978–1979) in two deep oligotrophic lakes in northern Canada. The lakes were situated on the same river system, about 5 km from one another. While they exhibited similar temperature conditions, there were slight differences in the ionic content of the water. Overall, changing temperature was the most important factor influencing the duration of the growth cycles of phytoplankton and zooplankton. Nutrients generally controlled the intensity but not the timing of algal blooms. A similar relationship was recorded for the effects of food supply on the development of the major species of herbivorous zooplankton. Although changing photoperiod likely initiated the growth of several important algal and zooplankton species in the spring and early summer, light had no measurable impact on the development of planktonic communities throughout the remainder of the growing season. The higher ionic content of the water in one lake may have promoted the growth of protozoans during the fall and early winter.     

Impact of Entomopathogenic Nematodes on Different Soil-dwelling Stages of Western Flower Thrips, Frankliniella occidentalis (Thysanoptera: Thripidae), in the Laboratory and Under Semi-field Conditions

The impact of entomopathogenic nematodes (EPN) on mortality of soil-dwelling stages of western flower thrips (WFT), Frankliniella occidentalis (Thysanoptera: Thripidae) with different insect stage combinations was studied in the laboratory and under semi-field conditions. In laboratory experiments, the efficacy of Steinernema feltiae strain Sylt (Rhabditida: Steinernematidae) at a concentration of 400 infective juveniles (IJs) cm -2 was tested against different proportions of soil-dwelling stages of WFT, i.e. late second instar larvae (L2), prepupae and pupae. Soil was used as the testing medium. S. feltiae significantly affected the mortality of all soil-dwelling life stages of WFT at all tested insect stage combinations. The proportion of late L2 in the population negatively correlated to EPN-induced mortality. WFT prepupa and pupa were similarly susceptible to S. feltiae and their proportion in the population did not affect the EPN-induced mortality under laboratory conditions. The highest mortality (80%) was recorded when the population consisted only of prepupae and/or pupae. In the semi-field study, the impact of S. feltiae , S. carpocapsae strain DD136 and Heterorhabditis bacteriophora strain HK3 (Rhabditida: Heterorhabditidae) ( H. bacteriophora ) at concentrations of 400 and 1000 IJs cm -2 was evaluated against WFT reared on green beans, Phaseolus vulgaris L., as host plant in pot experiments in a controlled climate chamber. All tested EPN strains at both dose rates significantly reduced the WFT populations. Up to 70% reduction of the WFT population was obtained at the higher EPN concentration.