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Some behavioural effects of risperidone in rats: comparison with haloperidol
European Neuropsychopharmacology 9 (1999) 421–426 www.elsevier.com / locate / euroneuro
Some behavioural effects of risperidone in rats: comparison with haloperidol ~ Elzbieta Nowakowska a , *, Alfons Chodera a , Krzysztof Kus a , Janusz Rybakowski b b
a Department of Pharmacology, Karol Marcinkowski University of Medical Sciences in Poznan˜ , 10 Fredry Street, 61 -701 Poznan˜ , Poland Department of Adult Psychiatry, Karol Marcinkowski University of Medical Sciences in Poznan˜ , 10 Fredry Street, 61 -701 Poznan˜ , Poland
Received 23 June 1998; received in revised form 5 January 1999; accepted 19 April 1999
Abstract Risperidone is a dopaminergic as well as a 5-HT 2 antagonist. The drug was found to exert beneficial effects on both positive and negative symptoms of schizophrenia. Since recently, schizophrenia is regarded as a composite of not only positive and negative but also affective and cognitive symptoms, in this study the effects of risperidone compared with typical neuroleptic haloperidol, on affective and cognitive functions were investigated in rats (anxiolytic, antidepressive and memory tests). We found, that in contrast to haloperidol, risperidone had antidepressive, anxiolytic and memory enhancing effects. The results obtained correspond with favourable effects of risperidone on mood disturbances and cognitive functions of schizophrenic patients observed under clinical conditions. 1999 Elsevier Science B.V. All rights reserved. Keywords: Risperidone; Haloperidol; Anxiolytic and memory improving effects; Forced swimming test
1. Introduction Risperidone was developed following studies which showed, that apart from antipsychotic effect, also the negative symptoms of schizophrenia were improved and the number of EPS diminished, when ritanserin, a selective antagonist of 5-HT 2 and 5-HT 2C receptors was combined with haloperidol (Berzani et al., 1986). In risperidone both activities are present – it is a dopaminergic as well as a 5-HT 2 antagonist. Beneficial effects of risperidone on negative symptoms of schizophrenia were reported (Claus et al., 1992; Chouinard et al., 1993). Especially, in the last study (a multicenter trial) a trend was observed towards superiority of risperidone to haloperidol, both on the negative symptoms score and the extrapiramidal rating scale. Recently, the psychopathology of schizophrenia is regarded as a composite of at least four groups of symptoms: positive, negative, affective and cognitive (Lindenmayer et al., 1995). It has been suggested that two later groups of *Corresponding author. Tel.: 148-861-521-161, ext. 204; fax: 148861-520-455.
symptoms may be favourably influenced by new generation of neuroleptic drug possessing serotonergic and dopaminergic antagonistic properties. Risperidone was found to exert antidepressant effect in psychotic patients (Hillert et al., 1992). Neuropsychological studies also suggest a possibility of improving by risperidone several aspects of cognitive functions such as e.g. verbal working memory (Green et al., 1997). In view of this, the experimental studies comparing risperidone and haloperidol were carried out including anxiolytic and antidepressive tests as well as an labyrinth test assessing working memory.
2. Experimental procedures
2.1. Animals Male Wistar rats, 180–200 g, bought from a breeder (licence of the Ministry of Agriculture Warsaw, Poland) were used in this study. The animals were housed in standard laboratory conditions under a 12 h light / dark cycle, light on at 6 a.m., in
0924-977X / 99 / $ – see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S0924-977X( 99 )00021-8
422
E. Nowakowska et al. / European Neuropsychopharmacology 9 (1999) 421 – 426
a temperature controlled room 21628C, humidity 60% with free access to granulated standard foot and tap water. The rats were kept four per cage (30330320 cm). Each experimental and control group consisted of 8–10 animals.
2.2. Drugs • Sodium carboxymethyl cellulose (CMC), Koch-Light Laboratories Ltd., London, UK. • Risperidone (0.15 mg / kg po), Janssen Belgium. • Haloperidol (0.15 mg / kg po), Polfa Warszawa. Both drugs (risperidone and haloperidol) were suspended in 0.5% solution of CMC and administered orally. The dose and administration time were determined in initial experiments: (1) a dose without a sedative effect was chosen, which caused a significant effect at least in one behavioural test (0.15 mg / kg for risperidone). We chose for comparison, the same dose of haloperidol (0.15 mg / kg) as for risperidone; (2) the time point after which the effect was most pronounced was 60 min after administration of risperidone and haloperidol. In the chronic experiments risperidone and haloperidol have been administered to the rats during 2 weeks. In each week after 1 day ‘‘drug-free’’ to wash out remnants of the last dose, the test was performed, after the usual dose of the drugs.
2.3. Locomotor activity test Locomotor activity was measured in treated and control groups using eight 20.5328321 cm wire grid cages each with two horizontal infrared photocell beams along the long axis 3 cm above the floor. Photocell interruptions were recorded by electromechanical counters in an adjacent room. After 30 min of habituation to the novel cage, rats were injected with the risperidone and then photocell activity was recorded at 10 min intervals for 1 h. This test provided an index of basal locomotor activity of animals in a familiar environment, necessary to indicate the presence of central stimulant effects of the drug used in the novelty test.
2.4. Forced swimming test Measurement of immobility according to Porsolt (Porsolt et al., 1978). • Pretest: 24 h before the experiments the rats were placed individually in Plexiglas cylinders (height 40 cm, diameter 18 cm) containing water at 258C, up to 17 cm and 15 min later they were removed to a 308C drying room for 30 min. • Test: The drugs were administered 24 h after the pretest and 60 min after the administration of risperidone and haloperidol the animals were placed once again in the
cylinders and immobility was measured for 5 min. A rat was judged to be immobile when it remained floating in the water, in an upright position, making only very small movements necessary to keep its head above water. The total duration of immobility during 5 min was recorded by an observer who did not know which treatment the rats had received. • After prolonged administration (7 and 14 days) the drug action was tested as under (b). The water was changed after observation of each rat.
2.5. Anxiolytic effects The anxiolytic effects were determined according to the ‘‘Two-compartment exploratory test’’ of Crawley (Crawley, 1981) in modification of Merlo-Pich and Samanin (1989).
2.5.1. Procedure The apparatus employed to test ‘‘approach-avoidance behaviour’’ was a conventional open field (1003100 cm), the floor consisting of a sheet of white plastic painted with a black grid dividing the field into 25 (535) equal squares. This surface was divided into two compartments, one consisting of a squared area (40340 cm) (4 squares) in one corner of the open field with all the surfaces blackened and a roof, fitted 35 cm from the floor, to prevent light entering from above. The second compartment was the remaining part of the open field (21 squares), uniformly lit by a fluorescent lamp. No partitions were provided between the two compartments, transition lines consisting of the internal half perimeter of the black in the corner. At the beginning of the test, all rats were placed gently in the same peripheral lighted ‘‘white’’ square near to the ‘‘black’’ compartment. The number of transitions between the two-compartments (BWT), square entries in the black compartment (BSE) and square entries in the white compartment (WSE) were recorded for 5 min by an observer sitting quietly 2 m away, unaware of the treatment. Whenever the animal crossed the transition line or the square border with all four legs, an event was recorded. On removal of the rat the floor was thoroughly cleaned. Each rat was assessed in the novelty test only once, always between 10.00 a.m. and 2.00 p.m. (only on test day). 2.6. Memory testing The memory assessment was performed by means of the maze test. Before the test, the animals were deprived of food (rats were individually housed with limited access to food – 3 pellets per day) but had unlimited access to water. During 2 weeks the rats were trained in the maze, with food placed in the end-point of a complex route. The food was the
E. Nowakowska et al. / European Neuropsychopharmacology 9 (1999) 421 – 426
reward for finding the way. The animals were put always in the same place of the maze (start place), only one animal at a time. Every two days the rats were fed without limitations (after test) for 30 min. After a two week training, only those rats were selected for the test which needed less than 30 s for finding the way to food. The mean time in the 4 groups before starting the experiment (without drugs) was similar – between 22 and 25 s. During the tests CMC, risperidone and haloperidol were administered.
2.7. Statistics The data are shown as means6SEM. Statistical analysis was performed using two-way ANOVA followed by Student’s t-test (Ther, 1965) for dependent samples and using Friedman test. Statistical analysis for locomotor activity test was done by Dunnett’s test. The confidence limit of p,0.05 was considered statistically significant. The F interaction values are stated in the tables.
423
Table 1 The influence of risperidone and haloperidol on immobility time in Porsolt’s test Drug
Immobility time (s) Single administration x¯ 6S.E.M.
Prolonged administration (7 days) x¯ 6S.E.M.
(14 days) x¯ 6S.E.M. 204.3621.0 F 1 – 7 52.25 F 7 – 14 50.52 160.0615.4 † F C-R 52.89 F 1 – 14 54.48 198.2624.0 F C-H 50.04 F 1 – 7 51.22
Control group (C) CMC p.o.
247.8620.0
224.3618.0 F 1 – 7 50.76
Risperidone (R) 0.15 mg / kg p.o.
220.4624.0 F C-R 50.77
Haloperidol (H) 0.15 mg / kg p.o.
232.0619.0 F C-H 50.33
107.0612.0 * ,† F C-R 50.29 F 1 – 7 517.86 195.4622.0 F C-H 51.03 F 1 – 7 51.58
* Statistically significant differences vs. control group ( p,0.05). † Statistically significant differences vs. single administration group ( p,0.05).
3. Results
and 14 days a strong sedating effect – the locomotor activity was diminished by a factor of 7 times. In contrast to this, after risperidone no such effect was seen, the locomotor activity was also after 7 and 14 days treatment not changed, not decreased (Fig. 1).
3.1. Locomotor test
3.2. Porsolt’ s test for antidepressive activity
Haloperidol had after first application as well as after 7
After single administration neither haloperidol or ris-
Fig. 1. The influence of risperidone and haloperidol on locomotor activity in rats, after single and prolonged administration.
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E. Nowakowska et al. / European Neuropsychopharmacology 9 (1999) 421 – 426
Fig. 2. The effects of risperidone (0.15 mg / kg p.o.) and haloperidol (0.15 mg / kg p.o.) in the ‘‘two compartment exploratory test’’ for exploring anxiolytic activities.
E. Nowakowska et al. / European Neuropsychopharmacology 9 (1999) 421 – 426
425
Table 2 The influence of risperidone and haloperidol after single and prolonged administration on memory processes in the maze test in rats Drug
Doses
Food finding time (s) Single administration x¯ 6S.E.M.
Prolonged administration 7 days x¯ 6S.E.M.
14 days x¯ 6S.E.M.
19.061.4 F 1 – 7 51.33 18.461.7 F C – R 50.07 F 1 – 7 51.86 20.462.1 F C – H 50.31 F 1 – 7 50.84
17.361.5 F 1 – 14 53.86 16.962.5 F C – R 50.02 F 1 – 14 50.27 22.462.4 F C – H 53.25 F 1 – 14 50.08
Control group CMC (C) Risperidon (R)
0.5% p.o.
21.261.3
0.15 mg / kg p.o.
15.461.4 * F C – R 59.22
Haloperidol (H)
0.15 mg / kg p.o.
23.462.5 F C – H 50.61
* Statistically significant differences vs. control group ( p,0.05).
peridone showed any influence on immobility time. However, after a treatment prolonged to 7 days, after risperidone the immobility time was diminished to less than half the time of control and was still present after 14 days. With haloperidol, no such effect was seen (Table 1).
3.3. Two compartment exploratory test of Crawley for assessing anxiolytic activity Risperidone had, after single administration a marked influence on the behaviour of rats. Especially augmented was the number of white square entrances, the number of black-white transitions was also higher then in control rats. These clearly anxiolytic effects disappeared however after 7 days of treatment and were also absent after 14 days of treatment (Fig. 2). Contrary to risperidone, haloperidol did not show any influence on the behaviour of rats in Crawley’s test.
3.4. The maze test for memory The time in which the rats found the food at the end of the labyrinth was shortened significantly after single administration of risperidone, after prolonged administration this effect disappeared. Haloperidol after single and chronic administration showed no significant differences on food finding time in comparison with the control group (Table 2).
4. Discussion As shown by receptor binding studies, risperidone has not only antidopaminergic but also antiserotonergic properties (Leysen, 1997). This may make it more effective than conventional antipsychotic agents in the treatment of the negative symptoms of schizophrenia (Carman et al., 1995). Several authors (Svensson and Tung, 1989; Svensson et
al., 1993; Wolkin et al., 1992; Opler et al., 1994; Breier, 1995) proposed that risperidone reverses the serotonin dysfunction and prefrontal hypoactivity, that are thought to be responsible for the pathogenesis of negative symptoms. Drugs which possess the potency to block both serotonergic (5-HT 2A ) as well as dopaminergic (D 2 ) receptors – like risperidone and sertindole produce a reliable response rate both to the positive as well as to the negative symptoms of schizophrenia (Carman et al., 1995; King, 1998; Mendelowith and Liebermann, 1995). It deserves noting, that both drugs have a calming effect at doses below the EPS threshold, unlike haloperidol (Casey, 1996). It is true, that haloperidol is more potent in blocking motility (Megens et al., 1992; Nowakowska et al., 1998), but at the risk of increased EPS (Greeb, 1996) and impaired cognitive function (Gallhofer et al., 1996). The results of our experiments, my also correspond with favourable effect of risperidone an mood and cognition found in schizophrenic patient (Hillert et al., 1992; Green et al., 1997) Risperidone, in contrast to haloperidol, had a distinct anxiolytic effect and an antidepressive activity, appearing after a 7 days latency time. Our experiments also show, that risperidone unlike haloperidol is effective in improving cognitive functions such as working memory, though only after acute treatment. After prolonged treatment tolerance to the memory enhancing effect appears. We are aware of the possibilities of erroneous interpretation in behavioural and also memory tests. We tried to exclude them by introducing, only for this aim. the locomotor activity test and selecting a dose, non active in this respect. The parallel experiments in Crawley’s test made sure that the animals were relaxed in the test. But also control animals were not anxious, because they were trained in the food maze for 2 week and they knew the apparatus quite well. In concluding, we may state that the antidepressive, anxiolytic and memory improving effects of risperidone found in our animal experiments as well as its LSD-
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E. Nowakowska et al. / European Neuropsychopharmacology 9 (1999) 421 – 426
antagonism proved by other authors (Meert et al., 1989), may help the understanding of multiple action mechanism of the drug in psychotic patients. It may be then assumed, that thanks to the additional effect of risperidone on 5-HT 2 receptors, this drug, in contrast to haloperidol, acts therapeutically on negative symptoms of schizophrenia, but also may exert beneficial effect on mood and cognition in there patients.
References Berzani, G., Grispini, A., Marini, S., Pasini, A., Valducii, M., Ciani, N., 1986. Neuroleptic induced EPS: clinical perspectives with ritanserin, a new selective 5-HT 2 receptor blocking agent. Curr. Ther. Res. 40, 492–499. Breier, A., 1995. Serotonin, schizophrenia and antipsychotic drug action. Schizophrenia Research 14, 187–202. Carman, J., Peuskens, J., Vangeneugden, A., 1995. Risperidone in the treatment of negative symptoms of schizophrenia: a meta-analysis. International Clinic Psychopharmacol. 10, 207–213. Casey, D.E., 1996. Behavioural effects of setindole risperidone, clozapine and haloperidol in Cebus monkeys. Psychopharmacology 124, 134– 140. Chouinard, G., Jones, B., Remington, G., Bloom, D., Addington, D., MacEwan, W., Labelle, A., Beauclain, L., Arnott, W., 1993. A Canadian multicentre, placebo controlled study of risperidone and haloperidol in the treatment of chronic schizophrenic patients. J. Clin. Psychopharmacol. 13, 25–40. Claus, A., Bollen, J., De-Cuyper, A., Eneman, M., Malfroid, M., Penskens, J., Heylen, S., 1992. Risperidon versus haloperidol in the treatment of chronic schizophrenic inpatients. Acta Psychiatr. Scand. 85, 295–305. Crawley, J.N., 1981. Neuropharmacological specifity of single animal model for the behavioral action of benzodiazepines. Pharmacol. Biochem. Behav. 15, 695–699. Gallhofer, B., Bauner, U., Lis, S., Krieger, S., Grouppe, H., 1996. Cognitive dysfunction in schizophrenia: comparison of treatment with atypical antipsychotic agents and conventional neuroleptic drugs. Europ. Neuropsychopharmacology 6 (S.2), 13–20. Greeb. J., 1996. Will novel antipsychotics be the nest standard of care for patients with schizophrenia? A worldwide report on risperidone. Symposium on novel antipsychotic. Melbourne 23-27.06, Abstr., p. 12.
Green, M.F., Marshall, B.D., Nirshing, W.C., Ames, D., Marder, S.R., McGurk, S., Kern, R.S., Mintz, J., 1997. Does risperidone improve verbal working memory in treatment – resistant schizophrenia? Am. J. Psychiatry 154, 799–804. Hillert, A., Maier, W., Wetzel, H., Benkart, O., 1992. Risperidone is the treatment of disorders with a combined psychotic and depressive syndrome – a functional approach. Pharmacopsychiatry 25, 213–217. King, D.J., 1998. Drug treatment of the negative symptoms of schizophrenia. Eur. Neuropsychopharmacol. 8, 33–42. Leysen, J., 1997. Receptor binding profiles and tolerability of antipsychotics. Schizophrenia Review 5, 2. Lindenmayer, J.P., Grochowski, S., Hyman, R.B., 1995. Five factor model of schizophrenia: replication across samples. Schizophrenia Res. 14, 229–234. Meert, T.F., DeHaes, P., Janssen, P.A., 1989. Risperidone (R64766), a potent and complete LSD antagonist in drug discrimination in rats. Psychopharmacol. (Berl.) 97, 206–212. Megens, A.P.H., Niemegers, C.J.E., Awouters, F.H.L., 1992. Drug Developmental Res. 26, 129–145. Mendelowith, A., Liebermann, J., 1995. New findings in the use of atypical antipsychotic drugs. I. Focus on risperidone. J. Clin. Psych. 2, 1–11. Merlo-Pich, E., Samanin, R., 1989. A two-compartment exploratory model to study anxiolytic / anxiogenic effects of drugs in the rat. Pharmacol. Res. 21, 595–602. Nowakowska, E., Chodera, A., Kus, K., 1998. An anxiolytic-like effect of ondansetron disappears in oxazepam-tolerant rats. Pharmacol. Biochem. Behav. 59 (4), 935–938. Opler, L.A., Albert, D., Ramirez, P.M., 1994. Psychopharmacologic treatment of negative schizophrenic symptoms. Comprehensive Psychiatry 35, 16–28. Porsolt, R.D., Anton, G., Blavet, N., Jalfre, M., 1978. Behavioral despair in rats: a new model sensitive to antidepressant treatments. Eur. J. Pharmacol. 47, 379–391. Svensson, T.H., Nomikos, G.G., Anderson, J.L., 1993. Modulation of dopaminergic neurotransmition by 5-HT 2 antagonism. In: Serotonin From Cell Biology To Pharmacology and Therapeutics, 2nd ed., Kluwer Academic, Dordrecht, pp. 263–370. Svensson, T.H., Tung, C.S., 1989. Local cooling of prefrontal incuses pacemaker like firing of dopamine neurons in rat central segmental area in vivo. Acta Psychiol. Scand. 136, 135–136. ¨ Ther, L., 1965. Grundlagen der exp. Arzneimittelforschung, Wiss. Verlagsgesellschaft, Stuttgart. Wolkin, A., Sanfilipo, M., Wolf, A.P., Angoist, B., Brodie, J.B., Rotrosen, J., 1992. Negative symptoms and hypofrontality in chronic schizophrenia. Archives of General Psychiatry 49, 959–963.
Some behavioural effects of risperidone in rats: comparison with haloperidol ~ Elzbieta Nowakowska a , *, Alfons Chodera a , Krzysztof Kus a , Janusz Rybakowski b b
a Department of Pharmacology, Karol Marcinkowski University of Medical Sciences in Poznan˜ , 10 Fredry Street, 61 -701 Poznan˜ , Poland Department of Adult Psychiatry, Karol Marcinkowski University of Medical Sciences in Poznan˜ , 10 Fredry Street, 61 -701 Poznan˜ , Poland
Received 23 June 1998; received in revised form 5 January 1999; accepted 19 April 1999
Abstract Risperidone is a dopaminergic as well as a 5-HT 2 antagonist. The drug was found to exert beneficial effects on both positive and negative symptoms of schizophrenia. Since recently, schizophrenia is regarded as a composite of not only positive and negative but also affective and cognitive symptoms, in this study the effects of risperidone compared with typical neuroleptic haloperidol, on affective and cognitive functions were investigated in rats (anxiolytic, antidepressive and memory tests). We found, that in contrast to haloperidol, risperidone had antidepressive, anxiolytic and memory enhancing effects. The results obtained correspond with favourable effects of risperidone on mood disturbances and cognitive functions of schizophrenic patients observed under clinical conditions. 1999 Elsevier Science B.V. All rights reserved. Keywords: Risperidone; Haloperidol; Anxiolytic and memory improving effects; Forced swimming test
1. Introduction Risperidone was developed following studies which showed, that apart from antipsychotic effect, also the negative symptoms of schizophrenia were improved and the number of EPS diminished, when ritanserin, a selective antagonist of 5-HT 2 and 5-HT 2C receptors was combined with haloperidol (Berzani et al., 1986). In risperidone both activities are present – it is a dopaminergic as well as a 5-HT 2 antagonist. Beneficial effects of risperidone on negative symptoms of schizophrenia were reported (Claus et al., 1992; Chouinard et al., 1993). Especially, in the last study (a multicenter trial) a trend was observed towards superiority of risperidone to haloperidol, both on the negative symptoms score and the extrapiramidal rating scale. Recently, the psychopathology of schizophrenia is regarded as a composite of at least four groups of symptoms: positive, negative, affective and cognitive (Lindenmayer et al., 1995). It has been suggested that two later groups of *Corresponding author. Tel.: 148-861-521-161, ext. 204; fax: 148861-520-455.
symptoms may be favourably influenced by new generation of neuroleptic drug possessing serotonergic and dopaminergic antagonistic properties. Risperidone was found to exert antidepressant effect in psychotic patients (Hillert et al., 1992). Neuropsychological studies also suggest a possibility of improving by risperidone several aspects of cognitive functions such as e.g. verbal working memory (Green et al., 1997). In view of this, the experimental studies comparing risperidone and haloperidol were carried out including anxiolytic and antidepressive tests as well as an labyrinth test assessing working memory.
2. Experimental procedures
2.1. Animals Male Wistar rats, 180–200 g, bought from a breeder (licence of the Ministry of Agriculture Warsaw, Poland) were used in this study. The animals were housed in standard laboratory conditions under a 12 h light / dark cycle, light on at 6 a.m., in
0924-977X / 99 / $ – see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S0924-977X( 99 )00021-8
422
E. Nowakowska et al. / European Neuropsychopharmacology 9 (1999) 421 – 426
a temperature controlled room 21628C, humidity 60% with free access to granulated standard foot and tap water. The rats were kept four per cage (30330320 cm). Each experimental and control group consisted of 8–10 animals.
2.2. Drugs • Sodium carboxymethyl cellulose (CMC), Koch-Light Laboratories Ltd., London, UK. • Risperidone (0.15 mg / kg po), Janssen Belgium. • Haloperidol (0.15 mg / kg po), Polfa Warszawa. Both drugs (risperidone and haloperidol) were suspended in 0.5% solution of CMC and administered orally. The dose and administration time were determined in initial experiments: (1) a dose without a sedative effect was chosen, which caused a significant effect at least in one behavioural test (0.15 mg / kg for risperidone). We chose for comparison, the same dose of haloperidol (0.15 mg / kg) as for risperidone; (2) the time point after which the effect was most pronounced was 60 min after administration of risperidone and haloperidol. In the chronic experiments risperidone and haloperidol have been administered to the rats during 2 weeks. In each week after 1 day ‘‘drug-free’’ to wash out remnants of the last dose, the test was performed, after the usual dose of the drugs.
2.3. Locomotor activity test Locomotor activity was measured in treated and control groups using eight 20.5328321 cm wire grid cages each with two horizontal infrared photocell beams along the long axis 3 cm above the floor. Photocell interruptions were recorded by electromechanical counters in an adjacent room. After 30 min of habituation to the novel cage, rats were injected with the risperidone and then photocell activity was recorded at 10 min intervals for 1 h. This test provided an index of basal locomotor activity of animals in a familiar environment, necessary to indicate the presence of central stimulant effects of the drug used in the novelty test.
2.4. Forced swimming test Measurement of immobility according to Porsolt (Porsolt et al., 1978). • Pretest: 24 h before the experiments the rats were placed individually in Plexiglas cylinders (height 40 cm, diameter 18 cm) containing water at 258C, up to 17 cm and 15 min later they were removed to a 308C drying room for 30 min. • Test: The drugs were administered 24 h after the pretest and 60 min after the administration of risperidone and haloperidol the animals were placed once again in the
cylinders and immobility was measured for 5 min. A rat was judged to be immobile when it remained floating in the water, in an upright position, making only very small movements necessary to keep its head above water. The total duration of immobility during 5 min was recorded by an observer who did not know which treatment the rats had received. • After prolonged administration (7 and 14 days) the drug action was tested as under (b). The water was changed after observation of each rat.
2.5. Anxiolytic effects The anxiolytic effects were determined according to the ‘‘Two-compartment exploratory test’’ of Crawley (Crawley, 1981) in modification of Merlo-Pich and Samanin (1989).
2.5.1. Procedure The apparatus employed to test ‘‘approach-avoidance behaviour’’ was a conventional open field (1003100 cm), the floor consisting of a sheet of white plastic painted with a black grid dividing the field into 25 (535) equal squares. This surface was divided into two compartments, one consisting of a squared area (40340 cm) (4 squares) in one corner of the open field with all the surfaces blackened and a roof, fitted 35 cm from the floor, to prevent light entering from above. The second compartment was the remaining part of the open field (21 squares), uniformly lit by a fluorescent lamp. No partitions were provided between the two compartments, transition lines consisting of the internal half perimeter of the black in the corner. At the beginning of the test, all rats were placed gently in the same peripheral lighted ‘‘white’’ square near to the ‘‘black’’ compartment. The number of transitions between the two-compartments (BWT), square entries in the black compartment (BSE) and square entries in the white compartment (WSE) were recorded for 5 min by an observer sitting quietly 2 m away, unaware of the treatment. Whenever the animal crossed the transition line or the square border with all four legs, an event was recorded. On removal of the rat the floor was thoroughly cleaned. Each rat was assessed in the novelty test only once, always between 10.00 a.m. and 2.00 p.m. (only on test day). 2.6. Memory testing The memory assessment was performed by means of the maze test. Before the test, the animals were deprived of food (rats were individually housed with limited access to food – 3 pellets per day) but had unlimited access to water. During 2 weeks the rats were trained in the maze, with food placed in the end-point of a complex route. The food was the
E. Nowakowska et al. / European Neuropsychopharmacology 9 (1999) 421 – 426
reward for finding the way. The animals were put always in the same place of the maze (start place), only one animal at a time. Every two days the rats were fed without limitations (after test) for 30 min. After a two week training, only those rats were selected for the test which needed less than 30 s for finding the way to food. The mean time in the 4 groups before starting the experiment (without drugs) was similar – between 22 and 25 s. During the tests CMC, risperidone and haloperidol were administered.
2.7. Statistics The data are shown as means6SEM. Statistical analysis was performed using two-way ANOVA followed by Student’s t-test (Ther, 1965) for dependent samples and using Friedman test. Statistical analysis for locomotor activity test was done by Dunnett’s test. The confidence limit of p,0.05 was considered statistically significant. The F interaction values are stated in the tables.
423
Table 1 The influence of risperidone and haloperidol on immobility time in Porsolt’s test Drug
Immobility time (s) Single administration x¯ 6S.E.M.
Prolonged administration (7 days) x¯ 6S.E.M.
(14 days) x¯ 6S.E.M. 204.3621.0 F 1 – 7 52.25 F 7 – 14 50.52 160.0615.4 † F C-R 52.89 F 1 – 14 54.48 198.2624.0 F C-H 50.04 F 1 – 7 51.22
Control group (C) CMC p.o.
247.8620.0
224.3618.0 F 1 – 7 50.76
Risperidone (R) 0.15 mg / kg p.o.
220.4624.0 F C-R 50.77
Haloperidol (H) 0.15 mg / kg p.o.
232.0619.0 F C-H 50.33
107.0612.0 * ,† F C-R 50.29 F 1 – 7 517.86 195.4622.0 F C-H 51.03 F 1 – 7 51.58
* Statistically significant differences vs. control group ( p,0.05). † Statistically significant differences vs. single administration group ( p,0.05).
3. Results
and 14 days a strong sedating effect – the locomotor activity was diminished by a factor of 7 times. In contrast to this, after risperidone no such effect was seen, the locomotor activity was also after 7 and 14 days treatment not changed, not decreased (Fig. 1).
3.1. Locomotor test
3.2. Porsolt’ s test for antidepressive activity
Haloperidol had after first application as well as after 7
After single administration neither haloperidol or ris-
Fig. 1. The influence of risperidone and haloperidol on locomotor activity in rats, after single and prolonged administration.
424
E. Nowakowska et al. / European Neuropsychopharmacology 9 (1999) 421 – 426
Fig. 2. The effects of risperidone (0.15 mg / kg p.o.) and haloperidol (0.15 mg / kg p.o.) in the ‘‘two compartment exploratory test’’ for exploring anxiolytic activities.
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Table 2 The influence of risperidone and haloperidol after single and prolonged administration on memory processes in the maze test in rats Drug
Doses
Food finding time (s) Single administration x¯ 6S.E.M.
Prolonged administration 7 days x¯ 6S.E.M.
14 days x¯ 6S.E.M.
19.061.4 F 1 – 7 51.33 18.461.7 F C – R 50.07 F 1 – 7 51.86 20.462.1 F C – H 50.31 F 1 – 7 50.84
17.361.5 F 1 – 14 53.86 16.962.5 F C – R 50.02 F 1 – 14 50.27 22.462.4 F C – H 53.25 F 1 – 14 50.08
Control group CMC (C) Risperidon (R)
0.5% p.o.
21.261.3
0.15 mg / kg p.o.
15.461.4 * F C – R 59.22
Haloperidol (H)
0.15 mg / kg p.o.
23.462.5 F C – H 50.61
* Statistically significant differences vs. control group ( p,0.05).
peridone showed any influence on immobility time. However, after a treatment prolonged to 7 days, after risperidone the immobility time was diminished to less than half the time of control and was still present after 14 days. With haloperidol, no such effect was seen (Table 1).
3.3. Two compartment exploratory test of Crawley for assessing anxiolytic activity Risperidone had, after single administration a marked influence on the behaviour of rats. Especially augmented was the number of white square entrances, the number of black-white transitions was also higher then in control rats. These clearly anxiolytic effects disappeared however after 7 days of treatment and were also absent after 14 days of treatment (Fig. 2). Contrary to risperidone, haloperidol did not show any influence on the behaviour of rats in Crawley’s test.
3.4. The maze test for memory The time in which the rats found the food at the end of the labyrinth was shortened significantly after single administration of risperidone, after prolonged administration this effect disappeared. Haloperidol after single and chronic administration showed no significant differences on food finding time in comparison with the control group (Table 2).
4. Discussion As shown by receptor binding studies, risperidone has not only antidopaminergic but also antiserotonergic properties (Leysen, 1997). This may make it more effective than conventional antipsychotic agents in the treatment of the negative symptoms of schizophrenia (Carman et al., 1995). Several authors (Svensson and Tung, 1989; Svensson et
al., 1993; Wolkin et al., 1992; Opler et al., 1994; Breier, 1995) proposed that risperidone reverses the serotonin dysfunction and prefrontal hypoactivity, that are thought to be responsible for the pathogenesis of negative symptoms. Drugs which possess the potency to block both serotonergic (5-HT 2A ) as well as dopaminergic (D 2 ) receptors – like risperidone and sertindole produce a reliable response rate both to the positive as well as to the negative symptoms of schizophrenia (Carman et al., 1995; King, 1998; Mendelowith and Liebermann, 1995). It deserves noting, that both drugs have a calming effect at doses below the EPS threshold, unlike haloperidol (Casey, 1996). It is true, that haloperidol is more potent in blocking motility (Megens et al., 1992; Nowakowska et al., 1998), but at the risk of increased EPS (Greeb, 1996) and impaired cognitive function (Gallhofer et al., 1996). The results of our experiments, my also correspond with favourable effect of risperidone an mood and cognition found in schizophrenic patient (Hillert et al., 1992; Green et al., 1997) Risperidone, in contrast to haloperidol, had a distinct anxiolytic effect and an antidepressive activity, appearing after a 7 days latency time. Our experiments also show, that risperidone unlike haloperidol is effective in improving cognitive functions such as working memory, though only after acute treatment. After prolonged treatment tolerance to the memory enhancing effect appears. We are aware of the possibilities of erroneous interpretation in behavioural and also memory tests. We tried to exclude them by introducing, only for this aim. the locomotor activity test and selecting a dose, non active in this respect. The parallel experiments in Crawley’s test made sure that the animals were relaxed in the test. But also control animals were not anxious, because they were trained in the food maze for 2 week and they knew the apparatus quite well. In concluding, we may state that the antidepressive, anxiolytic and memory improving effects of risperidone found in our animal experiments as well as its LSD-
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antagonism proved by other authors (Meert et al., 1989), may help the understanding of multiple action mechanism of the drug in psychotic patients. It may be then assumed, that thanks to the additional effect of risperidone on 5-HT 2 receptors, this drug, in contrast to haloperidol, acts therapeutically on negative symptoms of schizophrenia, but also may exert beneficial effect on mood and cognition in there patients.
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