Influence of antidepressant drugs on seizure susceptibility and the anticonvulsant activity of valproate in mice

Comorbid epilepsy and depression—pharmacokinetic and pharmacodynamic drug interactions

Background: Major depressive disorder may be encountered in 17% of patients with epilepsy and in patients with drug-resistant epilepsy its prevalence may reach 30%. This indicates that patients with epilepsy may require antidepressant treatment.

Purpose: Both pharmacodynamic and pharmacokinetic interactions between antiepileptic (antiseizure) and antidepressant drugs have been reviewed. Also, data on the adverse effects of co-administration of antiepileptic with antidepressant drugs have been added. This article was submitted to Neuropharmacology, a section of the journal Frontiers in Pharmacology.

Methods: The review of relevant literature was confined to English-language publications in PUBMED databases. Table data show effects of antidepressants on the seizure susceptibility in experimental animals, results of pharmacodynamic interactions between antiepileptic and antidepressant drugs mainly derived from electroconvulsions in mice, as well as results concerning pharmacokinetic interactions between these drugs in clinical conditions.

Conclusion: Antidepressant drugs may exert differentiated effects upon the convulsive threshold which may differ in their acute and chronic administration. Animal data indicate that chronic administration of antidepressants could reduce (mianserin, trazodone) or potentiate the anticonvulsant activity of some antiepileptics (fluoxetine, reboxetine, venlafaxine). There are also examples of neutral interactions (milnacipran).

How Antidepressant Drugs Affect the Antielectroshock Action of Antiseizure Drugs in Mice: A Critical Review

Depression coexists with epilepsy, worsening its course. Treatment of the two diseases enables the possibility of interactions between antidepressant and antiepileptic drugs. The aim of this review was to analyze such interactions in one animal seizure model-the maximal electroshock (MES) in mice. Although numerous antidepressants showed an anticonvulsant action, mianserin exhibited a proconvulsant effect against electroconvulsions. In most cases, antidepressants potentiated or remained ineffective in relation to the antielectroshock action of classical antiepileptic drugs. However, mianserin and trazodone reduced the action of valproate, phenytoin, and carbamazepine against the MES test. Antiseizure drug effects were potentiated by all groups of antidepressants independently of their mechanisms of action. Therefore, other factors, including brain-derived neurotrophic factor (BDNF) and glial-derived neurotrophic factor (GDNF) modulation, should be considered as the background for the effect of drug combinations.

Effect of acute and chronic treatment with milnacipran potentiates the anticonvulsant activity of conventional antiepileptic drugs in the maximal electroshock-induced seizures in mice

RATIONALE

Depression often coexists with epilepsy. Simultaneous therapy of the two diseases may be associated with pharmacodynamic and/or pharmacokinetic interactions between antiepileptic and antidepressant drugs.

OBJECTIVES

The aim of this study was to investigate the influence of acute and chronic treatment with intraperitoneal milnacipran (MLN), a selective serotonin/noradrenaline reuptake inhibitor, on the protective activity of valproate, carbamazepine (CBZ), phenytoin, or phenobarbital (PB) in the maximal electroshock (MES) test in mice.

MATERIALS AND METHODS

Electroconvulsions were produced by an alternating current (50 Hz, 25 mA) delivered via ear-clip electrodes. Motor coordination and long-term memory were evaluated in the chimney test and passive-avoidance task, respectively. Brain concentrations of antiepileptic drugs (AEDs) were assessed by immunofluorescence.

RESULTS

Given acutely, MLN at 10 mg/kg increased the convulsive threshold. Acute MLN applied at the subprotective dose of 5 mg/kg enhanced the anticonvulsant effects of CBZ and PB. Chronic treatment with MLN (5-30 mg/kg once daily for 2 weeks) did not affect either the electroconvulsive threshold or the anticonvulsant action of all studied conventional antiepileptic drugs. Since the antidepressant did not affect brain concentrations of antiepileptics used in the study, the revealed interactions seem to be of pharmacodynamic nature. Moreover, acute and chronic MLN, AEDs, and their combinations did not produce significant motor and long-term memory impairment.

CONCLUSIONS

Acute, but not chronic, treatment with MLN can increase the effectiveness of some AEDs against MES-induced seizures in mice. It seems that MLN may also be considered as a candidate drug for clinical trials in patients with epilepsy and depressive disorders.

Acute and chronic treatment with mianserin differentially affects the anticonvulsant activity of conventional antiepileptic drugs in the mouse maximal electroshock model

RATIONALE

Epilepsy often coexists with depression. Therefore, the probability of simultaneous treatment with antiepileptics and antidepressants and the possibility of interactions between them are relatively high.

OBJECTIVE

The effects of acute and chronic administration of mianserin on the protective activity of valproate (VPA), carbamazepine, phenytoin, and phenobarbital were evaluated in the maximal electroshock in mice.

MATERIALS AND METHODS

Animals were subjected to electroconvulsions. Undesired effects were evaluated in the chimney test (motor impairment) and passive-avoidance task (memory deficit). Brain concentrations of antiepileptic drugs were assessed by immunofluorescence.

RESULTS

When given acutely, mianserin (at doses greater than or equal to 20 mg/kg) significantly raised the electroconvulsive threshold. The antidepressant, at the subanticonvulsant doses, enhanced the anticonvulsant action of carbamazepine, phenytoin, and VPA. Mianserin administered chronically at 30 mg/kg significantly decreased the electroconvulsive threshold. In contrast to acute treatment, the antidepressant at subeffective doses diminished the anticonvulsant activity of VPA and phenytoin. Mianserin given either acutely or chronically did not affect the brain concentrations of antiepileptic drugs, so a pharmacokinetic contribution to the observed interactions is not probable. Acute and chronic treatment with mianserin and its combinations with antiepileptic drugs did not impair either motor coordination or long-term memory.

CONCLUSION

Although acute application of mianserin may potentiate the anticonvulsant action of some antiepileptics, its chronic administration can lead to the opposite effect. Therefore, as far as the presented results can be transferred to clinical conditions, the antidepressant therapy with mianserin should be limited or even avoided in epileptic patients.

Norepinephrine-deficient mice have increased susceptibility to seizure-inducing stimuli

Several lines of evidence suggest that norepinephrine (NE) can modulate seizure activity. However, the experimental methods used in the past cannot exclude the possible role of other neurotransmitters coreleased with NE from noradrenergic terminals. We have assessed the seizure susceptibility of genetically engineered mice that lack NE. Seizure susceptibility was determined in the dopamine beta-hydroxylase null mutant (Dbh -/-) mouse using four different convulsant stimuli: 2,2,2-trifluroethyl ether (flurothyl), pentylenetetrazol (PTZ), kainic acid, and high-decibel sound. Dbh -/- mice demonstrated enhanced susceptibility (i.e., lower threshold) compared with littermate heterozygous (Dbh +/-) controls to flurothyl, PTZ, kainic acid, and audiogenic seizures and enhanced sensitivity (i.e., seizure severity and mortality) to flurothyl, PTZ, and kainic acid. c-Fos mRNA expression in the cortex, hippocampus (CA1 and CA3), and amygdala was increased in Dbh -/- mice in association with flurothyl-induced seizures. Enhanced seizure susceptibility to flurothyl and increased seizure-induced c-fos mRNA expression were reversed by pretreatment with L-threo-3, 4-dihydroxyphenylserine, which partially restores the NE content in Dbh -/- mice. These genetically engineered mice confirm unambiguously the potent effects of the noradrenergic system in modulating epileptogenicity and illustrate the unique opportunity offered by Dbh -/- mice for elucidating the pathways through which NE can regulate seizure activity.