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The effect of different environments prior to electroconvulsive shock on the gradient of retrograde amnesia
Physiology and Behavior, Vol. 7, pp. 161-164. Pergamon Press, 1971. Printed in Great Britain
The Effect of Different Environments Prior to Electroconvulsive Shock on the Gradient of Retrograde Amnesia W. JOSEPH POTTS
Department of Pharmacology, G. D. Searle & Co., P.O. Box 5110, Chicago, Illinois 60680, U.S.A. (Received 29 A p r i l 1970) POTTS, W. J. The effect ol"different environments prior to electroconvulsive shock on the gradient of retrograde amnesia. PHYSIOL. BEHAV. 7 (2) 161-164, 1971.--Rats were administered eleetroconvulsive shock (ECS) at various intervals following footshock in a passive avoidance situation. One group remained in the goal compartment for the interval between footshock and ECS while another group was placed into a holding cage for the same interval. Retention of alearned response by rats placed into a holding cage was not impaired by ECS after intervals greater than 30 see. Rats held in the goal compartment showed impaired retention when the ECS was administered up to 1800 see after footshock. Retrograde amnesia gradient
Electroconvulsive shock
Passive avoidance
SEVERAL recent studies have demonstrated that an electroconvulsive shock (ECS) following a single-trial learning situation impaired the retention of a learned response. Some studies have shown that a relatively short interval (0-60 sec) exists during which the learned task is susceptible to impairment by ECS [2, 3, 14-16] while others have shown that a longer interval (up to one hour) exists during which retention of the learned responses can be impaired by ECS [1, 10-12]. The study by Ray and Bivens [17] demonstrated that the interval during which ECS impaired the learned response was dependent on the intensity of the footshock. Other studies have shown the interval between the ECS and testing to be an important variable in evaluating the disruptive effects of ECS [6-9]. Several recent reports have shown that the ability of amnesic agents to impair retention of a learned response can interact with environmental events preceding the application of the amnesic agent [4, 5, 13, 18, 19]. The purpose of this experiment was to determine the effect of two different environments for various intervals between the footshock (FS) and the ECS in rats.
compartments. The start compartment was painted black with a solid floor and was 5½ in. long. The goal compartment was painted white, had a grid floor and was 14½ in. long. Illumination was provided by a 6 W 110 V light near the top. The compartments were separated by a sliding door painted black on the start compartment side and white on the goal compartment side. The grid floor consisted of 0.375 in. stainless steel rods separated 0.875 in. between centers. The FS was a 1.0 m A neon-scrambled constant-current shock delivered from a 2400 V transformer through a 2.2 Mf~ resistor for 1.0 see. ECS was delivered from a Wahlquist Electro-convulsive shock apparatus through miniature alligator clips attached to the rat's ears. A series of electromechanical timers was used to automatically record response latencies and control the intervals between termination of FS and delivery of ECS. Testing was carried out in a darkened room.
Procedure Rats were removed from their home cages and were placed into individual holding cages for approximately 15 min prior to the training trial on Day 1. After removal from the holding cage, the ear clips were attached prior to each rat's placement into the start compartment of the passive avoidance apparatus. Following a 30 see acclimation in the start compartment, the door between the compartments was opened activating a microswitch which initiated the response latency timer. When the rat placed all four feet into the goal compartment the door was immediately d o s e d reactivating the microswitch which stopped the response latency timer and initiated a 1.0 m A shock for 1.0 sec. Rats were classified according to their treatment in the training trial on Day 1. Those groups which received the FS and remained in the goal compartment [GC] where they received ECS were designated FS-ECS [CK2]. The FS-ECS
METHOD
Animals The animals were 910 male Wistar rats (Manor Research), 90-100 days old. Animals were caged individually with free access to food and water and were randomly assigned to treatment groups. Approximately 3 per cent of the rats had to be replaced because of ECS-induced paralysis or refusal to leave the start compartment within 30 see on Day 1.
Apparatus The passive avoidance apparatus was a box with an open top, 20 in. long by 5½ in. wide by 14 in. high, divided into two 161
162
POTTS immediately following the FS and placed into a holding cage until the ECS was administered (FS-ECS [HC]) showed a remarkably different profile from those rats held in the goal compartment until the administration of the ECS (FS-ECS [GC]). Comparisons between G C and HC rats administered ECS at l, 2 and 4 sec were not possible because the rats could not reliably be removed from the goal compartment in less than eight sec. Comparisons between the FS-ECS [HC] and FS-ECS [GC] groups given ECS at eight sec and greater intervals were carried out by the method of Chi square. Consistently significant differences between the two groups were observed at FS-ECS intervals longer than 30 sec as shown in Fig. I. Comparing the FS-NoECS control group with the FSECS [HC] groups demonstrated that groups which received ECS at 8, 16 or 30 see after footshock showed a significantly greater percentage stepping through (z ~ :> 13.00, df== I, p < 0.001 in every case) while groups administered ECS at intervals longer than 30 sec after footshock were not significantly different (z * < 3.3, df-- I, p > 0.05 in every case). Comparison of the FS-NoECS control group with the FSECS [GC] groups demonstrated that all the latter groups had a significantly greater percentage of animals stepping through (z * > 18.0, d f : I, p < 0.001 in every case). Comparisons were also made between the NoFS-NoECS control group and the FS-ECS groups. After the FS-ECS [HC] treatment, all groups except the eight sec group differed significantly from the NoFS-NoECS group (z ~ > 7.6, df::: 1, p < 0.01 in every case). In the FS-ECS [GC] treatment, only the groups given ECS at 30, 60, 240, 960 and 1800 sec
intervals employed were 1, 2, 4, 8, 16, 30, 60, 120, 240, 480, 960 and 1800 sec. The ECS was 100 mA administered for 300 msec. Rats which were given no footshock but were held in the goal compartment for the above mentioned intervals (until delivery of the ECS) were designated NoFS-ECS [GC]. Additional groups received FS in the goal compartment but were then removed and placed into a holding cage [HC] where after intervals of 8, 16, 30, 60, 120, 240, 480, 960 or 1800 sec they received ECS. These groups were designated FS-ECS [HC]. Other groups received ECS at the above mentioned intervals in the holding cages without first receiving footshock and were designated NoFS-ECS [HC]. Two further groups served as controls and received N o F S NoECS or FS-No ECS. Both the N o F S - N o E C S and FS-NoECS groups were removed within 4-8 sec following their entry into the goal compartment. An additional group of rats was given only FS (i.e. FS-NoECS [GC]) and held in the goal compartment for intervals of 60, 120, 240, 480, 960 or 1800 sec. Twenty rats were included in all groups except the NoFS-ECS [HC] groups which had only ten rats per group. Rats which did not enter the goal compartment within 30 sec in the training trial were discarded. Rats were tested for retention of the FS 24 hr after the training trial. RESULTS
The percentage of rats stepping through into the goal compartment in less than 120 sec when tested on Day 2 is shown in Fig. 1. Rats removed from the goal compartment
•
100 =
H
C,, No FS-NoECS 90= 80=
I\
~'70v
"r"
O 60m
o 0 Z
50-
40= "
30,, 20"
f
10=
'
FS-NoECS FS-EC5 (Holgi~ C q e l
|
|
|
|
I
2
4
8
|
i
|
|
|
16 30 60 120 240 FS'ECS INTERVAL (See.)
|
~"
480
960
|
1800
FIG. 1. The percentage of rats i S . D . express~ as percentage stepping through in < 120 sec on the Day 2 test trial ( + indicates p < 0.05 and * indicates p < 0.01 signiflcaat difference between HC and C.~ groups).
ENVIRONMENTS AND GRADIENT OF AMNESIA were significantly different from the control group (x z : 4.4, x2 = 5.9, x ~ = 5.9, x 2 = 9.4, d f ~ 1, p < 0.05). Additional comparisons of the N o F S - N o E C S group with the NoFS-ECS groups at each of the intervals tested for both the HC and G C groups revealed no significant differences among any of them.
TABLE 1 THE PERCENTAGE OF RATS STEPPING THROUGH ON THE TEST TRIAL AFTER BEING HELD IN THE GOAL COMPARTMENT FOR VARIOUS INTERVALSFOLLOWING FOOTSHOCK
Time in Goal Compartment Following Footshock (sec)
Rats Stepping Through on Test Trial :/: 1 SD Expressed as a Percentage FS-NoECS [GC] FS-ECS [GC]
0 (FS-NoECS)~ 60 120 240 480 960 1800
15 4- 8.0 5 -4- 4.9 30 4-10.2 65 4-10.7" 554-11.1" 70 4-10.2" 70 4-10.2"
80 4- 8.9t 95 4- 4.9t 80 4- 8.9 1004- 0.0t 85 ± 8.0 70 4-10.2
*p < 0.01, ×2, df = 1 compared to the 0 (FS-NoECS) group. tp < 0.01, ×2, d r = 1 compared to comparable interval FSNo-ECS [GC] groups. :[:Removal from goal compartment was always accomplished in < 8 sec for this group.
As shown in Table 1, rats which were held in the goal compartment following FS (FS-NoECS [GC]) for either 60 or 120 see before being removed were not significantly different from the FS-NoECS control group. However, if the rats were held for intervals longer than 120 sec, they showed significantly impaired retention when compared to the FS-NoECS group. The comparisons of the FS-NoECS [GC] groups to the FS-ECS [GC] groups for comparable intervals showed that retention by the FS-ECS [GC] rats was significantly more impaired for the 60, 120 and 480 sec intervals, but for the remaining intervals the NoECS rats showed nearly the same degree of impairment as the ECS rats. These comparisons indicate that retention per se in the goal compartment can itself cause impaired memory retention at intervals longer than 120 sec. DISCUSSION
Rats which were given the ECS after being placed into a holding cage following the FS displayed amnesia if given the ECS within 30 sec of the FS. These results from the H C groups are quite similar to those previously reported using similar passive avoidance techniques [2, 14-16]. Confirmation of a more prolonged gradient [1, 10-12] was provided by those groups in which rats were allowed to remain in the goal compartment for the interval between FS and ECS administration. The G C groups showed impaired retention of the FS regardless of when the ECS was administered. N o effect of ECS alone was observed regardless of where the rats were held for the interval prior to ECS administration, as shown by the finding that the N o F S - N o E C S group did
163 not differ from the NoFS-ECS groups at any interval in either environment. The significant differences between the FS-ECS [HC] and FS-ECS [GC] groups at intervals longer than 30 see indicate that the disruptive effects of the ECS were influenced by the environment of the rat during the interval between FS and ECS. An additional study verified a portion of an earlier report by Quartermain et al. [16] who showed that the place where the ECS was administered was unrelated to the production of amnesia. In the present study, rats were allowed to remain in the goal compartment for 60 sec and were then transfered to the holding cage where the ECS was immediately administered. In both this group and the FS-ECS [GC] 60 sec group, 80% of the rats stepped through in less than 120 sec in the test trial. These results indicate that the G C environment during the interval between FS and ECS was the factor causing amnesia rather than the environment for administration of the ECS. Accordingly, the prolonged gradient of the FS-ECS [GC] groups cannot be explained by the place of administration of ECS. The present results may be explained by several hypotheses. One possible explanation is that the rats held in the goal compartment became less fearful of it through association with absence o f shock. Since the shock duration in the goal compartment was only one sec, and the rats remained in the goal compartment for intervals of 1-1800 sec, the time for association between no shock and the compartment certainly was much greater than the time for association between the compartment and shock. Thus, entry into the goal compartment on the D a y 2 test could be indicative of reduced fear of the goal compartment rather than amnesia for a painful experience. This explanation would apparently be valid for intervals of 240 sec or longer since rats given FS only, but held in the goal compartment for 60 or 120 sec after FS showed normal retention when tested the following day, while rats held longer than 120 sec in the goal compartment after receiving FS showed impaired retention. Thus, the large percentage of rats in the FS-ECS [GC] group which crossed into the goal compartment at 60 and 120 sec cannot be accounted for by this explanation, and the effect here can be attributed to the ECS. Chorover and Schiller [3] demonstrated that if rats escaped from the shock compartment after FS the ECS had no effect 60 sec later. However, if the rat was confined to the shock compartment, the ECS 60 sec later apparently interrupted the memory consolidation for the FS. They attributed the prolonged effect of the ECS in the confinement situation to inhibition of the freezing component of the conditioned emotional response (CER). Thus, the present experimental results may be explained by the F S - F ~ S [GC] groups having developed a CER which was susceptible to ECS for several hours. The results of the FS-ECS [HC] groups correspond to those of Chorover and Schiller for rats which escaped from the shock and thus did not develop CER. If this hypothesis is correct, the present data indicate that escape per se from the noxious stimulus is not necessary. However, removal from the threatening environment is necessary if memory consolidation is to occur within one minute. The present results are in close agreement with those of Robustelli et al. [18] who reported that mice which were detained for 10 min immediately following footshock in a passive avoidance procedure showed impaired retention when tested 24 hr later. The impairment was greatest when the mice were held in the testing apparatus but occurred even when they were detained outside the apparatus. The detention
164
POI I'S
procedure was also reported to potentiate the effects of ECS. One major difference between the present study and that of Robustelli et aL [18] is that the amnesic effects of detention in their study were relatively independent of the testing apparatus. In the present study only the rats detained in the apparatus for 240 sec or longer following FS (i.e. FSNoECS [GC]) showed amnesia while rats detained outside the apparatus (i.e. FS-ECS [HC]) showed normal retention when ECS was delayed at least 60 sec after FS. Robustelli and Jarvik [19] demonstrated in mice a relationship between the duration of detention and the magnitude of impairment, such that a detention interval of 5 or 30 min, but not 1 min, caused impaired retention of a passive avoidance task. Davis [4] and Davis and Klinger [5] demonstrated that the testing environment apparently can interact with the effects of anmesic agents in fish. They reported that amnesic agents were effective for longer periods after training if the fish were exposed to the testing environment prior to the treatment with the amnesic agent. The observation in the present study that rats held in the goal compartment longer than 120 sec after FS (i.e. FS-NoECS [GC]) showed a retention deficit is in agreement with the report by Davis [4] of impaired retention when fish were maintained in the testing environment for 2 4 4 8 hr following training. The
present study also tends to support the earlier work of Misanin et al. [13] who reported that retention was impaired when ECS was preceded by a reminder (i.e. conditioned stimulus) associated with a punishing footshock given 24 hr earlier. The present study and the previous studies [4, 13, 18, 19] seem to indicate that amnesic agents interact with the environment in rats, mice and fish. Although all of the mentioned hypotheses could explain the present data, none of them adequately explain some of the differences between the results of this study and the results of Quartermain et al. [16]. They reported a memory consolidation curve similar to the FS-ECS [HC] curve but administered the ECS in the goal compartment. In the present study, administration of ECS in the goal compartment resulted in impaired memory of the footshock at all intervals tested. Additional work utilizing another strain of rats and a different amnesic agent is presently being carried out to try to explain these differences and to further explore the complexities of memory consolidation.
The author wishes to express his appreciation to P. F. East for his assistance. The author is especially indebted to Dorothy Washington for her technical skills.
REFERENCES 1. Alpern, H. P. and J. L. McGaugh. Retrograde amnesia as a function of duration of electroshock stimulation. J. comp. physiol. Psychol. 65" 265-269, 1968. 2. Chorover, S. L. and P. H. Schiller. Short-term retrograde amnesia in rats. J. comp. physiol. Psychol. 59: 73-78, 1965. 3. Chorover, S. L. and P. H. Schiller. Re-examination of prolonged retrograde amnesia in one-trial learning. J. comp. physiol. Psychol. 61: 34-41, 1966. 4. Davis, R. E. Environmental control of memory fixation in goldfish. J. comp. physiol. Psychol. 65: 72-78, 1968. 5. Davis. R. E. and P. D. Klinger. Environmental control of amnesic effects of various agents in goldfish. Physiol. Behav. 4: 269-271, 1969. 6. Geller, A. and M. E. Jarvik. Electroconvulsive shock induced amnesia and recovery. Psychonorn. Sci. 10:15-16, 1968. 7. Geller, A. and M. E. Jarvik. The time relations of ECS induced amnesia. Psychonom. Sci. 12: 169-170, 1968. 8. Hughes, R. A., R. J. Barrett and O. S. Ray. Retrograde amnesia in rats as function of ECS-test interval and ECS intensity. Physiol. Behav. 5: 27-30, 1970. 9. Hughes, R. A., R. J. Barrett and O. S. Ray. Training to test interval as a determinant of a temporally graded ECS-produced response decrement in rats. J. comp. physiol. Psychol. 71: 318-324, 1970. 10. Kopp, R. The temporal gradient of retrograde amnesia to ECS in mice. Fed. Proc. 25: 262, 1966.
11. Kopp, R., Z. Bodanecky and M. E. Jarvik. Long temporal gradient of retrograde amnesia for a well discriminated stimulus. Science 153: 1547-1549, 1966. 12. McGaugh, J. L. Time-dependent processes in memory storage. Science 153: 1351-1358, 1966. 13. Misanin, J. R., R. R. Miller and D. J. Lewis. Retrograde amnesia produced by electroconvulsive shock after reactivation of a consolidated memory trace. Science 160: 554-555, 1968. 14. Paolino, R. M., D. Quartermain and H. M. Levy. Effect of electroconvulsive shock duration on the gradient of retrograde amnesia. Physiol. Behav. 4: 147-149, 1969. 15. Pinel, J. P. A short gradient of ECS-produced amnesia in a one trial appetitive learning situation. J. comp. physiol. Psychol. 68: 650-655, 1969. 16. Quartermain, D., R. M. Paolino and N. E. Miller. A brief temporal gradient of retrograde amnesia independent of situational change. Science 149:1116-1118, 1965. 17. Ray, O. S. and C. W. Bivens. Reinforcement magnitude as a determinant of performance decrement after electroconvulsive shock. Science 160: 330-332, 1968. 18. Robustelli, F., A. Geller and M. E. Jarvik. Detention, electroconvulsive shock, and amnesia. Proc. Am. PsychoL Assoc. 331-332, 1968. 19. Robustelli, F. and M. E. Jarvik. Retrograde amnesia from detention. Physiol. Behav. 3: 543-547, 1968.
The Effect of Different Environments Prior to Electroconvulsive Shock on the Gradient of Retrograde Amnesia W. JOSEPH POTTS
Department of Pharmacology, G. D. Searle & Co., P.O. Box 5110, Chicago, Illinois 60680, U.S.A. (Received 29 A p r i l 1970) POTTS, W. J. The effect ol"different environments prior to electroconvulsive shock on the gradient of retrograde amnesia. PHYSIOL. BEHAV. 7 (2) 161-164, 1971.--Rats were administered eleetroconvulsive shock (ECS) at various intervals following footshock in a passive avoidance situation. One group remained in the goal compartment for the interval between footshock and ECS while another group was placed into a holding cage for the same interval. Retention of alearned response by rats placed into a holding cage was not impaired by ECS after intervals greater than 30 see. Rats held in the goal compartment showed impaired retention when the ECS was administered up to 1800 see after footshock. Retrograde amnesia gradient
Electroconvulsive shock
Passive avoidance
SEVERAL recent studies have demonstrated that an electroconvulsive shock (ECS) following a single-trial learning situation impaired the retention of a learned response. Some studies have shown that a relatively short interval (0-60 sec) exists during which the learned task is susceptible to impairment by ECS [2, 3, 14-16] while others have shown that a longer interval (up to one hour) exists during which retention of the learned responses can be impaired by ECS [1, 10-12]. The study by Ray and Bivens [17] demonstrated that the interval during which ECS impaired the learned response was dependent on the intensity of the footshock. Other studies have shown the interval between the ECS and testing to be an important variable in evaluating the disruptive effects of ECS [6-9]. Several recent reports have shown that the ability of amnesic agents to impair retention of a learned response can interact with environmental events preceding the application of the amnesic agent [4, 5, 13, 18, 19]. The purpose of this experiment was to determine the effect of two different environments for various intervals between the footshock (FS) and the ECS in rats.
compartments. The start compartment was painted black with a solid floor and was 5½ in. long. The goal compartment was painted white, had a grid floor and was 14½ in. long. Illumination was provided by a 6 W 110 V light near the top. The compartments were separated by a sliding door painted black on the start compartment side and white on the goal compartment side. The grid floor consisted of 0.375 in. stainless steel rods separated 0.875 in. between centers. The FS was a 1.0 m A neon-scrambled constant-current shock delivered from a 2400 V transformer through a 2.2 Mf~ resistor for 1.0 see. ECS was delivered from a Wahlquist Electro-convulsive shock apparatus through miniature alligator clips attached to the rat's ears. A series of electromechanical timers was used to automatically record response latencies and control the intervals between termination of FS and delivery of ECS. Testing was carried out in a darkened room.
Procedure Rats were removed from their home cages and were placed into individual holding cages for approximately 15 min prior to the training trial on Day 1. After removal from the holding cage, the ear clips were attached prior to each rat's placement into the start compartment of the passive avoidance apparatus. Following a 30 see acclimation in the start compartment, the door between the compartments was opened activating a microswitch which initiated the response latency timer. When the rat placed all four feet into the goal compartment the door was immediately d o s e d reactivating the microswitch which stopped the response latency timer and initiated a 1.0 m A shock for 1.0 sec. Rats were classified according to their treatment in the training trial on Day 1. Those groups which received the FS and remained in the goal compartment [GC] where they received ECS were designated FS-ECS [CK2]. The FS-ECS
METHOD
Animals The animals were 910 male Wistar rats (Manor Research), 90-100 days old. Animals were caged individually with free access to food and water and were randomly assigned to treatment groups. Approximately 3 per cent of the rats had to be replaced because of ECS-induced paralysis or refusal to leave the start compartment within 30 see on Day 1.
Apparatus The passive avoidance apparatus was a box with an open top, 20 in. long by 5½ in. wide by 14 in. high, divided into two 161
162
POTTS immediately following the FS and placed into a holding cage until the ECS was administered (FS-ECS [HC]) showed a remarkably different profile from those rats held in the goal compartment until the administration of the ECS (FS-ECS [GC]). Comparisons between G C and HC rats administered ECS at l, 2 and 4 sec were not possible because the rats could not reliably be removed from the goal compartment in less than eight sec. Comparisons between the FS-ECS [HC] and FS-ECS [GC] groups given ECS at eight sec and greater intervals were carried out by the method of Chi square. Consistently significant differences between the two groups were observed at FS-ECS intervals longer than 30 sec as shown in Fig. I. Comparing the FS-NoECS control group with the FSECS [HC] groups demonstrated that groups which received ECS at 8, 16 or 30 see after footshock showed a significantly greater percentage stepping through (z ~ :> 13.00, df== I, p < 0.001 in every case) while groups administered ECS at intervals longer than 30 sec after footshock were not significantly different (z * < 3.3, df-- I, p > 0.05 in every case). Comparison of the FS-NoECS control group with the FSECS [GC] groups demonstrated that all the latter groups had a significantly greater percentage of animals stepping through (z * > 18.0, d f : I, p < 0.001 in every case). Comparisons were also made between the NoFS-NoECS control group and the FS-ECS groups. After the FS-ECS [HC] treatment, all groups except the eight sec group differed significantly from the NoFS-NoECS group (z ~ > 7.6, df::: 1, p < 0.01 in every case). In the FS-ECS [GC] treatment, only the groups given ECS at 30, 60, 240, 960 and 1800 sec
intervals employed were 1, 2, 4, 8, 16, 30, 60, 120, 240, 480, 960 and 1800 sec. The ECS was 100 mA administered for 300 msec. Rats which were given no footshock but were held in the goal compartment for the above mentioned intervals (until delivery of the ECS) were designated NoFS-ECS [GC]. Additional groups received FS in the goal compartment but were then removed and placed into a holding cage [HC] where after intervals of 8, 16, 30, 60, 120, 240, 480, 960 or 1800 sec they received ECS. These groups were designated FS-ECS [HC]. Other groups received ECS at the above mentioned intervals in the holding cages without first receiving footshock and were designated NoFS-ECS [HC]. Two further groups served as controls and received N o F S NoECS or FS-No ECS. Both the N o F S - N o E C S and FS-NoECS groups were removed within 4-8 sec following their entry into the goal compartment. An additional group of rats was given only FS (i.e. FS-NoECS [GC]) and held in the goal compartment for intervals of 60, 120, 240, 480, 960 or 1800 sec. Twenty rats were included in all groups except the NoFS-ECS [HC] groups which had only ten rats per group. Rats which did not enter the goal compartment within 30 sec in the training trial were discarded. Rats were tested for retention of the FS 24 hr after the training trial. RESULTS
The percentage of rats stepping through into the goal compartment in less than 120 sec when tested on Day 2 is shown in Fig. 1. Rats removed from the goal compartment
•
100 =
H
C,, No FS-NoECS 90= 80=
I\
~'70v
"r"
O 60m
o 0 Z
50-
40= "
30,, 20"
f
10=
'
FS-NoECS FS-EC5 (Holgi~ C q e l
|
|
|
|
I
2
4
8
|
i
|
|
|
16 30 60 120 240 FS'ECS INTERVAL (See.)
|
~"
480
960
|
1800
FIG. 1. The percentage of rats i S . D . express~ as percentage stepping through in < 120 sec on the Day 2 test trial ( + indicates p < 0.05 and * indicates p < 0.01 signiflcaat difference between HC and C.~ groups).
ENVIRONMENTS AND GRADIENT OF AMNESIA were significantly different from the control group (x z : 4.4, x2 = 5.9, x ~ = 5.9, x 2 = 9.4, d f ~ 1, p < 0.05). Additional comparisons of the N o F S - N o E C S group with the NoFS-ECS groups at each of the intervals tested for both the HC and G C groups revealed no significant differences among any of them.
TABLE 1 THE PERCENTAGE OF RATS STEPPING THROUGH ON THE TEST TRIAL AFTER BEING HELD IN THE GOAL COMPARTMENT FOR VARIOUS INTERVALSFOLLOWING FOOTSHOCK
Time in Goal Compartment Following Footshock (sec)
Rats Stepping Through on Test Trial :/: 1 SD Expressed as a Percentage FS-NoECS [GC] FS-ECS [GC]
0 (FS-NoECS)~ 60 120 240 480 960 1800
15 4- 8.0 5 -4- 4.9 30 4-10.2 65 4-10.7" 554-11.1" 70 4-10.2" 70 4-10.2"
80 4- 8.9t 95 4- 4.9t 80 4- 8.9 1004- 0.0t 85 ± 8.0 70 4-10.2
*p < 0.01, ×2, df = 1 compared to the 0 (FS-NoECS) group. tp < 0.01, ×2, d r = 1 compared to comparable interval FSNo-ECS [GC] groups. :[:Removal from goal compartment was always accomplished in < 8 sec for this group.
As shown in Table 1, rats which were held in the goal compartment following FS (FS-NoECS [GC]) for either 60 or 120 see before being removed were not significantly different from the FS-NoECS control group. However, if the rats were held for intervals longer than 120 sec, they showed significantly impaired retention when compared to the FS-NoECS group. The comparisons of the FS-NoECS [GC] groups to the FS-ECS [GC] groups for comparable intervals showed that retention by the FS-ECS [GC] rats was significantly more impaired for the 60, 120 and 480 sec intervals, but for the remaining intervals the NoECS rats showed nearly the same degree of impairment as the ECS rats. These comparisons indicate that retention per se in the goal compartment can itself cause impaired memory retention at intervals longer than 120 sec. DISCUSSION
Rats which were given the ECS after being placed into a holding cage following the FS displayed amnesia if given the ECS within 30 sec of the FS. These results from the H C groups are quite similar to those previously reported using similar passive avoidance techniques [2, 14-16]. Confirmation of a more prolonged gradient [1, 10-12] was provided by those groups in which rats were allowed to remain in the goal compartment for the interval between FS and ECS administration. The G C groups showed impaired retention of the FS regardless of when the ECS was administered. N o effect of ECS alone was observed regardless of where the rats were held for the interval prior to ECS administration, as shown by the finding that the N o F S - N o E C S group did
163 not differ from the NoFS-ECS groups at any interval in either environment. The significant differences between the FS-ECS [HC] and FS-ECS [GC] groups at intervals longer than 30 see indicate that the disruptive effects of the ECS were influenced by the environment of the rat during the interval between FS and ECS. An additional study verified a portion of an earlier report by Quartermain et al. [16] who showed that the place where the ECS was administered was unrelated to the production of amnesia. In the present study, rats were allowed to remain in the goal compartment for 60 sec and were then transfered to the holding cage where the ECS was immediately administered. In both this group and the FS-ECS [GC] 60 sec group, 80% of the rats stepped through in less than 120 sec in the test trial. These results indicate that the G C environment during the interval between FS and ECS was the factor causing amnesia rather than the environment for administration of the ECS. Accordingly, the prolonged gradient of the FS-ECS [GC] groups cannot be explained by the place of administration of ECS. The present results may be explained by several hypotheses. One possible explanation is that the rats held in the goal compartment became less fearful of it through association with absence o f shock. Since the shock duration in the goal compartment was only one sec, and the rats remained in the goal compartment for intervals of 1-1800 sec, the time for association between no shock and the compartment certainly was much greater than the time for association between the compartment and shock. Thus, entry into the goal compartment on the D a y 2 test could be indicative of reduced fear of the goal compartment rather than amnesia for a painful experience. This explanation would apparently be valid for intervals of 240 sec or longer since rats given FS only, but held in the goal compartment for 60 or 120 sec after FS showed normal retention when tested the following day, while rats held longer than 120 sec in the goal compartment after receiving FS showed impaired retention. Thus, the large percentage of rats in the FS-ECS [GC] group which crossed into the goal compartment at 60 and 120 sec cannot be accounted for by this explanation, and the effect here can be attributed to the ECS. Chorover and Schiller [3] demonstrated that if rats escaped from the shock compartment after FS the ECS had no effect 60 sec later. However, if the rat was confined to the shock compartment, the ECS 60 sec later apparently interrupted the memory consolidation for the FS. They attributed the prolonged effect of the ECS in the confinement situation to inhibition of the freezing component of the conditioned emotional response (CER). Thus, the present experimental results may be explained by the F S - F ~ S [GC] groups having developed a CER which was susceptible to ECS for several hours. The results of the FS-ECS [HC] groups correspond to those of Chorover and Schiller for rats which escaped from the shock and thus did not develop CER. If this hypothesis is correct, the present data indicate that escape per se from the noxious stimulus is not necessary. However, removal from the threatening environment is necessary if memory consolidation is to occur within one minute. The present results are in close agreement with those of Robustelli et al. [18] who reported that mice which were detained for 10 min immediately following footshock in a passive avoidance procedure showed impaired retention when tested 24 hr later. The impairment was greatest when the mice were held in the testing apparatus but occurred even when they were detained outside the apparatus. The detention
164
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procedure was also reported to potentiate the effects of ECS. One major difference between the present study and that of Robustelli et aL [18] is that the amnesic effects of detention in their study were relatively independent of the testing apparatus. In the present study only the rats detained in the apparatus for 240 sec or longer following FS (i.e. FSNoECS [GC]) showed amnesia while rats detained outside the apparatus (i.e. FS-ECS [HC]) showed normal retention when ECS was delayed at least 60 sec after FS. Robustelli and Jarvik [19] demonstrated in mice a relationship between the duration of detention and the magnitude of impairment, such that a detention interval of 5 or 30 min, but not 1 min, caused impaired retention of a passive avoidance task. Davis [4] and Davis and Klinger [5] demonstrated that the testing environment apparently can interact with the effects of anmesic agents in fish. They reported that amnesic agents were effective for longer periods after training if the fish were exposed to the testing environment prior to the treatment with the amnesic agent. The observation in the present study that rats held in the goal compartment longer than 120 sec after FS (i.e. FS-NoECS [GC]) showed a retention deficit is in agreement with the report by Davis [4] of impaired retention when fish were maintained in the testing environment for 2 4 4 8 hr following training. The
present study also tends to support the earlier work of Misanin et al. [13] who reported that retention was impaired when ECS was preceded by a reminder (i.e. conditioned stimulus) associated with a punishing footshock given 24 hr earlier. The present study and the previous studies [4, 13, 18, 19] seem to indicate that amnesic agents interact with the environment in rats, mice and fish. Although all of the mentioned hypotheses could explain the present data, none of them adequately explain some of the differences between the results of this study and the results of Quartermain et al. [16]. They reported a memory consolidation curve similar to the FS-ECS [HC] curve but administered the ECS in the goal compartment. In the present study, administration of ECS in the goal compartment resulted in impaired memory of the footshock at all intervals tested. Additional work utilizing another strain of rats and a different amnesic agent is presently being carried out to try to explain these differences and to further explore the complexities of memory consolidation.
The author wishes to express his appreciation to P. F. East for his assistance. The author is especially indebted to Dorothy Washington for her technical skills.
REFERENCES 1. Alpern, H. P. and J. L. McGaugh. Retrograde amnesia as a function of duration of electroshock stimulation. J. comp. physiol. Psychol. 65" 265-269, 1968. 2. Chorover, S. L. and P. H. Schiller. Short-term retrograde amnesia in rats. J. comp. physiol. Psychol. 59: 73-78, 1965. 3. Chorover, S. L. and P. H. Schiller. Re-examination of prolonged retrograde amnesia in one-trial learning. J. comp. physiol. Psychol. 61: 34-41, 1966. 4. Davis, R. E. Environmental control of memory fixation in goldfish. J. comp. physiol. Psychol. 65: 72-78, 1968. 5. Davis. R. E. and P. D. Klinger. Environmental control of amnesic effects of various agents in goldfish. Physiol. Behav. 4: 269-271, 1969. 6. Geller, A. and M. E. Jarvik. Electroconvulsive shock induced amnesia and recovery. Psychonorn. Sci. 10:15-16, 1968. 7. Geller, A. and M. E. Jarvik. The time relations of ECS induced amnesia. Psychonom. Sci. 12: 169-170, 1968. 8. Hughes, R. A., R. J. Barrett and O. S. Ray. Retrograde amnesia in rats as function of ECS-test interval and ECS intensity. Physiol. Behav. 5: 27-30, 1970. 9. Hughes, R. A., R. J. Barrett and O. S. Ray. Training to test interval as a determinant of a temporally graded ECS-produced response decrement in rats. J. comp. physiol. Psychol. 71: 318-324, 1970. 10. Kopp, R. The temporal gradient of retrograde amnesia to ECS in mice. Fed. Proc. 25: 262, 1966.
11. Kopp, R., Z. Bodanecky and M. E. Jarvik. Long temporal gradient of retrograde amnesia for a well discriminated stimulus. Science 153: 1547-1549, 1966. 12. McGaugh, J. L. Time-dependent processes in memory storage. Science 153: 1351-1358, 1966. 13. Misanin, J. R., R. R. Miller and D. J. Lewis. Retrograde amnesia produced by electroconvulsive shock after reactivation of a consolidated memory trace. Science 160: 554-555, 1968. 14. Paolino, R. M., D. Quartermain and H. M. Levy. Effect of electroconvulsive shock duration on the gradient of retrograde amnesia. Physiol. Behav. 4: 147-149, 1969. 15. Pinel, J. P. A short gradient of ECS-produced amnesia in a one trial appetitive learning situation. J. comp. physiol. Psychol. 68: 650-655, 1969. 16. Quartermain, D., R. M. Paolino and N. E. Miller. A brief temporal gradient of retrograde amnesia independent of situational change. Science 149:1116-1118, 1965. 17. Ray, O. S. and C. W. Bivens. Reinforcement magnitude as a determinant of performance decrement after electroconvulsive shock. Science 160: 330-332, 1968. 18. Robustelli, F., A. Geller and M. E. Jarvik. Detention, electroconvulsive shock, and amnesia. Proc. Am. PsychoL Assoc. 331-332, 1968. 19. Robustelli, F. and M. E. Jarvik. Retrograde amnesia from detention. Physiol. Behav. 3: 543-547, 1968.