Free-access to a running wheel shortens the period of free-running rhythm in blinded rats

The limbic system and food-anticipatory circadian rhythms in the rat: ablation and dopamine blocking studies

Rats behaviorally anticipate a fixed, daily opportunity to feed by entrainment of circadian oscillators that are physically separate from the light-entrainable circadian pacemaker that has been localized to the suprachiasmatic nucleus. Neural substrates mediating food-entrained rhythms are unknown. A variety of anatomical and functional observations suggest possible involvement of the limbic system and its dopaminergic component in the regulation of these rhythms. To test this hypothesis, the activity rhythms of rats bearing large, combined ablations of the hippocampus and amygdala or nucleus accumbens and medical forebrain anterior to the thalamus were examined under ad-lib feeding, 2 h daily feeding, and total food deprivation conditions. Some hippocampal-ablated rats showed alterations of free-running rhythms under ad-lib feeding, but none of the ablations impaired the rats' ability to anticipate daily feeding, or 'remember' the phase of feeding time during subsequent food deprivation. Additional groups of intact rats were treated with the dopamine antagonist haloperidol (0.3 mg/kg or 2.0 mg/kg) 30 min prior to daily feeding, but this also did not prevent the emergence of food-entrained rhythms. The limbic and dopamine systems do not appear to play a necessary role in the generation or entrainment of food-anticipatory circadian rhythms.

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.

Influence of running wheel activity on free-running sleep/wake and drinking circadian rhythms in mice

Previous studies have indicated that manipulation of activity levels can modify characteristics of sleep/wake and activity rhythms. The generality of these observations was evaluated by simultaneously measuring drinking and sleep/wake rhythms while mice had free or no access to a running wheel in constant conditions (DD). Robust circadian rhythms in all parameters were observed in the "wheel free" (unrestricted) condition. When wheels were locked, the peak amplitude of the sleep/wake circadian rhythm decreased by approximately 50% without affecting the amplitude of the drinking rhythm. Total wake time decreased 11% per circadian day when wheels were locked with increases in both NREM and REM sleep. Whereas the amplitude of the drinking waveform was unaffected, wheel restriction caused an equivalent increase in period length (tau) for both rhythms. These results indicate that, unlike the generalized effects of activity on tau, activity restriction influences on rhythm amplitude do not generalize to all behavioral and/or physiological variables. This work also supports the notion that activity influences on sleep/wake rhythm amplitude reflect behavioral "masking" rather than a fundamental change in the direct coupling mechanisms of the biological clock.

The effects of short periods of immobilization on the hamster circadian clock

Recent findings indicate that stimuli which induce an acute increase in locomotor activity can induce phase shifts in the circadian clock of hamsters. Support for the actual role of the acute increase in activity in the mediation of these phase shifts is provided by the observation that immobilization can totally block phase shifts in the activity rhythm that are normally induced in response to exposure to two of these stimuli, either a pulse of darkness or an injection of a benzodiazepine. In order to further examine the effects of immobilization on the circadian system of hamsters, 3 studies were carried out. In a first study, the effects of a 3-h period of immobilization procedure on the phase of the free running circadian rhythm of locomotor activity were tested at 8 different circadian times. Immobilization during the highly active part of the animal's activity cycle resulted in phase delays in the activity rhythm, while immobilization at other circadian times had little or no effect on the circadian time-keeping system. In two other studies, we reported that immobilization had no effect on phase shifts normally induced by 3-h pulses of light or injections of the protein synthesis inhibitor, cycloheximide, two stimuli that are clearly not associated with an increase in locomotor activity in hamsters. Thus, the ability of immobilization to block stimulus-induced phase shifts in the circadian clock appears to be specific to those stimuli that induce an acute increase in locomotor activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Methamphetamine effects on rat circadian clock depend on actograph

Methamphetamine effects on the rest-activity rhythm were examined in 12 blinded rats using two different actographs, an Animex and a running-wheel. D-Methamphetamine was administered chronically by dissolving it in drinking water. During methamphetamine treatment, the rest-activity rhythm measured by an Animex showed a clear sign of relative coordination in addition to the general enhancement of activity level. Analyses of pre- and posttreatment activity rhythms revealed that neither the phase nor the period was affected by methamphetamine treatment. On the other hand, the circadian period was lengthened by methamphetamine treatment when locomotor activity was measured by a running-wheel. These results confirmed our previous findings that the chronic treatment of methamphetamine modified the expression of the circadian rhythms but did not affect the underlying oscillation when measured by an Animex, and further indicated that methamphetamine could affect the underlying oscillation when rats had free access to a running-wheel. It is concluded that the effects of methamphetamine on the circadian clock depend on actograph.

Motor activity correlates negatively with free-running period, while positively with serotonin contents in SCN in free-running rats

Free-running period of blinded rats kept in a cage with a running wheel varied markedly, while it varied little in rats kept in a cage without a running wheel. The mean free-running period of the former group is significantly shorter than that of the latter. In the former, the free-running period correlated negatively with motor activity, indicating that activity affects the free-running period. In both groups, essentially similar diurnal patterns of biogenic amines and their metabolites were observed in various discrete areas in the brain examined. However, there was a significant difference between the two groups in several areas. In the SCN, 5-HT content correlated positively with motor activity, consequently correlated negatively to the free-running period at 3 out of 4 sampling times over 24 h but no such correlation was observed in other monoamines and their metabolites examined. These facts suggest that 5-HT may be associated with modification of the free-running period.

Location of the suprachiasmatic nucleus grafts in rats which restored circadian rhythmicity after transplantation

In Wistar male rats whose circadian wheel running activity rhythms were disrupted by bilateral suprachiasmatic nuclei (SCN) lesions, transplantation of neonatal rat SCN into the 3rd ventricle was performed. Out of 49 rats from which adequate wheel running activity records were obtained, 15 rats showed restoration of circadian rhythm starting 2 to 13 weeks (average 1 month) after transplantation. The existence of active SCN neurons in the graft was shown by immunocytochemical reactivity to vasopressin- and VIP-like substances. In all rats, effective grafts were found in the diencephalon, mostly on the wall of the 3rd ventricle.

Relationship between free-running period and motor activity in blinded rats

The free-running rhythms of motor activity in blinded rats were measured by two different devices, an Automex or a running wheel. The period of free-running rhythm measured by a running wheel was likely to be shorter than that measured by an Automex, indicating that subtle environmental difference, such as whether a cage is equipped with a wheel or not, can affect the free-running period. In addition, we found a negative correlation not only between the free-running period measured by a running wheel and that measured by an Automex, but between the free-running period and the number of wheel revolutions per day. This is the first evidence that motor activity, other than the external factors such as light intensity and temperature, may be related to change in the free-running period.

Effects of chronic clonidine administration and withdrawal on free-running circadian activity rhythms

This study examined the effects of the alpha 2-adrenergic agonist clonidine on free-running circadian activity rhythms in rats, using a dosing regimen similar to one previously shown to induce behavioral depression in the swim test. In constant light, clonidine consistently shortened the free-running circadian period, reduced circadian amplitude, and reduced the overall level of locomotor activity. These effects were reversed after the termination of clonidine treatment. In constant darkness, clonidine reduced circadian amplitude, but both increases and decreases in free-running period and activity level were observed. Clonidine-induced changes in free-running period and activity level were systematically related to individual differences in baseline activity in both constant light and constant darkness. These results demonstrate that clonidine can alter both the rhythmicity and the level of spontaneous activity, and are consistent with the hypothesis that monoaminergic systems may mediate relationships between behavioral state and circadian rhythmicity.

Methamphetamine induced locomotor rhythm entrains to restricted daily feeding in SCN lesioned rats

Rats were lesioned in the SCN and treated with methamphetamine dissolved in drinking water. A robust rhythm appeared in spontaneous locomotor activity which was not affected by blinding. Periodic food restriction (RF) of a 24 hr period was imposed on SCN lesioned rats with free-access to food for 4 or 6 hr per day, while water was given ad lib. The locomotor rhythm induced by methamphetamine treatment was phase-set by RF immediately in most cases but with transients in some. The phase-angle difference (psi) between food presentation and the activity onset became more negative by increasing the dose of methamphetamine. Because there was a positive correlation between methamphetamine dose and the period of locomotor rhythm, the change in psi was most likely due to lengthening of the period. After the termination of the RF schedule, the locomotor rhythm started to free-run from the prior phase set by RF. These results indicate that the methamphetamine dependent locomotor rhythm entrains to RF.

Effect of running wheel availability on circadian patterns of sleep and wakefulness in mice

Sleep/wake expression in mice varies predictably with circadian phase. Such circadian rhythms are known to depend on intact suprachiasmatic nuclei (SCN) in the hypothalamus, but the mechanism by which SCN activity modulates sleep/wake expression is unknown. This paper examines the possibility that circadian patterns of sleep/wake derive partly from circadian timing of waking behaviors that are incompatible with sleep, such as locomotor activity. Voluntary locomotor activity was restricted in five mice adapted to a running wheel by locking the wheel in place. Continuous electrographic monitoring of sleep and wakefulness over multiple circadian cycles revealed: (1) during the active phase, shorter wake bouts and more frequent bouts of sleep, resulting in greater sleep/wake fragmentation and more time spent asleep; (2) during the rest phase, a small compensatory reduction in NREM sleep; (3) reduced amplitude of circadian sleep/wake rhythms and a greater amount of sleep overall. Thus, voluntary locomotor activity has an important influence on sleep/wake expression in mice, and the normal circadian pattern of sleep/wake depends on circadian timing of activity. Previous reports of damped circadian sleep/wake rhythms in rodents may therefore be explained by coincident diminutions in locomotor activity associated with age or health status. Our results also support analogous findings in human subjects, and we propose that elderly humans may benefit from therapies that augment daytime activity.