Intracranial self-stimulation motivates weight-lifting exercise in rats
R. P. Garner, L. Terracio, T. K. Borg and J. Buggy
The purpose of this study was to determine the feasibility of using a positive reinforcement protocol to motivate weight-lifting exercise in rats. Intracranial self-stimulation was used to induce weight-lifting exercise. Bipolar electrodes were implanted in the ventral tegmental area of rats, and the animals were trained to bar press on a continuous reinforcement schedule for electrical brain stimulation. Animals with response rates of 1,200-1,500 presses/h were then trained with a discriminative light stimulus to alternate between a normally positioned bar and an elevated bar that could be reached only by standing on the hindlimbs. The animals were fitted with a weighted jacket at a starting resistance of 5-10% of their body weight. Weight-training sessions were conducted 5 days/wk for 10 wk. Training consisted of 600 presses/session, alternating every 15 presses between the low and high bars. At the beginning of each subsequent week, the resistance was progressively increased, with some animals eventually training at resistances greater than 50% of their body weight. At the end of the training period, the rats were lifting over 550% of the starting weight. Gastrocnemius size and mean fiber diameter were increased in the weight-lifting animals. This model combines exercise with positive incentive and has the advantages of being relatively easy to implement and not producing any apparent physical or mental trauma in the animal.
Mirror neurons and the simulation theory of mind-reading
A new class of visuomotor neuron has been recently discovered in the monkey's premotor cortex: mirror neurons. These neurons respond both when a particular action is performed by the recorded monkey and when the same action, performed by another individual, is observed. Mirror neurons appear to form a cortical system matching observation and execution of goal-related motor actions. Experimental evidence suggests that a similar matching system also exists in humans. What might be the functional role of this matching system? One possible function is to enable an organism to detect certain mental states of observed conspecifics. This function might be part of, or a precursor to, a more general mind-reading ability. Two different accounts of mind-reading have been suggested. According to ‘theory theory', mental states are represented as inferred posits of a naive theory. According to ‘simulation theory', other people's mental states are represented by adopting their perspective: by tracking or matching their states with resonant states of one's own. The activity of mirror neurons, and the fact that observers undergo motor facilitation in the same muscular groups as those utilized by target agents, are findings that accord well with simulation theory but would not be predicted by theory theory.
Measurements of muscle stiffness and the mechanism of elastic storage of energy in hopping kangaroos.
1. A kangaroo hopping above a certain speed appears to consume less oxygen than a quadrupedal mammal, of similar weight, running at the same speed (Dawson & Taylor, 1973). This is thought to be achieved by storage of elastic energy in tendons and ligaments. 2. Energy can be stored in a tendon by stretching it, but only if the muscle fibres in series with it are stiff enough to resist most of the length change. We have measured length and tension changes in the contracting gastrocnemius muscle of the wallaby Thylogale during rapid, controlled stretches, and from this determined the amount of movement in muscle fibres and tendon (method of Morgan, 1977). 3. When the muscle was developing close to its maximum isometric tension, up to eight times as much movement occurred in the tendon as in the muscle fibres. This is made possible by the wallaby having a long and compliant tendon. 4. Measurement of work absorption by the muscle with a full length of free tendon and when the tendon had been shortened, showed that with the shortened tendon a larger proportion of movement occurred in the muscle fibres, producing a steep rise in work absorption by the muscle and a consequent increase in energy loss.
Beneficial Effects of Exercise on Growth of Rats During Intermittent Fasting
An 8-wk trial was conducted to compare the effects of exercise and intermittent fasting, either singly or combined, on growth responses of rats. Four-week-old male Wistar rats, 85–110 g each, were assigned to one of four groups (n = 9): 1) control, 2) exercise on a motor-driven treadmill, 3) fasting every other day (EOD) and 4) fasting EOD and exercise combined. At the end of the trial, the exercised rats had consumed 7% less feed, had gained 7% less weight and had 36% less carcass fat than the control rats. Fasting on alternate days markedly reduced the growth rate of the young rats. Fasted-EOD rats weighed less than half as much as the control rats, had 64% less carcass fat and 51% less lean mass and had smaller livers, kidneys, hearts, tibias and tibialis anterior muscles. The addition of exercise to the fasting EOD regimen improved the growth of the animals. When the fasted-EOD rats were also exercised, they gained 29% more weight, consumed 11% more feed and had carcasses that contained 29% more lean mass and 18% less fat than the fasted-EOD rats. The data suggest that exercise may be beneficial where feed restriction is episodic, allowing some capacity for catch-up growth.
Adaptation of Equine Locomotor Muscle Fiber Types to Endurance and Intensive High Speed Training
Journal of Equine Veterinary Science, Volume 28, Issue 7, Pages 395-401
K. Leisson, Ü. Jaakma, T. Seene
bstract
Skeletal muscle constitutes the largest organ system in the mammalian body and is essential for movement and force generation. Muscle tissue has the unique ability to adapt and remodel with regular exercise. Adaptation of equine contractile apparatus to exercise training with a different character occurs at the structural to the cellular and molecular levels and depends on age, breed, and sex. In Andalusian and Arabian horses from 3 months to 24 years of age, it was found that the mean cross-sectional area occupied by IIA and IIX fibers was greater in stallions than in mares. In muscle of Dutch Warmblood foals from birth to 1 year of age, a significant number of fibers coexpress either developmental and type IIa or cardiac–alpha and type I myosin heavy chain (MyHC) isoforms. Endurance training results in increased mitochondrial density, capillary supply, changes in key metabolic enzymes, and increased maximal oxygen uptake and promotes a transition from type II to type I muscle fiber. In horses, prolonged aerobic exercise training has been shown to induce a further decline in the percentage of type IIx MyHC isoform expression and an increase of type I and IIa MyHC isoform expression. Short-duration, high-intensity exercise training stimulates type IIA and hybrid (IIA/IIX) fibers. Therefore, intensive high-speed trotting facilitates muscle fiber hypertrophy and increases the oxidative capacity of type IIX fibers.
