Short communication
Effect of combined treatment with mirtazapine and risperidone on the MK-801-induced changes in the object recognition test in mice
Zofia Rogó¿
Department of Pharmacology, Institute of Pharmacology, Polish Academy of Sciences, Smêtna 12, PL 31-343 Kraków, Poland
Correspondence: Zofia Rogó¿, e-mail: rogoz@if-pan.krakow.pl
Abstract:
Background: Several clinical reports have suggested that the mirtazapine-induced augmentation of risperidone activity may effec- tively improve treatment of the negative and certain cognitive symptoms of schizophrenia.
Methods: The aim of the present study was to evaluate the effect of mirtazapine and risperidone, given separately or jointly, on the impact of MK-801(an NMDA receptor antagonist), given prior to the first introductory session, on the object recognition memory in mice. To this end, we used the object recognition test in which animals were tested for the ability to discriminate between an old, fa- miliar and a novel object. Mirtazapine (2.5 or 5 mg/kg) and risperidone (0.01 mg/kg) were given 30 min before MK-801, and MK-801 (0.1 or 0.2 mg/kg) was administered 30 min before the first introductory session. Memory retention was evaluated 1.5 h after the introductory session.
Results: The obtained results showed that MK-801 (0.2 mg/kg) decreased memory retention when given before the introductory session. Co-treatment with risperidone (0.01 mg/kg) and mirtazapine (2.5 or 5 mg/kg) abolished the effect of MK-801, whereas those drugs given separately did not change the action of MK-801.
Conclusions: The obtained results suggest that mirtazapine may enhance the antipsychotic-like effect of risperidone in the animal test modeling some cognitive symptoms of schizophrenia. Further studies are necessary to elucidate its mechanism of action.
Key words:
mirtazapine, risperidone, MK-801, object recognition test, mice
Introduction
Several clinical and preclinical studies have suggested that some atypical antipsychotic drugs (e.g., risperi- done, olanzapine, aripiprazole) alleviate not only positive symptoms of schizophrenia, but also negative ones (e.g., flat affect, poverty of speech); furthermore, they bring considerable benefit compared to the typi- cal antipsychotic drugs [3, 7, 11]. Additionally, the role of antidepressant drugs as adjuncts to the treat-
ment of schizophrenic patients with negative symp- toms has been described by several authors [8, 16].
Atypical antipsychotic agents, e.g., risperidone, whose low doses block mainly serotonin 5-HT2Areceptors and higher dopamine D2 ones [12, 15], are known to produce minimal extrapyramidal side-effects com- pared to classic antipsychotics. Moreover, it has also been shown that mirtazapine, a novel antidepressant, enhances noradrenergic and 5-HT1A-mediated seroto- nergic neurotransmission by antagonizing central a2-auto- and hetero-adrenoreceptors, but does not in-
Pharmacological Reports 2013, 65, 14011406 ISSN 1734-1140
Copyright © 2013 by Institute of Pharmacology Polish Academy of Sciences
finity for histamine H1ones [5]. Some clinical reports have suggested that the mirtazapine-induced augmen- tation of risperidone activity may show therapeutic ef- ficacy against both negative and some cognitive symptoms of schizophrenia [1, 4, 18, 19]. On the other hand, Berk et al. [2] demonstrated that the ad- junctive mirtazapine was not superior to an adjunctive placebo when used with atypical antipsychotics.
Hence, the role of antidepressants in general and of mirtazapine in particular, in the treatment of schizo- phrenia is still unclear.
The role of glutamate in memory processes has been widely examined, and there is a substantial evi- dence for an involvement of N-methyl-D-aspartate (NMDA) receptors in memory and learning, espe- cially with respect to the encoding stage [13]. The NMDA receptor antagonist MK-801 has been studied in a number of memory tasks, but it is unclear if it af- fects the whole strategy of memory formation.
The object recognition test in rodents is based on the animals’ spontaneous behavior and takes advantage of their natural interest for investigating their environment.
The test is quite similar to tasks used in humans and should, therefore, have a significant level of predictive validity. Adequate recognition of an object is reflected by the animal spending relatively more time exploring an unfamiliar object than a recently presented object.
Studies on MK-801 effect on object recognition mem- ory suggest a decreased memory retention when MK- 801 is given before the first, introductory session [6, 9].
To understand the mechanism of the clinical efficacy of a combination of an antidepressant and risperidone in the therapy of schizophrenia, the aim of the present study was to evaluate the effect of mirtazapine and risperidone, given separately or jointly, on the effect of MK-801, given before the first introductory session, on the object recognition in mice. To this end, we used the object recognition test in which animals were tested for their ability to discriminate between an old, familiar and a novel object.
Materials and Methods
Animals
The experiments were carried out on male Albino- Swiss mice (25 ± 2 g) (Charles River Laboratories,
cycle (the light on at 7 a.m.). The mice had free access to food and water before the experiments. Each ex- perimental group consisted of 10–12 animals/dose.
All the experiments were conduced during the light phase and were carried out according to the proce- dures approved by the Animal Care and Use Commit- tee at the Institute of Pharmacology, Polish Academy of Sciences in Kraków.
Drugs administration
Mirtazapine and risperidone (Tocris Bioscience, Bris- tol, UK) were suspended in a 1% aqueous solution of Tween 80, and (+)-MK-801 maleate (MK-801, Tocris Bioscience, Bristol, UK) was dissolved in a 0.9%
NaCl. All the drugs were given intraperitoneally (ip) in a volume of 10 ml/kg. Mirtazapine (2.5 or 5 mg/kg) and risperidone (0.01 mg/kg) were given 30 min before MK-801, and MK-801 (0.1 or 0.2 mg/kg) was administered 30 min before the first introductory session.
The object recognition test in mice
On the day of the experiment the animals were trans- ferred to the laboratory, labeled and weighed, and thereafter left to acclimate to the new environment for approximately 2 h before the testing started. In the first, i.e., introductory session each mouse was placed in a white plastic box (57 × 35 × 20 cm). Objects to discriminate were: a black metal box (4 × 6 cm) and a green glass cone (4 × 6 cm). Objects were placed in two opposite corners with the center of the object 24 cm from the corner. The mice were placed in the middle of the arena and presented with two identical object, A1 and A2, during 5 min (half of the animals were presented two black metal boxes and the other half two green glass cones). After a 1.5 h delay in the home cage, the mice were again placed in the same plastic box as earlier and presented with two objects, the old familiar A1, and a new object B during 5 min (recognition session). Object A2 was always the one that was replaced. Object exploration was defined as mice sniffing or touching the object with its nose and/or forepaws. The objects were cleaned with 10%
ethanol between each mouse and session. Each group consisted of 12 mice.
Locomotor activity test
The locomotor activity of mice was recorded using the Opto-M3 System (Columbus Instruments, Colum- bus, OH, USA), which is a multi-channel activity monitor supporting sensors (0.5” beam spacing) at- tached to the computer, which measures both ambula- tory activity and total counts for 5 min. Each group consisted of 10 mice.
Statistical analysis
The data were evaluated by a one-way analysis of variance (ANOVA) followed by individual compari- sons using Dunnett’s test.
Results and Discussion
The aim of the present study was to evaluate the effect of mirtazapine and risperidone, given separately or jointly, on the impact of MK-801, given prior to the first introductory session, on the object recognition memory in mice. To this end, we used the object rec- ognition test in which an animal was tested for its ability to discriminate between an old, familiar and a novel object.
In the introductory session, where MK-801 (0.1 or 0.2 mg/kg) or saline was given 30 min before the test, there was no difference between the groups in the time spent on exploring the two similar objects (Tab.
1), which indicated that there was no preference for a certain position of the objects in the area. During the recognition session (Tab. 1) both control animals and
mice receiving the lowest MK-801 dose (0.1 mg/kg) spent significantly more time exploring the novel ob- ject, while mice receiving MK-801 at dose of 0.2 mg/kg showed no preference for a particular ob- ject. During the introductory session, mice receiving MK-801 at a dose of 0.2 mg/kg spent less total time on exploring both objects (A1 + A2) compared with control group (p < 0.001, Tab. 1), while during the recognition session there was no difference between the groups in the total object exploring time.
In the locomotor activity test, where MK-801 (0.1 and 0.2 mg/kg) was given 30 min before the test (like as in the object recognition test), the dose of 0.2 mg/kg only (but not 0.1 mg/kg) increased the total locomotor activity of mice by ca. 176% vs. control group [F(2, 27) = 17.27; p < 0.001], moreover, in these mice 90 min later, MK-801 in both studied group (0.1 and 0.2 mg/kg) increased locomotor activ- ity by ca. 156% and 276%, respectively, F(2, 27) = 18.86; p < 0.001, Tab. 2), what suggested that the im- paired recognition at the higher dose of MK-801 (0.2 but not 0.1 mg/kg) was not connected with increased locomotor activity.
Our studies are also in line with the previous inves- tigations [6, 9] which showed that MK-801 appeared to decrease memory retention when given prior to the introductory session. In addition, another study [10]
showed that MK-801 given directly after the introduc- tory session or before the recognition session might induce interest for a novel object, but did not decrease memory retention. The above authors suggest that the activation of NMDA receptors is a requisite for en- coding of recognition memory in mice but not for consolidation and retrieval processes. The increased interest for the novel object showing up when MK- 801 was given directly after the introductory session
Mirtazapine and risperidone treatment and object recognition test
Zofia Rogó¿
Tab. 1. The effect of MK-801 (0.1 or 0.2 mg/kg, ip) or saline on the recognition memory in mice
Compound (mg/kg, ip)
Introductory session Mean ± SEM Recodnition session Mean ± SEM
A1 A2 A1 + A2 A B A + B
Vehicle 23.7 ± 0.5 24.8 ± 0.8 48.5 ± 0.9 11.8 ± 1.0 31.3 ± 1.6# 43.1 ± 2.3 MK-801 (0.1) 24.0 ± 1.4 25.3 ± 1.2 49.3 ± 2.5 11.8 ± 1.4 33.3 ± 4.7# 45.1 ± 5.0 MK-801 (0.2) 15.8 ± 1.1 16.2 ± 1.4 32.0 ± 2.2* 20.2 ± 1.8 21.4 ± 1.4 41.6 ± 2.2
MK-801 (0.1 or 0.2 mg/kg) was administered 30 min prior to the introductory session, and recognition memory was tested 1.5 h later. The re- sults are shown as the mean ± SEM (in seconds) spent on exploring two similar objects (object A1 and object A2) during the introductory ses- sion and in recognition session the familiar object A vs. the novel object B. Each group consisted of 12 mice. The data were statistically evalu- ated by ANOVA, followed by individual comparison using Dunnett’s test. * p < 0.001 vs. vehicle-treatment group,#p < 0.001 vs. object A
or before the recognition session may reflect a facili- tation of retention.
The present results also showed that risperidone at a higher dose (0.1 mg/kg) inhibited the decrease in memory retention of the object recognition evoked by MK-801 (0.2 mg/kg) (F(1, 22) = 8.64; p < 0.01, B group vs. A1 group, Fig. 2A), but neither did it change the time spent on exploring the two similar object in the introductory session nor the total time spent on the exploring two objects in both sessions (Figs. 1 and 2).
Moreover, risperidone at a lower dose (0.01 mg/kg) and mirtazapine (2.5 or 5 mg/kg) did not change the effect of MK-801 (0.2 mg/kg) on the object recogni- tion memory, while combined treatment with ineffec- tive dose of risperidone (0.01 mg/kg) and mirtazapine (2.5 or 5 mg/kg) abolished the effect of MK-801 (0.2 mg/kg); F(1, 22) = 23.51, p < 0.001 and F(1, 22)
= 14.35; p < 0.001, B group vs. A1 group, respec- tively (Fig. 2B).
During the introductory session, mice receiving mirtazapine (2.5 and 5 mg/kg) plus MK-801 (0.2 mg/kg) spent less total time exploring the two similar objects by ca. 34.9 and 34.7%, respectively;
F(2, 33) = 9.79, p < 0.001, compared with control group (Fig. 1A). Similarly, mice receiving mirtazap- ine (2.5 and 5 mg/kg) and risperidone (0.01 mg/kg) plus MK-801 (0.2 mg/kg) also spent less total time exploring the two similar objects by ca. 27.9 and 33.7%, respectively; F(2, 33) = 6.22, p < 0.01, com- pared with control group (Fig. 1A), but there was no difference between the groups in the time spent on ex- ploring the two similar objects (Fig. 2A).
Our earlier study showed that co-treatment with mirtazapine (2.5 or 5 mg/kg) and risperidone
(0.01 mg/kg) inhibited the locomotor hyperactivity induced by D-amphetamine or MK-801. Moreover, co-administration of mirtazapine (1.25 or 2.5 mg/kg) and risperidone (0.01 mg/kg) reduced the number of head twitches induced by DOI, whereas those drugs given separately changed neither the locomotor hy- peractivity induced by D-amphetamine or MK-801 nor the syndrome induced by DOI (a 5-HT2Areceptor agonist), what suggested that lower doses of mir- tazapine might enhance the antipsychotic-like effect of risperidone in animal tests modeling positive symptoms of schizophrenia [14].
(mg/kg, ip) 30 min after MK-801 administration
Mean ± SEM
1.5 h later Mean ± SEM
Vehicle 740.2 ± 84.1 259.9 ± 61.4
MK-801 (0.1) 1173.0 ± 97.8 669.5 ± 37.6*
MK-801 (0.2) 2043.4 ± 242.0* 979.1 ± 124.6*
MK-801 (0.1 or 0.2 mg/kg) was given 30 min before the test. Locomo- tor activity was assessed 30 min after MK-801 administration and 1.5 h later for 5 min. The results represent the mean ± SEM; n = 10.
The data were statistically evaluated by ANOVA followed by individ- ual comparison using Dunnett’s test. * p < 0.001 vs. vehicle- treatment group
Fig. 1. The effect of mirtazapine (MIR, 2.5 and 5 mg/kg, ip) given alone or in combination with risperidone (RIS, 0.01 mg/kg, ip) on the recognition memory in mice. MK-801 (0.1 or 0.2 mg/kg, ip) was ad- ministered 30 min prior to the introductory session (A), and recogni- tion memory (B) was tested 1.5 h later. MIR and RIS were given 30 min before MK-801 administration. The results are shown as the mean ± SEM total time (in seconds) spent on exploring two similar objects in the introductory session (A) and in the recognition session (B). Each group consisted of 12 mice. The data were statistically evaluated by ANOVA, followed by individual comparisons using Dun- nett’s test. * p < 0.001 vs. vehicle-treated group
All the above behavioral data are in line with the previously clinical studies which showed that aug- menting risperidone with mirtazapine could effec- tively improve therapy of both negative and some cognitive symptoms of schizophrenia [1, 4, 18, 19].
Possible mechanisms which could account for this re- sults are: negative and cognitive improvement from mirtazapine augmentation due to serotonin 5-HT2 blocking [5], moreover, a2-adrenergic antagonism in the prefrontal cortex can activate the serotonin and noradrenaline neurons, associated with negative and cognitive symptoms [17]. In addition, risperidone also
demonstrated a potent a2-adrenergic, 5-HT2A and 5-HT7antagonism [12, 15] potentially related to the therapeutic efficacy against both negative and some cognitive symptoms of schizophrenia.
In summary, the obtained results showed that MK- 801 decreased memory retention when given prior to the introductory session. Co-treatment with risperi- done at a lower dose and mirtazapine abolished the ef- fect of MK-801, whereas those drugs given separately did not change the action of MK-801. The obtained results suggest that mirtazapine may enhance the antipsychotic-like effect of risperidone in animal tests of some cognitive symptoms of schizophrenia. Fur- ther studies are necessary to elucidate its mechanism of action.
Acknowledgments:
This study was financially supported by statutory funds of the Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland. The author would like to thank Ms. Katarzyna Kamiñska for her skilful technical assistance.
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Zofia Rogó¿
Fig. 2. The effect of mirtazapine (MIR, 2.5 and 5 mg/kg, ip) given alone or in combination with risperidone (RIS, 0.01 mg/kg, ip) on the recognition memory in mice. MK-801 (0.1 or 0.2 mg/kg, ip) was ad- ministered 30 min prior to the introductory session (A), and recogni- tion memory (B) was tested 1.5 h later. MIR and RIS were given 30 min before MK-801 administration. The results are shown as the mean ± SEM time (in seconds) spent on exploring two similar objects (object A1 and object A2) during the introductory session (A) and (B) the familiar (object A) vs. the novel object (object B) during the recog- nition session. Each group consisted of 12 mice. The data were sta- tistically evaluated by ANOVA, followed by individual comparisons using Dunnett’s test. * p < 0.001 between groups; time spent on ex- ploring object B vs. time exploring object A
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Received: August 14, 2013; in the revised form: September 3, 2013;
accepted: September 4, 201.
