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Effect of deprivation and time of refeeding on food intake
Physiology and Behavior, Vol. 14, pp. 43-46. Brain Research Publications Inc., 1975. Printed in the U.S.A.
Effect of Deprivation and Time of Refeeding on Food Intake L. L. BELLINGER AND V. E. MENDEL
Department o f Animal Science, University o f California Davis, California 95616
(Received 19 July 1974) BELLINGER, L. L. AND V. E. MENDEL. Effect of deprivation and time of refeeding on food intake. PHYSIOL. BEHAV. 14(1) 43-46, 1975. - T h e amount of food eaten in a two hour trial by male Sprague Dawley rats was recorded after periods of food deprivation up to 42 hr in length. Rats ate 50-78% more when refed during the dark phase than when refed during the light phase. This occurred even when light fed animals were fasted for longer periods than the dark fed animals. Rats eat in a rhythmic pattern after deprivation. These data are in good agreement with data previously reported and extend it by increasing the number of observations, increasing the length of deprivation, and comparing different age groups. Rats
Feeding behavior
Circadian
Deprivation
MUCH animal behavior is subject to rhythmic control by some internal clock. Just where the clock is located or how it operates is not fully understood [18,19] ; however, there is some evidence that an area which controls rhythmic drinking behavior, locomotor activity and corticosterone secretion patterns is situated in the suprachiasmatic nucleus of the hypothalamus [14,25]. Some rhythmic behavior is associated with environmental changes, such as the l i g h t dark cycle. One behavior that is closely correlated to the l i g h t - d a r k cycle is that of eating and drinking in the rat [2, 17, 23, 24, 26]. Rats that are fed and watered ad lib tend to eat the majority of their food and water during the dark phase of their day [2, 17, 23, 26]. The exact nature of what drives this l i g h t - d a r k feeding behavior and triggers the animals to start eating as soon as the lights go out is not entirely clear. Animals that have been meal-fed for long periods during the light phase will revert to a normal feeding pattern when fed and watered ad lib; the reversion requires about 9 to 10 days [8]. Rats that are subjected to a reversal of their light-dark cycle begin to eat during the new dark phase after about 7 days [26]. Rats subjected to constant illumination for ten days tend to eat equally throughout the day [24]. Krieger [12] has found that corticosterone rhythm in rats subjected to constant illumination breaks down while rats that are blinded tend to eat most of their food during the dark phase although they do tend to eat a slightly greater amount than the controls during the light phase [26]. There is no apparent breakdown of corticosterone rhythm in rats subjected to constant dark [15]. Thus, there may be a relationship
between at least one hormonal rhythm and feeding behavior in the rat. Another possibility of why the animal starts to eat when the lights go out may be related to the animal's internal energy belance. Rats store glycogen during the night when they are feeding and use the glycogen stored in the liver during the day when they are not feeding. The hypothesis of liver glycogen receptors formulated by Russek and coworkers [16, 21, 22] states that the animal will begin to eat when the liver glycogen is depleted to a certain level. In the normal rat liver glycogen stores may be depleted to such a level that feeding is initiated as the lights go out. Bare [3] and Bare and Cicala [4] reported that rats deprived of food for 2 to 24 hours tend to show normal cyclic differences in rate of intake. Bare did not measure food intake directly but measured the number of times the rat would press a bar that delivered food. It is unclear from his procedure whether the animals were on a solid floor or a sawdust floor. Rats are known to hoard food [7], thus, without measuring food intake the animals may have simply been hoarding the food. If sawdust or wire floors were used the 45 mg pellets could easily have been left in the cage or dropped through a wire floor and gone unnoticed. He also used only 3 to 4 animals per group which is quite a small number of animals considering the variation found in most feeding trials. The present study was conducted to validate and expand the data of Bare [3,4]. Food intake was measured on each individual animal and the period of deprivation extended in some groups. The age of the animal was also investigated to see whether age affected the cyclic feeding behavior. 43
44
B E L L I N G E R AND M E N D E L METHOD
1 2 0 0 - 1 4 0 0 h r period of Day 1 (Fig. 1). The a m o u n t of food the rats ate during the 1 9 0 0 - 2 1 0 0 h r trial was a p p r o x i m a t e l y 50% more than the a m o u n t eaten during the 1 2 0 0 - 1 4 0 0 h r trial (/)<0.01). The a m o u n t of food eaten during the 0 1 0 0 - - 0 3 0 0 hr trial of Day 3 was also higher than the a m o u n t eaten during the 1 2 0 0 - 1 4 0 0 hr trial of Day 2 with the rats eating a p p r o x i m a t e l y 65% more (/)<0.01). F o o d intake during the 0 8 0 0 - 1000 hr period of Day 3 was not significantly different from the 12001400 hr period of Day 2. The food intake during 0 8 0 0 - 1 0 0 0 hr on Day 3 was significantly less than the a m o u n t eaten during the 1 9 0 0 - 2 1 0 0 hr period of Day 2 (/9<0.025) and the 0 1 0 0 - 0 3 0 0 period of Day 3 (/)<0.005).
Animals Sixteen, male, Sprague Dawley rats were housed in individual cages under a l i g h t - d a r k ( L : D ) ratio of 14:10 with lights on at 0500 hr. The animals were allowed to b e c o m e a c c u s t o m e d to their cages for 7 days before the study began. At the start of the e x p e r i m e n t the animals weighed b e t w e e n 2 2 0 - 2 4 0 g. The animals were fed and watered ad lib, except when food was removed during the periods of deprivation. They were fed Purina rat chow in a Fisher cup placed on the floor of the cage inside a larger dish. Daffy food retake was measured taking care to measure any spillage.
Experiment 2
Procedure
Again food intake of the rats was significantly lower during the light phase of Days 2 and 3 than during the dark phase (Fig. 2). The rats ate a p p r o x i m a t e l y 78% more during the 1900-2100 h r period when compared to the 0 8 0 0 - 1 0 0 0 hr period of Day 2 (p<0.001). Food intake on Day 3, during the 1 2 0 0 - 1 4 0 0 hr period was significantly less than the 1 9 0 0 - 2 1 0 0 hr period o f Day 2 ( p < 0 . 0 0 1 ) . The a m o u n t eaten during the 0 8 0 0 - 1 0 0 0 hr trial of Day 2 was not significantly different than the a m o u n t eaten during the 1 2 0 0 - 1 4 0 0 hr period of Day 3.
Experiment 1. During each trial, food was removed from the animals at 1800 hr on Day 1. F o o d was then returned at either 1200 or 1900 hr on Day 2 or at 0100 or 0800 hr on Day 3. When food was returned, the first 2 hr of ad lib feeding was recorded. The periods of deprivation were r a n d o m so the animals would not anticipate when t h e y would be fed. F o u r to 5 days were allowed b e t w e e n trials. The a m o u n t of food an animal ate during the 2 hr of recorded feeding was expressed as a percent of his average daily intake for the 2 days preceding the trial. The data were handled this way because the e x p e r i m e n t t o o k about 3 weeks to run and the animal's daily intake increased slightly as the animals became older and larger. Experiment 2. To d e t e r m i n e whether age had an effect u p o n the feeding r h y t h m the first e x p e r i m e n t was repeated when the animals weighed b e t w e e n 3 7 0 - 4 5 0 g. F o o d was removed at 1800 hr on Day 1 and returned at either 0800 or 1900 hr on Day 2 or at 1200 hr on Day 3. Once again 4 to 5 days were allowed b e t w e e n trials and the data were handled the same as in E x p e r i m e n t 1. Data were analyzed using Student's t test.
DISCUSSION The data show that deprived rats consistently eat 5 0 - 7 8 % more in the first 2 hr of refeeding when refed during the dark phase than when refed in the light phase. This periodicity persists during 42 hr of deprivation and is not affected by the age of the animal. The animals which were refed during the light phase even after 3 8 - 4 2 hr of deprivation, ate only as m u c h as after 1 4 - 1 8 hr of deprivation. Measuring food intake for the first 2 hr of refeeding and using this as a determinant of the immediate hunger state of the rat at refeeding suggests the animals eat in a r h y t h m i c pattern even after deprivation. These data are in fairly good agreement with the data of Bare [3,4] and extend it by increasing the n u m b e r of observations and by
RESULTS
Ex/)erirnent 1 Food
intake
of
I.,k.I I'-" Z
the
rats
was
lowest
during
the
40 , ,¢' ,. / / . ,
30
/ / / J i . i / /
>....J
i z /
20
¢ 1 / J z / e l i
I.l.J ¢.D
r/..,
¢ / I ¢ z /
r.//
10
¢ / /
I.U
V'/./ ¢ 1 /
I
1800
I
0800 12001400 TIME
1~0300 08001000
FIG. 1. On every trial food was removed at 1800 hr on Day 1 and returned at the various times indicated; f'trst 2 hr of food intake was measured and recorded as a percent of that animals average daily intake (-+ S.E.). Each trial was done on separate days allowing 4 - 5 days recovery between each experiment. The rats weighed between 220-240 g. N = 16.
DEPRIVATION AND TIME OF R E F E E D I N G ON FOOD INTAKE
45
50"
4O
F.... z >.
30
"t~ '
20
"'
10
//./ ///
/-/-/ ¢-// f/'/ t'// f// f/J 1// f//
/// /// /// ,///
Ill fJ/ f// ¢'J/ ¢~¢'11#
//./ /// l.-/ +++ •
I
1800
1900 2100
1201 1400
TIME FIG. 2. On every trial food was removed at 1800 hr on Day 1 and returned at the various times indicated; first 2 hr of food intake was measured and recorded as a percent of that animal's average daily intake (-+ S.E.). Each trial was done on separate days allowing 4 - 5 days recovery between each experiment. The rats weighed between 370-450 g. N = 16.
actually measuring food intake and by observing that the feeding rhythm persists after 42 hr of deprivation. A question that arises is what causes the animal to eat less during a period of light and more during a period of dark. An inherent rhythm appears to be strong in nature since animals fed in light ate less than animals fed in dark even though some of the animals fed in the light were deprived much longer. The rhythmic eating behavior cannot be controlled by liver glycogen receptors [16, 21, 22] since liver glycogen would have been utilized to a level that, according to Russek, would start the animal to eat as the lights went out on Day 1. Yet the animals ate less during the mornings of the second and third days of deprivation than during the night. Liver glycogen should have been very low throughout the entire second and third day of deprivation. Blood glucose levels would start to decrease rapidly after one day of deprivation [5]. The glucose levels would remain low as compared to that of fed animals [5]. Considering the glucostatic hypothesis of Mayer [13] or the caloric hypothesis of Adolf [1] one would expect the fasted animals, who had low circulating plasma glucose levels, to be very hungry by Day 3 and to eat as much as or more than others did during the night of Day 2, but they did not. In support of the theories of Russek, Mayer and Adolf it
should be noted that the animals ate some food at all times of refeeding, but they always ate less during the light phase. The precise location of the clock that directs rhythmic feeding behavior is unknown but it probably resides, at least partially, in the hypothalamus [14, 20, 25]. Normal circadian feeding patterns can be interrupted by lesioning the ventromedial hypothalamus (VMH) [9,11]. Animals with VMH lesions shift their eating patterns so they also eat during the light phase. Bernardis [6] has noted a disruption of diurnal feeding behavior in dorsal-medial-hypothalamic (DMN) lesioned rats. The DMN lesioned rats, although hypophagic, eat equally during the light and dark phases. Lesions of the VMH area are known to cause hyperinsulinemia [10], while depressing growth hormone (GH) release [10]. Lesioning of the DMN has no effect on insulin and GH levels. Lesioning the suprachiasmatic nucleus of the hypothalamus eliminates the rhythm of corticosterone secretion [14]. The effect on other hormone levels has not been fully elucidated. It is important that one consider not just the concentrations of hormones but also their circadian patterns when studying hormonal effects on food intake patterns. On the other hand, Richter [19] has suggested that the circadian feeding behavior may be totally neural in origin and not work through or in conjunction with the hormones at all.
REFERENCES
1. Adolf, F. Urges to eat and drink in rats. Am. J. Physiol. 151: 110-125, 1947. 2. Balagura, S. and D. Cosina. Periodicity of food intake in the rat as measured by an operant response. Physiol. Behav. 3: 641-643, 1968. " 3. Bare, J. Hunger, deprivation and the day night cycle. J. comp. physiol. Psychol. 52: 129-131, 1959. 4. Bare, J. and G. Cicala. Deprivation and time of testing as determinants of food intake. J. comp. physiol. Psychol. 53: 151-154, 1960.
5. Bellinger, L., V. Mendel and G.P. Moberg. Fasting and circadian STH, insulin and B. J. Anita. Sci. 37: 301, 1973, Abstract. 6. Bernadis, L. Description of diurnal feeding and weight gain cycles in weanling rats by ventromedial and dorsomedial hypothalamic lesions. Physiol. Behav. 10: 855-861, 1973. 7. Bindra, D. The nature of motivation for hoarding food. J. comp. physiol. Psychol. 41: 211-218, 1948. 8. Bolles, R.C. and S.A. Moot. The rat's anticipation of two meals a day. J. comp. physiol. Psychol. 83: 510-514, 1973.
46 9. Brooks, C., R. Lockwood and M. Wiggins. A study of the effect of hypothalamic lesions on the eating habits of the albino rat. Am. J. Physiol. 221: 711-718, 1971. 10. Frohman, L. H. and L. Bernardis. Growth hormone and insulin levels in weanling rats with ventromedial hypothalamic lesions. Endocrinology 8 2 : 1 1 2 5 - 1 1 3 2 , 1968. 11. Kakolewski, J., E. Deaux, J. Christensen and B. Case. Diurnal patterns in water and food intake and body weight changes in rats with hypothalamic lesions. Am. J. Physiol. 2 2 1 : 7 1 1 - 7 1 8 , 1971. 12. Krieger, D. T. Effect of ocular enucleation and altered lighting regimens of various ages on the circadian periodicity of plasma corticosteroid levels in rats. Endocrinology 93:1077, 1973. 13. Mayer, J. Glucostatic mechanism of regulation of food intake. New Engl. J. Meal. 249: 13-16, 1953. 14. Moore, Robert Y. Visual pathways and the central neural control of diurnal rhythms. In: The Neurosciences, Third Study Program, edited by Francis O. Schmitt and Frederic G. Worden. Cambridge, Massachusetts: MIT Press, 1974. 15. Nalbandov, A.V., Editor. Advances in Neuroendocrinology. Urbana: University of Illinois Press, 1963, pp. 392. 16. Penaloza-Rojas, J. and M. Russek. Anorexia produced by direct-current blockade of the vagus nerve. Nature 200: 176, 1963. 17. Richter, C. Animal .behavior and internal drives. Q. Rev. Biol. 2: 307-343, 1927.
BELLINGER AND MENDEL 18. Richter, C. P. Hormones and rhythms in man and animals. Recent Prog. Horm. Res. 13: 105-159, 1957. 19. Richter, C.P. Biological Clocks in Medicine and Psychiatry. Springfield: Charles C. Thomas, 1965. 20. Richter, C. Sleep and activity: their relationship to the 24-hour clock. In: Sleep and Altered States of Consciousness. Proc. Ass. Res. nerv. ment. Dis. 45: 8, 1965. 21. Russek, M. and P. Morgane. Anorexic effect of intraperitoneal glucose in the hypothalamic hyperphagic cat. Nature 199: 1004-1005, 1963. 22. Russek, M., A. Rodriquez-Zendejas and S. Pina. Hypothetical liver receptors and the anorexia caused by adrenaline and glucose. Physiol. Behav. 3: 249-257, 1968. 23. Siegel, P. and H. E. Stuckey. Diurnal course of water and food intake in the normal mature rat. J. comp. physiol. Psychol. 40: 365-370, 1947. 24. Siegel, P. Food and water intake in the rat in relation to the light-dark cycle. J. comp. physiol. Psychol. 54: 294-301, 1961. 25. Stephan, F. K. and I. Zucker. Circadian rhythms in drinking behavior and locomotor activity of rats are eliminated by hypothalamic lesions. Proc. natn. Acad. Sci. US.A. 69: 1583, 1972. 26. Zucker, I. Light-dark rhythms in rat eating and drinking behavior. Physiol. Behav. 6 : 1 1 5 - 1 1 6 , 1971.
Effect of Deprivation and Time of Refeeding on Food Intake L. L. BELLINGER AND V. E. MENDEL
Department o f Animal Science, University o f California Davis, California 95616
(Received 19 July 1974) BELLINGER, L. L. AND V. E. MENDEL. Effect of deprivation and time of refeeding on food intake. PHYSIOL. BEHAV. 14(1) 43-46, 1975. - T h e amount of food eaten in a two hour trial by male Sprague Dawley rats was recorded after periods of food deprivation up to 42 hr in length. Rats ate 50-78% more when refed during the dark phase than when refed during the light phase. This occurred even when light fed animals were fasted for longer periods than the dark fed animals. Rats eat in a rhythmic pattern after deprivation. These data are in good agreement with data previously reported and extend it by increasing the number of observations, increasing the length of deprivation, and comparing different age groups. Rats
Feeding behavior
Circadian
Deprivation
MUCH animal behavior is subject to rhythmic control by some internal clock. Just where the clock is located or how it operates is not fully understood [18,19] ; however, there is some evidence that an area which controls rhythmic drinking behavior, locomotor activity and corticosterone secretion patterns is situated in the suprachiasmatic nucleus of the hypothalamus [14,25]. Some rhythmic behavior is associated with environmental changes, such as the l i g h t dark cycle. One behavior that is closely correlated to the l i g h t - d a r k cycle is that of eating and drinking in the rat [2, 17, 23, 24, 26]. Rats that are fed and watered ad lib tend to eat the majority of their food and water during the dark phase of their day [2, 17, 23, 26]. The exact nature of what drives this l i g h t - d a r k feeding behavior and triggers the animals to start eating as soon as the lights go out is not entirely clear. Animals that have been meal-fed for long periods during the light phase will revert to a normal feeding pattern when fed and watered ad lib; the reversion requires about 9 to 10 days [8]. Rats that are subjected to a reversal of their light-dark cycle begin to eat during the new dark phase after about 7 days [26]. Rats subjected to constant illumination for ten days tend to eat equally throughout the day [24]. Krieger [12] has found that corticosterone rhythm in rats subjected to constant illumination breaks down while rats that are blinded tend to eat most of their food during the dark phase although they do tend to eat a slightly greater amount than the controls during the light phase [26]. There is no apparent breakdown of corticosterone rhythm in rats subjected to constant dark [15]. Thus, there may be a relationship
between at least one hormonal rhythm and feeding behavior in the rat. Another possibility of why the animal starts to eat when the lights go out may be related to the animal's internal energy belance. Rats store glycogen during the night when they are feeding and use the glycogen stored in the liver during the day when they are not feeding. The hypothesis of liver glycogen receptors formulated by Russek and coworkers [16, 21, 22] states that the animal will begin to eat when the liver glycogen is depleted to a certain level. In the normal rat liver glycogen stores may be depleted to such a level that feeding is initiated as the lights go out. Bare [3] and Bare and Cicala [4] reported that rats deprived of food for 2 to 24 hours tend to show normal cyclic differences in rate of intake. Bare did not measure food intake directly but measured the number of times the rat would press a bar that delivered food. It is unclear from his procedure whether the animals were on a solid floor or a sawdust floor. Rats are known to hoard food [7], thus, without measuring food intake the animals may have simply been hoarding the food. If sawdust or wire floors were used the 45 mg pellets could easily have been left in the cage or dropped through a wire floor and gone unnoticed. He also used only 3 to 4 animals per group which is quite a small number of animals considering the variation found in most feeding trials. The present study was conducted to validate and expand the data of Bare [3,4]. Food intake was measured on each individual animal and the period of deprivation extended in some groups. The age of the animal was also investigated to see whether age affected the cyclic feeding behavior. 43
44
B E L L I N G E R AND M E N D E L METHOD
1 2 0 0 - 1 4 0 0 h r period of Day 1 (Fig. 1). The a m o u n t of food the rats ate during the 1 9 0 0 - 2 1 0 0 h r trial was a p p r o x i m a t e l y 50% more than the a m o u n t eaten during the 1 2 0 0 - 1 4 0 0 h r trial (/)<0.01). The a m o u n t of food eaten during the 0 1 0 0 - - 0 3 0 0 hr trial of Day 3 was also higher than the a m o u n t eaten during the 1 2 0 0 - 1 4 0 0 hr trial of Day 2 with the rats eating a p p r o x i m a t e l y 65% more (/)<0.01). F o o d intake during the 0 8 0 0 - 1000 hr period of Day 3 was not significantly different from the 12001400 hr period of Day 2. The food intake during 0 8 0 0 - 1 0 0 0 hr on Day 3 was significantly less than the a m o u n t eaten during the 1 9 0 0 - 2 1 0 0 hr period of Day 2 (/9<0.025) and the 0 1 0 0 - 0 3 0 0 period of Day 3 (/)<0.005).
Animals Sixteen, male, Sprague Dawley rats were housed in individual cages under a l i g h t - d a r k ( L : D ) ratio of 14:10 with lights on at 0500 hr. The animals were allowed to b e c o m e a c c u s t o m e d to their cages for 7 days before the study began. At the start of the e x p e r i m e n t the animals weighed b e t w e e n 2 2 0 - 2 4 0 g. The animals were fed and watered ad lib, except when food was removed during the periods of deprivation. They were fed Purina rat chow in a Fisher cup placed on the floor of the cage inside a larger dish. Daffy food retake was measured taking care to measure any spillage.
Experiment 2
Procedure
Again food intake of the rats was significantly lower during the light phase of Days 2 and 3 than during the dark phase (Fig. 2). The rats ate a p p r o x i m a t e l y 78% more during the 1900-2100 h r period when compared to the 0 8 0 0 - 1 0 0 0 hr period of Day 2 (p<0.001). Food intake on Day 3, during the 1 2 0 0 - 1 4 0 0 hr period was significantly less than the 1 9 0 0 - 2 1 0 0 hr period o f Day 2 ( p < 0 . 0 0 1 ) . The a m o u n t eaten during the 0 8 0 0 - 1 0 0 0 hr trial of Day 2 was not significantly different than the a m o u n t eaten during the 1 2 0 0 - 1 4 0 0 hr period of Day 3.
Experiment 1. During each trial, food was removed from the animals at 1800 hr on Day 1. F o o d was then returned at either 1200 or 1900 hr on Day 2 or at 0100 or 0800 hr on Day 3. When food was returned, the first 2 hr of ad lib feeding was recorded. The periods of deprivation were r a n d o m so the animals would not anticipate when t h e y would be fed. F o u r to 5 days were allowed b e t w e e n trials. The a m o u n t of food an animal ate during the 2 hr of recorded feeding was expressed as a percent of his average daily intake for the 2 days preceding the trial. The data were handled this way because the e x p e r i m e n t t o o k about 3 weeks to run and the animal's daily intake increased slightly as the animals became older and larger. Experiment 2. To d e t e r m i n e whether age had an effect u p o n the feeding r h y t h m the first e x p e r i m e n t was repeated when the animals weighed b e t w e e n 3 7 0 - 4 5 0 g. F o o d was removed at 1800 hr on Day 1 and returned at either 0800 or 1900 hr on Day 2 or at 1200 hr on Day 3. Once again 4 to 5 days were allowed b e t w e e n trials and the data were handled the same as in E x p e r i m e n t 1. Data were analyzed using Student's t test.
DISCUSSION The data show that deprived rats consistently eat 5 0 - 7 8 % more in the first 2 hr of refeeding when refed during the dark phase than when refed in the light phase. This periodicity persists during 42 hr of deprivation and is not affected by the age of the animal. The animals which were refed during the light phase even after 3 8 - 4 2 hr of deprivation, ate only as m u c h as after 1 4 - 1 8 hr of deprivation. Measuring food intake for the first 2 hr of refeeding and using this as a determinant of the immediate hunger state of the rat at refeeding suggests the animals eat in a r h y t h m i c pattern even after deprivation. These data are in fairly good agreement with the data of Bare [3,4] and extend it by increasing the n u m b e r of observations and by
RESULTS
Ex/)erirnent 1 Food
intake
of
I.,k.I I'-" Z
the
rats
was
lowest
during
the
40 , ,¢' ,. / / . ,
30
/ / / J i . i / /
>....J
i z /
20
¢ 1 / J z / e l i
I.l.J ¢.D
r/..,
¢ / I ¢ z /
r.//
10
¢ / /
I.U
V'/./ ¢ 1 /
I
1800
I
0800 12001400 TIME
1~0300 08001000
FIG. 1. On every trial food was removed at 1800 hr on Day 1 and returned at the various times indicated; f'trst 2 hr of food intake was measured and recorded as a percent of that animals average daily intake (-+ S.E.). Each trial was done on separate days allowing 4 - 5 days recovery between each experiment. The rats weighed between 220-240 g. N = 16.
DEPRIVATION AND TIME OF R E F E E D I N G ON FOOD INTAKE
45
50"
4O
F.... z >.
30
"t~ '
20
"'
10
//./ ///
/-/-/ ¢-// f/'/ t'// f// f/J 1// f//
/// /// /// ,///
Ill fJ/ f// ¢'J/ ¢~¢'11#
//./ /// l.-/ +++ •
I
1800
1900 2100
1201 1400
TIME FIG. 2. On every trial food was removed at 1800 hr on Day 1 and returned at the various times indicated; first 2 hr of food intake was measured and recorded as a percent of that animal's average daily intake (-+ S.E.). Each trial was done on separate days allowing 4 - 5 days recovery between each experiment. The rats weighed between 370-450 g. N = 16.
actually measuring food intake and by observing that the feeding rhythm persists after 42 hr of deprivation. A question that arises is what causes the animal to eat less during a period of light and more during a period of dark. An inherent rhythm appears to be strong in nature since animals fed in light ate less than animals fed in dark even though some of the animals fed in the light were deprived much longer. The rhythmic eating behavior cannot be controlled by liver glycogen receptors [16, 21, 22] since liver glycogen would have been utilized to a level that, according to Russek, would start the animal to eat as the lights went out on Day 1. Yet the animals ate less during the mornings of the second and third days of deprivation than during the night. Liver glycogen should have been very low throughout the entire second and third day of deprivation. Blood glucose levels would start to decrease rapidly after one day of deprivation [5]. The glucose levels would remain low as compared to that of fed animals [5]. Considering the glucostatic hypothesis of Mayer [13] or the caloric hypothesis of Adolf [1] one would expect the fasted animals, who had low circulating plasma glucose levels, to be very hungry by Day 3 and to eat as much as or more than others did during the night of Day 2, but they did not. In support of the theories of Russek, Mayer and Adolf it
should be noted that the animals ate some food at all times of refeeding, but they always ate less during the light phase. The precise location of the clock that directs rhythmic feeding behavior is unknown but it probably resides, at least partially, in the hypothalamus [14, 20, 25]. Normal circadian feeding patterns can be interrupted by lesioning the ventromedial hypothalamus (VMH) [9,11]. Animals with VMH lesions shift their eating patterns so they also eat during the light phase. Bernardis [6] has noted a disruption of diurnal feeding behavior in dorsal-medial-hypothalamic (DMN) lesioned rats. The DMN lesioned rats, although hypophagic, eat equally during the light and dark phases. Lesions of the VMH area are known to cause hyperinsulinemia [10], while depressing growth hormone (GH) release [10]. Lesioning of the DMN has no effect on insulin and GH levels. Lesioning the suprachiasmatic nucleus of the hypothalamus eliminates the rhythm of corticosterone secretion [14]. The effect on other hormone levels has not been fully elucidated. It is important that one consider not just the concentrations of hormones but also their circadian patterns when studying hormonal effects on food intake patterns. On the other hand, Richter [19] has suggested that the circadian feeding behavior may be totally neural in origin and not work through or in conjunction with the hormones at all.
REFERENCES
1. Adolf, F. Urges to eat and drink in rats. Am. J. Physiol. 151: 110-125, 1947. 2. Balagura, S. and D. Cosina. Periodicity of food intake in the rat as measured by an operant response. Physiol. Behav. 3: 641-643, 1968. " 3. Bare, J. Hunger, deprivation and the day night cycle. J. comp. physiol. Psychol. 52: 129-131, 1959. 4. Bare, J. and G. Cicala. Deprivation and time of testing as determinants of food intake. J. comp. physiol. Psychol. 53: 151-154, 1960.
5. Bellinger, L., V. Mendel and G.P. Moberg. Fasting and circadian STH, insulin and B. J. Anita. Sci. 37: 301, 1973, Abstract. 6. Bernadis, L. Description of diurnal feeding and weight gain cycles in weanling rats by ventromedial and dorsomedial hypothalamic lesions. Physiol. Behav. 10: 855-861, 1973. 7. Bindra, D. The nature of motivation for hoarding food. J. comp. physiol. Psychol. 41: 211-218, 1948. 8. Bolles, R.C. and S.A. Moot. The rat's anticipation of two meals a day. J. comp. physiol. Psychol. 83: 510-514, 1973.
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