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Effects of two body weight reduction regimens on schedule dependent and schedule induced behavior
Physiology & Behavior, Vol. 21, pp. 639--645.Pergamon Press and Brain Research Publ., 1978. Printed in the U.S.A.
Effects of Two Body Weight Reduction Regimens on Schedule Dependent and Schedule Induced Behavior M. J. WAYNER, J. M. STEIN, C. C. LOULLIS, F. C. BARONE, F. B. J O L I C O E U R A N D D. B. R O N D E A U Brain Research Laboratory, Syracuse University, 601 University A v e n u e , Syracuse, N Y 13210 ( R e c e i v e d 18 J a n u a r y 1978) WAYNER, M. J., J. M. STEIN, C. C. LOULLIS, F. C. BARONE, F. B. JOLICOEUR AND D. B. RONDEAU. Effects of two body weight reduction regimens on schedule dependent and schedule induced behavior. PHYSIOL. BEHAV. 21(4) 639--645, 1978.--Fifteen male hooded rats were divided into three equal groups on the basis of body weights. One group was allowed to eat ad lib and constituted the Control Group. The second group of animals was reduced over 7 days and adjusted to 80 percent of the body weight of the animals in the Control Group for a 23 day period and constituted the Adjusted Group. Animals in the third group were reduced to 80 percent of their own predeprivation body weight over 7 days and were maintained at this constant level for a 23 day period and constituted the Constant Group. The two experimental groups were then allowed to feed ad lib for the remainder of the experiment. Both the Adjusted and the Constant Groups were tested throughout restricted and ad lib eating periods on a FI 1 rain food reinforcement generator schedule. Schedule dependent lever pressing, schedule induced licking and drinking, food intake and body weights were recorded for the duration of the experiment. Results demonstrate that schedule induced licking and drinking and schedule dependent lever pressing increased in the Constant Group at reduced body weight. Animals in the Adjusted Group did not change significantly on these measures during the same periods. When animals were returned to ad lib feeding conditions, the Constant Group initially increased body weight at a faster rate, ate significantly more, and exhibited significantly increased schedule induced licking and drinking. These initial differences disappeared later during the same period. The two experimental groups did not attain the expected body weight of the normal Control Group during 78 days of ad lib eating. Apparently, when animals are initially deprived rapidly and maintained at relatively constant body weight reduction, a prolonged body weight deficit occurs even though these same animals eat normal amounts of food. Schedule induced polydipsia Drinking Lever pressing
Adjunctive behavior
A D J U N C T I V E behaviors occur following the intermittent delivery of food pellets to food deprived rats at reduced body weight. Several of these stereotyped postpellet behaviors have been studied under these conditions: drinking [4, 5, 10, 11], air licking [1], grooming [9], wheel running [8], lever pressing [10] and a variety of locomotor activities [9]. The magnitude or frequency at which these behaviors are evoked can be related within limits to the degree of body weight reduction [1, 4, 5]. Most schedule induced behaviors have been studied at 80% body weight. When animals are tested at 70% body weight, the effects on schedule induced behaviors are greater in comparison to those observed at 80% or 90% body weight [5]. Conversely, when body weights are increased above the 80% level, schedule induced behaviors decrease [1,4]. However, following a sufficient exposure to the generator schedule at reduced body weights, adjunctive behaviors persist when ad lib feeding conditions are reintroduced and body weight recovers [11]. Also, other adjunctive behaviors are evoked when motor activity itself is scheduled without deprivation and a reduction in body weight [7,12].
Body weight reduction
Food deprivation
Licking
The 80% body weight deprivation used in most studies is usually calculated relative to the body weight for each animal on the last day of ad lib eating and drinking. Since growing male rats are frequently employed, an arbitrary 80% body weight actually produces an uncontrolled and increasingly more severe deprivation condition throughout the duration of the experiment. F o r example, a 360 g male rat with free access to food and water gains about 3 g per day. Following a 20 day period of adjusted food rations which restricted the animal to 80% of its initial weight, the accumulated weight loss would represent 31% of the predicted weight including growth. Therefore, standard deprivation schedules introduce an artifact which has not been accounted for in the study of schedule induced behavior. However, schedule dependent lever pressing under two different body weight regimes due to food deprivation has been examined [3]. Rats maintained at 80% of 90-day-old body weight increased lever pressing during the experiment; whereas, animals maintained at 80% of the predicted nondeprived weight pressed at a relatively constant level over the same period. Significant differences in lever presses appeared between the two groups following
~Supported in part by grants from the NSF No. BNS--76--18520and NIMH MH-14258-03.
C o p y r i g h t © 1978 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/78/100639-07502.00/0
WAYNER ET AL. nine days of the differential treatment. Consequently, significant differences in schedule induced behaviors under similar conditions might be expected. The purpose of the present experiment was to determine the influence of two different body weight reduction regimes on schedule induced licking and drinking and schedule dependent lever pressing generated by a fixed interval 1 min food reinforcement schedule (FI 1 min). Results demonstrate large differences in these behaviors evoked in animals maintained at 80% initial body weight in comparison to those maintained at 80% of the predicted nondeprived weight. Differences in behavior occurred both at reduced body weight and when body weight recovered following reintroduction of ad lib feeding conditions. In addition, a prolonged body weight deficit was observed in reduced body weight animals when compared to nondeprived control group animals. METHOD
Fifteen male hooded rats, 3 months old and 319-345 g in weight, were selected from our colony and placed into individual cages, 25~28x30 cm. A 12 hr light-dark cycle began at 0700 hr and was followed by a 12 hr dark phase. The room temperature was maintained at 21 2 1°C. The test environment consisted of a standard LVE 1469 medium size operant chamber, a lever, a pellet delivery mechanism, a test light, a sound attenuated cubicle with a house light, and an exhaust fan. A glass shrouded stainless steel ball-point spout attached to a eudiometer tube, protruding 1.5 cm into the operant cage in the center of the back wall, 4.0 cm above the grid floor, was used for measuring licks and water intake. A standard food cup was mounted on the adjacent wall to the right, 10 cm above the floor. The lever was located 12.0 cm to the right of the food cup and 3.0 cm above the floor. The house light provided constant illumination during the test session. Delivery of each 45 mg Noyes pellet was preceded by the presentation of a test light. Duration of the light was 40 msec. Licks were measured by means of a contact lickometer. Number of licks, presses, and pellets delivered were recorded with counters and cumulative recorders. Procedure
For 10 days, Days l-10, animals were adapted to their home cages. During this period, body weights and ad lib food and water consumption were measured daily between 0900 and 1200 hr. On Day 11, animals were divided into 3 groups of 5 animals each: the Control Group, the Adjusted Group, and the Constant Group. Each group was matched for similar body weights based upon the body weight data collected during Days 6-10. In the Control Group, animals were weighed daily and continued to have free access to food and water during the entire experiment. These control animals were never tested in the operant chambers. Body weight data from these animals were used to derive a predicted body weight growth curve for all 15 experimental animals. In the Adjusted Group, on Days 11-17, progressively smaller food rations were offered until body weights were 80% of the individual body weights on Day 11 plus the mean increment in body weight observed in the Control Group. Daily adjustments were made during the re-
duced body weight period. The traditional 80% weight reduction method was used for the animals in the Constant Group. On Days 11-17, these animals were presented with progressively smaller food rations until body weights were reduced to 80% of their individual body weights on Day 11. A constant or fixed body weight, 80% of initial body weight, was maintained throughout this phase of the experiment. On Days 18-20, animals in the Constant and Adjusted Groups were placed in the operant chambers and shaped to lever press for 45 mg food pellets under a continuous reinforcement schedule. During Days 21-41, the reduced body weight period, animals in the Constant and Adjusted Groups were tested daily in the operant chambers in a fixed interval 1 min (FI 1) schedule of reinforcement for 60 min. Following each session animals were returned to their home cages and presented with sufficient food to maintain the 80% Adjusted or Constant body weight reduction for each group. During Days 4247, animals in the Constant and Adjusted Groups were not tested in the operant chamber and were offered gradually increasing food rations for several days while body weights increased and were then placed on ad lib food and water conditions for the remainder of the experiment. During Days 48-65, the ad lib feeding period, animals in these groups were tested daily in the operant chamber on an FI 1 min schedule of reinforcement for 60 min. During Days 66 128, the weekly test period, animals in the Constant and Adjusted Groups were tested once per week for 60 min for 9 weeks on an identical FI 1 min food reinforcement schedule. RESULTS
Body weights for the Control, Constant, and Adjusted Groups were analyzed by means of a 3 x 16 analysis of variance with repeated measures [13]. In addition, number of lever presses and licks and water intakes for the Constant and Adjusted Groups were analyzed by means of 2x 16 analyses of variance with repeated measures. The factors for each analysis were groups and days. The 16 levels of the days factor consisted of seven 3-day means during the reduced body weight period, six 3-day means during ad lib feeding and three 3-week means during the weekly test period. Food pellets delivered during the test sessions in the Constant and Adjusted Groups were analyzed by means of a 2 x 3 analysis of variance. The factors were groups and treatments. The 3 levels of the treatment factor were the mean number of pellets delivered to each animal during the reduced body weight, ad lib feeding, and weekly test periods. Total daily food intakes representing the combined intakes in both the home cage and in the operant chamber for each animal were analyzed by means of a 3 ~6 analysis of variance. The factors were groups and days. The 6 levels of the days factor consisted of the mean intakes of each animal on Days 6-10 during the baseline period, on Days 21-23 and 39-41 during the reduced body weight period, on Days 48-50 and 63-65 during ad lib feeding, and on Days 122-126 during the weekly test period. In each analysis, simple main effects tests were performed for each significant groups by days interaction. Further analysis was performed using post hoc Tukey A tests to compare the mean body weights, licks, lever presses, water intakes, pellets or total daily food intakes over days between and within the groups. Analysis of body weights indicated significant differences between groups, F(2,12)=18.44, ~~0.01, and days F(l5,180)=273.08, ~~0.01. The groups by days interaction was also significant, F(30,180)=9.4l,p
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FIG. 1. Mean body weight in g for the Control, Adjusted, and Constant Groups as a function of the means of days during the experiment. Days 21 through 65 indicate the 3-day means for each animal in the three groups. Days 66 through 128 are indicated by 3 points, each derived from the mean of 3 weekly tests for each animal in the three groups. The introduction of ad lib eating is indicated by an arrow located between the three-day means 41 and 50. The beginning of the 9 weekly testing sessions is also indicated by an arrow between the means of Days 65 and 86.
shown in Fig. 1. Simple main effects analysis between the 3 groups and Tukey A tests revealed significantly higher body weights in the Control Group compared to the Adjusted or Constant Groups during the entire reduced body weight, ad lib feeding, and weekly test period, p<0.01. Similarly, simple main effects analyses and Tukey A tests were performed within groups and indicated that during the reduced body weight period body weights in the Control and Adjusted Groups, but not in the Constant Group, increased across days, p <0.01. There were significantly higher body weights on Days 26-41 during the reduced body weight period in the Adjusted Group compared to the Constant Group, p<0.01. Body weights in all 3 groups significantly increased as a function of days during the ad lib feeding and weekly test periods, p<0.01. There were no significant differences in body weights between the Constant and Adjusted Groups during either the ad lib feeding period or the weekly test period. However, analysis with Sheffe tests examining the net body weight gain during the ad lib feeding period between groups revealed a significantly greater body weight gain in the Constant Group compared to the Adjusted Group, p<0.01. In summary, animals in the Constant Group had significantly lower body weights compared to either the Control or Adjusted Groups during most of the reduced body weight period. During this same period, the body weights in the Adjusted Group were significantly lower compared to the body weights in the Control Group. On Day 41, the last day of reduced body weight, the body weights in the Constant and Adjusted Groups were 67% and 80%, respectively, of the
body weight of the Control Group. The reintroduction of free feeding produced rapid increases in body weights in both previously food deprived groups. The body weight gain was greater in the Constant Group compared to the Adjusted Group. However, both groups did not reach the body weight attained in the nondeprived Control Group. This was observed during both the ad lib feeding and weekly test periods. Analysis of lever presses indicated significant differences between groups, F(1,8)=27.12, p<0.01, and days, F(15,120)=18.03, p<0.01. The groups by days interaction was also significant, F(15,120)=5.37,p<0.01. These data are presented in Fig. 2. Simple main effects analysis between the Constant and Adjusted Groups revealed significant differences in lever presses on Days 23-41 during reduced body weight,/7<0.01. There were no significant differences between groups during the ad lib feeding or weekly test period. Similarly, simple main effects analyses and Tukey A tests were performed within groups and indicated that there were significantly fewer lever presses on Day 23 compared to Days 38 and 41 during reduced body weight in the Constant Group, p<0.05. There were no significant changes in lever presses in the Adjusted Group during this same period. Comparison of the mean number of lever presses on Days 35, 38 and 41 during reduced body weight with the mean number of lever presses during either the ad lib feeding or weekly test periods revealed a significantly greater number of lever presses in the Constant Group, p<0.01, and no significant differences between the periods in the Adjusted
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FIG. 4. Same as Fig. 1 for mean water consumption in ml.
Group. There were no significant differences in either group between the mean number of lever presses during the ad lib feeding period compared to the weekly test period. In summary, lever presses in the Constant and Adjusted Groups during reduced body weight were significantly different. Lever presses in the Adjusted Group remained stable during the reduced body weight period while lever presses in the Constant Group increased. There were no significant differences in lever presses during either the ad lib feeding or weekly test periods between the Constant and Adjusted Groups. Lever presses in the Constant Group were significantly lower during ad lib feeding compared to lever presses recorded on the last days of the reduced body weight period. There were no differences in lever pressing between the 3 periods of the experiment in the Adjusted Group. Analysis of licks indicated significant differences between days, F(15,120)=11.22, p<0.01. Groups were not significantly different F(1,8)=4.75. The groups by days interaction was also significant, F(14,120)=7.49, p<0.01. These data are presented in Fig. 3. Simple main effects analyses between the Constant and Adjusted Groups indicated that significant differences in the number of licks occurred between groups on Days 26--41 during reduced body weight, and on Days 50-59 during the ad lib feeding period, p<0.01. Similarly, simple main effects analyses and Tukey A tests were performed within groups and indicated that in the Constant Group there were significantly fewer licks on Day 23 compared to Days 26-128, p<0.01. There was also a significantly greater number of licks in the Constant Group on Days 50-56 early during the ad lib feeding period compared to Days 59--65, later during the same period, p<0.01. Significant differences were not observed across days in the Adjusted
Group. In summary, licks were significantly different between groups during most of the reduced body weight period and during the beginning of the ad lib feeding period. Licks in the adjusted group remained stable across days during the reduced body weight period while licks in the Constant Group increased. There were no significant differences between the groups during the last days of ad lib feeding and during the entire weekly test period. Licks in the Constant Groups were significantly decreased during the ad lib feeding period when compared to licks recorded during the last days of the reduced body weight period. There were no significant differences in licks between the 3 periods of the experiment in the Adjusted Group. Analysis of water intakes indicated significant differences between groups F(1,8)=8.50, p<0.05, and days F(14,120)=24.56, p<0.01. The groups by days interaction was also significant, F(15,120)=28.32, p<0.01. These data are shown in Fig. 4. Simple main effects analysis between groups revealed significant differences in water intakes on Days 26--41 during the reduced body weight period, on Days 50--65 during ad lib feeding and on Days 86--128 during the weekly test period, p<0.01. Similarly, simple main effects analysis and Tukey A tests were performed within groups and indicated that in the Constant Group there were significantly lower water intakes on Day 23 compared to Days 26-41 during reduced body weight, p<0.01. No significant differences across days were observed during reduced body weight in the Adjusted Group. Comparison of the mean water intakes on Days 35--41 during reduced body weight with the mean water intakes during either the ad lib feeding or weekly test periods revealed significant decreases in the Constant Group, p<0.01, and no significant differences in
644
WAYNER E T AL.
TABLE 1 MEAN -+ SEM PELLETSDELIVEREDIN THE CONSTANTAND ADJUSTEDGROUPS Experimental Period Reduced Body Weight Ad Lib Feeding Weekly Test
Constant Group (n-5)
Adjusted Group (n-5)
56.9 --- 0.4 53.8 -+ 1.1 51.8 --_ 2.3
53.8 + 1.0 49.5 -+ 2.5 50.5 - 1.7
the Adjusted Group. There were significantly higher water intakes during the weekly test period compared to the ad lib feeding period in the Adjusted Group, p<0.01, and no significant differences between these phases in the Constant Group. In summary, there were significant differences in water intakes between groups during reduced body weight, ad lib feeding, and weekly test periods. Water intakes in the Adjusted Group remained stable across days during the reduced body weight period while water intakes in the Constant Group increased. Water intakes in the Constant Group were significantly lower during ad lib feeding compared to the water intakes observed on the last days of the reduced body weight period. There were significant increases in water intakes in the Adjusted Group when animals were tested once per week compared to daily water intakes during ad lib feeding. Analysis of food pellets indicated significant differences between the three experimental periods, F(2,16)=6.84, p <0.01. No significant differences occurred between groups, F(1,8)=3.34. The groups by days interaction was also not significant, F(2,16)=0.76. These data are listed in Table 1. Further main effects analysis with Tukey A tests revealed a significantly greater number of food pellets delivered during reduced body weight compared to the number of pellets delivered during the ad lib feeding period, p<0.01. There were no significant differences between the number of pellets delivered during ad lib feeding compared to the weekly test period. A more detailed analysis of variance was also performed and revealed no significant differences in the number of pellets delivered within each group across days during each of the 3 test phases. In summary, there were no significant differences in the number of food pellets delivered in the Adjusted Group compared to the Constant Group during the entire experiment. There were, however, significant decreases in the number of food pellets delivered in both groups during the ad lib feeding and weekly test periods compared to the reduced body weight period. There were no significant differences in the number of pellets delivered in each group during each of the 3 experimental periods. Finally, observations made during each test session indicated that each rat ate every pellet which was delivered. Analysis of total daily food intakes indicated significant differences between groups, F(2,12)=13.21, p<0.01, and days, F(5,60)=72.55, p<0.01. The groups by days interaction was also significant, F(10,60)=16.17, p<0.01. Simple main effects analysis between the Constant, Adjusted, and Control Groups revealed significant differences on Days 21-23 and 39--41 during reduced body weight, on Days 48-50 and 63-65 during ad lib feeding and on Days 122-126 during the weekly test period, p<0.01. There were no significant differences in total daily food intakes on Days 6-10 during
the baseline period. Further analysis with Tukey A tests revealed significantly lower food intakes on Days 21-23 and 39-41 during the reduced body weight period in the Constant and Adjusted Groups compared to the Control Group, p<0.01. On Days 39-41 food intakes were significantly higher in the Adjusted Group compared to the Constant Group, p<0.05. On Days 48-50 during the ad lib feeding period, food intakes were significantly higher in the Constant Group compared to the Adjusted Group, p<0.01. There were no significant differences between groups on Days 6-10, 63-65, or 122-126. Simple main effects tests were also performed on the total daily food intakes within each group between Days 6-10, 21-23, 39-41, 48-50, 63-65, and 122126. There were significant differences across days in the Constant and Adjusted Groups, p<0.01, and in the Control Group, p<0.05. Further analysis with Tukey A tests revealed significant decreases in food intakes on Days 21-23 and 39-41 during the reduced body weight period compared to the food intakes on Days 6-10, 48-50, 63-65, or 122-126 within the Constant and Adjusted Groups, p<0.01. Food intakes in the Constant and Adjusted Groups ranged between 40.3-49.4% and 61.5-72.4%, respectively, of baseline intakes during the reduced body weight period. There were no significant differences across days within the Control Group. In summary, total daily food intakes were not significantly different during the baseline period. Food intakes were significantly lower in the Constant and Adjusted Groups compared to the Control Group during the reduced body weight period. Food intakes were only significantly lower in the Constant Group compared to the Adjusted Groups on Days 39-41 and not on Days 21-23. Reintroduction of free access to food initially produced significantly higher food intakes in the Constant Group compared to the Adjusted Group. The difference disappeared by the end of the ad lib feeding period. There were no differences in food intakes between groups during the weekly test period. DISCUSSION These data confirm the results of a previous study [3] which demonstrated that lever pressing increases when animals are maintained at a fixed percentage of some previous body weight during daily testing on a variable interval food reinforcement schedule. Lever pressing in animals under similar conditions but with body weights adjusted to a fixed percentage of an ad lib control group remained stable over the same period. Schedule dependent lever pressing in the Constant Group of the present study increased when at reduced body weight; whereas, there were no increases in lever presses in the Adjusted Group over the same period. Also, the Constant Group pressed significantly more. Differences in schedule induced behavior between the two groups are very interesting. The expected and dramatic increases in schedule induced licking and drinking occur only in the Constant Group and after approximately one week on the schedule. The increases in licking and drinking in the Adjusted Group over days were not significant during the same period. However, schedule induced licking and drinking did occur. The excessive schedule induced licking and drinking characteristic of the so-called schedule induced polydipsia occurs only with progressive increases in body weight deficits, as compared to normal animals, associated with the procedures of the constant body weight regimen. When animals in the two experimental groups were returned to ad lib feeding conditions, the Constant Group re-
BODY W E I G H T A N D A D J U N C T I V E B E H A V I O R
645
covered body weight at a faster rate. The Constant Group recovered 84 g and the Adjusted Group only 44 g during the first 3 days of ad lib feeding. Both groups reached approximately the same mean weights over the next 10 days. L e v e r pressing decreased significantly only in the Constant Group. There were no significant differences between the two experimental groups under these conditions. Licking and drinking decreased in the Constant Group between the reduced body weight and ad lib feeding periods. Also, the Constant Group exhibited decreases in licking and drinking during the 15 days of ad lib eating and daily testing. Consequently, the differences in licking between the two groups were significant only during the early part of this period, since there were no significant changes in the Adjusted Group between the two periods and during the 15 day ad lib period. Drinking was significantly different between the two groups throughout the daily ad lib testing period. During the ad lib weekly test period there were no differences between the Adjusted and Constant Groups in body weight, lever presses, and licks. However, water consumption was significantly greater in the Constant Group during the same period. The increase which occurred in water consumption for the Adjusted Group during the weekly period is significant when compared to the water consumed at 80% body weight and when tested daily during ad lib eating. The relatively large water intakes when tested weekly on ad lib eating confirm the results of a previous study [11]. During the 78 days of ad lib feeding, it is interesting that
both experimental groups did not attain the expected body weight of the normal controls. Although food intakes were significantly lower in the two experimental groups during the reduced body weight period, there were no differences in food intakes between all the groups during the ad lib weekly test phase. It should also be noted that during the latter part of the daily ad lib period and during the weekly ad lib period the persistence of the adjunctive behaviors cannot be attributed solely to the constant body weight reduction procedure. Results of a previous study [11] indicate that normal animals, such as the ControI Group, display very little of these behaviors under similar conditions. The low body weights of the Constant and Adjusted Groups as compared to the Control Group upon return to ad lib eating were unexpected. Results of previous studies following acute periods o f starvation, refeeding anorexia [6], and relatively longer periods of chronic food restriction [2] indicated that food deprived rats recovered normal body weights within a reasonable period of time following a return to ad lib eating even when the amounts of food refed were adjusted to normal intakes [2]. Results of the present study indicate that if animals are initially deprived more rapidly and maintained at a relatively constant reduction of body weight then body weights recover more gradually even though animals eat normal amounts. The phenomena of refeeding anorexia and recovery of body weight following restricted food consumption when animals are returned to ad lib feeding requires further investigation.
REFERENCES
1. Chillag, D. and J. Mendelson. Schedule-induced airlicking as a function of body weight deficit in rats. Physiol. Behav. 6: 603605, 1971. 2. Collier, G. Body weight loss as a measure of motivation in hunger and thirst. Ann. N.Y. Acad. Sci. 157: 594-609, 1969. 3. Davenport, D. G. and L. R. Goulet. Motivational artifact in standard food-deprivation schedules. J. comp. physiol. Psychol. 56: 237-240, 1964. 4. Falk, J. Conditions producing psychogenic polydipsia in animals. Ann. N.Y. Acad. Sci. 157: 569-592, 1969. 5. Freed, E. and N. Hymowitz. Effect of schedule, percent body weight, and magnitude of reinforcement on acquisition of schedule-induced polydipsia. Psychol. Rep. 31: 95-101, 1972. 6. Hamilton, C. L. Problems of refeeding after starvation in the rat. Ann. N.Y. Acad. Sci. 157: 1004-1014, 1969. 7. Singer, G., M. J. Wayner, J. Stein, K. Cimino and K. King. Adjunctive behavior induced by wheel running. Physiol. Behav. 12: 651-657, 1975.
8. Skinner, B. F. and W. H. Morse. Concurrent activity under fixed-interval reinforcement. J. comp. physiol. Psychol. 50: 279-281, 1957. 9. Staddon, J. E. R. and S. L. Ayres. Sequential and temporal properties of behavior induced by a schedule of periodic food delivery. Behaviour 54: 26-49, 1975. 10. Wayner, M. J. and I. Greenberg. Schedule dependence of schedule induced polydipsiaand lever pressing. Physiol. Behav. 10: 965-966, 1973. 11. Wayner, M. J. and D. B. Rondeau. Schedule dependent and schedule-induced behavior at reduced and recovered body weight. Physiol. Behav. 17: 325-336, 1976. 12. Wayner, M. J., G. Singer, K. Cimino, J. Stein and L. Dwoskin. Adjunctive behavior induced by different conditions of wheel running. Physiol. Behav. 14: 507-510, 1975. 13. Winer, B. J. Statistical Principles in Experimental Design. New York: McGraw-Hill, 1971.
Effects of Two Body Weight Reduction Regimens on Schedule Dependent and Schedule Induced Behavior M. J. WAYNER, J. M. STEIN, C. C. LOULLIS, F. C. BARONE, F. B. J O L I C O E U R A N D D. B. R O N D E A U Brain Research Laboratory, Syracuse University, 601 University A v e n u e , Syracuse, N Y 13210 ( R e c e i v e d 18 J a n u a r y 1978) WAYNER, M. J., J. M. STEIN, C. C. LOULLIS, F. C. BARONE, F. B. JOLICOEUR AND D. B. RONDEAU. Effects of two body weight reduction regimens on schedule dependent and schedule induced behavior. PHYSIOL. BEHAV. 21(4) 639--645, 1978.--Fifteen male hooded rats were divided into three equal groups on the basis of body weights. One group was allowed to eat ad lib and constituted the Control Group. The second group of animals was reduced over 7 days and adjusted to 80 percent of the body weight of the animals in the Control Group for a 23 day period and constituted the Adjusted Group. Animals in the third group were reduced to 80 percent of their own predeprivation body weight over 7 days and were maintained at this constant level for a 23 day period and constituted the Constant Group. The two experimental groups were then allowed to feed ad lib for the remainder of the experiment. Both the Adjusted and the Constant Groups were tested throughout restricted and ad lib eating periods on a FI 1 rain food reinforcement generator schedule. Schedule dependent lever pressing, schedule induced licking and drinking, food intake and body weights were recorded for the duration of the experiment. Results demonstrate that schedule induced licking and drinking and schedule dependent lever pressing increased in the Constant Group at reduced body weight. Animals in the Adjusted Group did not change significantly on these measures during the same periods. When animals were returned to ad lib feeding conditions, the Constant Group initially increased body weight at a faster rate, ate significantly more, and exhibited significantly increased schedule induced licking and drinking. These initial differences disappeared later during the same period. The two experimental groups did not attain the expected body weight of the normal Control Group during 78 days of ad lib eating. Apparently, when animals are initially deprived rapidly and maintained at relatively constant body weight reduction, a prolonged body weight deficit occurs even though these same animals eat normal amounts of food. Schedule induced polydipsia Drinking Lever pressing
Adjunctive behavior
A D J U N C T I V E behaviors occur following the intermittent delivery of food pellets to food deprived rats at reduced body weight. Several of these stereotyped postpellet behaviors have been studied under these conditions: drinking [4, 5, 10, 11], air licking [1], grooming [9], wheel running [8], lever pressing [10] and a variety of locomotor activities [9]. The magnitude or frequency at which these behaviors are evoked can be related within limits to the degree of body weight reduction [1, 4, 5]. Most schedule induced behaviors have been studied at 80% body weight. When animals are tested at 70% body weight, the effects on schedule induced behaviors are greater in comparison to those observed at 80% or 90% body weight [5]. Conversely, when body weights are increased above the 80% level, schedule induced behaviors decrease [1,4]. However, following a sufficient exposure to the generator schedule at reduced body weights, adjunctive behaviors persist when ad lib feeding conditions are reintroduced and body weight recovers [11]. Also, other adjunctive behaviors are evoked when motor activity itself is scheduled without deprivation and a reduction in body weight [7,12].
Body weight reduction
Food deprivation
Licking
The 80% body weight deprivation used in most studies is usually calculated relative to the body weight for each animal on the last day of ad lib eating and drinking. Since growing male rats are frequently employed, an arbitrary 80% body weight actually produces an uncontrolled and increasingly more severe deprivation condition throughout the duration of the experiment. F o r example, a 360 g male rat with free access to food and water gains about 3 g per day. Following a 20 day period of adjusted food rations which restricted the animal to 80% of its initial weight, the accumulated weight loss would represent 31% of the predicted weight including growth. Therefore, standard deprivation schedules introduce an artifact which has not been accounted for in the study of schedule induced behavior. However, schedule dependent lever pressing under two different body weight regimes due to food deprivation has been examined [3]. Rats maintained at 80% of 90-day-old body weight increased lever pressing during the experiment; whereas, animals maintained at 80% of the predicted nondeprived weight pressed at a relatively constant level over the same period. Significant differences in lever presses appeared between the two groups following
~Supported in part by grants from the NSF No. BNS--76--18520and NIMH MH-14258-03.
C o p y r i g h t © 1978 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/78/100639-07502.00/0
WAYNER ET AL. nine days of the differential treatment. Consequently, significant differences in schedule induced behaviors under similar conditions might be expected. The purpose of the present experiment was to determine the influence of two different body weight reduction regimes on schedule induced licking and drinking and schedule dependent lever pressing generated by a fixed interval 1 min food reinforcement schedule (FI 1 min). Results demonstrate large differences in these behaviors evoked in animals maintained at 80% initial body weight in comparison to those maintained at 80% of the predicted nondeprived weight. Differences in behavior occurred both at reduced body weight and when body weight recovered following reintroduction of ad lib feeding conditions. In addition, a prolonged body weight deficit was observed in reduced body weight animals when compared to nondeprived control group animals. METHOD
Fifteen male hooded rats, 3 months old and 319-345 g in weight, were selected from our colony and placed into individual cages, 25~28x30 cm. A 12 hr light-dark cycle began at 0700 hr and was followed by a 12 hr dark phase. The room temperature was maintained at 21 2 1°C. The test environment consisted of a standard LVE 1469 medium size operant chamber, a lever, a pellet delivery mechanism, a test light, a sound attenuated cubicle with a house light, and an exhaust fan. A glass shrouded stainless steel ball-point spout attached to a eudiometer tube, protruding 1.5 cm into the operant cage in the center of the back wall, 4.0 cm above the grid floor, was used for measuring licks and water intake. A standard food cup was mounted on the adjacent wall to the right, 10 cm above the floor. The lever was located 12.0 cm to the right of the food cup and 3.0 cm above the floor. The house light provided constant illumination during the test session. Delivery of each 45 mg Noyes pellet was preceded by the presentation of a test light. Duration of the light was 40 msec. Licks were measured by means of a contact lickometer. Number of licks, presses, and pellets delivered were recorded with counters and cumulative recorders. Procedure
For 10 days, Days l-10, animals were adapted to their home cages. During this period, body weights and ad lib food and water consumption were measured daily between 0900 and 1200 hr. On Day 11, animals were divided into 3 groups of 5 animals each: the Control Group, the Adjusted Group, and the Constant Group. Each group was matched for similar body weights based upon the body weight data collected during Days 6-10. In the Control Group, animals were weighed daily and continued to have free access to food and water during the entire experiment. These control animals were never tested in the operant chambers. Body weight data from these animals were used to derive a predicted body weight growth curve for all 15 experimental animals. In the Adjusted Group, on Days 11-17, progressively smaller food rations were offered until body weights were 80% of the individual body weights on Day 11 plus the mean increment in body weight observed in the Control Group. Daily adjustments were made during the re-
duced body weight period. The traditional 80% weight reduction method was used for the animals in the Constant Group. On Days 11-17, these animals were presented with progressively smaller food rations until body weights were reduced to 80% of their individual body weights on Day 11. A constant or fixed body weight, 80% of initial body weight, was maintained throughout this phase of the experiment. On Days 18-20, animals in the Constant and Adjusted Groups were placed in the operant chambers and shaped to lever press for 45 mg food pellets under a continuous reinforcement schedule. During Days 21-41, the reduced body weight period, animals in the Constant and Adjusted Groups were tested daily in the operant chambers in a fixed interval 1 min (FI 1) schedule of reinforcement for 60 min. Following each session animals were returned to their home cages and presented with sufficient food to maintain the 80% Adjusted or Constant body weight reduction for each group. During Days 4247, animals in the Constant and Adjusted Groups were not tested in the operant chamber and were offered gradually increasing food rations for several days while body weights increased and were then placed on ad lib food and water conditions for the remainder of the experiment. During Days 48-65, the ad lib feeding period, animals in these groups were tested daily in the operant chamber on an FI 1 min schedule of reinforcement for 60 min. During Days 66 128, the weekly test period, animals in the Constant and Adjusted Groups were tested once per week for 60 min for 9 weeks on an identical FI 1 min food reinforcement schedule. RESULTS
Body weights for the Control, Constant, and Adjusted Groups were analyzed by means of a 3 x 16 analysis of variance with repeated measures [13]. In addition, number of lever presses and licks and water intakes for the Constant and Adjusted Groups were analyzed by means of 2x 16 analyses of variance with repeated measures. The factors for each analysis were groups and days. The 16 levels of the days factor consisted of seven 3-day means during the reduced body weight period, six 3-day means during ad lib feeding and three 3-week means during the weekly test period. Food pellets delivered during the test sessions in the Constant and Adjusted Groups were analyzed by means of a 2 x 3 analysis of variance. The factors were groups and treatments. The 3 levels of the treatment factor were the mean number of pellets delivered to each animal during the reduced body weight, ad lib feeding, and weekly test periods. Total daily food intakes representing the combined intakes in both the home cage and in the operant chamber for each animal were analyzed by means of a 3 ~6 analysis of variance. The factors were groups and days. The 6 levels of the days factor consisted of the mean intakes of each animal on Days 6-10 during the baseline period, on Days 21-23 and 39-41 during the reduced body weight period, on Days 48-50 and 63-65 during ad lib feeding, and on Days 122-126 during the weekly test period. In each analysis, simple main effects tests were performed for each significant groups by days interaction. Further analysis was performed using post hoc Tukey A tests to compare the mean body weights, licks, lever presses, water intakes, pellets or total daily food intakes over days between and within the groups. Analysis of body weights indicated significant differences between groups, F(2,12)=18.44, ~~0.01, and days F(l5,180)=273.08, ~~0.01. The groups by days interaction was also significant, F(30,180)=9.4l,p
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shown in Fig. 1. Simple main effects analysis between the 3 groups and Tukey A tests revealed significantly higher body weights in the Control Group compared to the Adjusted or Constant Groups during the entire reduced body weight, ad lib feeding, and weekly test period, p<0.01. Similarly, simple main effects analyses and Tukey A tests were performed within groups and indicated that during the reduced body weight period body weights in the Control and Adjusted Groups, but not in the Constant Group, increased across days, p <0.01. There were significantly higher body weights on Days 26-41 during the reduced body weight period in the Adjusted Group compared to the Constant Group, p<0.01. Body weights in all 3 groups significantly increased as a function of days during the ad lib feeding and weekly test periods, p<0.01. There were no significant differences in body weights between the Constant and Adjusted Groups during either the ad lib feeding period or the weekly test period. However, analysis with Sheffe tests examining the net body weight gain during the ad lib feeding period between groups revealed a significantly greater body weight gain in the Constant Group compared to the Adjusted Group, p<0.01. In summary, animals in the Constant Group had significantly lower body weights compared to either the Control or Adjusted Groups during most of the reduced body weight period. During this same period, the body weights in the Adjusted Group were significantly lower compared to the body weights in the Control Group. On Day 41, the last day of reduced body weight, the body weights in the Constant and Adjusted Groups were 67% and 80%, respectively, of the
body weight of the Control Group. The reintroduction of free feeding produced rapid increases in body weights in both previously food deprived groups. The body weight gain was greater in the Constant Group compared to the Adjusted Group. However, both groups did not reach the body weight attained in the nondeprived Control Group. This was observed during both the ad lib feeding and weekly test periods. Analysis of lever presses indicated significant differences between groups, F(1,8)=27.12, p<0.01, and days, F(15,120)=18.03, p<0.01. The groups by days interaction was also significant, F(15,120)=5.37,p<0.01. These data are presented in Fig. 2. Simple main effects analysis between the Constant and Adjusted Groups revealed significant differences in lever presses on Days 23-41 during reduced body weight,/7<0.01. There were no significant differences between groups during the ad lib feeding or weekly test period. Similarly, simple main effects analyses and Tukey A tests were performed within groups and indicated that there were significantly fewer lever presses on Day 23 compared to Days 38 and 41 during reduced body weight in the Constant Group, p<0.05. There were no significant changes in lever presses in the Adjusted Group during this same period. Comparison of the mean number of lever presses on Days 35, 38 and 41 during reduced body weight with the mean number of lever presses during either the ad lib feeding or weekly test periods revealed a significantly greater number of lever presses in the Constant Group, p<0.01, and no significant differences between the periods in the Adjusted
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Group. There were no significant differences in either group between the mean number of lever presses during the ad lib feeding period compared to the weekly test period. In summary, lever presses in the Constant and Adjusted Groups during reduced body weight were significantly different. Lever presses in the Adjusted Group remained stable during the reduced body weight period while lever presses in the Constant Group increased. There were no significant differences in lever presses during either the ad lib feeding or weekly test periods between the Constant and Adjusted Groups. Lever presses in the Constant Group were significantly lower during ad lib feeding compared to lever presses recorded on the last days of the reduced body weight period. There were no differences in lever pressing between the 3 periods of the experiment in the Adjusted Group. Analysis of licks indicated significant differences between days, F(15,120)=11.22, p<0.01. Groups were not significantly different F(1,8)=4.75. The groups by days interaction was also significant, F(14,120)=7.49, p<0.01. These data are presented in Fig. 3. Simple main effects analyses between the Constant and Adjusted Groups indicated that significant differences in the number of licks occurred between groups on Days 26--41 during reduced body weight, and on Days 50-59 during the ad lib feeding period, p<0.01. Similarly, simple main effects analyses and Tukey A tests were performed within groups and indicated that in the Constant Group there were significantly fewer licks on Day 23 compared to Days 26-128, p<0.01. There was also a significantly greater number of licks in the Constant Group on Days 50-56 early during the ad lib feeding period compared to Days 59--65, later during the same period, p<0.01. Significant differences were not observed across days in the Adjusted
Group. In summary, licks were significantly different between groups during most of the reduced body weight period and during the beginning of the ad lib feeding period. Licks in the adjusted group remained stable across days during the reduced body weight period while licks in the Constant Group increased. There were no significant differences between the groups during the last days of ad lib feeding and during the entire weekly test period. Licks in the Constant Groups were significantly decreased during the ad lib feeding period when compared to licks recorded during the last days of the reduced body weight period. There were no significant differences in licks between the 3 periods of the experiment in the Adjusted Group. Analysis of water intakes indicated significant differences between groups F(1,8)=8.50, p<0.05, and days F(14,120)=24.56, p<0.01. The groups by days interaction was also significant, F(15,120)=28.32, p<0.01. These data are shown in Fig. 4. Simple main effects analysis between groups revealed significant differences in water intakes on Days 26--41 during the reduced body weight period, on Days 50--65 during ad lib feeding and on Days 86--128 during the weekly test period, p<0.01. Similarly, simple main effects analysis and Tukey A tests were performed within groups and indicated that in the Constant Group there were significantly lower water intakes on Day 23 compared to Days 26-41 during reduced body weight, p<0.01. No significant differences across days were observed during reduced body weight in the Adjusted Group. Comparison of the mean water intakes on Days 35--41 during reduced body weight with the mean water intakes during either the ad lib feeding or weekly test periods revealed significant decreases in the Constant Group, p<0.01, and no significant differences in
644
WAYNER E T AL.
TABLE 1 MEAN -+ SEM PELLETSDELIVEREDIN THE CONSTANTAND ADJUSTEDGROUPS Experimental Period Reduced Body Weight Ad Lib Feeding Weekly Test
Constant Group (n-5)
Adjusted Group (n-5)
56.9 --- 0.4 53.8 -+ 1.1 51.8 --_ 2.3
53.8 + 1.0 49.5 -+ 2.5 50.5 - 1.7
the Adjusted Group. There were significantly higher water intakes during the weekly test period compared to the ad lib feeding period in the Adjusted Group, p<0.01, and no significant differences between these phases in the Constant Group. In summary, there were significant differences in water intakes between groups during reduced body weight, ad lib feeding, and weekly test periods. Water intakes in the Adjusted Group remained stable across days during the reduced body weight period while water intakes in the Constant Group increased. Water intakes in the Constant Group were significantly lower during ad lib feeding compared to the water intakes observed on the last days of the reduced body weight period. There were significant increases in water intakes in the Adjusted Group when animals were tested once per week compared to daily water intakes during ad lib feeding. Analysis of food pellets indicated significant differences between the three experimental periods, F(2,16)=6.84, p <0.01. No significant differences occurred between groups, F(1,8)=3.34. The groups by days interaction was also not significant, F(2,16)=0.76. These data are listed in Table 1. Further main effects analysis with Tukey A tests revealed a significantly greater number of food pellets delivered during reduced body weight compared to the number of pellets delivered during the ad lib feeding period, p<0.01. There were no significant differences between the number of pellets delivered during ad lib feeding compared to the weekly test period. A more detailed analysis of variance was also performed and revealed no significant differences in the number of pellets delivered within each group across days during each of the 3 test phases. In summary, there were no significant differences in the number of food pellets delivered in the Adjusted Group compared to the Constant Group during the entire experiment. There were, however, significant decreases in the number of food pellets delivered in both groups during the ad lib feeding and weekly test periods compared to the reduced body weight period. There were no significant differences in the number of pellets delivered in each group during each of the 3 experimental periods. Finally, observations made during each test session indicated that each rat ate every pellet which was delivered. Analysis of total daily food intakes indicated significant differences between groups, F(2,12)=13.21, p<0.01, and days, F(5,60)=72.55, p<0.01. The groups by days interaction was also significant, F(10,60)=16.17, p<0.01. Simple main effects analysis between the Constant, Adjusted, and Control Groups revealed significant differences on Days 21-23 and 39--41 during reduced body weight, on Days 48-50 and 63-65 during ad lib feeding and on Days 122-126 during the weekly test period, p<0.01. There were no significant differences in total daily food intakes on Days 6-10 during
the baseline period. Further analysis with Tukey A tests revealed significantly lower food intakes on Days 21-23 and 39-41 during the reduced body weight period in the Constant and Adjusted Groups compared to the Control Group, p<0.01. On Days 39-41 food intakes were significantly higher in the Adjusted Group compared to the Constant Group, p<0.05. On Days 48-50 during the ad lib feeding period, food intakes were significantly higher in the Constant Group compared to the Adjusted Group, p<0.01. There were no significant differences between groups on Days 6-10, 63-65, or 122-126. Simple main effects tests were also performed on the total daily food intakes within each group between Days 6-10, 21-23, 39-41, 48-50, 63-65, and 122126. There were significant differences across days in the Constant and Adjusted Groups, p<0.01, and in the Control Group, p<0.05. Further analysis with Tukey A tests revealed significant decreases in food intakes on Days 21-23 and 39-41 during the reduced body weight period compared to the food intakes on Days 6-10, 48-50, 63-65, or 122-126 within the Constant and Adjusted Groups, p<0.01. Food intakes in the Constant and Adjusted Groups ranged between 40.3-49.4% and 61.5-72.4%, respectively, of baseline intakes during the reduced body weight period. There were no significant differences across days within the Control Group. In summary, total daily food intakes were not significantly different during the baseline period. Food intakes were significantly lower in the Constant and Adjusted Groups compared to the Control Group during the reduced body weight period. Food intakes were only significantly lower in the Constant Group compared to the Adjusted Groups on Days 39-41 and not on Days 21-23. Reintroduction of free access to food initially produced significantly higher food intakes in the Constant Group compared to the Adjusted Group. The difference disappeared by the end of the ad lib feeding period. There were no differences in food intakes between groups during the weekly test period. DISCUSSION These data confirm the results of a previous study [3] which demonstrated that lever pressing increases when animals are maintained at a fixed percentage of some previous body weight during daily testing on a variable interval food reinforcement schedule. Lever pressing in animals under similar conditions but with body weights adjusted to a fixed percentage of an ad lib control group remained stable over the same period. Schedule dependent lever pressing in the Constant Group of the present study increased when at reduced body weight; whereas, there were no increases in lever presses in the Adjusted Group over the same period. Also, the Constant Group pressed significantly more. Differences in schedule induced behavior between the two groups are very interesting. The expected and dramatic increases in schedule induced licking and drinking occur only in the Constant Group and after approximately one week on the schedule. The increases in licking and drinking in the Adjusted Group over days were not significant during the same period. However, schedule induced licking and drinking did occur. The excessive schedule induced licking and drinking characteristic of the so-called schedule induced polydipsia occurs only with progressive increases in body weight deficits, as compared to normal animals, associated with the procedures of the constant body weight regimen. When animals in the two experimental groups were returned to ad lib feeding conditions, the Constant Group re-
BODY W E I G H T A N D A D J U N C T I V E B E H A V I O R
645
covered body weight at a faster rate. The Constant Group recovered 84 g and the Adjusted Group only 44 g during the first 3 days of ad lib feeding. Both groups reached approximately the same mean weights over the next 10 days. L e v e r pressing decreased significantly only in the Constant Group. There were no significant differences between the two experimental groups under these conditions. Licking and drinking decreased in the Constant Group between the reduced body weight and ad lib feeding periods. Also, the Constant Group exhibited decreases in licking and drinking during the 15 days of ad lib eating and daily testing. Consequently, the differences in licking between the two groups were significant only during the early part of this period, since there were no significant changes in the Adjusted Group between the two periods and during the 15 day ad lib period. Drinking was significantly different between the two groups throughout the daily ad lib testing period. During the ad lib weekly test period there were no differences between the Adjusted and Constant Groups in body weight, lever presses, and licks. However, water consumption was significantly greater in the Constant Group during the same period. The increase which occurred in water consumption for the Adjusted Group during the weekly period is significant when compared to the water consumed at 80% body weight and when tested daily during ad lib eating. The relatively large water intakes when tested weekly on ad lib eating confirm the results of a previous study [11]. During the 78 days of ad lib feeding, it is interesting that
both experimental groups did not attain the expected body weight of the normal controls. Although food intakes were significantly lower in the two experimental groups during the reduced body weight period, there were no differences in food intakes between all the groups during the ad lib weekly test phase. It should also be noted that during the latter part of the daily ad lib period and during the weekly ad lib period the persistence of the adjunctive behaviors cannot be attributed solely to the constant body weight reduction procedure. Results of a previous study [11] indicate that normal animals, such as the ControI Group, display very little of these behaviors under similar conditions. The low body weights of the Constant and Adjusted Groups as compared to the Control Group upon return to ad lib eating were unexpected. Results of previous studies following acute periods o f starvation, refeeding anorexia [6], and relatively longer periods of chronic food restriction [2] indicated that food deprived rats recovered normal body weights within a reasonable period of time following a return to ad lib eating even when the amounts of food refed were adjusted to normal intakes [2]. Results of the present study indicate that if animals are initially deprived more rapidly and maintained at a relatively constant reduction of body weight then body weights recover more gradually even though animals eat normal amounts. The phenomena of refeeding anorexia and recovery of body weight following restricted food consumption when animals are returned to ad lib feeding requires further investigation.
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1. Chillag, D. and J. Mendelson. Schedule-induced airlicking as a function of body weight deficit in rats. Physiol. Behav. 6: 603605, 1971. 2. Collier, G. Body weight loss as a measure of motivation in hunger and thirst. Ann. N.Y. Acad. Sci. 157: 594-609, 1969. 3. Davenport, D. G. and L. R. Goulet. Motivational artifact in standard food-deprivation schedules. J. comp. physiol. Psychol. 56: 237-240, 1964. 4. Falk, J. Conditions producing psychogenic polydipsia in animals. Ann. N.Y. Acad. Sci. 157: 569-592, 1969. 5. Freed, E. and N. Hymowitz. Effect of schedule, percent body weight, and magnitude of reinforcement on acquisition of schedule-induced polydipsia. Psychol. Rep. 31: 95-101, 1972. 6. Hamilton, C. L. Problems of refeeding after starvation in the rat. Ann. N.Y. Acad. Sci. 157: 1004-1014, 1969. 7. Singer, G., M. J. Wayner, J. Stein, K. Cimino and K. King. Adjunctive behavior induced by wheel running. Physiol. Behav. 12: 651-657, 1975.
8. Skinner, B. F. and W. H. Morse. Concurrent activity under fixed-interval reinforcement. J. comp. physiol. Psychol. 50: 279-281, 1957. 9. Staddon, J. E. R. and S. L. Ayres. Sequential and temporal properties of behavior induced by a schedule of periodic food delivery. Behaviour 54: 26-49, 1975. 10. Wayner, M. J. and I. Greenberg. Schedule dependence of schedule induced polydipsiaand lever pressing. Physiol. Behav. 10: 965-966, 1973. 11. Wayner, M. J. and D. B. Rondeau. Schedule dependent and schedule-induced behavior at reduced and recovered body weight. Physiol. Behav. 17: 325-336, 1976. 12. Wayner, M. J., G. Singer, K. Cimino, J. Stein and L. Dwoskin. Adjunctive behavior induced by different conditions of wheel running. Physiol. Behav. 14: 507-510, 1975. 13. Winer, B. J. Statistical Principles in Experimental Design. New York: McGraw-Hill, 1971.