Anticipatory Activity Rhythms Research Articles

Food as circadian time cue for appetitive behavior.

Feeding schedules entrain circadian clocks in multiple brain regions and most peripheral organs and tissues, thereby synchronizing daily rhythms of foraging behavior and physiology with times of day when food is most likely to be found. Entrainment of peripheral clocks to mealtime is accomplished by multiple feeding-related signals, including absorbed nutrients and metabolic hormones, acting in parallel or in series in a tissue-specific fashion. Less is known about the signals that synchronize circadian clocks in the brain with feeding time, some of which are presumed to generate the circadian rhythms of food-anticipatory activity that emerge when food is restricted to a fixed daily mealtime. In this commentary, I consider the possibility that food-anticipatory activity rhythms are driven or entrained by circulating ghrelin, ketone bodies or insulin. While evidence supports the potential of these signals to participate in the induction or amount of food-anticipatory behavior, it falls short of establishing either a necessary or sufficient role or accounting for circadian properties of anticipatory rhythms. The availability of multiple, circulating signals by which circadian oscillators in many brain regions might entrain to mealtime has supported a view that food-anticipatory rhythms of behavior are mediated by a broadly distributed system of clocks. The evidence, however, does not rule out the possibility that multiple peripheral and central food-entrained oscillators and feeding-related signals converge on circadian oscillators in a defined location which ultimately set the phase and gate the expression of anticipatory activity rhythms. A candidate location is the dorsal striatum, a core component of the neural system which mediates reward, motivation and action and which contains circadian oscillators entrainable by food and dopaminergic drugs. Systemic metabolic signals, such as ghrelin, ketones and insulin, may participate in circadian food anticipation to the extent that they modulate dopamine afferents to circadian clocks in this area.

Cryptochrome-dependent circadian periods in the arcuate nucleus

The circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus is responsible for controlling behavioral activity rhythms, such as a free running rhythm in constant darkness. Rodents have several circadian oscillators in other brain regions including the arcuate nucleus (ARC). In specific conditions such as food anticipatory activity rhythms in the context of timed restricted feeding, an alternative circadian pace-making system has been assumed by means of circadian oscillators like the SCN. Despite extensive lesion studies, the anatomic locations of extra-SCN circadian pacemakers responsible for regulating behavioral rhythms have not been found. In the present study, we investigated circadian rhythms in the SCN and extra-SCN region of the arcuate nucleus (ARC) by analyzing PER2::LUCIFERASE expression in specific regions from wild-type C57BL/6, Cry1−/−, and Cry2−/− mice. Compared to wild-type animals, we observed period shortening in both the SCN and ARC of Cry1−/− mice and period lengthening in Cry2−/− mice. Interestingly, the periods in the ARC of both genotypes were identical to those in the SCN. Moreover, the amplitudes of PER2::LUC rhythms in the ARC of all animals were decreased compared to those in the SCN. These data suggest that the ARC is a candidate circadian pacemaker outside the SCN.

Dopaminergic regulation of circadian food anticipatory activity rhythms in the rat.

Circadian activity rhythms are jointly controlled by a master pacemaker in the hypothalamic suprachiasmatic nuclei (SCN) and by food-entrainable circadian oscillators (FEOs) located elsewhere. The SCN mediates synchrony to daily light-dark cycles, whereas FEOs generate activity rhythms synchronized with regular daily mealtimes. The location of FEOs generating food anticipation rhythms, and the pathways that entrain these FEOs, remain to be clarified. To gain insight into entrainment pathways, we developed a protocol for measuring phase shifts of anticipatory activity rhythms in response to pharmacological probes. We used this protocol to examine a role for dopamine signaling in the timing of circadian food anticipation. To generate a stable food anticipation rhythm, rats were fed 3h/day beginning 6-h after lights-on or in constant light for at least 3 weeks. Rats then received the D2 agonist quinpirole (1 mg/kg IP) alone or after pretreatment with the dopamine synthesis inhibitor α-methylparatyrosine (AMPT). By comparison with vehicle injections, quinpirole administered 1-h before lights-off (19h before mealtime) induced a phase delay of activity onset prior to the next meal. Delay shifts were larger in rats pretreated with AMPT, and smaller following quinpirole administered 4-h after lights-on. A significant shift was not observed in response to the D1 agonist SKF81297. These results provide evidence that signaling at D2 receptors is involved in phase control of FEOs responsible for circadian food anticipatory rhythms in rats.

Scheduled Daily Mating Induces Circadian Anticipatory Activity Rhythms in the Male Rat

Daily schedules of limited access to food, palatable high calorie snacks, water and salt can induce circadian rhythms of anticipatory locomotor activity in rats and mice. All of these stimuli are rewarding, but whether anticipation can be induced by neural correlates of reward independent of metabolic perturbations associated with manipulations of food and hydration is unclear. Three experiments were conducted to determine whether mating, a non-ingestive behavior that is potently rewarding, can induce circadian anticipatory activity rhythms in male rats provided scheduled daily access to steroid-primed estrous female rats. In Experiment 1, rats anticipated access to estrous females in the mid-light period, but also exhibited post-coital eating and running. In Experiment 2, post-coital eating and running were prevented and only a minority of rats exhibited anticipation. Rats allowed to see and smell estrous females showed no anticipation. In both experiments, all rats exhibited sustained behavioral arousal and multiple mounts and intromissions during every session, but ejaculated only every 2–3 days. In Experiment 3, the rats were given more time with individual females, late at night for 28 days, and then in the midday for 28 days. Ejaculation rates increased and anticipation was robust to night sessions and significant although weaker to day sessions. The anticipation rhythm persisted during 3 days of constant dark without mating. During anticipation of nocturnal mating, the rats exhibited a significant preference for a tube to the mating cage over a tube to a locked cage with mating cage litter. This apparent place preference was absent during anticipation of midday mating, which may reflect a daily rhythm of sexual reward. The results establish mating as a reward stimulus capable of inducing circadian rhythms of anticipatory behavior in the male rat, and reveal a critical role for ejaculation, a modulatory role for time of day, and a potential confound role for uncontrolled food intake.

Evidence for Time-of-Day Dependent Effect of Neurotoxic Dorsomedial Hypothalamic Lesions on Food Anticipatory Circadian Rhythms in Rats

The dorsomedial hypothalamus (DMH) is a site of circadian clock gene and immediate early gene expression inducible by daytime restricted feeding schedules that entrain food anticipatory circadian rhythms in rats and mice. The role of the DMH in the expression of anticipatory rhythms has been evaluated using different lesion methods. Partial lesions created with the neurotoxin ibotenic acid (IBO) have been reported to attenuate food anticipatory rhythms, while complete lesions made with radiofrequency current leave anticipatory rhythms largely intact. We tested a hypothesis that the DMH and fibers of passage spared by IBO lesions play a time-of-day dependent role in the expression of food anticipatory rhythms. Rats received intra-DMH microinjections of IBO and activity and body temperature (T b) rhythms were recorded by telemetry during ad-lib food access, total food deprivation and scheduled feeding, with food provided for 4-h/day for 20 days in the middle of the light period and then for 20 days late in the dark period. During ad-lib food access, rats with DMH lesions exhibited a lower amplitude and mean level of light-dark entrained activity and T b rhythms. During the daytime feeding schedule, all rats exhibited food anticipatory activity and T b rhythms that persisted during 2 days without food in constant dark. In some rats with partial or total DMH ablation, the magnitude of the anticipatory rhythm was weak relative to most intact rats. When mealtime was shifted to the late night, the magnitude of the food anticipatory activity rhythms in these cases was restored to levels characteristic of intact rats. These results confirm that rats can anticipate scheduled daytime or nighttime meals without the DMH. Improved anticipation at night suggests a modulatory role for the DMH in the expression of food anticipatory activity rhythms during the daily light period, when nocturnal rodents normally sleep.

Effects of Medial Hypothalamic Lesions on Feeding-Induced Entrainment of Locomotor Activity and Liver Per2 Expression in Per2::luc Mice

Restricted feeding induces anticipatory activity rhythm and also entrains the peripheral circadian clocks, although the underlying brain mechanisms have not been fully elucidated. The dorsomedial hypothalamus (DMH) has been implicated in the regulation of restricted feeding-induced anticipatory activity rhythms (FAA), but the role of the DMH in restricted feeding- induced entrainment of peripheral circadian clocks is still unknown. In the present study, the role of the DMH in entrainment of the peripheral circadian clock was examined using Per2::luciferase knock-in mice. The results indicate that lesions that destroy the large mediobasal hypothalamic (MBH) lesions destroying the DMH, ventrolateral hypothalamus (VMH), and arcuate nucleus (ARC) significantly reduce daily locomotor activity rhythms and FAA formation. In addition, these lesions phase advanced the peak of liver Per2 expression by 2 h when compared to sham-operated mice. Following the administration of MBH lesions, the animals run less and start later in the restricted feeding- induced FAA rhythm but do not have any alterations in the restricted feeding- induced phase shift of the liver Per2 rhythm. These results demonstrate that the hypothalamus, including the MBH, is an important brain area for maintaining the locomotor rhythm and FAA formation. However, it is not necessary for restricted feeding-induced entrainment of the liver clock.

Phenotyping Food Entrainment: Motion Sensors and Telemetry Are Equivalent

Rats can anticipate a daily meal by entrainment of a circadian timekeeping mechanism that is anatomically separate from the light-entrainable circadian pacemaker located in the suprachiasmatic nucleus. The dorsomedial nucleus of the hypothalamus (DMH) has been claimed to be critical for the expression of circadian rhythms of food anticipatory activity, but efforts to confirm this finding have so far failed. Failure to confirm that DMH ablation disrupts or eliminates food anticipatory rhythms has been attributed to the use of overhead motion sensors rather than telemetry to measure locomotor activity. To examine the relationship between motion sensor and telemetric measures of locomotor activity, transponders were implanted into the peritoneal cavity of adult male rats, and activity was recorded continuously by both telemetry and infrared motion sensors. Activity counts were approximately 4 fold higher as detected by telemetry, but normalized activity patterns were virtually identical for the two measures during ad-lib food access, 4 h/day food restriction and total food deprivation after food restriction. Overhead motion sensors and telemetry are equivalent measures of food anticipatory activity in rats. Telemetry is an effective tool for continuous recording of body temperature but has no advantages over infrared motion sensors for measuring food anticipatory activity rhythms.

Lack of Food Anticipation in Per2 Mutant Mice

Predicting time of food availability is key for survival in most animals. Under restricted feeding conditions, this prediction is manifested in anticipatory bouts of locomotor activity and body temperature. This process seems to be driven by a food-entrainable oscillator independent of the main, light-entrainable clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus . Although the SCN clockwork involves self-sustaining transcriptional and translational feedback loops based on rhythmic expression of mRNA and proteins of clock genes , the molecular mechanisms responsible for food anticipation are not well understood. Period genes Per1 and Per2 are crucial for the SCN's resetting to light . Here, we investigated the role of these genes in circadian anticipatory behavior by studying rest-activity and body-temperature rhythms of Per1 and Per2 mutant mice under restricted feeding conditions. We also monitored expression of clock genes in the SCN and peripheral tissues. Whereas wild-type and Per1 mutant mice expressed regular food-anticipatory activity, Per2 mutant mice did not show food anticipation. In peripheral tissues, however, phase shifts of clock-gene expression in response to timed food restriction were comparable in all genotypes. In conclusion, a mutation in Per2 abolishes anticipation of mealtime, without interfering with peripheral synchronization by feeding cycles.

Restricted-feeding-induced anticipatory activity rhythm is associated with a phase-shift of the expression of mPer1 and mPer2 mRNA in the cerebral cortex and hippocampus but not in the suprachiasmatic nucleus of mice.

Daily restricted feeding (RF) can produce food-entrainable oscillations in both intact and suprachiasmatic nucleus (SCN)-lesioned animals. Thus, there are two circadian rhythms, one of which is SCN-dependent and the other SCN-independent. Recently, it has been established that several mouse clock genes, such as mPer1, mPer2 and mPer3 are expressed in the SCN and other brain tissues. Although the role of mPer genes expressed in the SCN has recently been evaluated in the SCN-dependent rhythm, their function in the SCN-independent rhythm is still poorly understood. In order to understand the role of these genes in SCN-independent rhythm, we examined the expression pattern of mPer1 and mPer2 mRNA in each brain area of mice under RF. Mice were allowed access to food for 4 h during either the daytime under a light-dark cycle or the subjective daytime under constant dark. After 6 days of scheduled RF, the night-time or subjective night-time peak of mPer mRNA changed to a daytime peak in the cerebral cortex and hippocampus, with moderate expression in the striatum, pyriform cortex and paraventricular nucleus, and no expression in the SCN. The daytime peak in the cerebral cortex returned to a night-time peak after the release of RF to a free-feeding schedule. Although the basal rhythm of mPer expression disappeared in SCN-lesioned mice, RF produced mPer mRNA rhythm in the cerebral cortex of these mice. The present results provide evidence of an association between food-entrainable oscillations and the expression of mPer1 and mPer2 in the cerebral cortex and hippocampus.

Neonatal monosodium glutamate alters circadian organization of feeding, food anticipatory activity and photic masking in the rat

In rodents, parenteral administration of monosodium glutamate (MSG) induces marked degeneration of the retina and arcuate nucleus (AN) and disrupts daily rhythms of food intake. We quantified the effects of neonatal MSG (2 mg/g SC, postnatal days 1, 3, 5, 7, 9) on the expression of feeding and activity rhythms in adult rats under schedules of light–dark (LD), constant dark (DD), restricted daily feeding and total food deprivation. AN lesions were confirmed by neuropeptide Y (NPY) immunocytochemistry and Nissl stain. Compared to age-matched control rats, the amplitude (quantified as LD ratios) of daily food intake and food-bin activity rhythms was significantly attenuated in MSG rats in LD 12:12 and on the first day of DD. Control rats, but not MSG rats, showed lower amplitude rhythms in DD compared to LD. The phase angle of feeding and activity rhythms did not differ between groups in either condition. In a short LD cycle (2:2), control rats, but not MSG rats, showed significant inhibition (masking) of activity during the 2 h light periods. When food access was restricted to a 4 h daily meal, MSG rats showed enhanced expression and persistence of food-entrained anticipatory activity rhythms by comparison with control rats. These results indicate that attenuation of daily feeding rhythms in MSG rats is due in part to loss of direct inhibitory effects of light on behavior, and that the AN likely modulates, but does not mediate entrainment of feeding-related rhythms to daily cycles of LD or food access.

P–477 - Aniracetam ameliorates food-motivated anticipatory activity rhythm impaired in aged rats

P–477 - Aniracetam ameliorates food-motivated anticipatory activity rhythm impaired in aged rats

Aging impairs methamphetamine-induced free-running and anticipatory locomotor activity rhythms in rats

In the present experiment, under drinking of 0.01% methamphetamine (MA), young rats exhibited free-running locomotor rhythm ranging from 24.6 to 30.9 h period under light-dark cycle. In contrast, 24-month-old rats showed a low activity and did not exhibit MA-induced free-running rhythm. When MA was injected at a fixed time of day (14:00), young rats exhibited intense locomotor activity from 1–2 h before drug-injection time. This preinjection activity was still detected on the withdrawal day. In addition, intense locomotor activity was observed for 12:00–17:00, even on the withdrawal day (MA-associated anticipatory activity). Thus, MA-associated activity of the withdrawal day became an another good index for MA anticipatory activity rhythms whereas old rats did not exhibit this anticipatory activity. The present study suggests that aging strongly impairs the manifestation of MA-induced free-running and anticipatory activity rhythms in rats.

P-660 - Involvement of dopamine D1 and NMDA receptor mechanisms in methamphetamine-induced anticipatory activity rhythm.

P-660 - Involvement of dopamine D1 and NMDA receptor mechanisms in methamphetamine-induced anticipatory activity rhythm.

Anticipatory activity rhythms under daily schedules of water access in the rat.

Rats anticipate a fixed daily feeding time by entrainment of a component of their multioscillatory circadian system. The range of stimuli capable of entraining this component is little studied. Previous studies suggest that restricted water access is not an effective entrainment stimulus, as measured by general locomotion. The present study re-examined the issue, using two other measures of activity: wheel running and activity at a food-water delivery bin. Rats restricted to 1 hr of water each day in the middle of the light and to food in the 12-hr dark period showed no anticipation of this event in the wheel-running measure, but some rats did show anticipation in the delivery bin activity measure. Rats (bin activity measure only) restricted to 1 hr of water and 1 hr of food separated by intervals of 7, 10, or 12 hr, in either the light or the dark, showed consistent anticipation of food access time but little or no anticipation of water access time. Water access time also did not sustain food anticipatory rhythms in animals whose food-water schedules were reversed. However, deprivation of water or of both food and water for 72 or 90 hr was usually associated with specific increases in bin activity at both the usual feeding and drinking times. Water access, like food, appears to provide cues capable of entraining an anticipatory circadian mechanism. Differences in the type and amount of anticipatory activity preceding these events may reflect differences in the strengths of the two entrainment cues and/or in the activity levels or specific behavioral strategies promoted by hunger and thirst.

Palatable daily meals entrain anticipatory activity rhythms in free-feeding rats: Dependence on meal size and nutrient content

Circadian wheel-running rhythms were monitored continuously in 3 groups of female Sprague-Dawley rats under different palatable food availability schedules. All rats had free access to standard rat chow and water throughout the study. In addition, Group 1 rats received a palatable nutrient-rich mash for 2 hr each day for 28 days, beginning 3 hr after light onset of a 12:12 LD cycle. Group 2 rats received the same mash but were limited to 4 g daily. Group 3 rats received a palatable non-nutritive mash. Ten of 13 Group 1 rats, 2 of 13 Group 2 rats, and 0 of 13 Group 3 rats showed anticipatory running prior to the daily palatable meal. Palatable mash intake was generally lower among Group 3 rats than among Group 1 rats. However, several Group 3 rats consumed non-nutritive mash in amounts which equalled or exceeded the nutritive mash intake of Group 1 rats showing anticipatory running. The results indicate that temporally limited daily access to a palatable food can entrain anticipatory wheel-running in rats that are not food-deprived. They also indicate that entrainment to periodic food availability depends on stimuli associated with the concentrated intake of nutrients rather than on the absolute size or palatability of a meal.