Acute and chronic administration of clozapine produces greater proconvulsant actions than haloperidol on focal hippocampal seizures in freely moving rats

Do Psychotropic Drugs Cause Epileptic Seizures? A Review of the Available Evidence

Psychiatric comorbidities in patients with epilepsy are common. A bidirectional relationship has been well described where not only patients with epilepsy have a higher prevalence of psychiatric comorbidities but also patients with primary psychiatric disorders are at an increased risk of developing seizures. The aim of this review is to highlight the complex relationship between epilepsy and common psychiatric disorders and to answer the question whether psychotropic medications are proconvulsant by reviewing the preclinical and clinical literature. The evidence shows that the majority of psychotropic medications are not proconvulsant when used in therapeutic doses with the exception of a subset of medications, mainly bupropion IR and certain antipsychotic drugs such as clozapine. An effective treatment of psychiatric comorbidities in patients with epilepsy must consider not only the potential therapeutic effect of the drug, but also its potential iatrogenic effects on the seizure disorder.

Effects of Tianeptine on Adult Rats Following Prenatal Stress

Objective

Exposing a pregnant female to stress during the critical period of embryonic fetal brain development increases the risk of psychiatric disorders in the offspring. The objective of this study was to investigate the effect of antidepressant tianeptine on prenatally stressed (PNS) rats.

Methods

In this study, a repeated variable stress paradigm was applied to pregnant rats during the last week of gestation. To investigate the effects of antidepressant tianeptine on PNS rats, behavioral and protein expression analyses were performed. Forced swim test, open field test, and social interaction test were performed to determine changes in PNS rats compared to non-stressed offspring. Haloperidol was used as a positive control as an antipsychotic drug based on previous studies.

Results

Behavioral changes were restored after treatment with tianeptine or haloperidol. Western blot and immunohistochemical analyses of the prefrontal cortex revealed downregulation of several neurodevelopmental proteins in PNS rats. After treatment with tianeptine or haloperidol, their expression levels were increased.

Conclusion

Downregulation of several proteins in PNS rats might have caused subsequent behavioral changes in PNS rats. After tianeptine or haloperidol treatment, behavioral changes in PNS rats were restored. Therefore, tianeptine might decrease incidence of prenatal stress related-psychiatric disorders such as depression and schizophrenia.

Comparative analysis of the treatment of chronic antipsychotic drugs on epileptic susceptibility in genetically epilepsy-prone rats

Antipsychotic drugs (APs) are of great benefit in several psychiatric disorders, but they can be associated with various adverse effects, including seizures. To investigate the effects of chronic antipsychotic treatment on seizure susceptibility in genetically epilepsy-prone rats, some APs were administered for 7 weeks, and seizure susceptibility (audiogenic seizures) was evaluated once a week during treatment and for 5 weeks after drug withdrawal. Furthermore, acute and subchronic (5-day treatment) effects were also measured. Rats received haloperidol (0.2-1.0 mg/kg), clozapine (1-5 mg/kg), risperidone (0.03-0.50 mg/kg), quetiapine (2-10 mg/kg), aripriprazole (0.2-1.0 mg/kg), and olanzapine (0.13-0.66 mg/kg), and tested according to treatment duration. Acute administration of APs had no effect on seizures, whereas, after regular treatment, aripiprazole reduced seizure severity; haloperidol had no effects and all other APs increased seizure severity. In chronically treated rats, clozapine showed the most marked proconvulsant effects, followed by risperidone and olanzapine. Quetiapine and haloperidol had only modest effects, and aripiprazole was anticonvulsant. Finally, the proconvulsant effects lasted at least 2-3 weeks after treatment suspension; for aripiprazole, a proconvulsant rebound effect was observed. Taken together, these results indicate and confirm that APs might have the potential to increase the severity of audiogenic seizures but that aripiprazole may exert anticonvulsant effects. The use of APs in patients, particularly in patients with epilepsy, should be monitored for seizure occurrence, including during the time after cessation of therapy. Further studies will determine whether aripiprazole really has a potential as an anticonvulsant drug and might also be clinically relevant for epileptic patients with psychiatric comorbidities.

Seizure risk associated with neuroactive drugs: data from the WHO adverse drug reactions database

PURPOSE

To explore the association between the use of neuroactive drugs and reports of epileptic seizures.

MATERIAL

Using the WHO adverse drug reactions (ADR) database, VigiBase, we surveyed reports of suspected seizures from 1968 until February 2006. Case reports of ADRs, that were classified as convulsions were collected and compared to the total number of ADRs reported.

RESULTS

The total number of ADRs was 7,375,325. The number of convulsive events was 71,471. The ratio of convulsive ADRs to the total number of ADRs reported for each drug was evaluated and expressed as a percentage. The 10 drugs most frequently associated with convulsive ADRs were maprotilene (14.42%), escitaloprame (9.78%), buproprione (9.49%), clozapine (9.0%), chlorprothiexene (8.89%), amoxapine (8.74%), donepezil (8.40%), rivastigmine (6.41%), quetiapine (5.90%) and trimipramine (5.69%).

CONCLUSIONS

Based on the reports in VigiBase, ADR reports relating to antidepressants, antipsychotic and cholinomimetic drugs included seizures more often than other neuroactive drugs.

Acute clozapine suppresses synchronized pyramidal synaptic network activity by increasing inhibition in the ferret prefrontal cortex

Recent studies have indicated that impaired neural circuitry in the prefrontal cortex is a prominent feature of the neuropathology of schizophrenia. Clozapine is one of the most effective antipsychotic drugs used for this debilitating disease. Despite its effectiveness, the mechanism by which clozapine acts on prefrontal cortical circuitry remains poorly understood. In this study, in vitro multiple whole cell recordings were performed in slices of the ferret prefrontal cortex. Clozapine, which effectively inhibited the spontaneous synchronized network activities in the prefrontal neurons, achieved the suppressive effect by decreasing the recurrent excitation among pyramidal neurons and by enhancing the inhibitory inputs onto pyramidal cells through a likely network mechanism. Indeed, under the condition of disinhibition, the depressing effects were reversed and clozapine enhanced the recurrent excitation. These results suggest that the therapeutic actions of clozapine in alleviating the positive symptoms of schizophrenia are achieved, at least partially, through the readjustment of synaptic balance between the excitation and inhibition in the prefrontal cortical circuitry.

Interaction of dopamine D1 and NMDA receptors mediates acute clozapine potentiation of glutamate EPSPs in rat prefrontal cortex

The atypical antipsychotic drug clozapine effectively alleviates both negative and positive symptoms of schizophrenia via unclear cellular mechanisms. Clozapine may modulate both glutamatergic and dopaminergic transmission in the prefrontal cortex (PFC) to achieve part of its therapeutic actions. Using whole cell patch-clamp techniques, current-clamp recordings in layers V-VI pyramidal neurons from rat PFC slices showed that stimulation of local afferents (in 2 microM bicuculline) evoked mixed [AMPA/kainate and N-methyl-D-aspartate (NMDA) receptors] glutamate receptor-mediated excitatory postsynaptic potentials (EPSPs). Clozapine (1 microM) potentiated polysynaptically mediated evoked EPSPs (V(Hold) = -65 mV), or reversed EPSPs (rEPSP, V(Hold) = +20 mV) for >30 min. The potentiated EPSPs or rEPSPs were attenuated by elevating [Ca(2+)](O) (7 mM), by application of NMDA receptor antagonist 2-amino5-phosphonovaleric acid (50 microM), or by pretreatment with dopamine D1/D5 receptor antagonist SCH23390 (1 microM) but could be further enhanced by a dopamine reuptake inhibitor bupropion (1 microM). Clozapine had no significant effect on pharmacologically isolated evoked NMDA-rEPSP or AMPA-rEPSPs but increased spontaneous EPSPs without changing the steady-state resting membrane potential. Under voltage clamp, clozapine (1 microM) enhanced the frequency, and the number of low-amplitude (5-10 pA) AMPA receptor-mediated spontaneous EPSCs, while there was no such changes with the mini-EPSCs (in 1 microM TTX). Taken together these data suggest that acute clozapine can increase spike-dependent presynaptic release of glutamate and dopamine. The glutamate stimulates distal dendritic AMPA receptors to increase spontaneous EPSCs and enabled a voltage-dependent activation of neuronal NMDA receptors. The dopamine released stimulates postsynaptic D1 receptor to modulate a lasting potentiation of the NMDA receptor component of the glutamatergic synaptic responses in the PFC neuronal network. This sequence of early synaptic events induced by acute clozapine may comprise part of the activity that leads to later cognitive improvement in schizophrenia.

Dopaminergic modulation of ventilation in obese Zucker rats

To investigate the hypothesis that the impaired respiratory drive noted in morbid obesity was attributable to altered dopaminergic mechanisms acting on peripheral and/or central chemoreflex sensitivity, seven obese and seven lean Zucker rats were studied at 11 wk of age. Ventilation (VE) was measured by the barometric technique during hyperoxic (100% O(2)), normoxic (21% O(2)), hypoxic (10% O(2)), and hypercapnic (7% CO(2)) exposures after the administration of vehicle (control), haloperidol [Hal, 1 mg/kg, a central and peripheral dopamine (Da) receptor antagonist], or domperidone (Dom, 0.5 mg/kg, a peripheral Da receptor antagonist). In both lean and obese rats, Hal increased tidal volume and decreased respiratory frequency during hyperoxia or normoxia, resulting in an unchanged VE. In contrast, Dom did not affect tidal volume, frequency, or VE during hyperoxia or normoxia. During hypoxia, however, VE significantly increased from 1,132 +/- 136 to 1,348 +/- 98 ml. kg(-1). min(-1) (P < 0.01) after the administration of Dom in obese rats, whereas no change was observed in lean rats. Hal significantly decreased VE during hypoxia compared with control in lean but not obese rats. In both lean and obese rats, Hal decreased VE in response to hypercapnia, whereas Dom had no effect. Our major findings suggest that peripheral chemosensitivity to hypoxia in obese Zucker rats is reduced as a result of an increased dopaminergic receptor modulation in the carotid body.

Clozapine inhibits synaptic transmission at GABAergic synapses established by ventral tegmental area neurones in culture

Elucidation of the mechanism of action of the atypical antipsychotic clozapine is complicated by the finding that this molecule interacts with multiple targets including dopaminergic and serotonergic receptors. Binding studies have suggested that clozapine also antagonises GABA(A) receptors, but physiological evidence for such a block at functional synapses is lacking. In this study, we explored this antagonism by using electrophysiological techniques on GABAergic neurones of the ventral tegmental area in culture. Inhibitory post-synaptic currents (IPSCs) evoked in isolated GABAergic neurones were found to be dose-dependently inhibited by clozapine. Compatible with a post-synaptic mechanism, we found that membrane currents evoked by exogenous applications of GABA were similarly dose-dependently inhibited by clozapine. An analysis of miniature inhibitory post-synaptic currents (mIPSCs) showed that clozapine reduced the amplitude of quantal events in a way similar to SR-95531, a specific GABA(A) receptor antagonist. Both drugs caused a similar leftward shift of the cumulative probability distribution of mIPSC amplitudes. This suggests that clozapine acts on both synaptic and extrasynaptic GABA(A) receptors. In conclusion, our work demonstrates that clozapine produces a functional antagonism of GABA(A) receptors at synapses. Because this effect occurs at concentrations that could be found in the brain of patients treated with clozapine, a reduction in GABAergic synaptic transmission could be implicated in the therapeutic actions and/or side-effects of clozapine.

Dizocilpine-induced neuropathological changes in rat retrosplenial cortex are reversed by subsequent clozapine treatment

In this study, we examined the effect of post-treatment with clozapine on the neuropathological changes in the rat retrosplenial cortex induced by the administration of non-competitive NMDA receptor antagonist dizocilpine ((+)-MK-801). The maximal increase in vacuolized neurons, which are representative of neuropathology, was observed 4 hours after a single injection of dizocilpine (0.5 mg/kg s.c.), with a complete reversal of the neuropathology after 16-24 hours. The administration of clozapine (10 mg/kg, i.p.,) 4 hours after the administration of dizocilpine significantly decreased the number of vacuolized neurons in the retrosplenial cortex 6, 8 or 10 hours after administration of dizocilpine, compared to vehicle-treated animals. Furthermore, the administration of clozapine (5, 10 or 20 mg/kg i.p.) 4 hours after the administration of dizocilpine produced a significant decrease in the number of vacuolized neurons in the retrosplenial cortex in a dose-dependent manner when measure 6 hours post-dizocilpine. These results show that neuropathological changes in the rat retrosplenial cortex produced by dizocilpine can be attenuated by post-treatment with clozapine.