Similarities and differences between the subchronic and withdrawal effects of clozapine and olanzapine on forelimb force steadiness

Quantitative behavioral models for high-resolution measurement and characterization of tremor in rodents

Tremor is an involuntary, rhythmic movement disorder. Despite its prevalence, the underlying pathophysiology remains poorly understood and effective treatment options are limited. Animal models are essential in enhancing our understanding of the mechanisms of tremorogenesis and developing new therapeutic interventions. Although tremor is amenable to measurement by automated systems, visual observation is still the most prevalent method for recording tremor in animal studies. This review gives a brief summary of two behavioral methods that enable quantitative measurement of forelimb tremor (the press-while-licking task) and whole-body tremor (the force-plate actometer) in rodents. These methods utilize force transducer and computing technologies to generate high-resolution force-time waveforms for automated detection and characterization of tremor. The focus will be on the sensitive, precise, and quantitative measurement of tremors induced in rodents by low-dose pharmacological agents, brain lesion, physical training, and genetic mutations. The methods reviewed here provide new tools that can facilitate preclinical assessment of treatment strategies for tremor.

Experiencing antipsychotic discontinuation: results from a survey of Australian consumers

Despite high reported rates of antipsychotic non-adherence, little is known about consumer experiences during discontinuation. This study was designed to increase understanding of antipsychotic discontinuation from consumer perspectives. In 2011-2012, 98 Australian consumers involved with participating organizations completed an anonymous survey detailing past antipsychotic discontinuation attempts. Of the 88 participants who reported at least one discontinuation attempt, over half (n = 47, 54.7%) reported stopping without clinician knowledge or support. This group was 35% (confidence interval 15.4-54.6%) more likely to stop abruptly than those (n = 41, 45.3%) stopping with clinician support (P = 0.002). Only 10 participants (23.3%) recalled being given information about discontinuation symptoms other than relapse; however, 68 participants (78.2%) reported experiencing a range of discontinuation symptoms including physical, cognitive, emotional, psychotic or sleep-related disturbances. Findings cannot be readily generalized because of sampling constraints. However, the significant number of participants who reported discontinuation symptoms, in addition to psychosis, is consistent with previous research. This study provides new insight into consumer motivations for discontinuation and possible problems in clinical communication that may contribute to frequent non-collaborative discontinuation attempts. Mental health nurses, who play a pivotal role in medication communication events, may benefit from increased awareness of consumer perspectives on this topic.

Antipsychotic discontinuation syndromes: a narrative review of the evidence and its integration into Australian mental health nursing textbooks

In light of the high number of people discontinuing antipsychotics each year, it is essential that nurses develop a robust understanding of all aspects of the discontinuation experience. While there is a large body of published work documenting post-discontinuation relapse rates, less is known about other aspects of the discontinuation experience. This paper presents the results of a narrative review of international studies of antipsychotic discontinuation syndromes and their relevance to nursing practice. Four key mental health nursing textbooks used in student nurse education in Australia are examined to assess how this evidence has been incorporated into clinical recommendations. This review finds that the evidence for discontinuation syndromes could be more widely disseminated and applied than it is at present. Strikingly, this evidence has not been incorporated into key mental health nursing textbooks in Australia at all. Slow integration into nursing published work may be influenced by a number of clinical and research uncertainties. We consider the impact of this silence on key nursing roles of psycho-education and adverse event monitoring during antipsychotic discontinuation periods. Further robust research should be conducted into discontinuation syndromes as a matter of urgency. Given the high number of consumers potentially impacted upon by discontinuation syndromes, nurse authors and educators should consider revising key nursing textbooks to include the currently available information about discontinuation syndromes.

Cannabinoid-induced upregulation of serotonin 2A receptors in the hypothalamic paraventricular nucleus and anxiety-like behaviors in rats

Recent behavioral reports suggest that repeated exposure to cannabis and synthetic cannabinoid agonists is linked with mental disorders associated with dysfunction of serotonin 2A (5-HT2A) receptor neurotransmission such as anxiety and depression. Here, we studied the effect of a nonselective cannabinoid agonist, CP55940, on the activity of 5-HT2A receptors in hypothalamic paraventricular nucleus (PVN). We detected that repeated exposure to CP55940 enhanced the prolactin and corticosterone neuroendocrine responses mediated by 5-HT2A receptors and increased the membrane-associated levels of 5-HT2A receptors in PVN. Importantly, we also detected increased anxiety-like behaviors in CP55940 treated rats compared to controls. The data presented here suggest that the mechanisms mediating the cannabinoid-induced upregulation of 5-HT2A receptors would be brain-region specific, as we were unable to detect a CP55940-induced upregulation of 5-HT2A mRNA. Our results might provide insight into the molecular mechanism by which repeated exposure to cannabinoids could be associated with the pathophysiology of neuropsychiatric disorders.

Young and middle-aged rats exhibit isometric forelimb force control deficits in a model of early-stage Parkinson's disease

Deficits in manual motor control often accompany the early stages of Parkinson's disease (PD), and are often revealed through isometric force tasks. In order to determine whether similar deficits occur in a rat model of early-stage PD, young (8 months) and middle-aged (18 months) rats were trained to produce sustained press-hold-release isometric forelimb responses that allowed for analyses of force output and spectral analysis of forelimb stability and tremor. Rats then received a 6-hydroxydopamine (6-OHDA) infusion into the striatum contralateral to the trained forelimb and were tested for 4 weeks post-lesion. The resulting partial striatal dopamine depletions (which at 41±12% and 43±6% in young and middle-aged rats, respectively, did not differ between the two groups) resulted in isometric forelimb deficits. Specifically, rats exhibited significantly diminished force stability and increased high frequency (10-25Hz) tremor, indicating potential postural disturbances and increased postural tremor, respectively. Durations of press-hold-release bouts were also increased post-lesion, suggesting difficulty in task disengagement. Despite pre-lesion differences in some of the force measures, the effects of partial nigrostriatal DA depletion did not differ between the two age groups. These results support the use of the press-while-licking task in preclinical studies modeling isometric force control deficits in PD.

Olanzapine withdrawal/discontinuation-induced hyperthermia in rats

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 > 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.

Quetiapine (Seroquel) shows a pattern of behavioral effects similar to the atypical antipsychotics clozapine and olanzapine: studies with tremulous jaw movements in rats

RATIONALE

Previous studies demonstrated that clozapine and olanzapine suppressed tacrine-induced jaw movements at lower doses than those required for suppression of lever pressing.

OBJECTIVE

The present studies were undertaken to evaluate the novel atypical antipsychotic quetiapine using the jaw movement model.

METHODS

The effect of acute quetiapine on the suppression of tacrine-induced tremulous jaw movements was examined. To determine the relative potency of this effect compared with other behavioral effects of quetiapine, suppression of lever pressing also was studied. In other studies, rats received quetiapine for 14 consecutive days to study the effects of repeated injections of this drug.

RESULTS

Acute quetiapine injections decreased tacrine-induced jaw movements and lever pressing. The ratio of the ED50 for suppression of jaw movements divided by the ED50 for suppression of lever pressing was used as an index of liability to produce motor side effects, and the present results demonstrate that quetiapine has a ratio similar to that previously shown for clozapine and olanzapine. In the repeated-administration studies, quetiapine failed to induce jaw movements. On day 14, quetiapine reduced tacrine-induced tremulous jaw movements, and in a parallel experiment quetiapine significantly suppressed lever pressing on days 1-14. Repeated injections of quetiapine reduced tacrine-induced jaw movements over a dose range lower than that required for suppression of lever pressing.

CONCLUSIONS

On tests of jaw movement activity and lever pressing after both acute and repeated drug administration, quetiapine showed a profile somewhat similar to clozapine and olanzapine. A theoretical model is offered suggesting that atypical antipsychotics that act on 5-HT or muscarinic receptors have intrinsic antiparkinsonian actions that work in opposition to the motor effects produced by dopamine antagonism.

Validation of the tremulous jaw movement model for assessment of the motor effects of typical and atypical antipychotics: effects of pimozide (Orap) in rats

Drug-induced tremulous jaw movements (TJMs) in rats have been used as a model of parkinsonian tremor. Previous studies demonstrated that the typical antipsychotic haloperidol induced TJMs after acute or subchronic administration, while atypical antipsychotics did not. Moreover, it has been suggested that the relative potency for suppression of tacrine-induced TJMs relative to the suppression of lever pressing can be used to discriminate between typical and atypical antipsychotics. In order to validate this model with additional drugs, the present studies assessed the effects of the typical antipsychotic pimozide. In the first series of experiments, the effects of acute pimozide on tacrine-induced TJMs and lever pressing were examined. As with haloperidol, pimozide failed to suppress tacrine-induced TJMs, even at doses considerably higher than those that suppressed lever pressing. In the second group of experiments, rats were given single daily injections of pimozide (0.125-1.0 mg/kg) or tartaric acid vehicle for 13 days, and were observed for TJMs on days 1, 7, and 13. Pimozide induced TJMs in a dose-related manner on all days. The jaw movements occurred largely in the 3-7 Hz frequency range characteristic of parkinsonian tremor. These data support the hypothesis that typical antipsychotics can induce TJMs in rats, and demonstrate that chronic administration of typical antipsychotics is not necessary for induction of TJMs. TJMs induced by acute or subchronic pimozide may be related to early-onset motor syndromes such as drug-induced parkinsonism.

Clozapine treatment attenuated somatic and affective signs of nicotine and amphetamine withdrawal in subsets of rats exhibiting hyposensitivity to the initial effects of clozapine

BACKGROUND

Based on the phenomenologic similarity between symptoms of drug withdrawal and the negative symptoms of schizophrenia (e.g., anhedonia), we hypothesized that treatment with clozapine may be effective against nicotine and amphetamine withdrawal.

METHODS

A rate-independent discrete-trial threshold procedure was used to assess brain stimulation reward in rats prepared with electrodes in the lateral hypothalamus. Somatic signs of nicotine withdrawal were also assessed.

RESULTS

Clozapine administration (.75 or 1.5 mg/kg) during nicotine or amphetamine withdrawal did not affect the threshold elevations associated with drug withdrawal. The.75 mg/kg clozapine dose reversed the increased number of somatic signs of nicotine withdrawal. Ten days of clozapine treatment (3 mg/kg/b.i.d.) before exposure to nicotine prevented the threshold elevations in a subset of rats and the increases in somatic signs in all subjects. Fourteen-day pretreatment with clozapine (6 mg/kg/day) decreased the duration of amphetamine withdrawal.

CONCLUSIONS

Correlational analyses indicated that the ability of clozapine to prevent the affective aspects of drug withdrawal depended on low sensitivity to acute clozapine under baseline conditions. The results are consistent with the clinical situation where clozapine is partially effective against the negative symptoms of schizophrenia and more effective in some individuals than others. These results indicate that lack of sensitivity to the initial negative effects of clozapine may predict its a subsequent therapeutic response. Finally, the data suggest that there may be commonalities in the neurosubstrates mediating affective aspects of drug withdrawal and the negative symptoms of schizophrenia.

Effects of olanzapine infusions to the ventral tegmental area on lordosis and midbrain 3alpha,5alpha-THP concentrations in rats

RATIONALE

The progesterone metabolite and neurosteroid 5alpha-pregnane-3alpha-ol-20-one (3alpha,5alpha-THP) facilitates sexual behavior of estradiol-primed rodents through its actions in the ventral tegmental area (VTA). Olanzapine, an atypical antipsychotic, may exert some of its actions by increasing 3alpha,5alpha-THP levels.

OBJECTIVE

If olanzapine has effects by increasing 3alpha,5alpha-THP levels, then olanzapine administration to the VTA should facilitate feminine sexual behavior of estradiol-primed rodents concomitant with increasing midbrain levels of 3alpha,5alpha-THP. METHODS. In experiment 1, ovariectomized rats with bilateral cannulae to the VTA were primed with estradiol at 0 h, infused with olanzapine (10 or 20 microg) or vehicle at 47 h, and tested for sexual behavior at 47.5 h. In experiment 2, estradiol-primed ovariectomized rats were infused with olanzapine (10 microg) or vehicle, tested for sexual behavior, then tissues were collected for measurement of midbrain progesterone and 3alpha,5alpha-THP, and plasma corticosterone, progesterone, and 3alpha,5alpha-THP. In experiment 3, estradiol-primed, ovariectomized rats were administered progesterone (500 microg, SC), tested for sexual behavior, then tissues were collected for midbrain and plasma progesterone and 3alpha,5alpha-THP levels.

RESULTS

Infusions of 10 or 20 microg olanzapine to the VTA significantly increased the incidence and intensity of lordosis, and the occurrence of proceptive and aggressive behaviors. Rats infused with olanzapine to the VTA had significantly greater levels of midbrain 3alpha,5alpha-THP than did vehicle-administered rats. Olanzapine did not increase progesterone or corticosterone levels.

CONCLUSIONS

Olanzapine increases lordosis and midbrain 3alpha,5alpha-THP when infused to the VTA which suggest that olanzapine's behavioral effects may result, in part, through actions of 3alpha,5alpha-THP, independent of progesterone or corticosterone.

Olanzapine's effects to reduce fear and anxiety and enhance social interactions coincide with increased progestin concentrations of ovariectomized rats

Administration of olanzapine, an antipsychotic drug, can dose-dependently increase the levels of progesterone's metabolite, 5 alpha-pregnane-3 alpha-ol-20-one (3 alpha,5 alpha-THP) in the brain, which may have anxiolytic effects. The purpose of this experiment was to investigate the effects of olanzapine administration on anxiety behavior and progestin levels. Ovariectomized (ovx) rats (N=33) were administered olanzapine (i.p.: 5.0 or 10.0 mg/kg) or vehicle (saline buffered with acetic acid) and an hour later were tested for motor and anxiety behavior (n=8 per group) or had tissue collected for measurement of progestin concentrations (n=3 per group). Rats that were administered 5.0 or 10.0 mg/kg of olanzapine spent less time freezing in response to shock in the defensive burying task, spent more time on the open arms of the elevated plus-maze, and spent more time in social interaction with a conspecific than did vehicle-administered rats. Olanzapine (5.0 or 10.0 mg/kg, i.p.) significantly increased plasma and produced non-significant increases in whole brain concentrations of progesterone and 3 alpha,5 alpha-THP compared to that seen following vehicle administration. Together, these data are consistent with the hypothesis that olanzapine reduces fear, has anxiolytic effects, and may enhance social interaction in part due to increasing progestin concentrations.

Olanzapine and sulpiride: a preliminary study of combination/augmentation in patients with treatment-resistant schizophrenia

Coadministration of olanzapine, an atypical neuroleptic, with sulpiride, a selective D2 antagonist, is suggested as an efficient strategy for treating patients with resistant unremitting schizophrenia. The psychopharmacologic rationale that may account for the enhanced clinical efficacy of combining sulpiride with olanzapine and vice versa is the difference in affinity of the two drugs to brain receptors. Olanzapine affinity is related more to serotonin 5-HT2 than to dopamine-2, whereas sulpiride is considered a selective D2 blocker. The adjunction of a selective D2 antagonist to olanzapine may act as the olanzapine's augmentor by enhancing D2 blockage. This mode of treatment was introduced to six patients with chronic schizophrenia who showed noteworthy and rapid clinical improvement, supported by a decrease in their scores on the Positive and Negative Syndrome Scale and Brief Psychiatric Rating Scale. No bothersome side effects were noticed. This clinical approach is in accordance with the findings of previous reports assessing the efficacy of the combined treatment of clozapine and sulpiride. The grounds for this treatment regimen using olanzapine rather than clozapine are discussed, calling for further studies to affirm the hypothesis and clinical results.

Clozapine-like motor effects of the atypical antipsychotic risperidone in rats

A behavioral preparation that affords concurrent measurement of forelimb force, lick rhythm, and forelimb tremor in rats was used to assess the effects of the atypical antipsychotic risperidone. Rats that were trained to press downward on an isometric force transducer while simultaneously licking water reinforcement were administered risperidone (0.08, 0.12, and 0.16 mg/kg). Risperidone suppressed task engagement and increased the duration of individual press-hold-release bouts, effects shared with both typical and atypical antipsychotic drugs in this task. Although risperidone did not significantly affect forelimb force output as clozapine does, it did significantly decrease tremor power in the high-frequency (10-25 Hz) band of the power spectrum. Risperidone dose-dependently decreased the dominant 6 Hz frequency of the power spectrum, a reflection of slowed lick rhythm which is an effect that is shared by other atypical antipsychotic drugs in this task. The results reported in the present study suggest that, although risperidone may not possess the exceptionally low extrapyramidal side-effect profile that clozapine does, its effects are more similar to clozapine than to the extrapyramidal side-effect-producing haloperidol in this task.