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Schedule-induced airlicking as a function of body-weight deficit in rats
Physiology and Behavior, Vol. 6, pp. 603-605. Pergamon Press, 1971. Printed in Great Britain
BRIEF COMMUNICATION Schedule-Induced Airlicking as a Function of Body-Weight Deficit in Rats' DANA
CHILLAG I AND JOSEPH MENDELSON
Department of Psychology, Brain Research Laboratory, Rutgers University, New Brunswick, New Jersey 08903, U.S.A. (Received 29 S e p t e m b e r 1970) CHILLAG,D. ANDJ. MENDELSON. Schedule-inducedairlickingas a function of body-weight deficit in rats. PHYSIOL.BEHAV. 6 (5) 603--605, 1971.--Water-deprived rats were given three 30-rain periods of exposure to an alrstream flowing through a standard drinking tube; all of them learned to airlick. They were then given water ad lib and maintained at 80 per cent of their pre-experimental body weights by food restriction. Each day they were given a 90-rain session of scheduled feeding in the presence of an airstreara; one 45-rag food pellet was delivered each rain. All the rats developed strong airlicking behavior. This behavior was then studied as a function of the magnitude of body-weight deficit, as each rat's weight was allowed to recover to within 5 per cent of normal and then to drop back down to 80 per cent of normal. For each rat schedule-induced airlicking was found to be an increasing function of body-weight deficit. Airlicking
Schedule-induced airlicking
WI~N rats are deprived of food they restrict their ad lib water intake. However, if after a period of food deprivation they are fed according to certain temporal schedules their water intake increases precipitously to highly polydipsic levels, more than compensating for the decrease in water intake selfimposed during food deprivation. This phenomenon is usually referred to as schedule-induced polydipsia [2]. It now appears that polydipsia is one of a variety of behaviors which tend to occur when food-deprived animals are exposed to certain feeding schedules [3]. F o r example, if the water in the drinking tube is replaced by a stream of air (6500-8000 dynes/cm s pressure), food-deprived rats lick the airstream even more persistently than they would lick water [6, 7]. It is possible that the reinforcers that are involved in maintaining schedule-induced drinking are the same as those that support schedule-induced airlicking. If this is so, then both behaviors should be similarly sensitive to the same parameters. F a l k [2, 3] has reported that the degree of polydipsia is an increasing function of the body-weight deficit brought about by food deprivation. The purpose of the present experiment was to determine the relation between bodyweight deficit and schedule-induced airlicking.
affixed to the base of one wall of each box and from a hole in the opposite wall, 6 cm above the floor, a metal drinking tube protruded 1 cm into the box. Through the orifice of the tube (3 m m dia.) flowed a continuous stream of roomtemperature air at a pressure of approximately 6000 dynes/ cm s. Contacts with the drinking tubes were detected by Grason-Stadler drinkometers and were recorded by counters and event markers. F o u r naive male hooded rats (400-500 g) were reduced to 80 per cent o f their pre-experimental body weights by water deprivation and were then given a 30-min session of exposure to an airstream in a test chamber on each of 3 days. At least 1 hr after the end of each of the first 2 sessions water rations were given in the home cage in order to maintain the body weight at 80 per cent of normal. On both the second and third session each animal spent more than 10 min licking the airstream, After the third session water was made available ad lib, and food, which had been continuously available, was withdrawn. The next day the airstream was turned off and each animal was allowed to eat from the food cup which was kept supplied with 45-mg Noyes pellets. On the following day scheduled feeding sessions were initiated. With the airstream available one pellet was delivered each minute for 90 rain. One-three hr after the end of each session rations of Purina rat chow were given in the home cage; the magnitude of these rations was varied to achieve the desired body-weight level. All the rats rapidly developed the schedule-induced pattern
METHOD
The test chambers consisted of two similar Plexiglas boxes (22 × 25 x 21 cm high) with wire-mesh floors located in a sound-attenuated, ventilated enclosure. A food cup was
1Supported in part by NIMH grant MH-14410 and NSF grant GB7370 to J.M. ~D.C. is now at Syracuse University, Syracuse, N.Y. 603
604
CHILLAG AND MENDELSON
of airlicking which we have described previously [7]. Each animal was maintained at 80 4- 2 per cent of its pre-experimental body weight until the amount of its airlicking was fairly stable for at least 5 sessions. Then its daily food ration was increased to allow its body weight to recover to a new, predetermined level. The body weight was held at that level for 3-9 sessions and then brought to another new level. The animals were tested every day, even when their body weights were between the desired levels, but the data selected for graphic presentation and statistical analysis included only those gathered on days when the body weight was within 2 per cent of the desired level. The body-weight deficits used and the number of sessions administered at each level are indicated in Fig. 1.
DISCUSSION
RESULTS The results for each rat are shown in Fig. 1. It can be seen that as the body weight deficit decreased gradually from
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20 to 0-5 per cent, the per cent of session time spent airlicking fell from a mean of 51.2 per cent to a mean of 7.2 per cent. This occurred despite the fact that the animals continued to approach the food cup and to avidly consume the food as soon as it was delivered. When body-weight deficit was gradually increased back to 20 per cent, schedule-induced airlicking recovered to at least its previous level in 3 of the rats, the fourth rat (AL27) showing only partial recovery. Each limb of each animal's graph was analyzed statistically for trend by Ferguson's non-parametric trend analysis [4]. In each case the trend was significant at p < 0.01 (2 tailed test) except the ascending limb of rat AL27 for which p < 0.012 and the descending limb of rat A L 36 for which p < 0.016.
21 4.
I0 15 ;~1
MEAN % BODY WEIGHT DEFICIT
FIG. 1. Mean percentage of time spent airlicking during 90-rain sessions by each of 4 rats as a function of body-weight deficit brought about by food deprivation. Each rat was receiving one 45-mg food pellet per rain throughout each session. The number of sessions at each level of deprivation is indicated above each point on the graphs. The vertical lines give the ranges and the horizontal lines intersecting the vertical ones indicate the S.E. of the mean.
Falk [2, 3] found no decrease in schedule-induced polydipsia until his rats' body-weight deficit declined from 20 to 5 per cent, while in the present experiment a decrease in scheduleinduced airlicking could be detected by the time body-weight deficit declined to 10 per cent. However, the two experiments are not strictly comparable since Falk's rats lever-pressed for food on an F I 90-see schedule, while the rats in the present experiment were automatically given pellets on an F I 60-see schedule. There may be an interaction between body-weight deficit and the reinforcement schedule in their conjoint determination of the intensity of schedule-induced behavior. If so, then as body-weight deficit is decreased from the 20 per cent level, the point at which schedule-induced behavior begins to fall off in intensity may be a function of reinforcement schedule. Therefore, the slightly different functions generated in the present experiment with airlicking and in Falk's [2, 3] experiment with drinking should not be regarded as reflecting the operation of fundamentally different processes underlying these two forms of schedule-induced behavior. The fact that the intensity of schedule-induced drinking and schedule-induced airlicking are similarly sensitive to variations in body-weight deficit lends support to the notion that both behaviors are maintained by the same reinforcers. What is the nature of these reinforcers ? It has been shown that schedule-induced drinking is relatively insensitive to large stomach preloads o f water [2]. Furthermore, direct measurements o f blood samples obtained from rats engaged in scheduleinduced drinking have revealed that the animals are overhydrated [8], Both of these observations suggest that the animals are not ingesting larger quantities of water in order to alter their body-fluid balance. It seems more likely that the reward for licking consists of a certain kind of sensory feedback, and that this feedback signal is provided equally well by licking an airstream as by licking water. Since the sensory effects of the airstream are limited to the tongue and oral cavity, it is conceivable that the crucial sensory effects of the water are likewise so restricted. I f this is the case, then sehedulerinduced drinking should be particularly sensitive to experimental manipulations which interfere with the transmission of normal feedback from the tongue. F o r example, sensory denervation of the tongue might induce large decrements in schedule-induced drinking although it leaves normal drinking largely unaffected [1, 5]. Further research will have to be undertaken to elucidate this point.
SCHEDULE-INDUCED AIRLICKING AND BODY WEIGHT
605
REFERENCES 1. Bellows, R. T. and W. P. Van Wagenen. The effect of resection of the olfactory, gustatory and trigcminal nerves on water drinking in dogs with and without diabetes insipidus. Am. J. Physiol. 126: 13-19, 1939, 2. Falk, J. L. Conditions producing psychogenic polydipsia in animals. Ann. N.Y. Acad. Sci. 157: 569-589, 1969. 3. Fallq J. L. The nature and determinants of adjunctive behavior. Physiol. Behav. 6: 577-588. 4. Ferguson, O. A. Nonparametric Trend Analysis. Montreal: McGill University Press, 1965.
5. Fossott, C. K., Jr. and F. R. Treichler. Air-drinkingby partially ageustic rats. Paper presented at the 1970 meeting of the Eastern Psychological Association, Atlantic City, N.J. 6. Mendelson, J. and D. Chillag. Schedule-induc~l air-licking in rats. Am. ZooL 8: 744, 1968. 7. Mcndelson, J. and D. Chillag. Schedule-induced air licking in rats. Physiol. Behav. 5: 535-537, 1970. 8. Stricker, E. M. and E. R. Adair. Body fluid balance, taste and postprandial factors in schedule-induced polydipsia. J. comp. physiol. Psychol. 62: 449-454, 1966.
BRIEF COMMUNICATION Schedule-Induced Airlicking as a Function of Body-Weight Deficit in Rats' DANA
CHILLAG I AND JOSEPH MENDELSON
Department of Psychology, Brain Research Laboratory, Rutgers University, New Brunswick, New Jersey 08903, U.S.A. (Received 29 S e p t e m b e r 1970) CHILLAG,D. ANDJ. MENDELSON. Schedule-inducedairlickingas a function of body-weight deficit in rats. PHYSIOL.BEHAV. 6 (5) 603--605, 1971.--Water-deprived rats were given three 30-rain periods of exposure to an alrstream flowing through a standard drinking tube; all of them learned to airlick. They were then given water ad lib and maintained at 80 per cent of their pre-experimental body weights by food restriction. Each day they were given a 90-rain session of scheduled feeding in the presence of an airstreara; one 45-rag food pellet was delivered each rain. All the rats developed strong airlicking behavior. This behavior was then studied as a function of the magnitude of body-weight deficit, as each rat's weight was allowed to recover to within 5 per cent of normal and then to drop back down to 80 per cent of normal. For each rat schedule-induced airlicking was found to be an increasing function of body-weight deficit. Airlicking
Schedule-induced airlicking
WI~N rats are deprived of food they restrict their ad lib water intake. However, if after a period of food deprivation they are fed according to certain temporal schedules their water intake increases precipitously to highly polydipsic levels, more than compensating for the decrease in water intake selfimposed during food deprivation. This phenomenon is usually referred to as schedule-induced polydipsia [2]. It now appears that polydipsia is one of a variety of behaviors which tend to occur when food-deprived animals are exposed to certain feeding schedules [3]. F o r example, if the water in the drinking tube is replaced by a stream of air (6500-8000 dynes/cm s pressure), food-deprived rats lick the airstream even more persistently than they would lick water [6, 7]. It is possible that the reinforcers that are involved in maintaining schedule-induced drinking are the same as those that support schedule-induced airlicking. If this is so, then both behaviors should be similarly sensitive to the same parameters. F a l k [2, 3] has reported that the degree of polydipsia is an increasing function of the body-weight deficit brought about by food deprivation. The purpose of the present experiment was to determine the relation between bodyweight deficit and schedule-induced airlicking.
affixed to the base of one wall of each box and from a hole in the opposite wall, 6 cm above the floor, a metal drinking tube protruded 1 cm into the box. Through the orifice of the tube (3 m m dia.) flowed a continuous stream of roomtemperature air at a pressure of approximately 6000 dynes/ cm s. Contacts with the drinking tubes were detected by Grason-Stadler drinkometers and were recorded by counters and event markers. F o u r naive male hooded rats (400-500 g) were reduced to 80 per cent o f their pre-experimental body weights by water deprivation and were then given a 30-min session of exposure to an airstream in a test chamber on each of 3 days. At least 1 hr after the end of each of the first 2 sessions water rations were given in the home cage in order to maintain the body weight at 80 per cent of normal. On both the second and third session each animal spent more than 10 min licking the airstream, After the third session water was made available ad lib, and food, which had been continuously available, was withdrawn. The next day the airstream was turned off and each animal was allowed to eat from the food cup which was kept supplied with 45-mg Noyes pellets. On the following day scheduled feeding sessions were initiated. With the airstream available one pellet was delivered each minute for 90 rain. One-three hr after the end of each session rations of Purina rat chow were given in the home cage; the magnitude of these rations was varied to achieve the desired body-weight level. All the rats rapidly developed the schedule-induced pattern
METHOD
The test chambers consisted of two similar Plexiglas boxes (22 × 25 x 21 cm high) with wire-mesh floors located in a sound-attenuated, ventilated enclosure. A food cup was
1Supported in part by NIMH grant MH-14410 and NSF grant GB7370 to J.M. ~D.C. is now at Syracuse University, Syracuse, N.Y. 603
604
CHILLAG AND MENDELSON
of airlicking which we have described previously [7]. Each animal was maintained at 80 4- 2 per cent of its pre-experimental body weight until the amount of its airlicking was fairly stable for at least 5 sessions. Then its daily food ration was increased to allow its body weight to recover to a new, predetermined level. The body weight was held at that level for 3-9 sessions and then brought to another new level. The animals were tested every day, even when their body weights were between the desired levels, but the data selected for graphic presentation and statistical analysis included only those gathered on days when the body weight was within 2 per cent of the desired level. The body-weight deficits used and the number of sessions administered at each level are indicated in Fig. 1.
DISCUSSION
RESULTS The results for each rat are shown in Fig. 1. It can be seen that as the body weight deficit decreased gradually from
AL 26
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A L 27'
80
14
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40
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5
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I I0 19 20 I0 0 MEAN % BODY WEIGHT DEFIC!T
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20 to 0-5 per cent, the per cent of session time spent airlicking fell from a mean of 51.2 per cent to a mean of 7.2 per cent. This occurred despite the fact that the animals continued to approach the food cup and to avidly consume the food as soon as it was delivered. When body-weight deficit was gradually increased back to 20 per cent, schedule-induced airlicking recovered to at least its previous level in 3 of the rats, the fourth rat (AL27) showing only partial recovery. Each limb of each animal's graph was analyzed statistically for trend by Ferguson's non-parametric trend analysis [4]. In each case the trend was significant at p < 0.01 (2 tailed test) except the ascending limb of rat AL27 for which p < 0.012 and the descending limb of rat A L 36 for which p < 0.016.
21 4.
I0 15 ;~1
MEAN % BODY WEIGHT DEFICIT
FIG. 1. Mean percentage of time spent airlicking during 90-rain sessions by each of 4 rats as a function of body-weight deficit brought about by food deprivation. Each rat was receiving one 45-mg food pellet per rain throughout each session. The number of sessions at each level of deprivation is indicated above each point on the graphs. The vertical lines give the ranges and the horizontal lines intersecting the vertical ones indicate the S.E. of the mean.
Falk [2, 3] found no decrease in schedule-induced polydipsia until his rats' body-weight deficit declined from 20 to 5 per cent, while in the present experiment a decrease in scheduleinduced airlicking could be detected by the time body-weight deficit declined to 10 per cent. However, the two experiments are not strictly comparable since Falk's rats lever-pressed for food on an F I 90-see schedule, while the rats in the present experiment were automatically given pellets on an F I 60-see schedule. There may be an interaction between body-weight deficit and the reinforcement schedule in their conjoint determination of the intensity of schedule-induced behavior. If so, then as body-weight deficit is decreased from the 20 per cent level, the point at which schedule-induced behavior begins to fall off in intensity may be a function of reinforcement schedule. Therefore, the slightly different functions generated in the present experiment with airlicking and in Falk's [2, 3] experiment with drinking should not be regarded as reflecting the operation of fundamentally different processes underlying these two forms of schedule-induced behavior. The fact that the intensity of schedule-induced drinking and schedule-induced airlicking are similarly sensitive to variations in body-weight deficit lends support to the notion that both behaviors are maintained by the same reinforcers. What is the nature of these reinforcers ? It has been shown that schedule-induced drinking is relatively insensitive to large stomach preloads o f water [2]. Furthermore, direct measurements o f blood samples obtained from rats engaged in scheduleinduced drinking have revealed that the animals are overhydrated [8], Both of these observations suggest that the animals are not ingesting larger quantities of water in order to alter their body-fluid balance. It seems more likely that the reward for licking consists of a certain kind of sensory feedback, and that this feedback signal is provided equally well by licking an airstream as by licking water. Since the sensory effects of the airstream are limited to the tongue and oral cavity, it is conceivable that the crucial sensory effects of the water are likewise so restricted. I f this is the case, then sehedulerinduced drinking should be particularly sensitive to experimental manipulations which interfere with the transmission of normal feedback from the tongue. F o r example, sensory denervation of the tongue might induce large decrements in schedule-induced drinking although it leaves normal drinking largely unaffected [1, 5]. Further research will have to be undertaken to elucidate this point.
SCHEDULE-INDUCED AIRLICKING AND BODY WEIGHT
605
REFERENCES 1. Bellows, R. T. and W. P. Van Wagenen. The effect of resection of the olfactory, gustatory and trigcminal nerves on water drinking in dogs with and without diabetes insipidus. Am. J. Physiol. 126: 13-19, 1939, 2. Falk, J. L. Conditions producing psychogenic polydipsia in animals. Ann. N.Y. Acad. Sci. 157: 569-589, 1969. 3. Fallq J. L. The nature and determinants of adjunctive behavior. Physiol. Behav. 6: 577-588. 4. Ferguson, O. A. Nonparametric Trend Analysis. Montreal: McGill University Press, 1965.
5. Fossott, C. K., Jr. and F. R. Treichler. Air-drinkingby partially ageustic rats. Paper presented at the 1970 meeting of the Eastern Psychological Association, Atlantic City, N.J. 6. Mendelson, J. and D. Chillag. Schedule-induc~l air-licking in rats. Am. ZooL 8: 744, 1968. 7. Mcndelson, J. and D. Chillag. Schedule-induced air licking in rats. Physiol. Behav. 5: 535-537, 1970. 8. Stricker, E. M. and E. R. Adair. Body fluid balance, taste and postprandial factors in schedule-induced polydipsia. J. comp. physiol. Psychol. 62: 449-454, 1966.