Spontaneous Wheel Running Research Articles

Behavioral feedback regulation of circadian rhythm phase angle in light-dark entrained mice.

Induced and spontaneous wheel running can alter the phase and period (tau) of circadian rhythms in rodents. The relationship between spontaneous running and the phase angle (psi) of entrainment to 24-h light-dark (LD) cycles was evaluated in C57BL/6j mice. With a wheel freely available, psi was significantly correlated with the absolute (r = 0.32) and relative (r = 0.44) amount of activity during the first 2 h of the activity period. When wheels were locked during the first half of the night in LD and then unlocked in constant dark (DD), mice exhibited a delayed psi and lengthened tau compared with mice that had wheels locked during the second half of the night. In DD, tau correlated negatively with total daily activity. To evaluate if wheel running modulates the phase-resetting actions of LD, phase shifts to light pulses were measured at two time points in DD, when daily activity levels differed by 40%. Phase delays to light were 56% greater when activity levels were lower. However, in a counterbalanced follow-up experiment, phase advances and delays to light pulses were not affected by the availability of wheels, although an effect of time in DD was replicated. Spontaneous activity can regulate psi and tau without altering the response of the pacemaker to light.

Spontaneous wheel running attenuates cardiovascular responses to stress in rats.

We investigated the effect of chronic, 10-week spontaneous wheel running (SWR) exercise on stress-induced cardiovascular responses in free-moving male rats, using a biotelemetry system. During cage-switch stress or immobilization stress, blood pressure and heart rate were significantly increased in both the SWR (P<0.001 for each stress) and control groups (P<0.001 for each stress). However the blood pressure response was attenuated significantly in the SWR group (P<0.001) during cage-switch stress, and the blood pressure and heart rate responses were attenuated significantly in the SWR group (P<0.0001 and 0.01, respectively) during immobilization stress. The plasma norepinephrine (NE) response induced by immobilization stress tended to be attenuated in the SWR group, but the groups showed no significant differences in the plasma NE and epinephrine (E) responses to both stresses. These results suggest that daily SWR in rats has beneficial effects in suppressing excessive blood pressure and heart rate responses induced by two different types of stress. The mechanisms responsible for the greater resistance to these stresses in the SWR rats should be investigated further.

Immunomodulation by 8-week voluntary exercise in mice.

This study was designed to evaluate the effects of voluntary exercise on macrophage and lymphocyte functions in mice. Male A/He inbred mice aged 19 weeks were divided into two groups: a group given voluntary exercise and a control group (n = 10 in each group). Exercise consisted of spontaneous running in wheels for 8 weeks (3 days week-1). Glucose consumption of peritoneal macrophages in the exercise group during incubation up to 72 h was significantly higher than that in the control group (70 and 13%, respectively). Also, activities of acid phosphatase (APH) (10.75 +/- 0.37 IU), beta-glucuronidase (GLU) (1.55 +/- 0.07 IU) and lactate dehydrogenase (LDH) (43.3 +/- 0.7 IU) in the peritoneal macrophages in the exercise group was significantly increased (P < 0.01). Compared with the control group, the exercise group had a significant increase of about twofold in macrophage production of nitric oxide (NO2-) stimulated by lipopolysaccharide (LPS) (11.1 +/- 0.1 vs. 5.9 +/- 0.1 microM mL-1 in exercise and control groups, respectively; P < 0.01). Stimulation indices both by concanavalin A (Con A) and phytohaemagglutinin were also significantly higher in the exercise group (P < 0.01). A significant increase in the splenocyte production of interleukin-2 (IL-2) stimulated by Con A was noticed in the exercise group (354.1 +/- 28.8 vs. 218.9 +/- 23.5 pg mL-1 in exercise and control groups, respectively; P < 0.01). These findings suggest that voluntary exercise enhances not only macrophage function but also lymphocyte responsiveness in mice. In the studies of voluntary exercise, evaluation of NO2- production, as an indicator of macrophage function, is recommended.

Taste aversion induced by confinement in a running wheel

Opportunities of spontaneous wheel running induced aversion in rats to the taste consumed before the running. Eight thirsty rats of Wistar strain were daily allowed to drink one of two taste solutions (sucrose or sodium chloride, say A) followed by confinement in a wheel or another taste solution (say B) followed by confinement in a Skinner box. Repeated training with Tastes A and B made the rats drink Taste A less than Taste B. Post-training two-bottle choice tests also showed clear demonstration of wheel-running-induced aversion to Taste A. These results confirmed those from Lett’s laboratory and expanded the generality of the phenomenon in respect to strain of rats, deprivation conditions of the subjects, tastes, and other details. Furthermore, our procedure rejected three accounts alternative to wheel-induced aversion to Taste A.

Spontaneous wheel running attenuates cardiovascular responses to stress in rats

Spontaneous wheel running attenuates cardiovascular responses to stress in rats

Effect of long-term caloric restriction and exercise on muscle bioenergetics and force development in rats.

We evaluated the hypothesis that long-term caloric restriction and exercise would have beneficial effects on muscle bioenergetics and performance in the rat. By themselves, each of these interventions is known to increase longevity, and bioenergetic improvements are thought to be important in this phenomenon. Accordingly, we investigated rats that underwent long-term caloric restriction and were sedentary, ad libitum-fed rats permitted to exercise by daily spontaneous wheel running (AE), and the combination of the dietary and exercise interventions (RE). Ad libitum-fed, sedentary rats comprised the control group. 31P NMR spectra of the gastrocnemius muscle (GM) were collected in vivo at rest and during two periods of electrical stimulation. Neither caloric restriction nor exercise affected the ratio of phosphocreatine to ATP or pH at rest. During the first stimulation and after recovery, the RE group had a significantly smaller decline in pH than did the other groups (P < 0.05). During the second period of stimulation, the decrease in pH was much smaller in all groups than during the first stimulation, with no differences observed among the groups. The combination of caloric restriction and exercise resulted in a significant attenuation in the decline in developed force during the second period of stimulation (P < 0.05). A biochemical correlate of this was a significantly higher concentration of citrate synthase in the GM samples from the RE rats (32.7 +/- 5.4 micromol. min-1. g-1) compared with the AE rats (17.6 +/- 5.7 micromol. min-1. g-1; P < 0.05). Our experiments thus demonstrated a synergistic effect of long-term caloric restriction and free exercise on muscle bioenergetics during electrical stimulation.

Apoptosis of myofibres and satellite cells: exercise-induced damage in skeletal muscle of the mouse.

Apoptosis is well accepted as a type of cell death occurring in the development of mammalian muscles, but the death of adult myofibres in neuromuscular disorders and exercise-induced muscle damage is usually explained in terms of muscle necrosis. The current view that apoptosis precedes necrosis in death of dystrophin-deficient muscle fibres of mdx mouse has been well substantiated. Moreover, apoptotic myonuclei have been reported to increase in mdx mice 2 days after spontaneous exercise. To investigate the contribution of apoptosis to exercise-induced damage of normal muscle fibre a time-course analysis has been performed in adult C57BL/6 mice. Groups of five mice were sacrificed immediately after the end of the exercise, and after a rest period of 6 or 96 h. The amount of apoptosis in leg muscles was assessed by electron microscopy, by the terminal deoxynucleotidyl transferase assay and by electrophoretic detection of fragmented DNA; the expression of Bcl-2, Bax, Fas, ICE, p53 and ubiquitin was examined by immunohistochemistry and Western blot. Absent in muscles of normal 'sedentary' mice, apoptotic myonuclei peak in muscles of normal mice after a night of spontaneous wheel-running (4% +/- 3.5, immediately and 2.5% +/- 1.8 after 6 h rest, P < 0.05 vs non-runner mice); they then decrease but are present 4 days later (0.8% +/- 1.5). Satellite cells are also involved in the apoptotic process. Myofibre content of Bcl-2 decreases whereas Bax, Fas, ICE and ubiquitin modify their pattern of expression in correlation with the changes in apoptotic myonuclei. Apoptosis of endothelial cells is present after the night of wheel-running and with a twofold increase 4 days later (1.5 +/- 2.3 and 4.8 +/- 4.4 P < 0.05, respectively). Satellite cells are also involved in the apoptotic process. Thus, spontaneous running in unaccustomed mice increases the number of apoptotic nuclei in adult muscle fibres and in endothelial cells. It remains to be established whether muscle apoptosis is restricted to the repair mechanisms, as often suggested in many pathologic processes, or it is also part of pathogenesis of muscle damage. Regardless of whether these results are extended to human dystrophies, the clinical implications in terms of secondary pathogenetic mechanisms and muscle training are obvious.

Increase in nitric oxide formation after chronic voluntary exercise in spontaneously hypertensive rats.

The effect of chronic voluntary exercise on the plasma level of nitrate, a major stable metabolite of nitric oxide (NO) was studied in spontaneously hypertensive rats (SHR). Exercise consisted of spontaneous running in wheels for 3-35 days. Blood samples were collected after 3, 7, 14, 21 and 35 days of exercise and all samples were drawn after the running wheel had been locked during the preceding 12 h. The plasma nitrate level was significantly (P < 0.05) elevated in SHR after 35 days of exercise. Surprisingly after 7 days of exercise a significant (P < 0.001) decrease in the nitrate level in plasma was noted. Further research is needed to elucidate this biphasic change in nitrate seen in this study. The elevated level of plasma nitrate seen after 35 days of voluntary exercise was still present up to 36 h after termination of exercise. We conclude that exercise training in SHR elicits an enhanced formation of NO.

Development of Degenerative Muscle Weakness by Chronic Administration of β, β′-Iminodipropionitrile in the Drinking Water to Rats: A Model for Motorneuropathy

Kitahara, Y., T. Maki and K. Torii. Development of degenerative muscle weakness by chronic administration of β, β′-iminodipropionitrile in the drinking water to rats: A model for motorneuropathy. Physiol Behav 62(3)443–451, 1997.—Progressive muscle weakness accompanied by progressive muscle atrophy was investigated in rats administered β, β′-iminodipropionitrile (IDPN) chronically in the drinking water. Spontaneous running wheel activity declined slowly and reached a constant low level before postural muscle weakness was apparent. The rats being offered IDPN in the drinking water showed definite postural muscle weakness about 25 weeks after first being given IDPN, and muscle strength declined gradually throughout the remainder of the experiment (to 66 weeks). Flaccid paralysis became apparent in the hind limbs in the later stages of the experiment. Neurogenic muscle atrophy, measured by group atrophy of the muscle fibers, also progressed slowly, almost in parallel with the loss of muscle strength. At the end of the experiment, muscle weight of the gastrocnemius had decreased to about 20% that of control [ F(2, 12) = 40.4, p < 0.05]. Plasma creatinine in the rats given IDPN in the drinking water for 66 weeks was significantly elevated over that of controls [ F(2, 12) = 20.1, p < 0.05]. On the other hand, in rats given IDPN intraperitoneally, postural muscle weakness and muscle atrophy were less apparent, and plasma creatinine was normal. However, in these animals, abnormal behaviors, such as hyperexcitement, circling, and choreic movement (ECC syndrome), were apparent. These results suggest that the present model, which administers IDPN chronically in the drinking water ad lib and does not show involuntary movements and ECC syndrome, is of potential importance for investigation of chronic diseases of progressive muscle weakness with progressive muscle atrophy, and for assessing the efficacy of drugs and therapies for treating chronic neuromuscular diseases.

Modifications in dietary self-selection specifically attributable to voluntary wheel running and exercise training in the rat

To explore the effects of physical exercise on total caloric intake, body weight gain, and dietary self-selection in rats, female rats of the Dark Agouti strain were placed on macronutrient self-selection. They had free access to running wheels during the whole experimental period. After 16 days of voluntary exercise only, they were trained on a motor-driven treadmill (16 m/min) at the beginning of the dark period. Runtime was progressively increased and reached 3 h per day (plateau). When trained, the rats decreased spontaneous wheel running. Voluntary wheel running did not modify body weight gain. However it increased both carbohydrate and total caloric intakes. Exercise training reduced body weight gain, but did not further modify total caloric intake. Moreover it increased protein and reduced fat intakes. Most of the training-induced modifications were not side effects of fasting during exercise training.

Apoptosis, DNA damage and ubiquitin expression in normal and mdx muscle fibers after exercise

The current view indicates that after eccentric exercise myofibers are mechanically damaged and therefore an inflammatory and necrotic process occurs. In the present paper we examine the possibility that apoptosis plays a role in normal and dystrophin-deficient muscles after running. We analysed for apoptosis normal and dystrophin-deficient mouse muscles after a night of spontaneous wheel-running followed by two days of rest. Terminal deoxynucleotidyl transferase-mediated endlabeling of DNA in nuclei in tissue sections and gel electrophoresis of extracted DNA showed the presence of fragmented DNA. Furthermore, ubiquitin, a protein whose appearance is related to apoptosis, increased in muscles of both dystrophic and normal runner mice. The present findings which confirm that DNA damage is absent in muscles of sedentary mice but present in muscles of runner mice offer a new hypothesis on early events of muscle damage.

Diurnal variation of intensive running in food-deprived rats.

Manipulation of the food supply can induce either intense hyperactive wheel running or a fatal activity anorexia in rats that is strongly analogous to that seen in humans. The abnormal behaviour is accompanied by alterations in the diurnal pattern of activity. As part of a detailed study of hyperactivity and anorexia, spontaneous wheel running by male rats was studied under three conditions: ad libitum feeding; restriction to 15 g of food per day; and restriction to a single 90-min meal per day. Ad libitum fed rats increased their running at the rate of 440 +/- 60 m/day per day, stabilizing after day 10 at 6045 +/- 3010 m/day. The running occurred in short bursts throughout the dark period and at the beginning of the light period. Rats restricted to 15 g/day increased their running at the significantly greater (p < 0.001) rate of 1230 +/- 120 m/day per day, reaching 12 200 +/- 4 090 m/day by day 10 and thereafter stabilizing at 13 600 +/- 4 160 m/day. The running was initially triphasic and confined to the dark period but eventually progressed to a biphasic pattern. The rats restricted to a single 90-min access period to food each day showed an even greater rate of increase in running, attaining 1930 +/- 288 m/day per day (p < 0.02 vs. 15 g/day group). These animals decreased eating and decompensated by day 4. The diurnal pattern of activity was disturbed from day 1 of the protocol, and by day 4 the rats ran essentially continuously throughout the daily cycle. The sensitivity to hyperactivity is a function of the severity of food restriction in this animal model of hyperactivity. It is paralleled by a marked disturbance of the diurnal pattern of activity, suggesting that the hyperactivity is related to a basic central nervous system dysfunction.

Changes in Mobility of the Golden Hamster with Induction of an IL‐1‐Induced Arthritis

Many studies in animals have examined biochemical, immune and histological changes during arthritis; however, the study of the effects of arthritis on mobility has been largely neglected. Interleukin-1, administered by the intraarticular route into hamster knee joints, resulted in inhibition of spontaneous wheel running activity; however, the effect was transient, lasting only through the evening following IL-1 administration. A further injection of IL-1 2 days later showed still greater inhibition of running. The effect again did not extend beyond the first evening after injection. IL-1α and IL-1β showed equivalent effects on mobility, and no evidence was seen for cooperative interaction between them. A 50% inhibition of running occurred at a dose of approximately 10 ng/knee of IL-1α. The effect appeared not to be systemic since intraperitoneal injection required microgram amounts of IL-1 for an equivalent inhibition. At the time mobility had been restored to normal, histological examination showed the continued presence of inflammatory cells, soft tissue swelling and cartilage proteoglycan loss. These results suggest a lack of correlation between inhibition of mobility and histopathological changes in cartilage and soft tissue.

Cerebrospinal fluid dynorphin-converting enzyme activity is increased by voluntary exercise in the spontaneously hypertensive rat

The activity in cerebrospinal fluid (CSF) of dynorphin-converting enzyme (DCE) has been studied after voluntary exercise in the spontaneously hypertensive (SH) rat. The exercise consisted of spontaneous running in wheels for 4–5 weeks and the average running distance during the last two weeks was 4.0 km/24h. CSF samples were obtained under anaesthesia from the cisterna magna after penetration of the atlanto-occipital membrane. DCE transforms the members of the dynorphin family of opioid peptides into Leu-enkephalin-Arg 6. In the present investigation a radioimmunoassay was used for quantitation of Leu-enkephalin-Arg 6 release from dynorphin A 1–17 and dynorphin B 1–13. The rats that were running had a DCE activity (vs. both substrates) in CSF that was approximately 6–12 times higher than in animals not given the running opportunity. A statistically significant correlation between the two prodynorphin-derived substrate peptides was found in terms of DCE activity. We therefore propose that a single enzyme activity may be responsible for the hydrolysis of dynorphin B 1–13 and dynorphin A 1–17. Furthermore, a significant correlation was also found between running activity and DCE activity 12–14 h before the CSF was withdrawn. Besides measurement of DCE activity by radioimmunoassay, the formation of Leu-enkephalin-Arg 6 was identified by reversed-phase micro-column liquid chromatography and plasma desorption mass spectrometry. The experiment shows that voluntary exercise affects opioid peptidergic mechanisms.

Activity Feedback to the Mammalian Circadian Pacemaker: Influence on Observed Measures of Rhythm Period Length

In the mouse, activity is precisely timed by the circadian clock and is normally most intense in the early subjective night. Since vigorous activity (e.g., wheel running) is thought to induce phase shifts in rodents, the temporal placement of daily exercise/activity could be a determinant of observed circadian rhythm period. The relationship between spontaneous running-wheel activity and the circadian period of free-running rhythms was studied to assess this possibility. With ad libitum access to a running wheel, mice exhibited a free-running period (tau) of 23.43 +/- 0.08 hr (mean +/- SEM). When running wheels were locked, tau increased (23.88 +/- 0.04 hr, p less than 0.03), and restoration of ad libitum wheel running again produced a shorter period (tau = 23.56 +/- 0.06 hr, p less than 0.05). A survey of free-running activity patterns in a population of 100 mice revealed a significant correlation between the observed circadian period and the time of day in which spontaneous wheel running occurred (r = 0.7314, p less than 0.0001). Significantly shorter periods were observed when running was concentrated at the beginning of the subjective night (tau = 23.23 +/- 0.04), and longer periods were observed if mice ran late in the subjective night (tau = 23.89 +/- 0.04), F (1, 99) = 34.96, p less than 0.0001. It was previously believed that the period of the circadian clock was primarily responsive to externally imposed tonic or phasic events. Systematic influences of spontaneous exercise on tau demonstrate that physiological and/or behavioral determinants of circadian timekeeping exist as well.

Plasticity of presynaptic and postsynaptic elements of neuromuscular junctions repeatedly observed in living adult mice

In order to assay the extent of ongoing synaptic remodelling in adult mouse neuromuscular junctions, dynamic structural changes of identified neuromuscular junctions were monitored in vivo over periods up to three months. Nerve terminal outgrowths as small as 1 micron were detectable with a new fluorescent tetanus toxin C-fragment stain combined with fluoresceinated alpha-bungarotoxin to stain postsynaptic acetylcholine receptors. With limited illumination, the new stain did not affect miniature endplate potential frequency, nor morphometric parameters of repeatedly observed neuromuscular junctions. At each observation, areas of presynaptic nerve terminal extending beyond underlying acetylcholine receptor ('preprojections'), and areas of acetylcholine receptor without overlying nerve terminal ('postprojections') were measured. Regions of the neuromuscular junction in which nerve terminal-postsynaptic acetylcholine receptor complexes either 'lengthened' or 'shortened' between observations were also measured. The total area of pre- and postprojections (relative to total junctional area) remained the same over three months but most had been replaced; only 20% of preprojections gave rise to lengthenings, the rest retracted or were unchanged. Lengthening and shortening of branches were about 1-2% of junctional area per month. These more permanent changes occurred against a background of ongoing transient nerve terminal outgrowth and retraction (which constituted 80% of all neuromuscular junction shape changes from one observation to the next, compared with 20% for the postsynaptic component). Breaks in the continuity of the underlying acetylcholine receptor were also observed between observations as were instances where acetylcholine receptor continuity was re-established. A newly observed form of plasticity was a shift in position and angle of pre-existing branches. Establishment of new acetylcholine receptor-positive synaptic regions was mostly preceded by nerve terminal outgrowth on the previous observation. In animals in which spontaneous wheel-running increased locomotor activity approximately tenfold over a period of 35 days, the findings were identical to those in unexercised mice. In summary, in the adult neuromuscular junction, the nerve terminal, not the postsynaptic component, is the dynamic entity, continually changing shape on the scale of micrometers, with relatively small permanent changes. These ongoing exploratory excursions may supply the substrate for synaptic plasticity, which would involve regulation of the dynamics or stability of nerve outgrowth.

Cerebrospinal fluid immunoreactive β-endorphin concentration is increased by voluntary exercise in the spontaneously hypertensive rat

The effect of voluntary exercise on cerebrospinal fluid (CSF) levels of immunoreactive β-endorphin has been studied in the spontaneously hypertensive rat (SHR). The exercise consisted of 5–6 weeks of spontaneous running in wheels and the average running distance was 3.5 ± 0.4 km/24 h. CSF samples were obtained under anaesthesia from the cisterna magna. Five experimental groups were examined, four groups of runners and one group of sedentary controls. The runners were sampled either (a) shortly (0–3 h) after termination of exercise, or after the wheel had been locked for (b) 24, (c) 48 or (d) 96 h. The runners in group a had significantly higher immunoreactive β-endorphin levels than the controls. The levels remained increased as compared with controls after 24 and 48 h of enforced abstinence but had returned to control after 96 h. The data indicate that voluntary exercise induces adaptive changes in central β-endorphin systems.

Effect of voluntary exercise on open-field behavior and on aggression in the spontaneously hypertensive rat (SHR)

In the present study we investigated the influence of voluntary exercise on exploratory behavior and on aggression in the spontaneously hypertensive rat (SHR). Twenty-four SHR (8 weeks old) were randomly assigned to either an exercise group or a sedentary control group. The animals in the exercise group exhibited a spontaneous wheel running activity of 5-6 km/day during 6 weeks. The characteristic hyperexploratory behavior of SHR was lowered in the exercise group (p less than .001) as compared to the control group. The runners also showed a tendency for less aggression. In the postexercise period, when the runners' wheels were locked, the exercise group had a significant rise in aggression (p less than .01) vs the controls. The exploratory behavior returned immediately to the level of the controls, but we found no further increase in any of the parameters measured. However, the runners showed a type of displaced aggression exhibited as digging and biting in the test cage. This evidence suggests that voluntary exercise lowers the hyperexploratory behavior and aggression in the SHR and that an abrupt stop in exercise gives an "abstinence" reaction.

Rostral hypothalamic microinfusions of 5,7 dihydroxytryptamine produce anatomically and neurochemically selective depletions of hippocampal serotonin and increase the influence of estrogen and food deprivation on locomotor activity

Ovariectomized Long-Evans rats received bilateral rostral hypothalamic infusions of 5,7-dihydroxytryptamine (5,7-DHT). Neurochemical determination of catecholamines (CA) and indoleamines in the hippocampus, hypothalamus and mesencephalon revealed that 5,7-DHT infusions had no effect on CA content in these areas nor in mesencephalic serotonin or 5-hydroxyindoleacetic acid (5-HIAA). However, the neurotoxin produced significant decreases in hippocampal serotonin and 5-HIAA. Serotonin-depleted animals exhibited an increase in both spontaneous and estradiol-induced wheel running. In addition it was found that serotonin-depleted animals exhibit an enhanced activity response to starvation. Because estrogen is thought to decrease serotonergic transmission, the enhanced activity response to estrogen may be secondary to an estrogen-related exaggeration of the 5,7-DHT-induced serotonin depletion. The increased activity effect of starvation may indicate that serotonin-depleted animals do not effectively mobilize energy stored as lipid.

Spontaneous running in wheels. A microprocessor assisted method for measuring physiological parameters during exercise in rodents.

When examining physiological parameters during exercise in rodents most techniques use forced exercise on treadmills or forced swimming which undoubtedly will employ stress to the animals. This paper describes a convenient method to measure physiological parameters during spontaneous exercise in rodents. Hamsters and rats develop a spontaneous running pattern in wheels. The hamsters are reaching maximal activity almost immediately. In contrast, rats increase their running activity with time and need about 4 weeks to reach an average of about 7 km/day. The amount of running is measured by a microprocessor system. With this technique pain threshold, blood pressure and heart rate for example could be measured for extended periods of time, without changing the environment of the animals.