Annals of Neurosciences, Vol 12, No 4 (2005)
Annals of Neurosciences, Volume 12, Issue 4 (October), 2005
MODULATORY EFFECT OF NIMESULIDE ON APOMORPHINE INDUCED STEREOTYPY AND MK-801 INDUCED HYPERLOCOMOTION
Corresponding author
Prof. S.K Kulkarni
Pharmacology Division University Institute of Pharmaceutical
Sciences, Panjab University Chandigarh-160014
Email:
Abstract
Cyclooxygenase-2 is expressed on neurons in structures critically involved in the pathology of schizophrenia such as hippocampus and amygdala. With this background, the present study was designed to explore the possible effect of COX-2 inhibitor nimesulide on apomorphine-induced stereotypy and MK-801-induced hyperlocomotion in animals. Stereotypy was induced by injecting apomorphine (1 mg/kg, i.p). Mean rearing, sniffing and licking response was recorded. Locomotor activity was measured by using an actophotometer. Nimesulide (2.5–10mg/kg, i.p) was tested on these two models. To see the mechanism of action, nimesulide was combined with dopaminergic modulator apomorphine (1 mg/kg) or NMDA modulator MK-801 (0.1 mg/kg) in mice. Nimesulide was effective in combating apomorphine-induced compulsive behavior. Nimesulide also decreased the locomotor activity per se. From the above study, we concluded that nimesulide decreased apomorphine-induced stereotypy and MK-801-induced hyperlocomotion. Therefore, nimesulide may have potential adjuvant role in the drug therapy of schizophrenia.
Key Words: Cyclooxygenase; Schizophrenia: Stereotypy; Locomotor activity; Nimesulide
Introduction
Schizophrenia is a devastating disorder affecting about 1 % of the population worldwide (1). Phospholipids make up 60 % of the brains dry weight and play a key role in many brain signal transduction mechanisms. Cyclooxygenase is the key enzyme that converts arachidonic acid derived from membrane phospholipids into prostaglandins (2). Recently, cyclooxygenase enzyme is known to be significantly expressed in different areas of brain and spinal cord. COX-2 is expressed on neurons critically involved in the pathology of Schizophrenia such as basal ganglia and cortex. Dr. Horrobins (1980) hypothesized that the occurrence of schizophrenia might be due to a failure of normal prostaglandin synthesis in brain (3). Therefore, it seems the use of COX-inhibitors could be an attractive strategy for development of novel therapeutics for schizophrenia.
Method
Albino mice (Laka strain) of male sex weighing between 18–22 g bred in Central Animal House (CAH) facility of Panjab University, Chandigarh were used. Animals were acclimatized to laboratory conditions before the experiment. All the experiments were carried out between 0900 and 1300 h, using a randomized design. The experimental protocols were approved by Institutional Animal Ethics Committee (IAEC) and conducted according to the Indian National Science Academy Guidelines for the use and care of experimental animals.
Apomorphine-induced stereotype
Apomorphine at 1 mg/kg, i.p. was used to induce stereotypy. Stereotypy was measured by placing the mice individually in 500 ml glass beakers. Intensity of rearing, sniffing and licking behrivior was noted at different time intervals. The severity of response was scored as + = Presence, ++ = Moderately severe, +++ = intense and continuous action. The cumulative stereotypy score was calculated by adding all the scores for the purpose of comparison (4).
Locomotor activity
Locomotor activity (ambulations) was measured by using computerized actophotometer (IMCORP). An array of 16 infrared emitter/detector pairs measured the animal activity along single axis of motion, the digital data being displayed on the front panel meters as ambulatory movements. Briefly after 45 minutes of drug treatment mice were individually placed in a transparent plastic cage (30× 23× 22 cm) and mice were allowed to acclimatize to the observation chamber for a period of 2 minutes. The activity was continuously monitored for a period of 5 min. The locomotion was expressed in terms of total photobeams counts per 5 min per animal. Percentage increase or decrease in locomotor activity was calculated (4).
Drugs
Nimesulide (Panacea Biotec, India), was suspended in 0.25% carboxymethylcellulose (CMC). Apomorphine hydrochloride (Sigma, St.Louis, Mo.), was dissolved in distilled water. All the drugs were administered intraperitoneally. Drug doses were selected from our previous studies and those reported in the literature. All drugs were administered intraperitoneally in a constant volume of 1 ml per 100g of body weight of mice. Nimesulide was administered intraperitoneally (i.p) 45 minutes before starting the behavioral assessment. Apomorphine was given 15 min before the behavioral measurements. In combination studies, nimesulide (2.5–10 mg/kg) was administered 10 min before the administration of MK-801 and after 35 minutes measured the various locomotor activity.
Statistical analysis
One specific group of mice was assigned to one specific drug treatment condition and each group comprised of minimum 6 mice. All the values are expressed as mean ± SEM. The data was analyzed by using one way analysis of variance (ANOVA) followed by Mann Whitney U test. In all tests, the criterion for statistical significance was p< 0.05.
Results
Apomorphine significantly induced stereotypy as indicated by the increase in the mean rearing, sniffing, licking behaviors in mice. The pre treatment with selective COX-2 inhibitor nimesulide significantly decreased the stereotypy scores (Fig. 1).
(Fig: 1): Apo: Apomorphine., Nime: Nimesulide. Effect of nimesulide against apomorphine-(l mg/kg) induced stereotypy. Nimesulide was administered 45 minutes before apomorphine injection and stereotypy index was measured up to 30 minutes, (a) P<0.05 as compared to vehicle treated group (One way ANOVA followed Mann Whitney U test), (b) P<0.05 as compared to apomorphine treated group (One way ANOVA followed Mann Whitney U test).
When checked against locomotor movements nimesulide per se decreased the ambulatory movements in mice (Fig. 2). Nimesulide (2.5 mg/kg) was found to be most effective in decreasing the ambulations. However, this decrease in locomotion was not dose dependent. Therefore, nimesulide was further chosen to see the effect against MK-801-induced hyperlocomotion. MK-801 (0.1 mg/kg) increased the ambulations in mice. Nimesulide (2.5 mg/ kg) antagonized the hyperlocomotion induced by MK-801.
(Fig: 2): Effect of nimesulide on the ambulatory movements in mice. Nimesulide was administered 45 minutes before measuring locomotor activity. Animals were placed in Actophotometer and were given two minutes to habituate the environment and then locomotor activity was measured for 5 minutes, (a) P<0.05 as compared to vehicle treated group (One way ANOVA followed by Mann Whitney U test).
(Fig: 3): Effect of nimesulide against MK-801- (0.1 mg/kg) induced hyperlocomotion. Nimesulide (2.5–10 mg/kg) was administered 10 minutes before MK-801 administration and after 35 minutes measured the locomotor activity. Results are expressed as mean ±SEM. (a) P<0.05 as compared to MK-801 treated group (One Way ANOVA followed by Dunnett's test).
Discussion
Different animal models have been used for the study of psychotic disorder schizophrenia (5) based on different neurochemical pathophysiological theories, e.g. the administration of dopamine and NMDA modulatory drugs. These models each show some but not all of the changes in animal behavior that are considered to be related to psychosis e.g. continuous explorative behavior stereotypes and aggression. There are some clinical reports in which Muller et al, reported that celecoxib, a COX-2 inhibitor, add-on-therapy, compared with risperidone in schizophrenia, showed significant improvement in both positive and negative symptoms as compared to risperidone alone treated group (6,7).
Direct or indirect stimulation of dopamine receptors increased locomotor activity in mice. Prostaglandins in brain are hypothesized to cause dopaminergic stimulation (8). Apomorphine causes stereotypy and hyperlocomotion by stimulating dopaminergic receptors, as apomorphine is a mixed dopaminergic agonist acting on both Dl and D2 receptors. Nimesulide decreased the apomorphine-induced stereotypy in the present study. In our study, COX-2 inhibitor nimesulide decreased the mean cumulative stereotypic response as compared to apomorphine treated group. When comapared all the doses of COX-2 inhibtors per se in locomotor activity nimesulide (2.5 mg/kg ) decreased the locomotion activity (mean counts/5 minute) was found to be most effective and after that there was ceiling type of effect with further increased doses of nimesulide.
In addition to the dopaminergic and other hypothesis of psychotic disorders, a dysfunction in the main excitatory neurotransmitter system of the brain, the excitatory amino acids have been suggested in psychosis. MK-801 and phencyclidine cause increased locomotion, stereotypes and ataxia. Functional interaction between glutamate and dopamine has been speculated (9). The agents which antagonize MK-801 induced-behavior may have beneficial effect as antipsychotic agents in clinics. Several studies have shown that neuroleptics with dopamine antagonistic properties reduce NMD A antagonist-induced behavior. MK-801 at 0.1 mg/kg increased the locomotor activity to about 40 %. Pretreatment with nimesulide at various doses was assessed and we found that nimesulide at 2.5 mg/kg was effective in antagonizing the hyperlocomotion induced by MK-801. This may be due to the reason that lower dose may only be capable of increasing excitatory amino acid activity. Activation of NMDA receptors leads to opening of calcium channel, leading a number of postsynaptic events. Calcium ions activate the enzyme phospholipase A2 which converts membrane phospholipids into arachidonic acid which in turn forms various prostaglandins.
The result of the present study suggested that there exists a possible modulatory role of nimesulide on dopamine-related behaviors.
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