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discontinuation-induced hyperthermia in rats
Progress in Neuro-Psychopharmacology & Biological Psychiatry 31 (2007) 1500 – 1503 www.elsevier.com/locate/pnpbp
Olanzapine withdrawal/discontinuation-induced hyperthermia in rats Andrew J. Goudie a,⁎, Jon C. Cole a , Harry R. Sumnall b a
School of Psychology, University of Liverpool, Eleanor Rathbone Building, Bedford Street North, Liverpool, L69 7ZA, UK b Centre for Public Health, Liverpool John Moores University, Liverpool, UK Received 25 April 2007; received in revised form 6 July 2007; accepted 6 July 2007 Available online 13 July 2007
Abstract In female rats olanzapine (4 mg/kg b.i.d., i.p.) induced acute hypothermia, followed by very rapid full tolerance. With more prolonged treatment (over N 10 days) the hypothermic effect of olanzapine was reinstated. Subsequent withdrawal after 18 days of treatment induced very rapid onset (within 1 day) hyperthermia, which was time limited, dissipating completely over 3–4 days. These findings are similar to previous findings with clozapine [Goudie A Smith J Robertson A Cavanagh C (1999). Clozapine as a drug of dependence. Psychopharmacology; 142: 369–374.]. Although the mechanism(s) involved in the secondary hypothermic effect of olanzapine are, at present, unclear; the withdrawal hyperthermia observed represents the first report of a clear discontinuation effect of olanzapine. Such discontinuation effects are probably observed with many antipsychotic drugs. Since they have been suggested to facilitate relapse to psychosis and to interfere with subsequent clinical responses to antipsychotics, they merit further detailed analysis in both clinical and preclinical studies. © 2007 Elsevier Inc. All rights reserved. Keywords: Antipsychotic; Discontinuation; Olanzapine; Relapse; Tolerance; Withdrawal
1. Introduction Some years ago we reported that in rats clozapine induces acute hypothermia, tolerance to such hypothermia with chronic treatment, and subsequent time-related withdrawal-induced hyperthermia (Goudie et al., 1999). We therefore reviewed the possible clinical significance of the clozapine withdrawal/ discontinuation syndrome (Goudie, 2000), and suggested that clozapine discontinuation induces somatic withdrawal signs (such as hyperthermia), and that the “stress” experienced when such withdrawal signs occur may facilitate relapse to psychosis (see also Baldessarini et al., 1999a,b; Healy and Tranter, 1999). We suggested that it was important to study in much greater detail antipsychotic drug (APD) discontinuation syndromes both pre-clinically and clinically. Despite these findings, subsequent studies in this area have been relatively limited. Abbreviations: APD, Antipsychotic drug; D1, Dopamine1 (receptor); D2, Dopamine2 (receptor); D3, Dopamine3 (receptor); 5-HT1A, Serotonin1A (receptor); 5-HT2A, Serotonin2A (receptor). ⁎ Corresponding author. Tel.: +44 151 794 1124; fax: +44 151 794 2945. E-mail address: [email protected] (A.J. Goudie). 0278-5846/$ - see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.pnpbp.2007.07.007
Moncrieff (2006) recently reviewed the literature on APD withdrawal and its possible relationship to relapse. She concluded that withdrawal effects in the clinic are more often observed following treatment with clozapine than with other APDs, and that some withdrawal effects are suggestive of responses which are not simply attributable to the return of an underlying disorder (e.g. psychotic symptoms in subjects with no psychiatric history). She therefore suggested that APD discontinuation may facilitate relapse above the level expected due to the underlying disorder. However, she stressed that the available data are limited and the underlying mechanisms unclear (see also Goudie, 2000). Moreover, she stressed that there is a need for further research in this area. This may be of particular importance given that there is some evidence that APD discontinuation may interfere with subsequent clinical responses to APDs (Grassi et al., 1999; Meltzer et al., 1996; Tollefson et al., 1999; Fernandez et al., 2005; Miodownik et al., 2006; although cf. Pickar and Bartko, 2003). With these various considerations in mind, we set out to extend our work with clozapine, by examining the consequences of olanzapine withdrawal in rats. Specifically, we examined the effects of acute and chronic administration of olanzapine and
A.J. Goudie et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 31 (2007) 1500–1503
subsequent olanzapine withdrawal, on the assumption that we might be able to observe acute olanzapine-induced hypothermia, tolerance to such hypothermia, and subsequent withdrawal/ discontinuation-induced hyperthermia. Thus we set out to determine whether withdrawal/discontinuation effects of olanzapine can be detected in rats, in the hope that such studies will be of value in developing this important field of research.
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the last drug or vehicle treatment, the next 24 h later, etc. Body temperatures were recorded in gently restrained rats in a temperature and humidity controlled room with a Comark™ microprocessor thermometer attached to a lubricated rectal probe. Temperature recordings were taken to the nearest 0.1 °C 20 s after insertion of the probe. 2.3. Statistics
2. Methods The work reported was conducted in accord with The Animals (Scientific Procedures) Act 1986 under U.K. Home Office licensing. 2.1. Subjects 44 individually housed female Wistar rats (circa 300 g at the start of the study) were maintained in a temperature and humidity controlled room, on an ad lib diet of standard chow (Bantin and Kingman, Hull, U.K.). They had unlimited access to water, and were habituated to their housing for 7 days prior to the study. The 12:12 h light/dark cycle was set so that lights were on during the day. 2.2. Procedure The study involved two phases. Chronic treatment (days 1–18) was followed by withdrawal (days 19–22). A control group (n = 14) received vehicle both during the chronic treatment phase and during the withdrawal phase. An experimental group (n = 30) received olanzapine during the chronic treatment phase and vehicle during the withdrawal phase. Initially we intended to run a dose/response study in which half of the drugged rats received 2 mg/kg of olanzapine and half 4 mg/kg. However, administration of these two specific doses on day 1 of the study (to 15 rats at each of the two doses) indicated that olanzapine at 4 mg/kg just failed to induce significant hypothermia relative to controls and olanzapine at 2 mg/kg had a smaller hypothermic effect (see Results). Thus on day 2 all 30 experimental rats received olanzapine at 4 mg/kg. This procedure was adopted in order to increase the power of the study to detect a significant hypothermic effect of olanzapine at 4 mg/kg. On day 2, olanzapine at 4 mg/kg induced significant hypothermia relative to vehicle treated controls (see Results), and this dose was therefore administered to all drugged rats on all subsequent treatment days (3–18). Olanzapine was administered b.i.d. as it has a short half life in rats (Aravagiri et al., 1999), and short duration behavioural effects in female rats after i.p injection in our laboratory (Goudie et al., 2007). During the chronic treatment phase olanzapine treated rats received their first daily dose in the morning (1000 h) and their second daily dose 4.5 h later. Controls received matched vehicle treatments. Body temperature recordings during the chronic treatment phase were always taken 1 h after the first daily injection of either olanzapine or vehicle. Body temperature recordings were taken in the withdrawal phase of the study at exactly the same time as during the chronic treatment phase, i.e. the first recording in this phase of the study was taken 20.5 h after
Data from the two phases of the study were initially analysed separately. As the drugged rats received 4 mg/kg of olanzapine b.i.d. on days 2–18 only (see above), these chronic treatment data were subjected to a factorial (2) groups × (17) days repeated measures ANOVA. The withdrawal data obtained over days 19–22 were subjected to a similar factorial (2) groups × (4) days repeated measures ANOVA. Post hoc tests for pairwise comparisons between the two groups on each day involved t-tests with Bonferroni correction. All analyses were conducted with SPSS (v14.0). 2.4. Drugs Olanzapine (Eli Lilly, UK) was administered i.p., dissolved in a few drops of 0.1 M HCl, diluted with distilled water and buffered back with NaOH to a pH around 5.5 and injected at a volume of 2 ml/kg. 3. Results On day 1, when half the 30 drugged rats received 2 mg/kg of olanzapine and half 4 mg/kg (see Methods), the Mean (SE) body temperatures recorded in °C were:— Controls 37.121 (0.094), 2 mg/kg treated rats 36.927 (0.119), 4 mg/kg treated rats 36.807 (0.151). A t test indicated that the 4 mg/kg treated rats just failed to differ significantly from the Controls (p = 0.094, two tailed). Thus on day 2, and on all following days, olanzapine was administered at the higher 4 mg/kg dose to all 30 drugged rats to enhance the power of the study, and thus ensure that we observed statistically significant olanzapine-induced hypothermia at the 4 mg/kg dose. Group mean temperatures recorded throughout the rest of the study (i.e. from day 2 onwards) are shown in Fig. 1. For the chronic treatment phase of the study (days 2–18) there was a group × days interaction (F(16, 672)= 3.476 p = 0.0001). Subsequent post hoc tests revealed that olanzapine treated rats showed significant hypothermia on the first day of group treatment with olanzapine at 4 mg/kg (i.e. on day 2), and on intermittent days towards the end of treatment (see Fig. 1). The data show that olanzapine at 4 mg/kg induced significant initial hypothermia, to which full tolerance developed rapidly. This persisted until day 11. However, on day 12, and on intermittent following days, significant drug-induced hypothermia relative to controls returned. Olanzapine treated rats showed lower body temperatures than controls throughout days 12–18, even if the hypothermia was not actually significant on specific days (i.e. on days 15 and 16). Group mean temperatures recorded throughout the withdrawal phase of the study (days 19–22 — see Fig. 1) revealed a
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Fig. 1. Group Mean (and SE) temperatures (°C) recorded in rats treated with either Olanzapine or Vehicle (controls) during the Chronic Treatment phase of the study, and during the Withdrawal phase of the study when both groups were treated with vehicle. Specific days on which Olanzapine treated rats differed significantly from Vehicle treated rats are indicated by ⋆ (Repeated measures ANOVAs followed by t tests with Bonferroni correction).
group effect (F(1, 42) = 4.057 p = 0.05). Post hoc tests revealed that olanzapine pretreated rats showed significant hyperthermia in withdrawal on the first day of withdrawal (day 19), but not on later days, although there was a time-related reduction in body temperature over days in these rats. Between group t tests comparing the temperatures recorded in these rats on day 19, on the first day of withdrawal, with those recorded in controls on the first (day 2) and last (day 18) day of the chronic treatment phase of the study indicated that there was significant hyperthermia in the olanzapine pretreated rats for both comparisons (two tailed ps = 0.0001 and 0.0009 respectively), confirming that olanzapine withdrawal induced significant hyperthermia on day 19. In summary, olanzapine at 4 mg/kg b.i.d. induced initial hypothermia, which was short lived as full tolerance developed rapidly. However, with further chronic treatment drug-induced hypothermia returned. On olanzapine withdrawal, significant hyperthermia was observed very rapidly, although this dissipated over days. 4. Discussion As expected, olanzapine induced hypothermia. Such an effect has been observed with both olanzapine and clozapine in humans and experimental animals (Blessing, 2004), although the receptors involved in mediating olanzapine-induced hypothermia are not clear, as a very wide range of different receptors (D1, D3, alpha-adrenoceptor1, 5-HT1A and 5-HT2A) have all been implicated in APD effects on thermoregulation (Goudie et al., 1999; Blessing, 2004). The initial olanzapine-induced hypothermia showed rapid, full tolerance. However, after the development of full tolerance, olanzapine-induced hypothermia was observed consistently after day 12, thus the drug effect appeared to be reinstated. There are various potential explanations for these data. It is possible that olanzapine accumulation developed over days of treatment and
reinstated the drug effect. However, this seems an unlikely explanation for these findings as on the first day of withdrawal marked hyperthermia was observed. Alternatively, in female rats, as used in this study, olanzapine induces weight gain (Goudie et al., 2002; Cooper et al., 2005; Patil et al., 2006). This might have altered the pharmacokinetics of olanzapine, and thus resulted in the reinstatement of hypothermia. Such effects of APDs on body weight and adiposity are not seen in female rodents treated with clozapine (Baptista et al., 1993a; Albaugh et al., 2006). Thus differences between this study and our study with clozapine in which APD-induced hypothermia was not reinstated after tolerance developed (Goudie et al., 1999) might be explicable in terms of pharmacokinetic factors related to body composition. A further potential explanation for the reinstatement of hypothermia may relate to the fact that such hypothermia can be induced by APD actions at many different receptors (Blessing, 2004). It is possible that tolerance to olanzapine's initial effect mediated at one receptor subsequently “unmasked” a similar effect mediated at a different receptor, although this hypothesis clearly requires further research. Olanzapine withdrawal-induced hyperthermia showed rapid onset, was brief in duration and time related, returning to control levels after 3 to 4 days, as reported for clozapine withdrawalinduced hyperthermia (Goudie et al., 1999). To the best of our knowledge, this is the first study to report a discontinuation effect for olanzapine. Clozapine withdrawal in humans induces various somatic withdrawal signs such as vomiting, insomnia, diarrhoea, agitation and headache, as well as signs of psychosis such as delusions and hallucinations, and motoric effects (Moncrieff, 2006; Goudie, 2000; Stanford and Fowler, 1997). Thus our data clearly do not represent a full characterisation of the olanzapine discontinuation syndrome, which requires full characterisation. Since the receptor mechanism(s) involved in the acute hypothermia induced by olanzapine are unclear, it should be obvious that the neuroadaptations(s) involved in the observed withdrawal hyperthermia are also unclear. However, we have shown that it is possible to induce tolerance in rats discriminating clozapine (Goudie et al., 2007). Such tolerance was spontaneously fully reversible and was therefore probably pharmacodynamic. The neuroadaptations(s) involved in such tolerance were possibly the same as those involved in clozapine discontinuation phenomena. We have also shown that spontaneously fully reversible cross-tolerance to clozapine can be induced by olanzapine (Goudie et al., 2007), implying that these two APDs induce similar neuroadaptations(s), in accord with the idea that they may induce similar discontinuation phenomena. Baptista (1989) and Baptista et al. (1993b) reported that chronic treatment with sulpiride in rats induces initial hyperphagia, followed by withdrawal-induced hypophagia. Since withdrawal-induced hypophagia was accompanied by enhanced amphetamine-induced anorexia, Baptista et al. (1993b) suggested that it was mediated by treatment-induced enhanced D2 receptor sensitivity. In accord with this theorising, tolerance to the effects of APDs in a conditioned avoidance response paradigm in rats has recently been associated with progressively developing enhanced dopamine receptor activity, leading the
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authors to conclude that progressively developing “breakthrough dopamine supersensitivity” opposing dopamine antagonist actions of APDs causes therapeutic tolerance to APDs (Samaha et al., 2007). 5. Conclusions The data reported here show that, like clozapine, olanzapine withdrawal induced a rapid onset, time-limited somatic discontinuation effect. This study is, we believe, the first to demonstrate a discontinuation effect with olanzapine. Withdrawal of various types of APDs, including older APDs, can induce discontinuation effects, although these tend to be neglected (Tranter and Healey, 1998; Healy and Tranter, 1999). The study reported, and other studies of APD tolerance, cross-tolerance and withdrawal (Baptista, 1989; Baptista et al., 1993b; Goudie et al., 2007; Stanford and Fowler, 1997; Samaha et al., 2007) suggest that these phenomena and APD-induced neuroadaptations can readily be studied in experimental animals. Parallel clinical studies are clearly needed. In particular, the important questions as to whether APD withdrawal effects facilitate relapse to psychosis and/or interfere with subsequent clinical responses to APDs need investigation. References Albaugh L, Henry C, Bello N, Hajnal A, Lynch S, Halle B, et al. Hormonal and metabolic effects of olanzapine and clozapine related to body weight. Obesity 2006;14:36–51. Aravagiri M, Teper Y, Marder S. Pharmacokinetics and tissue distribution of olanzapine in rats. Biopharm Drug Dispos 1999;999(20):369–77. Baldessarini R, Viguera A, Tondo L. Discontinuing psychotropic agents. J Psychopharmacol 1999a;13:292–3. Baldessarini R, Tondo L, Viguera A. Discontinuing lithium maintenance treatment in bipolar disorder: risks and implications. Bipolar Disord 1999b;1:17–24. Baptista T. Hypophagia after long term administration of sulpiride in adult female rats: a model of D2 dopamine receptor supersensitivity. Med Hypotheses 1989;30:5–8. Baptista T, Mata A, Teneud L, De Quijada M, Han H-W, Hernandez L. Effects of long term administration of clozapine on body weight and food intake in rats. Pharmacol Biochem Behav 1993a;45:51–4. Baptista T, Teneud L, Hernandez L. Enhancement of amphetamine anorexia after chronic sulpiride administration in rats. Pharmacol Biochem Behav 1993b;45:45–9.
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Blessing W. Clozapine and olanzapine, but not haloperidol, reverse coldinduced and lipopolysaccharide-induced cutaneous vasoconstriction. Psychopharmacology 2004;175:481–93. Cooper G, Pickavance L, Wilding J, Halford J, Goudie A. A parametric analysis of olanzapine-induced weight gain in female rats. Psychopharmacology 2005;181:80–9. Fernandez H, Trieschmann M, Okun M. Rebound psychoses: effect of discontinuation of antipsychotics in Parkinson's disease. Mov Disord 2005;20:104–15. Goudie A. What is the clinical significance of the discontinuation syndrome seen with clozapine? J Psychopharmacol 2000;14:188–92. Goudie A, Smith J, Robertson A, Cavanagh C. Clozapine as a drug of dependence. Psychopharmacology 1999;142:369–74. Goudie A, Smith J, Halford J. Characterization of olanzapine induced weight gain in rats. J Psychopharmacol 2002;16:291–6. Goudie A, Cole J, Sumnall H. Olanzapine and JL 13 induce cross-tolerance to the clozapine discriminative stimulus in rats. Behav Pharmacol 2007;18:9-17. Grassi B, Ferrari R, Epifani M, Dragoni C, Cohen S, Scarone S. Clozapine lacks previous clinical efficacy when restarted after a period of discontinuation. A case series. Eur Neuropsychopharmacol 1999;9:479–81. Healy D, Tranter R. Pharmacological stress/diathesis syndromes. J Psychopharmacol 1999;13:287–90. Meltzer H, Lee M, Ranjan R, Mason E, Cola P. Relapse following clozapine withdrawal. Psychopharmacology 1996;124:176–87. Miodownik C, Lerner V, Kibari A, Toder D, Cohen H. The effect of sudden clozapine discontinuation on management of schizophrenic patients: a retrospective controlled study. J Clin Psychiatry 2006;67:1204–8. Moncrieff J. Does antipsychotic withdrawal provoke psychosis? Review of the literature on rapid onset psychosis (supersensitivity psychosis) and withdrawal-related relapse. Acta Psychiatr Scand 2006;114:3-13. Patil B, Kulkarni N, Unger B. Elevation of systolic blood pressure in an animal model of olanzapine induced weight gain. Eur J Pharmacol 2006;551:112–5. Pickar D, Bartko J. Effect size of symptom status in withdrawal of typical antipsychotics and subsequent clozapine treatment in patients with treatment resistant schizophrenia. Am J Psychiatry 2003;160:1133–8. Samaha A, Seeman P, Stewart J, Rajabi H, Kapur S. “Breakthrough” dopamine supersensitivity during ongoing antipsychotic treatment leads to treatment failure over time. J Neurosci 2007;27:2979–86. Stanford J, Fowler S. Similarities and differences between the subchronic and withdrawal effects of clozapine and olanzapine on forelimb steadiness. Psychopharmacology 1997;132:408–14. Tollefson G, Dellva M, Mattler C, Kane J, Wirshing D, Kinon B. Controlled doubleblind investigation of clozapine discontinuation symptoms with conversion to either olanzapine or placebo. J Clin Psychopharmacol 1999;19:435–43. Tranter R, Healey D. Neuroleptic discontinuation syndromes. J Psychopharmacol 1998;12:401–6.
Olanzapine withdrawal/discontinuation-induced hyperthermia in rats Andrew J. Goudie a,⁎, Jon C. Cole a , Harry R. Sumnall b a
School of Psychology, University of Liverpool, Eleanor Rathbone Building, Bedford Street North, Liverpool, L69 7ZA, UK b Centre for Public Health, Liverpool John Moores University, Liverpool, UK Received 25 April 2007; received in revised form 6 July 2007; accepted 6 July 2007 Available online 13 July 2007
Abstract In female rats olanzapine (4 mg/kg b.i.d., i.p.) induced acute hypothermia, followed by very rapid full tolerance. With more prolonged treatment (over N 10 days) the hypothermic effect of olanzapine was reinstated. Subsequent withdrawal after 18 days of treatment induced very rapid onset (within 1 day) hyperthermia, which was time limited, dissipating completely over 3–4 days. These findings are similar to previous findings with clozapine [Goudie A Smith J Robertson A Cavanagh C (1999). Clozapine as a drug of dependence. Psychopharmacology; 142: 369–374.]. Although the mechanism(s) involved in the secondary hypothermic effect of olanzapine are, at present, unclear; the withdrawal hyperthermia observed represents the first report of a clear discontinuation effect of olanzapine. Such discontinuation effects are probably observed with many antipsychotic drugs. Since they have been suggested to facilitate relapse to psychosis and to interfere with subsequent clinical responses to antipsychotics, they merit further detailed analysis in both clinical and preclinical studies. © 2007 Elsevier Inc. All rights reserved. Keywords: Antipsychotic; Discontinuation; Olanzapine; Relapse; Tolerance; Withdrawal
1. Introduction Some years ago we reported that in rats clozapine induces acute hypothermia, tolerance to such hypothermia with chronic treatment, and subsequent time-related withdrawal-induced hyperthermia (Goudie et al., 1999). We therefore reviewed the possible clinical significance of the clozapine withdrawal/ discontinuation syndrome (Goudie, 2000), and suggested that clozapine discontinuation induces somatic withdrawal signs (such as hyperthermia), and that the “stress” experienced when such withdrawal signs occur may facilitate relapse to psychosis (see also Baldessarini et al., 1999a,b; Healy and Tranter, 1999). We suggested that it was important to study in much greater detail antipsychotic drug (APD) discontinuation syndromes both pre-clinically and clinically. Despite these findings, subsequent studies in this area have been relatively limited. Abbreviations: APD, Antipsychotic drug; D1, Dopamine1 (receptor); D2, Dopamine2 (receptor); D3, Dopamine3 (receptor); 5-HT1A, Serotonin1A (receptor); 5-HT2A, Serotonin2A (receptor). ⁎ Corresponding author. Tel.: +44 151 794 1124; fax: +44 151 794 2945. E-mail address: [email protected] (A.J. Goudie). 0278-5846/$ - see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.pnpbp.2007.07.007
Moncrieff (2006) recently reviewed the literature on APD withdrawal and its possible relationship to relapse. She concluded that withdrawal effects in the clinic are more often observed following treatment with clozapine than with other APDs, and that some withdrawal effects are suggestive of responses which are not simply attributable to the return of an underlying disorder (e.g. psychotic symptoms in subjects with no psychiatric history). She therefore suggested that APD discontinuation may facilitate relapse above the level expected due to the underlying disorder. However, she stressed that the available data are limited and the underlying mechanisms unclear (see also Goudie, 2000). Moreover, she stressed that there is a need for further research in this area. This may be of particular importance given that there is some evidence that APD discontinuation may interfere with subsequent clinical responses to APDs (Grassi et al., 1999; Meltzer et al., 1996; Tollefson et al., 1999; Fernandez et al., 2005; Miodownik et al., 2006; although cf. Pickar and Bartko, 2003). With these various considerations in mind, we set out to extend our work with clozapine, by examining the consequences of olanzapine withdrawal in rats. Specifically, we examined the effects of acute and chronic administration of olanzapine and
A.J. Goudie et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 31 (2007) 1500–1503
subsequent olanzapine withdrawal, on the assumption that we might be able to observe acute olanzapine-induced hypothermia, tolerance to such hypothermia, and subsequent withdrawal/ discontinuation-induced hyperthermia. Thus we set out to determine whether withdrawal/discontinuation effects of olanzapine can be detected in rats, in the hope that such studies will be of value in developing this important field of research.
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the last drug or vehicle treatment, the next 24 h later, etc. Body temperatures were recorded in gently restrained rats in a temperature and humidity controlled room with a Comark™ microprocessor thermometer attached to a lubricated rectal probe. Temperature recordings were taken to the nearest 0.1 °C 20 s after insertion of the probe. 2.3. Statistics
2. Methods The work reported was conducted in accord with The Animals (Scientific Procedures) Act 1986 under U.K. Home Office licensing. 2.1. Subjects 44 individually housed female Wistar rats (circa 300 g at the start of the study) were maintained in a temperature and humidity controlled room, on an ad lib diet of standard chow (Bantin and Kingman, Hull, U.K.). They had unlimited access to water, and were habituated to their housing for 7 days prior to the study. The 12:12 h light/dark cycle was set so that lights were on during the day. 2.2. Procedure The study involved two phases. Chronic treatment (days 1–18) was followed by withdrawal (days 19–22). A control group (n = 14) received vehicle both during the chronic treatment phase and during the withdrawal phase. An experimental group (n = 30) received olanzapine during the chronic treatment phase and vehicle during the withdrawal phase. Initially we intended to run a dose/response study in which half of the drugged rats received 2 mg/kg of olanzapine and half 4 mg/kg. However, administration of these two specific doses on day 1 of the study (to 15 rats at each of the two doses) indicated that olanzapine at 4 mg/kg just failed to induce significant hypothermia relative to controls and olanzapine at 2 mg/kg had a smaller hypothermic effect (see Results). Thus on day 2 all 30 experimental rats received olanzapine at 4 mg/kg. This procedure was adopted in order to increase the power of the study to detect a significant hypothermic effect of olanzapine at 4 mg/kg. On day 2, olanzapine at 4 mg/kg induced significant hypothermia relative to vehicle treated controls (see Results), and this dose was therefore administered to all drugged rats on all subsequent treatment days (3–18). Olanzapine was administered b.i.d. as it has a short half life in rats (Aravagiri et al., 1999), and short duration behavioural effects in female rats after i.p injection in our laboratory (Goudie et al., 2007). During the chronic treatment phase olanzapine treated rats received their first daily dose in the morning (1000 h) and their second daily dose 4.5 h later. Controls received matched vehicle treatments. Body temperature recordings during the chronic treatment phase were always taken 1 h after the first daily injection of either olanzapine or vehicle. Body temperature recordings were taken in the withdrawal phase of the study at exactly the same time as during the chronic treatment phase, i.e. the first recording in this phase of the study was taken 20.5 h after
Data from the two phases of the study were initially analysed separately. As the drugged rats received 4 mg/kg of olanzapine b.i.d. on days 2–18 only (see above), these chronic treatment data were subjected to a factorial (2) groups × (17) days repeated measures ANOVA. The withdrawal data obtained over days 19–22 were subjected to a similar factorial (2) groups × (4) days repeated measures ANOVA. Post hoc tests for pairwise comparisons between the two groups on each day involved t-tests with Bonferroni correction. All analyses were conducted with SPSS (v14.0). 2.4. Drugs Olanzapine (Eli Lilly, UK) was administered i.p., dissolved in a few drops of 0.1 M HCl, diluted with distilled water and buffered back with NaOH to a pH around 5.5 and injected at a volume of 2 ml/kg. 3. Results On day 1, when half the 30 drugged rats received 2 mg/kg of olanzapine and half 4 mg/kg (see Methods), the Mean (SE) body temperatures recorded in °C were:— Controls 37.121 (0.094), 2 mg/kg treated rats 36.927 (0.119), 4 mg/kg treated rats 36.807 (0.151). A t test indicated that the 4 mg/kg treated rats just failed to differ significantly from the Controls (p = 0.094, two tailed). Thus on day 2, and on all following days, olanzapine was administered at the higher 4 mg/kg dose to all 30 drugged rats to enhance the power of the study, and thus ensure that we observed statistically significant olanzapine-induced hypothermia at the 4 mg/kg dose. Group mean temperatures recorded throughout the rest of the study (i.e. from day 2 onwards) are shown in Fig. 1. For the chronic treatment phase of the study (days 2–18) there was a group × days interaction (F(16, 672)= 3.476 p = 0.0001). Subsequent post hoc tests revealed that olanzapine treated rats showed significant hypothermia on the first day of group treatment with olanzapine at 4 mg/kg (i.e. on day 2), and on intermittent days towards the end of treatment (see Fig. 1). The data show that olanzapine at 4 mg/kg induced significant initial hypothermia, to which full tolerance developed rapidly. This persisted until day 11. However, on day 12, and on intermittent following days, significant drug-induced hypothermia relative to controls returned. Olanzapine treated rats showed lower body temperatures than controls throughout days 12–18, even if the hypothermia was not actually significant on specific days (i.e. on days 15 and 16). Group mean temperatures recorded throughout the withdrawal phase of the study (days 19–22 — see Fig. 1) revealed a
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Fig. 1. Group Mean (and SE) temperatures (°C) recorded in rats treated with either Olanzapine or Vehicle (controls) during the Chronic Treatment phase of the study, and during the Withdrawal phase of the study when both groups were treated with vehicle. Specific days on which Olanzapine treated rats differed significantly from Vehicle treated rats are indicated by ⋆ (Repeated measures ANOVAs followed by t tests with Bonferroni correction).
group effect (F(1, 42) = 4.057 p = 0.05). Post hoc tests revealed that olanzapine pretreated rats showed significant hyperthermia in withdrawal on the first day of withdrawal (day 19), but not on later days, although there was a time-related reduction in body temperature over days in these rats. Between group t tests comparing the temperatures recorded in these rats on day 19, on the first day of withdrawal, with those recorded in controls on the first (day 2) and last (day 18) day of the chronic treatment phase of the study indicated that there was significant hyperthermia in the olanzapine pretreated rats for both comparisons (two tailed ps = 0.0001 and 0.0009 respectively), confirming that olanzapine withdrawal induced significant hyperthermia on day 19. In summary, olanzapine at 4 mg/kg b.i.d. induced initial hypothermia, which was short lived as full tolerance developed rapidly. However, with further chronic treatment drug-induced hypothermia returned. On olanzapine withdrawal, significant hyperthermia was observed very rapidly, although this dissipated over days. 4. Discussion As expected, olanzapine induced hypothermia. Such an effect has been observed with both olanzapine and clozapine in humans and experimental animals (Blessing, 2004), although the receptors involved in mediating olanzapine-induced hypothermia are not clear, as a very wide range of different receptors (D1, D3, alpha-adrenoceptor1, 5-HT1A and 5-HT2A) have all been implicated in APD effects on thermoregulation (Goudie et al., 1999; Blessing, 2004). The initial olanzapine-induced hypothermia showed rapid, full tolerance. However, after the development of full tolerance, olanzapine-induced hypothermia was observed consistently after day 12, thus the drug effect appeared to be reinstated. There are various potential explanations for these data. It is possible that olanzapine accumulation developed over days of treatment and
reinstated the drug effect. However, this seems an unlikely explanation for these findings as on the first day of withdrawal marked hyperthermia was observed. Alternatively, in female rats, as used in this study, olanzapine induces weight gain (Goudie et al., 2002; Cooper et al., 2005; Patil et al., 2006). This might have altered the pharmacokinetics of olanzapine, and thus resulted in the reinstatement of hypothermia. Such effects of APDs on body weight and adiposity are not seen in female rodents treated with clozapine (Baptista et al., 1993a; Albaugh et al., 2006). Thus differences between this study and our study with clozapine in which APD-induced hypothermia was not reinstated after tolerance developed (Goudie et al., 1999) might be explicable in terms of pharmacokinetic factors related to body composition. A further potential explanation for the reinstatement of hypothermia may relate to the fact that such hypothermia can be induced by APD actions at many different receptors (Blessing, 2004). It is possible that tolerance to olanzapine's initial effect mediated at one receptor subsequently “unmasked” a similar effect mediated at a different receptor, although this hypothesis clearly requires further research. Olanzapine withdrawal-induced hyperthermia showed rapid onset, was brief in duration and time related, returning to control levels after 3 to 4 days, as reported for clozapine withdrawalinduced hyperthermia (Goudie et al., 1999). To the best of our knowledge, this is the first study to report a discontinuation effect for olanzapine. Clozapine withdrawal in humans induces various somatic withdrawal signs such as vomiting, insomnia, diarrhoea, agitation and headache, as well as signs of psychosis such as delusions and hallucinations, and motoric effects (Moncrieff, 2006; Goudie, 2000; Stanford and Fowler, 1997). Thus our data clearly do not represent a full characterisation of the olanzapine discontinuation syndrome, which requires full characterisation. Since the receptor mechanism(s) involved in the acute hypothermia induced by olanzapine are unclear, it should be obvious that the neuroadaptations(s) involved in the observed withdrawal hyperthermia are also unclear. However, we have shown that it is possible to induce tolerance in rats discriminating clozapine (Goudie et al., 2007). Such tolerance was spontaneously fully reversible and was therefore probably pharmacodynamic. The neuroadaptations(s) involved in such tolerance were possibly the same as those involved in clozapine discontinuation phenomena. We have also shown that spontaneously fully reversible cross-tolerance to clozapine can be induced by olanzapine (Goudie et al., 2007), implying that these two APDs induce similar neuroadaptations(s), in accord with the idea that they may induce similar discontinuation phenomena. Baptista (1989) and Baptista et al. (1993b) reported that chronic treatment with sulpiride in rats induces initial hyperphagia, followed by withdrawal-induced hypophagia. Since withdrawal-induced hypophagia was accompanied by enhanced amphetamine-induced anorexia, Baptista et al. (1993b) suggested that it was mediated by treatment-induced enhanced D2 receptor sensitivity. In accord with this theorising, tolerance to the effects of APDs in a conditioned avoidance response paradigm in rats has recently been associated with progressively developing enhanced dopamine receptor activity, leading the
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authors to conclude that progressively developing “breakthrough dopamine supersensitivity” opposing dopamine antagonist actions of APDs causes therapeutic tolerance to APDs (Samaha et al., 2007). 5. Conclusions The data reported here show that, like clozapine, olanzapine withdrawal induced a rapid onset, time-limited somatic discontinuation effect. This study is, we believe, the first to demonstrate a discontinuation effect with olanzapine. Withdrawal of various types of APDs, including older APDs, can induce discontinuation effects, although these tend to be neglected (Tranter and Healey, 1998; Healy and Tranter, 1999). The study reported, and other studies of APD tolerance, cross-tolerance and withdrawal (Baptista, 1989; Baptista et al., 1993b; Goudie et al., 2007; Stanford and Fowler, 1997; Samaha et al., 2007) suggest that these phenomena and APD-induced neuroadaptations can readily be studied in experimental animals. Parallel clinical studies are clearly needed. In particular, the important questions as to whether APD withdrawal effects facilitate relapse to psychosis and/or interfere with subsequent clinical responses to APDs need investigation. References Albaugh L, Henry C, Bello N, Hajnal A, Lynch S, Halle B, et al. Hormonal and metabolic effects of olanzapine and clozapine related to body weight. Obesity 2006;14:36–51. Aravagiri M, Teper Y, Marder S. Pharmacokinetics and tissue distribution of olanzapine in rats. Biopharm Drug Dispos 1999;999(20):369–77. Baldessarini R, Viguera A, Tondo L. Discontinuing psychotropic agents. J Psychopharmacol 1999a;13:292–3. Baldessarini R, Tondo L, Viguera A. Discontinuing lithium maintenance treatment in bipolar disorder: risks and implications. Bipolar Disord 1999b;1:17–24. Baptista T. Hypophagia after long term administration of sulpiride in adult female rats: a model of D2 dopamine receptor supersensitivity. Med Hypotheses 1989;30:5–8. Baptista T, Mata A, Teneud L, De Quijada M, Han H-W, Hernandez L. Effects of long term administration of clozapine on body weight and food intake in rats. Pharmacol Biochem Behav 1993a;45:51–4. Baptista T, Teneud L, Hernandez L. Enhancement of amphetamine anorexia after chronic sulpiride administration in rats. Pharmacol Biochem Behav 1993b;45:45–9.
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