Costs and benefits of flocking in foraging white-fronted geese (Anser albifrons): effects of resource depletion

This study investigated the costs and benefits of flocking in white-fronted geese Anser albifrons foraging on rice grains in Japan. The time budgets of focal geese were recorded, and the effects of flock size on the proportions of time spent in vigilant and agonistic behaviour were tested. The results showed that the decline in vigilance level and consequent increase in foraging time were beneficial results of flocking whereas agonistic interactions, a potential cost of flocking, did not increase with increasing flock size. However, seasonal variation in flock size suggested that exploitative competition could be a cost of flocking; the sizes of flocks in spring, when resource depletion had progressed, were significantly reduced compared with those in autumn. An experimental increase in rice density resulted in a significant increase in flock size. We conclude that the flock size of foraging white-fronted geese is a result of compromise between a constant benefit of flocking (i.e. decline in vigilance level) and a cost of flocking varying with food abundance (i.e. exploitative competition).     

Prolonged muscle vibration increases stretch reflex amplitude, motor unit discharge rate, and force fluctuations in a hand muscle.

The purpose of this study was to compare the influence of prolonged vibration of a hand muscle on the amplitude of the stretch reflex, motor unit discharge rate, and force fluctuations during steady, submaximal contractions. Thirty-two young adults performed 10 isometric contractions at a constant force (5.0 +/- 2.3% of maximal force) with the first dorsal interosseus muscle. Each contraction was held steady for 10 s, and then stretch reflexes were evoked. Subsequently, 20 subjects had vibration applied to the relaxed muscle for 30 min, and 12 subjects received no vibration. The muscle vibration induced a tonic vibration reflex. The intervention (vibration or no vibration) was followed by 2 sets of 10 constant-force contractions with applied stretches (After and Recovery trials). The mean electromyogram amplitude of the short-latency component of the stretch reflex increased by 33% during the After trials (P < 0.01) and by 38% during the Recovery trials (P < 0.01). The standard deviation of force during the steady contractions increased by 21% during the After trials (P < 0.05) and by 28% during the Recovery trials (P < 0.01). The discharge rate of motor units increased from 10.3 +/- 2.7 pulses/s (pps) before vibration to 12.2 +/- 3.1 pps (P < 0.01) during the After trials and to 11.9 +/- 2.6 pps during the Recovery trials (P < 0.01). There was no change in force fluctuations or stretch reflex magnitude for the subjects in the Control group. The results indicate that prolonged vibration increased the short-latency component of the stretch reflex, the discharge rate of motor units, and the fluctuations in force during contractions by a hand muscle. These adjustments were necessary to achieve the target force due to the vibration-induced decrease in the force capacity of the muscle.     

Blood flow restriction during low-intensity resistance exercise increases S6K1 phosphorylation and muscle protein synthesis.

Low-intensity resistance exercise training combined with blood flow restriction (REFR) increases muscle size and strength as much as conventional resistance exercise with high loads. However, the cellular mechanism(s) underlying the hypertrophy and strength gains induced by REFR are unknown. We have recently shown that both the mammalian target of rapamycin (mTOR) signaling pathway and muscle protein synthesis (MPS) were stimulated after an acute bout of high-intensity resistance exercise in humans. Therefore, we hypothesized that an acute bout of REFR would enhance mTOR signaling and stimulate MPS. We measured MPS and phosphorylation status of mTOR-associated signaling proteins in six young male subjects. Subjects were studied once during blood flow restriction (REFR, bilateral leg extension exercise at 20% of 1 repetition maximum while a pressure cuff was placed on the proximal end of both thighs and inflated at 200 mmHg) and a second time using the same exercise protocol but without the pressure cuff [control (Ctrl)]. MPS in the vastus lateralis muscle was measured by using stable isotope techniques, and the phosphorylation status of signaling proteins was determined by immunoblotting. Blood lactate, cortisol, and growth hormone were higher following REFR compared with Ctrl (P < 0.05). Ribosomal S6 kinase 1 (S6K1) phosphorylation, a downstream target of mTOR, increased concurrently with a decreased eukaryotic translation elongation factor 2 (eEF2) phosphorylation and a 46% increase in MPS following REFR (P < 0.05). MPS and S6K1 phosphorylation were unchanged in the Ctrl group postexercise. We conclude that the activation of the mTOR signaling pathway appears to be an important cellular mechanism that may help explain the enhanced muscle protein synthesis during REFR.     

Isoform-Specific Redistribution of Calcineurin Aα and Aβ in the Hippocampal CA1 Region of Gerbils After Transient Ischemia

Abstract: To investigate isoform-specific roles of Ca²⁺/calmodulin-dependent phosphatase [calcineurin (CaN)] in ischemia-induced cell death, we raised antibodies specific to CaN Aα and CaN Aβ and localized the CaN isoforms in the hippocampal CA1 region of Mongolian gerbils subjected to a 5-min occlusion of carotid arteries. In the nonischemic gerbil, immunoreactions of both isoforms were highly enriched in CA1 regions, especially in the cytoplasm and apical dendrites of CA1 pyramidal neurons. At 4–7 days after the induced ischemia, immunoreactivities of the CaN Aα isoform in CA1 pyramidal cells were markedly reduced, whereas they were enhanced in the CA1 radiatum and oriens layers. In contrast, CaN Aβ immunoreactivities were reduced in all layers of the ischemic CA1 region, whereas they were enhanced in activated astrocytes, colocalizing with glial fibrillary acidic protein. These findings suggest that up-regulation of CaN Aα in afferent fibers in CA1 and up-regulation of CaN Aβ in reactive astrocytes may be involved in neuronal reorganization after ischemic injury.     

Studies on the Hill reaction of membrane fragments of blue-green algae II. The reaction steps inactivated at high water concentration

DPIP-photoreduction by membrane fragments of Anabaena cylindricaand A. variabilis was studied to determine which step(s) ofthe Hill reaction system is inactivated on incubation of themembrane fragments in a medium with a high water concentration(cf. 1). Supplementary experiments were done with Anacystisnidulans and Plectonema boryanum. After inactivation of the Hill system at a high water concentration,DPIP-photo-reducing activity was strongly enhanced in the A.variabilis system but less so in the A. cylindrica system byadding DPC, NH₂OH, Mn⁺⁺ or H₂0₂. The activity supported by theadded electron donor was inhibited by DCMU. The steady statelevel of chlorophyll fluorescence was lowered by the inactivationtreatment. In the A. variabilis system, the fluorescence yieldincreased to the original level on the addition of an electrondonor. In the A. cylindrica system, the yield was not so stronglyenhanced as in the A. variabilis system. We inferred that, in A. variabilis, inactivation occurs in thereaction system before the site which receives electrons fromartificial donors, probably including the water oxidation system.In A. cylindrica, besides this site, a site at or near the photochemicalsystem is also blocked. Similar types of inactivation were observed in DPIP-Hill reactionsusing Anacystis nidulans and Plectonema boryanum preparations.The characteristic stability of the Hill reaction system observedin two Anabaena preparations is probably common to the blue-greenalgae. (Received December 10, 1971; )     

DNA cytofluorometry on large and small cell nuclei stained with pararosaniline Feulgen

Summary To examine reliability of DNA cytofluorometry with conventional Feulgen staining, measurement was carried out on smears of small and large neurons of human cerebellum, using a Digital-Microfluorometer with incident green light excitation. Nuclear fluorescence of the inner granule neuron and the Purkinje cell came to good agreement with each other when the staining was reduced so that the maximal extinction of the excitation beam nowhere exceeded the value of 0.1. The reduction of the feulgen staining is realized with unimpaired proportionality by treatment with 0.05% Schiff's reagent (pH 2.3) at 7–10° C for 10 min. It is concluded that this staining condition assures accurate determination of DNA content irrespective of size of the nucleus and of pattern of the chromatin distribution.