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Effects of social isolation on quinine tolerance
Physiology and Behavior. Vol. 4, pp. 435--437. Pergamon Press, 1969. Printed in Great Britain
BRIEF COMMUNICATION Effects of Social Isolation on Quinine Tolerance ELLEN ROSEN BAUER
The College of WzTliam and Mary, Williamsburg, Virginia 23185 AND F. S A M U E L B A U E R
Department of Psychology, University of Illinois, Urbana, Illinois 61801 (Received 2 December 1968) /
BAtn~a, E. R. Atn3 F. S. BAUER. Effects of social isolation on quinine tolerance. PHYSIOL.BmIAV.4 (3) 435-437, 1969.Changes in behavior that occur after social isolation of rats might result from a change in reactivity to stimulation. This hypothesis predicts that isolated female rats will e ~ t e their normal responses to preferred and to non-preferred stimuli, thus drinltln~ less of a quinine solution and more tap water than non-isolated animals during the half-hour test period. In fact, isolated rats did drink less quinine solution than rats housed in community cages, but the prediction for tap water was not confirmed. Isolation
Palatability
Quinine tolerance
Water deprivation
AN~O,LS in social isolation can undergo pervasive changes in "personality" [1, 3, 8]. For example, animals living in individual cages are more aggressive than when housed in groups of ten [3]. Also, isolated animals tend to eat more per kilogram body weight than those living with at least one other animal, even when room temperature is not below
normal (77 -4-2~F) [5]. A previous study [7] led to a hypothesis which explains these behavioral changes as a result of an alteration in sensitivityor reactivityto external stimulation brought about, in this case, by the loss of stimulation from a companion. Animals Hying in isolation suffer at least some deprivation of tactile stimulation, since animals gravitate toward each other when confined together [4]. As a result of this change in sensitivity, normal responses to stimulation that does occur are exaggerated. Thus, an individually-housed animal offered water will exaggerate this normal response: if the water is palatable he will over-ingest ; if unpalatable (bitter) he will reject it with vehemence.
METHOD
Naive female H o l t z m rats, 78 days old, were housed either in individual cages (9 Ss) or in one large cage (9 Ss). They were allowed ad libitum food (Purina Breeder Blox) and water for the first eight days. Light was continuous. After the eighth day, water was removed from the living cages, and, thereafter was available only for ½ hr per day in a
Drinking
special drinking box, in which no food was present. Drinking boxes were used to provide a measure o f the intake for individual rats in the group condition, and to avoid confounding of intake data by social facilitation of the drinking response. Adaptation to the deprivation schedule and living conditions continued for 13 additional days during which water intake and body weight were recorded. The last three days of this period were considered the baseline for water intake. On the fourteenth day of deprivation (22nd day of social isolation), a 0.25 mg/ml quinine hydrochloride solution (in tap water) was substituted. This solution previously was shown by the author t o reduce normal intake to about 2 5 ~ and 63 ~0 in a first and second exposure respectively under deprivation. This change was made at the end of the third week of isolation because this is the beginning of the period, at least for mice, in which the increases in consumption have been observed [8]. Quinine was continued for three days, after which the drinking fluid was changed back to water for three days, in order to allow the rats to recover from the voluntary increase in deprivation brought about by quinine adulteration. Then a second three day test period of quinine intake was begun to determine whether there was an ameliorating effect of prior experience on tolerance to quinine adulteration for animals on a deprivation schedule. During the entire 30-day period of the experiment, all fluids which were given to the animals had been standing for at least 24 hr and were at about room temperature (8 I*F). 435
436
BAUER AND BAUER the first (baseline) period, probably because they are more dehydrated during the second period. The living condition, contrary to the hypothesis, d i d not produce a significant difference in intake of tap water. This may be because the animals were female rats, for whom response to social isolation is less pronounced than for males [6]. This result may have occurred also because tap water is a "neutral" stimulus, and the hyper-reactivity may become apparent only when the test stimulus is unusual. Thus, a preferential
RESULTS AND DISCUSSION
The results are summarized in Fig. 1 and Table 1. Due to faulty equipment, the data for one of the isolated animals were lost. Thus, because of unequal Ns, unweighted means analyses of variance were performed. From Table 1 it is apparent that for the two periods of water intake (baseline and rest period) the only significant factor is the test period. That is, rats drink more in the second (rest) period than in
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DAYIS OF D E P R I V A T I O N
FIG. 1. Averqle daily fluid intake of beth ~ and n o n - ~ rats d ~ all phases of the e x i t (from the ~ t h ~ of isolation until the 30th day of isolation).
TABLE 1 SUMMAaYOF ANALYBSOF VAmJANCe Water Source
df
MS
Between Ss Livens Condition (L) Error Wit]~ S:
16 I 15 85
1 1 15 2 2 30 2 2 30
Test Pe~'iod (P) LX P Error Dsy (D) Lx D Error Px D L × Px D Error *Significant at 0.01 level.
Q-Shine F
MS
F
1.02 I 1,56
< I
182.95 7.85
23.31"
98.25 0.00 3.21 5.80 2.46 4.48 1.40 4.62 3.35
30.61" <1
121.12 0.17 9.18 184.78 1.40 7.33 52.30 11.86 4.40
13.19" ~1
1.29 <1 <1 1.38
25.21" <1 11.89" 2.70
SOCIAL ISOLATION AND QUININE TOLERANCE
437
response to a saccharine solution, which is normally preferred to tap water, might have shown an exaggerated preference by the isolated animals even though the tap water did not. The analyses for the two quinine periods are also presented in Table 1. The significant factors are living condition, test period, day within period and the test by day interaction. Means for the two groups during the first test period were significantly different at the 0.01 level (one-tailed) for the first two days (t = 2.15 and 2.87 respectively; d f - 15) but not for the third day (t --- 1.35; d f = 15). For the second quinine period, the two groups were significantly different at least at the 0.05 level (one-tailed) on each day (t = 1.89, 1.9, and 3.29; d f = 15). Also from Fig. 1 it is apparent that the animals drank more quinine in the second period than during the first period. On each quinine day the animals drank more than on the prior day, again probably because of the increased deprivation due to refusal of the adulterated water on the previous day. The significant test by day interaction
is due to the much higher intake on the first day of the second test than on the first day of the first test. This is a result of experience with quinine: on the first day of the first test quinine adulterated water is a completely novel aversive stimulus, but on the first day of the second test period, though still aversive, it is no longer novel. As a consequence of its loss of novelty, it loses some of its impact and thus is no longer as potent an energizer of behavior [2, p. 25]. The hypothesis of hyper-reactivity to stimulation as a result of social isolation has thus been supported in one instance. The socially isolated animals rejected an unpalatable solution with greater vigor than animals maintained in a group-living condition. In addition to the theoretical implicatious of the present experiment, there is also an important procedural implication of these results. Namely, in experiments such as this, in which appetitive responses are the dependent variable, all rats should be housed under the same conditions of social contact.
REFERENCES 1. Barnes, T. C. Effects of tranquilizers and anti-epileptic drugs on EEG-flicker response and on convulsive behavior. Fedn Prec. 18: 365, 1959. 2. Fiske, A. and S. Maddi. Functions o f varied experience. Homewood, Illinois: Dorsey Press, 1961. 3. Hatch, A., T. Balazs, G. S. Wiberg and H. C. Grice. Long-term isolation stress in rats. Science. 142: 507, 1963. 4. Latane, B. and D. C. Glass. Social and nonsocial attraction in rats. J. personality and social Psychol. 9: 142-146, 1968.
5. Prychodko, W. Effect of aggregation of laboratory mice (mus musculus) on food intake at different temperatures. Ecology. 39: 500-503, 1958. 6. Prychodko, W. and A. P. Long. Effect of isolation on the body weight of laboratory mice. Anat. Rec. 138: 377, 1960. 7. Rosen, E. F. Amygdaloid complex and medial hypothalamic nucleus functioning in food regulation. Physiol. Behav. 3: 567-570, 1968. 8. Weltman, A. S., A. M. Sachler and S. B. Sparber. Endocrine, metabolic and behavioral aspects of isolation stress on female albino mice. Aerospace Med. 37: 804-810, 1966.
BRIEF COMMUNICATION Effects of Social Isolation on Quinine Tolerance ELLEN ROSEN BAUER
The College of WzTliam and Mary, Williamsburg, Virginia 23185 AND F. S A M U E L B A U E R
Department of Psychology, University of Illinois, Urbana, Illinois 61801 (Received 2 December 1968) /
BAtn~a, E. R. Atn3 F. S. BAUER. Effects of social isolation on quinine tolerance. PHYSIOL.BmIAV.4 (3) 435-437, 1969.Changes in behavior that occur after social isolation of rats might result from a change in reactivity to stimulation. This hypothesis predicts that isolated female rats will e ~ t e their normal responses to preferred and to non-preferred stimuli, thus drinltln~ less of a quinine solution and more tap water than non-isolated animals during the half-hour test period. In fact, isolated rats did drink less quinine solution than rats housed in community cages, but the prediction for tap water was not confirmed. Isolation
Palatability
Quinine tolerance
Water deprivation
AN~O,LS in social isolation can undergo pervasive changes in "personality" [1, 3, 8]. For example, animals living in individual cages are more aggressive than when housed in groups of ten [3]. Also, isolated animals tend to eat more per kilogram body weight than those living with at least one other animal, even when room temperature is not below
normal (77 -4-2~F) [5]. A previous study [7] led to a hypothesis which explains these behavioral changes as a result of an alteration in sensitivityor reactivityto external stimulation brought about, in this case, by the loss of stimulation from a companion. Animals Hying in isolation suffer at least some deprivation of tactile stimulation, since animals gravitate toward each other when confined together [4]. As a result of this change in sensitivity, normal responses to stimulation that does occur are exaggerated. Thus, an individually-housed animal offered water will exaggerate this normal response: if the water is palatable he will over-ingest ; if unpalatable (bitter) he will reject it with vehemence.
METHOD
Naive female H o l t z m rats, 78 days old, were housed either in individual cages (9 Ss) or in one large cage (9 Ss). They were allowed ad libitum food (Purina Breeder Blox) and water for the first eight days. Light was continuous. After the eighth day, water was removed from the living cages, and, thereafter was available only for ½ hr per day in a
Drinking
special drinking box, in which no food was present. Drinking boxes were used to provide a measure o f the intake for individual rats in the group condition, and to avoid confounding of intake data by social facilitation of the drinking response. Adaptation to the deprivation schedule and living conditions continued for 13 additional days during which water intake and body weight were recorded. The last three days of this period were considered the baseline for water intake. On the fourteenth day of deprivation (22nd day of social isolation), a 0.25 mg/ml quinine hydrochloride solution (in tap water) was substituted. This solution previously was shown by the author t o reduce normal intake to about 2 5 ~ and 63 ~0 in a first and second exposure respectively under deprivation. This change was made at the end of the third week of isolation because this is the beginning of the period, at least for mice, in which the increases in consumption have been observed [8]. Quinine was continued for three days, after which the drinking fluid was changed back to water for three days, in order to allow the rats to recover from the voluntary increase in deprivation brought about by quinine adulteration. Then a second three day test period of quinine intake was begun to determine whether there was an ameliorating effect of prior experience on tolerance to quinine adulteration for animals on a deprivation schedule. During the entire 30-day period of the experiment, all fluids which were given to the animals had been standing for at least 24 hr and were at about room temperature (8 I*F). 435
436
BAUER AND BAUER the first (baseline) period, probably because they are more dehydrated during the second period. The living condition, contrary to the hypothesis, d i d not produce a significant difference in intake of tap water. This may be because the animals were female rats, for whom response to social isolation is less pronounced than for males [6]. This result may have occurred also because tap water is a "neutral" stimulus, and the hyper-reactivity may become apparent only when the test stimulus is unusual. Thus, a preferential
RESULTS AND DISCUSSION
The results are summarized in Fig. 1 and Table 1. Due to faulty equipment, the data for one of the isolated animals were lost. Thus, because of unequal Ns, unweighted means analyses of variance were performed. From Table 1 it is apparent that for the two periods of water intake (baseline and rest period) the only significant factor is the test period. That is, rats drink more in the second (rest) period than in
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DAYIS OF D E P R I V A T I O N
FIG. 1. Averqle daily fluid intake of beth ~ and n o n - ~ rats d ~ all phases of the e x i t (from the ~ t h ~ of isolation until the 30th day of isolation).
TABLE 1 SUMMAaYOF ANALYBSOF VAmJANCe Water Source
df
MS
Between Ss Livens Condition (L) Error Wit]~ S:
16 I 15 85
1 1 15 2 2 30 2 2 30
Test Pe~'iod (P) LX P Error Dsy (D) Lx D Error Px D L × Px D Error *Significant at 0.01 level.
Q-Shine F
MS
F
1.02 I 1,56
< I
182.95 7.85
23.31"
98.25 0.00 3.21 5.80 2.46 4.48 1.40 4.62 3.35
30.61" <1
121.12 0.17 9.18 184.78 1.40 7.33 52.30 11.86 4.40
13.19" ~1
1.29 <1 <1 1.38
25.21" <1 11.89" 2.70
SOCIAL ISOLATION AND QUININE TOLERANCE
437
response to a saccharine solution, which is normally preferred to tap water, might have shown an exaggerated preference by the isolated animals even though the tap water did not. The analyses for the two quinine periods are also presented in Table 1. The significant factors are living condition, test period, day within period and the test by day interaction. Means for the two groups during the first test period were significantly different at the 0.01 level (one-tailed) for the first two days (t = 2.15 and 2.87 respectively; d f - 15) but not for the third day (t --- 1.35; d f = 15). For the second quinine period, the two groups were significantly different at least at the 0.05 level (one-tailed) on each day (t = 1.89, 1.9, and 3.29; d f = 15). Also from Fig. 1 it is apparent that the animals drank more quinine in the second period than during the first period. On each quinine day the animals drank more than on the prior day, again probably because of the increased deprivation due to refusal of the adulterated water on the previous day. The significant test by day interaction
is due to the much higher intake on the first day of the second test than on the first day of the first test. This is a result of experience with quinine: on the first day of the first test quinine adulterated water is a completely novel aversive stimulus, but on the first day of the second test period, though still aversive, it is no longer novel. As a consequence of its loss of novelty, it loses some of its impact and thus is no longer as potent an energizer of behavior [2, p. 25]. The hypothesis of hyper-reactivity to stimulation as a result of social isolation has thus been supported in one instance. The socially isolated animals rejected an unpalatable solution with greater vigor than animals maintained in a group-living condition. In addition to the theoretical implicatious of the present experiment, there is also an important procedural implication of these results. Namely, in experiments such as this, in which appetitive responses are the dependent variable, all rats should be housed under the same conditions of social contact.
REFERENCES 1. Barnes, T. C. Effects of tranquilizers and anti-epileptic drugs on EEG-flicker response and on convulsive behavior. Fedn Prec. 18: 365, 1959. 2. Fiske, A. and S. Maddi. Functions o f varied experience. Homewood, Illinois: Dorsey Press, 1961. 3. Hatch, A., T. Balazs, G. S. Wiberg and H. C. Grice. Long-term isolation stress in rats. Science. 142: 507, 1963. 4. Latane, B. and D. C. Glass. Social and nonsocial attraction in rats. J. personality and social Psychol. 9: 142-146, 1968.
5. Prychodko, W. Effect of aggregation of laboratory mice (mus musculus) on food intake at different temperatures. Ecology. 39: 500-503, 1958. 6. Prychodko, W. and A. P. Long. Effect of isolation on the body weight of laboratory mice. Anat. Rec. 138: 377, 1960. 7. Rosen, E. F. Amygdaloid complex and medial hypothalamic nucleus functioning in food regulation. Physiol. Behav. 3: 567-570, 1968. 8. Weltman, A. S., A. M. Sachler and S. B. Sparber. Endocrine, metabolic and behavioral aspects of isolation stress on female albino mice. Aerospace Med. 37: 804-810, 1966.