NEUROSCIENCE RESEARCH COMMUNICATIONS, VOL. 31, NO. 3

EFFECTS OF ACUTE AMITRIPTYLINE ADMINISTRATION ON MEMORY, ANXIETY AND

ACTIVITY IN MALE AND FEMALE MICE

And& Parra*, Estrella Everss, Santiago Monleon, Conception Vinader-Caerols and M. Carmen Arenas

Area de Psicobiologia, Facultad de Psicologia, Universitat de Valencia. Blasco Ibifiez, 2 1. 460 10 Valencia, Spain. *E-mail: andres.parra@uv.es

(Accepted September 25, 2002)

SUMMARY The effects of acute administration of amitriptyline on memory consolidation in male and female

CD1 mice were investigated. Three doses of this tricyclic antidepressant (7.5, 15 and 30 .mg/kg) were administered immediately after inhibitory avoidance training. Forty-five minutes after injection, subjects explored the elevated plus-maze for five minutes. Subjects were tested for avoidance twenty- four hours later. Amitriptyline impaired inhibitory avoidance consolidation at doses 7.5, 15 and 30 mg/kg in males, and at doses 7.5 and 30 mg/kg in females. In the elevated plus-maze, amitriptyline had no effect on anxiety (percentage of open arm entries) and induced a dose-dependent impairment of activity (number of closed arm entries). The observed sex differences were limited to subtle stronger effects of amitriptiline in males than in females on inhibitory avoidance. These results indicate that acute amitriptyline administration produces retrograde amnesia on inhibitory avoidance, which does not seem be mediated by anxiolytic effects.

KEY WORDS: antidepressants; elevated plus-maze; retrograde amnesia

inhibitory avoidance; memory consolidation,

INTRODUCTION

Antidepressants are widely prescribed for anxiety and other disorders, apart from depression (1).

But, as well as other psychotropic medications, antidepressants have limitations such as delayed onset

of clinical response, none of them can be said to cure, all have an important part of consumers that are

non-responders, and the mechanism responsible for the therapeutic action is hardly known. With

respect to the latter limitation, and taking into account that antidepressants have different

0 2002 Wiley-Liss, Inc. DO1 10.1002/nrc.l0046

136 NEUROSCIENCE RESEARCH COMMUNICATIONS, VOL. 31, NO. 3

neuropharmacological mechanisms of action, and that they share a similar therapeutic output, what

they have in common could be found at the psychological level.

The evaluation of memory impairing and enhancing substances in the forced swimming test (2), a

test widely used for testing new antidepressants (3), as well as results of behavioural experiments,

gave us the view that this test had some characteristics of short tests to assess memory (4, 5, 6). If the

forced swimming test can be considered a memory test and antidepressants impair performance in

this test (subjects swim more than controls the second time that are forced to swim) it could be the

case that antidepressants impair memory, at least the kind of memory involved in the forced

swimming test. It is interesting to note that the alternative treatments for depression, REM sleep

deprivation and electroconvulsive shock, impair learning and memory (7, 8). This understanding of

the relationship between antidepressant therapy and memory is new in the field (9). The most

common view of such a relationship considers memory impairment as a symptom (lo), an adverse

effect of antidepressants (1 l), or a factor in differentiating dementia from depressive pseudodementia

(12) .

In our laboratory, using mice as experimental subjects, we have recently started to study the effects

of several antidepressants, such as amitriptyline, maprotiline and fluoxetine on inhibitory avoidance,

a task widely used in memory studies (13, 14, 15, 16). Although chronic treatment is needed in the

therapeutic use of antidepressants, acute administration of drugs to subjects submitted to one trial

learning tasks, e.g., inhibitory avoidance, allows one to choose specific moments for injection in

which specific memory processes are involved (17).

The aim of the present paper was to assess the effects of amitriptyline, a mixed serotoninergic and

noradrenergic uptake inhibitor with a strong anticholinergic effect (IS), on memory, anxiety, and

activity in the same experimental animals, as a consequence of a sole administration. There are good

reasons for studying whether the impairing effects of amitriptyline on inhibitory avoidance are

mediated by its effects on anxiety. Anxiolytic effects are well documented after chronic treatment in

patients (19) but no effects (20), or increased anxiety (21) have been described in animals after acute

administration. The impairing effects of anxiolitics on memory is well established in animals and

humans (22). As anxiolysis is closely correlated to sedation, and &r-en et al. (23) found amitriptyline

the most sedative of nine antidepressants in the average of scores obtained in six animal models of

sedation, sedative effects of amitriptyline were also studied.

In the present study, we have used the elevated plus-maze, an animal model of anxiety (24),

because it provides separate measures of anxiety and activity in the same experimental session.

Female mice were included in the study, not just because it is representative of nature but also

NEUROSCIENCE RESEARCH COMMUNICATIONS, VOL. 31, NO. 3 137

because sex differences in inhibitory avoidance have been reported (25), besides differences in

depression and the effects of antidepressants (26).

MATERIALS AND METHODS Subjects: Forty-eight male and forty-eight female CD1 mice of 42 days of age obtained from

CRIFFA (Lyon, France) were used as experimental subjects. Animals were housed in groups of 4 in standard translucent plastic cages of 27x27~15 cm3 (Panlab S.L., Barcelona, Spain), stored in a temperature controlled room (21 rt 2 “C) and under a reversed light-dark cycle (lights off: 07:30- 19:30 h, local time). Food and tap water were available ad Zibitum. The tests were always carried out during the dark phase of the light-dark cycle. Animals were body-marked for individual recognition. The experimental protocol and the use of animal subjects were in compliance with the European Communities Council Directive of 24 November 1986 (86/609/EEC) and the Spanish Real Decreto 22311988.

Drugs: Amitriptyline Hydrochloride (Sigma-Aldrich Quimica, Madrid, Spain) was diluted in saline solution (0.9O/, NaCl). The mice received an intraperitoneal injection of saline or amitriptyline: 7.5 mg/kg, 15 mg/kg or 30 mg/kg, in a volume of 0.01 ml/g

Apparatus: An inhibitory avoidance box for mice (Ugo Basile, Comerio-Varese, Italy) was used. The cage, made of Perspex sheets, was divided into two sections (15x9.5x16.5 cm3, each) separated by an automatical-sliding door. A light (24 V, 10 W) was always in the ceiling of the starting side, which was painted in white (the other side was black and always remained dark). The floor was made of 48 stainless bars of 0.7 mm in diameter and 8 mm apart. The elevated plus-maze (Cibertec, S.A., Madrid, Spain) was made up of two open (30x5 cm2, each) and two enclosed arrns (30x5~15 cm3, each) extended from a common central square (5x5 cm2) and elevated 50 cm above floor level on five pedestals. The maze floor was made of black Plexiglas while the walls of the enclosed arms were made of clear Plexiglas. The external side of walls were covered with black paper. The open arms had no walls. The illumination in the experimental room consisted of four neon tubes on the ceiling. The video camera recorder employed to record the elevated plus-maze task was a SONY Handycam CCD-TR401 E, Sony Corporation (Tokyo, Japan).

Procedure: The animals were randomly assigned by sex to one of four groups (n = 12): 7.5, 15 or 30 “g/kg of amitriptyline or physiological saline. Training and test of inhibitory avoidance task began with a 90-set adaptation period to the apparatus in the light compartment. The door between the compartments remained closed during this period. In the training phase the door was removed and the mouse could stay in the light side for a maximum of 300 set, but if it entered the dark compartment an inescapable footshock of 0.5 mA was delivered for 5 sec. The time taken to enter the dark compartment, defined as latency, was automatically measured in tenths of a second, and manually recorded after each trial. Then, each mouse received saline or amitriptyline treatment and was returned to its home cage.

The elevated plus-maze procedure took place 45 min after treatment administration. At the start of the session mice were individually placed onto the central square and recorded over a 5-min period via the video camera under white light. After that, the animal was returned to its home cage and the elevated plus-maze was throughly cleaned with alcohol and water.

The number of entries onto open and closed arms (arm entries = all four paws enter an arm) were scored by a trained observer blind as to the group. This provided independent measures of anxiety, i.e. the percentage of open arm entries [(open/open + closed) X 1001, and activity, i.e. the number of closed arm entries. The rationale to select these measures can be found in Pellow et al. (27), Lister (28) and File (24, 29).

138 NEUROSCIENCE RESEARCH COMMUNICATIONS, VOL. 31, NO. 3

The inhibitory avoidance test was carried out 24 h later following the same procedure as indicated above for the inhibitory avoidance training, except that no shock was delivered.

Statistical Analysis: Data from the inhibitory avoidance experiment were subjected, for each sex, to nonparametric Kruskal-Wallis analysis of variance followed by the Mann-Whitney U-test. Wilcoxon matched pairs test was carried out to compare training vs test latencies in each group. Mann-Whitney U-tests were used to compare males and females of the saline groups. The elevated- plus maze behaviours were separately analysed with ANOVA, in which Treatment and Sex were factors, and Newman-Keuls-tests were used as post-hoc analysis. The performance of saline groups was assessed with t-test analyses. All analyses were performed with the “Statistica” software package, version 5.5 for Windows (30).

RESULTS

There were no significant differences in the training in both males, H(3, N = 48) = 0.27, p > .05,

and females, H(3, N = 48) = 0.77, p > .05. In the test, the treatment was statistically significant in

males, H(3, N = 48) = 8.23, p < .05, but not in the case of female mice, H(3, N = 48) = 1.59, p > .05.

The post-hoc analyses indicated that the male 7.5 mg/kg amitriptyline group had significantly shorter

latencies than the saline male group, U = 25, p < .Ol. Comparisons between training vs test latencies

within each group revealed that learning took place, i.e. latencies on test were longer than on training,

in male, T = 11, p < .05, and female, T = 11, p < .05, saline groups, and in 15 mg/kg amitriptyline

female group, T = 6, p < .Ol . The remaining comparisons showed that there were no statistically

significant differences between phases (see Fig 1). The presence of sex differences in inhibitory

avoidance in non-treated mice was tested and no sex differences were found neither in training, U =

56.50, p > .05, nor in test phases, U = 63.00, p > .05.

180 * 1 E!ITFtAlNING

160 G 140 _ 1 ii 120

g 80 f 60 4 40

SAL 7,5 15 30 SAL 7,5 15 30

MALES FEMALES

Fig. 1: Effect of post-training acute administration of saline (SAL) or amitriptyline (7.5, 15 or 30 mgkg) on step-through latencies of an inhibitory avoidance task in male and female mice (median, rt

NEUROSCIENCE RESEARCH COMMUNICATIONS, VOL. 31, NO. 3 139

interquartile range). * p < .05 or ** p < .Ol compared with training (Wilcoxon test); # p < .Ol compared with test latencies of saline group (Mann-Whitney U-test).

In the elevated plus-maze, the analysis of the measure of anxiety, percentage of open arm entries,

showed that neither the main effects nor the interaction were statistically significant: Treatment, F(3,

81) = 0.56,~ > .05, Sex, F(l, 81) = 0.92,~ > .05, Treatment X Sex, F(3, 81) = 1.02,~ > .05. The

degrees of freedom in these analyses appear reduced because two males and five females of the 30

mg/kg amitriptyline groups were discarded in obtaining the percentage (dividing by zero). The

difference between these two proportions, 2/12 and 5/12, was not statistically significant @ > .05).

There were no statistically significant differences between males and females of the saline condition,

t(22) = 1.21, p > ,051. The analysis of activity, closed arm entries, revealed that the Treatment was

highly significant, F(3, 88) = 35.05, p < .OOOOOl. The post-hoc analyses showed that the reduction in

activity was dose-dependent: the comparison of saline vs 7.5 mg/kg amitriptyline did not reach

statistical significance (p = 0.09), the comparisons of saline vs 15 mg/kg or 30 mg/kg amitriptyline

were statistically significant (p < .OOl), the comparison of 7.5 mg/kg vs 15 mg/kg or 30 mg/kg

amitriptyline were statistically significant (p < .OOl), and the comparison of 15 mg/kg vs 30 mg/kg

amitriptyline was statistically significant (p < .Ol) (see Fig 2). There were no statistically significant

differences between males and females, F(l, 88) = 2.72, p > .05. The interaction Treatment X Sex

was not statistically significant, F(3, 88) = 0.44, p > .05, which means that the treatment reduced the

activity of males and females in the same way. In the saline-treated animals there were no sex

differences in this measure, t(22) = 0.5 1, p > .05.

14 - co w 12- z g IO- W E 8- a! 4 69

2 co 4- 0 J 0 2-

0

*

SAL

*

I

795 AMITRIPTYLINE (mglkg)

Fig. 2: Effect of acute administration of saline (SAL) or amitriptyline (7.5, 15 or 30 mg/kg) on number of closed arm entries in the elevated plus-maze test (mean, rf: standard error of mean). * p <

140 NEUROSCIENCE RESEARCH COMMUNICATIONS, VOL. 31, NO. 3

.OOl compared with saline group; # p < .OOl compared with the 15 mg/kg group (Newman-Keuls test).

with the 7.5 mg/kg group; +p < .Ol compared

DISCUSSION

In this work, the effects of amitriptyline on inhibitory avoidance consolidation, and on elevated

plus-maze, have been studied. Both saline-treated males and females showed learning in inhibitory

avoidance: these groups had significantly longer test than training latencies. But the amitriptyline-

treated groups of male and female mice did not significantly increase their crossing latencies in the

test, except for the case of 15 mg/kg female group. There were no sex differences in the saline-treated

animals. In the elevated plus-maze, amitriptyline showed no effect on the percentage of open arm

entries, and a reduction of entries into closed arms in a dose-dependent fashion, which are considered

measures respectively of anxiety and activity (24, 27, 28, 29). No statistically significant sex

differences between saline-treated animals were found in either measure of the elevated plus-maze.

Kumar and Kulkami (3 1) have previously reported an impairing effect of 5 and 10 mg/kg of

amitriptyline, given i.p. after training, in a step-down avoidance procedure in mice. Our results are in

agreement with this study and data from our laboratory (13), these obtained using different apparatus

and strain of subjects (shuttle-box and OF1 mice, respectively).

In rats, amitriptyline administration, i.p. 60 and 30 min before training, produced inhibitory

avoidance acquisition impairment at a dose of 4 mg/kg (32). Other authors have reported results

consistent with those of Shimizu-Sasamata. The latency of step-through inhibitory avoidance in rats

was shortened by i.p. administration of 4 mg/kg of amitriptyline (33), and at the same dose,

amitriptyline potentiated scopolamine-induced memory deficit when administered before step-

through inhibitory avoidance training (34).

Our results show that amitriptyline-blocking effects on inhibitory avoidance consolidation are not

due to the motor effects of the drug, because the drug was administered after training, so that it would

not influence this or the activity in the test phase. This is clear if we take into account that the half-life

of amitriptyline is approximately 3 hours (35) and test was performed 24 hours later. Thus, we

consider that in our experiment this drug only influenced memory consolidation, not performance.

Latencies of saline-treated females were not statistically different from those of saline-treated

males. In spite of the fact that some studies have shown sex differences in inhibitory avoidance in

non-treated animals (e.g. 25), our results (no sex differences) agree with those published by Lamberty

and Gower (36) and Berger-Sweeney et al. (37). In our laboratory, sex differences in inhibitory

NEUROSCIENCE RESEARCH COMMUNICATIONS, VOL. 31, NO. 3 141

avoidance have been observed in some experiments, but not in others. When differences appear

females show higher avoidance latencies than males (e.g. 15).

However, subtle differences between males and females were present in our study. The Kruskal-

Wallis analysis of variance showed effect of treatment in males but not in females, and the Wilcoxon

test showed three amitriptyline doses effective in males, and two in females. These differences are

another example of stronger effects of drugs in male than in female mice. We have found this trend

studying the effects of several neuroleptics on active avoidance (for a review see 38).

The absence of anxiolytic effects of amitriptyline, as assessed. in the elevated plus-maze, is

important in order to explain the characteristics of amnesic effects observed in inhibitory avoidance.

It is interesting to gather evidence that anxiolysis is not involved in the memory impairment effect,

especially because many anxiolytic substances have clear amnesic effects (39). The elevated plus-

maze test is a good behavioural tool to separate influences of drugs on sedation and anxiety.

The clear dose-dependent effect of amitriptyline on activity (see Fig 2), was expected because of

the effect of this drug on spontaneous motor activity (40, 41, 42, 43). A number of animals of the 30

mg/kg amitriptyline groups, two males and five females, did not move from where-they were

positioned at the beginning of the test, i.e. the centre of the elevated plus-maze. This is a consequence

of a strong sedative effect of this dose of amitriptyline. None of the subjects in the other experimental

groups remained for the complete duration of the test in the centre of the apparatus.

The work of Kameyama et al. (40) deserves special comments. Mice that received electric shocks,

showed a marked suppression of motor activity when placed in the same cage 24 hours after the

administration of shock. Acute administration of 5 or 10 mg/kg amitriptyline reduced this conditioned

suppression, i.e. these mice showed more activity than non drug-treated animals. Nevertheless, the

same treatment reduced the motor activity of non-shocked mice. Amitriptyline appears to have

specific learning and memory impairing effects, independently of its effects on spontaneous motor

activity.

Taken together, these data confirmed the amnesic effect of an acute administration of amitriptyline

when given immediately after the inhibitory avoidance training phase, and that this impairment was

observed without detecting anxiolytic effects.

The authors wish to thank Ana J. Martos Mula and Elisa Gimenez for their kind help in the course of this experiment. This investigation was supported by the Generalitat Valenciana, Valencia, Spain (Grant “Antidepressants and memory” GV97-SH-22-89).

142 NEUROSCIENCE RESEARCH COMMUNICATIONS, VOL. 31, NO. 3

REFERENCES

1. Baldessarini RJ. Drugs and the treatment of psychiatric disorders: depression and anxiety disorders. In: Hardman JG, Limbird LE, Gilman AG, editors. Goodman & Gilman’s The pharmacological basis of therapeutics, 10th edition. New York: McGraw-Hi11;2001. p 447-483.

2. Porsolt RD, Le Pichon M, Jalfre M. Depression: a new animal model sensitive to antidepressant treatments. Nature 1977;266:730-2.

3. Lucki I. The forced swimming test as a model for core and component behavioral effects of antidepressant drugs. Behav Pharmacol 1997;8:523-32.

4. De Pablo JM, Parra A, Segovia S, Guillamon A. Learned immobility explains the behavior of rats in the forced swimming test. Physiol Behav. 1989;46:229-37.

5. Martos AJ, Vinader-Caerols C, Monleon S, Arenas MC, Parra A. Efectos de la fisostigmina y de la nicotina sobre la inmovilidad aprendida en la prueba de natacion forzada. Psicothema 1999; 11:63 l-9.

6. Parra A, Vinader-Caerols C, Monleon S, Simon VM. The learned immobility is also involved in the forced swimming test in mice. Psicothema 1999; 11:239-46.

7. Dujardin K, Guerrien A, Leconte P. Sleep, brain activation and cognition. Physiol Behav 1990;47:1271-8.

8. Mondadori C, Waser P.G, Huston J.P. Time-dependent effects of post-trial reinforcement, punishment or ECS on passive avoidance learning. Physiol Behav 1977; 18: 1103-9.

9. Parra press).

A. A common role for psychotropic medications: memory impairment. Med Hypotheses (in

10. Antikainen R, Hanninen T, Honkalampi IS, Hintikka J, Koivumaa-Honkanen H, Tanskanen A, Viinamaki H. Mood improvement reduces memory complaints in depressed patients. Eur Arch Psychiatry Clin Neurosci 200 1;25 1:6- 11.

11. Riedel WJ, van Praag HIM. Avoiding and managing anticholinergic effects of antidepressants. CNS Drugs 1995;3:245-59.

12. Yousef G, Ryan WJ, Lambert T, Pitt B, Kellett J. A preliminary report: a new scale to identify the pseudodementia syndrome. Int J Geriatr Psychiatry 1998; 13:389-99.

13. Everss E, Arenas MC, Vinader-Caerols C, Monleon S, Parra A. Effects of amitriptyline on memory consolidation in male and female mice. Med Sci Res 1999;27:237-9.

14. Parra A, Martos A, Monleon S, Arenas MC, Vinader-Caerols C. Effects of acute and chronic maprotiline administration on inhibitory avoidance in male mice. Behav Brain Res 2000; 109: l-7.

15. Monleon S, Casino A, Vinader-Caerols C, Arenas MC. Acute effects of fluoxetine on inhibitory avoidance consolidation in male and female OF1 mice. Neurosci Res Commun 2001;28: 123-30.

16. Monleon S, Urquiza A, Arenas MC, Vinader-Caerols C, Parra A. Chronic administration of fluoxetine impairs inhibitory avoidance in male but not female mice. Behav Brain Res (in press).

17. Gold PE. The use of avoidance training in studies of modulation of memory storage. Behav Neural Biol 1986;46:87-98.

18. Stahl SM. Basic psychopharmacology of antidepressants. Part 1: Antidepressants have seven distinct mechanism of action. J Clin Psychiat 1998;59:5-14.

19. Feighner JP. Overview of antidepressants currently used to treat anxiety disorders. J Clin Psychiatry. 1999;60 Suppl22: 18-22.

NEUROSCIENCE RESEARCH COMMUNICATIONS, VOL. 31, NO. 3 143

20. Zethof TJ, Van der Heyden JA, Tolboom JT, Olivier B. Stress-induced hyperthermia as a putative anxiety model. Eur J Pharmacol. 1995;294: 125-35.

21. Bodnoff SR, Suranyi-Cadotte B, Quirion R, Meaney MJ. A comparison of the effects of diazepam versus several typical and atypical anti-depressant drugs in an animal model of anxiety. Psychopharmacology (Berl). 1989;97:277-9.

22. Griffiths RR, Weerts EM. Benzodiazepine self-administration in humans and laboratory animals-- implications for problems of long-term use and abuse. Psychopharmacology (Berl). 1997; 134: l-37.

23. &i-en SO, Cott JM, Hall H. Sedative/anxiolytic effects of antidepressants in animals. Acta Psychiatr Stand Suppl 198 1;290:277-88.

24. File SE. Factors controlling measures of anxiety and responses to novelty in the mouse. Behav Brain Res 2001;125:151-7.

25. Heinsbroek R, Feenstra M, Boon P, van Haaren F, van de Poll N. Sex differences in passive avoidance depend on the integrity of the central serotoninergic system. Pharmacol Biochem Behav 1988;3 1:499-503.

26. Frackiewicz EJ, Sramek JJ, Cutler NR. Gender differences in depression and antidepressant pharmacokinetics and adverse events. Ann Pharmacother 2000;34:80-8.

27. Pellow S, Chopin P, File S, Briley M. Validation of open:closed arm entries in an elevated plus- maze as a measure of anxiety in the rat. J Neurosci Meth 1985; 14: 149-67. . 28. Lister RG. The use of a plus-maze to measure anxiety in the mouse. Psychopharmacology 1987;92:180-5.

29. File SE. Behavioural detection of anxiolitic action. In: Elliot JM, Heal DJ, Marsden CA, editors. Experimental approaches to anxiety and depression. Chichester: John Wiley & Sons, 1992, p 25-44.

30. StatSoft Inc. STATISTICA for Windows [Computer program manual]. Tulsa, OK: StatSoft Inc., 2000.

3 1. Kumar S, Kulkami SK. Influence of antidepressant drugs on learning and memory paradigms in mice. Indian J Exp Biol 1996;34:43 l-5.

32. Shimizu-Sasamata M, Yamamoto M, Harada M. Cerebral activating properties of indeloxazine HCl and its optical isomers. Pharmacol Biochem Behav 1993;45:335-41.

33. Takahashi K, Yamamoto M, Suzuki M, Ozawa Y, Yamaguchi T, Andoh H, Ishikawa K. Effects of cerebral metabolic enhancers on brain function in rodents. Curr Ther Res 1995;56:478-85.

34. Yamaguchi T, Takahashi K, Suzuki M, Yamamoto M, Andoh H, Ishikawa K. Effects of indeloxazine hydrochloride, a cerebral activator, on brain function in rodents. Curr Ther Res 1995;56:436-43.

35. Coudore F, Fialip J, Eschalier A, Lavarenne J. Plasma and brain pharmacokinetics of amitriptyline and its dmethylated and hydroxylated metabolites after acute intraperitoneal injection in mice. Eur J Drug Metab Ph 1994; 19:5-l 1.

36. Lamberty Y, Gower AJ. Investigation into sex-related differences in locomotor activity, place learning and passive avoidance responding in NMRI mice. Physiol Behav 1988;44:787-90.

37. Berger-Sweeney J, Arnold A, Gabeau D, Mills J. Sex differences in learning and memory in mice: effects of sequence of testing and cholinergic blockade. Behav Neurosci 1995;5:859-73.

144 NEUROSCIENCE RESEARCH COMMUNICATIONS, VOL. 31, NO. 3

38. Parra A, Arenas MC, Monleon S, Vinader-Caerols C, Simon VM. Sex differences in the effects of neuroleptics on escape-avoidance behavior in mice: A review. Pharmacol. Biochem Behav 1999;64:813-20.

39. Izquierdo I, Medina JH. GABAA receptor modulation of memory: the role of endogenous benzodiazepines. Trends Pharmacol Sci 199 1; 12:260-5.

40. Kameyama T, Nagasaka M, Yamada K. Effects of antidepressant drugs on a quickly-learned conditioned-suppression response in mice. Neuropharmacology 1985;24:285-90.

41. Casas J, Gilbert-Rahola J, Chover AJ, Mica JA. Test-dependent relationship of the antidepressant and analgesic effects of amitriptyline. Meth Find Exp Clin Pharmacol 1995;17: 583-8.

42. Pavone F, Battaglia M, Sansone M. Prevention of amitriptyline-induced avoidance impairment by tacrine in mice. Behav. Brain Res 1997;89:229-36.

43. Brocco M, Dekeyne A, Veiga S, Girardon S, Millan MJ. Induction of hyperlocomotion in mice exposed to a novel environment by inhibition of serotonin reuptake. A pharmacological characterization of diverse classes of antidepressant agents. Pharmacol Biochem Behav 2002;71:667- 80.