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Persisting effects of chronic electroshock seizures on brain and behavior in two strains of rats
Physiology and Behavior. Vol. 5, pp. 1053-1055. Pergamon Press, 1970. Printed in Great Britain
Persisting Effects of Chronic Electroshock Seizures on Brain and Behavior in Two Strains of Rats GORDON
T, P R Y O R A N D L E O N S. O T I S
Departlnent o f Neurobiology, Stal!['ord Research hlstitute, Menlo Park, Cal(fortzia 94025, U.S.A. (Received 23 April 1970) PRYOR, G. T. AND L. S. OTIS. t'ersisthlg ([]'ects of chronic eh'ctro.~hock .wizm'es olt hraiJt and behavior in two strains of rats. PHVS1OL.BEHAV.5 (9) 1053-1055, 1970.--Fischer rats were given ininimal, maximal, or sham electroshock seizures daily, 5 times each week for 6 weeks beginning at 30 days of age. Groups were sacrificed 48 hr, 2 or 6 weeks after the last treatment. The initial depression in body weight and increase in cortical brain weight by the maximally convulsed group recovered to control values by 6 weeks. Monoamine oxidase activity was elevated throughout the brain 48 hr after thc last treatment and remained so in the ventral cortcx for 6 weeks. Buffalo rats exhibited only the decreased body weight and elevated monoamine oxidase activity after 6 weeks of treatment; treatment for 10 or 12 weeks produced some of the other changes observed in Fischer and Wistar strains. Treatment for 6 weeks did not affect acquisition of a successive brightness discrimination in an underwater T-maze in either strain when tested 48 hr or 4 weeks after the last treatment. Acquisition of a pole-displacement conditioned avoidance response was depressed in both strains at both test intervals.
Brain enzymes Brain weight Chronic clectroshock Conditioned pole-displacement avoidance Monoamine oxidas, Successive brightness discrimination
USING young Wistar rats we have previously demonstrated that a series of electroshocks resulted in (a) increased cortical weight, (b) increased acetylcholinesterase (ACHE) and cholinesterase (ChE) activities and total protein per sample that were roughly proportional to the increase in weight, (c) a highly reliable increase in monoamine oxidase (MAO) activity per unit weight, especially in the cortex, with a trend toward decreased aromatic L-amino acid decarboxylase (AAD) activity per unit weight in the cortex, and (d) relatively poorer performance in a simple, two trial spatial discrimination problem in an underwater T-maze [5-7]. In these experiments the animals were tested and sacrificed within 48 hr after the last treatment. This paper reports the results of experiments in which both behavioral and brain biochemical changes following chronic electroshock were observed to persist for several weeks after the last treatment. Also, the generality of our previous results with the Wistar strain are partially extended to two other strains of rats--Fischer and Buffalo. METHOD
The animals were 30-day-old male rats of the Fischer and Buffalo strains [3], housed singly with food and water available ad lib. They were assigned randomly within strains to 1 of 3 groups--Maximum Seizure, 5 times per week (MAX) ;
Minimum Seizure, 5 times per week (MIN); or Sham Control (CON). The treatment procedures have been described previously [5-7]. Fischcr rats were treated for 6 weeks (n -- 10 in each group) and sacrificed 48 hr after the last treatment. Similar groups were treated for 6 weeks and held for 2 or 6 weeks before sacrifice. Buffalo rats were treated for 6, 10 or 12 weeks (n -: 10 in each group at each treatment duration) and all groups were sacrificed 48 hr after the last treatment. Finally, Fischer and Buffalo rats were treated for 6 weeks and, beginning 48 hr after the last treatment, half of the animals in each group (n = 11-I 8/group) were given either training on a successive brightness discrimination problem or 20 trials in acquiring a pole-displacement conditioned avoidance response (CAR) in which the compound conditioned stimulus (an intermittent light and 2000 cps tone) preceded by 10 sec and overlapped a 1 mA scrambled shock which remained on until the animal responded or for a maximum of 30 sec. The CAR training procedure has been described previously [8]. Four weeks later the tests were reversed, i.e. the animals initially trained in avoidance were given training in successive brightness discrimination and vice versa. The training in successive brightness discrimination, which has not been described previously, was conducted in an underwater T-maze. The alleys of the maze were 4 in. wide and 6 in. deep. The distance from the start box to the choice point was 36 in. The arms consisted of 2 segments joined at
1This research was supported by Contract Nonr-2993 (00) between the Office of Naval Research and Stanford Research Institute. skilled technical assistance of Mrs. M. K. Scott, Miss A. Chang and Mr. V. Putnam is gratefully acknowledged. 2A longer version of this paper that includes complete tables is available from the senior author. 1053
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right angles. The first segment was 10 in. long and the second segment, which was directed back to the start box, was 20 in. long. A n escape ramp located 6 in. into the second segment allowed the animal to surface after a correct choice was made. A guillotine door at the choice point prevented retracing to the start box, and photocell beams permitted timing. Cue lights were positioned at the end of the first segment of each arm and at the choice point. A plastic lid prevented the animal from surfacing before reaching the correct escape ramp. Water temperature was maintained at 24°C. Each animal was trained in a single session (intertrial interval, approximately 5 min) until 9/10 correct choices were made or for a m a x i m u m of 40 trials. The correct arm of the T-maze was indicated by the state of the cue lights, and was varied randomly; when all the lights were on, the right arm was correct, when all the lights were off, the left arm was correct. A correction procedure was of necessity used. Correction of an error generally required the animal to remain submerged an additional 4-10 sec. The total time to complete a trial ranged from 5 to 40 sec depending on the stage of learning and whether an error was committed. In our experience rats tolerate up to 2 rain under water without drowning. After decapitation the brains were rapidly removed and grossly dissected into dorsal cortex, ventral cortex and remaining subcortex as described earlier [5, 6]. They were frozen on dry ice and stored at --25°C until assayed for A C h E [1], C h E [1], A A D [9] and M A O [10] activities and total protein [4]. RESULTS
The major results are presented in brackets as means of the respective groups followed by the significance of the difference from C O N , and, finally, the pooled standard errors of the means (SEM) from the residual error variance of the overall analyses of variance.
Weight and Biochemical Changes in the Fischer Strain Treated for 6 Weeks and Sacrificed 48 hr, 2 or 6 Weeks Later In the group sacrificed 48 hr after the last treatment, body weight (g) was reduced in the M A X group [CON -- 252, M A X = 212 (p < 0.01); S E M = 3.81, whereas the weights (g wet tissue) of the Ventral Cortex [CON -- 0.41, M I N -0.45 (p < 0.05), M A X -- 0.47 (p < 0.01; SEM ~ 0.01] and of the total recombined cortex (dorsal plus ventral cortex) [CON = 0.74, M I N -- 0.78 (p < 0.05), M A X -- 0.82 (p < 0.01); SEM = 0.01] were increased in both electroshocked groups. M A O activity (~.moles/hr/g tissue) was elevated in the dorsal cortex of the M A X group [CON 3.8, M A X = 4.6 (p < 0.01); SEM = 0.14], the ventral cortex of both electroshocked groups [CON = 4.2, M I N = 4.5 (p < 0.05), M A X ~ 4.9 (p < 0.01); SEM 0.09], and the remaining subcortex of the M A X group [CON -- 3.3, M A X = 3.8 (p < 0.05); SEM = 0.15]. Mean A C h E activity (m~moles/min/mg) was slightly increased throughout the cortex of the M A X group, but only the difference in the ventral cortex was significant [CON = 9.6, M A X = 10.5 (p < 0.05); S E M = 0.3]. Two weeks later body weight was still depressed in the M A X group [CON = 293, M A X = 253 (p < 0.01); SEM = 3.8]. The weights of the dorsal cortex [CON = 0.27, M A X -0.30 (p < 0.05); S E M = 0.01] and of the total recombined cortex [CON = 0.73, M A X = 0.78 (p < 0.05); SEM - 0.01]
were heavier only in the M A X group compared with C O N . A C h E activity was not significantly different a m o n g groups, whereas M A O activity was elevated in the dorsal cortex of both electroshocked groups [CON = 3.4, M I N = 4.1 (p < 0.01), M A X = 4.3 (p < 0.01); SEM = 0.14] and in the ventral cortex of the M A X group [CON -- 4.2, M A X = 4.9 (p < 0.01); SEM = 0.09]. After 6 weeks body and brain weights were normal in the M A X group, whereas the mean body weight of the M I N group exceeded that of the C O N group [CON - 305, M1N = 341 (p <." 0.01); SEM -- 3.8]. M A O activity was still significantly elevated in the ventral cortex of the M A X group [CON 4.6, M A X - 5.0 (p < 0.05); SEM = 0.09], whereas A C h E activity was now decreased in the dorsal cortex [CON 5.7, M A X = 5.1 (p < 0.01); SEM = 0.13].
Weight and Biochemical Changes in the Bltff(llo Strain Treated for 6, 1O, or 12 Weeks and Sacrificed 48 hr Later Originally we planned to treat the Buffalo strain as we did the Fischer strain. However, when the first groups treated for 6 weeks were sacrificed 48 hr after the last treatment, no changes in cortical tissue weight were observed. Therefore, it was decided to continue the treatment in the remaining groups until 10 and 12 weeks to determine whether this strain was unusually resistive to the effects of chronic electroshock. After 6 weeks of treatment, only reduced body weight [CON = 304, M A X = 244 (p < 0.01); S E M = 8.9] and elevated M A O activity in the ventral cortex [CON = 4.1, M A X = 4.5 (p -< 0.01); SEM = 0.09] were seen in the M A X group of this strain. After 10 weeks of treatment, in addition to the reduced body weight in the M A X group [CON -- 375, M A X -- 294 (p < 0.01); SEM = 8.9] there was an increase in the weight of the ventral cortex [CON = 0.42, M A X = 0.49 (p < 0.01); SEM - 0 . 0 1 ] and elevated M A O activity throughout the brain [dorsal cortex: C O N = 3.7, M A X = 4.7 (p < 0.01); SEM = 0.13; ventral cortex: C O N = 3.9, M A X -- 4.6 (p < 0.01); SEM = 0.09; subcortex: C O N = 3.9, M A X = 4.3 (p < 0.05); SEM = 0.12]. The results after 12 weeks of treatment were comparable in most respects to those seen after 10 weeks. The M I N groups of this strain were not appreciably affected by the treatment for any measures.
Behavioral Effects of 6 Weeks' Treatment in the Fischer and Buffalo Strains An analysis of variance of trials to reach criterion in the successive brightness discrimination revealed only one significant source of variance, that between strains (F = 17.60; d f -- 1/175; p < 0.001). The Buffalo strain (i~ = 25.6) reached the 9/10 criterion after fewer trials than the Fischer strain ()~ = 31.7). An analysis of variance of the C A R data also showed a significant strain difference (F = 5.23; d f = 1/187; p < 0.025). In contrast to their poorer performance in the maze problem, the Fischer strain made significantly more C A R s (2~ = 4.5) than the Buffalo strain ( ~ = 3.3). Chronic electroshock had a highly significant effect on performance of this t a s k ( F -- 16.00; d f = 2/187; p < 0.001). All M A X groups (,'~ = 2.0) performed more poorly than the C O N groups (~ 5.0). The effect on the M I N group appeared to be strain-dependent, as reflected by the significant strain × treatment interaction (F = 5.38; d f = 1/187; p < 0.025). The M I N groups of the Fischer strain ( ~ = 4.6) performed more poorly than their controls ( ~ = 5.7) on the average, -
-
PERSISTING EFFECTS OF CHRONIC SEIZURES
1055
whereas the MIN groups of the Buffalo strain (R = 5.0) performed better than their controls (X - 4.3). The delay between treatment and testing was also significant (F ~ 3.92; d f = 11187; p < 0.05). Animals tested 48 hr after the last treatment made fewer CARs (R -- 3.4), on the average, than those tested 4 weeks later (,'~ -- 4.4) but the delay × treatment interaction was not significant, indicating that the treatment had a persisting effect on this task that lasted at least 4 weeks. DISCUSSION
These results further extend our previous findings with rats [5-7] and those recently reported for mice [2]. The most consistently observed changes have been a decrease in body weight, an increase in cortical tissue weight, and an increase in MAO activity, especially in the cortex of maximally convulsed rats. AChE activity per unit weight has also frequently increased in the cortex. In the present experiment the activity of this enzyme was significantly increased 48 hr after the last treatment in the cortex of the MAX group of the Fischer strain, returned to normal 2 weeks later, and was significantly decreased 6 weeks after the last treatment. In the Buffalo strain only small and generally nonsignificant increases in cortical AChE activity were observed when sacrificed 48 hr after 6, 10 or 12 weeks of treatment. The activities of the other enzymes measured-ChE and A A D - - a n d total protein were not appreciably or consistently altered in the present experiments although there was a trend toward decreased cortical AAD activity that was consistent with previous findings [5].
Considered of major importance in the present experiments was the observation that some of the changes seen shortly after termination of the treatment persisted for some time in the Fischer strain; cortical weight and MAO activity in the ventral cortex were higher than controls for 2 and 6 weeks, respectively. Comparable data for the Buffalo strain are not available, since all groups were sacrificed 48 hr after the last treatment. The behavioral effects of chronic electroshock were selective in these experiments. In both strains, acquisition of a successive brightness discrimination in an underwater T-maze was unaffected by chronic electroshock, whereas acquisition of a CAR was proactively depressed for at least four weeks after the last treatment. The negative results using the underwater T-maze were unexpected since we have previously observed adverse effects of chronic electroshock on performance of a 2-trial spatial discrimination in this apparatus [6, 7]. The more difficult successive brightness discrimination was used in the present experiment because it was assumed to be more sensitive than the previous task and permitted a wider range of scores. It is possible that the treatment mainly affected the rats' initial learning in the maze. Such an effect would be maximally observable in the 2-trial procedure and go unnoticed in the multiple trial procedure. Although the significance of our findings must await further investigation, it is possible that some of the persisting behavioral consequences of electroshock----e.g, the proactive depression of CAR acquisition--may be related to one or or more of the biochemical changes we observed.
REFERENCES
1. Ellman, G. L., K. D. Courtney, V. N. Androes, Jr. and R.M. Featherstone. A new and rapid determination of acetyl[ cholinesterase activity. Biochem. Pharmac. 7: 88-95, 1961. 2. Greenough, W. T., J. K. Fulcher, A. Yuwiler and E. Geller. Enriched rearing and chronic electroshock: Effects on brain and behavior in mice. Physiol. Behav. 5: 371-373, 1970. 3. Jay, G. E., Jr. Genetic strains and stocks. In: Methodology hi Mammalian Genetics, edited by W. J. Burdette. San Francisco: Holden-Day, 1963, p. 83. 4. Lowry, O. H., N. J. Rosebrough, A. L. Farr and R. J. Randall. Protein measurement with the folin phenol reagent. J. biol. Chem. 193: 265-275, 1951. 5. Pryor, G. T. and L.tS. Otis. Brain biochemical and behavioral effects of 1, 2, 4 or 8 weeks' electroshock treatment. Life Sci. 8: 387-399, 1969.
6. Pryor, G. T., L. S. Otis, M. K. Scott and J. J. Colwell. Duration of chronic electroshock treatment in relation to brain weight, brain chemistry, and behavior. J. comp. physiol. Psychol. 63: 236-239, 1967. 7. Pryor, G. T., L. S. Otis and E. Uyeno. Chronic electroshock: Effects on brain weight, brain chemistry, and behavior. Psychonom. Sci. 4: 85-86, 1965. 8. Schlesinger, K., R. A. Schreiber and G. T. Pryor. Effects of p-ch|orophenylalanine on conditioned avoidance learning. Psychonom. Sci. 11: 225-226, 1968. 9. Snyder, S. H. and and J. Axelrod. A sensitive assay for 5hydroxytryptophan decarboxylase. Biochem. Pharmac. 13: 805-806, 1964. 10. Wurtman, R. J. and J. Axelrod. A sensitive and specific assay for the estimation of monoamine oxidase. Biochem. Pharmac. 13: 1439-1440, 1963.
Persisting Effects of Chronic Electroshock Seizures on Brain and Behavior in Two Strains of Rats GORDON
T, P R Y O R A N D L E O N S. O T I S
Departlnent o f Neurobiology, Stal!['ord Research hlstitute, Menlo Park, Cal(fortzia 94025, U.S.A. (Received 23 April 1970) PRYOR, G. T. AND L. S. OTIS. t'ersisthlg ([]'ects of chronic eh'ctro.~hock .wizm'es olt hraiJt and behavior in two strains of rats. PHVS1OL.BEHAV.5 (9) 1053-1055, 1970.--Fischer rats were given ininimal, maximal, or sham electroshock seizures daily, 5 times each week for 6 weeks beginning at 30 days of age. Groups were sacrificed 48 hr, 2 or 6 weeks after the last treatment. The initial depression in body weight and increase in cortical brain weight by the maximally convulsed group recovered to control values by 6 weeks. Monoamine oxidase activity was elevated throughout the brain 48 hr after thc last treatment and remained so in the ventral cortcx for 6 weeks. Buffalo rats exhibited only the decreased body weight and elevated monoamine oxidase activity after 6 weeks of treatment; treatment for 10 or 12 weeks produced some of the other changes observed in Fischer and Wistar strains. Treatment for 6 weeks did not affect acquisition of a successive brightness discrimination in an underwater T-maze in either strain when tested 48 hr or 4 weeks after the last treatment. Acquisition of a pole-displacement conditioned avoidance response was depressed in both strains at both test intervals.
Brain enzymes Brain weight Chronic clectroshock Conditioned pole-displacement avoidance Monoamine oxidas, Successive brightness discrimination
USING young Wistar rats we have previously demonstrated that a series of electroshocks resulted in (a) increased cortical weight, (b) increased acetylcholinesterase (ACHE) and cholinesterase (ChE) activities and total protein per sample that were roughly proportional to the increase in weight, (c) a highly reliable increase in monoamine oxidase (MAO) activity per unit weight, especially in the cortex, with a trend toward decreased aromatic L-amino acid decarboxylase (AAD) activity per unit weight in the cortex, and (d) relatively poorer performance in a simple, two trial spatial discrimination problem in an underwater T-maze [5-7]. In these experiments the animals were tested and sacrificed within 48 hr after the last treatment. This paper reports the results of experiments in which both behavioral and brain biochemical changes following chronic electroshock were observed to persist for several weeks after the last treatment. Also, the generality of our previous results with the Wistar strain are partially extended to two other strains of rats--Fischer and Buffalo. METHOD
The animals were 30-day-old male rats of the Fischer and Buffalo strains [3], housed singly with food and water available ad lib. They were assigned randomly within strains to 1 of 3 groups--Maximum Seizure, 5 times per week (MAX) ;
Minimum Seizure, 5 times per week (MIN); or Sham Control (CON). The treatment procedures have been described previously [5-7]. Fischcr rats were treated for 6 weeks (n -- 10 in each group) and sacrificed 48 hr after the last treatment. Similar groups were treated for 6 weeks and held for 2 or 6 weeks before sacrifice. Buffalo rats were treated for 6, 10 or 12 weeks (n -: 10 in each group at each treatment duration) and all groups were sacrificed 48 hr after the last treatment. Finally, Fischer and Buffalo rats were treated for 6 weeks and, beginning 48 hr after the last treatment, half of the animals in each group (n = 11-I 8/group) were given either training on a successive brightness discrimination problem or 20 trials in acquiring a pole-displacement conditioned avoidance response (CAR) in which the compound conditioned stimulus (an intermittent light and 2000 cps tone) preceded by 10 sec and overlapped a 1 mA scrambled shock which remained on until the animal responded or for a maximum of 30 sec. The CAR training procedure has been described previously [8]. Four weeks later the tests were reversed, i.e. the animals initially trained in avoidance were given training in successive brightness discrimination and vice versa. The training in successive brightness discrimination, which has not been described previously, was conducted in an underwater T-maze. The alleys of the maze were 4 in. wide and 6 in. deep. The distance from the start box to the choice point was 36 in. The arms consisted of 2 segments joined at
1This research was supported by Contract Nonr-2993 (00) between the Office of Naval Research and Stanford Research Institute. skilled technical assistance of Mrs. M. K. Scott, Miss A. Chang and Mr. V. Putnam is gratefully acknowledged. 2A longer version of this paper that includes complete tables is available from the senior author. 1053
Thc
1054
PRYOR A N D OTIS
right angles. The first segment was 10 in. long and the second segment, which was directed back to the start box, was 20 in. long. A n escape ramp located 6 in. into the second segment allowed the animal to surface after a correct choice was made. A guillotine door at the choice point prevented retracing to the start box, and photocell beams permitted timing. Cue lights were positioned at the end of the first segment of each arm and at the choice point. A plastic lid prevented the animal from surfacing before reaching the correct escape ramp. Water temperature was maintained at 24°C. Each animal was trained in a single session (intertrial interval, approximately 5 min) until 9/10 correct choices were made or for a m a x i m u m of 40 trials. The correct arm of the T-maze was indicated by the state of the cue lights, and was varied randomly; when all the lights were on, the right arm was correct, when all the lights were off, the left arm was correct. A correction procedure was of necessity used. Correction of an error generally required the animal to remain submerged an additional 4-10 sec. The total time to complete a trial ranged from 5 to 40 sec depending on the stage of learning and whether an error was committed. In our experience rats tolerate up to 2 rain under water without drowning. After decapitation the brains were rapidly removed and grossly dissected into dorsal cortex, ventral cortex and remaining subcortex as described earlier [5, 6]. They were frozen on dry ice and stored at --25°C until assayed for A C h E [1], C h E [1], A A D [9] and M A O [10] activities and total protein [4]. RESULTS
The major results are presented in brackets as means of the respective groups followed by the significance of the difference from C O N , and, finally, the pooled standard errors of the means (SEM) from the residual error variance of the overall analyses of variance.
Weight and Biochemical Changes in the Fischer Strain Treated for 6 Weeks and Sacrificed 48 hr, 2 or 6 Weeks Later In the group sacrificed 48 hr after the last treatment, body weight (g) was reduced in the M A X group [CON -- 252, M A X = 212 (p < 0.01); S E M = 3.81, whereas the weights (g wet tissue) of the Ventral Cortex [CON -- 0.41, M I N -0.45 (p < 0.05), M A X -- 0.47 (p < 0.01; SEM ~ 0.01] and of the total recombined cortex (dorsal plus ventral cortex) [CON = 0.74, M I N -- 0.78 (p < 0.05), M A X -- 0.82 (p < 0.01); SEM = 0.01] were increased in both electroshocked groups. M A O activity (~.moles/hr/g tissue) was elevated in the dorsal cortex of the M A X group [CON 3.8, M A X = 4.6 (p < 0.01); SEM = 0.14], the ventral cortex of both electroshocked groups [CON = 4.2, M I N = 4.5 (p < 0.05), M A X ~ 4.9 (p < 0.01); SEM 0.09], and the remaining subcortex of the M A X group [CON -- 3.3, M A X = 3.8 (p < 0.05); SEM = 0.15]. Mean A C h E activity (m~moles/min/mg) was slightly increased throughout the cortex of the M A X group, but only the difference in the ventral cortex was significant [CON = 9.6, M A X = 10.5 (p < 0.05); S E M = 0.3]. Two weeks later body weight was still depressed in the M A X group [CON = 293, M A X = 253 (p < 0.01); SEM = 3.8]. The weights of the dorsal cortex [CON = 0.27, M A X -0.30 (p < 0.05); S E M = 0.01] and of the total recombined cortex [CON = 0.73, M A X = 0.78 (p < 0.05); SEM - 0.01]
were heavier only in the M A X group compared with C O N . A C h E activity was not significantly different a m o n g groups, whereas M A O activity was elevated in the dorsal cortex of both electroshocked groups [CON = 3.4, M I N = 4.1 (p < 0.01), M A X = 4.3 (p < 0.01); SEM = 0.14] and in the ventral cortex of the M A X group [CON -- 4.2, M A X = 4.9 (p < 0.01); SEM = 0.09]. After 6 weeks body and brain weights were normal in the M A X group, whereas the mean body weight of the M I N group exceeded that of the C O N group [CON - 305, M1N = 341 (p <." 0.01); SEM -- 3.8]. M A O activity was still significantly elevated in the ventral cortex of the M A X group [CON 4.6, M A X - 5.0 (p < 0.05); SEM = 0.09], whereas A C h E activity was now decreased in the dorsal cortex [CON 5.7, M A X = 5.1 (p < 0.01); SEM = 0.13].
Weight and Biochemical Changes in the Bltff(llo Strain Treated for 6, 1O, or 12 Weeks and Sacrificed 48 hr Later Originally we planned to treat the Buffalo strain as we did the Fischer strain. However, when the first groups treated for 6 weeks were sacrificed 48 hr after the last treatment, no changes in cortical tissue weight were observed. Therefore, it was decided to continue the treatment in the remaining groups until 10 and 12 weeks to determine whether this strain was unusually resistive to the effects of chronic electroshock. After 6 weeks of treatment, only reduced body weight [CON = 304, M A X = 244 (p < 0.01); S E M = 8.9] and elevated M A O activity in the ventral cortex [CON = 4.1, M A X = 4.5 (p -< 0.01); SEM = 0.09] were seen in the M A X group of this strain. After 10 weeks of treatment, in addition to the reduced body weight in the M A X group [CON -- 375, M A X -- 294 (p < 0.01); SEM = 8.9] there was an increase in the weight of the ventral cortex [CON = 0.42, M A X = 0.49 (p < 0.01); SEM - 0 . 0 1 ] and elevated M A O activity throughout the brain [dorsal cortex: C O N = 3.7, M A X = 4.7 (p < 0.01); SEM = 0.13; ventral cortex: C O N = 3.9, M A X -- 4.6 (p < 0.01); SEM = 0.09; subcortex: C O N = 3.9, M A X = 4.3 (p < 0.05); SEM = 0.12]. The results after 12 weeks of treatment were comparable in most respects to those seen after 10 weeks. The M I N groups of this strain were not appreciably affected by the treatment for any measures.
Behavioral Effects of 6 Weeks' Treatment in the Fischer and Buffalo Strains An analysis of variance of trials to reach criterion in the successive brightness discrimination revealed only one significant source of variance, that between strains (F = 17.60; d f -- 1/175; p < 0.001). The Buffalo strain (i~ = 25.6) reached the 9/10 criterion after fewer trials than the Fischer strain ()~ = 31.7). An analysis of variance of the C A R data also showed a significant strain difference (F = 5.23; d f = 1/187; p < 0.025). In contrast to their poorer performance in the maze problem, the Fischer strain made significantly more C A R s (2~ = 4.5) than the Buffalo strain ( ~ = 3.3). Chronic electroshock had a highly significant effect on performance of this t a s k ( F -- 16.00; d f = 2/187; p < 0.001). All M A X groups (,'~ = 2.0) performed more poorly than the C O N groups (~ 5.0). The effect on the M I N group appeared to be strain-dependent, as reflected by the significant strain × treatment interaction (F = 5.38; d f = 1/187; p < 0.025). The M I N groups of the Fischer strain ( ~ = 4.6) performed more poorly than their controls ( ~ = 5.7) on the average, -
-
PERSISTING EFFECTS OF CHRONIC SEIZURES
1055
whereas the MIN groups of the Buffalo strain (R = 5.0) performed better than their controls (X - 4.3). The delay between treatment and testing was also significant (F ~ 3.92; d f = 11187; p < 0.05). Animals tested 48 hr after the last treatment made fewer CARs (R -- 3.4), on the average, than those tested 4 weeks later (,'~ -- 4.4) but the delay × treatment interaction was not significant, indicating that the treatment had a persisting effect on this task that lasted at least 4 weeks. DISCUSSION
These results further extend our previous findings with rats [5-7] and those recently reported for mice [2]. The most consistently observed changes have been a decrease in body weight, an increase in cortical tissue weight, and an increase in MAO activity, especially in the cortex of maximally convulsed rats. AChE activity per unit weight has also frequently increased in the cortex. In the present experiment the activity of this enzyme was significantly increased 48 hr after the last treatment in the cortex of the MAX group of the Fischer strain, returned to normal 2 weeks later, and was significantly decreased 6 weeks after the last treatment. In the Buffalo strain only small and generally nonsignificant increases in cortical AChE activity were observed when sacrificed 48 hr after 6, 10 or 12 weeks of treatment. The activities of the other enzymes measured-ChE and A A D - - a n d total protein were not appreciably or consistently altered in the present experiments although there was a trend toward decreased cortical AAD activity that was consistent with previous findings [5].
Considered of major importance in the present experiments was the observation that some of the changes seen shortly after termination of the treatment persisted for some time in the Fischer strain; cortical weight and MAO activity in the ventral cortex were higher than controls for 2 and 6 weeks, respectively. Comparable data for the Buffalo strain are not available, since all groups were sacrificed 48 hr after the last treatment. The behavioral effects of chronic electroshock were selective in these experiments. In both strains, acquisition of a successive brightness discrimination in an underwater T-maze was unaffected by chronic electroshock, whereas acquisition of a CAR was proactively depressed for at least four weeks after the last treatment. The negative results using the underwater T-maze were unexpected since we have previously observed adverse effects of chronic electroshock on performance of a 2-trial spatial discrimination in this apparatus [6, 7]. The more difficult successive brightness discrimination was used in the present experiment because it was assumed to be more sensitive than the previous task and permitted a wider range of scores. It is possible that the treatment mainly affected the rats' initial learning in the maze. Such an effect would be maximally observable in the 2-trial procedure and go unnoticed in the multiple trial procedure. Although the significance of our findings must await further investigation, it is possible that some of the persisting behavioral consequences of electroshock----e.g, the proactive depression of CAR acquisition--may be related to one or or more of the biochemical changes we observed.
REFERENCES
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