Thirst and saccharin preference in rats

Physiology and Behavior. Vol. 6. pp. 287-292. Pergamon Press. 1971. Printed in Great Britain

Thirst and Saccharin Preference in Rats! ANDREW STROUTHES State University of New York at Binghamton, N. Y. 13901, U.S.A, (Received 6 July 1970) STROUTHES, A. Thirst and saccharin preference in rats. PHYSIOL. ~EHAV. 6 (4),287-292, 1971.-Three experi,me~ts with 112 water-deprived rats initially showed higher water than saccharIn c,onsumplio~ regar~less of whether th~ lIqUids were presented singly or as a choice, and whether food was available or withheld dUrIng testmg. More sacch~rm, than water was consumed later. The reversal from water to saccharin was positivelY,related to hours of water deprIvatIOn and per cent saccharin concentration and occurred with either continuous or mterrupted expos~r~. It was conc,luded, that rats must first drink water in order to reduce their water deficit to some threshold before saccharIn IS drunk. PostmgestlOnal and oral factors then become responsible for ingestion of large quantities of saccharin. Saccharin Saccharin-soda bicarbonate Consummatory behavior

Water deprivation

UNDEPRIVED rats offered a continuous choice between water and saccharin generally consumed more saccharin than water [8, 13]. Saccharin preference was also shown in investigations in which either concentrations, procedures, or hunger and combined hunger and thirst were varied [1--4, 7, 12]. On the other hand, water deprived rats presented with a choice between saccharin and water consumed more water in the initial 90 min but total saccharin intake 48 hr later was significantly higher than total water. The switch to saccharin was positively related to hours of water deprivation and per cent saccharin concentration [9]. These findings were confirmed in a later study [5] in which water deprived animals were permitted 90 min of water and saccharin daily. In this study, Experiments 1 and 2 were designed to determine whether thirsty rats, and hence hungry because of selfimposed food deprivation, would still prefer water t? saccharin even when food was withheld during presentation of the liquids. Withholding food should increase the likelihood of saccharin selection both for its water and for its taste. In Experiment 2 only a single tube was made available. This arrangement eliminates response competition. Secondly, if thirst and/or hunger reduction are attained they have to be by means of a substance with which the animals have practically no prior experience. Furthermore, the effect of saccharin at both the sensory and postingestional levels are not confounded by water drinking. In Experiment 3 an attempt was made to obtain evidence which would permit detailed examination of the consumption shift from water to saccharin. For this purpose both water deprivation and testing were repeated on numerous consecutive sessions. METHOD

Animals, Apparatus, and General Procedures for the three experiments were as follows:

Food withholding during test

Palatability

Animals The animals were Sprague-Dawley, male, albino rats ranging from 105 to 110 days of age at the start of the experiment. They had no prior experience with either water or food deprivation or saccharin. Apparatus and Procedure The apparatus and basic procedures were identical to those described in an earlier study [9]. The rats were housed individually in 25! X 18 X 19 cm stainless steel living cages on the front of which were holes for insertion of Richter tubes. In the choice condition one tube contained deionized water the other 0.1 per cent or 1.0 per cent saccharin. In the single tube condition the tube contained anyone of the three substances. Since percentage concentration was achieved by 100 X saccharin/water saccharin and since only 50 per cent of the tablet was sodium of saccharin, the cited per cent saccharin concentration values ought to be multiplied by!. (The cited percentage concentration values were retained to maintain uniformity between this and the previous studies.) In the choice condition the forced-sampling procedure was used. It involved inserting singly, first one tube then the other, each time until the substance was tasted. Withdrawal of the second tube was immediately followed by simultaneous introduction of both tubes. Timing began when the rat licked one of the two tubes following simultaneous introduction. The presentation order and the positions of the two liquids were counterbalanced. In the single tube case, timing started when the rat licked the tube. In all experiments, liquid intakes were recorded every 10 min during the first 90 min of the experiment. Experimental sessions began at 3,00 p.m. in an air conditioned vivarium which was illuminated from 6.30 a.m to 6.30 p.m. and the ambient temperature of which was maintained at approximately 21°C.

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'The saccharin used in this and all studies involving this author was purchased in commercial tablet form from Norwich Pharmacal Co., Norwich, New York. It consisted of half sodium saccharin and half soda bicarbonate, 287

288

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EXPERIMENT

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Animals and Design

The animals were 32 110-day old rats which were deprived of water for 48 hr prior to the test. Two groups of eight animals each were offered a choice between water and 0.1 per cent or 1.0 per cent saccharin. Food (F), Purina Laboratory Chow, was continuously available for these two groups. They were labelled 48-H0.1F and 48-H1F and they constituted part of an earlier study [9] henceforth referred to as Exp. O. The other two groups of eight rats each were offered No Food (NF) during the test. They were labelled 48-H0.1 NF and 48HINF for choice between water and 0.1 per cent and water and 1.0 per cent respectively. Food was removed when the liquids were inserted and was withheld throughout the experiment. The experiment lasted 48 hr. Intakes were recorded during the first 90 min and 24 (Day 1) and 48 (Day 2) hr following continuous liquid exposure. Results Figure 1 shows the mean 90-min 0.1 per cent and 1.0 per cent saccharin and water intakes per to-min intervals by the F and NF groups. Figure 1, A and B, represents performance by the two F groups from Exp. O. It is reproduced here for comparison purposes. Figure 1, C and D, represents the two NF groups. It was found that the 48-HO.INF mean water intake was higher than the mean saccharin consumption, though the differences were not significant at any to-min point, throughout the first 60 min. By the 70th min saccharin and water intakes reversed. There were no significant differences at any point during the remainder of the 90 min. The 48-HINF mean water intake on the other hand, significantly exceeded their mean saccharin not only during the first to

min (t = 5.84, p < 0.001) but also for the entire 90-min interval (t = 8.11, p < 0.001). Consumption comparisons between corresponding groups, choice-NF (Fig. 1, C and D) and choice-F (Fig. 1, A and B) revealed that for the first 90 min the saccharin and water intake trends were similar. The differences in saccharin and in water for corresponding groups in the two conditions were not significant, and although total liquid consumption (saccharin water) appeared higher by the higher concentration F groups it was in the 0.1 per cent groups that any differences were substantial: the 48-HO.1 F drank reliably more than the 48-H0.1NF (t = 3.43, p < 0.01). In Fig. 2 under Experiment 1, are presented the mean Day 1 and Day 2 water and saccharin consumptions by the F and NF 48-H0.1 and 48-Hl groups. (The mean intake of saccharin + water by the same groups are also shown.) Groud 48-HO.l NF saccharin intake, lower than water during the first 90 min, exceeded water intake at both Day 1 (t = 8.58, p < 0.001) and Day 2 (t = 8.49, p < 0.001). The effect was more pronounced when comparisons were made between saccharin and water intakes for the higher concentration group, 48-HINF. Here the rats preferred saccharin to water on Day 1 (t = 8.14, p < 0.001) and on Day 2 (t = 12.00, p < 0.001), though the reverse was the case during the first 90 min of testing. The 48-HINF consumed more saccharin than the 48-HIF (t = 3.37, p < 0.01 and t = 6.57, p < 0.001 for Days 1 and 2 respectively). With regard to their water intakes the reverse held: the F animals drank more water than the NF animals (t = 4.69, p < 0.001, and t = 3.86, p < 0.01 for Days 1 and 2 respectively). Like the 48-Hl, the saccharin intakes by the 48-HO.l differed in favor of NF (t = 2.23 and 3.69, at p < 0.05 and < 0.01 for Days 1 and 2 respectively). Unlike the 48-Hl, the water intakes by the F and the NF groups did

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Resulls Figure 3, A and B, shows the single tube intakes for the first 90 min of drinking. Figure 3 A shows consumptions by the F groups. It was found that for the first 10 min, group 48-HF drank more than group 48-0.1F(1 = 2.24, p < 0.05), and still more than group 48-IF (t = 7.19, p < 0.001). Group 48-0.1F drank more than group 48-IF (t = 2.36, p < 0.05). By 90 min, however, the mean total consumptions were not reliably different. In Fig. 3B are shown the mean intakes by the NF groups. Here the consumptions in the first 10 min were in the same order as those obtained under F conditions (Fig. 3A) only the differences were more pronounced. For instance, intake by group 48-HNF was higher than intake by group 48-0.INF (I = 3.12, p < 0.01), and still higher than that by group 48-1NF (I = 6.39,p < 0.001). Group 48-0.1NF drank more than Group 48-1NF (I = 3.96, p < 0.01). Unlike under F conditions (Fig. 3A), the NF conditions yielded consumptions by the 48-H group which were reliably higher than consumptions by the 48-.1 group (I = 2.31, p < 0.05). Incidentally, though group 48-0.1NF drank more than group 48-1NF at 10 min, by the end of the 90-min test period, intake by group 48-0.1 NF dropped below that of group 48INF.

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FIG. 2. Daily mean consumptions of water and 0.1 per cent, water and 1.0 per cent, water, 0.1 per cent, and of 1.0 per cent on two consecutive days by 48-hr water deprived rats in choice (Experiment 1) and single (Experiment 2), allowed Food or No Food during testing. Mean saccharin + water are shown for choice groups.

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not differ (t = 1.86 and 0.30 for Days I and 2 respectively) though whatever differences existed were in favor of the F groups. Saccharin water consumptions between the F and the NF groups showed: (a) that the NF consumed more liquid than the F groups; (b) that the effect was more marked for the higher than for the lower concentration groups; and, (c) that the effect was larger on Day 2 than on Day I (I = 2.74, p < 0.05, and 1= 6.31, p < 0.001 for 48-HI Day I and 2 respectively; I-values for 48-HO.I Day I and 2 were 1.58, p > 0.05 and 3.67, p < 0.01 respectively).

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Animals and Design Whereas in Experiment I, 48-hr water deprived rats were presented with a choice between water and either 0.1 per cent or 1.0 per cent saccharin, in Experiment 2, rats at 48-hr water deprivation were offered a single tube of either water or 0.1 per cent or 1.0 per cent saccharin. There were 50 110-day old rats randomly assigned to three conditions designated as 48-H, 48-0.1 and 48-1. In each of the three conditions half of the animals were with food (F) during the test whereas for the other half there was no food (NF) from the time of liquid insertion to termination of the experiment. All groups but 48-HF and 48-IF, consisted of 8 animals each. The exceptions had 9 each. Experiment 2 and half of Experiment I (NF conditions) were run simultaneously. As in Experiment 1, records were taken during the first 90 min and 24 (Day 1) and 48 (Day 2) hr following continuous liquid exposure.

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FIG. 3. Mean 90-min consumptions of water, 0.1 per cent, and of 1.0 per cent per 10 min intervals by 48-hr water deprived rats allowed Food or No Food during testing. Numbers represent mean intakes for entire 90 min.

Ninety-min consumption comparisons between analogous groups under F and under NF conditions showed that the F conditions led to higher liquid consumption. This is a reproducable finding reflecting water requirement in the metabolic process. The 48-0.1 groups yielded the largest difference (I = 4.14, p < 0.001) whereas the 48-H and 48-1 groups yielded I-values of 2.61 (p < 0.05) and 1.90 (p > 0.05) respectively.

290

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Figure 2 under Experiment 2, shows 48 hr of single tube drinking by F and NF groups recorded twice, 24 hr apart (Day 1 and Day 2). Comparisons between these groups on Day 1 revealed that only the 48-H groups differed; the 48-HF drank more than the 48-HNF (t = 2.57, p < 0.05). The F and the NF groups for 48-0.1 and 48-1 yielded t-values of 0.47 and 1.99 respectively, neither of which was significant. Comparisons among the F groups showed that the saccharin groups drank more than the water group; e.g. 48-H vs. 48-1 and 48-H vs. 48-0.1 yielded t-values of 2.85 and 2.90 both at p < 0.05, while the 48-1 vs. 48-0.1 was not significant (t = 0.37). However, similar tests of significance for the NF groups showed that only 48-1 drank more than 48-H (t = 3.67, p < 0.01). In the other comparisons, though the higher concentration groups drank more, the differences were not significant (HNF vs. O.INF, t = 1.22; O.1NF vs. INF, t = 1.64). Test of significance for analogous groups were carried out for Day 2 intakes. The findings showed that the 48-HF group again drank significantly more than the 48-HNF (t = 2.86, p < 0.05); the 48-o.1F did drink more than the 48-0.1NF though not significantly so (t = 0.98, p > 0.05); and the 48-1 groups differed in favor of the NF condition (t = 3.60, p < 0.01). Significance tests for the similarly treated groups showed more reliable differences on Day 2 than on Day 1. The tvalues for F groups 48-H, vs. 48-0.1, 48-H vs. 48-1, and 48-0.1 vs. 48-1, were 2.56 (p < 0.05), 3.49 (P < 0.01), and 1.84 (p > 0.05) respectively. Similarly, the NF group comparisons yielded t-values of 1.64 (p > 0.05), 7.58 (P < 0.001), and 5.05 (p < 0.001), for the 48-H vs. 48-0.1, 48-H vs. 48-1 and 48-0.1 vs. 48-1 respectively. To summarize, excepting 48-1, the F groups consumed more than the NF groups; these differences

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became more in number and larger in magnitude by Day 2. Viewing the entire Fig. 2, and considering in the choice water), it is clear situation total liquid intakes (saccharin that in all but two cases, intakes decreased from Day 1 to Day 2.

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EXPERIMENT

Animals and Design

Thirty lOS-day old rats were employed in Experiment 3. They were randomly assigned to three groups of 10 each. They were labeled: 24-H, 24-HO.l, and 24-H1. That is, 24-hour water deprived rats were presented either with water only, or with a choice between water and 0.1 per cent, or water and 1.0 per cent saccharin, respectively. Food was continuously available. The same testing procedure repeated itself 7 more times over 8 consecutive days separated by 221 hr during which water was withheld. This design was intended to provide data which would reflect on the features of the shift from water to saccharin. In addition it constituted for the first 90 min of testing a replication of two of the conditions of Exp. O. Results

Figure 4 shows the liquid consumptions by the three groups recorded every 10 min on eight 90-min sessions separated by 24 hr. Day 1 mean cumulative water consumption values by the 24-Hl (Fig. 4, top) were reliably higher than saccharin at every lO-min point. For example, t-values at 10 min, 50 min, and 90 min, were 9.26, 6.61 and 3.27 respectively (all at p < 0.01). Water was more preferred still on Days 2 and 3 both at 10 min and the entire 9O-min period. The tvalues at 90 min were 3.87 (p < 0.002), and 3.36, (p < 0.01)

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90

THIRST AND SACCHARIN PREFERENCE IN RATS

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for Days 2 and 3 respectively. On Day 4 a reversal occurred. At 10 min water was preferred though not reliably (t = 0.69, p > 0.05), but by 90 min of the same day saccharin became the preferred substance (t = 2.44, p < 0.05). The trend continued for the next 2 days: at 10 min though preferred, 1.0 per cent saccharin was not significantly higher than water (t = 1.35 and 0.99, p > 0.05 for the 5th and 6th days respectively) but by 90 min the saccharin preference was indeed marked (t = 4.06, p < 0.001 for Day 5; t = 5.18, p < 0.001 for Day 6). Finally, on Days 7 and 8 saccharin was preferred at both 10 min (t = 5.32 and 6.97, p < 0.001 for Days 7 and 8 respectively) and at 90 min (t = 10.73 and 8.38, p < 0.001 for Days 7 and 8 respectively). Thus, given a choice between water and 1.0 per cent saccharin, 24-hr thirsty rats consumed more water at the beginning of each 90-min session. Within each session water progressively dropped whereas saccharin increased. Similarly over the 8 sessions: while water consumption started high and decreased, the saccharin intake behaved in the reverse fashion. Unlike group 24-HI, group's 24-H0.1 water consumption (Fig. 4, center) was not different from saccharin at 10 min (t = 1.55, p > 0.05) nor was it by the end of the 90-min session (t = 0.16, p > 0.05) of Day I. By Day 2, 0.1 per cent saccharin was preferred to water (t = 2.19, p < 0.05) and from Day 3 on, saccharin became progressively more preferred. Comparisons of 90-min saccharin and water intakes yielded t-values of 3.02 (p < 0.01) and 5.68 (p < 0.001) for Days 3 and 8 respectively. The shift is nicely demonstrated in Fig. 5 also in which the saccharin and water means for the entire 90 min were plotted.

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FIG. 5. Mean 90-min consumptions of water, water and 0.1 per cent, and of water and 1.0 per cent per day for 8 days 24 hr apart, by 24-hr water deprived rats in Experiment 3.

Water consumption by the 24-H group shown in Figs. 4 (bottom) and 5 remained remarkably steady over the 8-day test. Comparisons revealed no significant differences in water intake between any two sessions. Finally, the 3 groups' total liquid intakes (saccharin + water in the case of 24-H0.1 and 24-Hl) were compared.

Mean liquid intakes by any two groups yielded no significant differences on Day 1. By Day 8, however, mean water by the 24-H group was lower than mean liquid by 24-HI (t = 3.28, p < 0.01) and mean liquid by 24-H0.1 (t = 3.27, P < 0.01). The two saccharin groups' liquid intakes were not reliably different on Day 8. DISCUSSION Previous experiments have shown that undeprived, hungry, and hungry and thirsty rats prefer saccharin to water. However, the combined findings from this series of experiments show that within 90 min of testing rats consume more water than 0.1 per cent or 1.0 per cent saccharin whether the substances are offered singly or as a choice, and, whether food is present or absent during testing. By 24 or 48 hr of continuous exposure, saccharin becomes preferred. This reversal has been found to be related to both hours of water deprivation and saccharin concentration, and occurs after one deprivation and continuous liquid exposure (Experiments I and 2) or after a number of deprivations and liquid exposures (Experiment 3). Thus, different deprivation states do influence preferred concentrations of saccharin [11]. The 48-hr water deprivation then, seems to have the initial effect of reversing the saccharin-water relationship typically exhibited by undeprived, hungry, and hungry and thirsty rats. In these experiments both the single and the choice situations yielded data which reflect on the preference values of the two substances in the course of testing. In the choice situation water deprived animals, free to select and consume as much of whichever substance they choose to, did select the water and drank more and possibly enough of it so that for a short time at least, these animals did not differ from the normally undeprived in the sense that they, like the undeprived, became disposed to drinking saccharin. The single saccharin tube is a situation in which an animal does not reduce its thirst by drinking water from the water tube. In this case it is assumed that thirsty rats drink their water out of the saccharin solution. When they are rendered less thirsty, or a certain threshold has been reached, then they become disposed to drinking it as saccharin. The data from Experiment 3 also lend support to the argument that rats must drink water first before drinking saccharin. At the beginning of each session animals drank water and then gradually shifted to saccharin. This reversal occurred both within sessions and as a function of repetitions. It was not until Day 7 in the case of 1.0 per cent and sooner for 0.1 per cent, that rats drank more saccharin than water soon after they were exposed to the two substances. The 90-min intakes in these experiments show no effects which bear positively on the position that " ... a normal rat treats a saccharin solution as either a food or a fluid depending upon its state of deprivation. When hungry it eats a saccharin solution, and when thirsty it drinks the saccharin" ([10], p. 58). On the question of saccharin preference by water deprived rats in the presence or absence of food during testing, the findings do not support the hypothesis that thirsty rats choose saccharin for its food-like taste as well as for its water. Those who hold this view would expect the NF saccharin group, and especially the single tube group, to drink more than say, the NF water group. Their reason is that in the case of the single tube condition, both the single saccharin and single water"... would drink for water but the saccharin group, being somewhat hungry because of dry food without water during water deprivation would also drink to get the taste." (Sheffield F. D., personal communication, April,

292

STROUTHES

1968.) The results are unequivocal and certainly contrary to such expectations. By 10 min, and regardless of food availability, the single water drank more than the single saccharin. The NF groups then, initially do not drink saccharin, certainly not for taste. If they do eat it at all, they do so only after a certain degree of thirst reduction. After the initial stage when rats have already reduced thirst to some degree, they switch to saccharin and consume large quantities of it. This is not necessarily support for the position that rats, water-deprived prior to the test and therefore also hungry, drink saccharin for taste any more than animals undeprived of both food and water select and drink almost exclusively large quantities of saccharin for 2 days [9]; or, any more than animals in the later stages of Experiment 3 choose saccharin over water. More simply viewed then, rats

on a water deprivation cycle first drink water. They do this either from the water-tube or from the saccharin solution and with training perhaps directly from saccharin solution in order to reduce thirst to a certain threshold. At or beyond this threshold, as in the case of undeprived rats, stimulation of the mouth receptors may assume direct control of saccharin ingestion including the instrumental responses which lead to such ingestion [6]. In the case of those without food during testing, they too drink for water whether from the water tube or from the saccharin solution itself, in order to achieve some thirst reduction at and beyond which saccharin becomes palatable. Thereafter postingestional effects perhaps optimally elicited in the NF groups by large saccharin quantities may be responsible for continued drinking and leading to what appears exaggerated quantities drunk for taste.

REFERENCES I. Bacon, W. E., H. L. Snyder and S. H. Hulse. Saccharine preference in satiated and deprived rats. J. compo physio/. Psycho/. 55: 112-114, 1962. 2. Beebe-Center, J. G., P. Black, A. C. Hoffman and M. Wade. Relative per diem consumption as a measure of preference in the rat. J. compo physio/. Psycho/. 41: 239-251, 1948. 3. Hausmann, M. F. The behavior of albino rats in choosing foods: II. Differentiation between sugar and saccharin. J. compo Psychol. 15: 419-428, 1933. 4. Hulse, S. H., H. L. Snyder and W. E. Bacon. Instrumental licking behavior as a function of schedule, volume. and concentration of a saccharine reinforcer. J. expo Psychol. 60: 359-364, 1960. 5. Navarick, D. J. and A. Strouthes. Relative intake of saccharine and water on a restricted drinking schedule. Psychonom. Sci. 15: 158-159, 1969. 6. Pfaffmann, C. The pleasures of sensation. Psycho/. Rev. 67: 253-268, 1960. 7. Sheffield, F. D. and T. B. Roby. Reward value of a nonnutritive sweet taste. J. compo physiol. Psycho!. 43: 471-481, 1950.

8. Strouthes, A. Long range two-choice saccharine and water consumption in rats. J. compo physio/. Psychol. 73: 123-134, 1970. 9. Strouthes, A. and D. J. Navarick. Saccharine and H 20 consumption as a function of H 20 deprivation. PsycllOnom. Sci. 9: 523-524, 1967. 10. Teitelbaum, P. Disturbances in feeding and drinking behavior after hypothalamic lesions. In: Nebraska Symposium on Motivation, edited by M. R. Jones. Lincoln: University of Nebraska Press, 1961. II. Young, P. T. The role of affective processes in learning and motivation. Psycho!. Rev. 66: 104-125, 1959. 12. Young, P. T. and J. T. Green. Relative acceptability of saccharine solutions as revealed by different methods. J. compo physiol. Psycho/. 46: 295-298, 1953. 13. Young, P. T. and H. W. Richey. Diurnal drinking patterns in the rat. J. compo physiol. Psychol. 45: 80-87, 1952.