ISSN 1916-6958

2010; Volume 1 (Number 2): Pages 62-71

ORIGINAL RESEARCH

Behavioral
and neurochemical evaluation in rats withdrawn from
repeated cocaine treatment and exposed to the forced swimming and open field
tests

Maria Izabel GOMES SILVA, Maria do Carmo DE Oliveira Citó,  Jeferson FALCÃO DO AMARAL, Manuel Rufino DE
AQUINO NETO, Brinell ARCANJO MOURA, Patrícia FREIRE DE VASCONCELOS, Silvânia
Maria MENDES DE VASCONCELOS, Marta Maria DE FRANÇA FONTELES, Glauce Socorro DE
BARROS VIANA, Danielle SILVEIRA MACÊDO and Francisca Cléa FLORENÇO DE SOUSA*

Department of Physiology and Pharmacology, Faculty of Medicine,

Federal University of Ceará, Fortaleza, Brazil

*Corresponding author:
[email-masked]; [email-masked]

ABSTRACT

Objective:
We aimed to investigate possible behavioral
alterations in the forced swimming (FST) and open field tests (OFT), and
monoamine level changes in rats withdrawn for one and seven days from repeated
cocaine administration. Methods:
Animals were treated once a day during a week with cocaine 20 mg kg-1
or saline (control), intraperitoneally. Following one or seven days of cocaine
administration, animals were submitted to the FST or OFT, while another one was
decapitated and their brain striatum was removed for determination of dopamine
(DA) and serotonin (5-HT) and their metabolites levels determined by HPLC
analysis. Results: Cocaine was able
to induce a significant decrease in the immobility time of animals in FST and a
significant increase in the exploratory activity in OFT after both withdrawal
times. During the abstinence periods, monoamine levels were significantly
increased, while DA and 5-HT turnovers were decreased. Conclusions: Results indicate that 20 mg kg-1 of cocaine
administered during 7 consecutive days to rats were not sufficiently able to
promote depression-like symptoms 24 h or 7 days after treatment
discontinuation.

Key words

Animal models; Biogenic monoamines; Drug
withdrawal symptoms

RÉSUMÉ

Objectif: Investigation des altérations possibles du
comportement lors des tests de natation forcée (TNF) et de champ ouvert (TCO)
et du taux des monoamines chez des rats un et sept jours après administration
répétée de cocaïne. Méthodes: Les
animaux ont reçu une fois par jour pendant une semaine 20 mg kg-1 de
cocaïne ou du sérum physiologique (témoin) en i.p. Après un ou sept jours
d’administration de cocaïne les animaux ont été soumis au TNF ou au TCO, ou ont
été décapités pour analyse par HPLC des taux de dopamine (DA), de sérotonine
(5-HT) et de leurs métabolites dans le striatum. Résultats: La cocaïne entraîne une réduction significative du temps
d’immobilité des animaux lors du TNF et une augmentation significative de
l’activité exploratrice lors du TCO, lors des deux périodes de sevrage. Lors
des périodes d’abstinence le taux des monoamines est significativement augmenté
et le renouvellement de DA et de 5-HT est réduit. Conclusions: L’administration de 20 mg kg-1 de cocaïne à
des rats pendant 7 jours consécutifs n’est pas suffisante pour produire des
symptômes de dépression 24 h ou 7 jours après l’arrêt du traitement.

Mots clés

Modèles animaux;
Monoamines biogéniques; Symptômes de sevrage

RESUMEN

Objetivo: Investigar las posibles alteraciones
conductuales posibles en las pruebas de natación forzada (forced swimming test;
FST) y de campo abierto (open field test; OFT) así como también en los niveles
de monoaminas en ratas a las cuales se les retiró el consumo de cocaína después
de uno y siete días de administración repetida de cocaína. Métodos: Los animales recibieron diariamente una dosis única de cocaína
(20 mg kg-1) o solución salina (control), intraperitonealmente.
Después de uno o siete días de la última administración de cocaína, diferentes
grupos de animales fueron sometidos a la
FST o a la
OFT. Otro grupo fue sacrificado y el cerebro (cuerpo
estriado) fue removido para cuantificación de dopamina (DA) y serotonina (5-HT)
y sus metabolitos por HPLC. Resultados:
La administración de cocaína indujo una disminución significativa en el tiempo
de inmovilidad de los animales en la
FST y un aumento significativo en la actividad exploratoria
en la OFT tanto
al día uno como al séptimo post-administración de cocaína. Durante los períodos
de abstinencia, los niveles de monoaminas aumentaron significativamente,
mientras que el metabolismo de DA y 5-HT disminuyó. Conclusión: Los resultados indican que 20 mg kg-1 de
cocaína administrada durante 7 días consecutivos en ratas, no fueron
suficientes para producir síntomas de depresión 24 h ó 7 días después de
descontinuar el tratamiento.

Palabras clave

Modelos
animales; Monoaminas biogénicas; Síntomas de abstinencia a drogas

INTRODUCTION

Cocaine addiction has been a serious
medical and social problem in recent years and intensive research has been
carried out in an attempt to explain the behavioral and neurobiological bases
of its development [1] [2] [3]. Previous studies using animal and human models have
shown that cocaine withdrawal is often accompanied by a collection of symptoms
including depression, anxiety, fatigue, and psychomotor retardation or
agitation [4]. As a result, there is a high likelihood of relapse
following prolonged periods of withdrawal [4] [5]. Such behavioral consequences have been credited to
induced changes in neurotransmitters, with the dopaminergic system represented
as the most responsible for the adverse effects of abstinence to cocaine [6] [7] [8]. Nevertheless, the serotonergic system also fulfills
an important role in functional cocaine effects [1] [9] [10] [11].

Neurobiological studies in literature about
withdrawal from cocaine administration are still conflicting. Results obtained
through a combination of behavioral animal models and microdialysis have
demonstrated that cocaine administration to rats concomitantly produced a
progressive augmentation in motor activity (known as behavioral sensitization)
and elevated DA and 5-HT release in the nucleus accumbens after discontinuing
daily treatments [1] [12] [13].

On the other hand, evidence for decreased
dopaminergic and serotonergic function during the withdrawal syndromes are also
associated with cocaine use [14]. In contrast, in a study by Alburgues et al. [6], the concentration of monoamines was monitored (using
HPLC-ECD) in rat central nervous system, following a dose schedule of 5, 10,
15, 20 and 25 mg kg-1, intraperitoneally (i.p.), for 21 days; 12 h
after the last cocaine injection, cortical and striatal concentrations of
monoamines and their metabolites were not significantly different in saline
versus cocaine-treated animals.

Since cocaine withdrawal can be associated
with symptoms of depression, some studies have also evaluated the behavioral
effects of animals treated with cocaine following forced swimming test [15] [16]. Among all animal models, the forced swimming test remains
one of the most used tools for evaluate antidepressants drug effects [17]. In this test, drugs with established antidepressant
activity, such as imipramine, reduce the time during which the animals remain
immobile, while depressant drugs exert opposite effects [18].

Hayase et al. [15], using forced swimming test (FST),  demonstrated that cocaine administered acutely,
at high doses (75 mg kg-1 i.p), promoted an acceleration of
behavioral despair in the Porsolt test similar to that observed in the
imipramine group after the disappearance of the acute toxic symptoms (5 h after
treatment).

In a subsequent study, Hayase et al. [16] verified increased immobility in the FST (depression
behavior) 12 h after large doses of cocaine (60 mg kg-1, i.p.) were
acutely administered. In addition, Grasing & Ghosh [14] have reported similar increase of immobility duration
in the FST during withdrawal from long-term amphetamine treatment, a
psychostimulant drug similar to cocaine. These behavioral effects were also
observed in the animals receiving large doses of amphetamine. Therefore,
studies using the FST to investigate possible changes occurring after
long-lasting withdrawal periods from repeated cocaine at lower doses are scarce
in literature.

Thus, it is hoped that additional
preclinical investigation about behavioral and neurobiological changes that
persist after cocaine discontinuation can be fundamental to understand the
mechanisms involved in addiction and craving. In the present study we investigated
possible behavioral and monoamine-level changes in rats one and seven days
after cocaine withdrawal.

MATERIALS AND METHODS

Animals

Male Wistar rats (180-200 g) were used in each
experiment and were maintained at a controlled temperature (23 ± 1°C) with a 12 h
dark/light cycle and free access to water and food. Animals were treated in
accordance to the current law and the NIH Guide for Care and Use of Laboratory
Animals and the study was performed under the consent and surveillance of the
Committee of Ethics in Animal Research, Department of Physiology and
Pharmacology, Faculty of Medicine, Federal University of Ceará, Brazil.

Drugs and Experimental Protocol

Cocaine (donated from the Federal Police of
Ceará State and checked for purity by the Chemistry Department of Federal
University of Ceará) was dissolved in distilled water and administered i.p. to
the test groups. Imipramine (IMP) 10 mg kg-1 (Geigy) and diazepam (DZP)
2 mg kg-1 (União Química/Brazil) were dissolved in distilled water
and injected i.p. prior the FST and OFT, respectively, as standard drugs (Table
1). All the control animals received saline.

Forty rats were treated once a day for 7
consecutive days with cocaine i.p. 20 mg kg-1 and 40 other rats were
treated with saline i.p. (control). On day 1 and 7 after the last cocaine
administration, two distinct groups of animals (n= 10, each group) were
submitted to the FST or OFT (Table 1). Similar
procedures were performed to the rats treated with saline. Imipramine (10 mg kg-1)
or diazepam (2 mg kg-1) was administered i.p. 30 minutes prior to
the respective FST or OFT tests.

Another group of rats was similarly treated
with cocaine, and 24 h (n= 8) or 7 days (n= 8) after the last administration,
animals were decapitated and their brain striatum removed for determination of
monoamines and metabolites levels (Table 1). Similar
procedures were performed to another set of rats treated with saline.

Table
1

Experimental
Protocol

Treatments

Treatment

period

Behavioral
tests

Forced Swimming Testa

Open Field Testb

Group
1 (n= 10)

Group
2 (n= 10)

Group
3 (n= 10)

Group
4 (n= 10)

24
h after the last administration

7
d after the last administration

24
h after the last administration

7
d after the last administration

Saline
(control)

7
days

X

X

X

X

Cocaine
(20 mg kg-1)

7
days

X

X

X

X

Animals
received either aimipramine (10 mg kg-1) or bdiazepam
(2 mg kg-1) i.p., 30 min prior the tests

Monoamines and metabolites
levelsc

Treatments

Treatment

period

Group
5 (n= 8)

Group
6 (n= 8)

24
h after the last administration

7
d after the last administration

Saline
(control)

7 days

X

X

Cocaine  (20 mg kg-1)

7 days

X

X

cAnimals
were decapitated and monoamine and metabolite levels were obtained in the brain
striatum.

Forced Swimming Test

The Porsolt et al. [18] swimming test includes two exposures to a water tank,
spaced 1 day apart. For the experiments, a vertical glass cylinder (diameter 22.5 cm and height 60 cm) containing about 35 cm water at 25ºC was used.
During the first exposure, rats were placed in the cylinder and monitored for
15 min. During the second exposure (test session), animals were placed in the
tank and monitored for 5 min during which immobility time was registered.

A rat was considered immobile when it
remained floating in the water, without struggling, making only very slight
movements necessary to keep its head above water. This prolonged floating time
(immobility time) during the second exposure to the tank has been interpreted
by Porsolt as reflecting the animal’s state of despair [17], elicited by the inescapable nature of the tank,
which was learned during pretest. Drugs with antidepressant activity reduce
that parameter (immobility time), while depressant ones exert opposite effects.

The animals were divided into four groups
(Control, COC-24h, COC-7d and IMI-10) of 8-10 animals per group. Each animal
was used only once.

Open Field Test

The open-field area was made of acrylic,
with transparent walls, black floor and divided into nine squares of equal
area. This apparatus was used to evaluate the exploratory activity of the
animal [19]. The
observed parameter was the number of squares crossed (with the four paws)
during five minutes.

HPLC Analysis

The striatum of control animals (n= 10) and
cocaine group (n= 7) were used for the preparation of a 10% homogenate (10%,
w/v). Brain tissue samples were sonicated in 0.5–1 mL of 0.1 M perchloric acid (HClO4,
Qeel, SP, Brazil)
for 30 s and centrifuged for 15 min at 26.000 g,
at 4ºC. Then, a 20 μL supernatant aliquot was injected directly
into the high performance liquid chromatography (HPLC) column. For the
monoamines analyses, a CLC-ODS (M) Shimadzu column was used. The mobile phase
was 0.163 M  citric acid (Vetec, RJ, Brazil), pH 3.0,
containing 0.02mM of ethylenediaminetetraacetic acid (EDTA, Vetec, RJ, Brazil),
with 0.69mM sodium octanesulfonic acid (SOS-Sigma, St. Louis, MO, USA), as ion
pairing reagent, 4% (v/v) acetonitrile (Carlo Erba Reagenti, MI, Italy) and
1.7% (v/v) tetrahydrofurane (Sigma). Dopamine (DA),
4-hydroxy-3-methoxy-phenylacetic acid (DOPAC), serotonin (5-HT),
5-hydroxyindoleacetic acid (5-HIAA) and homovanilic acid (HVA) were
electrochemically detected using an amperometric detector (Model L-ECD-6A;
Shimadzu Corp., Japan)
by oxidation on a glassy carbon electrode at 0.85V relative to an Ag–AgCl
reference electrode.

Amounts of neurotransmitters and
metabolites in the supernatants were calculated by comparing their peak heights
with that of standards determined the same day. Additionally, DA turnover was
expressed as the ratio of DOPAC/DA (intracellular DA turnover) or HVA/DA
(extracellular DA turnover), while 5-HT turnover as the ratio of 5-HT/5-HIAA.

Statistical analyses

All results are presented as mean ± S.E.M.
Data were analyzed by ANOVA followed by Student-Newman-Keuls
post-hoc test or by Student-t test. Results were considered significant at
p<0.05.

RESULTS

Cocaine was able to induce a significant
decrease in the immobility time in rats, as compared to control group (Figure 1). Imipramine, as expected of an anti-depressive
drug, promoted similar effects [F(3,33)= 41.1; P <0.001].

In relation to monoamine levels (Figure 2), there was a significant 42% [T(10)= 3.2; P
<0.01] and 37% [T(12)= 4.9; P <0.001] increase in
DA levels one and seven days after the last cocaine administration,
respectively, as compared to control animals. A decrease of 28% [T(10)= 4.0; P
<0.01] and 32% [T(11)= 5.3; P <0.001] was observed in DOPAC levels, while
HVA was decreased by 30% [T(10)= 3.3; P <0.01] and 44% [T(11)= 4.7; P <0.001]
following both withdrawals periods, respectively. Similar to the DA, 5-HT
levels increased by 102% [T(9)= 3.2; P <0.01] and 346% (T(9)= 12.9; P
<0.001) one and seven days after the last cocaine administration, as
compared to control, respectively. Its metabolite, 5-HIAA, also increased 45%
[T(10)= 3.7; P <0.01] and 31% [T(9)= 3.2; P <0.05], respectively, after
both periods. Table 2 shows the DA and 5-HT turnover;
the DOPAC/DA ratio was decreased 50% [T(8)= 5.6; P <0.001] from control
following one abstinence day and 51%
[T(10)= 6.9; P <0.001] after seven abstinence days. A decrease of 53%
[T(8)= 5.4; P <0.001 t=5.4 df=8] and 58% [T(10)= 6.5; P <0.001] was
observed in the HVA/DA ratio following both withdrawal times, respectively.
5-HIAA/5-HT ratio was decreased by 32% [T(9)= 2.4; P <0.5] and 73%  [T(9)= 5.5; P <0.001] following one and
seven days after the last cocaine administration, respectively.

Withdrawal times

(20 mg kg-1)

Figure 1

Forced swimming of groups of rat that
received saline solution (control), cocaine 20 mg kg-1 (COC-24h
and COC-7d) or imipramine 10 mg kg-1 (IMI-10). Animals received
cocaine (20 mg kg-1) during 7 days and were withdrawn one (COC-24h)
or seven (COC-7d) days after the last cocaine administration. The figure
shows immobility time (seconds) and results are presented as mean ± S.E.M.
Significant difference compared with control: ***P<0.001; ANOVA followed
by post-hoc Student-Newman-Keuls test.

Table 2

Determination
of DA and 5-HT turnover from monoamines levels and their metabolites

Monoamines
turnover one and seven days after

repeated cocaine (20
mg kg-1) discontinuation

Ratio
of Monoamines and their metabolites

Control

COC-24h

Control

COC-7d

DOPAC/DA

0.92 ±
0. 075

0.45 ±
0.037**

0.
91 ±
0.059

0.44
±
0.031**

HVA/DA

0.43 ±
0.041

0.20 ±
0.010**

0.42
±
0.036

0.17
±
0.010**

5-HIAA/5-HT

4.95 ±
0.685

3.34 ±
0.199*

4.49
±
0,653

1.20
±
0.037**

DA
turnover was expressed as the ratio of DOPAC/DA (intracellular DA turnover)
or HVA/DA (extracellular DA turnover), while 5-HT turnover as the ratio of
5-HT/5-HIAA.

DA=
dopamine, DOPAC= acid dihidroxifenilacetic, HVA= acid homovanilic, 5-HT=
serotonin, 5-HIAA= acid 5-hidroxiindolacetic.

The
results are presented as mean ± S.E.M. *P<0.05; **P<0.001; significant
difference compared with control (Student t test).

DA

DOPAC

HVA

5-HT

5-HIAA

Figure 2

Determination
of monoamine levels and their metabolites in striatum of rats 24h and 7 days after
the last cocaine administration. Animals received cocaine (20 mg kg-1)
or saline, i.p., during seven days. DA: dopamine, DOPAC: acid
dihidroxifenilacetic, HVA: acid homovanilic, 5-HT: serotonin, 5-HIAA: acid
5-hidroxiindolacetic.

The
results are presented as mean ± S.E.M. *P<0.05; **P<0.01;
***P<0.001; significant differences compared with control (Student t
test).

Effects of cocaine or diazepam in the OFT
are presented in Figure 3. Both withdrawal times (one
and seven days) from repeated cocaine treatment increased the number of
crossings compared to controls; this parameter decreased in animals treated
with diazepam (2 mg kg-1) [F(3,49)= 41.0, P <0.05].

Withdrawal times

(20mg kg-1)

Figure 3

Open-field
test of groups of rat which received saline (control), cocaine 20 mg kg-1
(COC-24h and COC-7d) or DZP (2 mg kg-1). Animals received cocaine
(20 mg kg-1) during 7 days and were withdrawn one (COC-24h) or
seven (COC-7d) days after the last cocaine administration. The results are
presented as mean ± S.E.M.

Significant
difference compared with control: *P <0.05; **P <0.01; *** P <0.001;
ANOVA followed by post-hoc
Student-Newman-Keuls test.

DISCUSSION

It is well established that cocaine exerts
its action through binding with monoamine presynaptic plasma membrane
transporters, and blocking their uptake [20]. Therefore, behavioral effects of drug use have been
related to the increase in extraneuronal levels of DA and 5-HT in central
nervous system (CNS) [21] [22]. On the other hand, both preclinical and human data
suggest that depression symptoms from repeated cocaine withdrawal are the most
aggravated, indicating a drop or disruption of DA and 5-HT neurotransmission
secondary to cocaine withdrawal [1] [23].

In this way, the present study investigated
whether significant behavioral or monoamine level changes could be observed in
rats treated with cocaine, at 20 mg kg-1 dose, following two different
withdrawal times.

FST was developed by Porsolt in rats and
mice and is the most widely used tool for assessing antidepressant activity in
a preclinical setting [24]. In
addition, this test has been exploited for assessing animal models of
depression induced by pharmacological manipulation [25]. Our results from FST showed that rats treated with
cocaine (20 mg kg-1) during seven consecutive days, displayed significantly
increased mobility (i.e. spent more time swimming) one day after drug
abstinence, demonstrating a nonspecific anti-immobility effect related to
hyperactivity.

These findings did not agree with those
showed by Hayase and collaborators [16], who verified depressive behavior in FST 12h after
cocaine treatment. However, those authors used a much higher drug dose (60 mg
kg-1 i.p) as compared to that used in present study, and treatments using high doses may induce
severe behavioral, neurochemical, and anatomical adaptations leading to a more
pronounced withdrawal syndrome, including measurable depression-like behavioral
changes [26].

Although our
results oppose the general assumption that cocaine withdrawal induces
behavioral markers of depression-like states, they are in accord with those of Erhardt et al. [27], who reported that mice acutely treated with cocaine
5, 10 and 20 mg kg-1 presented higher locomotion in FST 1, 5 and 24h
after the treatment. Also, similar results were observed between our findings
and those reported by Hédou and collaborators [26]. These authors demonstrated that 2 days of withdrawal from the repeated
administration of cocaine over a 5-day period were not able to induce
depressive-like behavior in rats in FST.

Grasing
and Ghosh [14] showed that opiate withdrawal increased immobility in
response to a forced warm water swim test performed during the second and third
weeks of abstinence following the withdrawal. Such behavioral alterations were
related to long-term changes in dopaminergic function following opiate
withdrawal.

As both cocaine and opiates present similar
action and addiction mechanisms, we decided to investigate whether a larger
period of cocaine abstinence would also be able to promote behavioral changes
in animals submitted to FST, as observed with opiates [14]. Similar to initial findings in this study after one
day of abstinence, animals also significantly increased mobility in the FST
following seven days of cocaine discontinuation. Taken together, our results
suggest that, possibly, 20 mg kg-1 of cocaine administered during 7
consecutive days were not sufficiently able to promote depression-like symptoms
24h or 7 days after treatment discontinuation.

The two neurotransmitter systems that may
be most critically involved in the association between depression and stimulant
dependence may be serotonin and dopamine [11], and it is well known that the striatum is the main
site of cocaine’s action in the brain [8]. Therefore, to corroborate the behavioral changes
observed in the forced swimming test, we decided to also quantify monoamine (DA
and 5-HT) and metabolite (DOPAC, HVA and 5-HIAA, respectively) levels in brain
striatum of rats submitted to the same treatment regime and period of
withdrawal previously described. In order to avoid possible monoamine level
alterations related to stress from FST [28], we resolved to use a distinct animal group for
quantifying monoamines.

Results obtained by HPLC analysis showed an
increase in DA and 5-HT levels in rats’ brain striatum one and seven days after
the cocaine discontinuation, while a decrease was seen in DOPAC and HVA
metabolites in both abstinence periods, and 5-HIAA was increased. Our findings
are in disagreement with studies which present evidence for decreased
dopaminergic and serotonergic function during the withdrawal syndromes [14], as well as to those that report lack of change in
basal monoamines after cessation of cocaine treatment [6]. On the other hand, our results are in accordance
with some studies which have assumed that DA and 5-HT release is elevated in
the nucleus accumbens after long-lasting cocaine discontinuation [12] and also corroborate with the behavioral alterations
initially observed in the present study in FST.

The major theory of depressive disorder,
the monoamine hypothesis, proposes that decreasing the levels of one or more of
the brain monoamine neurotransmitters, such as 5-HT, noradrenaline, or DA, can
produce such disturbances [24]. Therefore, the increase of monoamines observed in
present study one and seven days after cocaine discontinuation supports our
hypothesis generated from FST, that cocaine at relatively low doses is not
enough to promote depression symptoms after short abstinence periods.

In order to understand, at least in part,
the potential mechanism that may underlie the increased monoamine levels
measured by HPLC analysis, we determined the intracellular and extracellular DA
turnover, as well as 5-HT turnover. Our results showed decreased DA and 5-HT
turnover in both withdrawal times observed. Such decrease in monoamine turnover
can begin to explain the increased monoamine levels detected in present study.
It is known that cocaine blocks
the uptake of monoamines during
administration and, therefore, there is an increase in extracellular levels of
these neurotransmitters [21]. However,
prolonged blockade of reuptake may cause depletion of monoamines [6].

Thus, it is reasonable to hypothesize that,
at the pharmacological scheme evaluated herein, a decreased monoamine
degradation could be occurring in the abstinence periods as a compensatory
mechanism to the blockade in the reuptake of neurotransmitters promoted by
repeated administrations of cocaine.

Data from literature show that drugs that
increase general motor activity may provide significantly less immobility in
FST [29]. In order to test our previous hypothesis, we decided
to study the effects of early (one day) and long last (seven days) withdrawal
from repeated cocaine intake by monitoring the number of squares crossed on
open-field test, a classical animal model used to evaluate autonomic effects of
drugs and general activity of animals [30].

Our study showed that in both abstinence
times cocaine significantly increased the motor activity in animals,
differently from DZP (2 mg kg-1), which decreased this parameter.
Therefore, the effects previously observed in FST are based on the stimulation
of general motor activity, suggesting that animals stayed stimulated one and
seven days following the cocaine abstinence, probably due to elevated
monoamines levels observed in both withdraw periods.

CONCLUSION

In summary, animals did not present
depressant-like behavior in FST and OFT and monoamine levels remained increased
24 h and 7 days after discontinuation from cocaine (20 mg kg-1)
sub-chronic treatment, suggesting that such therapeutic scheme and abstinence
periods were not enough to promote depression symptoms in animals. Thus, the
critical dosage and treatment duration to induce a withdrawal syndrome detectable by the FST and OFT
requires further investigation.

AUTHORS’ PARTICIPATION

MI GS, MC dOC & FC FdS designed
the study; MI GS, MR
AN, BA M, MM dFF & D SM performed the
behavioral experiments;
MI GS, MC dOC, J FdA, SM MdV & P FdV performed
the neurochemical experiments; MI GS drafted the manuscript; GS dBV & FC FdS
guided and reviewed the manuscript.

ACKNOWLEDGEMENTS

The authors are thankful to the CNPq and
CAPES for financial support.

CONFLICT OF INTERESTS/DISCLAIMERS

FC FdS is member of the Editorial Board.
There are no other conflicts of interests to declare.

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