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Electroconvulsive shock effects on food and water intake as a function of prior deprivational state
Physiology & Behavior, Vol. 27, pp. 171-173.PergamonPress and BrainResearch Publ., 1981. Primedin the U.S.A.
Electroconvulsive Shock Effects on Food and Water Intake as a Function of Prior Deprivational State M. K. WALKER, W. B. G U M M A N D H. D. D A Y D e p a r t m e n t o f P s y c h o l o g y , Texas W o m a n ' s University, D e n t o n , T X 76204 R e c e i v e d 2 M a r c h 1981 WALKER, M. K., W. B. GUMM AND H. D. DAY. Electroconvulsive shock effects on food and water intake as a function of prior deprivational state. PHYSIOL. BEHAV. 27(1) 171-173, 1981.--Two experiments, each using approximately 30 male and 30 female hooded rats, examined the effects of electroconvulsive shock (ECS) on water intake as a function of the water deprivation state of the animal and food intake and body weight as a function of food deprivation state. In Experiment 1, half the animals were subjected to water deprivation prior to ECS or sham ECS, and the other half were watered ad lib; in Experiment 2, food deprivation was the pre-ECS manipulation. As predicted, ECS produced a decrease in water intake in the ad lib watered animals but not in the deprived ones. A similar treatment by deprivation interaction was not found for food intake or body weight. In the males, food intake was decreased for one day by the treatment but recovered to a normal level two days following ECS; however, such an effect of ECS on food intake did not occur in the females. Since food and water intake was not differentially affected by ECS and sham ECS in deprived animals, previous cautions regarding ECS effects on motivational states may not be germane to many studies using appetitive conditioning paradigms. ECS Food intake Water intake Physiology of motivation
Eating
Drinking
E L E C T R O C O N V U L S I V E shock (ECS) has been repeatedly demonstrated to disrupt the performance of a response learned just prior to the ECS. Although the most commonly invoked explanation of this effect is that ECS interferes with some aspect of the memory of the learned response [8], ECS may affect behavior in ways unrelated to amnesia [2]. Increases in both acetylcholinesterase activity levels and free acetylcholine concentration following ECS have been found [1, 3, 13]. Since alterations in cholinergic systems have been shown to coincide with differences in task performance [4] and changes in appetitive motivation [l l], post-ECS performance deficits may result from a neurochemically produced change in motivation. ECS treatments have been found to reduce water intake and consumption of food delivered either in powdered chow form [10,1 I] or dispensed following the animal's lever press [7, 9, 15]. Such findings have led some to recommend unspecified controls for the effects of ECS on motivational states in those ECS studies involving food or water reinforced behavior [9,1 I]. Since investigations of the effects of ECS on food and water intake generally apply ECS following ad lib feeding and watering [7, 9, 10, 11, 15], the findings of
Food deprivation
Water deprivation
these studies may not be germane to the amnesia studies that normally deprive the animals of food and water prior to treatment (e.g., [2, 12, 14]). That deprivation state affects changes in consummatory behavior following ECS was shown by one study [9] which found that rats maintained on an ad lib feeding schedule before ECS showed reduced food intake and body weight following ECS, while animals maintained on a food deprivation schedule showed increases in food intake following ECS. Since this study applied a series of l0 ECS treatments to the animals, and most contemporary experiments use a single ECS treatment, the purpose of the present studies was to determine if food and water deprivation schedules affect post-ECS food and water intake following a single ECS application. Two experiments were conducted, the first involving the effects of water deprivation on post-ECS water intake, and the second examining the effects of food deprivation on post-ECS food intake and body weight. It was expected that animals on ad lib food and water schedules prior to ECS would show a reduction in food or water intake following ECS, while deprived animals would show the usual post-deprivation increases in food or water intake following ECS.
1This research was supported by a grant awarded to the third author by Texas Woman's University. The authors gratefully acknowledge the technical assistance of Dr. Bill C. Smith.
C o p y r i g h t © 1981 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/81/070171-03502.00/0
172
W A L K E R , GUMM AND I)A5 METHOD
Subjects were laboratory raised male and female hooded rats, 90 days old at the beginning of the experiments and individually housed in wire mesh cages on a 12-hr light-dark cycle. In Experiment 1, 15 males and 16 females were randomly assigned to the deprived condition while 16 males and 16 females were placed in the ad lib condition. In Experiment 2, 16 males and 15 females were assigned to both deprivation conditions. During a 10-day deprivation period, the animals in Experiment ! were 23-hr water deprived and received powdered Purina Chow ad lib. The deprived animals in Experiment 2 were maintained at 85% initial body weight for 10 days while experiencing ad lib watering. For the duration of Experiment 2, the entire daily allotment of food for both deprived and ad lib animals was powdered Purina Chow made available in 6-cm diameter, 4-cm tall, cylindrical containers secured to the inside front of the cages by metal clips. In Experiment 1, tap water was delivered to all animals in 250 ml bottles attached to the outside of the cages. At the end of the deprivation period in Experiment 1, eight males and eight females in each deprivation condition received ECS while the remaining animals experienced sham-ECS (SECS). Similarly, nine deprived and eight ad lib males and eight deprived and seven ad lib females received ECS following the deprivation period in Experiment 2. In each experiment, ECS animals were hand-held while receiving 0.5 sec of 50 mA peak ECS across the ears via padded, saline-soaked spring-clip electrodes. Current was 60 Hz from a variable transformer at an average head resistance of approximately 2000 12. F o r the SECS animals, electrodes were placed on the ears, but no current was delivered. In Experiment 2, two males in the ad Iib-ECS condition and two males in the deprived-ECS group were destroyed following ECSproduced paraplegia. No post-ECS debilitation was observed in Experiment 1. Immediately following ECS or SECS in both experiments, all animals were placed on ad lib feeding and watering schedules. In Experiment 1, 24 hr following ECS or SECS and occurring every 24 hr for nine more days thereafter, daily water intake was measured to the nearest milliliter. Similarly, in Experiment 2, daily food intake and body weight were measured to the nearest gram for 10 days following the ECS or SECS treatments. Food intake and body weight in Experiment 1 and water intake in Experiment 2 were not measured during either the deprivation or post-treatment period. RESULTS
To examine the effects of treatment (ECS or SECS), deprivation state, sex, and days since treatment, water intake in Experiment 1 and food intake and body weight in Experiment 2 were subjected to unbalanced 2 x 2 x 2 x 10 univariate analyses of variance with the 10 days of measurement (trials) the only within-subjects factor. Since asymmetry of the variance/covariance matrix was demonstrated for each analysis, only the effects significant at a=0.01 will be interpreted for the repeated measures analyses. Although the main effect for treatment was not significant (p >0.05), the research hypothesis for water intake was supported by a significant treatment x deprivation interaction in Experiment l, F(1,53)=9.06, p=0.004, 6oz=0.15. The analysis of simple main effects and Fig. 1 reveal that ECS animals watered ad lib prior to treatment showed a reduction
42 41 40
O ECS
39 0
38
m
37
]¢
"T"
--] SECS
36 35 34 33 32 31 30 29 0 AD LIB DEPRIVATION
DEPRIVED CONDITION
FIG. 1. Mean daily water intake for the interaction of treatment (ECS vs SECS) and deprivation condition (ad lib vs deprived). Bars indicate standard errors.
in water intake following ECS: ECS, however, apparently had no effect on this variable in animals water deprived before treatment. No other interaction involving treatment reached significance. On the day following treatment, the ad lib ECS animals showed a 30% reduction in water intake from the average of the last three pre-ECS measurements, a finding that agrees very well with the 26% decrease reported previously [11]. Significant sex and deprivation effects did not occur for water intake: however, significant trials, sex x trials, deprivation x trials, and sex z deprivation x trials interactions (ps<0.001) revealed that the male deprived animals consumed more water than other groups during the first few days following treatment. In Experiment 2, neither the treatment main effect nor the predicted treatment x deprivation interaction for food intake or body weight occurred ( F s < l ) . Significant sex, deprivation, trials, sex x trials, deprivation x trials, and sex × deprivationxtrials effects (ps<0.01), however, occurred for food intake in directions similar to those for water intake, and sex, trials, sexxtrials, and deprivationxtrials effects also occurred for body weight (ps<0.01). The failure to find a reduction in food intake following ECS was puzzling. Only one other study has used chow consumption as the measure of food intake following a single ECS [I1]. In that study, daily food consumption was measured for five days following ECS; however, in demonstrating the reduction in food intake following ECS, measurements for only the first post-ECS day were subjected to statistical analysis. We therefore, examined food intake for the first day following ECS in a 2 x 2 x 2 univariate analysis of variance. Although the treatment effect was not significant (p = 0.057), the treatment x sex interaction was (p = 0.005). On this first day following ECS, the SECS males had a mean food intake of 28.3 g while the ECS males had a mean intake of 22.8 g. Similar mean intakes for the females were 20.5 and
ECS E F F E C T S ON FOOD AND WATER I N T A K E
173
22.1 g. ECS, therefore, reduced food intake for the males but not for the females, and since only males were used in the previous study [1t], the discrepancy revealed by the initial repeated measures analysis of the present study seem to be explained. In fact, the present difference of 19% between the ECS and SECS males is similar to the 16% reduction in food intake previously reported [11]. Similar analyses of variance for food intake on subsequent days following the treatment did not yield significant treatment effects, an indication that food intake had recovered to control levels by the second day following ECS. DISCUSSION The treatmentxdeprivation interaction for water intake indicates that the physiological changes associated with reduced water consumption in rats watered ad lib prior to ECS are in some way countered by changes resulting from a period of water deprivation. Such an interaction can be explained by postulating that water deprivation and ECS have opposite and additive effects on the same neurochemical system involved in the regulation of water intake, e.g., a cholinergic system; however, evidence that water intake induced by cholinergic stimulation and drinking following water deprivation are not mediated by the same system [6] suggests that ECS and water deprivation may affect different mechanisms related to water intake.
The failure to find a treatment×deprivation interaction for food intake disagrees with a single previous report [9]. Since that report used bar press frequency as the measure of food intake, the differences between it and the present study are difficult to evaluate. Confirmation of the present findings will extend the evidence that distinctive central mechanisms regulate food and water intake (e.g., [5]). Previous studies [7, 9, 10, 11, 15] reporting that ECS reduces food intake have used only male animals, and the present finding that ECS reduces food intake for males but not for females demonstrates an interesting sex difference in response to ECS. Following reports of apparent changes in the subjects' motivational states after ECS, some authors [9,11] have suggested that studies of ECS-induced amnesia utilizing appetitive conditioning paradigms may be confounded by ECS-induced motivational changes. Since the usual procedure in appetitive conditioning is to create a motivational state in the animal by appropriate deprivation experiences, it seems that the data most directly pertinent to this question would be from animals receiving ECS immediately following a period of deprivation. In the present study, the deprivedECS and deprived-SECS rats did not differ on either water or food consumption following treatment. We, therefore, are not convinced that the results of previous ECS studies using animals deprived of food or water are compromised by uncontrolled motivational changes related to the ECS experience.
REFERENCES
1. Adams, H. E., R. R. Hoblit and P. B. Sutker. Electroconvulsive shock, brain acetylcholinesterase activity and memory. Physiol. Behav. 4: 113-116, 1969. 2. Adams, H. E., L. J. Peacock and D. D. Hamrick. ECS and one-trial learning: Retrograde amnesia or disinhibition? Physiol. Behav. 2: 435--437, 1967. 3. Essman, W. B. Neurochemical changes in ECS and ECT. Sernins Psychiat. 4: 67-69, 1972. 4. Gammon, W. D. and R. K. Thomas. Interactive effects of light/ dark cycle, ECS, physostigmine, and scopolamine on one-way avoidance learning in rats. Physiol. Psychol. 8: 72-76, 1980. 5. Grossman, S. P. Eating or drinking elicited by direct adrenergic or cholinergic stimulation of hypothalamus. Science 132: 301302, 1960. 6. Krikstone, B. J. and R. A. Levitt. Interactions between water deprivation and chemical brain stimulation. J. comp. physiol. PsychoL 71: 334-340, 1970. 7. Layden, T. A. and H. Birch. The effect of electroconvulsive shock on body weight, food intake and water intake in the rat. Physiol. Behav. 4: 1015-1017, 1969. 8. McGaugh, J. L. Time-dependent processes in memory storage. Science 153: 1351-1358, 1966.
9. Mirsky, A. F. and H. E. Rosvold. The effect of electroconvulsive shock on food intake and hunger drive in the rat. J. cornp. physiol. Psychol. 46: 153-157, 1953. 10. Prewett, M. J., P. K. Van Allen and J. S. Milner. Multiple electroconvulsive shocks and feeding and drinking behavior in the rat. Bull. Psychon. Soc. 12: 137-139, 1978. 11. Prewett, M. J. and J. S. Milner. Effects of electroconvulsive shock on food and water intake in the rat. Physiol. Behav. 19: 341-343, 1977. 12. Pinel, J. P. J. A short gradient of ECS-produced amnesia in a one-trial appetitive learning situation. J. comp. physiol. Psychol. 68: 650-655, 1969. 13. Richter, D. and J. Crossland. Variation in acetylcholine content of the brain with physiological state. Am. J. Physiol. 159: 247255, 1949. 14. Schiller, P. J. and S. L. Chorover. Short-term amnestic effects of electroconvulsive shock in a one-trial maze learning paradigm. Neuropsychologia 5: 155-163, 1967. 15. Stein, L. Anticholinergic drugs and the central control of thirst. Science 139: 46-48, 1963.
Electroconvulsive Shock Effects on Food and Water Intake as a Function of Prior Deprivational State M. K. WALKER, W. B. G U M M A N D H. D. D A Y D e p a r t m e n t o f P s y c h o l o g y , Texas W o m a n ' s University, D e n t o n , T X 76204 R e c e i v e d 2 M a r c h 1981 WALKER, M. K., W. B. GUMM AND H. D. DAY. Electroconvulsive shock effects on food and water intake as a function of prior deprivational state. PHYSIOL. BEHAV. 27(1) 171-173, 1981.--Two experiments, each using approximately 30 male and 30 female hooded rats, examined the effects of electroconvulsive shock (ECS) on water intake as a function of the water deprivation state of the animal and food intake and body weight as a function of food deprivation state. In Experiment 1, half the animals were subjected to water deprivation prior to ECS or sham ECS, and the other half were watered ad lib; in Experiment 2, food deprivation was the pre-ECS manipulation. As predicted, ECS produced a decrease in water intake in the ad lib watered animals but not in the deprived ones. A similar treatment by deprivation interaction was not found for food intake or body weight. In the males, food intake was decreased for one day by the treatment but recovered to a normal level two days following ECS; however, such an effect of ECS on food intake did not occur in the females. Since food and water intake was not differentially affected by ECS and sham ECS in deprived animals, previous cautions regarding ECS effects on motivational states may not be germane to many studies using appetitive conditioning paradigms. ECS Food intake Water intake Physiology of motivation
Eating
Drinking
E L E C T R O C O N V U L S I V E shock (ECS) has been repeatedly demonstrated to disrupt the performance of a response learned just prior to the ECS. Although the most commonly invoked explanation of this effect is that ECS interferes with some aspect of the memory of the learned response [8], ECS may affect behavior in ways unrelated to amnesia [2]. Increases in both acetylcholinesterase activity levels and free acetylcholine concentration following ECS have been found [1, 3, 13]. Since alterations in cholinergic systems have been shown to coincide with differences in task performance [4] and changes in appetitive motivation [l l], post-ECS performance deficits may result from a neurochemically produced change in motivation. ECS treatments have been found to reduce water intake and consumption of food delivered either in powdered chow form [10,1 I] or dispensed following the animal's lever press [7, 9, 15]. Such findings have led some to recommend unspecified controls for the effects of ECS on motivational states in those ECS studies involving food or water reinforced behavior [9,1 I]. Since investigations of the effects of ECS on food and water intake generally apply ECS following ad lib feeding and watering [7, 9, 10, 11, 15], the findings of
Food deprivation
Water deprivation
these studies may not be germane to the amnesia studies that normally deprive the animals of food and water prior to treatment (e.g., [2, 12, 14]). That deprivation state affects changes in consummatory behavior following ECS was shown by one study [9] which found that rats maintained on an ad lib feeding schedule before ECS showed reduced food intake and body weight following ECS, while animals maintained on a food deprivation schedule showed increases in food intake following ECS. Since this study applied a series of l0 ECS treatments to the animals, and most contemporary experiments use a single ECS treatment, the purpose of the present studies was to determine if food and water deprivation schedules affect post-ECS food and water intake following a single ECS application. Two experiments were conducted, the first involving the effects of water deprivation on post-ECS water intake, and the second examining the effects of food deprivation on post-ECS food intake and body weight. It was expected that animals on ad lib food and water schedules prior to ECS would show a reduction in food or water intake following ECS, while deprived animals would show the usual post-deprivation increases in food or water intake following ECS.
1This research was supported by a grant awarded to the third author by Texas Woman's University. The authors gratefully acknowledge the technical assistance of Dr. Bill C. Smith.
C o p y r i g h t © 1981 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/81/070171-03502.00/0
172
W A L K E R , GUMM AND I)A5 METHOD
Subjects were laboratory raised male and female hooded rats, 90 days old at the beginning of the experiments and individually housed in wire mesh cages on a 12-hr light-dark cycle. In Experiment 1, 15 males and 16 females were randomly assigned to the deprived condition while 16 males and 16 females were placed in the ad lib condition. In Experiment 2, 16 males and 15 females were assigned to both deprivation conditions. During a 10-day deprivation period, the animals in Experiment ! were 23-hr water deprived and received powdered Purina Chow ad lib. The deprived animals in Experiment 2 were maintained at 85% initial body weight for 10 days while experiencing ad lib watering. For the duration of Experiment 2, the entire daily allotment of food for both deprived and ad lib animals was powdered Purina Chow made available in 6-cm diameter, 4-cm tall, cylindrical containers secured to the inside front of the cages by metal clips. In Experiment 1, tap water was delivered to all animals in 250 ml bottles attached to the outside of the cages. At the end of the deprivation period in Experiment 1, eight males and eight females in each deprivation condition received ECS while the remaining animals experienced sham-ECS (SECS). Similarly, nine deprived and eight ad lib males and eight deprived and seven ad lib females received ECS following the deprivation period in Experiment 2. In each experiment, ECS animals were hand-held while receiving 0.5 sec of 50 mA peak ECS across the ears via padded, saline-soaked spring-clip electrodes. Current was 60 Hz from a variable transformer at an average head resistance of approximately 2000 12. F o r the SECS animals, electrodes were placed on the ears, but no current was delivered. In Experiment 2, two males in the ad Iib-ECS condition and two males in the deprived-ECS group were destroyed following ECSproduced paraplegia. No post-ECS debilitation was observed in Experiment 1. Immediately following ECS or SECS in both experiments, all animals were placed on ad lib feeding and watering schedules. In Experiment 1, 24 hr following ECS or SECS and occurring every 24 hr for nine more days thereafter, daily water intake was measured to the nearest milliliter. Similarly, in Experiment 2, daily food intake and body weight were measured to the nearest gram for 10 days following the ECS or SECS treatments. Food intake and body weight in Experiment 1 and water intake in Experiment 2 were not measured during either the deprivation or post-treatment period. RESULTS
To examine the effects of treatment (ECS or SECS), deprivation state, sex, and days since treatment, water intake in Experiment 1 and food intake and body weight in Experiment 2 were subjected to unbalanced 2 x 2 x 2 x 10 univariate analyses of variance with the 10 days of measurement (trials) the only within-subjects factor. Since asymmetry of the variance/covariance matrix was demonstrated for each analysis, only the effects significant at a=0.01 will be interpreted for the repeated measures analyses. Although the main effect for treatment was not significant (p >0.05), the research hypothesis for water intake was supported by a significant treatment x deprivation interaction in Experiment l, F(1,53)=9.06, p=0.004, 6oz=0.15. The analysis of simple main effects and Fig. 1 reveal that ECS animals watered ad lib prior to treatment showed a reduction
42 41 40
O ECS
39 0
38
m
37
]¢
"T"
--] SECS
36 35 34 33 32 31 30 29 0 AD LIB DEPRIVATION
DEPRIVED CONDITION
FIG. 1. Mean daily water intake for the interaction of treatment (ECS vs SECS) and deprivation condition (ad lib vs deprived). Bars indicate standard errors.
in water intake following ECS: ECS, however, apparently had no effect on this variable in animals water deprived before treatment. No other interaction involving treatment reached significance. On the day following treatment, the ad lib ECS animals showed a 30% reduction in water intake from the average of the last three pre-ECS measurements, a finding that agrees very well with the 26% decrease reported previously [11]. Significant sex and deprivation effects did not occur for water intake: however, significant trials, sex x trials, deprivation x trials, and sex z deprivation x trials interactions (ps<0.001) revealed that the male deprived animals consumed more water than other groups during the first few days following treatment. In Experiment 2, neither the treatment main effect nor the predicted treatment x deprivation interaction for food intake or body weight occurred ( F s < l ) . Significant sex, deprivation, trials, sex x trials, deprivation x trials, and sex × deprivationxtrials effects (ps<0.01), however, occurred for food intake in directions similar to those for water intake, and sex, trials, sexxtrials, and deprivationxtrials effects also occurred for body weight (ps<0.01). The failure to find a reduction in food intake following ECS was puzzling. Only one other study has used chow consumption as the measure of food intake following a single ECS [I1]. In that study, daily food consumption was measured for five days following ECS; however, in demonstrating the reduction in food intake following ECS, measurements for only the first post-ECS day were subjected to statistical analysis. We therefore, examined food intake for the first day following ECS in a 2 x 2 x 2 univariate analysis of variance. Although the treatment effect was not significant (p = 0.057), the treatment x sex interaction was (p = 0.005). On this first day following ECS, the SECS males had a mean food intake of 28.3 g while the ECS males had a mean intake of 22.8 g. Similar mean intakes for the females were 20.5 and
ECS E F F E C T S ON FOOD AND WATER I N T A K E
173
22.1 g. ECS, therefore, reduced food intake for the males but not for the females, and since only males were used in the previous study [1t], the discrepancy revealed by the initial repeated measures analysis of the present study seem to be explained. In fact, the present difference of 19% between the ECS and SECS males is similar to the 16% reduction in food intake previously reported [11]. Similar analyses of variance for food intake on subsequent days following the treatment did not yield significant treatment effects, an indication that food intake had recovered to control levels by the second day following ECS. DISCUSSION The treatmentxdeprivation interaction for water intake indicates that the physiological changes associated with reduced water consumption in rats watered ad lib prior to ECS are in some way countered by changes resulting from a period of water deprivation. Such an interaction can be explained by postulating that water deprivation and ECS have opposite and additive effects on the same neurochemical system involved in the regulation of water intake, e.g., a cholinergic system; however, evidence that water intake induced by cholinergic stimulation and drinking following water deprivation are not mediated by the same system [6] suggests that ECS and water deprivation may affect different mechanisms related to water intake.
The failure to find a treatment×deprivation interaction for food intake disagrees with a single previous report [9]. Since that report used bar press frequency as the measure of food intake, the differences between it and the present study are difficult to evaluate. Confirmation of the present findings will extend the evidence that distinctive central mechanisms regulate food and water intake (e.g., [5]). Previous studies [7, 9, 10, 11, 15] reporting that ECS reduces food intake have used only male animals, and the present finding that ECS reduces food intake for males but not for females demonstrates an interesting sex difference in response to ECS. Following reports of apparent changes in the subjects' motivational states after ECS, some authors [9,11] have suggested that studies of ECS-induced amnesia utilizing appetitive conditioning paradigms may be confounded by ECS-induced motivational changes. Since the usual procedure in appetitive conditioning is to create a motivational state in the animal by appropriate deprivation experiences, it seems that the data most directly pertinent to this question would be from animals receiving ECS immediately following a period of deprivation. In the present study, the deprivedECS and deprived-SECS rats did not differ on either water or food consumption following treatment. We, therefore, are not convinced that the results of previous ECS studies using animals deprived of food or water are compromised by uncontrolled motivational changes related to the ECS experience.
REFERENCES
1. Adams, H. E., R. R. Hoblit and P. B. Sutker. Electroconvulsive shock, brain acetylcholinesterase activity and memory. Physiol. Behav. 4: 113-116, 1969. 2. Adams, H. E., L. J. Peacock and D. D. Hamrick. ECS and one-trial learning: Retrograde amnesia or disinhibition? Physiol. Behav. 2: 435--437, 1967. 3. Essman, W. B. Neurochemical changes in ECS and ECT. Sernins Psychiat. 4: 67-69, 1972. 4. Gammon, W. D. and R. K. Thomas. Interactive effects of light/ dark cycle, ECS, physostigmine, and scopolamine on one-way avoidance learning in rats. Physiol. Psychol. 8: 72-76, 1980. 5. Grossman, S. P. Eating or drinking elicited by direct adrenergic or cholinergic stimulation of hypothalamus. Science 132: 301302, 1960. 6. Krikstone, B. J. and R. A. Levitt. Interactions between water deprivation and chemical brain stimulation. J. comp. physiol. PsychoL 71: 334-340, 1970. 7. Layden, T. A. and H. Birch. The effect of electroconvulsive shock on body weight, food intake and water intake in the rat. Physiol. Behav. 4: 1015-1017, 1969. 8. McGaugh, J. L. Time-dependent processes in memory storage. Science 153: 1351-1358, 1966.
9. Mirsky, A. F. and H. E. Rosvold. The effect of electroconvulsive shock on food intake and hunger drive in the rat. J. cornp. physiol. Psychol. 46: 153-157, 1953. 10. Prewett, M. J., P. K. Van Allen and J. S. Milner. Multiple electroconvulsive shocks and feeding and drinking behavior in the rat. Bull. Psychon. Soc. 12: 137-139, 1978. 11. Prewett, M. J. and J. S. Milner. Effects of electroconvulsive shock on food and water intake in the rat. Physiol. Behav. 19: 341-343, 1977. 12. Pinel, J. P. J. A short gradient of ECS-produced amnesia in a one-trial appetitive learning situation. J. comp. physiol. Psychol. 68: 650-655, 1969. 13. Richter, D. and J. Crossland. Variation in acetylcholine content of the brain with physiological state. Am. J. Physiol. 159: 247255, 1949. 14. Schiller, P. J. and S. L. Chorover. Short-term amnestic effects of electroconvulsive shock in a one-trial maze learning paradigm. Neuropsychologia 5: 155-163, 1967. 15. Stein, L. Anticholinergic drugs and the central control of thirst. Science 139: 46-48, 1963.