Anxiolytic effects of lamotrigine and JZP-4 in the elevated plus maze and in the four plate conflict test

Lamotrigine as a mood stabilizer: insights from the pre-clinical evidence

INTRODUCTION

Lamotrigine (LTG) is a well-established anticonvulsant that is also approved for the prevention of mood relapses in bipolar disorder. However, the mechanisms underlying LTG mood stabilizing effects remain unclear. Areas covered: Herein, the pre-clinical evidence concerning LTG's' mode of action in depression and mania is reviewed. Bottlenecks and future perspectives for this expanding and promising field are also discussed. Pre-clinical studies have indicated that neurotransmitter systems, especially serotoninergic, noradrenergic and glutamatergic, as well as non-neurotransmitter pathways such as inflammation and oxidative processes might play a role in LTG's antidepressant effects. The mechanisms underlying LTG's anti-manic properties remain to be fully explored, but the available pre-clinical evidence points out to the role of glutamatergic neurotransmission, possibly through AMPA-receptors. Expert opinion: A major limitation of current pre-clinical investigations is that there are no experimental models that recapitulate the complexity of bipolar disorder. Significant methodological differences concerning time and dose of LTG treatment, administration route, animal strains, and behavioral paradigms also hamper the reproducibility of the findings, leading to contradictory conclusions. Moreover, the role of other mechanisms (e.g. inositol phosphate and GSK3β pathways) implicated in the mode of action of different mood-stabilizers must also be consolidated with LTG.

True alignment of preclinical and clinical research to enhance success in CNS drug development: a review of the current evidence

Central nervous system pharmacological research and development has reached a critical turning point. Patients suffering from disorders afflicting the central nervous system are numerous and command significant attention from the pharmaceutical industry. However, given the numerous failures of promising drugs, many companies are no longer investing in or, indeed, are divesting from this therapeutic area. Central nervous system drug development must change in order to develop effective therapies to treat these patients. Preclinical research is a cornerstone of drug development; however, it is frequently criticised for its lack of predictive validity. Animal models and assays can be shown to be more predictive than reported and, on many occasions, the lack of thorough preclinical testing is potentially to blame for some of the clinical failures. Important factors such as translational aspects, nature of animal models, variances in acute versus chronic dosing, development of add-on therapies and understanding of the full dose-response relationship are too often neglected. Reducing the attrition rate in central nervous system drug development could be achieved by addressing these important questions before novel compounds enter the clinical phase. This review illustrates the relevance of employing these criteria to translational central nervous system research, better to ensure success in developing new drugs in this therapeutic area.

Lamotrigine positively affects the development of psychiatric comorbidity in epileptic animals, while psychiatric comorbidity aggravates seizures

Several clinical and preclinical studies have focused on the relationship between epilepsy and psychological disturbances. Although behavior in some experimental models of epilepsy has been studied, only few of them can be considered as models of epilepsy and mood disorder comorbidity. Since several models of epilepsy or psychiatric disorders are already available, we wondered whether a mixture of the two could experimentally represent a valid alternative to study such comorbidity. Here, we present a possible experimental protocol to study drug effects and physiopathogenesis of psychiatric comorbidity in epileptic animals. Pentylentetrazol-kindled animals were subjected to the chronic mild stress (CMS) procedure; furthermore, we tested the effects of chronic lamotrigine treatment on the development of comorbidity. We found that epileptic-depressed animals showed more pronounced behavioral alterations in comparison to other mice groups, indicating that kindled animals develop more pronounced CMS-induced behavioral alterations than nonepileptic mice; lamotrigine was able to prevent the development of comorbidities such as anxiety, depression-like behavior, and memory impairment.

Effects of mood stabilizers on marble-burying behavior in mice: involvement of GABAergic system

RATIONALE

Obsessive-compulsive disorder (OCD) is characterized by recurrent unwanted thoughts (obsessions), usually accompanied by repetitive behaviors (compulsions) intended to alleviate anxiety. Marble-burying behavior is a pharmacological model for study of OCD.

OBJECTIVES

In the present study, we examined the effects of mood stabilizers on marble-burying behavior in mice, as well as the role of GABA receptors in this behavior.

METHODS

The effects of treatment with valproate, carbamazepine, lithium carbonate, lamotrigine, muscimol and baclofen on marble-burying behavior in mice were evaluated.

RESULTS

Valproate (10, 30 and 100 mg/kg, i.p.) and carbamazepine (30 and 100 mg/kg, p.o.) significantly reduced marble-burying behavior without affecting total locomotor activity in ICR mice. Lamotrigine (30 mg/kg, i.p.) also significantly reduced marble-burying behavior in ddY mice. On the other hand, lithium carbonate (10, 30 and 100 mg/kg, i.p.) reduced total locomotor activity without affecting marble-burying behavior in ddY mice. The selective GABA(A) receptor agonist muscimol (1 mg/kg) significantly reduced marble-burying behavior without affecting total locomotor activity, whereas the selective GABA(B) receptor agonist baclofen (3 mg/kg) reduced total locomotor activity without affecting marble-burying behavior. Moreover, the selective GABA(A) receptor antagonist bicuculline (3 mg/kg) significantly counteracted the decrease in marble-burying induced by the administration of muscimol (1 mg/kg) and valproate (100 mg/kg).

CONCLUSIONS

These results suggest that GABAergic mechanism is involved in marble-burying behavior, and that valproate, carbamazepine and lamotrigine reduce marble-burying behavior. Moreover, valproate reduces marble-burying behavior via a GABA(A) receptor-dependent mechanism.

Riluzole produces distinct anxiolytic-like effects in rats without the adverse effects associated with benzodiazepines

In this study, we investigated the anxiolytic-like effect of riluzole using three different innate anxiety models in rats. In the elevated plus-maze test, riluzole significantly increased the time spent in, and entries into, the open arm after 60 min administration. This finding was supported by results obtained from light/dark and open-field tests. The magnitude of the anxiolytic-like effects of riluzole in each of the behavioral models was similar to those produced by a benzodiazepine, diazepam, suggesting that riluzole has a robust anxiolytic-like activity in rats. To clarify the involvement of sodium channels in this anxiolytic activity, we examined the effect of a co-administered sodium channel activator, veratrine. The anxiolytic-like action of riluzole was diminished by veratrine in the elevated plus-maze, light/dark and open-field tests. Based on these results, it is suggested that the anxiolytic mechanism of riluzole is clearly distinct from that of diazepam. In addition, to examine whether riluzole directly and non-selectively affected the GABA(A)-benzodiazepine receptor complex, we performed three behavioral tests (footprint analysis, Y-maze test and the ethanol-induced sleeping time test) that are closely related to the GABA(A)-benzodiazepine pathways. In contrast to diazepam, riluzole produced no significant effects in these tests. Here, we provide the first report demonstrating that riluzole produces distinct anxiolytic-like effects in rats without the adverse effects associated with benzodiazepines.

The contextual fear conditioning deficit presented by spontaneously hypertensive rats (SHR) is not improved by mood stabilizers

OBJECTIVES

We have recently reported that spontaneously hypertensive rats (SHR) present a contextual fear conditioning (CFC) deficit. This deficit is improved by antipsychotic drugs, potentiated by proschizophrenia manipulations and not altered by acute administration of carbamazepine, lamotrigine and valproic acid. Nevertheless, the effects of lithium-a classical mood stabilizer-or repeated treatment with these drugs were not evaluated. The main aim of the present study was to extend our previous work by investigating a possible beneficial effect of acute and/or chronic treatments with lithium or lamotrigine on the acquisition deficit of CFC presented by SHR.

METHODS

Rats were submitted to CFC task after an acute treatment with lithium and/or a repeated treatment with lithium and lamotrigine.

RESULTS

Our data revealed that the CFC deficit presented by SHR is not improved by acute or repeated treatment with lithium. Repeated lamotrigine treatment potentiated the deficit presented by SHR and impaired CFC in control animals (Wistar Rats).

CONCLUSIONS

These data reinforce the absence of beneficial effects of mood stabilizers on the emotional context processing impairment modeled by SHR.