Incidence of food-deprivation polydipsia in the white Swiss mouse

Physiology and Behavior. Vol. 7, pp. 395--399. Pergamon Press, 1971. Printed in Great Britain

Incidence of Food-deprivation Polydipsia in the White Swiss Mouse C H A R L E S L. K U T S C H E R

Department of Psychology, Syracuse University, Syracuse, New York, U.S.A. (Received 29 March 1971) K~HER, C. L. Incidenceoffood-deprivation polydipsia in the whiteSwissmouse. PHYSIOL.BEHAV.7 (3) 395-399, 1971.-Polydipsia was observed in white Swiss mice given no food, ½-normal food rations, or a 2-hr daily feeding period. The last two food-deprivation schedules resulted in greater incidence of polydipsia than the no-food condition. The response was not sex-dependent and was not affected by the ingestion of non-nutritive stomach fill. It is suggested that the extreme variability of drinking under food deprivation may result from the random breeding of this mouse strain.

Circadian rhythm

Deprivation

Interaction (of feeding and drinking)

Mouse

Polydipsia

with regard to incidence and characteristics of polydipsia on three types of food-deprivation schedules.

LON~-~aM studies of growing rabbits [5] and rats [6] have shown that water intake increases in approximately linear manner with increases in food intake. Since the rat eating dry food seems to show maximal water conservation [24], total water intake in that species has been characterized [6] as a composite of the volume of water needed for the ingestion and digestion of food and the excretion of feces and the volume needed for the rat's other basal metabolic water requirements. During food deprivation, an animal's water needs should thus be less than when food is given ad lib because body water need not be diverted for food digestion [15] and because a portion of the water normally held in hydration in the gut contents is recovered as the gut empties [21]. Food deprivation has been found to produce a decrease in water intake in rats [1, 2, 6, 9, 11, 21], in dogs [10], and in female rabbits during the time when reproductive structures are active [5]. Paradoxically, other reports have shown that food deprivation leads to increased water intake in guinea pigs [4], male rabbits [5], gerbils and hamsters [11-13], and in one strain of rats [21]. Kutscher [11] found that food-deprived gerbils drank their body weight in water during the course of a 24-hr period and excreted dilute urine approximately equal in volume to the water intake [12]. Cizek [4] reported that food-deprived guinea pigs died from convulsive seizures presumably caused by severe overhydration resulting from the vigorous food-deprivation polydipsia (FDP). In order to determine physiological differences between animals showing FDP from those which do not, it is desirable to study FDP in a variety of species and strain.~ since available evidence indicates that polydipsic responses may differ in physiological characteristics and ori~n~ and possibly in behavioral characteristics. For example, FDP in the rabbit is related to sex hormones and sodium metabolism [5, 7], whereas in the gerbil it is not [12, 27]. This paper provides the first report of FDP in the randomly-bred male and female white Swiss mouse and attempts to describe the phenomenon

METHOD

Animals In this study animals were 136 randomly-bred Swiss albino mice (MIL/Ha/ICR) obtained from ARS/Sprague Dawley Co., Millerton, N.Y. Seventy-four were males and 62 were females. Seven mice were 280 days old and the remainder were 100-150 days old at the time of testing. Other animals tested in order to provide comparative data for the interpretation and evaluation of the mouse data were: Long-Evans rats, 14 males, 150-180 days old; Wistar rats, 5 males, 5 females, 150 days old; Holtzman rats, 5 males, 110 days old; gerbils, 21 males and 20 females, 100-180 days old. Long-Evans rats were obtained from the colony of the Psychology Department at Syracuse University, Holtzman rats from the Holtzman Co. (Madison, Wise.), Wistar rats from Manor Research (Staatsburg, N.Y.), and gerbils from Tumblehrook Farms (Brant Lake, N.Y.).

Apparatus Mice were housed in individual steel cages (5 × 5 x 5t in.) with tops of ¼in. hardware cloth. Floors were either covered with Sterolit, a granular clay material, or were fine mesh wire inserts placed in the cage to prevent the mice from eating the Stexolit. Gerbils and rats were housed in cages of steel and hardware cloth (10 x 8 x 7 in.) with wire mesh floors. Water intakes were measured by means of 100 ml eudiometer tubes (graduated in 0.2 ml units) or 100 ml cylinders (graduated in 1.0 ml units). Lights were on for 12 hr/day. Temperature and humidity were maintained at 21 4- I°C and 50%, respectively. Food was Purina Chow in pellet form. 395

396

KUTSCHER

Procedure Four types of feeding schedules were used in the mouse experiments: (a) no-food schedule (total food deprivation); (b) 22-hr food-deprivation schedule on which mice were allowed free access to food for 2 hr/day; (c) ~-food schedule on which mice were given food approximately equal in amount to ~ of their ad lib food intake, an amount found empirically to be approximately 7 per cent of predeprivation body weight; and, (d) a control condition on which food was given ad lib. In all conditions tap water was freely available at all times. Fifty-one mice, 29 males and 22 females, were tested under the no-food condition. F o r 27 mice cage floors were fine mesh screen and for 24, floors were covered with Sterolit. Under the 22-hr schedule 20 males and 20 females were tested, half on wire floors and half on Sterolit floors. In the I-food condition 20 mice, 10 males and 10 females, were tested, half on Sterolit and half on wire floors. Control animals were 15 males and 10 females, 15 housed on Sterolit and 10 on wire floors. Mice were placed in test cages and allowed at least three days to adapt to cages and drinking tubes. Water intakes were then measured for 7 - I 0 days with food given ad lib before deprivation was initiated. Under the 22-hr fooddeprivation schedule, food pellets were placed in the cage for a 2-hr period with intakes determined by weighing pellets before and after the feeding period. F o r the ½-food condition, pellets were carved to be equal in weight to 7 per cent of the mean predeprivation body weight of each animal. In the rat and gerbil experiments, only total food deprivation was used. Rats were observed over seven days of food deprivation, gerbils over three days. RESULTS

Inspection of the raw data on water intakes indicated that water intake patterns during deprivation were highly individualistic in the white Swiss mouse. This extreme behavioral variability precluded plotting of group means, except for the control group. F o r example, during food deprivation periods some mice showed only depressed drinking while some showed polydipsia either early or late in the schedule, or sporadically or consistently throughout the schedule. The pattern of polydipsia could not be related to sex, rate or level o f body weight loss, or availability of Sterolit. Water intakes are therefore presented in terms of the following arbitrary measures: (a) peak intake, defined as the mean daily water intake calculated on the two days of highest water intake during the deprivation schedule and expressed as a percentage of the mean 7-day water intake during the predeprivation period; (b) incidence of polydipsia, i.e. number of animals reaching the criterion of polydipsia, with the criterion defined as the peak intake measure equal to or exceeding 150 per cent; and, (c) percentage of individual test days when polydipsia appeared, for those mice reaching the polydipsic criterion, with a 1~lydipsic day dofined as a day on which water intake equalled or exceeded 150 per cent of the mean 7-day intake during t h e predcprivation period. Statistical comparisons involving incidence of polydi0sia, as defined by the peak intake water measure, were made with the Chi-square test comparing groups in terms o f numbers of polydipsic and nonpolydipsic mice. Comparisons involving the other two measures were made with t-tests. Statistical comparisons made between males and females, combining data over all deprivation conditions and both types of cage floors, revealed no significant sex differences

on the three measures taken. Similarly, no significant differences were found due to type of cage floor, combining data over both sexes and all deprivation conditions, in one subexperiment under the no-food schedule, mean weight of excreted boluses of Sterolit were 1.8, 1.1 and 0.5 gm for the first three days of deprivation, respectively. The Sterolit ingestion thus provided a small amount of bulk in the gastrointestinal tract, but probably provided no nutritive value whatever and had no significant effect on polydipsia. Data on polydipsia shown in Table 1 and Figs. 1 and 2 resulted from combining data from the various subexperiments within each deprivation condition. TABLE 1 CHARACTERISTICS OF FOOD-DEPRIVATION POLYD1PStA UNDER THREE TYPES OF FOOD DEPRIVATION IN WHITE SWISS MiCE

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l-food Schedule

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1.9 1-3

2.1 1-4

8.7 1-27

Test days/polydipsic animal Mean Range

3.6 2-5

6.2 3-7

26,3 8-30

53 20-75

36 14-67

33 3-90

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FIG. 1. Peak intake measures for control (nondoprived) mice during the first seven days and during the ¢ntirt 30 days ofobsorvation. On the x axis are plotted peak water intakes calculated as a percentage of mean 7-day baseline intakes. On the y axis are plotted frequencies of mice in each peak intake category. The vertical dotted line is the oolydipsia criterion (peak intake measure equals or exceeds 150 per cent).

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the 22-hr schedule (36 per cent) than on the no-food schedule (53 per cent). Observations were limited to a seven-day test period since many mice did not adapt well to the 22-hr schedule; however, four were maintained on schedule for an additional 24 days and probably would have survived much longer. The pattern of polydipsia onset and duration was different for each mouse and it was not possible to correlate onset of polydipsia with any particular level of weight loss. Of the 28 polydipsic mice, 11 showed polydipsia first on Day 1 of deprivation, four on Day 2, two on Day 3, nine on Day 4, and two on Day 5. On the two days of peak water intake for the polydipsic animals, 24 per cent of the mean daily water intake occurred during the 2-hr feeding period and 76 per cent occurred during the 22-hr period when no food was available, indicating that the bulk of water ingestion was not prandial.

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Control Groups Mean peak intake was 117 per cent for the first seven days of testing and 126 per cent for the entire 30 days of testing. One of the 25 control mice reached the polydipsic criterion, but only two days of polydipsia occurred out of 590 animaltest days for this group. The stability of water intake for the control group may be explained, in part, by the fact that body weight of the control mice did not change significantly during the 30-day test.

No-food Schedule Observations of water intakes under this schedule were limited because mice did not survive more than five days. Polydipsia, as defined by the peak intake measure, was demonstrated in 35 per cent of the mice; however, 42 per cent showed only depressed drinking, i.e. peak intakes less than 100 per cent. Figure 2 shows that considerable variability existed in the peak intake measures of the polydipsic animals on the no-food schedule, as well as on the other two deprivation schedules. Of the 18 polydipsic mice in the no-food condition, five showed polydipsia first on Day 1, nine on Day 2, two on Day 3, and two on Day 4.

Twenty-two-hr Schedule Compared to the no-food schedule, the 22-hr schedule produced longer survival times and greater incidence of polydipsia (70 per cent vs. 35 per cent, p < 0.01). Mean peak intake for the 22-hr schedule (216 per cent) was not significantly different from that of the no-food schedule 55 per cent). Mean prcentage of test days on which polydipsia appeared was less (p < 0.05) for polydipsic mice on

In general, mice adapted well to this schedule with many surviving for 35 days even though body weight losses were considerable (e.g. mean cumulative body weight loss was 38 per cent on Day 26 of the schedule). Thirty-five per cent of the mice did not show any polydipsia, as defined by the peak intake measure, in spite of the extended observation period and the substantial weight losses. Of the mice showing polydipsia, patterns of drinking were extremely individualistic. lndicidence of polydipsia on the ½-food schedule (65 per cent) was not significantly different from incidence on the 22-hr schedule (70 per cent), although it was greater (p < 0.05) than on the no-food schedule (35 per cent). Mean peak intake measure for the ½-food schedule group (239 per cent) did not differ from the other two groups, but percentage of test days on which polydipsia appeared (33 per cent) was less (p < 0.05) than that on the no-food schedule (53 per cent), but not different from that on the 22-hr schedule (36 per cent).

Rats and Gerbils Figure 3 presents the data on the peak intake measure for gerbils and the three rat strains. All rats showed depressed drinking and no polydipsia whatever, the usual finding in all rat experiments conducted in the author's laboratory. In the sample of 41 gerbils tested, every one met the polydipsia criterion although the variability in the peak intake measure was large. For 35 out of the 41 gerbils, water intakes increased progressively over the three days of total food deprivation.

Circadian Rhythms of Drinking Figure 4 shows the hourly water intakes of a group of seven mice observed on three ad lib days and on three days of total food deprivation. The four mice which became polydipsic (Fig. 4a) showed rather clear circadian rhythms with more water consumed during the dark phase than during the light phase. During polydipsia the circadian rhythms were preserved and drinking during the dark phase was greatly increased. The three nonpolydipsic mice also exhibited circadian rhythms during the ad lib days but the rhythms were somewhat obscured during the last two days of food deprivation. DISCUSSION

The results clearly indicate that FDP occurs in the MIL/ Ha/ICR strain of ~vhite Swiss mice although considerable variability exists concerning incidence, extent, and duration

398

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FIG. 4. Hourly water intakes for (a) four polydipsic mice and Co) three nonpolydipsic mice on Days 3, 6 and 7 of the 7-day prcdaprivation period tad lib) and for three days of total food deprivation (dep.). Thick horizontal bar indicates the dark cycle.

of the polydipsia. The F D P in the white Swiss mouse is unlike that in the rabbit [5] in that it is not sex-dependent. FDP was observed in sexually mature female mice in this study at a frequency and magnitude not siunifieantly different from that in male mice. Kutseher et al. [13] found that FDP in the hamster occurred in almost every animal tested, but

appeared toward the end of the deprivation schedule when weight losses were large and a few days before the animals were weakened by the schedule. In mice on the 22-hr or a-food schedules, however, water intakes were highly variable with polydipsia appearing early or late in the schedule, enduring throughout, or not occurring at all. In contrast, polydipsia in the gerbil appeared reliably in several experiments in the author's laboratory in approximately 95 per cent of the animals tested, and, although the response differed in magnitude among individuals, polydipsia could be reliably maintained for 2-4 weeks by appropriate deprivation schedules [11]. No convulsions due to water intoxication were observed in the mice such as those reported by Cizek [4] for the guinea pig, although some mice drank water equivalent in amount to their body weight during a 24-hr period. It is not known whether the apparent species differences in polydipsia can be related to differences in physiological changes consequent to food deprivation or to organic differences, e.g. peculiarities of renal function or hormone function during food deprivation. Figure 2 shows that within this single mouse strain there are both rat-like (depressed drinking) and gerbil-like (polydipsia) responses to food deprivation. Under the no-food condition, it may be that there was not time for polydipsia to develop in the 65 per cent of the group showing no polydipsia, but under the ~-food condition, 35 per cent of the mice did not become polydipsic even though they survived for more than 30 days on the schedule and incurred weight losses of 40 per cent of predeprivation body weight. This difference in type of response within a single mouse strain as well as the difference between rats and gerbils may be due to genetic differences which produce some as yet unspecified characteristics in the organisms resulting in a predisposition to a particular pattern of drinking during food deprivation. Using inbred mouse strains, Kutscher (unpublished observations) recently found that the C3H/HeJ and SWR/J strains consistently demonstrated FDP while the C57BL/6J strain never did. Because of its history of random breeding, the white Swiss strain may have genes which underlie both types of drinking responses. Possibly polydipsic and nonpolydipsic sublines could be developed from the white Swiss stock just as Roubicek and Ray [24] used selective breeding to develop polydipsic and nonpolydipsic sublines of rats. Similarly, Bovet et al. [3] found that various inbred mice have strain-specific patterns of performance in shuttle box avoidance learning with little variability in this behavior appearing within each strain. A randomly-bred white Swiss strain, however, showed large variability in performance and multiple response pattern. Genetic differences have also been found among inbred mouse strains in regard to such diverse types of behavior as alcohol preference [ 19], activity [ 16-18], and sexual behavior [20]. Correlations of water intakes for gerbils subjected to food deprivation on two occasions yielded correlation coefficients above +0.90 showing that individual gerbils are consistent in the degree of FDP exhibited [14]. The extreme variability in drinking during food deprivation could be used as a research tool since physiological and behavioral comparisons between polydipsic and nonpolydipsic mice of the same strain could be easier to make and interpret than differences between polydipsic and nonpolydipsic animals of different species, e.g. gerbils and rats. The identity and nature of the physiological variables underlying polydipsia cannot now be specified; however, the variables influencing water metabolism are well known [22]

FOOD-DEPRIVATION POLYDIPSIA

399

and can be easily investigated. It may be that crucial physiological differences between polydipsic and nonpolydipsic mice may be easier to identify and isolate than physiological differences underlying other types of behavior known to vary substantially among various mouse strains [16-20]. In the absence of data on water exchange, the internal environment and kidney function, one can only speculate on the possibility that F D P is a regulatory response occurring as a reaction to body-water deficit produced by food deprivation, but some relevant facts may be mentioned. Figure 4 shows that relatively little drinking occurred during the light phase of each 24-hr period for the polydipsic mice, especially on Days 1 and 2 of deprivation. If deprivation produced a sizable water deficit, more drinking during the light phase might be expected instead of increased drinking in the dark phase only. F o o d deprivation is known to produce or facilitate water diuresis in rats [21] and gerbils [12], although in both cases the polyuria was probably a response to water intakes exceeding body water needs and could be eliminated or attenuated by restriction of water intake volumes. Under the no-food condition, mean survival times and mean cumulative body weight losses were virtually identical for both polydipsic and nonpolydipsic animals, suggesting that the occurrence of polydipsia was not detrimental to the mice. The white Swiss mouse has the ability to maintain high rates of water exchange under self-induced water loads during

food deprivation. Palfai et aL [23] have shown that mice of the same strain maintained at approximately 70 per cent of ad lib body weight showed vigorous schedule-induced polydipsia and sometimes drank during a 3-hr test period water equivalent in amount to the deprivation body weight of the animal. Weight gain during the session often approximated the weight o f the food ingested, indicating that the large volumes of water consumed were readily excreted. Perhaps F D P occurs, not because of a deprivation-induced water deficiency, but because food deprivation increases motor excitability and thus facilitates release of all the various kinds of activities available to the animal, as suggested by Wayner [26]. The mice in this study had few behavioral possibilities open to them other than drinking in a cage rather barren of manipulanda. I f F D P is considered to be adjunctive behavior similar to schedule-induced polydipsia, two similarities are immediately apparent; both occur in the white Swiss mouse and both occur during food deprivation. On the other hand, scheduleinduced polydipsia appears in the tat [8], whereas depressed drinking in the home cage is usually reported during food deprivation [2, 6, 11]. Gerbils given multiple opportunities for non-nutritive oral activity showed an increase in drinking during food deprivation, but a decline or no change in all other oral activities [14]. Such observations have not yet been made on the mouse.

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