Physiology & Behavior, Vol. 23, pp. 777-783. Pergamon Press and Brain Research Publ., 1979. Printed in the U.S.A.
Nocturnal Feeding Pattern in the Prepubertal Rat: Influence of the Ventromedial Hypothalamus (VMH) G A R Y C. S I E C K * , D W I G H T M. N A N C E t A N D R O G E R A. G O R S K I *
Department of Anatomy and Brain Research Institute UCLA School of Medicine*, Los Angeles, CA 90024 and Department of Anatomy University of South Floridat, Tampa Florida 33612 R e c e i v e d 21 F e b r u a r y 1978 SIECK, G. C., D. M. NANCE AND R. A. GORSKI. Nocturnalfeeding pattern in the prepubertal rat: Influence of the ventromedial hypothalamus (VMH). PHYSIOL. BEHAV. 23(4) 777-783, 1979.--Daily feeding patterns, food intake and changes in body weight of male and female prepubertal rats were observed across a period from 21 to 50 days of age. Light/dark differences in feeding were found for both males and females throughout the recorded period, with feeding occurring predominantly during the dark period. The light/dark difference in feeding behavior gradually increased as the animals developed. Bilateral lesions placed in the VMH of female rats at 21 days ofnge disrupted the light/dark differences in feeding behavior primarily by decreasing dark period feeding. These lesions further resulted in a period of hypophagia and retarded body weight gain as well as a delay in pubertal onset. These data indicate that prepubertal rats regulate their feeding behavior so that food intake occurs principally during the dark period and that the integrity of the VMH is necessary for this regulation. Food intake
Feeding patterns
Body weight regulation
ADULT female rats eat most of their food during the dark period. This generally results from fight/dark differences in the number of meals (NM), meal duration (MD) and meal size (MS) [1, 18, 20, 27]. It has been proposed that a nocturnal pattern of food intake and feeding behavior in the adult rat is due to alternating metabolic states of the animal in which nutrient store repletion occurs during the dark period following their depletion during the light period [19,21]. Thus, it appears that the long-term maintenance of nutrient stores has an important influence on the light/dark distribution of feeding behavior. Several studies have shown that bilateral damage of the ventromedial hypothalamus (VMH) abolishes light/dark differences in feeding [2,16]. This effect of VMH damage in adult rats results primarily from a marked increase in feeding during the light period [2,16]. This altered light/dark distribution of feeding after placement of VMH lesions is consistent with the proposed role of the VMH in the long-term regulation of feeding to maintain nutrient stores [21,25]. Recently, we have shown that prepubertal female rats adjust their feeding patterns in response to challenges of long-term energy maintenance, and that the VMH is necessary for the animals to make adequate adjustments in their feeding behavior [25]. We concluded from this study that weanling rats display very accurate long-term regulation of feeding behav-
Ventromedial hypothalamus
ior, and that the VMH is involved in this regulation. However, it was not determined in this previous work whether or not long-term regulation of feeding in weanling rats would account for light/dark differences in feeding paterns during this developmental period. Bernardis [5] reported that light/ dark differences in food itnake in male weanling rats are attenuated by bilateral lesions placed in the medial hypothalamic area (both the ventromedial and dorsomedial hypothalamic nuclei). These results would suggest that damage of the medial hypothalamic area may also influence diurnal differences in feeding patterns in weanling animals. While a nocturnal pattern of food intake is present in weanling rats [12,30], it has been reported that only a light/ dark difference in the number of meals accounts for the greater food intake during the dark period at this age [12]. De Castro and Balagura [12] concluded that the absence of light/ dark differences in meal size and meal duration results from the immaturity of lateral hypothalamic regulatory influences on feeding; i.e., short-term control of food intake. However, if as suggested the long-term maintenance of balanced nutrient stores is an important factor in the nocturnal pattern of feeding, then such a distinction between the feeding patterns of adult and weanling animals could reflect a basic developmental change in the long-term regulation of feeding. Therefore, the purpose of this study was first, to examine
'Supported by NIH Grant AM-18254.
Copyright © 1979 Brain R e s e a r c h Publications Inc.--0031-9384/79/100777-07501.20/0
778
SIECK, NANCE AND GORSKI
FEEDING
CAGE
~
WATER
~
U
t
FOOD
x.._../l O,SH PHOTOCELL
4
3
n mint m . . . . .
' '~ ' ' 1 1 " : ' - ; - - , ' I , , , , , ' !fl" , ..... ,mall,! ...... ~. . . . . ! . . . . .
,. . . . .
.........
. . . . . . . . . . . . . . . . . . ....
*
'
t :. ....
. . . . .
i*:
* ......
FIG. 1. Feeding cage used to monitor eating time. Food dish placed at the end of a tunnel with photocell positioned across the front. Photobeam interruptions recorded on an Esterline-Angus event recorder. An example of a dark period recording (1 I/2 hour segment) of eating time indicated by upward pen deflections for six animals is shown.
the development of feeding patterns in wear/ling rats and, secondly, to determine the effect of bilateral VMH lesions on prepubertal feeding patterns. METHOD
At 21 days of age, six male and six female rats were placed in metabolic cages equipped with feeding tunnels. Food cups were placed at the end of these tunnels with photo cells positioned across the front of the food cups. Photo beam interruptions, as the animals fed, were continuously recorded on an Esterline-Angus event recorder (Fig. 1). Total eating time (ET) was determined for both the light and dark periods. The distribution of eating time within each photoperiod was further determined by defining separate meals or eating sessions, based upon estabfished criteria, i.e., eating sessions of a least one min duration and separated by more than ten min from the next eating session [18, 20, 26]. The number of meals (NM) and the average meal duration (MD) were then calculated for the light and dark periods. In addition, feeding rate was also calculated by dividing the daily food intake by the total dally eating time and, from this measure, the average size of each meal (MS) in g could be derived. Thus, four parameters of feeding behavior, i.e., ET, NM, MD and MS, were determined for both photoperiods each day, in addition to daily food intake (FI) and body weight (BWt) change. Although these procedures for assessing feeding patterns have been applied previously [20,26], we tested the validity of relating eating time to
amount of food consumed by determining the correlation of these measures across days of the experiment. For each of the control animals, correlations coefficients were calculated [28] to determine the relationships between ET and age (mean r=0.57 -+ 0.21 S.D.), FI and age(mean r=0.86 _ 0.09 S.D.), and ET and FI (mean r=0.81 - 0.!0 S.D.). Since there tended to be a positive correlation betweenthe age of the animals and both ET and F1, the partial correlation coefficient [28] was determined for the relationship between ET and FI, thus excluding the potential confounding influence of the age variable. In all 12 control rats, we found that despite the changes in both ET and FI as the animals matured, the correlation between these measures remained very high (partial correlation coefficient r=0.80). This correlation between ET and FI was highly significant (p
Nocturnal Feeding Pattern in the Prepubertal Rat: Influence of the Ventromedial Hypothalamus (VMH) G A R Y C. S I E C K * , D W I G H T M. N A N C E t A N D R O G E R A. G O R S K I *
Department of Anatomy and Brain Research Institute UCLA School of Medicine*, Los Angeles, CA 90024 and Department of Anatomy University of South Floridat, Tampa Florida 33612 R e c e i v e d 21 F e b r u a r y 1978 SIECK, G. C., D. M. NANCE AND R. A. GORSKI. Nocturnalfeeding pattern in the prepubertal rat: Influence of the ventromedial hypothalamus (VMH). PHYSIOL. BEHAV. 23(4) 777-783, 1979.--Daily feeding patterns, food intake and changes in body weight of male and female prepubertal rats were observed across a period from 21 to 50 days of age. Light/dark differences in feeding were found for both males and females throughout the recorded period, with feeding occurring predominantly during the dark period. The light/dark difference in feeding behavior gradually increased as the animals developed. Bilateral lesions placed in the VMH of female rats at 21 days ofnge disrupted the light/dark differences in feeding behavior primarily by decreasing dark period feeding. These lesions further resulted in a period of hypophagia and retarded body weight gain as well as a delay in pubertal onset. These data indicate that prepubertal rats regulate their feeding behavior so that food intake occurs principally during the dark period and that the integrity of the VMH is necessary for this regulation. Food intake
Feeding patterns
Body weight regulation
ADULT female rats eat most of their food during the dark period. This generally results from fight/dark differences in the number of meals (NM), meal duration (MD) and meal size (MS) [1, 18, 20, 27]. It has been proposed that a nocturnal pattern of food intake and feeding behavior in the adult rat is due to alternating metabolic states of the animal in which nutrient store repletion occurs during the dark period following their depletion during the light period [19,21]. Thus, it appears that the long-term maintenance of nutrient stores has an important influence on the light/dark distribution of feeding behavior. Several studies have shown that bilateral damage of the ventromedial hypothalamus (VMH) abolishes light/dark differences in feeding [2,16]. This effect of VMH damage in adult rats results primarily from a marked increase in feeding during the light period [2,16]. This altered light/dark distribution of feeding after placement of VMH lesions is consistent with the proposed role of the VMH in the long-term regulation of feeding to maintain nutrient stores [21,25]. Recently, we have shown that prepubertal female rats adjust their feeding patterns in response to challenges of long-term energy maintenance, and that the VMH is necessary for the animals to make adequate adjustments in their feeding behavior [25]. We concluded from this study that weanling rats display very accurate long-term regulation of feeding behav-
Ventromedial hypothalamus
ior, and that the VMH is involved in this regulation. However, it was not determined in this previous work whether or not long-term regulation of feeding in weanling rats would account for light/dark differences in feeding paterns during this developmental period. Bernardis [5] reported that light/ dark differences in food itnake in male weanling rats are attenuated by bilateral lesions placed in the medial hypothalamic area (both the ventromedial and dorsomedial hypothalamic nuclei). These results would suggest that damage of the medial hypothalamic area may also influence diurnal differences in feeding patterns in weanling animals. While a nocturnal pattern of food intake is present in weanling rats [12,30], it has been reported that only a light/ dark difference in the number of meals accounts for the greater food intake during the dark period at this age [12]. De Castro and Balagura [12] concluded that the absence of light/ dark differences in meal size and meal duration results from the immaturity of lateral hypothalamic regulatory influences on feeding; i.e., short-term control of food intake. However, if as suggested the long-term maintenance of balanced nutrient stores is an important factor in the nocturnal pattern of feeding, then such a distinction between the feeding patterns of adult and weanling animals could reflect a basic developmental change in the long-term regulation of feeding. Therefore, the purpose of this study was first, to examine
'Supported by NIH Grant AM-18254.
Copyright © 1979 Brain R e s e a r c h Publications Inc.--0031-9384/79/100777-07501.20/0
778
SIECK, NANCE AND GORSKI
FEEDING
CAGE
~
WATER
~
U
t
FOOD
x.._../l O,SH PHOTOCELL
4
3
n mint m . . . . .
' '~ ' ' 1 1 " : ' - ; - - , ' I , , , , , ' !fl" , ..... ,mall,! ...... ~. . . . . ! . . . . .
,. . . . .
.........
. . . . . . . . . . . . . . . . . . ....
*
'
t :. ....
. . . . .
i*:
* ......
FIG. 1. Feeding cage used to monitor eating time. Food dish placed at the end of a tunnel with photocell positioned across the front. Photobeam interruptions recorded on an Esterline-Angus event recorder. An example of a dark period recording (1 I/2 hour segment) of eating time indicated by upward pen deflections for six animals is shown.
the development of feeding patterns in wear/ling rats and, secondly, to determine the effect of bilateral VMH lesions on prepubertal feeding patterns. METHOD
At 21 days of age, six male and six female rats were placed in metabolic cages equipped with feeding tunnels. Food cups were placed at the end of these tunnels with photo cells positioned across the front of the food cups. Photo beam interruptions, as the animals fed, were continuously recorded on an Esterline-Angus event recorder (Fig. 1). Total eating time (ET) was determined for both the light and dark periods. The distribution of eating time within each photoperiod was further determined by defining separate meals or eating sessions, based upon estabfished criteria, i.e., eating sessions of a least one min duration and separated by more than ten min from the next eating session [18, 20, 26]. The number of meals (NM) and the average meal duration (MD) were then calculated for the light and dark periods. In addition, feeding rate was also calculated by dividing the daily food intake by the total dally eating time and, from this measure, the average size of each meal (MS) in g could be derived. Thus, four parameters of feeding behavior, i.e., ET, NM, MD and MS, were determined for both photoperiods each day, in addition to daily food intake (FI) and body weight (BWt) change. Although these procedures for assessing feeding patterns have been applied previously [20,26], we tested the validity of relating eating time to
amount of food consumed by determining the correlation of these measures across days of the experiment. For each of the control animals, correlations coefficients were calculated [28] to determine the relationships between ET and age (mean r=0.57 -+ 0.21 S.D.), FI and age(mean r=0.86 _ 0.09 S.D.), and ET and FI (mean r=0.81 - 0.!0 S.D.). Since there tended to be a positive correlation betweenthe age of the animals and both ET and F1, the partial correlation coefficient [28] was determined for the relationship between ET and FI, thus excluding the potential confounding influence of the age variable. In all 12 control rats, we found that despite the changes in both ET and FI as the animals matured, the correlation between these measures remained very high (partial correlation coefficient r=0.80). This correlation between ET and FI was highly significant (p
