Psychoneurosndocrinology, Vol. 17, No. 2/3, pp. 255-259, 1992
0306-4530/92 $5.00+0.00 ©1992 Pergamon Press Ltd.
Printed in Great Britain
SHORT C O M M U N I C A T I O N ADRENAL ACTIVITY DOES NOT MEDIATE ALARM SUBSTANCE REACTION IN THE FORCED SWIM TEST ERNEST L. ABEL and PATRICIA J. BILITZKE Department of Obstetrics and Gynecology and Fetal Alcohol Research Center, Wayne State University, Detroit, Michigan, U.S.A. (Received 2 April 1991; in final form 12 July 1991)
SUMMARY Rats tested in the forced swim test were more immobile in fresh water than in water soiled by other rats, which presumably contained an alarm substance. Adrenalectomy did not affect the behavior of the rats in fresh or soiled water, nor did it affect production of or response to the putative alarm substance. The results of this study indicate that the adrenals do not mediate the response to, or production of the alarm substance. INTRODUCTION RATS IMMERSEDin a cylinder of fresh water from which they cannot escape, initially paddle vigorously and then adopt a characteristic immobility response (e.g., Hawkins et al., 1978; Abel, 1991b). However, if animals are immersed in water that has been soiled by another rat, they exhibit almost no immobility (Abel & Bilitzke, 1990; Abel, 1991a). Since pretest foot shock and loud noise also have the effect of reducing immobility (Abel & Bilitzke, 1990), we have interpreted decreased immobility as reflecting increased stress or fear (Abel & Bilitzke, 1990). This interpretation of the immobility response is similar to that suggested by others (e.g., Hawkins et al., 1978; Borsini & Meli, 1988; Nishimura et al., 1988), although it is not shared by all investigators (e.g., Porsolt et al., 1978). Since rats are less immobile in soiled water than in fresh, and since decreased immobility reflects increased stress or fear, we have hypothesized that soiled water contains an alarm substance which rats produce during the forced swim test (Abel & Bilitzke, 1990; Abel, 1991a). We and others have previously reported that, when rats are tested in the forced swim test, their plasma corticosterone levels increase markedly (Satoh et al., 1985; Manev & Pericic, 1988; Abel, 1991b). This indicates that the test is indeed stressful, since increased corticosterone levels are often used as a marker for stress (Axelrod & Reisine, 1984). Veldhuis et al. (1985) reported that, while bilateral adrenalectomy significantly affected immobility times when rats were tested 24 hr after an initial 15-min immersion, adrenalecAddress correspondence and reprint requests to: Dr. Ernest L. Abel, C. S. Mott Center for Human Growth and Development, 275 East Hancock, Detroit M148201, USA. 255
256
E. L. ABEL and P, J. BILITZKE
t o m i z e d rats did not differ from sham-treated animals during the initial i m m e r s i o n (cf. also Jefferys et al., 1983). T h e adrenal gland, therefore, does not s e e m to m e d i a t e the acquired immobility response when animals are tested in fresh water, but could still mediate the production o f the alarm substance which rats secrete during acquisition o f immobility. However, it is possible that p h e r o m o n e s from stressed rats m a y be metabolites of adrenal hormones such as corticosterone (Cheal & Sprott, 1971; M a c k a y - S i m & Laing, 1980). A d r e n a l e c t o m y results in the loss o f m a t u r a t i o n - d e l a y i n g p h e r o m o n e in mice (Drickamer & Mclntosh, 1980), and it is p o s s i b l e that it also results in loss o f other p h e r o m o n a l effects. To test this h y p o t h e s i s , we compared immobility times for adrenalectomized and sham-treated rats tested in fresh water, in water soiled b y untreated rats, and immobility times in untreated rats tested in water soiled by adrenalectomized or sham-treated rats. The first comparison was done to corroborate Veldhuis et al.'s (1985) report showing that adrenalectomy did not affect acquisition o f the immobility response. The second was done to determine if adrenalectomy would affect response to alarm, and the third was conducted to determine if adrenalectomy eliminated production o f alarm substance. METHODS Animals Male Long Evans rats (Charles River, Portage, MI), 100-120 days of age, were housed in Plexiglas® cages in a temperature-controlled vivarium (21+ 1° C) with a 12-hr light:dark cycle. Food and water were available ad libitum. Surgery After a 2-wk adaptation period, animals were anesthetized with sodium pentobarbital (50 mg/kg). Bilateral adrenalectomy (ADX) was performed via bilateral lumbar incisions through which the adrenals were removed. For SHAM-operated animals, the adrenals were located but not manipulated. Following surgery, ADX animals were given 0.9% saline instead of tap water to prevent dehydration (Fan-is & Griffith, 1949). Animals were tested 2 wk after surgery. Apparatus and Test Procedure. Animals were immersed in a Plexiglas® cylinder (Coming Glass, Coming, NY) (45.7 cm height, 22.2 cm inside diameter) filled to a height of 38 cm with water at 27+1°C. Animals were immersed for 11 min. Behavior during the first minute was considered an adaptation period and was not recorded. Animals were scored for immobility, the criterion for which was floating in the water, making only those movements necessary to keep the nose above water (Borsini & Meli, 1988). Seven groups of animals were compared in the adrenalectomy study. Three groups were tested in fresh tap water: nontreated controls (N=16), ADX (N=6) and SHAM (N=6) animals. Soiled water was water previously swum in by another rat for 11 min. Four groups were tested in soiled water: two of these groups were ADX- or SHAM-treated animals (N= 4/group) that were immersed in water soiled by an untreated rat. The other two were untreated rats tested in water soiled by an ADX or SHAM rat (N=5/group). Animals were autopsied after testing and examined for adrenal tissue. Animals with incomplete adrenalectomies were not included in the data analysis. Data Analysis. Immobility times were subjected to logarithmic transformation to reduced skewed distributions between groups (Winer, 1971) and were then analyzed by analysis of variance (ANOVA) followed by post-hoc comparisons of groups with the Duncan Multiple Range Test.
257
ALARM SUBSTANCE
RESULTS AND DISCUSSION The data are shown in the figure. Animals tested in fresh water were significantly more immobile than those tested in soiled water (F= 110, df= 6,39, p < 0.00001). None of the groups tested in soiled water were significantly different from each other. Likewise, none of the groups tested in fresh water differed significantly from each other. The results pertaining to animals tested in soiled water corroborate our previous reports showing that animals tested in soiled water exhibit almost no immobility in this test (Abel & Bilitzke, 1990; Abel, 1991a). Since stressing an animal prior to immersion in fresh water also reduces immobility, we have interpreted absence of immobility in the rat in this test as reflecting heightened fear or stress (cf. Hawkins et al., 1978; Borsini & Meli, 1988; Nishimura et al., 1988). Although we have not yet characterized the chemical properties of the alarm substance in soiled water that causes rats subsequently tested in it to exhibit alarm-like behavior, we have been able to characterize some of its behavioral parameters. Thus far, we have found that it produces a dose response-like effect on recipients, i.e., the greater the concentration, the greater the inhibition of immobility (Abel, 1991a). It can be detected as long as 8 days after it has been released (Abel, 1991a), and it is not readily depleted by repeated testing (Abel, 1991a). The substance also satisfies all of the criteria for pheromones advanced by Beauchamp et al. (1976), i.e., it produces behavioral effects in recipients, its effects do not require experience for either emission or detection, it has species specificity, and its behavioral effects are not due to nonspecific arousal (Abel, 1991c). We also have shown that this substance has low volatility (Abel, 1991c). We have previously shown (Abel, 1991a) that, while animals do not react to their own alarm substance while they are producing it (i.e., during the initial immersion), if they are removed from the tank and retumed to it 10 min later, they react to their own alarm substance in the same way as a different rat does, i.e., they do not become immobile. The present results pertaining to adrenalectomized rats tested in fresh water corroborate
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ADX
ADX AFTER CONTROL 4
SHAM AFTER CONTROL
CONTROL AFTER ADX
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5
6
7
Soiled Water
FIo. 1: Effects of a d r e n a l e c t o m y {ADX) o n t h e immobility r e s p o n s e of r a t s in f r e s h or soiled w a t e r in t h e forced s w i m test. G r o u p s 1 - 3 : U n t r e a t e d (N=16), ADX (N=6) or SHAM (N=6) a n i m a l s t e s t e d in f r e s h water. G r o u p s 5 - 6 : ADX a n d SHAM a n i m a l s (N=4) g r o u p t e s t e d in w a t e r soiled by u n t r e a t e d r a t s . G r o u p s 7 - 8 : U n t r e a t e d a n i m a l s t e s t e d in w a t e r soiled b y ADX or SHAM a n i m a l s |N= 5/group). Vertical lines indicate SEM.
258
E. L. ABELand E J. BILITZKE
those of Veldhuis et al. (1985) and Jefferys et al. (1983), showing that adrenalectomy does not s i g n i f i c a n t l y affect a c q u i s i t i o n o f the i m m o b i l i t y r e s p o n s e in the f o r c e d s w i m test. Both Veldhuis et al. (1985) and Jefferys et al. (1983; 1984; 1985), however, found that adrenalectomy did have an effect when animals were tested 24 hr after their initial exposure. However, their paradigm, in which animals were tested 24 hr after initial immersion, m a y be evaluating l e a r n i n g / m e m o r y function, with immobility as the dependent variable (West, 1990). The absence o f i m m o b i l i t y in ADX and SHAM animals tested in soiled water indicates that the adrenals do not affect the response to the alarm substance p r e s u m a b l y present in soiled water. The absence o f i m m o b i l i t y in untreated animals tested in water soiled b y ADX animals also indicates that the adrenals do not influence production o f that alarm substance.
Acknowledgements: Supported in part by grant No. P50 AA 07606 from the National Institute on Alcohol Abuse and Alcoholism. REFERENCES Abel EL (1991a) Gradient of alarm substance in the forced swimming test. Physiol Behav 49: 321-323. Abel EL (1991b) Behavior and corticosteroid response of Maudsley reactive and nonreactive rats in the open field and forced swimming test. Physiol Behav 50:151-153.. Abel EL (1991e) Alarm substance emitted by rats in the forced swim test is a low volatile pheromone. Physiol Behav 50: 723-727. Abel EL, Bilitzke PJ (1990) A possible alarm substance in the forced swimming test. Physiol Behav 48: 233-239. Axelrod J, Reisine TD (1984) Stress hormones: their interaction and regulation. Science 224: 452-459. Beauchamp GK, Doty RL, Moulton DG, Mugford RA (1976) The pheromone concept in mammalian communication: a critique. In: Doty RL (Ed) Mammalian Olfaction, Reproductive Processes and Behavior. Academic Press, New York, pp 144-160. Borsini F, Meli A (1988) Is the forced swimming test a suitable model for revealing antidepressant activity? Psychopharmacology 94: 147-160. Cheal ML, Sprott RL (1971) Social olfaction: a review of the role of olfaction in a variety of animal behaviors. PsycholRep 29: 195-243. Drickamer LC, Mclntosh TK (1980) Effects of adrenalectomy on the presence of a maturation-delaying pheromone in the urine of female mice. Horm Behav 14: 146-152. Fan-is EJ, Griffith JQ (1949) Surgery of the rat. In: Farris EJ, Griffith JQ (Eds) The Rat in Laboratory Investigation. JB Lippincott, Philadelphia, pp 434-451. Hawkins J, Hicks RA, Phillips N, Moore JD (1978) Swimming rats and human depression. Nature 274: 512. Jefferys D, Copolov D, Irby D, Funder J (1983) Behavioral effect of adrenalectomy: reversal by glucocorticoids or [D-ALA2, MET] enkephalinamide. Eur J Pharmaco192: 99-103. Jefferys D, Copolov D, Funder JW (1984) Naloxone inhibits both glucocorticoid and [D-AIa2 Met5] enkephalinamide reversal of behavioral effect of adrenalectomy. Eur J Pharmacol 103: 205-210. Jefferys D, Boublik J, Funder JW (1985) A ~c-selective opioidergic pathway is involved in the reversal of a behavioral effect of adrenalectomy. Eur J Pharmacol 107" 331-335. Mackay-Sim A, Laing DG (1980) Discrimination of odors from stressed rats by non-stressed rats. Physiol Behav 24: 699-704. Manev H, Pericic D (1988) Effects of the potential antidepressant dehydroergosine in rats forced to swim: influence on plasma corticosterone. Psychoneuroendocrinology 13: 465-469. Nishimura H, Tsuda A, Oguchi M, Ida Y, Tanaka M (1988) Is immobility of rats in the forced swim test "behavioral despair?" PhysioIBehav 42: 93-95. Porsolt RD, Anton G, Blavet N, Jalfre M (1978) Behavioral despair in rats: a new model sensitive to antidepressant treatments. Eur J Pharmaco147: 379- 391. Satoh T, Yamada K, Tsuboi M (1985) Effect of imipramine on serum corticosterone levels in the forced swimming rats. Res Comm Psychol Psychiat Behav 10: 235-238.
ALARMSUBSTANCE
259
Veldhuis HD, Dekorte CMM, DeKloet ER (1985) Glucocorticoids facilitate the retention of acquired immobility during forced swimming. Eur J Pharmacol 115:211-217. West AP (1990) Neurobehavioral studies of forced swimming: the role of learning and memory in the forced swim test. Prog Neuro PsychopharmacolBiol Psychiat 14: 863- 867. Winer BJ (1971) Statistical Principles in Experimental Design. McGraw Hill, New York.
0306-4530/92 $5.00+0.00 ©1992 Pergamon Press Ltd.
Printed in Great Britain
SHORT C O M M U N I C A T I O N ADRENAL ACTIVITY DOES NOT MEDIATE ALARM SUBSTANCE REACTION IN THE FORCED SWIM TEST ERNEST L. ABEL and PATRICIA J. BILITZKE Department of Obstetrics and Gynecology and Fetal Alcohol Research Center, Wayne State University, Detroit, Michigan, U.S.A. (Received 2 April 1991; in final form 12 July 1991)
SUMMARY Rats tested in the forced swim test were more immobile in fresh water than in water soiled by other rats, which presumably contained an alarm substance. Adrenalectomy did not affect the behavior of the rats in fresh or soiled water, nor did it affect production of or response to the putative alarm substance. The results of this study indicate that the adrenals do not mediate the response to, or production of the alarm substance. INTRODUCTION RATS IMMERSEDin a cylinder of fresh water from which they cannot escape, initially paddle vigorously and then adopt a characteristic immobility response (e.g., Hawkins et al., 1978; Abel, 1991b). However, if animals are immersed in water that has been soiled by another rat, they exhibit almost no immobility (Abel & Bilitzke, 1990; Abel, 1991a). Since pretest foot shock and loud noise also have the effect of reducing immobility (Abel & Bilitzke, 1990), we have interpreted decreased immobility as reflecting increased stress or fear (Abel & Bilitzke, 1990). This interpretation of the immobility response is similar to that suggested by others (e.g., Hawkins et al., 1978; Borsini & Meli, 1988; Nishimura et al., 1988), although it is not shared by all investigators (e.g., Porsolt et al., 1978). Since rats are less immobile in soiled water than in fresh, and since decreased immobility reflects increased stress or fear, we have hypothesized that soiled water contains an alarm substance which rats produce during the forced swim test (Abel & Bilitzke, 1990; Abel, 1991a). We and others have previously reported that, when rats are tested in the forced swim test, their plasma corticosterone levels increase markedly (Satoh et al., 1985; Manev & Pericic, 1988; Abel, 1991b). This indicates that the test is indeed stressful, since increased corticosterone levels are often used as a marker for stress (Axelrod & Reisine, 1984). Veldhuis et al. (1985) reported that, while bilateral adrenalectomy significantly affected immobility times when rats were tested 24 hr after an initial 15-min immersion, adrenalecAddress correspondence and reprint requests to: Dr. Ernest L. Abel, C. S. Mott Center for Human Growth and Development, 275 East Hancock, Detroit M148201, USA. 255
256
E. L. ABEL and P, J. BILITZKE
t o m i z e d rats did not differ from sham-treated animals during the initial i m m e r s i o n (cf. also Jefferys et al., 1983). T h e adrenal gland, therefore, does not s e e m to m e d i a t e the acquired immobility response when animals are tested in fresh water, but could still mediate the production o f the alarm substance which rats secrete during acquisition o f immobility. However, it is possible that p h e r o m o n e s from stressed rats m a y be metabolites of adrenal hormones such as corticosterone (Cheal & Sprott, 1971; M a c k a y - S i m & Laing, 1980). A d r e n a l e c t o m y results in the loss o f m a t u r a t i o n - d e l a y i n g p h e r o m o n e in mice (Drickamer & Mclntosh, 1980), and it is p o s s i b l e that it also results in loss o f other p h e r o m o n a l effects. To test this h y p o t h e s i s , we compared immobility times for adrenalectomized and sham-treated rats tested in fresh water, in water soiled b y untreated rats, and immobility times in untreated rats tested in water soiled by adrenalectomized or sham-treated rats. The first comparison was done to corroborate Veldhuis et al.'s (1985) report showing that adrenalectomy did not affect acquisition o f the immobility response. The second was done to determine if adrenalectomy would affect response to alarm, and the third was conducted to determine if adrenalectomy eliminated production o f alarm substance. METHODS Animals Male Long Evans rats (Charles River, Portage, MI), 100-120 days of age, were housed in Plexiglas® cages in a temperature-controlled vivarium (21+ 1° C) with a 12-hr light:dark cycle. Food and water were available ad libitum. Surgery After a 2-wk adaptation period, animals were anesthetized with sodium pentobarbital (50 mg/kg). Bilateral adrenalectomy (ADX) was performed via bilateral lumbar incisions through which the adrenals were removed. For SHAM-operated animals, the adrenals were located but not manipulated. Following surgery, ADX animals were given 0.9% saline instead of tap water to prevent dehydration (Fan-is & Griffith, 1949). Animals were tested 2 wk after surgery. Apparatus and Test Procedure. Animals were immersed in a Plexiglas® cylinder (Coming Glass, Coming, NY) (45.7 cm height, 22.2 cm inside diameter) filled to a height of 38 cm with water at 27+1°C. Animals were immersed for 11 min. Behavior during the first minute was considered an adaptation period and was not recorded. Animals were scored for immobility, the criterion for which was floating in the water, making only those movements necessary to keep the nose above water (Borsini & Meli, 1988). Seven groups of animals were compared in the adrenalectomy study. Three groups were tested in fresh tap water: nontreated controls (N=16), ADX (N=6) and SHAM (N=6) animals. Soiled water was water previously swum in by another rat for 11 min. Four groups were tested in soiled water: two of these groups were ADX- or SHAM-treated animals (N= 4/group) that were immersed in water soiled by an untreated rat. The other two were untreated rats tested in water soiled by an ADX or SHAM rat (N=5/group). Animals were autopsied after testing and examined for adrenal tissue. Animals with incomplete adrenalectomies were not included in the data analysis. Data Analysis. Immobility times were subjected to logarithmic transformation to reduced skewed distributions between groups (Winer, 1971) and were then analyzed by analysis of variance (ANOVA) followed by post-hoc comparisons of groups with the Duncan Multiple Range Test.
257
ALARM SUBSTANCE
RESULTS AND DISCUSSION The data are shown in the figure. Animals tested in fresh water were significantly more immobile than those tested in soiled water (F= 110, df= 6,39, p < 0.00001). None of the groups tested in soiled water were significantly different from each other. Likewise, none of the groups tested in fresh water differed significantly from each other. The results pertaining to animals tested in soiled water corroborate our previous reports showing that animals tested in soiled water exhibit almost no immobility in this test (Abel & Bilitzke, 1990; Abel, 1991a). Since stressing an animal prior to immersion in fresh water also reduces immobility, we have interpreted absence of immobility in the rat in this test as reflecting heightened fear or stress (cf. Hawkins et al., 1978; Borsini & Meli, 1988; Nishimura et al., 1988). Although we have not yet characterized the chemical properties of the alarm substance in soiled water that causes rats subsequently tested in it to exhibit alarm-like behavior, we have been able to characterize some of its behavioral parameters. Thus far, we have found that it produces a dose response-like effect on recipients, i.e., the greater the concentration, the greater the inhibition of immobility (Abel, 1991a). It can be detected as long as 8 days after it has been released (Abel, 1991a), and it is not readily depleted by repeated testing (Abel, 1991a). The substance also satisfies all of the criteria for pheromones advanced by Beauchamp et al. (1976), i.e., it produces behavioral effects in recipients, its effects do not require experience for either emission or detection, it has species specificity, and its behavioral effects are not due to nonspecific arousal (Abel, 1991c). We also have shown that this substance has low volatility (Abel, 1991c). We have previously shown (Abel, 1991a) that, while animals do not react to their own alarm substance while they are producing it (i.e., during the initial immersion), if they are removed from the tank and retumed to it 10 min later, they react to their own alarm substance in the same way as a different rat does, i.e., they do not become immobile. The present results pertaining to adrenalectomized rats tested in fresh water corroborate
3.2 .--I--
2.8
~
2.4
-~ O
2.0
E
1.6
E ," ID
1.2
~
O.8
~O -.1
0.4 0.0
CONTROL
SHAM
1
2
Fresh Water
ADX
ADX AFTER CONTROL 4
SHAM AFTER CONTROL
CONTROL AFTER ADX
CONTROL AFTER SHAM
5
6
7
Soiled Water
FIo. 1: Effects of a d r e n a l e c t o m y {ADX) o n t h e immobility r e s p o n s e of r a t s in f r e s h or soiled w a t e r in t h e forced s w i m test. G r o u p s 1 - 3 : U n t r e a t e d (N=16), ADX (N=6) or SHAM (N=6) a n i m a l s t e s t e d in f r e s h water. G r o u p s 5 - 6 : ADX a n d SHAM a n i m a l s (N=4) g r o u p t e s t e d in w a t e r soiled by u n t r e a t e d r a t s . G r o u p s 7 - 8 : U n t r e a t e d a n i m a l s t e s t e d in w a t e r soiled b y ADX or SHAM a n i m a l s |N= 5/group). Vertical lines indicate SEM.
258
E. L. ABELand E J. BILITZKE
those of Veldhuis et al. (1985) and Jefferys et al. (1983), showing that adrenalectomy does not s i g n i f i c a n t l y affect a c q u i s i t i o n o f the i m m o b i l i t y r e s p o n s e in the f o r c e d s w i m test. Both Veldhuis et al. (1985) and Jefferys et al. (1983; 1984; 1985), however, found that adrenalectomy did have an effect when animals were tested 24 hr after their initial exposure. However, their paradigm, in which animals were tested 24 hr after initial immersion, m a y be evaluating l e a r n i n g / m e m o r y function, with immobility as the dependent variable (West, 1990). The absence o f i m m o b i l i t y in ADX and SHAM animals tested in soiled water indicates that the adrenals do not affect the response to the alarm substance p r e s u m a b l y present in soiled water. The absence o f i m m o b i l i t y in untreated animals tested in water soiled b y ADX animals also indicates that the adrenals do not influence production o f that alarm substance.
Acknowledgements: Supported in part by grant No. P50 AA 07606 from the National Institute on Alcohol Abuse and Alcoholism. REFERENCES Abel EL (1991a) Gradient of alarm substance in the forced swimming test. Physiol Behav 49: 321-323. Abel EL (1991b) Behavior and corticosteroid response of Maudsley reactive and nonreactive rats in the open field and forced swimming test. Physiol Behav 50:151-153.. Abel EL (1991e) Alarm substance emitted by rats in the forced swim test is a low volatile pheromone. Physiol Behav 50: 723-727. Abel EL, Bilitzke PJ (1990) A possible alarm substance in the forced swimming test. Physiol Behav 48: 233-239. Axelrod J, Reisine TD (1984) Stress hormones: their interaction and regulation. Science 224: 452-459. Beauchamp GK, Doty RL, Moulton DG, Mugford RA (1976) The pheromone concept in mammalian communication: a critique. In: Doty RL (Ed) Mammalian Olfaction, Reproductive Processes and Behavior. Academic Press, New York, pp 144-160. Borsini F, Meli A (1988) Is the forced swimming test a suitable model for revealing antidepressant activity? Psychopharmacology 94: 147-160. Cheal ML, Sprott RL (1971) Social olfaction: a review of the role of olfaction in a variety of animal behaviors. PsycholRep 29: 195-243. Drickamer LC, Mclntosh TK (1980) Effects of adrenalectomy on the presence of a maturation-delaying pheromone in the urine of female mice. Horm Behav 14: 146-152. Fan-is EJ, Griffith JQ (1949) Surgery of the rat. In: Farris EJ, Griffith JQ (Eds) The Rat in Laboratory Investigation. JB Lippincott, Philadelphia, pp 434-451. Hawkins J, Hicks RA, Phillips N, Moore JD (1978) Swimming rats and human depression. Nature 274: 512. Jefferys D, Copolov D, Irby D, Funder J (1983) Behavioral effect of adrenalectomy: reversal by glucocorticoids or [D-ALA2, MET] enkephalinamide. Eur J Pharmaco192: 99-103. Jefferys D, Copolov D, Funder JW (1984) Naloxone inhibits both glucocorticoid and [D-AIa2 Met5] enkephalinamide reversal of behavioral effect of adrenalectomy. Eur J Pharmacol 103: 205-210. Jefferys D, Boublik J, Funder JW (1985) A ~c-selective opioidergic pathway is involved in the reversal of a behavioral effect of adrenalectomy. Eur J Pharmacol 107" 331-335. Mackay-Sim A, Laing DG (1980) Discrimination of odors from stressed rats by non-stressed rats. Physiol Behav 24: 699-704. Manev H, Pericic D (1988) Effects of the potential antidepressant dehydroergosine in rats forced to swim: influence on plasma corticosterone. Psychoneuroendocrinology 13: 465-469. Nishimura H, Tsuda A, Oguchi M, Ida Y, Tanaka M (1988) Is immobility of rats in the forced swim test "behavioral despair?" PhysioIBehav 42: 93-95. Porsolt RD, Anton G, Blavet N, Jalfre M (1978) Behavioral despair in rats: a new model sensitive to antidepressant treatments. Eur J Pharmaco147: 379- 391. Satoh T, Yamada K, Tsuboi M (1985) Effect of imipramine on serum corticosterone levels in the forced swimming rats. Res Comm Psychol Psychiat Behav 10: 235-238.
ALARMSUBSTANCE
259
Veldhuis HD, Dekorte CMM, DeKloet ER (1985) Glucocorticoids facilitate the retention of acquired immobility during forced swimming. Eur J Pharmacol 115:211-217. West AP (1990) Neurobehavioral studies of forced swimming: the role of learning and memory in the forced swim test. Prog Neuro PsychopharmacolBiol Psychiat 14: 863- 867. Winer BJ (1971) Statistical Principles in Experimental Design. McGraw Hill, New York.
