Effects of lamotrigine on the 5-HT1A receptor function in healthy human males

Receptor targets for antidepressant therapy in bipolar disorder: an overview

The treatment of bipolar depression is one of the most challenging issues in contemporary psychiatry. Currently only quetiapine and the olanzapine-fluoxetine combination are officially approved by the FDA against this condition. The neurobiology of bipolar depression and the possible targets of bipolar antidepressant therapy remain relatively elusive. We performed a complete and systematic review to identify agents with definite positive or negative results concerning efficacy followed by a second systematic review to identify the pharmacodynamic properties of these agents. The comparison of properties suggests that the stronger predictors for antidepressant efficacy in bipolar depression were norepinephrine alpha-1, dopamine D1 and histamine antagonism, followed by 5-HT2A, muscarinic and dopamine D2 and D3 antagonism and eventually by norepinephrine reuptake inhibition and 5HT-1A agonism. Serotonin reuptake which constitutes the cornerstone in unipolar depression treatment does not seem to play a significant role for bipolar depression. Our exhaustive review is compatible with a complex model with multiple levels of interaction between the major neurotransmitter systems without a single target being either necessary or sufficient to elicit the antidepressant effect in bipolar depression.

The mood stabilizer lamotrigine produces antidepressant behavioral effects in rats: role of brain-derived neurotrophic factor

The anticonvulsant drug lamotrigine has been shown to produce strong antidepressant effects in the treatment of patients with bipolar disorder. However, to date there are few preclinical reports on its behavioral actions in animal models of depression or its underlying molecular mechanisms. The current study investigated the effects of lamotrigine in the forced swimming test and the learned helplessness test. The results demonstrate that both 15 and 30 mg/kg acute treatment of lamotrigine significantly reduced immobility in the forced swimming test without affecting locomotor activity. Sub-chronic twice daily injections of 30 mg/kg lamotrigine robustly decreased escape failures in animals that had developed learned helplessness symptoms. In parallel, the sub-chronic lamotrigine treatment also up-regulated frontal and hippocampal brain-derived neurotrophic factor expression in both naive and stressed animals and restored the stress-induced down-regulation of brain-derived neurotrophic factor expression. This study provides further evidence for the use of lamotrigine as a novel antidepressant in the treatment of bipolar disorders.

Serotonin 5-HT1A receptor stimulates c-Jun N-terminal kinase and induces apoptosis in Chinese hamster ovary fibroblasts

The 5-HT1A receptor is a prototypical member of the large and diverse serotonin receptor family. One key role of this receptor is to stimulate cell proliferation and differentiation via the extracellular signal regulated protein kinase (ERK) mitogen activated protein (MAP) kinase. There are few reports on the ability of the 5-HT1A receptor to modulate other MAP kinases such as c-Jun N-terminal kinase (JNK), which is activated by various extracellular stimuli, resulting in cell growth, differentiation, and programmed cell death. We report here for the first time that the 5-HT1A receptor stimulates JNK. JNK stimulation was Pertussis toxin-sensitive and was mediated by Rho family low molecular weight GTPases. The 5-HT1A receptor also increased apoptosis, which was mimicked by the MEK inhibitor PD98059, and blocked by the JNK inhibitor SP600125. These results suggest that the 5-HT1A receptor stimulates both ERK-dependent anti-apoptotic pathways and JNK-dependent pro-apoptotic pathways in CHO cells.

Lamotrigine: a review of its use in bipolar disorder

Lamotrigine (Lamictal), a phenyltriazine derivative, is a well established anticonvulsant agent that has shown efficacy in the prevention of mood episodes in adult patients with bipolar I disorder. The mechanism of action of the drug in patients with bipolar disorder may be related to the inhibition of sodium and calcium channels in presynaptic neurons and subsequent stabilisation of the neuronal membrane. Lamotrigine monotherapy significantly delayed time to intervention with additional pharmacotherapy or electroconvulsive therapy for any new mood episode (mania, hypomania, depression and mixed episodes), compared with placebo, in two large, randomised, double-blind trials of 18 months' duration. Additionally, lamotrigine was significantly superior to placebo at prolonging time to intervention for depression. These effects of lamotrigine were demonstrated in both recently manic/hypomanic and recently depressed patients. Lamotrigine showed efficacy in delaying manic/hypomanic episodes in pooled data only, although lithium was superior to lamotrigine on this measure. Two of four double-blind, short-term studies have shown lamotrigine to be more effective than placebo in the treatment of patients with treatment-refractory bipolar disorder or those with bipolar depression. Lamotrigine has not demonstrated efficacy in the treatment of acute mania. Lamotrigine was generally well tolerated in maintenance studies with the most common adverse events being headache, nausea, infection and insomnia. Incidences of diarrhoea and tremor were significantly lower in lamotrigine- than in lithium-treated patients. The incidence of serious rash with lamotrigine treatment was 0.1% in all studies of bipolar disorder and included one case of mild Stevens-Johnson syndrome. Lamotrigine did not appear to cause bodyweight gain. The dosage of lamotrigine is titrated over a 6-week period to 200 mg/day to minimise the incidence of serious rash. Adjustments to the initial and target dosages are required if coadministered with valproate semisodium or carbamazepine.

CONCLUSION

Lamotrigine has been shown to be an effective maintenance therapy for patients with bipolar I disorder, significantly delaying time to intervention for any mood episode. Additionally, lamotrigine significantly delayed time to intervention for a depressive episode and showed limited efficacy in delaying time to intervention for a manic/hypomanic episode, compared with placebo. Although not approved for the short-term treatment of mood episodes, lamotrigine has shown efficacy in the acute treatment of patients with bipolar depression but has not demonstrated efficacy in the treatment of acute mania. Lamotrigine is generally well tolerated, does not appear to cause bodyweight gain and, unlike lithium, generally does not require monitoring of serum levels.

Effect of acute and chronic lamotrigine on basal and stimulated extracellular 5-hydroxytryptamine and dopamine in the hippocampus of the freely moving rat

1. We have studied the effects of acute and chronic treatment with the anticonvulsant lamotrigine (LTG) on basal and stimulated extracellular 5-hydroxytryptamine (5-HT), dopamine (DA) and their metabolites in the hippocampus of freely moving rats using in vivo microdialysis. 2. Acute LTG (10 and 20 mg kg(-1)) decreased extracellular 5-HT, but had no effect on its metabolite 5-hydroxyindoleacetic acid (5-HIAA). Dialysate DA was also decreased by LTG as were its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). When transmitter release was stimulated by either 50 microm veratridine or 100 mm K(+), marked increases in the release of both transmitters occurred, but LTG was entirely without effect on this. 3. In chronic experiments, rats were dialysed after 2, 4, 7, 14 and 21 days of LTG treatment (5 mg kg(-1), twice daily). During this period a progressively different response to the drug was seen. After 2 days, basal extracellular 5-HT was significantly greater in treated rats than control rats. This effect persisted up to 14 days, but by 21 days 5-HT levels had returned to control values. 5-HIAA levels were unaltered and there was no effect of LTG on veratridine or K(+) stimulated 5-HT release. 4. Similarly, DA concentrations significantly increased after 2-7 days of LTG treatment, but returned and remained at basal values thereafter. During the treatment period LTG had no effect on extracellular DOPAC, but HVA followed a similar pattern to its parent transmitter. As with 5-HT, at no time point did LTG have any effect on stimulated DA release. 5. These neurochemical findings observed in these experiments are considered in relation to the use of LTG in bipolar disorder.

Potential mechanisms of action of lamotrigine in the treatment of bipolar disorders

Based on the mood-stabilizing properties of carbamazepine and valproate, new anticonvulsants have been explored for use in bipolar disorders. One such agent, lamotrigine, has a novel clinical profile in that it may "stabilize mood from below," as it appears to maximally impact depressive symptoms in bipolar disorders. In this paper, we review the mechanisms of action of lamotrigine in an effort to understand the basis of its distinctive clinical use in the management of bipolar disorders as well as its diverse antiseizure effects. We consider lamotrigine mechanisms, emphasizing commonalities and dissociations among actions of lamotrigine, older mood stabilizers, and other anticonvulsants. Although ion channel effects, especially sodium channel blockade, may importantly contribute to antiseizure effects, such actions may be less central to lamotrigine thymoleptic effects. Antiglutamatergic and neuroprotective actions are important candidate mechanisms for lamotrigine psychotropic effects. Lamotrigine has a variable profile in kindling and contingent tolerance experiments and does not appear to have robust gamma-aminobutyric acid or monoaminergic actions. Lamotrigine intracellular signaling effects warrant investigation. Although lamotrigine mechanisms overlap those of other mood-stabilizing anticonvulsants, important dissociations suggest candidate mechanisms, which could contribute to lamotrigine's distinctive psychotropic profile.

Lamotrigine in mood disorders

Lamotrigine is an anticonvulsant drug with good efficacy and safety in the treatment of epilepsy. There is now substantial evidence that lamotrigine is also useful in treating resistant depression, rapid cycling bipolar affective disorder, depressive episodes in bipolar affective disorder and in the maintenance phase or prophylaxis of bipolar affective disorder. There are possible roles in managing mood changes in borderline personality disorder, reducing chronic pain and treating schizoaffective disorder. The general range of doses found effective in affective disorders is from 50 to 300 mg daily. Clinical use seems to involve a titration of dose upwards over several weeks until the desired effect is obtained. However, further definitive double-blind, randomised controlled trials against gold standard treatments are required. Lamotrigine has a preferable side-effect profile compared to standard agents for bipolar affective disorder such as lithium or carbamazepine. Further research is certainly warranted and, given its tolerability, could point to lamotrigine as the treatment of choice for some affective disorders.

Lamotrigine induced selective changes in 5-HT(1A) receptor mediated response in rat brain

A new anticonvulsant drug lamotrigine (LTG) has recently been reported to be effective in treating patients with bipolar affective disorder, depression and schizoaffective disorder, suggesting that it is a mood stabilizer. However, the mechanism of action underlying its efficacy in mood disorders is not understood. This study examined the in vivo effect of LTG on 5-HT(1A) receptor-mediated adenylyl cyclase (AC) response in regions of rat brain, as this pathway has been implicated in the therapeutic action of various classes of mood stabilizers. The density of 5-HT(1A) receptors was measured by radioligand binding assay using [(3)H]8-OH-DPAT (0.05-0.8nM) in frontal cortex and hippocampus of rats treated orally with LTG (5mg/kg) for 7 days. AC activity was assayed using [(3)H]ATP. The oral administration of LTG significantly decreased the density of cortical (50%, P<0.001) but not hippocampal 5-HT(1A) receptors, without significant change in the affinity of [(3)H]8-OH-DPAT to 5-HT(1A) receptor in these regions. There was no significant alteration in basal or forskolin-stimulated AC activity in either of regions. However, a significant decrease (P<0.01) in the inhibition of forskolin-stimulated AC activity by 8-OH-DPAT was observed only in cortical membranes of LTG treated rats when compared to control. These results suggest that one mode of action of LTG may be by the downregulation of cortical 5-HT(1A) receptor-mediated AC response.

Serotonin in mania and in the mechanism of action of mood stabilizers: a review of clinical studies

OBJECTIVES

Serotonin (5-hydroxytryptamine, 5-HT) was implicated in the pathophysiology of manic-depressive illness as early as 1958. Although extensive evidence has accumulated since then to support 5-HT's role in depression, relatively fewer studies examined its role in mania. The purpose of this paper was to review and summarize the current state of knowledge on the role of 5-HT in mania and its treatment.

METHODS

We systemically reviewed clinical studies of 1) 5-HT function in mania and 2) 5-HT in the mechanism of action of mood stabilizers, including lithium and anticonvulsants.

RESULTS

Review showed that cerebrospinal fluid, postmortem, platelet, neuroendocrine challenge, and tryptophan depletion studies provided some evidence to support the hypothesis that a 5-HT deficit is involved in mania and that enhancement of 5-HT neurotransmission exerts a mood-stabilizing effect.

CONCLUSIONS

There is some evidence from clinical studies for the contribution of 5-HT in mania and in the mechanism of action of mood stabilizers. However, it is very likely that other neurotransmitters also play important roles. Future directions for research include 1) in vivo study of 5-HT receptor subtypes using positron emission tomography, 2) investigation of the interaction between 5-HT and other neurotransmitter systems, and 3) determination of the relationships between diagnostic subtypes of mania and 5-HT function and other neurotransmitter systems.

Lamotrigine and the treatment of mania in bipolar disorder

Anticonvulsants, including valproate and carbamazepine, have established efficacy in the treatment of mania. The anticonvulsant, lamotrigine. has been reported to have antimanic and antidepressant efficacy, and mood-stabilising effects in case reports and preliminary open trials. The efficacy and tolerability of lamotrigine has been compared with olanzapine and lithium in a randomised, prospective, controlled fashion over a period of 4 weeks treatment in a total of 45 hospitalised patients with DSM-IV-defined mania. Significant improvements of a similar magnitude were observed for all treatment groups and lamotrigine was well tolerated. Mechanisms of action proposed to explain the antimanic activity of lamotrigine include inhibition of voltage-sensitive and use-dependent sodium channels, inhibition of glutamate release and calcium channel blockade. Platelet studies have indicated supersensitivity of glutamate receptors and increased intracellular calcium concentrations in patients with mania. Further clinical and mechanistic studies of lamotrigine use in mania are warranted.