Decreased Wheel Running Research Articles

Role Of Brain Il-1b On Fatigue Following Downhill Running

Cytokines in the brain, induced by various inflammatory challenges have been linked to sickness behaviors, including fatigue. However, the brain cytokine response to exercise is not well understood. Preliminary data show that exaggerated fatigue following downhill vs uphill running is associated with increased brain IL-1b concentration. PURPOSE This study more specifically determined the role of brain IL-1b in this model using intracerebroventricular (ICV) injections of IL-b or IL-1b receptor antagonist (IL-1bra) in uphill and downhill runners, respectively. Methods 64 male C57BL/6 mice were assigned to 1 of 4 groups (UP-IL-1b, DWN-SAL & DWN-IL-Ira). Mice were initially run at 22 m/min and −14% or +14% grade, for 150-min. Fatigue was assessed 12–24hr later via voluntary wheel running (Exp.1) or treadmill running to fatigie) Exp. 2). In Exp 1, 8-hr after the initial run, UP runners received ICV injections of IL-1b (900pg/mouse in 2μ saline) or saline (2 μL), whereas DWN runners received IL-1ra (1.8μ/mouse in 2 μ saline) or saline (2 μL). Then, 2-hr later, all 4 groups were monitored for 24-hr voluntary wheel running patterns. In Exp.2, the protocol was identical except that injections were given 22-hr after the initial run and fatigue was assessed 2-hr later using a treadmill run time to fatigue test. RESULTS In Exp.1, injection of IL-1b in uphill runners decreased wheel running (distance, time and peak speed during the subsequent two 12-hr active cycles (lights out) vs. saline injected mice, and IL-1ra improved wheel running in Downhill runners vs. saline mice. In Exp.2, IL-1b injection decreased run-times to fatigue in the uphill group, and IL-1ra increased run time. CONCLUSION These results support the hypothesis that increased brain IL-1b plays an important role in fatigue following muscle-damaging exercise and perhaps other inflammatory challenges.

Opioid-mediated pain sensitivity in mice bred for high voluntary wheel running

We tested the hypothesis that thermal tail-flick latency, a common measure of pain sensitivity in rodents, would be altered in lines of mice that had been selectively bred for high voluntary wheel-running behavior. Specifically, we predicted that the selected (High-Runner) lines would show decreased pain sensitivity relative to their control (C; randombred) lines, and would respond differently to drugs that block opioid receptors. We first compared tail-flick latency between High-Runner and C female mice during the day (no wheel access) and at night (with wheel access). Second, we compared effects of the opioid antagonist naloxone (10 mg/kg, i.p.) on tail-flick latency during the day (no wheel access). Third, we compared effects of naloxone (5 and 10 mg/kg, i.p.) and naltrexone, a longer-lasting opioid antagonist (0.1, 1, 5, 10, 50, and 100 mg/kg, i.p.), on voluntary wheel running. Tail-flick latencies were longer at night (when mice were active on wheels), but mice from High-Runner and C lines did not differ during the day or night. Administration of naloxone (10 mg/kg, i.p.) decreased tail-flick latency measured during the day, equally in High-Runner and C mice. Naloxone (5 and 10 mg/kg, i.p.) and high doses of naltrexone (50 and 100 mg/kg, i.p.) decreased wheel running equally in High-Runner and C mice. Further studies will be required to determine whether other types of pain sensitivity have also failed to evolve in association with increased voluntary wheel running.

Behavioral Alterations in Male Golden Hamsters Exposed to Chlorodibromomethane

A number of behavioral parameters in male golden hamsters ( Mesocricetus auratus) exposed to chlorodibromomethane (CDBM) were registered over a 10-day (day −9 to day 0) pretest period and a 14-day (day 1 to day 14) test period beginning at 8 weeks of age. Whereas the subchronically treated group (5 mg/kg body weight) only showed significantly increased water bottle contacts on days 4–7 compared with vehicle controls, the acutely treated group (50 mg/kg body weight) exhibited significantly increased locomotor activity on days 3–6 and decreased wheel running at day 6 until day 9. In the open field, the acutely exposed males displayed significantly more flank-mark movements at days 4 and 7 than did the vehicle control animals. After day 9, the acutely treated males showed no differences in any parameter compared with the control males, indicating recovery. During the social confrontation on day 14, the subchronically exposed males bit and approached the intruder significantly less often than did the control males, indicating an impairment of selected social behavior affected by CDBM. Our results of low-level (5 mg/kg) behavioral effects contribute to the general characterization of CDBM and suggest that tests on social capabilities in behavioral toxicology provide significant results in a field of low-level and sublethal chronic application on small samples of experimental animals.