Palatable Meal Anticipation in Mice

The ability to sense time and anticipate events is a critical skill in nature. Most efforts to understand the neural and molecular mechanisms of anticipatory behavior in rodents rely on daily restricted food access, which induces a robust increase of locomotor activity in anticipation of daily meal time. Interestingly, rats also show increased activity in anticipation of a daily palatable meal even when they have an ample food supply, suggesting a role for brain reward systems in anticipatory behavior, and providing an alternate model by which to study the neurobiology of anticipation in species, such as mice, that are less well adapted to "stuff and starve" feeding schedules. To extend this model to mice, and exploit molecular genetic resources available for that species, we tested the ability of wild-type mice to anticipate a daily palatable meal. We observed that mice with free access to regular chow and limited access to highly palatable snacks of chocolate or “Fruit Crunchies” avidly consumed the snack but did not show anticipatory locomotor activity as measured by running wheels or video-based behavioral analysis. However, male mice receiving a snack of high fat chow did show increased food bin entry prior to access time and a modest increase in activity in the two hours preceding the scheduled meal. Interestingly, female mice did not show anticipation of a daily high fat meal but did show increased activity at scheduled mealtime when that meal was withdrawn. These results indicate that anticipation of a scheduled food reward in mice is behavior, diet, and gender specific

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

Circadian Clocks for All Meal-Times: Anticipation of 2 Daily Meals in Rats

Anticipation of a daily meal in rats has been conceptualized as a rest-activity rhythm driven by a food-entrained circadian oscillator separate from the pacemaker generating light-dark (LD) entrained rhythms. Rats can also anticipate two daily mealtimes, but whether this involves independently entrained oscillators, one ‘continuously consulted’ clock, cue-dependent non-circadian interval timing or a combination of processes, is unclear. Rats received two daily meals, beginning 3-h (meal 1) and 13-h (meal 2) after lights-on (LD 14∶10). Anticipatory wheel running began 68±8 min prior to meal 1 and 101±9 min prior to meal 2 but neither the duration nor the variability of anticipation bout lengths exhibited the scalar property, a hallmark of interval timing. Meal omission tests in LD and constant dark (DD) did not alter the timing of either bout of anticipation, and anticipation of meal 2 was not altered by a 3-h advance of meal 1. Food anticipatory running in this 2-meal protocol thus does not exhibit properties of interval timing despite the availability of external time cues in LD. Across all days, the two bouts of anticipation were uncorrelated, a result more consistent with two independently entrained oscillators than a single consulted clock. Similar results were obtained for meals scheduled 3-h and 10-h after lights-on, and for a food-bin measure of anticipation. Most rats that showed weak or no anticipation to one or both meals exhibited elevated activity at mealtime during 1 or 2 day food deprivation tests in DD, suggesting covert operation of circadian timing in the absence of anticipatory behavior. A control experiment confirmed that daytime feeding did not shift LD-entrained rhythms, ruling out displaced nocturnal activity as an explanation for daytime activity. The results favor a multiple oscillator basis for 2-meal anticipatory rhythms and provide no evidence for involvement of cue-dependent interval timing

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 (Tb) 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 Tb rhythms. During the daytime feeding schedule, all rats exhibited food anticipatory activity and Tb 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

Circadian adaptations to meal timing: Neuroendocrine mechanisms

Circadian rhythms of behavior and physiology are generated by central and peripheral circadian oscillators entrained by periodic environmental or physiological stimuli. A master circadian pacemaker in the hypothalamic suprachiasmatic nucleus is directly entrained by daily light-dark cycles, and coordinates the timing of other oscillators by direct and indirect neural, hormonal and behavioral outputs. The daily rhythm of food intake provides stimuli that entrain most peripheral and central oscillators, some of which can drive a daily rhythm of food anticipatory activity if food is restricted to one daily mealtime. The location of food-entrainable oscillators (FEOs) that drive food anticipatory rhythms, and the food-related stimuli that entrain these oscillators, remain to be clarified. Here, we critically examine the role of peripheral metabolic hormones as potential internal entrainment stimuli or outputs for FEOs controlling food anticipatory rhythms in rats and mice. Hormones for which data are available include corticosterone, ghrelin, leptin, insulin, glucagon, and glucagon-like peptide 1. All of these hormones exhibit daily rhythms of synthesis and secretion that are synchronized by meal timing. There is some evidence that ghrelin and leptin modulate the expression of food anticipatory rhythms, but none of the hormones examined so far are necessary for entrainment. Ghrelin and leptin likely modulate food-entrained rhythms by actions in hypothalamic circuits utilizing melanocortin and orexin signaling, although again food-entrained behavioral rhythms can persist in lesion and gene knockout models in which these systems are disabled. Actions of these hormones on circadian oscillators in central reward circuits remain to be evaluated. Food-entrained activity rhythms are likely mediated by a distributed system of circadian oscillators sensitive to multiple feeding related inputs. Metabolic hormones appear to play a modulatory role within this system

Scheduled feeding restores memory and modulates c-Fos expression in the suprachiasmatic nucleus and septohippocampal complex

Disruptions in circadian timing impair spatial memory in humans and rodents. Circadian-arrhythmic Siberian hamsters (Phodopus sungorus) exhibit substantial deficits in spatial working memory as assessed by a spontaneous alternation (SA) task. The present study found that daily scheduled feeding rescued spatial memory deficits in these arrhythmic animals. Improvements in memory persisted for at least 3 weeks after the arrhythmic hamsters were switched back to ad libitum feeding. During ad libitum feeding, locomotor activity resumed its arrhythmic state, but performance on the SA task varied across the day with a peak in daily performance that corresponded to the previous daily window of food anticipation. At the end of scheduled feeding, c-Fos brain mapping revealed differential gene expression in entrained versus arrhythmic hamsters in the suprachiasmatic nucleus (SCN) that paralleled changes in the medial septum and hippocampus, but not in other neural structures. These data show that scheduled feeding can improve cognitive performance when SCN timing has been compromised, possibly by coordinating activity in the SCN and septohippocampal pathway.National Institute of Mental Health [MH095837]; Science Foundation Arizona (SFAz); BIO5 Institute at the University of ArizonaThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Diagrammatic representation of experiments.

<p>“Experiment #1” comprises conditions used at Simon Fraser University measuring activity mainly with running wheels and “Experiment #2” comprises conditions used at Caltech using computer vision to assess activity. Days of treatments are indicated as numbers below the colored bars, red represented calorie restriction, blue for fruit crunchies, brown for chocolate, white for no treatment, and yellow for high fat diet. For experiment #1, mice were fed the palatable snack from ZT4-6. For experiment #2, male mice were provided with the palatable snack at ZT10 and the snack was not removed; for female mice the snack was presented at ZT7. RF, restricted feeding; CR, calorie restriction.</p

Body weight, food intake, and caloric intake of female mice in Experiment 2.

<p>(A) The mean (± SEM) body weight of female mice receiving 0.8 g of high fat daily (yellow) and their respective controls (blue). (B) Female mice fed high fat show a significant decrease in normal chow intake in comparison to mice with ad libitum access. (C) Female mice fed high fat show a significant decrease in total caloric intake in comparison to mice with <i>ad libitum</i> access. Caloric intake values were estimated from nutritional facts provided by the manufacturers. (D) The percent of total caloric intake per day provided by the palatable meal. Unpaired t-test * denotes p<0.05, ** denotes p<0.01, and *** denotes p<0.001.</p

Home cage activity and food bin entry of female mice in Experiment 2 during palatable meal access and withdrawal.

<p>(A) The fraction of all recorded frames within a 24 hour period during which the female mice were walking, hanging, jumping, or rearing. There were no significant differences in the fraction of frames during which the female mice exhibited high intensity activity. (B) The total seconds of walking, hanging, jumping, and rearing during the 2 h before the palatable meal is received. There is no significant difference between the female mice receiving a once-daily palatable meal and controls. (C) For each individual mouse the sum of the total seconds of walking, hanging, jumping, and rearing during the 2 h before the palatable meal is delivered divided by the total seconds of walking, hanging, jumping, and rearing during both recording periods within a 24 hour window. There is no significant difference between the female mice receiving a once-daily palatable meal and those that are disturbed by a pellet of normal chow. (D) The fraction of all recorded frames within a 24 h period during which the female mice inserted their nose into the food bin. The mice spent significantly less time with their nose in the food bin on all recorded days (day 0, 7, 14, 21, and 28) with the exception of the second day of withdrawal of the palatable meal. (E) The total seconds of food bin entry during the 2 h before the palatable meal is received. There is no significant difference between the female mice receiving a once-daily palatable meal and those that are disturbed by a pellet of normal chow. (F) For each individual mouse the sum of the total seconds of food bin entry during the 2 h before the palatable meal is divided by the total seconds of food bin entry during both recording periods within a 24 h window. There is only a significant difference between the female mice receiving a once-daily palatable meal and those that are disturbed by a pellet of normal chow on day 21 of the special feeding regimen. (G) The total sum of seconds of walking, hanging, jumping, or rearing observed during each hour of the 48 hour high fat withdrawal. Shaded boxes represent lights off; arrows represent expected meal time. (H) Sum of high intensity activity during the two hours following expected palatable treat access on day 1 and 2 of withdrawal. High fat entrained mice show more high intensity activity than ad libitum controls on both days of the withdrawal. (I) Total sum of seconds of food bin entry observed during each hour of the 48 hour high fat withdrawal. Shaded boxes represent lights off; arrows represent expected meal time. (J) Sum of food bin entry during the two hours following expected palatable treat access on day 1 and 2 of withdrawal. High fat entrained mice show more food bin entry than ad libitum controls on both days of the withdrawal, although it is only significantly greater on the second day. Arrows indicate the bin in which palatable meal would have been delivered. Bars show medians and interquartile ranges; the statistical test used was Mann-Whitney where * denotes p<0.05, ** denotes p<0.01, and *** denotes p<0.001. Note that no palatable meals were administered on day 28 and 29 (equivalent to withdrawal days 1 and 2), but all mice retained ad libitum access to food and water.</p