189 research outputs found
Impaired associative learning after chronic exposure to pesticides in young adult honey bees
Neonicotinoids are the most widespread insecticides in agriculture, preferred for their low toxicity to mammals and their systemic nature. Nevertheless, there have been increasing concerns regarding their impact on non-target organisms. Glyphosate is also widely used in crops and, therefore, traces of this pesticide are likely to be found together with neonicotinoids. Although glyphosate is considered a herbicide, adverse effects have been found on animal species, including honey bees. Apis mellifera is one of the most important pollinators in agroecosystems and is exposed to both these pesticides. Traces can be found in nectar and pollen of flowers that honey bees visit, but also in honey stores inside the hive. Young workers, which perform in-hive tasks that are crucial for colony maintenance, are potentially exposed to both these contaminated resources. These workers present high plasticity and are susceptible to stimuli that can modulate their behaviour and impact on colony state. Therefore, by performing standardised assays to study sublethal effects of these pesticides, these bees can be used as bioindicators. We studied the effect of chronic joint exposure to fieldrealistic concentrations of the neonicotinoid imidacloprid and glyphosate on gustatory perception and olfactory learning. Both pesticides reduced sucrose responsiveness and had a negative effect on olfactory learning. Glyphosate also reduced food uptake during rearing. The results indicate differential susceptibility according to honey bee age. The two agrochemicals had adverse effects on different aspects of honey bee appetitive behaviour, which could have repercussions for food distribution, propagation of olfactory information and task coordination within the nest.Fil: Mengoni Goñalons, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; ArgentinaFil: Farina, Walter Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; Argentin
Effects of Sublethal Doses of Imidacloprid on Young Adult Honeybee Behaviour
Imidacloprid (IMI), a neonicotinoid used for its high selective toxicity to insects, is one of the most commonly used pesticides. However, its effect on beneficial insects such as the honeybee Apis mellifera L is still controversial. As young adult workers perform in-hive duties that are crucial for colony maintenance and survival, we aimed to assess the effect of sublethal IMI doses on honeybee behaviour during this period. Also, because this insecticide acts as a cholinergic-nicotinic agonist and these pathways take part in insect learning and memory processes; we used IMI to assess their role and the changes they suffer along early adulthood. We focused on appetitive behaviours based on the proboscis extension response. Laboratory reared adults of 2 to 10 days of age were exposed to sublethal IMI doses (0.25 or 0.50ng) administered orally or topically prior to behavioural assessment. Modification of gustatory responsiveness and impairment of learning and memory were found as a result of IMI exposure. These outcomes differed depending on age of evaluation, type of exposure and IMI dose, being the youngest bees more sensitive and the highest oral dose more toxic. Altogether, these results imply that IMI administered at levels found in agroecosystems can reduce sensitivity to reward and impair associative learning in young honeybees. Therefore, once a nectar inflow with IMI traces is distributed within the hive, it could impair in-door duties with negative consequences on colony performance.Fil: Mengoni Goñalons, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; ArgentinaFil: Farina, Walter Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; Argentin
Intracellular inclusions of uncultured magnetotactic bacteria
Magnetotactic bacteria produce magnetic crystals in organelles called magnetosomes. The bacterial cells may also have phosphorus-containing granules, sulfur globules, or polyhydroxyalkanoate inclusions. In the present study, the ultrastructure and elemental composition of intracellular inclusions from uncultured magnetotactic bacteria collected in a marine environment are described. Magnetosomes contained mainly defect-free, single magnetite crystals with prismatic morphologies. Two types of phosphorus-containing granules were found in magnetotactic cocci. The most common consisted of phosphorus-rich granules containing P, O, and Mg; and sometimes also C, Na, Al, K, Ca, Mn, Fe, Zn, and small amounts of S and Cl were also found. In phosphorus-sulfur-iron granules, P, O, S, Na, Mg, Ca, Fe, and frequently Cl, K, and Zn, were detected. Most cells had two phosphorus-rich granules, which were very similar in elemental composition. In rod-shaped bacteria, these granules were positioned at a specific location in the cell, suggesting a high level of intracellular organization. Polyhydroxyalkanoate granules and sulfur globules were less commonly seen in the cells and had no fixed number or specific location. The presence and composition of these intracellular structures provide clues regarding the physiology of the bacteria that harbor them and the characteristics of the microenvironments where they thrive. [Int Microbiol 2005; 8(2):111-117
The effect of short-term endurance and strength training on motor unit conduction velocity
AIM: The aim of this study was to investigate the effect of strength and endurance training on the conduction velocity of vastus medialis obliquus and lateralis single motor units during voluntary sustained knee extensions.
METHODS: Seventeen sedentary healthy men (age, mean ± SD, 26.3 ± 3.9 yr) were randomly assigned to one of 2 groups: strength training (ST, n= 8) or endurance training (ET, n= 9). Conventional endurance and strength training was performed three days per week, over a period of 6 weeks. Motor unit conduction velocity (MUCV), maximum voluntary force (MVC) and time-to-task failure at 30% MVC of the knee extensors were measured before and immediately following training. To assess MUCV, multi-channel surface and intramuscular EMG signals were concurrently recorded from the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles during 60-s isometric knee extensions at 10% and 30% of MVC.
RESULTS: After 6 weeks of training, MVC increased in the ST group (16.7 ± 7.4 %; P < 0.05) whereas time to task failure was prolonged in the ET group (33.3 ± 14.2 %; P < 0.05). Both training programs induced an increase in motor unit conduction velocity at both 10% and 30% MVC (P < 0.01). Furthermore after both training programs, the reduction in MUCV over time during the sustained contractions occurred at slower rates compared to baseline (P < 0.01).
CONCLUSION: These results indicate that short-term endurance and strength training induce similar alterations of the electrophysiological membrane properties of the muscle fiber and in their changes during sustained contractionsGrant SFRH/BD/31796/2006 from Fundação para a Ciência e a Tecnologia (FCT) of Portuga
Adjustments in motor unit properties during fatiguing contractions after training
The objective of the study was to investigate the
effect of strength and endurance training on muscle fiber membrane properties and discharge rates of low-threshold motor units of the
vasti muscles during fatiguing contractions. Methods: Twenty-five sedentary healthy men (age (mean T SD) = 26.3 T 3.9 yr) were
randomly assigned to one of three groups: strength training, endurance training, or a control group. Conventional endurance and strength
training was performed 3 dIwkj1, during a period of 6 wk. Motor unit conduction velocity and EMG amplitude of the vastus medialis
obliquus and lateralis muscles and biceps femoris were measured during sustained isometric knee extensions at 10% and 30% of the
maximum voluntary contraction before and immediately after training. Results: After 6 wk of training, the reduction in motor unit conduction
velocity during the sustained contractions at 30% of the maximum voluntary force occurred at slower rates compared with baseline
(P G 0.05). However, the rate of decrease was lower after endurance training compared with strength training (P G 0.01). For all groups,
motor unit discharge rates declined during the sustained contraction (P G 0.001), and their trend was not altered by training. In addition, the
biceps femoris–vasti coactivation ratio declined after the endurance training. Conclusions: Short-term strength and endurance training
induces alterations of the electrophysiological membrane properties of the muscle fiber. In particular, endurance training lowers the rate
of decline of motor unit conduction velocity during sustained contractions more than strength trainin
Changes in H reflex and V wave following short-term endurance and strength training
This study examined the effects
of 3 wk of either endurance or strength training on plasticity of
the neural mechanisms involved in the soleus H reflex and V wave.
Twenty-five sedentary healthy subjects were randomized into an
endurance group (n 13) or strength group (n 12). Evoked
V-wave, H-reflex, and M-wave recruitment curves, maximal voluntary
contraction (MVC), and time-to-task-failure (isometric contraction
at 40% MVC) of the plantar flexors were recorded before and
after training. Following strength training, MVC of the plantar flexors
increased by 14.4 5.2% in the strength group (P 0.001), whereas
time-to-task-failure was prolonged in the endurance group (22.7
17.1%; P 0.05). The V wave-to-maximal M wave (V/Mmax) ratio
increased significantly (55.1 28.3%; P 0.001) following strength
training, but the maximal H wave-to-maximal M wave (Hmax/Mmax)
ratio remained unchanged. Conversely, in the endurance group the
V/Mmax ratio was not altered, whereas the Hmax/Mmax ratio increased
by 30.8 21.7% (P 0.05). The endurance training group also
displayed a reduction in the H-reflex excitability threshold while the
H-reflex amplitude on the ascending limb of the recruitment curve
increased. Strength training only elicited a significant decrease in
H-reflex excitability threshold, while H-reflex amplitudes over the
ascending limb remained unchanged. These observations indicate that
the H-reflex pathway is strongly involved in the enhanced endurance
resistance that occurs following endurance training. On the contrary,
the improvements in MVC following strength training are likely
attributed to increased descending drive and/or modulation in afferents
other than Ia afferents
Motor unit conduction velocity during sustained contraction after eccentric exercise
BACKGROUND:Eccentric contractions induce muscle fiber damage that is associated with a decreased capacity to generate voluntary force and increased fiber membrane permeability. Changes in fiber membrane permeability results in cell depolarization that is expected to have an effect on the action potential propagation velocity of the muscle fibers.
PURPOSE:The aim of the study was to investigate the action potential propagation velocity in individual motor units before and 24 and 48 h after eccentric exercise.
METHODS:Multichannel surface and fine-wire intramuscular EMG signals were concurrently recorded from two locations of the right vastus medialis muscle of 10 healthy men during 60-s isometric contractions at 10% and 30% of the maximal force.
RESULTS:The maximal force decreased by 26.1 ± 16.1% (P < 0.0001) at 24 h and remained reduced by 23.6 ± 14.5% (P < 0.0001) 48 h after exercise with respect to baseline. With respect to baseline, motor unit conduction velocity decreased (P < 0.05) by (average over 24 and 48 h after exercise) 7.7 ± 2.7% (10% maximal voluntary contraction (MVC), proximal), 7.2 ± 2.8% (10% MVC, distal), 8.6 ± 3.8% (30% MVC, proximal), and 6.2 ± 1.5% (30% MVC, distal). Moreover, motor unit conduction velocity decreased over time during the sustained contractions at faster rates when assessed 24 and 48 h after exercise with respect to baseline for both contraction forces and locations (P < 0.05).
CONCLUSIONS:These results indicate that the electrophysiological membrane properties of muscle fibers are altered by exercise-induced muscle fiber damage.Ministry of Science, Research and Technology of Iran (N.H.) and the Danish Technical Research Council (project: Centre for Neuroengineering (CEN), contract no. 26-04-0100) (D.F.)
Greigite magnetosome membrane ultrastructure in ‘Candidatus Magnetoglobus multicellularis’
The ultrastructure of the greigite magnetosome membrane in the multicellular magnetotactic bacteria
‘Candidatus Magnetoglobus multicellularis’ was studied. Each cell contains 80 membrane-enclosed iron-sulfide magnetosomes. Cytochemistry methods showed that the magnetosomes are enveloped by a structure whose staining pattern and dimensions are similar to those of the cytoplasmic membrane, indicating that the magnetosome membrane likely originates
from the cytoplasmic membrane. Freeze-fracture showed intramembrane particles in the vesicles surrounding each magnetosome. Observations of cell membrane invaginations, the trilaminar membrane structure of immature magnetosomes, and
empty vesicles together suggested that greigite magnetosome formation begins by invagination of the cell membrane, as has been proposed for magnetite magnetosomes
Concorrência e as participações minoritárias entre firmas rivais
The objective of this paper is to analyze the impacts of minority shareholdings among rival firms on competition. The application of MHHI (Modified Herfindahl Hirschman Index), a measure of market concentration recently proposed in the literature, shows that these structural links may cause adverse effects on competition. Such losses are intensified with increasing market-shares and the controlling power that the acquiring firm has on the acquired one. However when these links are ignored or taken as full mergers, such losses are underestimated or overestimated, respectively. Therefore we conclude that the MHHI would be the most adequate measure of market concentration in the presence of minority shareholdings among rival firms.O objetivo deste trabalho é analisar quais os impactos sobre a concorrência de participações minoritárias entre firmas rivais. A aplicação do MHHI, índice de concentração recentemente proposto na literatura, indica que essas ligações estruturais podem causar efeitos adversos sobre a concorrência. Tais prejuízos se intensificam quanto maiores os market-shares e o poder de controle que a firma adquirente tem sobre a adquirida. Porém, quando essas ligações são ignoradas ou consideradas como fusões completas, tais prejuízos são subestimados ou superestimados, respectivamente. Assim, conclui-se que o MHHI é um indicador de concentração mais adequado na presença de participações minoritárias entre firmas rivais
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