Anti-cataleptic effects of clozapine, but not olanzapine and quetiapine, on SCH 23390- or raclopride-induced catalepsy in rats

Identifying the In Vivo Cellular Correlates of Antipsychotic Drugs

GPCRs such as 5-HT2A and D2 are implicated in the therapeutic and the side effects of antipsychotics. However, the pattern of brain activity that leads to the behavioral effects of antipsychotics is poorly understood. To address this question, we used the transgenic 'FosTRAP' mice (Mus musculus), where a fluorescent reporter marks the cells responsive to the stimulus of interest. Here, the stimulus was an administration of various antipsychotic drugs. In case of typical antipsychotics such as Haloperidol, the c-fos active cells were predominantly found in the striatum, whereas in case of the atypical antipsychotics (Clozapine and Olanzapine), c-fos-induced cells were more numerous in the cortical regions, e.g., orbital cortex, piriform cortex. Curiously, we also observed ependymal cells to be a novel cellular target of atypical antipsychotics. 5-HT2A is considered to be a major target for atypical antipsychotics. Therefore, we bred 'FosTRAP' mice with 5-HT2A knock-out (KO) mice and tested their response to the prototype of atypical antipsychotics, Clozapine. Interestingly, the absence of 5-HT2A did not significantly affect the number of c-fos-induced cells in the cortical regions. However, the ependymal cells showed a dramatically reduced response to Clozapine in the absence of 5-HT2A. In summary, the TRAP system has allowed us to identify various region-specific activity induced by antipsychotics and novel cellular targets of the antipsychotics. These results serve as a "proof of principle" study that can be extended to explore the biochemical and physiological changes brought about by antipsychotics and specifically identify antipsychotic-responsive cells in the live tissue.

Reverse microdialysis of a 5-HT2A receptor antagonist alters extracellular glutamate levels in the striatum of the MPTP mouse model of Parkinson's disease

Clinical observations have suggested that antagonism of 5-HT2A receptors may benefit patients with parkinsonian symptomatology. The mechanism of the antiparkinsonian effects of 5-HT2A receptor antagonists has not been fully elucidated. We have shown that the selective 5-HT2A receptor antagonist M100907 [R-(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenethyl)]-4-piperidinemethanol] improved motor impairments in mice treated with the parkinsonian neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In Parkinson's disease (PD) patients and animal models of parkinsonism dopamine denervation is associated with increased cortico-striatal glutamatergic transmission. We hypothesized that 5-HT2A receptor antagonists may exert their antiparkinsonian effects by decreasing striatal glutamate. Here, using in vivo microdialysis, we have shown an increased basal level of extracellular striatal glutamate when measured 3weeks after MPTP administration. The local administration of M100907 to the striatum significantly decreased striatal extracellular glutamate levels in MPTP-treated and saline treated mice. Basal extracellular serotonin (5-HT) levels were also elevated, whereas dopamine (DA) levels were significantly reduced in the striatum of MPTP-treated mice. Infusion of M100907 into the striatum produced no effect on dopamine or 5-HT levels. Local application of tetrodotoxin suppressed glutamate, 5-HT and DA concentrations in striatal dialysates in the presence or absence of M100907. The striatal expression of the glutamate transporter GLT1 was unchanged. However, there was an upregulation of the expression of 5-HT2A receptors in the striatum of MPTP-treated animals. Our data provide further evidence of enhanced glutamatergic neurotransmission in parkinsonism and demonstrate that blocking 5-HT2A receptors in the striatum will normalize glutamatergic neurotransmission.

The serotonergic system in Parkinson's disease

Although the cardinal manifestations of Parkinson's disease (PD) are attributed to a decline in dopamine levels in the striatum, a breadth of non-motor features and treatment-related complications in which the serotonergic system plays a pivotal role are increasingly recognised. Serotonin (5-HT)-mediated neurotransmission is altered in PD and the roles of the different 5-HT receptor subtypes in disease manifestations have been investigated. The aims of this article are to summarise and discuss all published preclinical and clinical studies that have investigated the serotonergic system in PD and related animal models, in order to recapitulate the state of the current knowledge and to identify areas that need further research and understanding.

Involvement of adenosine A2A and dopamine receptors in the locomotor and sensitizing effects of cocaine

Recent data indicate that cocaine locomotor responses may be influenced by dopamine (DA) neurotransmission and adenosine neuromodulation involving the A2A receptor (A2AR). Male Wistar rats were injected with MSX-3 (1-25 mg/kg; an antagonist of A2AR), CGS 21680 (0.05-0.2 mg/kg; an agonist of A2AR), SCH 23390 (0.125-0.25 mg/kg; an antagonist of DA D1/5R), raclopride (0.1-0.8 mg/kg; an antagonist of DA D2/3R), nafadotride (0.2-0.4 mg/kg; an antagonist of DA D3R) or 7-OH-PIPAT (0.01-1 mg/kg; an agonist of DA D3R) to verify the hypothesis that adenosine A2AR and DA receptors and their antagonistic interactions may control locomotor and sensitizing effects of cocaine. In well-habituated animals, MSX-3 (5 mg/kg) increased, while raclopride (0.4-0.8 mg/kg) decreased basal locomotor activation; the other drugs were inactive. The locomotor hyperactivation induced by acute cocaine (10 mg/kg) was enhanced by MSX-3 (5-25 mg/kg) or nafadotride (0.4 mg/kg), while CGS 21680 (0.2 mg/kg), SCH 23390 (0.25 mg/kg), raclopride (0.2-0.8 mg/kg) or 7-OH-PIPAT (0.1 mg/kg) decreased this effect of cocaine. Given during the development of sensitization (in combination with 5-daily cocaine, 10 mg/kg, injections), MSX-3 (5-25 mg/kg) increased, but CGS 21680 (0.2 mg/kg) and raclopride (0.8 mg/kg) reduced the locomotor response to a cocaine challenge dose (10 mg/kg) on day 10. When injected acutely with a cocaine challenge dose (on day 10), CGS 21680 (0.2 mg/kg), raclopride (0.2-0.8 mg/kg) or 7-OH-PIPAT (1 mg/kg) reduced, while MSX-3 (5 mg/kg) or nafadotride (0.4 mg/kg) enhanced the expression of cocaine sensitization. The present results show that adenosine A2ARs and DA D3Rs exert inhibitory actions on acute locomotor responses to cocaine and on the expression of cocaine sensitization, while DA D2Rs had an opposing role in such effects. Pharmacological stimulation of adenosine A2ARs protected against both the development and expression of cocaine sensitization, which may offer a therapeutic potential of A2AR agonists in the treatment of cocaine dependence. The results suggest an antagonistic role of A2ARs in D2R-mediated cocaine actions based at least in part on the existence of A2A/D2 heteromeric receptor complexes.

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-HT1A 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-HT1A 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-HT1A 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.

Haloperidol, but not clozapine, produces dramatic catalepsy in delta9-THC-treated rats: possible clinical implications

The effect on rat catalepsy induced by Delta9-tetrahydrocannabinol (Delta9-THC) in association with haloperidol (HP) or clozapine (CLOZ) administration was investigated. Delta9-THC dose-dependently increased HP (0.05-1 mg kg-1, s.c.)-induced rat catalepsy, while no catalepsy was observed after CLOZ (1-20 mg kg-1, s.c.) or Delta9-THC+CLOZ administration. The CB1 antagonist SR141716A (0.5-5 mg kg-1, i.p.) reversed the increase mediated by Delta9-THC on HP-induced catalepsy. The D2 agonist quinpirole completely reversed the catalepsy induced by both HP and HP+Delta9-THC; however, higher doses of quinpirole were needed in the presence of Delta9-THC. The M1 antagonist scopolamine and alpha2 antagonist yohimbine were able to reduce the catalepsy induced by HP and HP+Delta9-THC in a similar manner. CLOZ and the 5-HT2A/2C antagonists ritanserin, RS102221 and SB242084 were more effective in antagonizing HP than HP+Delta9-THC-induced catalepsy.7 HP and CLOZ failed to inhibit in vitro [3H]CP-55,940 binding, while Delta9-THC and SR141716A did not show an appreciable affinity for the D2 receptor. It was suggested that the different effects on rat catalepsy induced by Delta9-THC following HP or CLOZ administration may depend on the receptor-binding profiles of the two antipsychotics. The preferential use of CLOZ rather than HP in the treatment of psychotic symptoms in cannabis abusers was discussed.