Differing effects of intermittent food delivery on interim behavior in guinea pigs and rats

Physiology & Behavior, Vol. 22, pp. 621-625. Pergamon Press and Brain Research Publ., 1979. Printed in the U.S.A.

Differing Effects of Intermittent Food Delivery on Interim Behavior in Guinea Pigs and Rats CATHLEEN

URBAIN, ALAN POLING 2 AND TRAVIS THOMPSON

Psychiatry Research Unit, University of Minnesota, Box 392 Mayo, Minneapolis, MN 55455 ( R e c e i v e d 5 A u g u s t 1978) URBAIN, C., A. POLING AND T. THOMPSON. Differing effects of intermittent food delivery on interim behavior in guinea pigs and rats. PHYSIOL. BEHAV. 22(4) 621-625, 1979.--Six rats and eleven guinea pigs were food-deprived and

exposed to fixed-time (FT) food schedule values of 7-120 sec in either an ascending or descending order, with either one or three pellets presented per food delivery. Water was concurrently available contingent on licking a drinking tube under a fixed-ratio (FR) 1 schedule; presses on the two levers of the experimental chamber were recorded but had no programmed consequence. Rats evidenced polydipsic drinking under all conditions, guinea pigs, under none. Guinea pigs initially exposed to a descending order of FT values developed relatively high rates of lever pressing while rats and those guinea pigs first presented with an ascending order of FT values did not lever press with much frequency. These results are discussed in terms of the interaction between species' prepotent response tendencies and the contingencies of the experimental situation. Interim behavior Schedule-induced behavior Fixed-time schedule Rats Guinea pigs

Prepotent response tendencies

T H E intermittent delivery of small bits of food to a fooddeprived animal having access to water frequently produces copious drinking referred to as schedule-induced polydipsia [7]. Such drinking has been demonstrated in mice [24], rats (e.g. [6]), pigeons [32], Java macaques [18], Rhesus monkeys [29], and humans [17]. Several parameters of the food schedule influence the degree of polydipsia. In rats, the relation between interpellet delivery time and amount of liquid consumed describes an inverted u-shaped curve with maximum consumption occurring at an inter-pellet interval of two to three minutes [7]. Similarly, if the number of postreinforcement intervals is held constant, a bitonic relation obtains between number of pellets per delivery and amount of water consumed per interval [39]. To date there are no published studies of scheduleinduced polydipsia or other interim behaviors in guinea pigs, a species traditionally considered intractable for operant research [16]. The present experiment sought to explore the ubiquity of schedule-induced polydipsia across species by exposing guinea pigs and rats receiving dry food under fixed-time schedules to parametric manipulations involving length of inter-pellet interval and number of pellets per delivery. METHOD

Animals Eleven adult male Camm-Hartley guinea pigs (mean

Adjunctive behavior

wt=552 g) and six adult male Sprague Dawley rats (mean wt=419 g) were individually housed in a constantly illuminated room with an ambient temperature of 24°C. Water was freely available in the home cages. The six rats had served in a positive conditioned suppression experiment [28]; the guinea pigs were experimentally naive. Rats were fooddeprived to approximately 85% and guinea pigs to approximately 80% of free-feeding weights, and were maintained at these weights with supplemental feedings (Purina rat chow for rats, Purina guinea pig chow and fresh vegetables for guinea pigs) in their home cages immediately following experimental sessions. The difference in relative deprivation was arranged in consideration of the finding [25] that guinea pigs given unlimited access to food carry larger loads of body fats than other rodents, e.g. rats: a guinea pig deprived to 80% of free-feeding weight is considerably " f a t t e r " than a rat similarly deprived. It is, however, not clear how functionally equivalent deprivation levels can be produced in different species. Apparatus

Each of three sound-attenuated Gerbrands operant conditioning chambers was modified by the addition of a drinkometer and a protruding food cup. A solenoid-operated drinking tube as described by Lal and Zabic [20], was inserted through the side wall 3.5 cm above the chamber floor and 7 cm from the front panel and was attached to a 250 ml capacity water reservoir. The food cup rested on the floor of

~This research was supported by Grant AA00299 to Richard Meisch, and will be presented to the University of Minnesota as part of the

doctoral thesis by the senior author. ~Currently at Western Michigan University.

C o p y r i g h t © 1979 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.--0031-9384/79/040621-05502.00/0

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URBAIN, POLING AND THOMPSON

the chamber and extended 3.5 cm from the front wall. It was 4.5 cm wide by 1 cm deep, and was located 5.5 cm from the side wall in which the drinking tube was mounted. Two rounded metal Gerbrands levers extended from the front panel, each 1.5 cm from a side wall at a distance of 10 cm above the chamber floor; a downward force of 0.2 N was required for lever operation which had no programmed consequence. A 7-W white light located in the feeder opening from which the food cup extended flashed with each delivery of a 45 mg Noyes guinea pig pellet, and a 25-W white house light located on one wall of the chamber supplied ambient illumination. An exhaust fan provided ventilation and masking noise. Eiectromechanical programming and recording equipment were located in an adjacent room.

ONE

30

PELLET

DELIVERY

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/

20 = z ~, ~: 10 5 • 7

' 15

' 30

I 60 FT

Measured volume of water gone in the 23-hour home cage period was greater for the guinea pigs (mean=0.13 ml/g body weight) than for the rats (mean=0.08 ml/g body weight). The rats, however, drank more than the guinea pigs at all FT schedule values under both the one-and three-pellet delivery conditions: the overall ratio of session intake of water to home cage consumption was significantly higher (T=2.86, df=21, p<0.01) for rats (overall mean=2.6) than for guinea pigs (overall mean=0.3) and at each FT value this ratio was

DELIVERY

G. PIGS (des) A G. PI GS (asc)

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0

RESULTS

PELLET

:RATS

Procedure Food was presented under fixed-time (FT) schedules of 7-120 sec, with water concurrently available under a fixedratio 1 (FRI) schedule of reinforcement. With this procedure, food was delivered after a specific interval of time independent of the animal's behavior and each lick on the continuously available drinking tube delivered 0.1 ml (_+ 0.03 ml) of water. The six rats and six of the guinea pigs were exposed initially to the FT values in descending order. Of these, three rats and three guinea pigs received one pellet at each food delivery, and were presented with FT values 120, 60, 30, 15, and 7-sec. The other three rats and three guinea pigs received three pellets at each food delivery, and were exposed to FT values of 120, 60, 30, and 15-sec. The FT 7-sec value was eliminated with these animals because of the time required to consume three pellets: at that value, food was presented faster than it was eaten. The remaining five guinea pigs received one pellet per delivery and were initially exposed to ascending FT values of 7-120-sec. The schedule values were then repeated a second time in a randomized order. The animals remained at each schedule value until there was no obvious trend across five consecutive days in the number of licks per session. On the average, eight sessions were required to meet this criterion (range across conditions=5-13 sessions). For the six rats and the six guinea pigs initially exposed to the FT values in descending order, at the completion of the second presentation of each FT value, one session was given in which pellets equal in number to those received at the schedule value just completed were placed in the food cup at session onset; all other conditions remained the same. During all sessions, number of pellets delivered, number of licks, and number of presses of each lever were recorded. A single one-hour session for each animal was conducted at approximately the same time every day, seven days a week. Water consumption for the 23-hour home cage period was also recorded during the first three weeks of the experiment.

THREE

I 120 VALUE(sec)

;

;s

'

'

30

60

'

120

FIG. 1. Mean licks per interfood interval at all FT values. Each data point for the rats and descending guinea pigs represents the mean of 60 sessions (5 sessions when FT values were presented in descending order and 5 sessions when FT values were presented in random order to each of 6 animals). For the ascending guinea pigs, each data point represents the mean of 40 session (5 sessions when FT values were presented in ascending order to each of 5 animals plus 5 sessions when FT values were presented in random order to each of 3 animals). Conditions are explained in text. The variance estimate is 1 standard error; means without variance estimates indicate a variance too small to represent graphically.

30

ONE P E L L E T

THREE

DELIVERY I l l / [

25

PELLET

DELIVERY

• RATS • G. PIGS(des) & G. PIGS(asc)

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/

=> 2o

ffl a. lo

/

/1

o 7

15

30

60 FT

• 120 7 VALUE(sec)

v- 15

30

60

120

FIG. 2. Mean lever presses per interfood interval. Data are as described in Fig. 1.

greater than 1.0 for all rats (range across conditions = 1.5--4.0) and less than 1.0 for all guinea pigs (range across conditions = 0.05-0.6). The ratio of session intake of water to home cage consumption is often used as an index of polydipsia, with ratios of greater than 1.0 assumed to represent polydipsic intake [9]. The mean correlation coefficient between number of licks on the drinking tube and amount of water delivered was 0.96 for the guinea pigs and 0.98 for the rats. Licks per interval clearly described a positively accelerated curve only for the six rats initially presented the FT values in descending order and for those five guinea pigs originally exposed to the FT values in ascending order (Fig. 1). These five guinea pigs had a greater number of licks/interval at the three highest FT values than the one pellet

I N T E R I M B E H A V I O R IN G U I N E A PIGS A N D RATS

623

TABLE 1 MEAN NUMBER OF LICKS AND LEVER PRESSES BY RATS AND GUINEA PIGS (ORIGINALLY EXPOSED TO b-'r VALUESIN DESCENDING ORDER) WHEN PELLETS EQUAL IN NUMBER TO THOSE GIVEN UNDER THE SPECIFIC bT VALUE WERE PRESENTED IN BULK AT SESSION ONSET. MEAN TOTAL RESPONSES PER SESSION (ONE HOUR) ARE DIVIDED BY THE NUMBER OF INTERFOOD INTERVALSUNDER THE APPROPRIATEFT CONDITION(I.E. DATAARE EXPRESSED AS RESPONSES/ INTERVAL). NUMBERS IN PARENTHESES ARE RESPONSES/INTERVALAS PRESENTED IN FIGS. 1 AND 2 FT 120"

FT 60"

FT 30"

FT 15"

LICKS One Pellet Rats Guinea Pigs

6.14(21.07) 6.69(1.97)

5.61(14.14) 6.46(1.74)

4.20(10.36) 2.93(1.11)

5.63(4.31) 1.36(1.29)

Three Pellet Rats Guinea Pigs

8.34(23.55) 5.55(3.09)

5.88(13.51) 4.53(3.04)

10.01(4.75) 3.33(2.27)

1.99(2.41) 1.47(1.14)

LEVER PRESSES One Pellet Rats 0.79(0.90) Guinea Pigs 10.28(26.69)

0.47(0.20) 1.85(21.78)

0.06(0.09) 0.96(11.28)

0.05(0.04) 0.90(6.24)

2 Rats Guinea Pigs

0.25(0.30) 2.23(8.24)

0.03(0.05 ) 0.48(2.58)

0.04(0.06) 0.19(0.56)

0.90(2.34) 7.34(26.61)

descending guinea pigs, and at the two highest FT values than the three pellet descending guinea pigs. Lever pressing had no programmed consequences. However, guinea pigs originally trained on a descending order of FT values engaged in large amounts of this behavior (Fig. 2). Lever presses per interval were an increasing function of interval length for guinea pigs initially exposed to the highest FT value, while there was little correlation between lever pressing and interval length for the rats and for those guinea pigs first presented with the lowest FT value (Fig. 2). Licks per interval exceeded lever presses per interval at every FT value for guinea pigs originally exposed to an ascending order of FT values, a relation that also obtained for the six rats, but which was the reverse of that shown by guinea pigs originally presented with the FT values in descending order. Table 1 shows the results of the food probe condition in which those animals initially exposed to a descending order of FT values (6 guinea pigs and all rats) received at the beginning of the session pellets equal in number to those presented at the preceding FT value. F o r the rats, licks per interval generally decreased compared with FT performance and lever presses per interval remained about the same, while for the guinea pigs, licks per interval typically increased over FT responding and lever presses per interval decreased. DISCUSSION One important result of this study was the demonstration that healthy, experimentally-active guinea pigs could be maintained over many months of food deprivation. With notable exceptions [25,26], earlier studies indicated that guinea pigs were poor subjects for operant research involving food reinforcement since difficulties were encountered in adapting these animals to food deprivation [1, 16, 19], in finding a food that was consumed consistently and rapidly [2, 10, 16,

FT 7"

2.92(2.83) 1.19(0.65)

0.02(0.04) 0.88(1.29)

35], in attaining stable data without extremely long periods of adaptation to the experimental situation [5, 15, 22, 23], and in maintaining both healthy and motivated animals for longer than a few months [35]. However, none of these problems were encountered in the present study: animals adapted readily to both food deprivation and the experimental situation, consistently consumed Purina guinea pig pellets, and produced reliable data across 21 consecutive months. Under conditions engendering it in rats, guinea pigs did not develop schedule-induced polydipsia, and in fact consumed less water than under conditions in which bulk food was presented. Licks per interval, however, generally increased with increasing interval length, a time-related function also reported in rats for a low rate interim behavior engendered by a F T food schedule [36]. That guinea pigs will drink in an operant chamber from a variety of drinking devices has been demonstrated previously [4, 13, 28, 35], although schedule-induced drinking has not been reported. Parametric manipulations have proven important for producing schedule-induced polydipsia in the rat [7], and may prove to do so for the guinea pig, but under a range of typical inducing schedules, the guinea pig seemingly does not show excessive drinking. The golden hamster has also been reported as failing to develop such drinking [37]. Falk suggests that characteristics of a species' foraging behavior in the natural environment might determine whether or not it develops polydipsic drinking when food is intermittently pre~ sented [8], a reference to ethological and ecological factors as determinants of patterns of intake in experimental situations that has also been emphasized by Hirsch and Collier [12,13]. Guinea pigs originally trained on descending FT values developed high rates of lever pressing. As guinea pigs do not use their forepaws for manipulation, the lever was depressed by either pushing it with the j a w or biting it. Guinea pigs initially exposed to ascending FT values evidenced little

624

URBAIN, POLING AND THOMPSON

lever pressing. To date there have been no published studies indicating such a training effect on the development of interim behavior, although it has been reported that the classes of responses likely to occur during an interfood interval follow a probability hierarchy which is subject to modification. However, studies examining the sequencing of interim activities---activities strengthened by but not directly affecting food presentatiorr--have either employed a single schedule value [14, 21, 31] or presented varying schedule values in the same order to all subjects [33,34]. It is not obvious why in the present study early exposure to long FT values resulted in high rates of lever pressing by guinea pigs while initial exposure to shorter FT values failed to do so. That lever pressing or mouthing are easily established and can be maintained at high rates, even in nondeprived guinea pigs, has been shown by Hirsch and Collier [12,13]. The tendency of guinea pigs to mouth objects when intermittently presented with food has been reported by Poling and Poling [26]. The failure in this study of the guinea pigs initially exposed to short FT values to develop high rates of lever pressing may have been due to their having developed interim behaviors oriented around the food cup, proximity to which was maintained by the short inter-pellet delivery time. Stereotyped nosing or arcing with the nose, a

behavior which occurs in the wild [30] and which has been reported as occurring frequently both in the home cage and in the experimental chamber [25], was evident in this study, as were biting of the extended food dish and areas around the feeder hole and sucking or chewing on the drinking tube. Rats, initially presented the FT values in descending order, did not develop high rates of lever pressing. Their history of suppressing responding during noncontingent food delivery in the positive conditioned suppression procedure to which they had been earlier exposed confounds the low rate of lever pressing in the current study. To our knowledge, however, there are no reports of experimentally naive rats evidencing substantial rates of lever pressing under FT schedules of food delivery. Differential effects on lever pressing guinea pigs and rats have been previously reported in a conditioned emotional response procedure [351 and in a paradigm involving intracranial stimulation [38]. It appears that what behaviors develop in an experimental situation probably reflect the interaction between the species' prepotent response tendencies and the specific manipulations of the experiment. The function which these behaviors serve, and the extent to which they can be modified, are not yet known.

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