Schedule dependency of schedule-induced air-licking

Physiology and Behavior, Vol. 7, pp. 207-210. Pergamon Press, 1971. Printed in Great Britain

Schedule Dependency of Schedule-Induced Air-Licking' JOSEPH MENDELSON,

RON ZEC AND DANA CHILLAG 2

Department of Psychology, Brain Research Laboratory, Rutgers University, New Brunswick, New Jersey 08903, U.S.A. (Received 28 D e c e m b e r 1970) MENDELSON, J., R. ZEC AND D. CHILLAG. Schedule dependency of schedule-inducedair-licking. PHYSIOL.BEHAV. 7 (2) 207-210, 1971.--Rats deprived to 80 per cent of their preexperimental body weights were given one 90-rain session per day during which one 45-rag food pellet was delivered every rain. They were given access to an air-stream by licking a drinking tube through which air would be pumped while they licked it. Each rat rapidly developed the typical scheduleinduced pattern of air-licking which has been previously described. Then variations were introduced into the schedule of food presentation to determine whether the air-licking was indeed schedule dependent. Thus, each rat received a group of 15 pellets at the beginning of each session and every 15 rain thereafter. This resulted in a very large decrement in airlicking as did subsequent schedules under which larger meals were presented at greater intervals. In a second experiment the number of pellets delivered at the end of each minute was increased from one to three, resulting in a small decrement in air-licking which was partially attributed to increased satiation. It was concluded that schedule-induced airlicking is schedule dependent.

Schedule-induced behavior

Air-licking

AFTER rats have been deprived of food they will drink very large quantities of water if they are fed according to certain temporal schedules [4]. F o r example, when rats are reduced to 80 per cent of their normal body weights and allowed to work on a VI l-rain schedule for 45-mg food pellets, Falk found that some of them would drink an amount of water equal to one-half or two-thirds their body weight in a 3.5hr session [3]. One of Falk's rats weighing 144 gm at the beginning of a session would drink a mean of 132 ml during the session. When given an equivalent quantity of food all at once Falk's rats typically drink 9,5 ml [3], showing that the excessive drinking is indeed schedule dependent. We have previously reported that food-deprived rats being fed 45-mg pellets on a free F I l-rain schedule develop very strong and persistent air-licking (AL) behavior [6, 7] and that the amount of A L increases with per cent body-weight deficit brought about by food deprivation [1]. Under a 20 per cent deficit in body weight the animals spend up to 60 per cent of the 90 min session air-licking. To show that this A L is schedule dependent it behooves us to demonstrate that the amount of A L is sensitive to changes in the parameters of the feeding schedule, i.e. meal size and intermeal interval. This was the purpose of the present experiment. EXPERIMENT 1 METHOD

Animals were three adult male hooded rats. Two of them were naive and one (No. AL35) had been used in an experi-

ment studying schedule-induced A L as a function of bodyweight deficit [1]. While under water deprivation they were given preliminary A L training [1] in one of two similar Plexiglas boxes (22 × 25 x 21 cm high), each containing a standard drinking tube. The tube was hooked up to a twoway valve through which air was pumped at a pressure of about 6000 dynes/cm'. Each contact with the tube was detected by a Grason-Stadler drinkometer and it resulted in activating the valve in such a way as to permit the air to flow through the tube for 0.25 sec. If the rat touched the tube continuously or at intervals separated by less than 0.25 sec, the flow of air through the tube was continuous. The duration of valve closure (which approximated A L time) was recorded on running time meters. After each animal learned to air-lick during preliminary training it was provided with ad lib water and deprived of food such as to maintain its body weight at 80 per cent of its predeprivation weight. Then it was given one 90-rain session in the test chamber during which it was provided with its daily ration of food in a food cup located on the wall opposite to the drinking tube. No air was available from the tube on this session. On the following day scheduled feeding sessions were initiated. With the air-stream available one pellet per rain (pel/min) was delivered during each daily 90-min session. One to three hr after each session the rats were given their daily rations of Purina rat chow pellets. All animals rapidly developed the schedule-induced A L pattern which we have described previously [7]. After 6 sessions of stable AL,

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variations were introduced into the schedule of presentation of the 90 pellets. Since we suspected that providing the rats with the whole group of 90 pellets at the start of each session might lead to osmotic thirst due to the eating of so much dry food and that this thirst would sustain AL for the entire session, we decided to start off by introducing less dramadc changes in the feeding schedule. The first change consisted of providing each animal with 15 pellets at the start of each session and a group of 15 every 15 rain thereafter (for a total of 90 pellets per session). After 6-12 sessions on this schedule the initial schedule of 1 pel/min was reinstated. Then for one rat the 15 pel/15 min schedule was repeated for several sessions and followed again by the 1 pel/min schedule. The next variation in schedule consisted of starting the session with 45 pellets in the food cup and delivering a group of 45 pellets after 45 rain had elapsed. After 9-12 sessions on this schedule the animals were again switched back to 1 pel/min. The final variation in schedule consisted of providing all 90 pellets at the beginning of the session. After 3 such sessions the 1 pel/min schedule was run for 3-6 sessions. the exact numbers of sessions presented to each rat under each condition are indicated in Figs. 1--3.

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On all the schedules deviating from 1 pel/min AL was greatly reduced (Figs. 1-3). The extent of reduction was not systematically related to the parameters of the 3 deviant schedules. This probably occurred because the baseline rate of AL (measured with l pel/min) was fluctuating during the course of the experiment. Also the different schedules were inducing different amounts of osmotic thirst for varying portions of session time. For example, when the 90 pellets were all presented at the beginning of the session the animals ate them within 10-15 min. Eating this quantity of food (about 4 g) could induce a physiological thirst by producing hyperosmolarity of blood plasma within the first few rain of session time [2] and this would motivate the animals to air-lick during the remaining 65-70 min of the session. All the AL under this condition was probably motivated by osmotic thirst rather than by schedule factors.

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On the other hand, when the pellets were delivered in groups of 15 every 15 min, the build up of osmotic thirst was more gradual. Much of the AL under this schedule was probably motivated by schedule factors, with osmotic factors making only a minor contribution. The net result was to produce about the same amount of AL as did the most deviant schedule (all 90 pellets at the beginning). Thus, the fact that all the deviant schedules produced about the same decrement in AL does not mean that the same motivators were equally operative in the case of each schedule.

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BLOCKSOF 3 SESSIONS FIG. 1. The mean number of seconds spent air-licking by a fooddeprived rat during 90 min sessions as a function of the schedule of delivery of 45 mg food pellets: 1 pellet per min (filled circles); a group of 15 pellets at the beginning of each session and every t5 rain thereafter (open circles); 45 pellets at the beginningand middle of the session (triangles); and 90 pellets at the beginning of the session (squares).

EXPERIMENT 2 METHOD

Animals were four adult male hooded rats. Two had been used in Experiment 1 (Nos. AL35 and AL39) and three had been used in an experiment studying the relation between body-weight deficit and schedule-induced AL [1] (Nos. AL26, AL27 and AL35). Their food intake was restricted

SCHEDULE DEPENDENCY OF SCHEDULE-INDUCED AIR-LICKING

209

intervals and the mean amount of A L in each interval was computed for each meal size (Fig. 6). This type of analysis was particularly rewarding for rat AL35 which showed the largest decrement in response to trebling meal size. It can be seen in Fig. 6 that the decrement in A L in the first 30 min of the

such as to maintain their body weights at 80 per cent of their preexperimental levels. They were given daily 90-min sessions in the apparatus used in Experiment 1 in which one 45 mg pellet per min was delivered non-contingently and an air-stream was continuously available. After the animals reached a fairly stable level of A L the number of pellets delivered per min was increased to 3 ; they were presented successively within a 4-see period. The rats were tested in pairs. One pair was given 10 such sessions followed by 5 sessions with 1 pel/min. The other pair was given 3 such sessions, then 3 with 1 pel/min, 12 with 3 per min, and finally 11-14 with 1 per min.

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Initially all rats showed a decrement in A L when the number of pellets delivered each min was trebled (Figs. 4 and 5). Then 2 rats recovered to levels which approximated those previously and subsequently attained while receiving 1 pel/min (Fig. 4). Of the other 2 rats (Fig. 5) No. AL39 showed a small but significant decrement in A L (there was no overlap of the scores obtained under 1 pel/min with those obtained under 3 pel/min); No. AL35 showed a

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somewhat larger decrement, especially when compared to the subsequent level which it achieved with 1 pel/min. This variability in response to an increase in meal size is not surprising in view of the variable changes in polydipsia observed by Falk [3] in response to a VI 1-min schedule of reinforced bar-pressing when the reinforcement was shifted from one to two 45 mg pellets. One animal's intake dropped from 0.66 to 0.25 ml/reinforcement, another animal's intake remained unchanged at 0.20 ml/reinforcement, and the third animal increased its intake from 0.30 to 0.34 ml/ reinforcement. Subsequent research in Falk's laboratory [5] has indicated that the results for the latter 2 rats are more typical of what can be expected to happen in response to this type of experimental manipulation. Both schedule-induced polydipsia and A L are increasing functions of body-weight deficit [4, 7] and, presumably, level of satiation. Therefore it is likely that in the present study the decrements produced in 2 animals by trebling meal size were due to the greater satiating effect of the larger meals. This possibility is borne out by a finer analysis of the data. F o r each session the data were segmented into 15-min

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210

MENDELSON, ZEC AND CH1LLA~.;

session was fairly small but that thereafter the animal's A L fell off precipitously until, by the end of the session, it was only air-licking about 30 per cent as much as it was during the first half hour. In contrast, under the 1 pel/min condition no decrement was observed until the last 15 min, during which A L was only slightly reduced (by about 10 per cent). In contrast, the curves for rat AL39 run parallel to each other. They indicate that the tendency to air-lick fell off gradually throughout the session under both the 1 pel/min and 3 pel/min conditions. The difference between the curves varies within narrow limits (16-19 per cen0. This difference may reflect the fact that the rat spent three times as long feeding under the 3 pel/min condition. If it takes 3 sec to eat each 45 mg pellet then it would take 90 sec longer to eat

45 pellets than to eat 15. This difference can only partially account for the difference between the curves for AL3!L although it closely corresponds to the difference betwee~a the scores for AL35 during the first 15 min of its sessions, when increased satiation should be at a minimum. In conclusion, there seems to be a slight decrement in schedule-induced A L produced by increasing FI l-rain feedings from one to three 45-mg pellets which is not attributable to satiation. However, this effect is not nearly as great as that observed when 15-pellet meals are spaced at 15-rain intervals as in Experiment 1. The extent to which satiation contributes to the small decrements observed in Experiment 2 might best be determined in subsequent experiments by using animals that have been fistulated for sham feeding.

REFERENCES 1. Chillag, D. and J. Mendelson. Schedule-induced air-licking as a function of body-weight deficit in rats. Physiol. Behav. 6: 603-605, 1971. 2. Deaux, E., J. W. Kakolewski and E. Sato. Emergence of systemic cues evoking food-associated drinking. Physiol. Behav. 5: 1177-1179, 1970. 3. Falk, J. L. Control of schedule-induced polydipsia: Type, size, and spacing of meals. J. exp. Analysis Behav. 10: 199-206, 1967.

4. Falk, J. L. Conditions producing psychogenic polydipsia in animals. Ann. N. Y. Acad. Sci. 157: 569-589, 1969. 5. Flory, R. K. The control of schedule-induced polydipsia: frequency and magnitude of reinforcement. Unpublished Ph.D. Dissertation, Arizona State University, 1969. 6. Mendelson, J. and D. Chillag. Schedule-induced air-licking in rats. Am. Zool. 8: 744, 1968. 7. Mendelson, J. and D. Chillag. Schedule-induced air-licking in rats. Physiol. Behav. 5: 535-537, 1970.