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Scopolamine: effects on conditioned suppression
Neuropharmacology,
1972,11,347-350
SCOPOLAMINE:
Pergamon Press.
Printed in Gt. Britain.
EFFECTS ON CONDITIONED
SUPPRESSION
A. A. SMITH* and W. H. CALHOUN? Department of Psychology, University of Tennessee, Knoxville, Tennessee (Accepted 20 October 1971)
S~a~-~i~ were tested with a two-cham~red passive-avoidan~ apparatus. A mouse was placed in the apparatus, allowed a three-minute exploration period, and then either shocked in the smaller compartment or returned to the home cage. Twenty-four hours later the mice were retested. Locomotor activity in the large (noshock) compartment and time spent in the small (shock) compartment were recorded. The subjects received either 0.5 mg/kg of scopolamine or saline seventeen minutes prior to testing, The drug treatment increased activity and depressed the time spent in the small compartment, but did not interfere with either learning or retention of the passive avoidance response. IT HAS been reported that rats and mice pretreated with scopolamine hydrobromide fail to learn passive avoidance (MEYERS, 1965 ; BOHDANECKY and JARVIK, 1967 ; CALHOUN and SMITH, 1968). These results have been interpreted as showing that the drug produces amnesia for traumatic events; we have argued, however, that scopolamine treatment results in hyperactivity in mice, and that the increased activity is incompatible with immobility, the response usually conditioned during passive avoidance training (CALHOUN, SMITH and ADAXIS, 1967). This study was designed to assess passive avoidance performance by scopolamine treated mice in a situation where hyperactivity would not conflict with the passive avoidance response. Specifically, a two-compartment apparatus was used where activity change would be reflected in increased movement in the large (noshock) compartment, but the effect of shock would be reflected in decreased time spent in the small (shock) compartment. METHODS
Male ICR mice were obtained from Cumberland View Farms at weaning, and were housed 12 per cage until two days prior to experimentation at which time they were placed in individual cages. Subjects had free access to food and water at all times except during the brief testing period. A two-compartment device similar to that used by BURESOVA,BURES, BOHDANECKYand WEISS (1964), was constructed with grid floors and lucite walls with metal linings. The small compartment was 8-9 x 8.9 and 12-7 cm high; and the large compartment was 15.2 x 15.2 and 17.8 cm high; both were covered by hinged lids. The wall common to the two compartments contained a 5.1 x 5*1 cm opening set at floor level with a manually operated stainless steel guillotine door. Two light beams transected the large compartment 4 cm above the floor so the compartment was divided into three equal areas. A light beam break activated a Lafayette PC-45 *Present address: Department of Psychology, Southwestern Oklahoma State College, Weatherford, Ok~homa 95616. tPresent address: Department of Psychology, Indiana University, Bioomin~on, Indiana 47401. 347
348
A. A. SMITH and W. H. CALHOUN
photocell which actuated a counter. A Beede Model 250 constant current d.c. stimulator was connected through a scrambler to the grid in the small compartment. To determine noshock performance 40 mice (51-53 days of age) were randomly assigned in equal numbers to one of four groups : (A) drug-saline, (B) drug-drug, (C) saline-drug and (D) saline-saline. Seventeen minutes before the first day’s test the mice of Groups A and B received an i.p. injection of scopolamine hydrobromide 05 mg/kg dissolved in saline while the mice of Groups C and D received saline. Initially, each mouse was placed in the center of the large compartment facing away from the open door. It was permitted a 3-min period of exploration of both compartments and then returned to its home cage. Total time spent in the small compartment and light beam breaks in the large compartment were recorded. Twentyfour hours later each mouse was retested. Groups B and C received a drug injection 17 min prior to the second 3-min test period, while Groups A and D received saline. In the second stage of the experiment the added effect of shock was evaluated. Sixty mice (46-75 days of age) were randomly assigned to the four conditions as before (Groups E-H). However, immediately after the Day 13-min exploratory period each mouse was ushered into the small compartment, the door was closed, and the mouse was administered 55 set of O-5 mA shock. The 3-min test period 24 hr later served as a “retention” test; the same procedures were followed on this test as for the noshock groups.
RESULTS
The time measure was to be used as an index of the strength of avoidance conditioning; therefore the effect of the drug alone and in combination with shock on this measure is presented first (Table 1). For the noshock groups drugged on Day 1 (A and B) the average time scores were lower than for the saline groups (C and D). This general result was found for the shock groups as well, although groups E and F averaged considerably less time than Groups A and B. When Day 1 measures were taken Groups A, B, E and F had been treated alike; the lower medians for E and F reflect dissimilar ages and testing times for mice in the noshock and shock groups.
TABLE~.MEDIANTIMEINTHESMALLCOMPARTMENTWITHAVERAGEDEVIA~ONFORSHOCKED MICE
AND NONSHOCKED
Time (set) Day 2
Day 1 Group
Condition*
N
Median
Ave. dev.
Median
Ave. dev.
A B C D
Noshock
D-S D-D S-D s-s
10 10 10 10
67.5 68.5 82.5 81.5
17.7 19.6 9.2 17.0
68.5 56.0 68.0 80.5
25.4 30.2 20.2 24.0
E F G H
Shock
D-S D-D S-D s-s
15 15 15 15
52.0 52.0 73.0 82.0
23.4 19.1 18.5 21.2
43.0 4.0
27.3 17.3 10.1 17.1
2i.E
*D-S means mice in this group received an injection of drug on Day 1 and saline on Day 2.
Scopolamine
and conditioned
suppression
349
For the noshock condition, the drug affected the time measure on Day 2. The groups not drugged on Day 2 (A and D) averaged nearly identical times on Day 1 and 2, whereas the drugged groups (B and C) had a difference of -12 and -14 respectively (both statistically significant, Wilcoxen, P
A
Conditiont
Median
Median
Ave. dev.
Noshock
D-S D-D S-D s-s
10 10 10 10
0.88 0.90 0.76 0.81
0.08 0.10 0.08 0.10
0.18 0.96 0.84 0.67
0.10 0.13 0.14 0.10
Shock
D-S D-D S-D s-s
15 15 15 15
0.77 0.82 0.76 0.69
0.16 0.13 0.12 0.11
0.53 0.71 0.70 0.52
0.14 0.13 0.14 0.10
B C D E F G H
N
Day 2 Ave dev.
*Ratio of photocell breaks to time in the large compartment. tD-S means that mice in this group received an injection of drug on Day 1 and saline on Day 2.
their respective comparison groups. This finding is consistent with earlier observations that scopolamine increases activity level in mice with a similar recording device (CALHOUN,SMITH and ADAMS,1967). (The groups of the noshock part of the experiment generally averaged greater activity than their comparison group in the shock part reflecting the different ages and testing times.) The important comparison is the change in activity level from Day 1 to Day 2. Average activity on Day 2 was less for Groups A and D than on Day 1, demonstrating a decrement in activity with exposure to the apparatus, while mice that received a drug injection on Day 2 averaged more activity than on Day 1. The pattern of average activity change for the shock and noshock groups was similar, but for all the shock groups average activity decreased from Day 1 to 2. Therefore, the shock punishment reversed the drug’s affect on activity (Group B, +0*06; Group F, -0.06; and Group C, +O*OS; Group G, -0.10). The shocked groups which received scopolamine on Day 2 (F and G) had higher median activity scores than the saline groups (E and H). Thus, the scopolamine treated mice were “hyperactive” following the drug treatment but still showed “retention” of avoidance training because they spent very little time in the compartment in which they were previously shocked. D
A. A. SMITH and W. H. CALHOUN
350
DISCUSSION As stated, there are several reports of impaired learning of passive avoidance by scopolamine treated mice. We have suggested that a major effect of scopolamine is to increase locomotor activity which interferes with immobility, the response to be conditioned. In this experiment an apparatus was employed that would allow hyperactivity which would not interfere with shock avoidance (remaining out of the small compartment). The drug effect without shock was assessed because it has been shown that scopolamine interferes with habituation to a novel environment (CARLTONand VOGEL,1967). Therefore, it was expected that the change in behavior from Day 1 to 2 would not be the same for drugged and nondrugged mice due to differential habituation of exploratory tendencies, and this prediction was found to be correct. Mice, whether drugged on Day 1 or 2, averaged higher activity but lower time scores than saline-injected mice. These findings show that the shock punishment was effective in modifying the behavior of mice, even if they had been treated with scopolamine. However, these results show that there are several factors affecting the outcome. Exposure to the apparatus reduced activity scores but did not appreciably affect time (see Group D). Drug treatment increased activity, but reduced time while the shock treatment reduced both time and activity. The combined shock and drug effect appeared to be additive; the mice that received both drug and shock treatments spent virtually no time in the small compartment on Day 2 showing the summated effects of shock and drug treatment. Heightened activity due to the drug treatment was attenuated by the depressive effect of the shock on this variable. A careful analysis of the effects of exposure to an apparatus, drug treatment, and punishment must be made before one can conclude the drug affects retention. In this experiment the drug did not appear to interfere with learning; adjustment of the retention measure to account for the effect of the drug in the absence of punishment would demonstrate that the drugged mice performed as well as the nondrugged ones. Acknorvledgemenf-Supported
by NIMH Grant No. MH 16922 to the University of Tennessee, Knoxville.
REFERENCES
BOHDANECKY, Z. and JARVIK, M. E. (1967).Impairment of one-trial passive avoidance learning in mice by scopolamine,
scopolamine methylbromide
and physostigmine.
Znt. J. Neuropharmac.
6: 217-222.
BURESOVA, O., BURES,J., BOHDANECKY, Z. and WEISS,T. (1964). Effects of atropine on learning, extinction, retention and retrieval in rats. Psychopharmacologia (Berl.) 5: 255-263. CALHOUN,W. H. and SMITH,A. A. (1968). Effects of scopolamine on acquisition of passive avoidance. Psychopharmacologia (Berl.) 13: 201-209. CALHOUN,W. H., SMITH,A. A. and ADAMS,R. M. (1967). Passive avoidance learning: The relation of activity and retest latency. Paper read at the Psychonomic Society Annual Convention, Chicago. CARLTON,P. L. and VOGEL,J. R. (1967). Habituation and conditioning. J. Comp.physiol. Psychol. 63: 348-35 1. MEYERS,B. (1965). Some effects of scopolamine on a passive avoidance response in rats. Psychopharmacologia (Berl.)S: 111-119.
1972,11,347-350
SCOPOLAMINE:
Pergamon Press.
Printed in Gt. Britain.
EFFECTS ON CONDITIONED
SUPPRESSION
A. A. SMITH* and W. H. CALHOUN? Department of Psychology, University of Tennessee, Knoxville, Tennessee (Accepted 20 October 1971)
S~a~-~i~ were tested with a two-cham~red passive-avoidan~ apparatus. A mouse was placed in the apparatus, allowed a three-minute exploration period, and then either shocked in the smaller compartment or returned to the home cage. Twenty-four hours later the mice were retested. Locomotor activity in the large (noshock) compartment and time spent in the small (shock) compartment were recorded. The subjects received either 0.5 mg/kg of scopolamine or saline seventeen minutes prior to testing, The drug treatment increased activity and depressed the time spent in the small compartment, but did not interfere with either learning or retention of the passive avoidance response. IT HAS been reported that rats and mice pretreated with scopolamine hydrobromide fail to learn passive avoidance (MEYERS, 1965 ; BOHDANECKY and JARVIK, 1967 ; CALHOUN and SMITH, 1968). These results have been interpreted as showing that the drug produces amnesia for traumatic events; we have argued, however, that scopolamine treatment results in hyperactivity in mice, and that the increased activity is incompatible with immobility, the response usually conditioned during passive avoidance training (CALHOUN, SMITH and ADAXIS, 1967). This study was designed to assess passive avoidance performance by scopolamine treated mice in a situation where hyperactivity would not conflict with the passive avoidance response. Specifically, a two-compartment apparatus was used where activity change would be reflected in increased movement in the large (noshock) compartment, but the effect of shock would be reflected in decreased time spent in the small (shock) compartment. METHODS
Male ICR mice were obtained from Cumberland View Farms at weaning, and were housed 12 per cage until two days prior to experimentation at which time they were placed in individual cages. Subjects had free access to food and water at all times except during the brief testing period. A two-compartment device similar to that used by BURESOVA,BURES, BOHDANECKYand WEISS (1964), was constructed with grid floors and lucite walls with metal linings. The small compartment was 8-9 x 8.9 and 12-7 cm high; and the large compartment was 15.2 x 15.2 and 17.8 cm high; both were covered by hinged lids. The wall common to the two compartments contained a 5.1 x 5*1 cm opening set at floor level with a manually operated stainless steel guillotine door. Two light beams transected the large compartment 4 cm above the floor so the compartment was divided into three equal areas. A light beam break activated a Lafayette PC-45 *Present address: Department of Psychology, Southwestern Oklahoma State College, Weatherford, Ok~homa 95616. tPresent address: Department of Psychology, Indiana University, Bioomin~on, Indiana 47401. 347
348
A. A. SMITH and W. H. CALHOUN
photocell which actuated a counter. A Beede Model 250 constant current d.c. stimulator was connected through a scrambler to the grid in the small compartment. To determine noshock performance 40 mice (51-53 days of age) were randomly assigned in equal numbers to one of four groups : (A) drug-saline, (B) drug-drug, (C) saline-drug and (D) saline-saline. Seventeen minutes before the first day’s test the mice of Groups A and B received an i.p. injection of scopolamine hydrobromide 05 mg/kg dissolved in saline while the mice of Groups C and D received saline. Initially, each mouse was placed in the center of the large compartment facing away from the open door. It was permitted a 3-min period of exploration of both compartments and then returned to its home cage. Total time spent in the small compartment and light beam breaks in the large compartment were recorded. Twentyfour hours later each mouse was retested. Groups B and C received a drug injection 17 min prior to the second 3-min test period, while Groups A and D received saline. In the second stage of the experiment the added effect of shock was evaluated. Sixty mice (46-75 days of age) were randomly assigned to the four conditions as before (Groups E-H). However, immediately after the Day 13-min exploratory period each mouse was ushered into the small compartment, the door was closed, and the mouse was administered 55 set of O-5 mA shock. The 3-min test period 24 hr later served as a “retention” test; the same procedures were followed on this test as for the noshock groups.
RESULTS
The time measure was to be used as an index of the strength of avoidance conditioning; therefore the effect of the drug alone and in combination with shock on this measure is presented first (Table 1). For the noshock groups drugged on Day 1 (A and B) the average time scores were lower than for the saline groups (C and D). This general result was found for the shock groups as well, although groups E and F averaged considerably less time than Groups A and B. When Day 1 measures were taken Groups A, B, E and F had been treated alike; the lower medians for E and F reflect dissimilar ages and testing times for mice in the noshock and shock groups.
TABLE~.MEDIANTIMEINTHESMALLCOMPARTMENTWITHAVERAGEDEVIA~ONFORSHOCKED MICE
AND NONSHOCKED
Time (set) Day 2
Day 1 Group
Condition*
N
Median
Ave. dev.
Median
Ave. dev.
A B C D
Noshock
D-S D-D S-D s-s
10 10 10 10
67.5 68.5 82.5 81.5
17.7 19.6 9.2 17.0
68.5 56.0 68.0 80.5
25.4 30.2 20.2 24.0
E F G H
Shock
D-S D-D S-D s-s
15 15 15 15
52.0 52.0 73.0 82.0
23.4 19.1 18.5 21.2
43.0 4.0
27.3 17.3 10.1 17.1
2i.E
*D-S means mice in this group received an injection of drug on Day 1 and saline on Day 2.
Scopolamine
and conditioned
suppression
349
For the noshock condition, the drug affected the time measure on Day 2. The groups not drugged on Day 2 (A and D) averaged nearly identical times on Day 1 and 2, whereas the drugged groups (B and C) had a difference of -12 and -14 respectively (both statistically significant, Wilcoxen, P
A
Conditiont
Median
Median
Ave. dev.
Noshock
D-S D-D S-D s-s
10 10 10 10
0.88 0.90 0.76 0.81
0.08 0.10 0.08 0.10
0.18 0.96 0.84 0.67
0.10 0.13 0.14 0.10
Shock
D-S D-D S-D s-s
15 15 15 15
0.77 0.82 0.76 0.69
0.16 0.13 0.12 0.11
0.53 0.71 0.70 0.52
0.14 0.13 0.14 0.10
B C D E F G H
N
Day 2 Ave dev.
*Ratio of photocell breaks to time in the large compartment. tD-S means that mice in this group received an injection of drug on Day 1 and saline on Day 2.
their respective comparison groups. This finding is consistent with earlier observations that scopolamine increases activity level in mice with a similar recording device (CALHOUN,SMITH and ADAMS,1967). (The groups of the noshock part of the experiment generally averaged greater activity than their comparison group in the shock part reflecting the different ages and testing times.) The important comparison is the change in activity level from Day 1 to Day 2. Average activity on Day 2 was less for Groups A and D than on Day 1, demonstrating a decrement in activity with exposure to the apparatus, while mice that received a drug injection on Day 2 averaged more activity than on Day 1. The pattern of average activity change for the shock and noshock groups was similar, but for all the shock groups average activity decreased from Day 1 to 2. Therefore, the shock punishment reversed the drug’s affect on activity (Group B, +0*06; Group F, -0.06; and Group C, +O*OS; Group G, -0.10). The shocked groups which received scopolamine on Day 2 (F and G) had higher median activity scores than the saline groups (E and H). Thus, the scopolamine treated mice were “hyperactive” following the drug treatment but still showed “retention” of avoidance training because they spent very little time in the compartment in which they were previously shocked. D
A. A. SMITH and W. H. CALHOUN
350
DISCUSSION As stated, there are several reports of impaired learning of passive avoidance by scopolamine treated mice. We have suggested that a major effect of scopolamine is to increase locomotor activity which interferes with immobility, the response to be conditioned. In this experiment an apparatus was employed that would allow hyperactivity which would not interfere with shock avoidance (remaining out of the small compartment). The drug effect without shock was assessed because it has been shown that scopolamine interferes with habituation to a novel environment (CARLTONand VOGEL,1967). Therefore, it was expected that the change in behavior from Day 1 to 2 would not be the same for drugged and nondrugged mice due to differential habituation of exploratory tendencies, and this prediction was found to be correct. Mice, whether drugged on Day 1 or 2, averaged higher activity but lower time scores than saline-injected mice. These findings show that the shock punishment was effective in modifying the behavior of mice, even if they had been treated with scopolamine. However, these results show that there are several factors affecting the outcome. Exposure to the apparatus reduced activity scores but did not appreciably affect time (see Group D). Drug treatment increased activity, but reduced time while the shock treatment reduced both time and activity. The combined shock and drug effect appeared to be additive; the mice that received both drug and shock treatments spent virtually no time in the small compartment on Day 2 showing the summated effects of shock and drug treatment. Heightened activity due to the drug treatment was attenuated by the depressive effect of the shock on this variable. A careful analysis of the effects of exposure to an apparatus, drug treatment, and punishment must be made before one can conclude the drug affects retention. In this experiment the drug did not appear to interfere with learning; adjustment of the retention measure to account for the effect of the drug in the absence of punishment would demonstrate that the drugged mice performed as well as the nondrugged ones. Acknorvledgemenf-Supported
by NIMH Grant No. MH 16922 to the University of Tennessee, Knoxville.
REFERENCES
BOHDANECKY, Z. and JARVIK, M. E. (1967).Impairment of one-trial passive avoidance learning in mice by scopolamine,
scopolamine methylbromide
and physostigmine.
Znt. J. Neuropharmac.
6: 217-222.
BURESOVA, O., BURES,J., BOHDANECKY, Z. and WEISS,T. (1964). Effects of atropine on learning, extinction, retention and retrieval in rats. Psychopharmacologia (Berl.) 5: 255-263. CALHOUN,W. H. and SMITH,A. A. (1968). Effects of scopolamine on acquisition of passive avoidance. Psychopharmacologia (Berl.) 13: 201-209. CALHOUN,W. H., SMITH,A. A. and ADAMS,R. M. (1967). Passive avoidance learning: The relation of activity and retest latency. Paper read at the Psychonomic Society Annual Convention, Chicago. CARLTON,P. L. and VOGEL,J. R. (1967). Habituation and conditioning. J. Comp.physiol. Psychol. 63: 348-35 1. MEYERS,B. (1965). Some effects of scopolamine on a passive avoidance response in rats. Psychopharmacologia (Berl.)S: 111-119.