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A developmental study of schedule-induced polydipsia in the rat
A Developmental Study of Schedule-Induced Polydipsia in the Rat THOMAS
J. REYNOLDS,
JOHN T. KENNY,
AND JOHN W. WRIGHT
Fordham University, Johns Hopkins University, and Washington State University Rats 30, 60, 90, and 120 days of age were fed 105 45mg food pellets on a noncontingent VT 70-set schedule during 14 daily 2-hr sessions. Every animal became polydipsic on this schedule when compared with a schedule in which 105 pellets were presented at the beginning of the session. Mean polydipsic ratios (schedule intake/control intake) ranged from 2.9-5.4. Water intakes (milliliters per 1OOgbody weight) did not differ during the last five sessions as a function of age. The results are discussed with respect to the generality of the class of adjunctive behaviors.
Since Falk (1961) first reported excessive water consumption by rats barpressing for food on a VI 1-min schedule, studies of schedule-induced polydipsia have frequently focused upon potential controlling variables (see Falk, 1969). There has been some attempt to generalize beyond the mature laboratory rat, including the demonstration of polydipsia in rhesus monkey (Schuster & Woods, 1966), pigeon (Shanab & Peterson, 1969), albino Swiss mouse (Palfai, Kutscher, & Symons, 1971), chimpanzee (Deleher, cited in Falk, 1971), and humans (Kachanoff, Leveille, McLelland, & Wayner, 1973). Physiological data on adult animals have indicated that schedule-induced polydipsia appears not to be under the control of the recognized regulatory thirst stimuli (Kenny, Wright, & Reynolds, in press; Kissileff, 1973; Stricker & Adair, 1966). Recently, schedule-induced polydipsia has been analyzed for its theoretical importance, with Falk (1971) proposing that it is representative of a larger class of adjunctive behaviors including aggression, escape, wheel running, pica, and air licking. These responses are all characterized by their schedule and motivational dependence and their postreinforcement occurrence. Further, depending upon the specific environmental cues presented, these responses can substitute for each other. A major dimension missing from the literature is a systematic examination of schedule-induced polydipsia in the developing rat. In the present experiment, two developmental questions were addressed: (a) Do young rats respond to an intermittent reinforcement schedule by becoming Requests for reprints should be sent to Thomas J. Reynolds, Department of Psychology, Fordham University, Bronx, New York 10458. 284 Copyright All rights
0 1977 by Academic Press. Inc. of reproduction in any form reserved.
ISSN 0023-9690
DEVELOPMENTAL
polydipsic? (b) Is the drinking that of adult animals?
STUDY
OF
285
POLYDIPSIA
response of immature
rats comparable
to
METHOD Animals. Twenty-eight male albino Sprague-Dawley rats from seven litters born in our laboratory (Carworth stock) were weaned at 20 days and maintained, until testing began, in wire mesh group cages (39 x 35 x 17.5 cm) on a commercial dry diet and tap water at 17-24°C under a 12-12 light-dark cycle initiated at 0800 hr. Apparatus. Four commercial operant chambers with keys removed were equipped with food-pellet dispensers. A glass loo-ml graduated cylinder with a stainless steel drinking spout was attached to the outside of each chamber so that the spout tip was positioned 3.4 cm inside the chamber, 11.4 cm to the right of the food cup, and 3.8 cm above the hardware cloth floor. Food-pellet presentation was controlled by appropriate electromechanical equipment housed in the same darkened test room. Ambient white noise was maintained at 60-65 dB. Procedure. At weaning, four rats were randomly assigned to each of the following developmental groups: 30-, 60-, 90-, 120-day experimental groups; 30-, 60-, 90-day body-weight control groups. Ten days prior to these ages, the experimental animals were placed in individual cages (18 x 35 x 17.5 cm) and provided with demineralized water in loo-ml graduated cylinders with stainless steel drinking spouts. Water consumptions and body weights were recorded once daily between 1400 and 1600 hr. During the first 5 days after being placed in individual cages, experimental animals had food freely available. On the subsequent 5 days, body weights were reduced to 80% of their estimated free-feeding weights by restricting food intake. New estimates of free-feeding weights, based on the appropriate body-weight control group, were calculated at 3-day intervals for each animal according to the procedure of Kaplan & Kaplan (1965). Since pilot data indicated that 120-day-old animals did not gain weight significantly in the course of the testing period, this group served as its own body-weight control. On Days 1 l-24, 2-hr daily sessions were conducted between 1400 and 1600 hr with noncontingent delivery of 45-mg food pellets on a Variable Time (VT) 70-set schedule with demineralized water freely available. Pilot work indicated that session length should be set at 2 hr to avoid satiation of the younger animals. Water consumptions and body weights were recorded postsession, and a home-cage food supplement was given, when necessary, to maintain target body weights. Day 25 served as a control, with 105 pellets presented at the beginning of the session. Water intake under this condition was used as a session baseline for determining the degree of polydipsia previously maintained by the intermittent schedule.
286
REYNOLDS,
KENNY,
AND WRIGHT
TABLE MEAN
ABSOLUTE
WATER
INTAKES
FOR EACH
Baseline” Age (days) 30 60 90 120
Milliliters 9.0 23.8 41.3 32.8
k t 2 k
Milliliters per 100 g
AND
1 MEAN
CORRECTED
EXPERIMENTAL
WATER
VT 70-secb Milliliters
0.6e 23.0 2 0.3 18.4 0.9 11.3 + 1.2 32.9 1.3 12.2 2 1.3 47.6 0.7 9.4 5 0.3 51.6
k 1.6 -r- 1.7 + 3.0 2 1.2
INTAKES
GROUP
Control’
Milliliters per 100 g
Milliliters
Milliliters per 100 g
19.0 15.2 16.7 18.7
7.0 9.8 8.8 10.8
6.6 4.7 3.1 4.2
t k f +
2.7 0.8 1.1 0.5
2 2 t k
0.7 0.5 2.8 1.2
2 + + 2
1.9 0.3 1.0 0.5
Polydipsic ratiod 2.9 3.2 5.4 4.5
a Twenty-four-hour home-cage water consumption (Days l-5 of individual caging). b Two-hour polydipsia session with 105 pellets delivered on a VT 70-set schedule (Days 20-24 of individual caging). c Two-hour control session with 105 pellets delivered at the beginning (Day 25 of individual caging). d Polydipsic ratio = mean asymptotic water intake under VT 70-set schedule (Days 20-24)imean control water intake (Day 25). e Mean 2 standard error.
RESULTS Mean and standard errors (SE) of absolute water intakes (milliliters) are presented in Table 1 for baseline, VT 70-set schedule, and control conditions. Home-cage 24-hr baseline consumptions showed increases with age characteristic of growing rats (Richter & Brailey, 1929). Absolute intakes during schedule sessions likewise increased with age, paralleling growth. To provide comparability among groups, statistical analyses of consumptions with the intermittent schedule were corrected for body weight (milliliters per 1OOg body weight; see Table 1). The .05 level of significance was used in all statistical tests. An Age x Days repeated measures ANOVA comparing mean water intakes per 1OOgbody weight for the last 5 days of the VT 70-set schedule was not significant for either factor [F(3,12) = 0.24 and F(4,48) = 1.62, respectively], indicating that all age groups reached similar asymptotes of intake per body weight during the last 5 days. The groups also did not differ in their intakes relative to body weight under the control condition, when 105 pellets were given at the beginning of the session [F(3,12) = 1.751. The ratio of asymptotic intake to control consumption was employed as a measure of the degree of polydipsia (Falk, 1969). These mean polydipsic ratios ranged from 2.9-5.4, with every animal in all age groups easily surpassing Falk’s criterion for polydipsia by at least doubling its intake under the intermittent schedule (individual range = 2.4-9.5). Although the polydipsic ratios differed statistically [F(3,12) = 5.351 due to the higher mean for the 90-day group (Newman-Keuls), this effect appears to be the
DEVELOPMENTAL
30
STUDY OF POLYDIPSIA
60
90
120
287
AGE
FIG. 1. Mean k standard error water intakes corrected for body weight (milliliters per 1OOg body weight) during the first, seventh, and last daily 2-hr polydipsia session.
result of one 90-day rat which drank very little in the control session, thereby artifically inflating the mean ratio for its group. Figure 1 presents the mean f. SE corrected water consumptions (milliliters per 1OOgbody weight) for the first, seventh, and last polydipsia sessions. It is apparent that animals begun on an intermittent schedule at 30, 60, or 90 days exhibited the same full adult polydipsic response represented by 120-day-old rats. DISCUSSION The present results indicate that schedule-induced polydipsia occurs in the developing rat, with substantial increases in water consumption occurring during the first week of exposure to the intermittent schedule for 30-, 60-, and 90-day animals, in agreement with the pattern of rats 120 days old and older. Furthermore, the final levels of schedule-induced polydipsia (milliliters per 1OOgbody weight per 2-hr session) were comparable across the ages studied. Falk (197 1) has emphasized the need for more research aimed at broadening the scope of adjunctive behavior. The present investigation represents such a generalization by showing that adjunctive drinking is present in adult form at least as early as 30 days of age. Prandial drinking, i.e., alternately eating bits of food and drinking small drafts of water, is another nonregulatory drinking phenomenon. It appears to be largely under oropharyngeal control. With regard to its development, Kissileff (1971) reported that rats given solid food for the first time between 20 and 28 days are prandial drinkers, while those first fed after 34 days of age display normal adult eat-drink patterns consisting of larger meals associated with a single drink bout either before or after the meal (Kissileff, 1969). Schedule-induced polydipsia is similar to prandial drinking in that a drink burst follows each single-pellet meal. Whether or not scheduleinduced polydipsia and prandial drinking in animals younger than 30 days of age are related is yet to be determined.
288
REYNOLDS,
KENNY,
AND WRIGHT
REFERENCES Falk, J. L. Production of polydipsia in normal rats by an intermittent schedule. Science,
1961,
133, 195- 1%.
Falk, J. L. Conditions producing psychogenic polydipsia in animals. Annuls ofthe New York Academy of Sciences, 1969, 157, 569-593. Falk, J. L. The nature and determinants of adjunctive behavior. Physiology &Behavior, 1971, 6, 577-588. Kachanoff, R., Leveille, R., McLelland, J. P., & Wayner, M. J. Schedule-induced behavior in humans. Physiology & Behavior, 1973, 11, 395-398. Kaplan, M. & Kaplan, E. F. Estimated growth of inbred rats for behavioral and biological study. Psychological Reports, 1%5, 17, 419-423. Kenny, J. T., Wright, J. W., & Reynolds, T. J. Schedule-induced polydipsia: The role of oral and plasma factors. Physiology & Behavior, 1977, in press. Kissileff, H. R. Food-associated drinking in the rat. Journal of Comparative and Physiological Psychology, 1969, 67, 284-300. Kissileff, H. R. Acquisition of prandial drinking in weanling rats and in rats recovering from lateral hypothalamic lesions. Journal of Comparative and Physiological Psychology, 1971, 77, 97-109. Kissileff, H. R. Nonhomeostatic controls of drinking. In A. N. Epstein, H. R. Kissileff, & E. Stellar (Eds.), The nemopsychology of thirst: Newfindings and advances in concepts. Washington, D. C.: V. H. Winston & Sons, 1973, Pp. 163-198. Palfai, T., Kutscher, C. L., & Symons, J. P. Schedule-induced polydipsia in the mouse. Physiology & Behavior, 1971, 6, 461-462. Richter, C. P., & Brailey, M. E. Water intake and its relation to the surface area of the body. Proceedings of the National Academy of Sciences, 1929, 15, 570-578. Schuster, C. R., & Woods, .I. H. Schedule-induced polydipsia in the rhesus monkey. Psychological Reports, 1966, 19, 823-828. Shanab, M. E., & Peterson, J. L. Polydipsia in the pigeon. Psychonomic Science, 1969, 15, 51-52. Stricker, E. M., & Adair, E. R. Body fluid balance, taste, and postprandial factors in schedule-induced polydipsia. Journal of Comparative and Physiological Psychology, 1966, 62, 449-454. Received April 15, 1976 Revised May 20, 1976
J. REYNOLDS,
JOHN T. KENNY,
AND JOHN W. WRIGHT
Fordham University, Johns Hopkins University, and Washington State University Rats 30, 60, 90, and 120 days of age were fed 105 45mg food pellets on a noncontingent VT 70-set schedule during 14 daily 2-hr sessions. Every animal became polydipsic on this schedule when compared with a schedule in which 105 pellets were presented at the beginning of the session. Mean polydipsic ratios (schedule intake/control intake) ranged from 2.9-5.4. Water intakes (milliliters per 1OOgbody weight) did not differ during the last five sessions as a function of age. The results are discussed with respect to the generality of the class of adjunctive behaviors.
Since Falk (1961) first reported excessive water consumption by rats barpressing for food on a VI 1-min schedule, studies of schedule-induced polydipsia have frequently focused upon potential controlling variables (see Falk, 1969). There has been some attempt to generalize beyond the mature laboratory rat, including the demonstration of polydipsia in rhesus monkey (Schuster & Woods, 1966), pigeon (Shanab & Peterson, 1969), albino Swiss mouse (Palfai, Kutscher, & Symons, 1971), chimpanzee (Deleher, cited in Falk, 1971), and humans (Kachanoff, Leveille, McLelland, & Wayner, 1973). Physiological data on adult animals have indicated that schedule-induced polydipsia appears not to be under the control of the recognized regulatory thirst stimuli (Kenny, Wright, & Reynolds, in press; Kissileff, 1973; Stricker & Adair, 1966). Recently, schedule-induced polydipsia has been analyzed for its theoretical importance, with Falk (1971) proposing that it is representative of a larger class of adjunctive behaviors including aggression, escape, wheel running, pica, and air licking. These responses are all characterized by their schedule and motivational dependence and their postreinforcement occurrence. Further, depending upon the specific environmental cues presented, these responses can substitute for each other. A major dimension missing from the literature is a systematic examination of schedule-induced polydipsia in the developing rat. In the present experiment, two developmental questions were addressed: (a) Do young rats respond to an intermittent reinforcement schedule by becoming Requests for reprints should be sent to Thomas J. Reynolds, Department of Psychology, Fordham University, Bronx, New York 10458. 284 Copyright All rights
0 1977 by Academic Press. Inc. of reproduction in any form reserved.
ISSN 0023-9690
DEVELOPMENTAL
polydipsic? (b) Is the drinking that of adult animals?
STUDY
OF
285
POLYDIPSIA
response of immature
rats comparable
to
METHOD Animals. Twenty-eight male albino Sprague-Dawley rats from seven litters born in our laboratory (Carworth stock) were weaned at 20 days and maintained, until testing began, in wire mesh group cages (39 x 35 x 17.5 cm) on a commercial dry diet and tap water at 17-24°C under a 12-12 light-dark cycle initiated at 0800 hr. Apparatus. Four commercial operant chambers with keys removed were equipped with food-pellet dispensers. A glass loo-ml graduated cylinder with a stainless steel drinking spout was attached to the outside of each chamber so that the spout tip was positioned 3.4 cm inside the chamber, 11.4 cm to the right of the food cup, and 3.8 cm above the hardware cloth floor. Food-pellet presentation was controlled by appropriate electromechanical equipment housed in the same darkened test room. Ambient white noise was maintained at 60-65 dB. Procedure. At weaning, four rats were randomly assigned to each of the following developmental groups: 30-, 60-, 90-, 120-day experimental groups; 30-, 60-, 90-day body-weight control groups. Ten days prior to these ages, the experimental animals were placed in individual cages (18 x 35 x 17.5 cm) and provided with demineralized water in loo-ml graduated cylinders with stainless steel drinking spouts. Water consumptions and body weights were recorded once daily between 1400 and 1600 hr. During the first 5 days after being placed in individual cages, experimental animals had food freely available. On the subsequent 5 days, body weights were reduced to 80% of their estimated free-feeding weights by restricting food intake. New estimates of free-feeding weights, based on the appropriate body-weight control group, were calculated at 3-day intervals for each animal according to the procedure of Kaplan & Kaplan (1965). Since pilot data indicated that 120-day-old animals did not gain weight significantly in the course of the testing period, this group served as its own body-weight control. On Days 1 l-24, 2-hr daily sessions were conducted between 1400 and 1600 hr with noncontingent delivery of 45-mg food pellets on a Variable Time (VT) 70-set schedule with demineralized water freely available. Pilot work indicated that session length should be set at 2 hr to avoid satiation of the younger animals. Water consumptions and body weights were recorded postsession, and a home-cage food supplement was given, when necessary, to maintain target body weights. Day 25 served as a control, with 105 pellets presented at the beginning of the session. Water intake under this condition was used as a session baseline for determining the degree of polydipsia previously maintained by the intermittent schedule.
286
REYNOLDS,
KENNY,
AND WRIGHT
TABLE MEAN
ABSOLUTE
WATER
INTAKES
FOR EACH
Baseline” Age (days) 30 60 90 120
Milliliters 9.0 23.8 41.3 32.8
k t 2 k
Milliliters per 100 g
AND
1 MEAN
CORRECTED
EXPERIMENTAL
WATER
VT 70-secb Milliliters
0.6e 23.0 2 0.3 18.4 0.9 11.3 + 1.2 32.9 1.3 12.2 2 1.3 47.6 0.7 9.4 5 0.3 51.6
k 1.6 -r- 1.7 + 3.0 2 1.2
INTAKES
GROUP
Control’
Milliliters per 100 g
Milliliters
Milliliters per 100 g
19.0 15.2 16.7 18.7
7.0 9.8 8.8 10.8
6.6 4.7 3.1 4.2
t k f +
2.7 0.8 1.1 0.5
2 2 t k
0.7 0.5 2.8 1.2
2 + + 2
1.9 0.3 1.0 0.5
Polydipsic ratiod 2.9 3.2 5.4 4.5
a Twenty-four-hour home-cage water consumption (Days l-5 of individual caging). b Two-hour polydipsia session with 105 pellets delivered on a VT 70-set schedule (Days 20-24 of individual caging). c Two-hour control session with 105 pellets delivered at the beginning (Day 25 of individual caging). d Polydipsic ratio = mean asymptotic water intake under VT 70-set schedule (Days 20-24)imean control water intake (Day 25). e Mean 2 standard error.
RESULTS Mean and standard errors (SE) of absolute water intakes (milliliters) are presented in Table 1 for baseline, VT 70-set schedule, and control conditions. Home-cage 24-hr baseline consumptions showed increases with age characteristic of growing rats (Richter & Brailey, 1929). Absolute intakes during schedule sessions likewise increased with age, paralleling growth. To provide comparability among groups, statistical analyses of consumptions with the intermittent schedule were corrected for body weight (milliliters per 1OOg body weight; see Table 1). The .05 level of significance was used in all statistical tests. An Age x Days repeated measures ANOVA comparing mean water intakes per 1OOgbody weight for the last 5 days of the VT 70-set schedule was not significant for either factor [F(3,12) = 0.24 and F(4,48) = 1.62, respectively], indicating that all age groups reached similar asymptotes of intake per body weight during the last 5 days. The groups also did not differ in their intakes relative to body weight under the control condition, when 105 pellets were given at the beginning of the session [F(3,12) = 1.751. The ratio of asymptotic intake to control consumption was employed as a measure of the degree of polydipsia (Falk, 1969). These mean polydipsic ratios ranged from 2.9-5.4, with every animal in all age groups easily surpassing Falk’s criterion for polydipsia by at least doubling its intake under the intermittent schedule (individual range = 2.4-9.5). Although the polydipsic ratios differed statistically [F(3,12) = 5.351 due to the higher mean for the 90-day group (Newman-Keuls), this effect appears to be the
DEVELOPMENTAL
30
STUDY OF POLYDIPSIA
60
90
120
287
AGE
FIG. 1. Mean k standard error water intakes corrected for body weight (milliliters per 1OOg body weight) during the first, seventh, and last daily 2-hr polydipsia session.
result of one 90-day rat which drank very little in the control session, thereby artifically inflating the mean ratio for its group. Figure 1 presents the mean f. SE corrected water consumptions (milliliters per 1OOgbody weight) for the first, seventh, and last polydipsia sessions. It is apparent that animals begun on an intermittent schedule at 30, 60, or 90 days exhibited the same full adult polydipsic response represented by 120-day-old rats. DISCUSSION The present results indicate that schedule-induced polydipsia occurs in the developing rat, with substantial increases in water consumption occurring during the first week of exposure to the intermittent schedule for 30-, 60-, and 90-day animals, in agreement with the pattern of rats 120 days old and older. Furthermore, the final levels of schedule-induced polydipsia (milliliters per 1OOgbody weight per 2-hr session) were comparable across the ages studied. Falk (197 1) has emphasized the need for more research aimed at broadening the scope of adjunctive behavior. The present investigation represents such a generalization by showing that adjunctive drinking is present in adult form at least as early as 30 days of age. Prandial drinking, i.e., alternately eating bits of food and drinking small drafts of water, is another nonregulatory drinking phenomenon. It appears to be largely under oropharyngeal control. With regard to its development, Kissileff (1971) reported that rats given solid food for the first time between 20 and 28 days are prandial drinkers, while those first fed after 34 days of age display normal adult eat-drink patterns consisting of larger meals associated with a single drink bout either before or after the meal (Kissileff, 1969). Schedule-induced polydipsia is similar to prandial drinking in that a drink burst follows each single-pellet meal. Whether or not scheduleinduced polydipsia and prandial drinking in animals younger than 30 days of age are related is yet to be determined.
288
REYNOLDS,
KENNY,
AND WRIGHT
REFERENCES Falk, J. L. Production of polydipsia in normal rats by an intermittent schedule. Science,
1961,
133, 195- 1%.
Falk, J. L. Conditions producing psychogenic polydipsia in animals. Annuls ofthe New York Academy of Sciences, 1969, 157, 569-593. Falk, J. L. The nature and determinants of adjunctive behavior. Physiology &Behavior, 1971, 6, 577-588. Kachanoff, R., Leveille, R., McLelland, J. P., & Wayner, M. J. Schedule-induced behavior in humans. Physiology & Behavior, 1973, 11, 395-398. Kaplan, M. & Kaplan, E. F. Estimated growth of inbred rats for behavioral and biological study. Psychological Reports, 1%5, 17, 419-423. Kenny, J. T., Wright, J. W., & Reynolds, T. J. Schedule-induced polydipsia: The role of oral and plasma factors. Physiology & Behavior, 1977, in press. Kissileff, H. R. Food-associated drinking in the rat. Journal of Comparative and Physiological Psychology, 1969, 67, 284-300. Kissileff, H. R. Acquisition of prandial drinking in weanling rats and in rats recovering from lateral hypothalamic lesions. Journal of Comparative and Physiological Psychology, 1971, 77, 97-109. Kissileff, H. R. Nonhomeostatic controls of drinking. In A. N. Epstein, H. R. Kissileff, & E. Stellar (Eds.), The nemopsychology of thirst: Newfindings and advances in concepts. Washington, D. C.: V. H. Winston & Sons, 1973, Pp. 163-198. Palfai, T., Kutscher, C. L., & Symons, J. P. Schedule-induced polydipsia in the mouse. Physiology & Behavior, 1971, 6, 461-462. Richter, C. P., & Brailey, M. E. Water intake and its relation to the surface area of the body. Proceedings of the National Academy of Sciences, 1929, 15, 570-578. Schuster, C. R., & Woods, .I. H. Schedule-induced polydipsia in the rhesus monkey. Psychological Reports, 1966, 19, 823-828. Shanab, M. E., & Peterson, J. L. Polydipsia in the pigeon. Psychonomic Science, 1969, 15, 51-52. Stricker, E. M., & Adair, E. R. Body fluid balance, taste, and postprandial factors in schedule-induced polydipsia. Journal of Comparative and Physiological Psychology, 1966, 62, 449-454. Received April 15, 1976 Revised May 20, 1976