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The effects of raclopride on vacuous jaw movements in rats following acute administration
Physiology & Behavior, Vol. 60. No. 1,253-256, 1996 Copyright © 1996 Elsevier Science Inc. Printed in the USA. All rights reserved 0031-9384/96 $15.00 + .00
ELSEVIER
PII SO031-9384(96)00022-4
The Effects of Raclopride on Vacuous Jaw Movements in Rats Following Acute Administration R. E. STEINPREIS, 1 H . J . K A C Z M A R E K A N D A. H A R R I N G T O N
Department of Psychology, The University of Wisconsin--Milwaukee, 138 Garland Hall, 2441 East Hartford, Milwaukee, WI 53211 USA Received 19 January 1995 STEINPREIS, R. E., H. J. KACZMAREK AND A. HARRINGTON. The effects of raclopride on vacuous jaw movements in rats following acute administration. PHYSIOL BEHAV 60(1) 253-256, 1996.--Classic neuroleptics produce a syndrome of vacuous jaw movements in rats, whereas atypical neuroleptics like clozapine do not. The present study compared the effects of repeated administration of raclopride, clozapine, haloperidol, or vehicle on vacuous jaw movements in rats over a 4-week period. Rats received an IP injection of drug once a day. On days 1, 8, 15, and 29 the rats were observed for a 5-min period by two trained observers who recorded their vacuous jaw movements. The dose-response curves at which each drug produced vacuous jaw movements are presented and discussed in terms of their predictive capabilities of early onset extrapyramidal side effects. Vacuous jaw movements
Clozapine
Raclopride
EXTRAPYRAMIDAL side effects have been implicated in studies of medication noncompliance (46), poor social readjustment (15), and increased risk for depression and suicide (19,35). All of the classic antipsychotic drugs produce extrapyramidal side effects. The atypical antipsychotic, clozapine, has a low incidence of early onset extrapyramidal side effects (16) and low risk for the development of tardive dyskinesia (9). In rats, clozapine only produces catalepsy at very high doses (13) and it lacks the anti-apomorphine effects of classical neuroleptics (44). Clozapine also has relatively fewer effects on motor behavior when compared to classic neuroleptics (2). In recent years scientists have been using neuroleptic-induced vacuous jaw movements as an index of risk for extrapyramidal side effects. There is some controversy over whether these vacuous jaw movements constitute a model for early onset extrapyramidal side effects such as Parkinsonian tremor (24) or late-onset side effects such as tardive dyskinesia (40). There are several lines of evidence to suggest that vacuous jaw movements are a more appropriate model for Parkinsonian tremor than tardive dyskinesia. First of all, tardive dyskinesia takes months to develop and Parkinsonism can occur relatively early in the course of drug administration. Vacuous jaw movements have been found to occur in the first few days of administration (37,43). Second,
Haloperidol
Extrapyramidal side effects
anticholinergic drugs exacerbate tardive dyskinesia (17). Coadministration of anticholinergics attenuates haloperidol-induced vacuous jaw movements, and the rapid withdrawal of coadministration of the anticholinergic after 10 days produces a large increase in vacuous jaw movements in rats (43). This is exactly the opposite of what occurs in tardive dyskinesia in humans. When anticholinergics are withdrawn in humans, dyskinetic movements improve (8). Unlike haloperidol, clozapine does not produce vacuous jaw movements at doses analogous to its therapeutic range in humans (21,42). Therefore, haloperidol and clozapine will be used as the two target drugs for comparing raclopride's effects. Raclopride is a selective D 2 antagonist (27), which originally showed promise as a potential antipsychotic drug because it dose-dependently inhibits the behavioral changes induced by d-amphetamine and quinpirole (29,33). Raclopride also showed a high separation between the doses necessary to block apomorphine-induced hyperactivity and those doses that induce catalepsy (31), and chronic administration of 1.0 m g / k g of raclopride did not produce vacuous jaw movements (39). Because raclopride subsequently was shown to produce extrapyramidal side effects in human clinical trials (30), it could call into question the legitimacy of the vacuous jaw movement assay as a predictor of human extrapyra-
i To whom requests for reprints should be addressed.
253
254
STEINPREIS, KACZMAREK AND HARRINGTON
midal side effects. However, the previous research with raclopride in rats examined only a single low dose of raclopride and did not look at the effects of raclopride in the first month of administration, which would parallel the time course of the human clinical trials and allow for a prediction of early onset extrapyramidal side effects. Therefore, the goal of the present study was to introduce the first acute dose-response curve for the effects of raclopride on vacuous jaw movements to determine the consistency with which this assay is predictive of results in human clinical trials.
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The subjects in this experiment were 86 male Sprague-Dawley rats obtained from Harlan Sprague-Dawley (Indianapolis, IN). The rats were approximately 3 months of age at the start of the experiment and weighed between 250 and 300 g. All rats were housed individually in a colony room maintained at 20°C, with a 12-h light/dark cycle (lights on at 0700 h). Standard lab chow and water were available ad lib. Haloperidol was obtained from Sigma Chemical Company (St. Louis, MO) and injected in doses of 0.2, 0.4, and 0.8 mg/kg. Clozapine was obtained from Sandoz (St. Louis, MO) and injected in a dose of 2.0, 4.0, and 8.0 mg/kg. Raclopride was obtained from Astra Merck (Sodartalje, Sweden) and injected in a dose of 1.0, 3.0, and 6.0 mg/kg. All neuroleptics were dissolved a 0.3% tartaric acid vehicle. The 3 days before injections and observations began, rats were habituated to the observation tube each day for a 10-rain period. Rats received 29 single daily IP injections of either raclopride (n = 6), haloperidol (n = 8), clozapine (n = 6), or tartaric acid vehicle (n = 4 or n = 8 in each group). The rats were observed on the first day of neuroleptic administration, and then again after 1 and 2 weeks and 1 month (i.e., days 1, 8, 15, and 29). On each observation day, the rats were placed individually into a 12 × 3.5 in. Plexiglas observation tube 55 min after injection and allowed to habituate for a 5-min period. The 55 min postinjection start time for habituation to the tube was selected based on pilot data from our laboratory and previous studies using haloperidol (43). The tubes were mounted horizontally to a Plexiglas base and both ends of the tube were fitted with stainless steel wire mesh during observations to allow for air flow to the rat. Two trained observers, blind to the drug and dose each rat had received, recorded the frequency of vacuous jaw movements during a 5-min observation period, using electromechanical counters connected to a microcomputer. Vacuous jaw movements were defined as a rapid vertical deflection of the lower jaw, which was not directed at any particular stimulus. The observers also recorded tongue protrusions and yawning, but these behaviors did not occur with enough frequency for any of the drugs to be useful as a behavioral assay or for statistical analysis.
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*An asterisk indil~atee a significant difference from vehicle on that day.
FIG. 1. Mean+ SEM number of haloperidol-inducedvacuousjaw movements in rats. * Significantdifference from vehicle on that day.
action, F(12, 112)=4.78, p < 0.0001. On day 1, only the highest dose of haloperidol produced significant elevations in vacuous jaw movements compared to the vehicle group ( p < 0.05). By day 8 all three doses of haioperidol produced significant elevations in vacuous jaw movements compared to the vehicle group (from low to high: p <0.001, p < 0.01, and p < 0.001, respectively). There were also significant elevations on day 15 for all three dose groups (from low to high: p < 0.001, p < 0.001, and p < 0.005, respectively). On day 22, the mediumand high-dose groups were significantly higher in the mediumand high-dose haloperidol groups ( p < 0.001 and p < 0.05, respectively). On day 29, there were also significant elevations in vacuous jaw movements in the medium- and high-dose haloperidol groups compared to the vehicle group ( p < 0.001 and p < 0.0001, respectively). The data for clozapine are presented in Fig. 2. There were significant main effects for drug treatment, F(3, 28)= 29.9, p < 0.001, days, F(4, 112) = 7.81, p < 0.001, and the interaction, F(12, 112)= 3.99, p < 0.001. The only significant elevations in vacuous jaw movements were produced by the high dose of clozapine on day 1 ( p < 0.001), day 8 ( p < 0.001), day 15
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RESULTS Interrater reliabilities for the two observers were calculated for each day and for all days interrater reliability was found to be 0.96 or better. Therefore, all data analysis was performed on the arithmetic mean of the observer's scores. The effects of each drug on vacuous jaw movements was analyzed separately using a five by four factorial ANOVA, with repeated measures across the 5-day observations were recorded. To determine the differences between drug effects, separate Tukey tests were performed on each of the days. The data for haloperidol are presented in Fig. 1. There were significant main effects for drug treatment, F(3, 28)= 41.6, p < 0.0001), days, F(4, 112) = 16.36, p < 0.0001, and the inter-
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FIG. 2. Mean+ SEM number of clozapine-inducedvacuous jaw movements in rats. * Significantdifference from vehicle on that day.
ATYPICAL ANTIPSYCHOTICS
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FIG. 3. Mean + SEM number of raclopride-induced vacuous jaw movements in rats. * Significant difference from vehicle on that day. ( p < 0.001), and day 22 ( p < 0.01). The data for raclopride are presented in Fig. 3. There was a significant main effect for drug treatment, F(3, 18)= 31.96, p < 0,0001, but not days, F(4, 72) = 0.97, p > 0.05, or the interaction, F(12, 7 2 ) = 1.08, p > 0.05. Post hoc analysis revealed that, on day I, both the medium and high doses of raclopride produced significant elevations in vacuous jaw movements ( p < 0.001 and p < 0.005, respectively). This pattern also occurred on day 8 ( p < 0.001 and p < 0.05, respectively), day 15 ( p < 0.001 and p < ,001), day 22 ( p < 0.01 and p < 0.01, respectively), and day 29 ( p <0.0001 and p <0.01, respectively). DISCUSSION
A variety of behavioral assays have been used to predict the atypical antipsychotic profile, including the reversal of amphetamine- or apomorphine-induced locomotor activity (31,45), the measurement of catalepsy (26), the spontaneous withdrawal of fore- and hindlimbs (14), and the production of vacuous jaw movements (41,43). Preliminary pilot data from our laboratory have indicated that screening for vacuous jaw movements may detect risk for extrapyramidal side effects, not detected by screening for catalepsy (42). The results of the present experiment indicate that clozapine only produced significant elevations in vacuous jaw movements at its highest doses and these results are consistent with the literature (21,25). Research with humans has indicated that clozapine may even have a beneficial effect upon tremor (18,32). Haloperidol produced significant elevations in vacuous jaw movements in the present study, which is also consistent with the literature (36,41,43).
This study is the first to report that raclopride consistently produces vacuous jaw movements with acute administration and these results were apparent on the first day of administration. These results are consistent with the human clinical trials (30) and lend support to the use of the vacuous jaw movement assay as a predictor for early onset extrapyramidal side effects in humans. Although raclopride has been shown to have a lower propensity to induce catalepsy than haloperidol does (38), haloperidol and raclopride have been found to be equipment at blocking apomorphine- and amphetamine-induced hyperactivity (1,22,31) and appear to have similar patterns of response on conditioned avoidance tasks (23). Taken together, these findings may indicate that the vacuous jaw movement assay may be more sensitive to the production of early onset extrapyramidal side effects in humans than the catalepsy assay. The results of a more direct comparison between these two assays remains an empirical question. Our laboratory has recently demonstrated that vacuous jaw movements are detectable in the novel antipsychotic, amperozide (42). Amperozide was selected for human trials, in part due to its failure to produce catalepsy in rats or antagonize amphetamineinduced stereotypies (12). However, preliminary reports from human studies indicate that amperozide is producing abnormal motor responses in humans (3). Taken together, these findings argue for the additional use of screening for vacuous jaw movements. Catalepsy screening would continue to be included to narrow down the atypical profile and the failure to produce vacuous jaw movements would be the final selection determinant. Thus far, clozapine appears to be one of only two compounds that would safely pass through such a procedure (42). Melperone is the other compound that has demonstrated effective in the treatment of schizophrenia (5,6). This drug has been used in Scandinavia for two decades with very few reports of extrapyramidal side effects in humans (5,10), and it does not appear to produce vacuous jaw movements in rats (20). Like clozapine, this drug has been shown effective in the treatment of psychosis with few extrapyramidal side effects (7). Also, meiperone has a weaker affinity for D 2 dopamine receptor than the D 4 receptor (28) and a stronger effect on limbic as opposed to striatal dopamine (11). Also, clozapine and melperone have similar effects on fos-like immunoreactivity in the forebrain, which has been associated with the atypical antipsychotic profile (34). These neurochemical and human behavioral similarities between melperone and clozapine help support our contention that adding vacuous jaw movements to catalepsy screening will better predict antipsychotics with the atypical profile that do not produce extrapyramidal side effects in humans. There are numerous novel atypical antipsychotics that have not been screened for the production of vacuous jaw movements, and such information could have a valuable impact on shaping the selection process of antipsychotic compounds for human trials.
REFERENCES 1. Arnt, J.; Sanchez, C. Differential effects of anti psychotic drugs on amphetamine-induced hypermotility, stereotypy and discriminative stimulus effects in rats. Presented at the 23rd Annual Meeting for the Society for Neuroscience; 1993. 2. Arregi, A.; Azpiroz, A.; Simon, V. M.; Brain, P. F. Effects of two dopaminergic selective antagonists on etiologically assessed conflicts in male mice. Gen. Pharmacol. 24:353-356; 1993. 3. Axelsson, R.; Nilsson, A.; Christensson, E.; Bjork, A. Effects of amperozide in schizophrenia. Psychopharmacology (Berlin) 104:287-292; 1991. 4. Bjerkenstedt, L. Melperone in the treatment of schizophrenia. Work-
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Possible therapeutic implications. Eur. J. Pharmacol. 236:483-486; 1993. Loschmann, P. A.; Smith, L. A.; Lange, K. W.; Jaehnig, P.; Jenner, P.; Marsden, C. D. Motor activity following the administration of selective D 1 and D E dopaminergic drugs to normal common marmosets. Psychopharmacology (Berlin) 105:303-309; 1991. Nordstrom, A. L.; Farde, L.; Wiesel, F. A.; et al. Central De-dopamine receptor occupancy in relation to antipsychotic drug effects: A double-blind PET study of schizophrenic patients. Biol. Psychiatry 33:227-235; 1993. Ogren, S. O., Hall, H.; Kohler, C.; Magnussun, O.; Sjostrand, S. The selective D 2 receptor antagonist raclopride discriminates between dopamine-mediated motor functions. Psychopharmacology (Berlin) 90:287-294; 1986. Pakkenherg, H.; Pakkenberg, B. Clozapine in the treatment of tremor. Acta Neurol. Scand. 73:295-297; 1986. Petry, N.; Furmidge, L.; Tong, Z.; Martin, C.; Clark, D. Time sampling observation procedure for studying drug effects: Interaction between d-amphetamine and selective dopamine receptor antagonists in the rat. Pharmacol. Biochem. Behav. 44:167-180; 1993. Robertson, G. S.; Matsumura, H.; Fibiger, H. C. Induction patterns of Fos-like immunoreactivity in the forebrain as predictors of atypical antipsychotic activity. J. Pharmacol. Exp. Ther. 271:1058-1066; ?I?19XX. Roy, A. Depression, attempted suicide, and suicide in patients with chronic schizophrenia. Psychiatr. Clin. North Am. 99:193-207; 1986. Rupniak, N. M. J.; Jenner, P.; Marsden, C. D. Pharmaco logical characterization of spontaneous or drug-induced purposeless chewing movements in rats. Psychopharmacology (Berlin) 85:71-79; 1985. Rupniak, N. M. J.; Tye, S. J.; Iversen, S. D. Drug-induced purposeless chewing: Animal model of dyskinesia or nausea? Psychopharmacology (Berlin) 102:325-328; 1990. See, R. E.; Chapman, M. A.; Meshul, C. K. Comparison of chronic intermittent haloperidol and raclopride effects on striatal dopamine release and synaptic ultrastructure in rats. Synapse 12:147-154; 1992. See, R. E.; Ellison, G. Comparison of chronic administration of haloperidol and the atypical neuroleptics, clozapine and raclopride, in an animal model of tardive dyskinesia. Eur. J. Pharmacol. 181:175186; 1990. See R. E.; Leven, E.D.; Eillison, G. D. Characteristics of oral movements in rats during and after chronic haloperidol and fluphenazine administration. Psychopharmacology (Berlin) 94:421427; 1988. Steinpreis, R. E.; Baskin, P.; Salamone, J. D. Vacuous jaw movements induced by subchronic administration of haloperidol: Interactions with scopolamine. Psychopharmacology (Berlin) 111:99-105; 1993. Steinpreis, R. E.; Parret, F. A.; Suture, R.; Panos, J. J. The effects of acute and repeated administration of amperozide on vacuous jaw movements in rats. (unpublished observations). Steinpreis, R. E.; Salamone, J. D. Effects of acute haloperidol and reserpine administration on vacuous jaw movements in three different age groups of rats. Pharmacol. Biochem. Behav. 46:405-409; 1993. Stille, G.; Lauener, H.; Eichenberger, E. The pharmacology of 8chloro- 1 l-(4'-methyl- 1-piperazinyl)-5H-debenzo[b,e][1,4] diazepine (clozapine). Farm Ed. Prac. 26:603-625; 1971. Swerdlow, N. R.; Vaccarino, F. J.; Amalric, M.; Koob, G. F. The neural substrates for the motor-activating properties of psychostimulants: A review of recent findings. Pharmacol. Biochem. Behav. 25:233-248; 1986. Van Putten, T. Why do schizophrenic patients refuse to take their drugs? Arch. Gen. Psychiatry 31:67-72; 1974.
ELSEVIER
PII SO031-9384(96)00022-4
The Effects of Raclopride on Vacuous Jaw Movements in Rats Following Acute Administration R. E. STEINPREIS, 1 H . J . K A C Z M A R E K A N D A. H A R R I N G T O N
Department of Psychology, The University of Wisconsin--Milwaukee, 138 Garland Hall, 2441 East Hartford, Milwaukee, WI 53211 USA Received 19 January 1995 STEINPREIS, R. E., H. J. KACZMAREK AND A. HARRINGTON. The effects of raclopride on vacuous jaw movements in rats following acute administration. PHYSIOL BEHAV 60(1) 253-256, 1996.--Classic neuroleptics produce a syndrome of vacuous jaw movements in rats, whereas atypical neuroleptics like clozapine do not. The present study compared the effects of repeated administration of raclopride, clozapine, haloperidol, or vehicle on vacuous jaw movements in rats over a 4-week period. Rats received an IP injection of drug once a day. On days 1, 8, 15, and 29 the rats were observed for a 5-min period by two trained observers who recorded their vacuous jaw movements. The dose-response curves at which each drug produced vacuous jaw movements are presented and discussed in terms of their predictive capabilities of early onset extrapyramidal side effects. Vacuous jaw movements
Clozapine
Raclopride
EXTRAPYRAMIDAL side effects have been implicated in studies of medication noncompliance (46), poor social readjustment (15), and increased risk for depression and suicide (19,35). All of the classic antipsychotic drugs produce extrapyramidal side effects. The atypical antipsychotic, clozapine, has a low incidence of early onset extrapyramidal side effects (16) and low risk for the development of tardive dyskinesia (9). In rats, clozapine only produces catalepsy at very high doses (13) and it lacks the anti-apomorphine effects of classical neuroleptics (44). Clozapine also has relatively fewer effects on motor behavior when compared to classic neuroleptics (2). In recent years scientists have been using neuroleptic-induced vacuous jaw movements as an index of risk for extrapyramidal side effects. There is some controversy over whether these vacuous jaw movements constitute a model for early onset extrapyramidal side effects such as Parkinsonian tremor (24) or late-onset side effects such as tardive dyskinesia (40). There are several lines of evidence to suggest that vacuous jaw movements are a more appropriate model for Parkinsonian tremor than tardive dyskinesia. First of all, tardive dyskinesia takes months to develop and Parkinsonism can occur relatively early in the course of drug administration. Vacuous jaw movements have been found to occur in the first few days of administration (37,43). Second,
Haloperidol
Extrapyramidal side effects
anticholinergic drugs exacerbate tardive dyskinesia (17). Coadministration of anticholinergics attenuates haloperidol-induced vacuous jaw movements, and the rapid withdrawal of coadministration of the anticholinergic after 10 days produces a large increase in vacuous jaw movements in rats (43). This is exactly the opposite of what occurs in tardive dyskinesia in humans. When anticholinergics are withdrawn in humans, dyskinetic movements improve (8). Unlike haloperidol, clozapine does not produce vacuous jaw movements at doses analogous to its therapeutic range in humans (21,42). Therefore, haloperidol and clozapine will be used as the two target drugs for comparing raclopride's effects. Raclopride is a selective D 2 antagonist (27), which originally showed promise as a potential antipsychotic drug because it dose-dependently inhibits the behavioral changes induced by d-amphetamine and quinpirole (29,33). Raclopride also showed a high separation between the doses necessary to block apomorphine-induced hyperactivity and those doses that induce catalepsy (31), and chronic administration of 1.0 m g / k g of raclopride did not produce vacuous jaw movements (39). Because raclopride subsequently was shown to produce extrapyramidal side effects in human clinical trials (30), it could call into question the legitimacy of the vacuous jaw movement assay as a predictor of human extrapyra-
i To whom requests for reprints should be addressed.
253
254
STEINPREIS, KACZMAREK AND HARRINGTON
midal side effects. However, the previous research with raclopride in rats examined only a single low dose of raclopride and did not look at the effects of raclopride in the first month of administration, which would parallel the time course of the human clinical trials and allow for a prediction of early onset extrapyramidal side effects. Therefore, the goal of the present study was to introduce the first acute dose-response curve for the effects of raclopride on vacuous jaw movements to determine the consistency with which this assay is predictive of results in human clinical trials.
V A C U
S
8°f
70 68
AJ
501-
W
40~
. *
*
20 M
L
:
o
DAY8
DAY15
DAYS O F N E U R O L E P T I C
METHOD
VEH
'*
.__
*_L.;'
L .1
. . . . .
DAY1
The subjects in this experiment were 86 male Sprague-Dawley rats obtained from Harlan Sprague-Dawley (Indianapolis, IN). The rats were approximately 3 months of age at the start of the experiment and weighed between 250 and 300 g. All rats were housed individually in a colony room maintained at 20°C, with a 12-h light/dark cycle (lights on at 0700 h). Standard lab chow and water were available ad lib. Haloperidol was obtained from Sigma Chemical Company (St. Louis, MO) and injected in doses of 0.2, 0.4, and 0.8 mg/kg. Clozapine was obtained from Sandoz (St. Louis, MO) and injected in a dose of 2.0, 4.0, and 8.0 mg/kg. Raclopride was obtained from Astra Merck (Sodartalje, Sweden) and injected in a dose of 1.0, 3.0, and 6.0 mg/kg. All neuroleptics were dissolved a 0.3% tartaric acid vehicle. The 3 days before injections and observations began, rats were habituated to the observation tube each day for a 10-rain period. Rats received 29 single daily IP injections of either raclopride (n = 6), haloperidol (n = 8), clozapine (n = 6), or tartaric acid vehicle (n = 4 or n = 8 in each group). The rats were observed on the first day of neuroleptic administration, and then again after 1 and 2 weeks and 1 month (i.e., days 1, 8, 15, and 29). On each observation day, the rats were placed individually into a 12 × 3.5 in. Plexiglas observation tube 55 min after injection and allowed to habituate for a 5-min period. The 55 min postinjection start time for habituation to the tube was selected based on pilot data from our laboratory and previous studies using haloperidol (43). The tubes were mounted horizontally to a Plexiglas base and both ends of the tube were fitted with stainless steel wire mesh during observations to allow for air flow to the rat. Two trained observers, blind to the drug and dose each rat had received, recorded the frequency of vacuous jaw movements during a 5-min observation period, using electromechanical counters connected to a microcomputer. Vacuous jaw movements were defined as a rapid vertical deflection of the lower jaw, which was not directed at any particular stimulus. The observers also recorded tongue protrusions and yawning, but these behaviors did not occur with enough frequency for any of the drugs to be useful as a behavioral assay or for statistical analysis.
~
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DAY29
ADMINISTRATION
i~--~ 0.2 mg/kg HAL
, F _ j 0.4 mg/kg HAL
~
0.8 mg/kg HAL
*An asterisk indil~atee a significant difference from vehicle on that day.
FIG. 1. Mean+ SEM number of haloperidol-inducedvacuousjaw movements in rats. * Significantdifference from vehicle on that day.
action, F(12, 112)=4.78, p < 0.0001. On day 1, only the highest dose of haloperidol produced significant elevations in vacuous jaw movements compared to the vehicle group ( p < 0.05). By day 8 all three doses of haioperidol produced significant elevations in vacuous jaw movements compared to the vehicle group (from low to high: p <0.001, p < 0.01, and p < 0.001, respectively). There were also significant elevations on day 15 for all three dose groups (from low to high: p < 0.001, p < 0.001, and p < 0.005, respectively). On day 22, the mediumand high-dose groups were significantly higher in the mediumand high-dose haloperidol groups ( p < 0.001 and p < 0.05, respectively). On day 29, there were also significant elevations in vacuous jaw movements in the medium- and high-dose haloperidol groups compared to the vehicle group ( p < 0.001 and p < 0.0001, respectively). The data for clozapine are presented in Fig. 2. There were significant main effects for drug treatment, F(3, 28)= 29.9, p < 0.001, days, F(4, 112) = 7.81, p < 0.001, and the interaction, F(12, 112)= 3.99, p < 0.001. The only significant elevations in vacuous jaw movements were produced by the high dose of clozapine on day 1 ( p < 0.001), day 8 ( p < 0.001), day 15
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RESULTS Interrater reliabilities for the two observers were calculated for each day and for all days interrater reliability was found to be 0.96 or better. Therefore, all data analysis was performed on the arithmetic mean of the observer's scores. The effects of each drug on vacuous jaw movements was analyzed separately using a five by four factorial ANOVA, with repeated measures across the 5-day observations were recorded. To determine the differences between drug effects, separate Tukey tests were performed on each of the days. The data for haloperidol are presented in Fig. 1. There were significant main effects for drug treatment, F(3, 28)= 41.6, p < 0.0001), days, F(4, 112) = 16.36, p < 0.0001, and the inter-
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i ii~] 4.0 mg/kg CLOZ
~11 8.0 mg/kg CLOZ
*An asterisk inidcates a significant difference from vehicle on that day.
FIG. 2. Mean+ SEM number of clozapine-inducedvacuous jaw movements in rats. * Significantdifference from vehicle on that day.
ATYPICAL ANTIPSYCHOTICS
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DAYS OF NEUROLEPTIC ADMINISTRATION I m
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*An a s t e r i s k inidcate8 a s i g n i f i c a n t d i f f e r e n c e from vehicle on that day.
FIG. 3. Mean + SEM number of raclopride-induced vacuous jaw movements in rats. * Significant difference from vehicle on that day. ( p < 0.001), and day 22 ( p < 0.01). The data for raclopride are presented in Fig. 3. There was a significant main effect for drug treatment, F(3, 18)= 31.96, p < 0,0001, but not days, F(4, 72) = 0.97, p > 0.05, or the interaction, F(12, 7 2 ) = 1.08, p > 0.05. Post hoc analysis revealed that, on day I, both the medium and high doses of raclopride produced significant elevations in vacuous jaw movements ( p < 0.001 and p < 0.005, respectively). This pattern also occurred on day 8 ( p < 0.001 and p < 0.05, respectively), day 15 ( p < 0.001 and p < ,001), day 22 ( p < 0.01 and p < 0.01, respectively), and day 29 ( p <0.0001 and p <0.01, respectively). DISCUSSION
A variety of behavioral assays have been used to predict the atypical antipsychotic profile, including the reversal of amphetamine- or apomorphine-induced locomotor activity (31,45), the measurement of catalepsy (26), the spontaneous withdrawal of fore- and hindlimbs (14), and the production of vacuous jaw movements (41,43). Preliminary pilot data from our laboratory have indicated that screening for vacuous jaw movements may detect risk for extrapyramidal side effects, not detected by screening for catalepsy (42). The results of the present experiment indicate that clozapine only produced significant elevations in vacuous jaw movements at its highest doses and these results are consistent with the literature (21,25). Research with humans has indicated that clozapine may even have a beneficial effect upon tremor (18,32). Haloperidol produced significant elevations in vacuous jaw movements in the present study, which is also consistent with the literature (36,41,43).
This study is the first to report that raclopride consistently produces vacuous jaw movements with acute administration and these results were apparent on the first day of administration. These results are consistent with the human clinical trials (30) and lend support to the use of the vacuous jaw movement assay as a predictor for early onset extrapyramidal side effects in humans. Although raclopride has been shown to have a lower propensity to induce catalepsy than haloperidol does (38), haloperidol and raclopride have been found to be equipment at blocking apomorphine- and amphetamine-induced hyperactivity (1,22,31) and appear to have similar patterns of response on conditioned avoidance tasks (23). Taken together, these findings may indicate that the vacuous jaw movement assay may be more sensitive to the production of early onset extrapyramidal side effects in humans than the catalepsy assay. The results of a more direct comparison between these two assays remains an empirical question. Our laboratory has recently demonstrated that vacuous jaw movements are detectable in the novel antipsychotic, amperozide (42). Amperozide was selected for human trials, in part due to its failure to produce catalepsy in rats or antagonize amphetamineinduced stereotypies (12). However, preliminary reports from human studies indicate that amperozide is producing abnormal motor responses in humans (3). Taken together, these findings argue for the additional use of screening for vacuous jaw movements. Catalepsy screening would continue to be included to narrow down the atypical profile and the failure to produce vacuous jaw movements would be the final selection determinant. Thus far, clozapine appears to be one of only two compounds that would safely pass through such a procedure (42). Melperone is the other compound that has demonstrated effective in the treatment of schizophrenia (5,6). This drug has been used in Scandinavia for two decades with very few reports of extrapyramidal side effects in humans (5,10), and it does not appear to produce vacuous jaw movements in rats (20). Like clozapine, this drug has been shown effective in the treatment of psychosis with few extrapyramidal side effects (7). Also, meiperone has a weaker affinity for D 2 dopamine receptor than the D 4 receptor (28) and a stronger effect on limbic as opposed to striatal dopamine (11). Also, clozapine and melperone have similar effects on fos-like immunoreactivity in the forebrain, which has been associated with the atypical antipsychotic profile (34). These neurochemical and human behavioral similarities between melperone and clozapine help support our contention that adding vacuous jaw movements to catalepsy screening will better predict antipsychotics with the atypical profile that do not produce extrapyramidal side effects in humans. There are numerous novel atypical antipsychotics that have not been screened for the production of vacuous jaw movements, and such information could have a valuable impact on shaping the selection process of antipsychotic compounds for human trials.
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