We hypothesized that inactivity effects on diaphragm muscle contractile and morphometric properties are attenuated if phrenic motoneurons are also inactive. Three models of rat diaphragm inactivity were compared: 1) spinal isolation; 2) tetrodotoxin (TTX) nerve blockade; and 3) denervation (Dnv). Motoneuron and muscle fiber inactivities were matched only in spinal isolated animals. After 2 wk, maximum tetanic force decreased in all three groups compared with control group but to a greater extent in TTX and Dnv animals. Fatigue resistance improved, and maximum unloaded shortening velocity slowed only in TTX and Dnv groups. Type IIa fiber proportions decreased in all three groups, and type IIx fiber proportions increased in TTX and Dnv animals. Type I fiber cross-sectional area increased in all three groups but to a greater extent in TTX and Dnv animals. Type IIa fibers hypertrophied, whereas type IIx and IIb fibers atrophied only in TTX and Dnv groups. These results support the hypothesis that muscle adaptations to prolonged inactivity are attenuated when muscle fiber and motoneuron inactivities are matched.

We hypothesized that metabolic adaptations to muscle inactivity are most pronounced when neurotrophic influence is disrupted. In rat diaphragm muscle (Dia(m)), 2 wk of unilateral denervation or tetrodotoxin nerve blockade resulted in a reduction in succinate dehydrogenase (SDH) activity of type I, IIa, and IIx fibers (approximately 50, 70, and 24%, respectively) and a decrease in SDH variability among fibers (approximately 63%). In contrast, inactivity induced by spinal cord hemisection at C2 (ST) resulted in much less change in SDH activity of type I and IIa fibers (approximately 27 and 24%, respectively) and only an approximately 30% reduction in SDH variability among fibers. Actomyosin adenosinetriphosphatase (ATPase) activities of type I, IIx, and IIb fibers in denervated and tetrodotoxin-treated Dia(m) were reduced by approximately 20, 45, and 60%, respectively, and actomyosin ATPase variability among fibers was approximately 60% lower. In contrast, only actomyosin ATPase activity of type IIb fibers was reduced (approximately 20%) in ST Dia(m). These results suggest that disruption of neurotrophic influence has a greater impact on muscle fiber metabolic properties than inactivity per se.

The relationship between muscle fibre composition and fibre conduction velocity was investigated in 19 male track athletes, 12 sprinters and 7 distance runners, aged 20-24 years, using needle biopsy samples from vastus lateralis. Cross sectional areas of the fast twitch (FT) and slow twitch (ST) fibres were determined by histochemical analysis. The percentage of FT fibre areas ranged from 22.6 to 93.6%. Sprinters had a higher percentage of FT fibres than distance runners. Muscle fibre conduction velocity was measured with a surface electrode array placed along the muscle fibres, and calculated from the time delay between 2 myoelectric signals recorded during a maximal voluntary contraction. The conduction velocity ranged from 4.13 to 5.20 m.s-1. A linear correlation between conduction velocity and the relative area of FT fibres was statistically significant (r = 0.84, p less than 0.01). This correlation indicates that muscle fibre composition can be estimated from muscle fibre conduction velocity measured noninvasively with surface electrodes.

In chronic kidney disease (CKD), progressive nephron loss causes glomerular sclerosis, as well as tubulointerstitial fibrosis and progressive tubular injury. In this study, we aimed to identify molecular changes that reflected the histopathological progression of renal tubulointerstitial fibrosis and tubular cell damage. A discovery set of renal biopsies were obtained from 48 patients with histopathologically confirmed CKD, and gene expression profiles were determined by microarray analysis. The results indicated that hepatitis A virus cellular receptor 1 (also known as Kidney Injury Molecule-1, KIM-1), lipocalin 2 (also known as neutrophil gelatinase-associated lipocalin, NGAL), SRY-box 9, WAP four-disulfide core domain 2, and NK6 homeobox 2 were differentially expressed in CKD. Their expression levels correlated with the extent of tubulointerstitial fibrosis and tubular cell injury, determined by histopathological examination. The expression of these 5 genes was also increased as kidney damage progressed in a rodent unilateral ureteral obstruction model of CKD. We calculated a molecular score using the microarray gene expression profiles of the biopsy specimens. The composite area under the receiver operating characteristics curve plotted using this molecular score showed a high accuracy for diagnosing tubulointerstitial fibrosis and tubular cell damage. The robust sensitivity of this score was confirmed in a validation set of 5 individuals with CKD. These findings identified novel molecular markers with the potential to contribute to the detection of tubular cell damage and tubulointerstitial fibrosis in the kidney.

No abstract

The authors compared perception of the standard and reversed Müller-Lyer figures between pigeons (Columbia livia) and humans (Homo sapiens). In Experiment 1, pigeons learned to classify 6 lengths of target lines into "long" and "short" categories by pecking 2 keys on the monitor, ignoring the 2 brackets so placed that they would not induce an illusion. In the test that followed, all 3 birds chose the "long" key more frequently for the standard Müller-Lyer figures with inward-pointing brackets (><) than for the figures with outward-pointing brackets (<>). The subjects' responses were accountable by neither overall lengths of the figures nor horizontal gaps between the 2 brackets. For the reversed figures, effects of the brackets were absent. These results suggested that the pigeons perceived the standard Müller-Lyer illusion but not the reversed one. Experiment 2 confirmed that humans perceived both types of the illusion. Pigeons and humans may perceive the same illusory figures in different ways.

We examine the muscle fiber population and metabolic properties of skeletal muscles from the whole body in Thoroughbred horses. Postmortem samples were taken from 46 sites in six Thoroughbred horses aged between 3 and 6 years. Fiber type population was determined on muscle fibers stained with monoclonal antibody to each myosin heavy chain isoform and metabolic enzyme activities were determined spectrophotometrically. Histochemical analysis demonstrated that most of the muscles had a high percentage of Type IIa fibers. In terms of the muscle characteristic in several parts of the horse body, the forelimb muscles had a higher percentage of Type IIa fiber and a significantly lower percentage of Type IIx fiber than the hindlimb muscles. The muscle fiber type populations in the thoracic and trunk portion were similar to those in the hindlimb portion. Biochemical analysis indicated high succinate dehydrogenase activity in respiratory-related muscle and high phosphofructokinase activity in hindlimbs. We suggested that the higher percentage of Type IIa fibers in Thoroughbred racehorses is attributed to training effects. To consider further the physiological significance of each part of the body, data for the recruitment pattern of each muscle fiber type during exercise are needed. The muscle fiber properties in this study combined with the recruitment data would provide fundamental information for physiological and pathological studies in Thoroughbred horses.

Planning, the internal process of formulating an organized method about one's future behavior, should be advantageous for non-human animals as well as for humans. However, little is known about this process in avian species. We examined planning processes in pigeons (Columba livia) using a computerized maze task. In Experiment 1, we found that the pigeons plan their next one step, and in some cases even correctly adjust their actions after change of goal locations, while performing on a plus-shaped maze. We also showed that the pigeons might even plan two steps on familiar, well-practiced mazes. In Experiment 2, we discovered that the subjects plan the direction they would go first before starting to solve a four-arm shuriken (a Japanese traditional throwing knife)-shaped maze. The birds also corrected their previously planned actions after change of goal locations. Our results from these experiments suggest that planning ahead is within the cognitive capacity of a "bird brain", and that it may be more widespread in the animal kingdom than has been presumed.