Quinpirole, 8-OH-DPAT and ketanserin modulate catalepsy induced by high doses of atypical antipsychotics

The effect of the selective dopamine D2 receptor agonist quinpirole, the selective 5-HT1A receptor agonist 8-OH-DPAT and the selective 5-HT2A receptor antagonist ketanserin on catalepsy induced by atypical antipsychotics clozapine, risperidone, olanzapine and sertindole at higher doses was studied in rats. Haloperidol (0.5, 1 and 2 mg/kg), clozapine (50 and 75 mg/kg) and olanzapine (15 and 30 mg/kg) produced catalepsy dose-dependently while sertindole at doses up to 40 mg/kg failed to produce catalepsy in rats. However, sertindole (15, 30 and 45 mg/kg) produced a cataleptic effect in mice in a dose-dependent manner. At a high dose (5 mg/kg), risperidone produced catalepsy in rats. Quinpirole (0.05 and 0.1 mg/kg) reversed the cataleptic effect of haloperidol (2 mg/kg), risperidone (5 mg/kg), olanzapine (30 mg/kg) and sertindole (45 mg/kg). Quinpirole (0.05 and 0.1 mg/kg) reversed clozapine (75 mg/kg)-induced catalepsy. 8-OH-DPAT (0.15 and 0.3 mg/kg) dose-dependently reversed catalepsy induced by haloperidol (2 mg/kg) and risperidone (5 mg/kg) without affecting the cataleptic effect of olanzapine. However, the higher dose (0.45 mg/kg) of 8-OH-DPAT reversed it significantly. 8-OH-DPAT (0.3 mg/kg) reversed clozapine (75 mg/kg)-induced catalepsy. 8-OH-DPAT (0.15, 0.3 and 0.45 mg/kg) failed to reverse sertindole-induced catalepsy. Ketanserin (0.75 and 1.5 mg/kg) completely reversed catalepsy induced by haloperidol (2 mg/kg) and risperidone (5 mg/kg). Ketanserin (0.75 and 1.5 mg/kg) dose-dependently reversed olanzapine (30 mg/kg) and sertindole (45 mg/kg)-induced catalepsy without any effect on clozapine (75 mg/kg)-induced catalepsy. A higher dose (3 mg/kg) of ketanserin reversed clozapine-induced catalepsy. The present study suggests that atypical antipsychotics show fewer extrapyramidal symptoms (EPS) due to greater modulation of the serotonergic system. Therefore, an antipsychotic with dopamine D2/5-HT2A antagonistic action and 5-HT1A agonistic action may prove to be superior to the existing antipsychotics.     

Reversal of PCP-induced learning and memory deficits in the Morris’ water maze by sertindole and other antipsychotics

RATIONAL: In humans, the N-methyl-D-aspartate antagonist phencyclidine (PCP) induces behavioral changes that mimic schizophrenia symptoms, including positive and negative symptoms as well as cognitive deficits. In clinic, the cognitive deficits are closely associated with functional outcome. Thus, improvement of cognition may have high impact on patients' daily life. OBJECTIVE: In the present study, three second-generation antipsychotics (sertindole, risperidone, and clozapine) as well as the classical antipsychotic haloperidol were tested for the ability to reverse PCP-induced cognitive deficits in the Morris' water maze. RESULTS: The second-generation antipsychotics reversed the PCP-induced cognitive impairment: sertindole (0.63-2.5 mg/kg, s.c.), risperidone (0.04 mg/kg, s.c.; whereas 0.08 and 0.16 mg/kg were without significant effect), and clozapine (0.63 mg/kg, s.c.; while 1.3 mg/kg was without significant effect). The significant effect of sertindole was observed from day 2 onwards, while clozapine and risperidone only had significant effect at day 3. The classical antipsychotic haloperidol (0.010-0.020 mg/kg, s.c.) was ineffective. No compounds influenced swimming speed at the doses used, indicating that motor function was preserved. CONCLUSION: These results confirm that repeated PCP administration induces marked cognitive deficits. Further, second-generation antipsychotics like sertindole, clozapine, and risperidone within a certain, often narrow, dose range are able to reverse the impairment and thus might improve cognitive deficits in schizophrenic patients, whereas classical compounds like haloperidol lack this effect. The receptor mechanisms involved in the reversal of PCP's disruptive effect are discussed and likely include a delicate balance between effects on dopamine D(2), 5-HT(2A/6), alpha-adrenergic, muscarinic, and histaminergic H(1) receptors.     

A review of the efficacy, tolerability and safety of sertindole in clinical trials

Sertindole is a non-sedating atypical antipsychotic agent with high selectivity for dopaminergic neurons in the mesolimbic system. In pivotal clinical trials, sertindole has demonstrated significantly greater efficacy than placebo against both the positive and negative symptoms of schizophrenia. In addition, sertindole has had at least similar efficacy to haloperidol and risperidone against positive symptoms, and significantly greater efficacy than haloperidol and risperidone against negative symptoms. The incidence of extrapyramidal symptom (EPS)-related adverse events and the rate of medication used to treat EPS in patients receiving clinically effective doses of sertindole in clinical trials were similar to those observed in placebo recipients and significantly less than those in haloperidol recipients. The incidence of QTc interval prolongation of 500 ms or greater with therapeutic dosages of sertindole has also been low. In general, sertindole has been well tolerated in clinical trials. Unlike other antipsychotic agents, sertindole has not been associated with cognitive impairment, and can actually improve cognitive function. Observational studies have shown that the efficacy and tolerability of sertindole observed in the clinical trial situation are emulated in a naturalistic setting. Large cohort analyses (N > 8000) have shown that all-cause and cardiovascular mortality is no greater with sertindole than with risperidone or olanzapine.     

Sertindole : a review of its use in schizophrenia

Oral sertindole (Serdolect) is an atypical antipsychotic approved in the EU for once-daily use in patients with schizophrenia who are intolerant to at least one other antipsychotic agent.Extensive data from post-marketing studies do not indicate an excess of overall mortality with sertindole. Sertindole is at least as effective as haloperidol and risperidone in the treatment of neuroleptic-responsive schizophrenia. Sertindole improves negative symptoms, and is also effective for the treatment of neuroleptic-resistant schizophrenia. Sertindole is generally well tolerated and is associated with a low rate of extrapyramidal symptoms (EPS). Thus, sertindole is a useful option in the treatment of patients with schizophrenia.     

Discriminative-stimulus effects of clozapine in squirrel monkeys: comparison with conventional and novel antipsychotic drugs

 The effects of conventional and novel atypical antipsychotic drugs were compared to clozapine in squirrel monkeys that discriminated IM injections of clozapine (1.0 mg/kg) from saline in a two-lever drug discrimination procedure. Clozapine (0.03–3.0 mg/kg) produced dose-related increases in responding on the clozapine-associated lever with full substitution at the training dose in all monkeys. Dose-related increases in responding on the clozapine-associated lever and full substitution also were observed with structural analogues of clozapine including perlapine and fluperlapine (0.1–3.0 mg/kg), seroquel (0.1–5.6 mg/kg), and JL 5, JL 8 and JL 18 (0.1–3.0 mg/kg). Other clozapine analogues, including olanzapine, amoxapine, loxapine and clothiapine, and conventional antipsychotic drugs, including phenothiazines such as chlorpromazine and thioridazine, produced some clozapine-associated responding up to the highest doses that could be studied, but did not substitute for clozapine. Olanzapine did produce full clozapine-lever responding following pretreatment with the dopamine D₂-receptor agonist (+)-PHNO (0.003–0.01 mg/kg). Putatively atypical antipsychotics that are structurally unrelated to clozapine including risperidone (0.003–0.1 mg/kg), sertindole (0.03–1.0 mg/kg) and remoxipride (0.1–5.6 mg/kg) similarly failed to substitute for clozapine up to the highest doses. The present results indicate that some, but not all, structural analogs of clozapine have clozapine-like discriminative-stimulus effects and that novel antipsychotic drugs which purportedly have clozapine-like clinical efficacy may not produce its interoceptive stimulus effects. Received: 2 November 1996 / Final version: 13 January 1997     

Generalization testing with atypical and typical antipsychotic drugs in rats trained to discriminate 5.0 mg/kg clozapine from vehicle in a two‐choice drug discrimination task

Clozapine (CLZ) drug discrimination is used as a preclinical model to evaluate compounds for putative atypical antipsychotic properties. In rats, a 1.25 mg/kg CLZ training dose appears to have greater pharmacological specificity for atypical antipsychotic drugs than the traditional 5.0 mg/kg CLZ training dose; however, methodological differences among studies have precluded a direct comparison between these training doses. In the present study, rats were trained to discriminate a 5.0 mg/kg CLZ dose from vehicle in a two‐choice drug discrimination task using methods similar to those in a previous study from our laboratory that used a 1.25 mg/kg CLZ training dose. Clozapine produced full substitution (≥80% CLZ‐lever responding) for itself at the training dose (5.0 mg/kg). The atypical antipsychotics olanzapine, quetiapine, and ziprasidone also produced full substitution for 5.0 mg/kg CLZ, whereas the atypical antipsychotics risperidone and sertindole produced partial substitution (≥60% CLZ‐lever responding). The typical antipsychotic, thioridazine, produced full substitution for the 5.0 mg/kg CLZ training dose, but the typical antipsychotics chlorpromazine, fluphenazine, and haloperidol failed to substitute for clozapine. In a subgroup of 1.25 mg/kg CLZ‐trained rats, ziprasidone produced strong partial substitution (73.0 % CLZ‐lever responding) for the 1.25 mg/kg CLZ training dose. Based on these findings, some atypical antipsychotic drugs (i.e., quetiapine and ziprasidone) produce full substitution only for the 5.0 mg/kg CLZ training dose, whereas other atypical antipsychotic drugs (i.e., sertindole and risperidone) produce full substitution only for the 1.25 mg/kg CLZ training dose. Thus, both of these training doses are important for the screening of putative atypical antipsychotic drugs with the clozapine drug discrimination assay. Drug Dev. Res. 64:55–65, 2005. © 2005 Wiley‐Liss, Inc.     

A double-blind, controlled study of sertindole versus risperidone in the treatment of moderate-to-severe schizophrenia

Sertindole is a non-sedating atypical antipsychotic effective in the management of schizophrenia and is associated with placebo-level incidence of extrapyramidal symptoms (EPS). In this randomized, double-blind, parallel-group, flexible-dose, multi-centre study, the efficacy and tolerability of sertindole was directly compared with another atypical antipsychotic in patients with schizophrenia. A total of 187 patients were randomly assigned to treatment with sertindole (12-24 mg/day, n=98) or risperidone (4-10 mg/day, n=89) for 12 weeks. Although early termination reduced the power of the study, some significant between-group differences were evident. Sertindole reduced the mean Positive and Negative Syndrome Scale total scores to a greater extent than risperidone, and the difference reached statistical significance at endpoint for the Observed Cases (OC) dataset. Moreover, sertindole was superior for the treatment of negative symptoms compared to risperidone (P<0.05, Last Observation Carried Forward and OC). Both treatment groups were similarly effective in improving Clinical Global Impression (Severity and Improvement), the Drug Attitude Inventory and Global Assessment of Functioning scores. Sertindole and risperidone were both well tolerated. Numerically, fewer patients in the sertindole group (19%) reported EPS-related adverse events than in the risperidone group (28%), although significantly more sertindole-treated patients reported QT prolongation and abnormal ejaculation volume (P<0.05). In conclusion, sertindole was well tolerated and demonstrated clinically relevant efficacy advantages over risperidone.     

The behavioral effects of acute and chronic JL 13, a putative antipsychotic, in Cebus non-human primates

RATIONALE: Neuroleptic or antipsychotic drugs are the mainstay of treating acute and chronic psychosis. However, their efficacy is offset by a wide array of side effects, especially extrapyramidal syndromes (EPS). In an attempt to develop novel antipsychotic agents, several animal models have been developed to characterize the profile of new chemical entities. OBJECTIVE: To evaluate the behavioral characteristics of JL 13, a potentially unique antipsychotic agent, three separate studies across a wide dose range in Cebus monkeys were conducted and compared with two studies of oral and parenteral haloperidol. METHODS: Twelve Cebus monkeys were tested with single i.m. doses of JL 13 (0.1-2.5 mg/kg), single p.o. doses (1.0-50.0 mg/kg), and 35 days of continuous p.o. (up to 25 mg/kg) treatments and were blindly evaluated. The same twelve monkeys were also tested with haloperidol i.m. (0.01-0.25 mg/kg) and nine of the monkeys also received haloperidol p.o. (0.1-5.0 mg/kg). Behaviors scored included sedation/arousal, locomotor activity, EPS of parkinsonism and dystonia, as well as reactivity. RESULTS: JL 13 produced mild to moderate and dose-related increased sedation and decreased locomotor activity. Minimal decreases in eye blinking rates were also noted as a consequence of sedation. Mild dystonia and parkinsonian symptoms of slow movement developed at the highest dose tested of 50 mg/kg p.o. in only 6 of 12 monkeys. This is 50 times higher than oral doses of haloperidol that would be needed to produce similar EPS effects. Dose-related EPS of dystonia and bradykinesia occurred in relation to decreased locomotor activity and reactivity to stimuli with haloperidol i.m. and p.o., which are features characteristically seen with traditional neuroleptics. CONCLUSIONS: The behavioral effects of JL 13 in non-human primates suggest this compound is well tolerated and may have a favorable antipsychotic benefit/risk ratio in the clinic, especially if antipsychotic efficacy occurs at doses well below those that can cause EPS.     

Nicotine-antipsychotic drug interactions and attentional performance in female rats

Schizophrenia is marked by pronounced cognitive impairments in addition to the hallmark psychotic symptoms like hallucinations. Antipsychotic drugs can effectively reduce these hallucinations; however, the drugs have not resolved the cognitive impairment. Interestingly, nicotine, a drug commonly self-administered by people with schizophrenia, has been shown to significantly improve cognitive function of people with schizophrenia. The current study was conducted to determine the effect of typical (haloperidol) and atypical (clozapine and risperidone) antipsychotic drug treatment on sustained attention in rats performing a visual signal detection task. In addition, the interaction of haloperidol with chronic nicotine administration was assessed. Female Sprague-Dawley rats were injected subcutaneously with clozapine (0, 0.6, 1.25 and 2.5 mg/kg), risperidone (0, 0.025, 0.05 and 0.1 mg/kg) or haloperidol (0, 0.01, 0.02 and 0.04 mg/kg). In the second part of the study, the interaction of acute haloperidol (0, 0.005, 0.01 and 0.02 mg/kg) and chronic nicotine (5 mg/kg/day, for 4 weeks via osmotic minipump) was characterized. Clozapine, risperidone and haloperidol all caused dose-related impairments in percent hit performance. There was a significant linear dose-related impairment in percent hit caused by risperidone. All the doses of clozapine caused a significant impairment in percent hit at the higher luminance intensities in the visual signal detection task. The 0.01 and 0.02 mg/kg haloperidol doses caused significant decreases in percent hit. The 0.04 mg/kg haloperidol dose impaired performance of the task to the point that reliable choice accuracy measurements could not be made. Chronic nicotine infusion significantly diminished the impairing effects of haloperidol on performance during weeks 1-2. In summary, both typical and atypical antipsychotic drugs significantly impaired sustained attention in rats. Haloperidol was more detrimental than clozapine and risperidone. Chronic nicotine diminished the adverse effects of haloperidol on performance. This study establishes a paradigm to reliably determine the attentional impairment caused by antipsychotic drugs.     

Effect of sertindole on raised mesolimbic dopaminergic activity in the rat

The effect of sertindole in models of mesolimbic dopamine excess in the rat was evaluated. Sertindole (0.0057–0.011 μmol/kg = 2.5–5 μg/kg, sc) and haloperidol (0.13–0.27 μmol/kg = 50–100 μg/kg, ip) inhibited the hyperactivity caused by the acute intra-accumbens injection of amphetamine (20 μg). The administration of sertindole (0.0057–2.8 μmol/kg = 2.5 μg–1.25 mg/kg, sc daily), haloperidol (0.027–0.40 μmol/kg = 10–150 μg/kg, ip bd) or clozapine (15–31 μmol/kg = 5–10 mg/kg, ip, bd) during a 13-day period of dopamine infusion (25 μg/24 h) into the nucleus accumbens reduced the dopamine-induced hyperactivity response to control levels, except at the highest dose which reduced activity to below control levels. Locomotor activity remained at control levels after discontinuing the dopamine/sertindole treatment regimen, whereas discontinuation of the dopamine/haloperidol treatment regimen resulted in rebound hyperactivity. Sertindole (0.0057 μmol/kg = 2.5 μg/kg, sc) given either once daily or once every 2 days prevented the development of hyperactivity in the intra-accumbens dopamine infusion model. One injection given every 4 days failed to modify the response to a dopamine infusion. Sertindole (0.0057 μmol/kg = 2.5 μg/kg, sc daily) inhibited hyperactivity caused by unilateral infusion of dopamine (50 μg/24 h, 13 days) into the left amygdala of rats having right hemispheric dominance (as measured in a turn preference test). In contrast to haloperidol, sertindole failed to initiate circling behaviour following unilateral, intrastriatal injection. In conclusion, sertindole, like haloperidol and clozapine, can reduce raised mesolimbic dopaminergic activity in the rat. Sertindole differs from haloperidol by its ability to return the hyperactivity response to control levels. © 1994 Wiley-Liss, Inc.     

Low striatal and extra-striatal D2 receptor occupancy during treatment with the atypical antipsychotic sertindole

RATIONALE: Sertindole is a new atypical antipsychotic drug. Preclinical pharmacology suggests that sertindole has a preferential effect on the activity of limbic and cortical dopaminergic neurons. Clinical trials have shown antipsychotic efficacy and very few extrapyramidal symptoms (EPS) with sertindole at 20 mg/day. OBJECTIVES: This positron emission tomography (PET) study aimed to measure D(2) receptor occupancy in striatal and extra-striatal regions induced by clinically representative doses of sertindole in patients with schizophrenia. METHOD: Four stabilized schizophrenic out-patients received sertindole 20 mg/day for 6-8 weeks. PET was performed using [(11)C]raclopride to measure D(2) receptor occupancy in the striatum and [(11)C]FLB457 to measure occupancy in the neocortex and thalamus, i.e. regions with very low D(2) receptor density.RESULTS: Striatal D(2) receptor occupancy was 52-68%. Similar occupancies were found in the thalamus, and the temporal and frontal cortices. CONCLUSIONS: Sertindole appears efficacious at a low D(2) receptor occupancy, comparable to that produced by clozapine. This finding could explain the low risk of EPS. The functional limbic selectivity of sertindole was not reflected in regional differences in receptor occupancy.     

Combined treatment of quetiapine with haloperidol in animal models of antipsychotic effect and extrapyramidal side effects: comparison with risperidone and chlorpromazine

Rationale Quetiapine, an atypical neuroleptic, has beneficial antipsychotic effects in schizophrenic patients, but with a lower incidence of extrapyramidal symptoms (EPS) compared with typical antipsychotics. While typical antipsychotics are often switched to atypical agents when adverse effects become limiting, there is little preclinical information to support this strategy, both in terms of efficacy and side effects.Objectives The antipsychotic effects and EPS during concomitant administration of quetiapine with haloperidol, a typical antipsychotic agent, were evaluated in mice and compared with chlorpromazine and risperidone.Methods We first investigated the antipsychotic effects and EPS liability of quetiapine, risperidone, chlorpromazine, and haloperidol when administered alone to select optimal doses for subsequent combination studies. The second study was designed to evaluate the antipsychotic efficacy and EPS profile of concomitant administration of quetiapine, risperidone, or chlorpromazine with haloperidol. Antipsychotic effects were evaluated with the methamphetamine-induced hyperlocomotion test, and EPS liability was evaluated in a catalepsy-induction model.Results Quetiapine, risperidone, chlorpromazine, and haloperidol dose-dependently reduced methamphetamine-induced hyperlocomotion, with ED₅₀ values of 5.6, 0.020, 1.8, 0.035 mg/kg, respectively. In the catalepsy test, quetiapine only weakly induced catalepsy at the highest dose of 100 mg/kg, whereas risperidone, chlorpromazine, and haloperidol dose-dependently induced catalepsy with ED₅₀ values of 0.25, 4.6, and 0.10 mg/kg, respectively. While the combination of quetiapine (6 mg/kg) and haloperidol (0.04 mg/kg) significantly reduced methamphetamine-induced hyperlocomotion in comparison with haloperidol alone, quetiapine (10, 32 mg/kg) plus haloperidol did not potentiate the cataleptogenic activity of haloperidol. In contrast, risperidone (0.1, 0.32 mg/kg) or chlorpromazine (3.2 mg/kg) significantly augmented catalepsy induced by haloperidol. Catalepsy induced by co-administration of quetiapine (10 mg/kg) and haloperidol (0.1 mg/kg) was significantly potentiated by WAY100635, a 5-HT_1A antagonist, and catalepsy induced by co-administration of risperidone (0.1 mg/kg) and haloperidol (0.1 mg/kg) was significantly antagonized by 8-OH-DPAT, a 5-HT_1A agonist.Conclusion The present study demonstrated that the combined administration of quetiapine with haloperidol did not aggravate EPS, possibly because of its affinity for 5-HT_1A receptors. This finding may have the clinical implication that quetiapine could provide a successful regimen in switching from typical antipsychotic agents in the symptom management of schizophrenia, or even in adjunctive therapy with other antipsychotic agents.     

Evaluation of dopamine D-2 receptor occupancy by clozapine, risperidone, and haloperidol in vivo in the rodent and nonhuman primate brain using 18F-fallypride.

We have used the high-affinity dopamine D-2 receptor radioligand, 18F-fallypride for evaluating receptor occupancy by the antipsychotic drugs, clozapine, risperidone, and haloperidol in rodents and nonhuman primates. In rodents, clozapine (0.1 mg/kg to 100 mg/kg) competed with 18F-fallypride at all the doses administered. At doses over 40 mg/kg, clozapine was able to displace all the administered 18F-fallypride. A pseudobiphasic profile of receptor occupancy by clozapine was observed. This behavior was compared with such other neuroleptics as risperidone and haloperidol that exhibited over 90% receptor occupancy at doses over 0.1 mg/kg and did not exhibit a biphasic nature. Dopamine D-2 receptor occupancy in the monkeys was studied using positron emission tomography (PET) after acute subcutaneous doses of the various drugs. At therapeutically relevant doses, clozapine, risperidone, and haloperidol were able to compete significantly with the binding of 18F-fallypride in all brain regions in rhesus monkeys, and our analyses indicate that these drugs (clozapine, risperidone, and haloperidol) do not discriminate between the striatal (caudate and putamen) and the extrastriatal (thalamus and cortical regions) dopamine receptors. The following extent of D-2 receptor occupancies were measured in the monkey brain using PET: clozapine approximately 70% (dose of 9.7 mg/kg), risperidone approximately 75% (0.05 mg/kg), and haloperidol approximately 90% (0.05 mg/kg).     

Co-administration of 5-HT6 receptor antagonists with clozapine, risperidone, and a 5-HT2A receptor antagonist: effects on prepulse inhibition in rats

Rationale

Some novel antipsychotics manifest antagonistic activity at serotonin-6 receptors; however, little is known about the role of 5-HT6 receptors in ameliorating sensory gating deficits.

Objective

We evaluated the effects of the combined administration of the 5-HT6 receptor antagonist SB 271046 with clozapine and haloperidol, as well as the co-administration of SB 271046 or SB 399885 with risperidone and the 5-HT2A antagonist M100907, to overcome the deficits induced by MK-801 in the prepulse inhibition (PPI) test.

Results

MK-801 (0.1 mg/kg) produced reliable PPI deficits. Administration of SB 271046 (6 and 9 mg/kg), SB 399885 (3 and 6 mg/kg), clozapine (2.5 mg/kg), haloperidol (0.1 and 0.2 mg/kg), risperidone (0.25–1 mg/kg), and M100907 (0.5 and 1 mg/kg) did not affect the MK-801-induced deficits, but the administration of clozapine (5 mg/kg) did reverse the effects of MK-801. In MK-801-treated rats, the co-administration of inactive doses of clozapine (2.5 mg/kg) and SB 271046 (6 mg/kg) reversed the PPI impairments compared to animals that were administered inactive doses of either clozapine or SB 271046 alone. Co-administration of risperidone (1 mg/kg) or M100907 (0.5 mg/kg) with SB 271046 (6 mg/kg) or SB 399885 (3 mg/kg) also attenuated the MK-801-induced PPI deficits. In contrast, joint administration of haloperidol and SB 271046 had no effect on the PPI deficit.

Conclusion

The present results suggest that the 5-HT6 receptors may play adjunctive roles in antipsychotic drug action, and that the combination of 5-HT2A and 5-HT6 antagonism may represent an important element in the pharmacological profile of antipsychotic drugs.     

Olanzapine and clozapine increase the GABAergic neuroactive steroid allopregnanolone in rodents.

The neuroactive steroid allopregnanolone is a potent gamma-aminobutyric acid type A (GABA(A)) receptor modulator with anxiolytic and anticonvulsant effects. Olanzapine and clozapine also have anxiolytic-like effects in behavioral models. We therefore postulated that olanzapine and clozapine would elevate allopregnanolone levels, but risperidone and haloperidol would have minimal effects. Male rats received intraperitoneal olanzapine (2.5-10.0 mg/kg), clozapine (5.0-20.0 mg/kg), risperidone (0.1-1.0 mg/kg), haloperidol (0.1-1.0 mg/kg), or vehicle. Cerebral cortical allopregnanolone and peripheral progesterone and corticosterone levels were determined. Adrenalectomized animals were also examined. Both olanzapine and clozapine increased cerebral cortical allopregnanolone levels, but neither risperidone nor haloperidol had significant effects. Olanzapine and clozapine also increased serum progesterone and corticosterone levels. Adrenalectomy prevented olanzapine- and clozapine-induced elevations in allopregnanolone. Allopregnanolone induction may contribute to olanzapine and clozapine anxiolytic, antidepressant, and mood-stabilizing actions. Alterations in this neuroactive steroid may result in the modulation of GABAergic and dopaminergic neurotransmission, potentially contributing to antipsychotic efficacy.     

Sertindole: new drug. Another "atypical" neuroleptic; QT prolongation

(1) The first-line drug for the treatment of schizophrenic disorders is a neuroleptic such as haloperidol. Amisulpride may be preferable when haloperidol causes unacceptable neurological reactions. Overall, the risk-benefit balance of more recent, so-called atypical neuroleptics is no better. (2) Sertindole, a neuroleptic, was first marketed in 1996 in several European countries before being withdrawn two years later because of numerous cardiac adverse effects. It has once again been approved and should soon be available on the French market. (3) Two comparative double-blind trials suggest that a daily sertindole dose of 24 mg is about as effective as 10 mg of haloperidol. Sertindole was no more effective than risperidone in a trial comparing these two drugs. (4) Like other 'atypical' neuroleptics, sertindole has few short-term neurological adverse effects (extrapyramidal syndrome) at the doses used in clinical trials. However, it causes weight gain. Sertindole also has alpha blocking properties, which can cause postural hypotension and reduce ejaculate volume; it also has atropinic effects (constipation, dry mouth, etc.). (5) Sertindole provokes a dose-dependent increase in the QT interval more frequently than haloperidol in comparative trials, and apparently more frequently than other 'atypical' neuroleptics such as risperidone and olanzapine. Sertindole has been suspected of increasing cardiovascular mortality but this has not been established. (6) Sertindole is metabolised by cytochrome P450 isoenzymes CYP 2D6 and CYP 3A4, hence a high risk of pharmacokinetic interactions. (7) In practice, when haloperidol has to be withdrawn because of adverse effects, especially neurological reactions, it is better to continue to resort to amisulpride, for example, with close monitoring of adverse effects, rather than expose patients to the potential dangers of sertindole.     

Sertindole: efficacy and safety in schizophrenia

Sertindole is an antipsychotic drug with affinity for dopamine D2, serotonin 5-HT2A and 5-HT2C, and alpha1-adrenoreceptors. Preclinical studies suggest that sertindole acts preferentially on limbic and cortical dopaminergic neurons and clinical trials have confirmed that sertindole is effective at a low dopamine D2 occupancy level. The active substance has a long half-life. Oral administration once daily yields highly stable plasma levels. These features may explain the clinically observed low frequency of extrapyramidal side effects, including tardive dyskinesia. In contrast to most antipsychotics, sertindole seems to be void of sedative effects. However, although not strictly proven by objective neuropsychological tests, this asset of sertindole does not add to the cognitive problems inherent in schizophrenia. Administration of sertindole is more often associated with prolongation of QTc compared with most other currently used antipsychotics. However, large cohort analyses do not suggest that all-cause mortality is higher with sertindole than with, for example, risperidone or olanzapine. The effective antipsychotic dose range of sertindole is 12-20 mg/day, with small variations among patients. The frequency of most adverse events, for example extrapyramidal symptoms and somnolence, with such a dose does not differ from placebo. Three side effects have been more common than with placebo/haloperidol in short-term studies: weight gain, rhinitis and a decreased ejaculation volume. Two head-to-head comparisons (one in treatment-resistant patients) of sertindole and risperidone showed equivalent effects on positive symptoms. For negative symptoms, one study obtained equivalent effects and one a superior effect of sertindole. Sertindole should not be used as first-line treatment for first-episode patients with schizophrenia because of the QTc prolongation. It has a side-effect profile that makes it an interesting alternative for many patients who do not respond well to the initial choice of antipsychotic drug.     

Atypical antipsychotic drugs block selective components of amphetamine-induced stereotypy

Individual items of behavior produced by 1.0 or 5.0 mg/kg d-amphetamine were monitored in rats pretreated 15 minutes earlier with vehicle or with behaviorally relevant doses of haloperidol (0.1 or 0.25 mg/kg), clozapine (1.0 or 5.0 mg/kg), or thioridazine (1.0 or 5.0 mg/kg). Unlike haloperidol, the atypical antipsychotics failed to block all components of either the low- or high-dose response to amphetamine. These drugs, however, did block selective items of amphetamine-induced stereotyped behavior. Clozapine significantly attenuated the sniffing produced by 1.0 mg/kg d-amphetamine as well as the oral behavior (licking and/or biting) produced by 5.0 mg/kg d-amphetamine. Thioridazine, at a dose of 5.0 mg/kg, also reduced oral behavior and selectively blocked repetitive head bobbing. Taken together, these results suggest that although atypical antipsychotic drugs exert some common effects on the amphetamine behavioral response, these drugs do not influence all amphetamine-induced behaviors equally.     

Differential actions of classical and atypical antipsychotic drugs on spontaneous neuronal activity in the amygdaloid complex

Classical antipsychotic drugs such as haloperidol produce akinesia and catalepsy, whereas clozapine and related atypical antipsychotics fail to elicit these behaviors even at relatively high doses. Despite these behavioral differences, a cataleptic dose of haloperidol (2.0 mg/kg) produces changes in neuronal activity in the neostriatum and nucleus accumbens comparable to those produced by a non-cataleptic dose of clozapine (20.0 mg/kg). To further elucidate the brain mechanisms underlying the differential behavioral response to these drugs, an electrophysiological analysis was extended to neurons in the rat amygdaloid complex. Whereas an intraperitoneal injection of 2.0 mg/kg haloperidol generally failed to alter the firing rate of amygdaloid neurons, 20.0 mg/kg clozapine typically produced a prolonged increase in activity. Similarly, clozapine, but not haloperidol, reversed the depression of firing rate produced by 1.0 mg/kg d-amphetamine. The results suggest that neurons in the amygdaloid complex are more responsive to antipsychotic drugs devoid of extrapyramidal side effects than to antipsychotics which elicit parkinsonian-like motor dysfunctions.     

Olanzapine,an atypical antipsychotic,increases rates of punished responding in pigeons

The effects of olanzapine [LY 170053; 2-methyl-4-(4-methyl-1-piperazinyl)-10H-thieno[2, 3b][1,5]benzodiazepine), a potential atypical antipsychotic, were determined in pigeons whose keypeck responding was punished. These effects were compared to the anxiolytic agents chlordiazepoxide and pentobarbital, and to other antipsychotic agents. Keypeck behavior was maintained under a multiple FR30 FR30 schedule, signalled by white and red stimulus lights, respectively. Each component of the schedule alternated every 3 min with a 30-s timeout. During the white keylight component, responding was maintained by food presentation. During the red keylight component, responding was maintained by food and simultaneously suppressed by electric shock presentation, with response rates being only about 5% of those during the white stimulus light. Olanzapine (0.01–1.0 mg/kg) increased punished responding at doses below those which had an effect on unpunished responding. Clozapine (0.01–1.0 mg/kg), ritanserin (0.1–3.0 mg/kg), and, to a lesser extent, risperidone (0.1–1.0 mg/kg) were also effective at increasing punished responding. Generally, the maximum effect seen with olanzapine was equal to that seen with ritanserin, and it exceeded that seen with clozapine. However, these effects were generally less than those seen with chlordiazepoxide and pentobarbital. Haloperidol (0.01–0.1 mg/kg) was completely without effect on punished responding, while it caused decreases in unpunished behavior. These results provide further evidence that olanzapine has a profile in behavioral tests unlike the typical antipsychotic haloperidol. Moreover, this profile is similar to clozapine, a clinically effective antipsychotic with an atypical profile.