Physiology and Behavior, Vol. 15, pp. 21-24. Brain Research Publications Inc., 1975. Printed
in the
U.S.A.
Learned Taste Aversion Induced by Cortical Spreading Depression I F R A N K J. WINN JR., 2 MICHAEL A. KENT 3 AND T E R R Y M. LIBKUMAN
Central Michigan University, Mt. Pleasant, Michigan
(Received 25 February 1975) WlNN, F. J., M. A. KENT AND T. M. LIBKUMAN. Learned taste aversion induced by cortical spreading depression. PHYSIOL. BEHAV. 15(1) 21-24, 1975. - Male albino rats were cannulated and placed on a 24 hr water deprivation schedule. The animals were allowed 10 min access to water in a large animal cage for 5 days. On the sixth day of deprivation the animals were randomly divided into 6 groups and given either 12 percent KC1, 25 percent KC1, or Ringers solution applied unilaterally or bilaterally to the cortex immediately after access to 8 percent sucrose. On the seventh day of deprivation, each rat was placed in a two-choice situation with the sucrose solution and water. Only the unilateral and bilateral 12 percent KC1 groups developed an aversion to the sucrose. These results indicate that CSD has aversive as well as amnesic properties, there exists a gradient of amnesia, dependent on concentration, and that the cortex is not necessary for learning a taste aversion. Cortical spreading depression
Conditioned taste aversion
CORTICAL spreading depression (CSD), produced by extra dural application of KC1, has been used extensively to study the role o f the neocortex in learning and memory. In what might be considered the typical paradigm for this research, the organism is trained with one hemisphere depressed and subsequently tested for transfer with the other hemisphere depressed. Generally, this paradigm has not yielded clear-cut results with some studies obtaining transfer from the trained to the depressed hemisphere [2, 6, 7, 14] while others obtain no transfer [2, 3, 13, 15]. In attempting to reconcile these differences, one hypothesis which has received broad attention is the notion that transfer is a function of task complexity [ 10]. When a task is relatively simple it is mediated subcortically making learning available to both hemispheres and thus producing transfer. When the task is relatively complex it is mediated cortically with learning being restricted to the hemisphere that was functional during original training. An alternative explanation for at least some of the transfer findings might be that CSD has aversive as well as amnesic properties. Therefore, when placed into a situation with no clear response choice, as many transfer tests are, an animal will respond so as to avoid those cues previously associated with CSD. Such a possibility is suggested from a study done by Ray and Emley [13]. Rats were trained to make a light-dark discrimination under unilateral CSD. Upon reaching criterion performance, the animals were
Retrograde amnesia
Gradient of amnesia
placed on extinction and the unilateral depression was reversed. When the data for all animals was pooled, they not only failed to show transfer but they also failed to behave in a truly naive manner. Out of 24 test trials the animals chose the previously nonreinforced arm of the maze 22 times. Although Ray and Emley suggested this may have resulted from a release of inhibition of the incorrect response, it is possible that the cues provided by the maze and the CSD, acting as an aversive unconditioned stimulus, combined to produce an avoidance reaction. Such a possibility exists since CSD of one hemisphere does present a distinct stimulus configuration to an animal which differs significantly from that produced by depression of the other hemisphere [ 17 ]. Consistent with the notion that CSD is aversive are the observations of Bures and Buresova [4]. While inducing CSD with KC1, these authors noted that many of their animals reacted by squealing, attempting to flee, and trying to remove the soaked pledgers. On the basis of their observations Bures and Buresova suggested that CSD is painful until the dural nerve fibers have undergone depolarization. The purpose of the present study was to determine if CSD produced by the application of KC1 is aversive. This was accomplished with a learned taste aversion paradigm which makes use of the fact that thirsty animals undergoing an aversive state following consumption of a distinctly flavored solution, will subsequently avoid that solution but
t This paper is based upon a thesis by the first author submitted to the second author for the degree of Master of Arts. 2Now at Texas Tech University, Lubbock, Texas. 3Requests for reprints should be sent to: Michael A. Kent, Department of Psychology, Central Michigan University, Mt. Pleasant, MI 48859. 21
22
WlNN, KENT AND LIBKUMAN
will continue to drink other solutions [ 1 1]. This aversion can be readily produced in a single learning trial. Thus, taste aversion provides an excellent paradigm since with repeated KC1 applications there is an increasing difficulty in establishing CSD and an increasing possibility of cortical damage [91. METHOD
Animals Thirty male Sprague-Dawley rats approximately 150 days of age were used. The animals were randomly divided into 6 groups and designated as either receiving unilateral or bilateral applications of 0, 12, or 25 percent KC1 solutions. (The 0 percent KC1 group received a standard Ringers solution.) All animals were housed in individual cages and had free access to food.
Surgery The animals were surgically prepared under pentobarbital sodium anesthesia (45 mg/kg) according to the procedure outlined by Paulino and Levy [12]'. Briefly, this consisted of placing two holes (3 mm dia.) in the skull on either side of the saggital suture and posterior to bregma with care taken not to puncture the dura. Two nylon cannula bases were then positioned over the holes and permanently affixed to the skull using dental cement. Nylon cannula plugs were then inserted into the bases until the initiation of testing, at which time they were removed and replaced with cannulae. Following the experiment, all animals were sacrificed and perfused intracardially with saline followed by 9 percent Formalin. The heads were removed and stored in formalin for four days. Examinations of the cortex for edema and the dura for tears resulted in discarding l0 animals.
Procedure Following surgery, the animals were randomly assigned to the treatment conditions and placed on a 23 hr water deprivation schedule. A 10 min access to water was provided each day in a large animal cage (24.5 × 43.8 × 17.5 cm. deep) for 5 days. Each day the animals were removed from their cage, cannulae inserted, and placed into the test cage facing the rear to avoid a possible position bias. The position of the water bottle, containing 60 ml of tap water, was also randomly alternated on a daily basis between the right and left side. On the sixth day of deprivation, the animals were given access to 60 ml of an 8 percent sucrose solution prepared that day. At the end of 10 min each animal received its appropriate treatment: unilateral Ringers (n = 4), bilateral Ringers (n = 3) unilateral 12 percent KC1 (n = 4), bilateral 12 percent KC1 (n = 2), unilateral 25 percent KC1 (n = 3), or bilateral 25 percent KC1 (n = 4) solutions. To control for possible volume effects, all animals received 0.2 ml of the appropriate solutions. Spreading depression was verfied by checking the animals for loss of placing responses in the limbs contralateral to the depressed hemisphere. Following the treatment condition, the cannulae were removed, plugs reinserted, and the animals were returned to their home cages. On the seventh day of deprivation the cannulae were
again inserted and the animals were presented with a two-choice situation. On one side of the cage a bottle was available with tap water and on the other side a bottle with 8 percent sucrose solution. The amount of sucrose consumed on the sixth and seventh day was recorded as well as the amount of water and the time spent at each of the bottles on the seventh day. RESULTS The mean amount of sucrose consumed on Day 6 was 25.45 ml, while the mean amount of sucrose plus water consumed on Day 7 was 25.15 ml. (t = 0.29; df = 19; p>0.05) indicating that the CSD did not affect total fluid intake. In a previous analysis, Winn [18] reported null differences between unilateral and bilateral conditions for the Ringers, 12 percent KC1 and 25 percent KC1 solutions. The unilateral and bilateral conditions were thus pooled for each solution and the data for amount of sucrose consumed and time spent at the sucrose bottle were analyzed. The analysis revealed significant differences in sucrose intake (Kruskal-Wallis H-test; p
in the
U.S.A.
Learned Taste Aversion Induced by Cortical Spreading Depression I F R A N K J. WINN JR., 2 MICHAEL A. KENT 3 AND T E R R Y M. LIBKUMAN
Central Michigan University, Mt. Pleasant, Michigan
(Received 25 February 1975) WlNN, F. J., M. A. KENT AND T. M. LIBKUMAN. Learned taste aversion induced by cortical spreading depression. PHYSIOL. BEHAV. 15(1) 21-24, 1975. - Male albino rats were cannulated and placed on a 24 hr water deprivation schedule. The animals were allowed 10 min access to water in a large animal cage for 5 days. On the sixth day of deprivation the animals were randomly divided into 6 groups and given either 12 percent KC1, 25 percent KC1, or Ringers solution applied unilaterally or bilaterally to the cortex immediately after access to 8 percent sucrose. On the seventh day of deprivation, each rat was placed in a two-choice situation with the sucrose solution and water. Only the unilateral and bilateral 12 percent KC1 groups developed an aversion to the sucrose. These results indicate that CSD has aversive as well as amnesic properties, there exists a gradient of amnesia, dependent on concentration, and that the cortex is not necessary for learning a taste aversion. Cortical spreading depression
Conditioned taste aversion
CORTICAL spreading depression (CSD), produced by extra dural application of KC1, has been used extensively to study the role o f the neocortex in learning and memory. In what might be considered the typical paradigm for this research, the organism is trained with one hemisphere depressed and subsequently tested for transfer with the other hemisphere depressed. Generally, this paradigm has not yielded clear-cut results with some studies obtaining transfer from the trained to the depressed hemisphere [2, 6, 7, 14] while others obtain no transfer [2, 3, 13, 15]. In attempting to reconcile these differences, one hypothesis which has received broad attention is the notion that transfer is a function of task complexity [ 10]. When a task is relatively simple it is mediated subcortically making learning available to both hemispheres and thus producing transfer. When the task is relatively complex it is mediated cortically with learning being restricted to the hemisphere that was functional during original training. An alternative explanation for at least some of the transfer findings might be that CSD has aversive as well as amnesic properties. Therefore, when placed into a situation with no clear response choice, as many transfer tests are, an animal will respond so as to avoid those cues previously associated with CSD. Such a possibility is suggested from a study done by Ray and Emley [13]. Rats were trained to make a light-dark discrimination under unilateral CSD. Upon reaching criterion performance, the animals were
Retrograde amnesia
Gradient of amnesia
placed on extinction and the unilateral depression was reversed. When the data for all animals was pooled, they not only failed to show transfer but they also failed to behave in a truly naive manner. Out of 24 test trials the animals chose the previously nonreinforced arm of the maze 22 times. Although Ray and Emley suggested this may have resulted from a release of inhibition of the incorrect response, it is possible that the cues provided by the maze and the CSD, acting as an aversive unconditioned stimulus, combined to produce an avoidance reaction. Such a possibility exists since CSD of one hemisphere does present a distinct stimulus configuration to an animal which differs significantly from that produced by depression of the other hemisphere [ 17 ]. Consistent with the notion that CSD is aversive are the observations of Bures and Buresova [4]. While inducing CSD with KC1, these authors noted that many of their animals reacted by squealing, attempting to flee, and trying to remove the soaked pledgers. On the basis of their observations Bures and Buresova suggested that CSD is painful until the dural nerve fibers have undergone depolarization. The purpose of the present study was to determine if CSD produced by the application of KC1 is aversive. This was accomplished with a learned taste aversion paradigm which makes use of the fact that thirsty animals undergoing an aversive state following consumption of a distinctly flavored solution, will subsequently avoid that solution but
t This paper is based upon a thesis by the first author submitted to the second author for the degree of Master of Arts. 2Now at Texas Tech University, Lubbock, Texas. 3Requests for reprints should be sent to: Michael A. Kent, Department of Psychology, Central Michigan University, Mt. Pleasant, MI 48859. 21
22
WlNN, KENT AND LIBKUMAN
will continue to drink other solutions [ 1 1]. This aversion can be readily produced in a single learning trial. Thus, taste aversion provides an excellent paradigm since with repeated KC1 applications there is an increasing difficulty in establishing CSD and an increasing possibility of cortical damage [91. METHOD
Animals Thirty male Sprague-Dawley rats approximately 150 days of age were used. The animals were randomly divided into 6 groups and designated as either receiving unilateral or bilateral applications of 0, 12, or 25 percent KC1 solutions. (The 0 percent KC1 group received a standard Ringers solution.) All animals were housed in individual cages and had free access to food.
Surgery The animals were surgically prepared under pentobarbital sodium anesthesia (45 mg/kg) according to the procedure outlined by Paulino and Levy [12]'. Briefly, this consisted of placing two holes (3 mm dia.) in the skull on either side of the saggital suture and posterior to bregma with care taken not to puncture the dura. Two nylon cannula bases were then positioned over the holes and permanently affixed to the skull using dental cement. Nylon cannula plugs were then inserted into the bases until the initiation of testing, at which time they were removed and replaced with cannulae. Following the experiment, all animals were sacrificed and perfused intracardially with saline followed by 9 percent Formalin. The heads were removed and stored in formalin for four days. Examinations of the cortex for edema and the dura for tears resulted in discarding l0 animals.
Procedure Following surgery, the animals were randomly assigned to the treatment conditions and placed on a 23 hr water deprivation schedule. A 10 min access to water was provided each day in a large animal cage (24.5 × 43.8 × 17.5 cm. deep) for 5 days. Each day the animals were removed from their cage, cannulae inserted, and placed into the test cage facing the rear to avoid a possible position bias. The position of the water bottle, containing 60 ml of tap water, was also randomly alternated on a daily basis between the right and left side. On the sixth day of deprivation, the animals were given access to 60 ml of an 8 percent sucrose solution prepared that day. At the end of 10 min each animal received its appropriate treatment: unilateral Ringers (n = 4), bilateral Ringers (n = 3) unilateral 12 percent KC1 (n = 4), bilateral 12 percent KC1 (n = 2), unilateral 25 percent KC1 (n = 3), or bilateral 25 percent KC1 (n = 4) solutions. To control for possible volume effects, all animals received 0.2 ml of the appropriate solutions. Spreading depression was verfied by checking the animals for loss of placing responses in the limbs contralateral to the depressed hemisphere. Following the treatment condition, the cannulae were removed, plugs reinserted, and the animals were returned to their home cages. On the seventh day of deprivation the cannulae were
again inserted and the animals were presented with a two-choice situation. On one side of the cage a bottle was available with tap water and on the other side a bottle with 8 percent sucrose solution. The amount of sucrose consumed on the sixth and seventh day was recorded as well as the amount of water and the time spent at each of the bottles on the seventh day. RESULTS The mean amount of sucrose consumed on Day 6 was 25.45 ml, while the mean amount of sucrose plus water consumed on Day 7 was 25.15 ml. (t = 0.29; df = 19; p>0.05) indicating that the CSD did not affect total fluid intake. In a previous analysis, Winn [18] reported null differences between unilateral and bilateral conditions for the Ringers, 12 percent KC1 and 25 percent KC1 solutions. The unilateral and bilateral conditions were thus pooled for each solution and the data for amount of sucrose consumed and time spent at the sucrose bottle were analyzed. The analysis revealed significant differences in sucrose intake (Kruskal-Wallis H-test; p
