PhyMology and Behavior, Vol. 14, pp. 861--865. Brain Research Publications Inc., 1975. Printed in the U.S.A.

Hypothalamic Hyperphagia Despite Imposed Diurnal or Nocturnal Feeding and

Drinking Rhythms RICHARD M. GOLD

Department o f Psychology, University o f Massachusetts, Amherst MA O1002

GERRY SUMPRER

Department o f Psychology, University o f Dayton, Dayton OH 45469

HELEN M. UEBERACHER

Graduate School o f Nursing, Pace University, Pleasantville N Y 10010

AND

GREGORY KAPATOS

Department o f Psychology, University o f Pittsburgh, Pittsburgh PA 15213

(Received 29 November 1974)

GOLD, R. M., G. SUMPRER, H. M. UEBERACHER AND G. KAPATOS. Hypothalamic hyperphagia despite imposed diurnal or nocturnal feeding and drinking rhythms. PHYSIOL. BEHAV. 14(6) 861-865, 1975. - Rats normally do most of their eating at night. When ad lib fed rats are made hyperphagic with lesions or parasagittal hypothalamic knife cuts the increases in eating occur primarily during the day. This suggests that a disruption of circadian rhythms may mediate the overeating. However, when knife cut rats were food and water deprived all day excessive eating occurred at night. Similarly, when they were deprived all night overeating occurred during the day. Under both conditions of deprivation the food intakes and rapid weight gains of the ad lib fed knife cut group were defended. It was concluded that: (1) in hypothalamic hyperphagia either the excessive food intake or the excessive weight gain is defended when food and water are available only half of each day, and (2) disruption of nocturnal feeding and drinking rhythms is not the cause of hypothalamic hyperphagia.

Hypothalamus Hyperphagia Knife cuts Deprivation Eating rhythms Drinking rhythms

RATS do most of their eating and drinking at night [1, 3, 13, 15, 21, 22, 24]. Brain lesions in the VMH (ventro- medial hypothalamus - not the ventromedial nucleus) disrupt these nocturnal rhythms and produce hyperphagia and obesity [9] . If food is continuously available to VMH lesioned rats their nocturnal food and water intakes remain near preoperative levels, whereas daytime intakes increase dramatically. As a result they eat just about as much during the day as they do at night [2, 3, 5, 13]. The usual inter- pretation of this daytime overeating is that daytime feeding

and drinking may be necessary but not sufficient for the expression of hypothalamic obesity.

Hypothalamic obesity with normal feeding rhythms has not previously been reported, although the converse, a loss of nocturnal rhythms without overeating, is produced by VMH or dorsomedial hypothalamic lesions in weanling rats [4].

If a disrupted feeding rhythm were a necessary precursor to hypothalamic obesity, then the imposition of a noctur- nal rhythm onto appropriately brain lesioned rats would

t Supported by United States Public Health Service Grants MH-13561 and MH26251 to Richard M. Gold. 2Requests for reprints should be sent to Richard M. Gold, Department of Psychology, Tobin Hall, University of Massachusetts, Amherst

MA 01002.

861

862 GOLD, SUMPRER, VEBERACHER AND KAPATOS

prevent obesity. In this study a nocturnal rhythm is im- posed on lesioned rats by depriving them of food and water during the artificial day. Access to food and water is per- mitted only at night. In a second group of rats night time deprivation is used to impose a reversal of the normal rhythm. A control group is never deprived.

It has also been suggested that hyperphagic rats do not defend their excessive rate of weight gain [ 19,20]. As a test of this concept the day deprivation and night deprivation conditions can be viewed simply as a restriction by half of the total time each day during which food is available. If the excessive rate of weight gain seen in the ad lib fed hyperphagic rat is found to be defended despite 12 hr/day of food deprivation, then we would conclude that the hyperphagic rat is not released from all regulation, but rather regulates at an excessive rate of food intake or weight gain.

In this study, parasagittal hypothalamic knife cuts [7] are used to produce hyperphagia in place of the traditional electrolytic VMH lesions, as the damage produced by the cuts may be more selective. VMH lesions and parasagittal knife cuts both produce similar behavioral responses in regard to total food and water intake. However, these surgical procedures produce differential effects on measures of activity [19], estrous cycles [19], and linear body growth [ 10]. The question therefore arises as to whether parasagittal knife cuts and medial hypothalamic lesions produce differential effects in regard to rhythms of food and water consumption.

METHOD

Animals

Twenty-four adult female Carworth CFE albino rats (210-234 g) were used. They were housed singly in 18 × 35 × 18 cm high hanging stainless steel cages. Ambient temperatures were maintained at 72 +- 2 ° F.

Procedure

A high fat diet [8] was available in open bowls and water was available through sipper tubes. Green [16] over- head fluorescent lights (Sylvania) were automatically cycled (13 hr day; lights on at lO p.m., off at l l a.m.). Food and water intakes and body weights were measured every 12 hr, at the beginning and end of each artificial day. Food spill- age was collected on paper towels beneath the cages and water spillage estimates were obtained from control bottles on empty cages. Upon arrival in the laboratory the rats were placed either on daytime food and water deprivation (n = 8), nightime deprivation (n = 8) or ad lib food and water (n = 8).

In order to correct intakes for the food and water re- quired to maintain and locomote the greater bulk of obese rats, food and water intakes were expressed per kg of body weight raised to 3/4 power. The body weights at the end of the artificial night were used exclusively for this correction. Kleiber [ 14] has shown that across a wide range of body weights and mammalian species metabolic rates can be equated by expressing oxygen consumption per kg 3/4 body weight.

Surgery. After 23 days, adaptation to the artificial d a y - night cycle was complete, as indicated by stable suppressed daytime food and water intake by the ad lib group. Two rats from each group then received sham operations and the

remaining 6 received bilateral parasagittal retracting wire hypothalamic knife cuts [ 11 ] at a location previously shown to produce rapid weight gains [7]. The deprivation schedules continued without interruption. In order to minimize the disruptive effects on feeding of surgical trauma and anesthesia, the operations were performed under ether anesthesia during the first few hours of the rat's imposed day or night deprivation period. Rats on ad lib feeding were operated on in the first few hours of the day period as they normally did not eat during the day. The ad lib group was then deprived until the start of the first post- operative night.

Post-operative deprivation shifts. Eighteen days after surgery (Shift I) both the day deprivation and night depri- vation groups were switched to ad lib food and water and the ad lib group was shifted to daytime deprivation. After another 18 days (Shift II) all 3 groups were put on ad lib food and water.

Histology. The Knife cuts were reconstructed from thionin stained horizontal sections. Three rats, one from each group, were found to have severely asymmetrical cuts, and on this basis their data were discarded. The locations of the remaining knife cuts were consistent with previous reports [7,9].

RESULTS

Food Intake and Weight Gain

Neither deprivation condition had any apparent effect on the weight of the sham operated controls. Therefore body weight data for the 6 sham operated controls (2 each deprivation condition) were pooled.

Imposition of normal or reversed feeding and drinking cycles did not prevent or significantly retard hypothalamic hyperphagia (Fig. 1) or obesity (Fig. 2). All 3 knife cut groups gained weight rapidly as compared to the pooled controls (p's<0.001, Mann Whitney-U Test), whereas none of the small body weight differences amongst the knife cut groups were significant (p's> 0.1 ).

The shifts in deprivation schedules 18 and 36 days after surgery had at best only small non-significant effects on total food intake or weight gain. Prior to the first shift note in Figs. 1 and 2 that the day deprived cut group ate and gained slightly less than the ad lib cut group. These small differences reversed after the two groups exchanged depri- vation conditions. The magnitude of this non-significant observation (p's> 0.1) is however quite small, the overriding result being rapid weight gains despite imposed rhythms.

As obesity progressed the rates of weight gain gradually slowed and food intakes computed on a per kg 3/4 basis fell towards control values.

A breakdown of absolute food intakes into day and night components is shown in Fig. 3. These data are means for the 9 days preceding surgery and for the first 18 postcut days.

Preoperatively the ad lib group consumed 91 percent of its food at night, and the deprived groups, most notably the night deprived group, maintained normal total food ihtakes.

After knife cuts the night time intake of the ad lib group increased by only 17 percent whereas the daytime food intake jumped 86 percent. Thus, under ad lib conditions the bulk of the increased eating occurred during the day. As a result, postoperatively only 64 percent of the total food intake occurred at night. This 64 percent is, however, still

HYPERPHAGIA AND FEEDING RHYTHMS 863

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FIG. 1. Mean total daily food intakes per kg body weight raised to the 3/4 power [14]. Operations were parasagittal hypothalamic knife cuts or sham operations. Rats were on ad lib food (high fat diet) and water, daytime food and water deprivation, or nighttime

deprivation. Deprivation schedules were shifted as indicated.

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FIG. 2. Mean body weights. See legend of Fig. 1 for further details.

far above the 50 percent that total disruption of nocturnal rhythms would predict (p<0.01), and which is obtained with VMH lesions [3]. When the day deprivation and night deprivation knife cut groups were shifted to ad libitum feeding on the 18th day after surgery they also adopted disrupted feeding rhythms with night time food intakes of 64 and 57 percent respectively (based on means for Days 18 through 36).

Water In take

For water intakes (Fig. 4) the picture was radically dif- ferent from that seen for food intake.

Preoperatively day deprivation had no effect on total water intake (99 percent of ad lib intake) whereas night deprivation suppressed total water intake to 59 percent of the ad lib level (p<0.05).

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after parasagittal hypothalamic knife cuts (cut).

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FIG. 4. Day and night water intakes as per Fig. 3 legend.

After knife cuts neither day deprived nor night deprived knife cut rats drank as much as knife cut rats with ad lib food and water (p<0.05). There was virtually no water in- take compensation by the day deprived group (Fig. 4), whereas the night deprived group partially compensated.

864 GOLD, SUMPRER, VEBERACHER AND KAPATOS

Just as with food intake, the knife cuts suppressed but did not eliminate the normal nocturnal water rhythm. For the ad lib group night time water intake was 66 percent of total intake as compared with 82 percent preoperatively. Similarly, when the day deprived and night deprived groups were switched to ad lib they respectively consumed 70 percent and 62 percent of their water at night.

To summarize, the rats compensated rather precisely for imposed rhythms in terms of total food intake and body weight but they did not always compensate in terms of total water intake. Preoperatively only night deprivation suppressed water intake whereas postoperatively day depri- vation produced the greater suppression.

DISCUSSION

The most striking feature of this study is that when challenged with 12 hours/day of food and water depriva- tion, i.e. imposed normal or reversed day/night feeding and drinking rhythms, hyperphagic rats successfully defend their excessive food intakes (Fig. 1) and weight gains (Fig. 2). The excessive food intake is shifted into whatever 12 hr time of day that food is available (Fig. 3). The amount of food intake or perhaps the rate of weight gain appears to be regulated at a new higher level. This is in striking contrast to daily water intake, which is not defended (Fig. 4).

Nocturnal feeding and drinking rhythms are indeed dis- turbed in hypothalamic obesity, but hypothalamic obesity cannot be attributed to the disrupted rhythms, however attractive this hypothesis may appear based on ad libitum feeding data alone (Fig. 3).

In normal animals (preoperative data) only night depri- vation suppressed total water intake. This curious new find- ing may be related to a persistent rhythm such as a noctur- nal activity peak or a diurnal ADH peak. Unfortunately neither of these were measured, as the selective water in- take suppression was totally unanticipated.

In contrast, after knife cuts day deprivation exerted the greatest suppression on total water intake. Unless and until this postoperative differential is replicated we are inclined to believe that there was a fortuitous concentration in the night deprived group of rats whose cuts produced diabetes insipitus via damage to the paraventriculo-supraoptico- hypophyseal ADH system. A more interesting but less like- ly possibility is that night starvation tended to differentially suppress estrous cycling (not measured) and that a resulting

low level of estrogen constituted removal of a source of appetite and thirst suppression. The somewhat higher post- operative food intakes and body weight gains of the night deprived group are consistent with this rather speculative interpretation.

Even in the ad libitum situation knife-cut rats maintain a reduced circadian feeding rhythm (57 to 64 percent of food eaten at night vs 91 percent preoperatively) whereas lesions produce essentially total disruption (50 percent night feed- ing, [ 3,41 ).

The present findings were probably not influenced by our use of green light instead of the more conventional white, as in unpublished observations using white fluores- cent light Gold and Kapatos (1973) also obtained persistant but reduced nocturnal rhythms following parasagittal knife cuts. Eight obese animals with knife cuts exhibited dimin- ished feeding and drinking rhythms, consuming 57 percent of their food and 63 percent of their water in the dark, as compared with 93 percent and 96 percent for 8 sham operated controls. Food and water were always available ad lib, but in all other respects Gold and Kapatos' procedures were identical to those of the present study.

The residual nocturnal rhythms suggest that the neural substrates responsible for nocturnal rhythms are less severly damaged by parasagittal knife cuts than they are by medial hypothalamic lesions. In contrast, the rate of weight gain after knife cuts is comparable to that after lesions [12,19].

Medial hypothalamic lesions that produce obesity may damage the underlying median eminence or some of its afferent connections and thereby may prevent circadian peaks in the release of pituitary hormones such as growth hormone [18]. Medial hypothalamic lesions may also dam- age longitudinal retinofugal projections that appear to be necessary for light modulation of day/night cycles [6, 17, 23]. In contrast to medial hypothalamic lesions, para- sagittal hypothalamic knife cuts which produce obesity spare the median eminence and should also spare most lon- gitudinal projections. Perhaps the neural substrate for the nocturnal feeding rhythm is intact after parasagittal knife cuts but the rhythm is overcome by enhanced motivation [201.

We conclude that satiety and nocturnal rhythms may have separate though adjacent neural substrates.

We also conclude that hyperphagic rats can defend their rapid rate of weight gain, which suggests that body weight regulation is altered, not abandoned.

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