Schedule Induced Weight Loss in Female Rats:
Recovery and Reinstatement

Kristen Hurley
Saint Anselm College
Additional Information




    Activity-based anorexia is a dangerous disorder that occurs mostly in young females.  This study attempts to answer the question of whether activity-based anorexia occurs faster, slower, or at the same pace in a reinstated trial compared to the initial trial.  The subjects included six female Sprague Dowley rats, three of which were six months old and three of which were a year old.  All of the rats were housed in Whymann Running Wheels with passages controlled by a sliding door.  To find significant differences between and within the groups in the initial and reinstated trials, independent and dependent t- tests were used.  It was found that weight loss actually occurs slower in the reinstated trial, which was opposite of what was predicted.  However, the rats ran for longer distances in the reinstated trial.  These finding can be used as a starting point for further research on activity-based anorexia and the effects of relapse.



    Activity-based anorexia can be studied in rats in order to gain a better understanding of the parallel between physical activity and anorexia in humans.  In modern Western culture thinness and activity are valued, especially for women.  Today thinness is a sign of beauty, but unfortunately, some people would go to any length to obtain the “perfect body,” which is often a body that is too thin.   If a person obsesses about his or her body image and takes steps to reduce food intake and increase exercise, anorexia could result.  Anorexia, the self-starvation eating disorder, can lead to health problems and even death.  It has been noted that anorexics tend to be restless and have a higher level of hyperactivity than those who are not anorexic (Crisp, 1972).  Excessive exercise is associated with a higher risk of an eating disorder (Epling & Pierce, 1983).   In an attempt to gain a better understanding of why this phenomenon occurs, activity- based anorexia can be induced in rats in an attempt to model how activity and anorexia are related, and apply this knowledge to humans.
     Activity-based anorexia can be induced in rats when placed under several conditions.  If rats are placed on a restricted feeding schedule and are allowed access to a running wheel, the rats will begin to consume less food and exercise excessively until the point of starvation.  It has been shown that increased physical activity interferes with food ingestion in rats (Epling & Pierce, 1991).  In other words, when rats are allowed access to a running wheel, they will actually ingest less food than a control condition where rats do not have access to a running wheel (Dwyer & Boaks, 1997).  The reason for the phenomenon of consuming less food while increasing exercise can be explored by examining several studies.  In a study by Boakes and Dwyer (1997), weight loss in rats produced by failure to adapt to a restricted feeding schedule was investigated.  Boakes and Dwyer hypothesized that rats that run excessively may fail to adapt to a restricted feeding schedule.  In the study, rats were exposed to a running wheel for two hours prior to a one and a half hour food access.  The cycle caused a decrease in food intake, increase in running, and a drop in body weight.  There was a delay before weight recovery began.  It was observed that young rats with a low initial body weight predicted a greater chance of activity-based anorexia.  The experiment concluded that activity-based anorexia is related to a failure to adapt to a new feeding schedule, which is consistent with Boakes and Dwyer’s original hypothesis.
    Hebebrand et al. (2003) compared hyperactivity in patients with anorexia nervosa and in semi starved rats.  It has been observed that mice treated with leptin will decrease body weight and increase spontaneous activity levels.  Therefore, leptin may play a direct role in increased activity.  In mice, a decreased level of serum leptin was observed as a response to food deprivation.  Leptin treatments have a reversing effect on hormonal responses to food deprivation.  However, the effects of leptin on a free feeding paradigm have shown to have minor effects on hormonal responses.  Therefore, it can be concluded that leptin may act as a starvation signal.  Rats that are food deprived and exposed to running wheels may have decreased levels of serum leptin, enforcing the role of leptin as a signal of starvation.  Therefore, leptin can represent a signal that triggers hyperactivity.  The study contained two groups, one experimental group in which the rats received leptin and one control group where no leptin was administered.  The lighting consisted of twelve hours of light and twelve hours of darkness.  Rats that were given leptin with a free feeding schedule remained active during the dark period.  During the food restriction phase, the rats were given food one hour before the dark cycle.  In the control rats, a significant increase of anticipatory behavior was noted that was associated with feeding time, which was diminished as a result of leptin infusion.  When in the dark period, the activity level of the rats was also diminished as a result of the leptin infusion.  The suppressive effects of the leptin can be observed in both the dark and light conditions.  The leptin-treated animals showed reduced semi-starvation induced hyperactivity.  However, the decrease in body weight was the equivalent to those in the control group.  The reason for this equivalency between the experimental and control groups may have to do with the tachymetabolic effect of leptin in food-restricted rats.  In food restricted mice, the metabolic rate becomes elevated to its normal level as a result of the leptin injections; however the leptin had no effect under the free feeding paradigm (Hebebrand et al.,  2003).
     Rats with semi-starvation induced hyperactivity have similar parallels to symptoms of anorexia nervosa seen in humans.  Such symptoms include food restriction, weight loss, and hyperactivity.  However, caution must be used when generalizing semi-starvation induced hyperactivity from rats to humans.  Humans with anorexia nervosa may experience drive for thinness weight phobia, and other psychopathological features that animals do not experience.  Therefore, research on this topic can be extremely helpful to gain a better understanding for the biological aspects of semi-starvation induced hyperactivity but caution must be used when generalizing findings to humans because of the psychological features that occur in anorexia nervosa patients (Hebebrand, et al., 2003).
     Several studies have focused on various aspects of activity based anorexia in rats including the injection of benzodiazepines, effects of food anticipatory behavior, and a variety of other studies.  It is important to observe the rate at which rats recover from activity induced anorexia and how quickly body mass decreases in a reinstatement as compared to the first trial.  These findings may help researchers gain a better understanding of how recovery and relapse into an anorexic state can have an effect in humans.  Many anorexics successfully recover from the disease but relapse can occur at any time during recovery.  It is important to understand what relapse in anorexia entails.  Since relapse is a prevalent possibility in individuals suffering with anorexia, it would be extremely helpful to understand the nature of how relapse compares to the initial anorexic state.  In learning more about initial relapses, hopefully future relapses can be prevented.  In this study, rats will be given access to a running wheel and will be placed on a restricted feeding schedule.  The rats will be weighed once a day and will remain on the restricted feeding schedule for a ten day period.  If the rat loses thirty percent of its body weight before the ten days are finished, the rat will be removed from the study.  After ten days the rats will be taken off the restricted feeding schedule and allowed to gain back their original body weight.  The rats will then be reinstated into the activity induced anorexic condition for ten days.  The rate at which the body mass decreases will be compared to the original condition.  This process will be conducted twice in an attempt to determine if body weight is lost faster in a reinstated trial.




    The subjects in this experiment consisted of six female Sprague Dowley rats.  Three of the rats were one year old and the remaining three rats were six months old.  All of the rats were obtained from the psychology department, which obtained the rats from Harlan Breeders in Indianapolis.  The rats were housed individually in separate cages.  All rats were allowed scheduled feedings of one hour per day and access to water at all times.  The rats were weighed at 8:15 am each morning.  The lighting schedule consisted of twelve hours of light and twelve hours of darkness.


    Six Whymann Running Wheels with odometers were used to house each rat.  The running wheels were connected to home cages with passages controlled by sliding doors.  Each of the rats was weighed individually on a standard scale, each morning.  Water was provided in bottles for each rat at all times.  The rats were kept at room temperature in the laboratory at all times.  Access to the laboratory was limited strictly to weighing and feedings to avoid interference with activity.


    Six rats were placed in cages with a running wheel attachment.  The rats had access to the running wheels at all times, except during a one hour duration feeding time.  On day one of the experiment, the rats were weighed in order to obtain an initial body weight.  The rats were then placed in their individual cages and given ad lib access to food in order to obtain baseline data.  On successive days, the rats were restricted to a one hour feeding period, from 8:15am until 9:15am.  The morning feedings of one hour continued for ten days.  If a rat lost thirty percent of its initial body weight or more, the rat was removed from the study.  After ten days the rats were placed into cages with no running wheels.  The rats were fed and allowed to gain their original body weights back.  When the rats obtained their original body weights, they were placed into the cages with the attached running wheels.  The rats were weighed and placed on the same restricted feeding schedule as the initial trial.  In this second procedure, the exact same procedure as the initial procedure was used.  Originally, the rats were supposed to be housed in the cages with the attached running wheel until each rat lost thirty percent of its original body weight.  However, due to a time restriction, the rats were not allowed to reach criterion.  Therefore, the rats were compared based on ten day time spans.  The rats were housed in the cages with the attached running wheel for ten days in the initial trial and the reinstated.  The data was based on the comparison between the initial ten days and the reinstated ten days instead of a thirty percent weight loss criterion.  One of the younger rats in the initial trial lost just under thirty percent of its original body weight at the end of the tenth day.  However, because the rat exercised excessively, the rat died.



    The hypothesis stated that the rats would lose more weight and lose it faster in the reinstatement of the experiment.  However, both t-tests indicated that there was no difference between or within the two groups or the two trials in the amount of weight that was lost.  Also, both t-tests indicated that there was no difference between the two groups or the two trials in the amount of food consumed.  Although the results for the number of revolutions between subjects were not significant, the results for the number of revolutions within subjects were significant.  This means that the rats ran a significantly greater distance in the reinstated trial compared to themselves in how far they ran in the first trial.
    Although few significant differences were found between the groups, some of the differences in the groups  results would have been more accurate with a larger sample size.  Some of the results were close to being significant, for example, the number of revolutions measured by an independent t-test equaled .074.  Perhaps with a larger sample size this difference would have proved to be significant.  This study only contained two young rats and three older rats.  The research presented can be used as a starting point in later research with a larger sample size to obtain more accurate results.



    The results of this study indicate that activity based anorexia in female rats actually does not significantly occur faster in a reinstated trial.  However, the rats did run significantly more revolutions in the second trial.  The reason the rats did not lose weight faster the second time may have to do with the fact that the rats consumed more food in the reinstated trail.  Although the difference in food intake in the reinstatement compared to the first trial did not reach statistical significance, the small sample size may have been a factor.  Therefore, if there were more subjects in the population, food intake in the reinstatement may have shown a significant increase.
    One possible confounding variable in this study may be the fact that one of the younger rats had died of activity based anorexia in the first trial.  The data for this rat could not be included in the reinstatement phase.  Therefore, the population was even smaller than at the start of the study.  The rat which was lost in the first trail had lost just under thirty-percent of its original body weight and ran almost three and a half miles in a twenty four hour period.  This amount of running was extraordinary compared to that of the rest of the rats in the sample.



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