Alcohol, Vol. 7, pp. 133--136.©PergamonPress plc, 1990. Printedin the U.S.A.
0741-8329/90$3.00 + .00
The Influence Of Control Over Appetitive and Aversive Events on Alcohol Preference in Rats J O S E P H R. V O L P I C E L L I 1
Departments of Psychiatry and Psychology, University of Pennsylvania, Philadelphia, PA 19104 AND R O N A L D R. U L M
Department of Psychology, Salisbury State University, Salisbury, MD 21801 Received 5 July 1988; Accepted 29 July 1989
VOLPICEIJ.I, J. R. AND R. R. ULM. The influence of control over appetitive and aversive events on alcoholpreference in rats. ALCOHOL 7(2) 133-136, 1990.-- The effect of control of food reinforcement or shock termination on alcohol drinking was examined in two experiments. In the In'st experiment, rats unable to control the delivery of food pellets preferred alcohol more than rats which had control over food. Similarly, in the second experiment, rats unable to control electric footshoek termination preferred alcohol more than rats which could escape shock. These results showed that the psychological dimension of control over environmental events influences alcohol preference in rats. Stress
Alcohol self-selection
Rats
Uncontrollable shock
ANIMALS and humans lacking control over aversive events exhibit a variety of behavioral and physiological changes which have been commonly referred to as helplessness effects (9). These experiments always use the yoked control procedure. This procedure involves matching pairs of subjects such that all physical stimuli are held constant, but one subject controls the presentation or termination of the important stimulus event. For example, in the typical helplessness experiment, shock presentations are identical for each pair of rats, but one of the rats can escape from shock (master rat) while shock termination occurs at the same time regardless of the behavior of its yoked partner (helpless rat). In this way, only the controllability of the important stimulus event is varied while the physical properties of the event are held constant. Thus, the duration, intensity, and pattern of shocks is identical within each pair. Using this yoked control procedure, Maier and Seligman (9) have demonstrated that uncontrollably shocked rats are more passive in new situations than rats exposed to equivalent amounts of controllable shock. Others have shown that uncontrollable shock leads to immunosuppression (7), gastric ulceration (19), decreased resistance to a tumor challenge (15), higher catecholamine and corticosterone levels (14), and higher 13-endorphin levels
Uncontrollable food
Tension reduction hypothesis
in peripheral blood (12). In the few studies which have systematically examined the influence of controllability on appetitive events, similar behavioral helplessness effects have been observed. Goodkin et al. (6) found that, following uncontrollable food pellets, rats were slower to learn a new response to obtain food reward and were more passive in a novel shock escape task than rats exposed to equivalent amounts of controllable food. Similarly, Engberg et al. (4) found that, following uncontrollable food pellets, rats were also slower to escape in a new shock escape task. There is some indication that the psychological dimension of control over environmental events may be related to alcohol drinking. Human alcoholics, for example, report feelings of lack of control over alcohol drinking as well as other aspects of their lives (2). However, there is little systematic research that investigates this relationship. One exception is a study that showed increased alcohol drinking following unsolvable problems in female social drinkers (11). Alcohol per se may lead to increased feelings of lack of control, or conversely, uncontrollable events may lead to alcoholism. The present experiments attempt to clarify this issue by systematically assessing the effects of controllability on alcohol drinking in rats.
~Requests for reprints should be addressed to Joseph R. Volpicelli, M.D., Ph.D., Addiction Research Center, 3910 Chestnut St., University of Pennsylvania, Philadelphia, PA 19104.
133
134
VOLPICELLI AND ULM
EXPERIMENT 1: APPETITIVE CONTROL There have been several attempts to elicit excessive alcohol drinking in rats using appetitive events. For example, Falk and Samson (5), found that food-deprived rats with access to a 5% alcohol solution drank large amounts of alcohol when a food pellet was delivered uncontrollably about once every two minutes. This procedure has been termed scheduled-induced polydipsia and it has been used to induce animals to drink an excessive amount of many fluids including water. Since the controllability dimension was not systematically varied, however, it is not clear from this research whether rats drank alcohol, 1) for some reinforcing pharmacological effect of alcohol related to the lack of control over food pellets, 2) because drinking is nonspecifically directed at alcohol because it is the only fluid available or 3) to compensate for their restricted caloric schedule. Therefore, our first experiment systematically investigated the effects of controllability over food pellets using the yoked control procedure. Since alcohol preference is examined in a two-bottle test with both alcohol and water continuously available, and rats receive equivalent amounts of food, differences between the yoked and control subjects can be attributed to the psychological effects of lack of control over food. METHOD
Subjects Subjects were 10 male Sprague-Dawley rats (N=5/group) obtained from Holtzman Co., Madison, WI. Rats were obtained at 60 days of age and were individually housed and raised in a 14 hr light-10 hr dark environment. During the first seven days subjects were gradually reduced to 80% body weight and then paired according to weight and placed in operant chambers, with control versus yoked assignment randomly determined.
Apparatus Subjects lived in a modified Skinner box with a lever mounted on the front of the chamber and two graduated cylinders mounted at the rear of the chamber so that both alcohol and water were freely available at all times. Rats obtained fluid by licking narrow metal drinking spouts that protruded 2 cm into the cage. This technique was used to eliminate the spillage that can occur with other types of drinking tubes.
Procedure Following assignment into the yoked or control groups, rats were placed in operant chambers for the next 28 days. Water and 10% alcohol sweetened with 0.25% sodium saccharin was freely available to all subjects. Food pellets (45 mg Noyes pellets) were delivered to both the control and its yoked partner when the control rat pressed the lever. On day 1, each lever-press resulted in a food pellet and on subsequent days lever-pressing was reinforced on a VI-60 second schedule (range 10 to 120 sec). Since subjects in both groups ate the pellets immediately when it was delivered, the only difference between the two groups was that the control group could control food presentations by lever-pressing while the yoked rats had no control over food presentations. This appetitive schedule control feeding was in effect 24 hr/day. Dally measurements of the weight and fluid consumption of each rat were made and followed by placing a fresh supply of water or alcohol into the graduated cylinders. To avoid position biases the fluid cylinders were rotated daily. RESULTS AND DISCUSSION
In order to control for difference in total fluid consumption, the
100T
uJ
80-
c
60-
U3
X TJO'~ I O~ o •
T
O.
TT-T -i
....
a_
40-
c
o.
t ?..
20-
o o
o.-'" T
• /'~)
--i
. . . . . .
+"i
o
e - - e
[
o ..... o Control Food
Yoked Food
I
I
I
I
I
I
I
2
4
6
8
10
12
14
Two Duy Means
FIG. 1. Mean ethanol preference for rats with control over food pellets and rats which received yoked pellet presentations across 14 blocks of two-day averages.
TABLE
1
MEANS, STANDARD ERRORS, AND t-TESTS FOR WATER, ETHANOL, AND TERMINAL WEIGHT FOR THE CONTROL AND YOKED CONDITIONS OF EXPERIMENT 1
Water (ml) Ethanol (g/kg) Terminal Weight (g)
Control Group
Yoked Group
t-test
19.34 (2.19) 5.08 (0.89) 409 (10.00)
13.5 (2.09) 9.14 (0.69) 429 (8.17)
n.s. 3.21, p
0741-8329/90$3.00 + .00
The Influence Of Control Over Appetitive and Aversive Events on Alcohol Preference in Rats J O S E P H R. V O L P I C E L L I 1
Departments of Psychiatry and Psychology, University of Pennsylvania, Philadelphia, PA 19104 AND R O N A L D R. U L M
Department of Psychology, Salisbury State University, Salisbury, MD 21801 Received 5 July 1988; Accepted 29 July 1989
VOLPICEIJ.I, J. R. AND R. R. ULM. The influence of control over appetitive and aversive events on alcoholpreference in rats. ALCOHOL 7(2) 133-136, 1990.-- The effect of control of food reinforcement or shock termination on alcohol drinking was examined in two experiments. In the In'st experiment, rats unable to control the delivery of food pellets preferred alcohol more than rats which had control over food. Similarly, in the second experiment, rats unable to control electric footshoek termination preferred alcohol more than rats which could escape shock. These results showed that the psychological dimension of control over environmental events influences alcohol preference in rats. Stress
Alcohol self-selection
Rats
Uncontrollable shock
ANIMALS and humans lacking control over aversive events exhibit a variety of behavioral and physiological changes which have been commonly referred to as helplessness effects (9). These experiments always use the yoked control procedure. This procedure involves matching pairs of subjects such that all physical stimuli are held constant, but one subject controls the presentation or termination of the important stimulus event. For example, in the typical helplessness experiment, shock presentations are identical for each pair of rats, but one of the rats can escape from shock (master rat) while shock termination occurs at the same time regardless of the behavior of its yoked partner (helpless rat). In this way, only the controllability of the important stimulus event is varied while the physical properties of the event are held constant. Thus, the duration, intensity, and pattern of shocks is identical within each pair. Using this yoked control procedure, Maier and Seligman (9) have demonstrated that uncontrollably shocked rats are more passive in new situations than rats exposed to equivalent amounts of controllable shock. Others have shown that uncontrollable shock leads to immunosuppression (7), gastric ulceration (19), decreased resistance to a tumor challenge (15), higher catecholamine and corticosterone levels (14), and higher 13-endorphin levels
Uncontrollable food
Tension reduction hypothesis
in peripheral blood (12). In the few studies which have systematically examined the influence of controllability on appetitive events, similar behavioral helplessness effects have been observed. Goodkin et al. (6) found that, following uncontrollable food pellets, rats were slower to learn a new response to obtain food reward and were more passive in a novel shock escape task than rats exposed to equivalent amounts of controllable food. Similarly, Engberg et al. (4) found that, following uncontrollable food pellets, rats were also slower to escape in a new shock escape task. There is some indication that the psychological dimension of control over environmental events may be related to alcohol drinking. Human alcoholics, for example, report feelings of lack of control over alcohol drinking as well as other aspects of their lives (2). However, there is little systematic research that investigates this relationship. One exception is a study that showed increased alcohol drinking following unsolvable problems in female social drinkers (11). Alcohol per se may lead to increased feelings of lack of control, or conversely, uncontrollable events may lead to alcoholism. The present experiments attempt to clarify this issue by systematically assessing the effects of controllability on alcohol drinking in rats.
~Requests for reprints should be addressed to Joseph R. Volpicelli, M.D., Ph.D., Addiction Research Center, 3910 Chestnut St., University of Pennsylvania, Philadelphia, PA 19104.
133
134
VOLPICELLI AND ULM
EXPERIMENT 1: APPETITIVE CONTROL There have been several attempts to elicit excessive alcohol drinking in rats using appetitive events. For example, Falk and Samson (5), found that food-deprived rats with access to a 5% alcohol solution drank large amounts of alcohol when a food pellet was delivered uncontrollably about once every two minutes. This procedure has been termed scheduled-induced polydipsia and it has been used to induce animals to drink an excessive amount of many fluids including water. Since the controllability dimension was not systematically varied, however, it is not clear from this research whether rats drank alcohol, 1) for some reinforcing pharmacological effect of alcohol related to the lack of control over food pellets, 2) because drinking is nonspecifically directed at alcohol because it is the only fluid available or 3) to compensate for their restricted caloric schedule. Therefore, our first experiment systematically investigated the effects of controllability over food pellets using the yoked control procedure. Since alcohol preference is examined in a two-bottle test with both alcohol and water continuously available, and rats receive equivalent amounts of food, differences between the yoked and control subjects can be attributed to the psychological effects of lack of control over food. METHOD
Subjects Subjects were 10 male Sprague-Dawley rats (N=5/group) obtained from Holtzman Co., Madison, WI. Rats were obtained at 60 days of age and were individually housed and raised in a 14 hr light-10 hr dark environment. During the first seven days subjects were gradually reduced to 80% body weight and then paired according to weight and placed in operant chambers, with control versus yoked assignment randomly determined.
Apparatus Subjects lived in a modified Skinner box with a lever mounted on the front of the chamber and two graduated cylinders mounted at the rear of the chamber so that both alcohol and water were freely available at all times. Rats obtained fluid by licking narrow metal drinking spouts that protruded 2 cm into the cage. This technique was used to eliminate the spillage that can occur with other types of drinking tubes.
Procedure Following assignment into the yoked or control groups, rats were placed in operant chambers for the next 28 days. Water and 10% alcohol sweetened with 0.25% sodium saccharin was freely available to all subjects. Food pellets (45 mg Noyes pellets) were delivered to both the control and its yoked partner when the control rat pressed the lever. On day 1, each lever-press resulted in a food pellet and on subsequent days lever-pressing was reinforced on a VI-60 second schedule (range 10 to 120 sec). Since subjects in both groups ate the pellets immediately when it was delivered, the only difference between the two groups was that the control group could control food presentations by lever-pressing while the yoked rats had no control over food presentations. This appetitive schedule control feeding was in effect 24 hr/day. Dally measurements of the weight and fluid consumption of each rat were made and followed by placing a fresh supply of water or alcohol into the graduated cylinders. To avoid position biases the fluid cylinders were rotated daily. RESULTS AND DISCUSSION
In order to control for difference in total fluid consumption, the
100T
uJ
80-
c
60-
U3
X TJO'~ I O~ o •
T
O.
TT-T -i
....
a_
40-
c
o.
t ?..
20-
o o
o.-'" T
• /'~)
--i
. . . . . .
+"i
o
e - - e
[
o ..... o Control Food
Yoked Food
I
I
I
I
I
I
I
2
4
6
8
10
12
14
Two Duy Means
FIG. 1. Mean ethanol preference for rats with control over food pellets and rats which received yoked pellet presentations across 14 blocks of two-day averages.
TABLE
1
MEANS, STANDARD ERRORS, AND t-TESTS FOR WATER, ETHANOL, AND TERMINAL WEIGHT FOR THE CONTROL AND YOKED CONDITIONS OF EXPERIMENT 1
Water (ml) Ethanol (g/kg) Terminal Weight (g)
Control Group
Yoked Group
t-test
19.34 (2.19) 5.08 (0.89) 409 (10.00)
13.5 (2.09) 9.14 (0.69) 429 (8.17)
n.s. 3.21, p
