Role of serotonin in the anticonvulsant effect of fluoxetine in genetically epilepsy-prone rats

Evaluating bexicaserin for the treatment of developmental epileptic encephalopathies

INTRODUCTION

Developmental epileptic encephalopathies (DEEs) pose significant challenges due to their refractory nature and limited treatment options. Despite advancements in genetic understanding, effective therapies targeting underlying pathophysiology are lacking. Serotoninergic dysfunction has been implicated in epilepsy, sparking interest in serotonin as a therapeutic target.

AREA COVERED

This article explores the potential of bexicaserin, a selective 5-HT2C receptor agonist, as an adjunctive antiseizure medication in DEEs. Bexicaserin is thought to modulate GABAergic neurotransmission, suppressing central hyperexcitability. Preclinical studies demonstrate its efficacy across various seizure models. Clinical trials, including the Pacific Study, reveal promising results in reducing motor seizures. However, challenges such as adverse effects and treatment discontinuation underscore the need for further investigation.

EXPERT OPINION

The efficacy of 5-HT2C serotoninergic agonists, validated in preclinical and clinical studies, highlights serotonin's role in DEEs. Bexicaserin offers new therapeutic possibilities, potentially synergizing with existing antiseizure medications. Polypharmacotherapy, targeting distinct pathways, may enhance therapeutic outcomes. Monitoring pharmacological interactions and addressing central nervous system comorbidities are crucial for optimizing treatment strategies. Further research is needed to elucidate bexicaserin's mechanisms and potential antiepileptogenic effects.

In silico and in vivo analysis of the relationship between ADHD and social isolation in pups rat model: Implication of redox mechanisms, and the neuroprotective impact of Punicalagin

Attention deficit hyperactivity disorder (ADHD) has high incidence rate among children which may be due to excessive monosodium glutamate (MSG) consumption and social isolation (SI).

AIM

We aimed to explore the relationships between MSG, SI, and ADHD development and to evaluate the neuroprotective potential of Punicalagin (PUN).

METHODS

Eighty male rat pups randomly distributed into eight groups. Group I is the control, and Group II is socially engaged rats treated with PUN. Groups III to VII were exposed to ADHD-inducing factors: Group III to SI, Group IV to MSG, and Group V to both SI and MSG. Furthermore, Groups VI to VIII were the same Groups III to V but additionally received PUN treatment.

KEY FINDINGS

Exposure to MSG and/or SI led to pronounced behavioral anomalies, histological changes and indicative of ADHD-like symptoms in rat pups which is accompanied by inhibition of the nuclear factor erythroid 2-related factor 2 (Nrf2)/Heme-oxygenase 1 (HO-1)/Glutathione (GSH) pathway, decline of the brain-derived neurotrophic factor (BDNF) expression and activation of the Toll-like receptor 4 (TLR4)/Nuclear factor kappa B (NF-kB)/NLR Family Pyrin Domain Containing 3 (NLRP3) pathway. This resulted in elevated inflammatory biomarker levels, neuronal apoptosis, and disrupted neurotransmitter equilibrium. Meanwhile, pretreatment with PUN protected against all the previous alterations.

SIGNIFICANCE

We established compelling associations between MSG consumption, SI, and ADHD progression. Moreover, we proved that PUN is a promising neuroprotective agent against all risk factors of ADHD.

Sigma-1 receptor and seizures

Over the last decade, sigma-1 receptor (Sig1R) has been recognized as a valid target for the treatment of seizure disorders and seizure-related comorbidities. Clinical trials with Sig1R ligands are underway testing therapies for the treatment of drug-resistant seizures, developmental and epileptic encephalopathies, and photosensitive epilepsy. However, the direct molecular mechanism by which Sig1R modulates seizures and the balance between excitatory and inhibitory pathways has not been fully elucidated. This review article aims to summarize existing knowledge of Sig1R and its involvement in seizures by focusing on the evidence obtained from Sig1R knockout animals and the anti-seizure effects of Sig1R ligands. In addition, this review article includes a discussion of the advantages and disadvantages of the use of existing compounds and describes the challenges and future perspectives on the use of Sig1R as a target for the treatment of seizure disorders.

Monosodium glutamate induces cortical oxidative, apoptotic, and inflammatory challenges in rats: the potential neuroprotective role of apigenin

Monosodium glutamate (MSG) is used as a flavor, and a taste enhancer was reported to evoke marked neuronal impairments. This study investigated the neuroprotective ability of flavonoid apigenin against neural damage in MSG-administered rats. Adult male rats were allocated into four groups: control, apigenin (20 mg/kg b.wt, orally), MSG (4 g/kg b.wt, orally), and apigenin + MSG at the aforementioned doses for 30 days. Regarding the levels of neurotransmitters, our results revealed that apigenin augmented the activity of acetylcholinesterase (AChE) markedly, and levels of brain monoamines (dopamine, norepinephrine, and serotonin) accompanied by lessening the activity of monoamine oxidase (MAO) as compared to MSG treatment. Moreover, apigenin counteracted the MSG-mediated oxidative stress by decreasing the malondialdehyde (MDA) levels together with elevating the glutathione (GSH) levels. In addition, pretreatment with apigenin induced notable increases in the activities of cortical superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR). Furthermore, apigenin attenuated the cortical inflammatory stress as indicated by lower levels of pro-inflammatory mediators such as interleukin-1 b (IL-1b), tumor necrosis factor-α (TNF-α), and nitric oxide (NO) as well as downregulated inducible nitric oxide synthase (iNOS) expression levels. Histopathological screening validated the abovementioned results and revealed that apigenin restored the distorted cytoarchitecture of the brain cortex. Thus, the present findings collectively suggest that apigenin exerted significant protection against MSG-induced neurotoxicity by enhancing the cellular antioxidant response and attenuating inflammatory machineries in the rat brain cortex.

Monoamine neurotransmitters in early epileptic encephalopathies: New insights into pathophysiology and therapy

AIM

To study neurotransmitter status in children with early epileptic and developmental and epileptic encephalopathy (DEE) and to explore the clinical response to dopaminergic and serotoninergic therapies in a group of patients.

METHOD

Two hundred and five patients (111 males [54.1.%] and 94 females [45.9%], mean age 10 months at the onset of epilepsy [SD 1 year 1 month], range 0-3 year) with epileptic encephalopathy/DEE were recruited, including those with West syndrome, Ohtahara syndrome, early myoclonic encephalopathy, epilepsy of infancy with migrating focal seizures, myoclonic encephalopathy in non-progressive disorders, infantile spasms, Doose syndrome, Lennox-Gastaut syndrome, Landau-Kleffner syndrome, and those unclassified. Cerebrospinal fluid (CSF) neurotransmitter studies and patients' medical records were reviewed. Additionally, we present clinical data of 10 patients with low CSF neurotransmitter levels who received dopaminergic/serotoninergic treatments.

RESULTS

Abnormal neurotransmitter values were identified in 68 (33%) patients. 5-Hydroxyindoleacetic acid (5-HIAA) deficit was the most prevalent alteration (91%). Low CSF 5-HIAA levels were significantly higher in 1- to 3-year-old children. A negative significant correlation was found between 5-HIAA levels and epilepsy duration before CSF study (Spearman's ρ=-0.191, p=0.007). Abnormalities in deep grey matter were associated with low levels of CSF homovanillic acid and 5-HIAA. Ten patients with low CSF neurotransmitter levels received dopamine and/or serotonin therapies. Six of them showed initial decrease of seizure frequency and severity and maintained improvement in some neurodevelopmental skills.

INTERPRETATION

A considerable number of patients showed neurotransmitter abnormalities. Age at seizure onset and duration of epilepsy before CSF study were the principal factors related to neurotransmitter depletion. Early monoamine supplementation would seem advisable as a neuroprotective strategy.

WHAT THIS PAPER ADDS

5-Hydroxyindoleacetic acid homeostasis is especially vulnerable in patients with epileptic encephalopathy/developmental and epileptic encephalopathy. Age of seizure onset and duration of epilepsy are determinants of neurotransmitter depletion.

The role of monoaminergic neurons in modulating respiration during sleep and the connection with SUDEP

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death among epilepsy patients, occurring even more frequently in cases with anti-epileptic drug resistance. Despite some advancements in characterizing SUDEP, the underlying mechanism remains incompletely understood. This review summarizes the latest advances in our understanding of the pathogenic mechanisms of SUDEP, in order to identify possible targets for the development of new strategies to prevent SUDEP. Based on our previous research along with the current literature, we focus on the role of sleep-disordered breathing (SDB) and its related neural mechanisms to consider the possible roles of monoaminergic neurons in the modulation of respiration during sleep and the occurrence of SUDEP. Overall, this review suggests that targeting the monoaminergic neurons is a promising approach to preventing SUDEP. The proposed roles of SDB and related monoaminergic neural mechanisms in SUDEP provide new insights for explaining the pathogenesis of SUDEP.

Anticonvulsant Effect of Asparagus racemosus Willd. in a Mouse Model of Catamenial Epilepsy

Asparagus racemosus Willd. (Family Liliaceae), also known as female reproductive tonic, is traditionally used across the Sub-Himalayan region in Uttarakhand, India for treatment of epilepsy and disorders of female reproductive system. Therefore, in this study, we investigated the anticonvulsant effect of A. racemosus in a mouse model of catamenial epilepsy. We artificially increased progesterone and neurosteroid levels (a state of pseudo-pregnancy) in adult Swiss albino female mice by injecting pregnant mares' serum gonadotropin (PMSG) (5 IU s.c.), followed by human chorionic gonadotropin (HCG) (5 IU s.c.) after 46 h. In the following 10 days, A. racemosus treatment was given along with measurement of progesterone, estradiol, and corticosterone levels in the blood. Neurosteroid withdrawal was induced by finasteride (50 mg/kg, i.p.) on treatment day 9. Twenty-four hours after finasteride administration (day 10 of treatment), seizure susceptibility was evaluated with the sub-convulsant pentylenetetrazole (PTZ) dose (40 mg/kg i.p.). Four hours after PTZ, animals were assessed for depression like phenotypes followed by euthanasia and separation of brain parts (cortex and hippocampus). The results showed that PMSG and HCG treatment elevated progesterone and estradiol levels. Treatment with finasteride increased seizure susceptibility and depression due to decreased progesterone and elevated estrogen levels coupled with decreased monoamine and elevated corticosterone levels. A. racemosus treatment, on the other hand, significantly decreased seizure susceptibility and depression like behaviors, possibly because of increased progesterone, restored estradiol, corticosterone, and monoamine levels. We concluded that herbal formulations using A. racemosus root extracts may be used as monotherapy or adjuvant therapy along with available AEDs for the better and safe management of catamenial epilepsy as well as comorbid depression.

Serotonin Pretreatment Abolishes Sex-specific NMDA-induced Seizure Behavior in Developing Rats

Neuronal excitability and susceptibility to excitotoxic damage can be sex-specific, with neurons from males usually being more 'easily excitable' compared to neurons from females, especially during development. Increased excitability at an individual neuronal level can lead to the formation of hyperexcitable neuronal networks, which, consequently can make the brain more seizure prone. Both animal and clinical data suggest that males experience more frequent and severe seizures than do females. Serotonin (5-hydroxytryptamine; 5-HT) can mediate neuronal excitability and seizure behavior, often serving as an anticonvulsant. Importantly, 5-HT signaling during parts of the perinatal period is sexually dimorphic. Sex differences during development have been reported in both serotonin levels and receptor type (excitatory vs. inhibitory) expression in a manner that may leave the male brain more vulnerable to over-excitation. Thus, we aimed to determine if the anticonvulsant effects of 5-HT were sex- and/or age-dependent in juvenile animals. We report a baseline sex difference in N-methyl-d-aspartate (NMDA)-induced seizure behavior and hippocampal neuronal loss, with postnatal day (PND) 14 males exhibiting more severe seizure behavior compared to females. Pretreatment with the general 5-HT receptor agonist 5-methoxytryptamine (5-MT) abolishes baseline sex differences, providing an anticonvulsant effect for males only. These sex differences appear to be at least in part organized by testosterone, as females given neonatal androgen exhibit a seizure behavior profile in between that of males and females.

Drug Treatment of Epilepsy Neuropsychiatric Comorbidities in Children

There is increasing recognition that epilepsy can be associated with a broad spectrum of comorbidities. While epileptic seizures are an essential element of epilepsy in children, there is a spectrum of neurological, mental health and cognitive disorders that add to the disease burden of childhood epilepsy resulting in a decreased quality of life. The most common comorbid conditions in childhood epilepsy include depression, anxiety, autism spectrum disorders, sleep disorders, attention deficits, cognitive impairment, and migraine. While epilepsy can result in comorbidities, many of the comorbidities of childhood have a bi-directional association, with the comorbid condition increasing risk for epilepsy and epilepsy increasing the risk for the comorbid condition. The bidirectional feature of epilepsy and the comorbidities suggest a common underlying pathological basis for both the seizures and comorbid condition. While recognition of the comorbid conditions of pediatric epilepsies is increasing, there has been a lag in the development of effective therapies partly out of concern that drugs used to treat the comorbid conditions could increase seizure susceptibility. There is now some evidence that most drugs used for comorbid conditions are safe and do not lower seizure threshold. Unfortunately, the evidence showing drugs are effective in treating many of the childhood comorbidities of epilepsy is quite limited. There is a great need for randomized, placebo-controlled drug trials for efficacy and safety in the treatment of comorbidities of childhood epilepsy.

Physical exercise and 5-hydroxytryptophan, a precursor for serotonin synthesis, reduce penicillin-induced epileptiform activity

AIM

Previous studies have shown that 5- hydroxytryptophan (5-HTP) and exercise play an important role in the synthesis of serotonin independently. The effects of the treadmill exercise and 5- hydroxytryptophan (5-HTP) on seizure mechanisms created by epileptiform activity with penicillin model were investigated in rats.

METHOD

A total of 28 male albino Wistar rats were randomly divided into four groups: exercise (Ex), Control (Cnt), 5-hydroxytryptophan (5htp) and 5-hydroxytryptophan + exercise (5htpEx) groups. Treadmill exercise and gavage (25 mg/kg/day) were administered five days a week for ten weeks. Electrocorticogram data were recorded for 3 h at the end of the protocol using the Power-Lab data acquisition system. Spike frequency, amplitude, and latency time were analyzed offline. The significant differences among the groups were evaluated by one-way analysis of variance (ANOVA).

RESULTS

Spike frequency was observed at the highest level from the 20th minute in the Cnt group, and this continued until the end of the recording. The 5-HTP alone group did not affect epileptiform activity. At the 80th minute of penicillin injection, the epileptiform activity in the 5htpEx group decreased significantly compared with the Cnt, and this significance continued until the 110th minute. There was no statistical difference in the amplitude values of the groups. The 5htpEx group was significantly higher than both the Cnt and Ex group in the seizure latency times.

CONCLUSIONS

It was determined that exercise reduced the spike number and delayed seizure significantly by potentiating the effect of 5-HTP. Given that 5-HTP used in combination with exercise can perform useful actions such as reducing seizure sensitivity and consequently improving the quality of life for individuals with epilepsy, it may be a potential candidate for the treatment of epilepsy in nonpharmacological methods.

Serotonin abnormalities in Dravet syndrome mice before and after the age of seizure onset

Dravet syndrome (DS) is a genetic form of severe epilepsy often associated with mutation of the SCN1A gene encoding the voltage gated sodium channel Nav1.1. Typically refractive to conventional therapy, serotonin neurotransmission may be an innovative target for treatment. To further understand the role of serotonin in this disorder, in this study we examined the state of the endogenous serotonin system in an Scn1a^+/- mouse model of DS. Examined at an age before seizures appear, we found the hypothermic effect of 5-HT_1A receptor agonist administration was attenuated. HPLC analysis of brain monoamine content revealed modestly reduced serotonin levels in tissue samples of the midbrain that included the dorsal raphe nucleus but no changes elsewhere in the brain. The reduced sensitivity to 5-HT_1A agonist administration seen at young ages reversed after the age of seizure development when mice showed an exaggerated hypothermic response. Likewise, adult DS mice showed a pronounced hypersensitivity to a 5-HT_2A/2C agonist. As adults however monoamine levels were not detectably altered. Thus there are alterations in the endogenous serotonin system that both precede and follow the appearance of seizure in DS mice, most strikingly in the response to agonist administration.

Estrogen and Serotonin: Complexity of Interactions and Implications for Epileptic Seizures and Epileptogenesis

A burgeoning literature documents the confluence of ovarian steroids and central serotonergic systems in the in-junction of epileptic seizures and epileptogenesis. Estrogen administration in animals reduces neuronal death from seizures by up-regulation of the prosurvival molecule i.e. Bcl-2, anti-oxidant potential and protection of NPY interneurons. Serotonin modulates epileptiform activity in either direction i.e administration of 5-HT agonists or reuptake inhibitors leads to the acti-vation of 5-HT3 and 5-HT1A receptors tending to impede focal and generalized seizures, while depletion of brain 5-HT along with the destruction of serotonergic terminals leads to expanded neuronal excitability hence abatement of seizure threshold in experimental animal models. Serotonergic neurotransmission is influenced by the organizational activity of ster-oid hormones in the growing brain and the actuation effects of steroids which come in adulthood. It is further established that ovarian steroids bring induction of dendritic spine proliferation on serotonin neurons thus thawing a profound effect on sero-tonergic transmission. This review features 5-HT1A and 5-HT3 receptors as potential targets for ameliorating seizure-induced neurodegeneration and recurrent hypersynchronous neuronal activity. Indeed 5-HT3 receptors mediate cross-talk be-tween estrogenic and serotonergic pathways, and could be well exploited for combinatorial drug therapy against epileptogen-esis.

Use and Future Prospects of in Vivo Microdialysis for Epilepsy Studies

Epilepsy is a common neurological disease characterized by recurrent unpredictable seizures. For the last 30 years, microdialysis sampling has been used to measure changes in excitatory and inhibitory neurotransmitter concentrations before, during, and after seizures. These advances have fostered breakthroughs in epilepsy research by identifying neurochemical changes associated with seizures and correlating them to electrophysiological data. Recent advances in methodology may be useful in further delineating the chemical underpinnings of seizures. A new model of ictogenesis has been developed that allows greater control over the timing of seizures that are similar to spontaneous seizures. This model will facilitate making chemical measurements before and during a seizure. Recent advancements in microdialysis sampling, including the use of segmented flow, "fast" liquid chromatography (LC), and capillary electrophoresis with laser-induced fluorescence (CE-LIF) have significantly improved temporal resolution to better than 1 min, which could be used to measure transient, spontaneous neurochemical changes associated with seizures. Microfabricated sampling probes that are markedly smaller than conventional probes and allow for a much greater spatial resolution have been developed. They may allow the targeting of specific brain regions important to epilepsy studies. Coupling microdialysis sampling to optogenetics and light-stimulated release of neurotransmitters may also prove useful for studying epileptic seizures.

Serotonin depletion increases seizure susceptibility and worsens neuropathological outcomes in kainate model of epilepsy

Serotonin is implicated in the regulation of seizures, but whether or not it can potentiate the effects of epileptogenic factors is not fully established. Using the kainic acid model of epilepsy in rats, we tested the effects of serotonin depletion on (1) susceptibility to acute seizures, (2) development of spontaneous recurrent seizures and (3) behavioral and neuroanatomical sequelae of kainic acid treatment. Serotonin was depleted by pretreating rats with p-chlorophenylalanine. In different groups, kainic acid was injected at 3 different doses: 6.5mg/kg, 9.0mg/kg or 12.5mg/kg. A single dose of 6.5mg/kg of kainic acid reliably induced status epilepticus in p-chlorophenylalanine-pretreated rats, but not in saline-pretreated rats. The neuroexcitatory effects of kainic acid in the p-chlorophenylalanine-pretreated rats, but not in saline-pretreated rats, were associated with the presence of tonic-clonic convulsions and high lethality. Compared to controls, a greater portion of serotonin-depleted rats showed spontaneous recurrent seizures after kainic acid injections. Loss of hippocampal neurons and spatial memory deficits associated with kainic acid treatment were exacerbated by prior depletion of serotonin. The present findings are of particular importance because they suggest that low serotonin activity may represent one of the major risk factors for epilepsy and, thus, offer potentially relevant targets for prevention of epileptogenesis.

Genetically epilepsy-prone rats (GEPRs) and DBA/2 mice: Two animal models of audiogenic reflex epilepsy for the evaluation of new generation AEDs

This review summarizes the current knowledge about DBA/2 mice and genetically epilepsy-prone rats (GEPRs) and discusses the contribution of such animal models on the investigation of possible new therapeutic targets and new anticonvulsant compounds for the treatment of epilepsy. Also, possible chemical or physical agents acting as proconvulsant agents are described. Abnormal activities of enzymes involved in catecholamine and serotonin synthesis and metabolism were reported in these models, and as a result of all these abnormalities, seizure susceptibility in both animals is greatly affected by pharmacological manipulations of the brain levels of monoamines and, prevalently, serotonin. In addition, both genetic epileptic models permit the evaluation of pharmacodynamic and pharmacokinetic interactions among several drugs measuring plasma and/or brain level of each compound. Audiogenic models of epilepsy have been used not only for reflex epilepsy studies, but also as animal models of epileptogenesis. The seizure predisposition (epileptiform response to sound stimulation) and substantial characterization of behavioral, cellular, and molecular alterations in both acute and chronic (kindling) protocols potentiate the usefulness of these models in elucidating ictogenesis, epileptogenesis, and their mechanisms. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

Serotonin Regulates the Firing of Principal Cells of the Subiculum by Inhibiting a T-type Ca2+ Current

The subiculum is the main output of the hippocampal formation. A high proportion of its principal neurons fire action potentials in bursts triggered by the activation of low threshold calcium currents. This firing pattern promotes synaptic release and regulates spike-timing-dependent plasticity. The subiculum receives a high density of fibers originating from the raphe nuclei, suggesting that serotonin (5-HT) modulates subicular neurons. Here we investigated if and how 5-HT modulates the firing pattern of bursting neurons. By combining electrophysiological analysis with pharmacology, optogenetics and calcium imaging, we demonstrate that 5-HT_2C receptors reduce bursting activity by inhibiting a low-threshold calcium current mediated by T-type Ca²⁺ channels in principal cells of the subiculum. In addition, we show that the activation of this novel pathway decreases bursting activity and the occurrence of epileptiform discharges induced in in vitro models for temporal lobe epilepsy (TLE).

Pharmacokinetic/pharmacodynamic considerations for epilepsy - depression comorbidities

INTRODUCTION

Epilepsy may be frequently associated with psychiatric disorders and its co-existence with depression usually results in the reduced quality of life of patients with epilepsy. Also, the efficacy of antiepileptic treatment in depressed patients with epilepsy may be significantly reduced.

AREAS COVERED

Results of experimental studies indicate that antidepressants co-administered with antiepileptic drugs may either increase their anticonvulsant activity, remain neutral or decrease the protective action of antiepileptic drugs in models of seizures. Apart from purely pharmacodynamic interactions, pharmacokinetic mechanisms have been proven to contribute to the final outcome. We report on clinical data regarding the pharmacokinetic interactions of enzyme-inducing antiepileptic drugs with various antidepressants, whose plasma concentration may be significantly reduced. On the other hand, antidepressants (especially selective serotonin reuptake inhibitors) may influence the metabolism of antiepileptics, in many cases resulting in the elevation of plasma concentration of antiepileptic drugs.

EXPERT OPINION

The preclinical data may provide valuable clues on how to combine these two groups of drugs - antidepressant drugs neutral or potentiating the anticonvulsant action of antiepileptics are recommended in this regard. Avoidance of antidepressants clearly decreasing the convulsive threshold or decreasing the anticonvulsant efficacy of antiepileptic drugs (f.e. bupropion or mianserin) in patients with epilepsy is recommended.

Low-dose fenfluramine in the treatment of neurologic disorders: experience in Dravet syndrome

In this paper, we review the experience with fenfluramine in epileptic and other paroxysmal disorders. Since the best available data are from the treatment of Dravet syndrome, we will focus primarily on this condition. Originally fenfluramine was launched as an anorectic agent. As early as 1985, seizure reduction in children could be demonstrated in a few cases with photosensitive, self-induced epilepsy. Hereafter, a small study was launched in patients with self-induced epilepsy. Results showed a significant seizure reduction, and review of the patient data showed that 5 of the 12 patients had Dravet syndrome. During that observation period, fenfluramine was withdrawn from the market because of cardiovascular side effects associated with prescribing higher doses in combination with phentermine for weight loss. In March 2002, a Belgian Royal Decree was issued permitting further study of fenfluramine in pediatric patients with intractable epilepsy. In 2011 under the Royal Decree, a prospective study of patients with Dravet syndrome treated with low-dose fenfluramine was initiated and is currently ongoing. The initial results are promising in terms of reduction of seizure frequency and overall tolerability.

Antidepressants but not antipsychotics have antiepileptogenic effects with limited effects on comorbid depressive-like behaviour in the WAG/Rij rat model of absence epilepsy

BACKGROUND AND PURPOSE

Two of the most relevant unmet needs in epilepsy are represented by the development of disease-modifying drugs able to affect epileptogenesis and/or the study of related neuropsychiatric comorbidities. No systematic study has investigated the effects of chronic treatment with antipsychotics or antidepressants on epileptogenesis. However, such drugs are known to influence seizure threshold.

EXPERIMENTAL APPROACH

We evaluated the effects of an early long-term treatment (ELTT; 17 weeks), started before seizure onset (P45), with fluoxetine (selective 5-HT-reuptake inhibitor), duloxetine (dual-acting 5-HT-noradrenaline reuptake inhibitor), haloperidol (typical antipsychotic drug), risperidone and quetiapine (atypical antipsychotic drugs) on the development of absence seizures and comorbid depressive-like behaviour in the WAG/Rij rat model. Furthermore, we studied the effects of these drugs on established absence seizures in adult (6-month-old) rats after a chronic 7 weeks treatment.

KEY RESULTS

ELTT with all antipsychotics did not affect the development of seizures, whereas, both ELTT haloperidol (1 mg · kg(-1) day(-1)) and risperidone (0.5 mg · kg(-1) day(-1)) increased immobility time in the forced swimming test and increased absence seizures only in adult rats (7 weeks treatment). In contrast, both fluoxetine (30 mg · kg(-1) day(-1)) and duloxetine (10-30 mg · kg(-1) day(-1)) exhibited clear antiepileptogenic effects. Duloxetine decreased and fluoxetine increased absence seizures in adult rats. Duloxetine did not affect immobility time; fluoxetine 30 mg · kg(-1) day(-1) reduced immobility time while at 10 mg · kg(-1) day(-1) an increase was observed.

CONCLUSIONS AND IMPLICATIONS

In this animal model, antipsychotics had no antiepileptogenic effects and might worsen depressive-like comorbidity, while antidepressants have potential antiepileptogenic effects even though they have limited effects on comorbid depressive-like behaviour.

The role of dopaminergic and serotonergic systems in neurodevelopmental disorders: a focus on epilepsy and seizure susceptibility

Introduction: The embryonic development of the vertebrate Central Nervous System (CNS) requires the induction of transcription factors regulating the expression of specific subsets of genes in restricted CNS regions. Among these transcription factors, homeobox-containing proteins play a crucial role, and altered expression of these factors can impact the embryonic as well as adult CNS functions. Importantly, the homeobox-containing genes Otx2, Engrailed-1 (En1), and Engrailed-2 (En2) have been described to crucially regulate differentiation of dopaminergic and serotonergic neurons during vertebrate CNS development. Dopaminergic and serotonergic neurons, located in midbrain and hindbrain regions respectively, diffusely innervate several forebrain areas including limbic system, contributing in regulating several physiological functions. Understanding the embryonic development of these neuronal populations is crucial to elucidate their physiological function including brain excitability in the adult brain. New evidence is emerging about the impact of an altered embryonic development of dopamine and serotonin neurons onto seizure susceptibility in the adult life.

Methods: In this mini-review, we summarized our kainic acid (KA) induced seizure susceptibility in adult mutant mouse lines with targeted manipulation of Otx2, En1, and En2 genes.

Results: Our results demonstrated that altered development of dopamine (DA) neurons does not interfere with KA seizure susceptibility, while increased serotonin (5-hydroxytryptamine, 5-HT) hyperinnervation leads to resistance to KA-induced seizure.

Conclusion: We propose that developmental alterations of serotonergic but not dopaminergic circuits play a crucial role in controlling seizure susceptibility in the adult life

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.

Fluoxetine suppresses synaptically induced [Ca²⁺]i spikes and excitotoxicity in cultured rat hippocampal neurons

Fluoxetine is a widely used antidepressant with an action that is primarily attributed to the inhibition of serotonin re-uptake into the synaptic terminals of the central nervous system. Fluoxetine also has blocking effects on various ion channels, including Ca(2+) channels. It remains unclear, however, how fluoxetine may affect synaptically induced [Ca(2+)](i) spikes. We investigated the effects of fluoxetine on [Ca(2+)](i) spikes, along with the subsequent neurotoxicity that is synaptically evoked by lowering extracellular Mg(2+) in cultured rat hippocampal neurons. Fluoxetine inhibited the synaptically induced [Ca(2+)](i) spikes in p-chloroamphetamine-treated and non-treated neurons, in a concentration-dependent manner. However, other selective serotonin reuptake inhibitors, such as paroxetine and citalopram, did not significantly affect the spikes. Pretreatment with fluoxetine for 5 min inhibited [Ca(2+)](i) increases induced by glutamate, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, and N-methyl-d-aspartate. Fluoxetine also inhibited α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-induced currents. In addition, fluoxetine decreased the [Ca(2+)](i) responses induced by the metabotrophic glutamate receptor agonist (S)-3,5-dihydroxyphenylglycine or the ryanodine receptor agonist caffeine. Fluoxetine inhibited [Ca(2+)](i) responses induced by 20mM KCl. Fluoxetine decreased the release of FM1-43 induced by electric field stimulation. Furthermore, fluoxetine inhibited 0.1mM [Mg(2+)](o)-induced cell death. Collectively, our results suggest that fluoxetine suppresses the spikes and protects neurons against excitotoxicity, particularly in cultured rat hippocampal neurons, presumably due to both direct inhibition of presynaptic glutamate release and postsynaptic glutamate receptor-mediated [Ca(2+)](i) signaling. In addition to an indirect inhibitory effect via 5-HT levels, these data suggest a new, possibly direct inhibitory action of fluoxetine on synaptically induced [Ca(2+)](i) spikes and neuronal cell death.

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.

Preclinical activity profile of α-lactoalbumin, a whey protein rich in tryptophan, in rodent models of seizures and epilepsy

PURPOSE

To evaluate the potential anticonvulsant activity of α-lactalbumin (ALAC), a whey protein rich in tryptophan (TRP) relative to other large neutral amino acids (LNAAs), in rodent models of seizures and epilepsy.

METHODS

The effects of ALAC administered per os were evaluated by standard protocols against audiogenic seizures in Genetic Epilepsy Prone Rats (GEPR-9 rats), maximal electroshock (MES)-induced seizures in rats, pilocarpine-induced seizures in mice, spontaneous chronic seizures in mice exposed to pilocarpine-induced status epilepticus (SE), and absence seizures in WAG/Rij rats. In some models, carbamazepine (CBZ) was included as an active control. Plasma TRP/LNAAs ratios were measured by GC-MS.

RESULTS

Single doses of ALAC up to 500 or 6000 mg/kg were devoid of anticonvulsant activity in all models tested. Conversely, 5- and 12-day treatment with ALAC (250-1000 mg/kg/day) in GEPR rats reduced dose-dependently seizure scores and prolonged latency to clonus onset, with full persistence of the effect for up to 12h. ALAC (125-500 mg/kg/day for 15 days) protected against seizures induced by 250 mg/kg pilocarpine, but was less effective against higher pilocarpine doses. Similarly to CBZ, ALAC (125-500 mg/kg/day for 15 days) was also effective against spontaneous seizures in the post-pilocarpine SE model. ALAC (up to 6000 mg/kg/day for 12 days) did not prevent MES-induced seizures, although it reduced the duration of tonic extension at doses between 250 and 1000 mg/kg/day. Absence seizures in WAG/Rij rats were not significantly affected by ALAC. Plasma TRP/LNAAS ratios increased 2- to 3-fold after dosing with ALAC (250 mg/kg/day) for 7 and 14 days, respectively.

CONCLUSIONS

ALAC exerts significant protective activity against seizures in animal models, the effect being especially prominent against audiogenic seizures in GEPR-9 rats, seizures induced by low-dose pilocarpine in mice, and spontaneous seizures in mice exposed to pilocarpine-induced SE. This action is likely to be mediated by increased availability of TRP in the brain, with a consequent increase in 5-HT mediated transmission.

The serotonin axis: Shared mechanisms in seizures, depression, and SUDEP

There is a growing appreciation that patients with seizures are also affected by a number of comorbid conditions, including an increase in prevalence of depression (Kanner, 2009), sleep apnea (Chihorek et al., 2007), and sudden death (Ryvlin et al., 2006; Tomson et al., 2008). The mechanisms responsible for these associations are unclear. Herein we discuss the possibility that underlying pathology in the serotonin (5-HT) system of patients with epilepsy lowers the threshold for seizures, while also increasing the risk of depression and sudden death. We propose that postictal dysfunction of 5-HT neurons causes depression of breathing and arousal in some epilepsy patients, and this can lead to sudden unexpected death in epilepsy (SUDEP). We further draw parallels between SUDEP and sudden infant death syndrome (SIDS), which may share pathophysiologic mechanisms, and which have both been linked to defects in the 5-HT system.

Which clinical and experimental data link temporal lobe epilepsy with depression?

The association of temporal lobe epilepsy with depression and other neuropsychiatric disorders has been known since the early beginnings of neurology and psychiatry. However, only recently have in vivo and ex vivo techniques such as Positron Emission Tomography, Magnetic Resonance Imaging and Magnetic Resonance Spectroscopy in combination with refined animal models and behavioral tests made it possible to identify an emerging pattern of common pathophysiological mechanisms. We now have growing evidence that in both disorders altered interaction of serotonergic and noradrenergic neurons with glutamatergic systems is associated with abnormal neuronal circuits and hyperexcitability. Neuronal hyperexcitability can possibly evoke seizure activity as well as disturbed emotions. Moreover, decreased synaptic levels of neurotransmitters and high glucocorticoid levels influence intracellular signaling pathways such as cAMP, causing disturbances of brain-derived and other neurotrophic factors. These may be associated with hippocampal atrophy seen on Magnetic Resonance Imaging and memory impairment as well as altered fear processing and transient hypertrophy of the amygdala. Positron Emission Tomography studies additionally suggest hypometabolism of glucose in temporal and frontal lobes. Last, but not least, in temporal lobe epilepsy and depression astrocytes play a role that reaches far beyond their involvement in hippocampal sclerosis and ultimately, therapeutic regulation of glial-neuronal interactions may be a target for future research. All these mechanisms are strongly intertwined and probably bidirectional such that the structural and functional alterations from one disease increase the risk for developing the other. This review provides an integrative update of the most relevant experimental and clinical data on temporal lobe epilepsy and its association with depression.

Localization of the serotonergic terminal fields modulating seizures in the genetically epilepsy-prone rat

Serotonin (5-HT) has been shown to exert antiepileptic effects in a variety of generalized convulsive seizure models, particularly the genetically epilepsy-prone rat (GEPR). The present study was designed to identify the region/site(s) where 5-HT exerts anticonvulsant effects in the GEPR-9, a model in which sound-evoked generalized tonic-clonic seizures (GTCS) are highly sensitive to manipulations in 5-HT concentration. Because the 5-HT reuptake inhibitor, fluoxetine, was known to exert anticonvulsant effects in GEPR-9s via a 5-HT-dependent mechanism, we utilized selective regional 5-HT depletion in combination with systemic fluoxetine administration to find the site where a 5-HT deficit would prevent the anticonvulsant action of fluoxetine. Widespread destruction of serotonergic terminal fields or regionally specific terminal field destruction was achieved using intracerebroventricular and more target specific infusions of 5,7-dihydroxytryptamine. The capacity of fluoxetine to suppress seizures in GEPR-9s following a loss of 5-HT was then examined. The present findings show the anticonvulsant action of fluoxetine is markedly attenuated following the loss of midbrain 5-HT, particularly in the region of the superior colliculus, while forebrain and spinal cord 5-HT do not appear to play a role in the action of fluoxetine. The importance of the deep layers of the SC was confirmed by demonstrating that direct microinfusion of fluoxetine into the SC can suppress seizures in rats pretreated with the 5-HT(1A) receptor antagonist pindolol.

Serotonin and epilepsy

In recent years, there has been increasing evidence that serotonergic neurotransmission modulates a wide variety of experimentally induced seizures. Generally, agents that elevate extracellular serotonin (5-HT) levels, such as 5-hydroxytryptophan and serotonin reuptake blockers, inhibit both focal and generalized seizures, although exceptions have been described, too. Conversely, depletion of brain 5-HT lowers the threshold to audiogenically, chemically and electrically evoked convulsions. Furthermore, it has been shown that several anti-epileptic drugs increase endogenous extracellular 5-HT concentration. 5-HT receptors are expressed in almost all networks involved in epilepsies. Currently, the role of at least 5-HT(1A), 5-HT(2C), 5-HT(3) and 5-HT(7) receptor subtypes in epileptogenesis and/or propagation has been described. Mutant mice lacking 5-HT(1A) or 5-HT(2C) receptors show increased seizure activity and/or lower threshold. In general, hyperpolarization of glutamatergic neurons by 5-HT(1A) receptors and depolarization of GABAergic neurons by 5-HT(2C) receptors as well as antagonists of 5-HT(3) and 5-HT(7) receptors decrease the excitability in most, but not all, networks involved in epilepsies. Imaging data and analysis of resected tissue of epileptic patients, and studies in animal models all provide evidence that endogenous 5-HT, the activity of its receptors, and pharmaceuticals with serotonin agonist and/or antagonist properties play a significant role in the pathogenesis of epilepsies.

The serotonergic and noradrenergic effects of antidepressant drugs are anticonvulsant, not proconvulsant

Contrary to existing evidence, convulsant liability of the antidepressants has been attributed to noradrenergic and serotonergic increments. This is a classic case of confusing treatment effects with the manifestations of illness. In fact, the remarkable anticonvulsant effectiveness of antidepressant-induced noradrenergic and serotonergic activation has been ignored. Some antidepressant drugs such as the specific serotonin reuptake inhibitor (SSRI) fluoxetine may be devoid of convulsant liability entirely, while having distinct anticonvulsant properties. Some authorities advance the notion that the seizure predisposition of patients with epilepsy increases risks for antidepressant-induced seizures. However, evidence does not support this contention. Instead, data increasingly support the concept that noradrenergic and serotonergic deficiencies contribute to seizure predisposition. Indeed, the antidepressants have the potential to overcome seizure predisposition in epilepsy. Whereas therapeutic doses of antidepressants elevate noradrenergic and serotonergic transmission, larger doses can activate other biological processes that may be convulsant.

Essentiality of central GABAergic neuroactive steroid allopregnanolone for anticonvulsant action of fluoxetine against pentylenetetrazole-induced seizures in mice

Fluoxetine, a selective serotonin reuptake inhibitor, is known to increase the cortical content of allopregnanolone (ALLO) without altering the level of other neurosteroids. In contrast to the proconvulsant effect of many antidepressants, fluoxetine exhibits anticonvulsant effects. The present study was undertaken to examine the role of ALLO in the anticonvulsant action of fluoxetine against pentylenetetrazole (PTZ)-induced seizures in mice. Prior administration of GABA(A) receptor agonist muscimol or neurosteroid ALLO or progesterone, a precursor of ALLO or neurosteroidogenic drugs like FGIN 1-27, an agonist at the mitochondrial diazepam binding inhibitor receptor (MDR) or metyrapone, an 11beta-hydroxylase inhibitor, significantly potentiated the anticonvulsant effect of fluoxetine. In contrast, the effect of fluoxetine was counteracted by inhibition of the neurosteroid biosynthesis using drugs like 5alpha-reductase inhibitor, finasteride; 3beta-hydroxysteroid dehydrogenase inhibitor, trilostane; 3alpha-hydroxysteroid dehydrogenase inhibitor, indomethacin; MDR antagonist, PK 11195; or the GABA(A) receptor antagonist, bicuculline. Further, bilateral adrenalectomy had no significant effect on the anticonvulsant action of fluoxetine, suggesting negligible contribution from peripheral steroidogenesis. The anticonvulsant effect of fluoxetine was partially abolished in 5,7-DHT treated mice, indicating that the effect may also, in part, be dependent on serotonergic transmission. Thus, our data indicate that increased synthesis of ALLO in CNS is a major factor that ultimately leads to anticonvulsant effects of fluoxetine against PTZ-induced seizures.

5-HT has contrasting effects in the frontal cortex, but not the hypothalamus, on changes in noradrenaline efflux induced by the monoamine releasing-agent, d-amphetamine, and the reuptake inhibitor, BTS 54 354

There is extensive evidence for functional interactions between central noradrenergic and serotonergic neurones. Here, dual-probe microdialysis was used in freely-moving rats to compare the effects of 5-HT on noradrenergic transmission in the rat frontal cortex and hypothalamus. We studied the effects of the 5-HT synthesis inhibitor, para-chlorophenylalanine (pCPA; which depleted 5-HT stores in both the frontal cortex and the hypothalamus), on spontaneous efflux of noradrenaline and on the noradrenergic responses to d-amphetamine, and the monoamine reuptake inhibitor, BTS 54 354. pCPA pretreatment alone did not affect spontaneous noradrenaline efflux in either brain region, whether or not alpha2-autoreceptors were inactivated by administration of the alpha2-antagonist, atipamezole (1 mg/kg i.p). However, in the frontal cortex, pCPA pretreatment augmented the amplitude of, and prolonged, the noradrenergic response to local infusion of d-amphetamine (10 microM). In contrast, pCPA abolished the increase in cortical noradrenaline efflux induced by local infusion of BTS 54 354 (50 microM). In the hypothalamus, pCPA did not affect the amplitude of the response to either of these agents but did prolong the effects of d-amphetamine on noradrenaline efflux. These findings suggest that serotonergic transmission has complex effects on the noradrenergic response to drugs that increase noradrenergic transmission in the frontal cortex, but has less influence in the hypothalamus.

Shared mechanisms of antidepressant and antiepileptic treatments: drugs and devices

Many treatments for the epilepsies and affective disorder share the properties of seizure suppression and mood stabilization. Moreover, affective disorders and the epilepsies appear to share partially similar pathogenic mechanisms. A component of the shared predisposition appears to arise from noradrenergic and serotonergic deficits. Increasing evidence supports the hypothesis that noradrenergic and/or serotonergic elevation is a mechanism of therapeutic benefit shared by most antidepressants and many antiepileptic medications. Medication induced alterations in GABAergic, glutamatergic, and CRH (corticotropin releasing hormone) containing neurons may also contribute to the shared therapeutic properties of antidepressant and antiepileptic medications.

Affective disorder and epilepsy comorbidity: implications for development of treatments, preventions and diagnostic approaches

Concepts pertaining to affective disorder and epilepsy comorbidity are contributing appreciably to improvements in patient care. Several antiepileptic treatments have become important components of the management of bipolar affective disorder. In contrast, little progress has emerged in developing clinical applications of the anticonvulsant properties of the antidepressants in the treatment of the epilepsies. The slow onset of action of the antidepressants remains a major impediment to fully effective treatment of depressive episodes. Nevertheless, studies from experimental epileptology demonstrate that the anticonvulsant effects of the antidepressants occur rapidly and as a consequence of noradrenergic and/or serotonergic activation. These studies also demonstrate that adequate initial doses of the antidepressants are essential to rapid onset of anticonvulsant action. Pharmacokinetically valid loading dose paradigms are seemingly avoided with antidepressant drugs in humans because of potential toxicities and/or patient unacceptability. However, substantial progress has been made in reducing the adverse effect liability of the antidepressants. No longer is convulsive liability considered to stem from the therapeutic mechanisms of the anti-depressants. Rather, noradrenergic and serotonergic influences have demonstrable anticonvulsant properties. Other side effects may also be separable from the anticonvulsant and antidepressive effects of antidepressive treatments. The concept that the protracted process of antidepressant-induced beta-noradrenergic down-regulation is an essential prelude to the onset of mood benefit is no longer a sustainable premise. Nevertheless, increasing evidence underlies the possibility that knowledge of serotonergic and noradrenergic regulatory processes can be used to design strategies that will hasten the onset of antidepressive action. Similar optimism pervades efforts to determine the possibility that dual inhibition of serotonin and norepinephrine transporters will hasten onset of antidepressive action. Moreover, because noradrenergic and serotonergic systems are determinants of predisposition to seizures and to dysfunctional affective episodes, augmentation strategies may also be applicable to the use of antidepressant drugs in epilepsy and to the use of antiepileptic drugs such as carbamazepine in mood disorders. Recent studies have demonstrated that, in part, the therapeutic effectiveness of carbamazepine may stem from its marked capacity to elevate serotonin concentrations in the extracellular fluid of the brain via mechanisms that differ from those of the membrane reuptake inhibitors. Evidence suggests that the epilepsies and affective disorders may arise from a multiplicity of neurobiological abnormalities. A disorder in one individual may arise via different mechanisms than a phenomenologically similar disorder in another individual. Thus, diagnostic tools are needed to make mechanistic distinctions among individuals so that treatments can be appropriately developed and selected. In terms of epileptogenesis and affective disorder progression, neuroprotective paradigms for one individual may differ from those needed for another. Moreover, diagnostic technologies that are adequate to detect genetically and/or experientially determined vulnerability before the onset of a seizure or dysfunctional affective episode may be valuable steps toward achieving goals of prevention.

5-HT2C receptors inhibit and 5-HT1A receptors activate the generation of spike–wave discharges in a genetic rat model of absence epilepsy

The present study was conducted to investigate the role of 5-HT(2C) and 5-HT(1A) receptors in the generation of spike-wave discharges (SWD) in the genetic absence epilepsy model Wistar Albino Glaxo rats from Rijswijk, Netherlands (WAG/Rij rats). We have determined the effects of the 5-HT(2C) receptor preferring agonist m-chlorophenyl-piperazine (m-CPP), the selective 5-HT(2C) receptor antagonist SB-242084, the selective 5-HT(1A) receptor antagonist WAY-100635, two selective serotonin re-uptake inhibitors (SSRI, fluoxetine and citalopram) and their combinations in this model. The 5-HT(2C) agonist m-CPP caused marked, dose-dependent decreases in the cumulative duration and number of SWD administered either intraperitoneally (0.9 and 2.5 mg/kg) or intracerebroventricularly (0.05 and 0.1 mg/kg). Treatment with SB-242084 (0.2 mg/kg, ip) alone failed to cause any significant change in SWD compared to vehicle. Pretreatment with SB-242084 (0.2 mg/kg, ip) eliminated the effects of m-CPP on SWD. Fluoxetine (5.0 mg/kg, ip) alone caused moderate increase in SWD. After pretreatment with SB-242084, the effect of fluoxetine was significantly enhanced. The combination of SB-242084 and citalopram (2.5 mg/kg, ip) caused a similar effect, namely an increase in SWD. In contrast, pretreatment with WAY-100635 significantly attenuated the effect of fluoxetine. In conclusion, these results indicate that the increase in endogenous 5-HT produces a dual effect on SWD; the inhibition of epileptiform activity is mediated by 5-HT(2C), the activation by 5-HT(1A) receptors.

Common pathogenic mechanisms between depression and epilepsy: an experimental perspective

Affective disorders and the epilepsies appear to share partially similar pathogenic mechanisms. Predisposition to both disorders is determined genetically and experientially. A component of the shared predisposition appears to arise from noradrenergic and serotonergic deficits. Shared GABAergic deficits coupled with CRHergic and glutamatergic excesses may trigger and maintain seizures as well as dysfunctional affective episodes, albeit via dissimilar neuronal interplay.

Effects of fluoxetine and TFMPP on spontaneous seizures in rats with pilocarpine-induced epilepsy

PURPOSE

Fluoxetine is a selective serotonin [5-hydroxytryptamine (5-HT)] reuptake inhibitor (SSRI) commonly used to treat depression. Some uncontrolled clinical studies have reported that SSRIs increase seizures, but animal experiments with evoked-seizure models have suggested that SSRIs at therapeutic doses decrease seizure susceptibility. We tested the hypothesis that fluoxetine and trifluoromethylphenylpiperazine (TFMPP, a nonselective 5-HT-receptor agonist) reduce the frequency of spontaneous motor seizures in pilocarpine-treated rats.

METHODS

Fluoxetine (20 mg/kg) and TFMPP (5 mg/kg) were administered to rats with pilocarpine-induced epilepsy. Phenobarbital (PB; 10 mg/kg) was a positive control, and saline (i.e., 0.5 ml) controlled for the injection protocol. Each rat received each treatment (intraperitoneally) once per day for 5 consecutive days with 1 week between treatments. Rats were continuously video-monitored for the last 72 h of each treatment.

RESULTS

When compared with saline over the entire 72-h observation period, PB and fluoxetine treatment, but not TFMPP, reduced the spontaneous-seizure rate. Plots of magnitude of the drug effect as a function of seizure frequency after saline treatment revealed larger drug effects for fluoxetine and PB in the rats with the highest control seizure rate. When the data from the five rats with the highest seizure frequency in saline were analyzed for the first 6 h after treatment, TFMPP also significantly reduced seizure frequency.

CONCLUSIONS

Animal models with spontaneous seizures can be used to screen potential antiepileptic drugs, and fluoxetine and TFMPP reduce spontaneous seizures in the pilocarpine model of temporal lobe epilepsy.

Neuronal hypersynchronization, creativity and endogenous psychoses

I have investigated a neuronal hypersynchronism, currently included under the general subject of epilepsy, and termed interictal activity. I suggest that it is a physiological activity of the mammalian brain and propose it be termed Hyperia. After a thorough study of the extraordinary psychic manifestations of this neuronal hypersynchronism shown by mystics and artists, I have reviewed several scientific publications bearing on my hypothesis. I conclude by elaborating on a variety of cerebral hypersynchronous functions whose cause I consider to be physiological. Such behaviour is a common basis for extraordinary psychic manifestations found not only in mystics and artists, but also in patients suffering from endogenous psychoses, especially Bipolar Disorder.

Anticonvulsant properties of N-salicyloyltryptamine in mice

A new tryptamine analogue, N-salicyloyltryptamine (STP), a potential central nervous system (CNS) depressant, was tested in the pentylenetetrazol (PTZ) and maximal electroshock (MES) models of epilepsy in mice. When administered concurrently, STP (100 mg/kg ip) significantly reduced the number of animals that exhibited PTZ-induced seizures and eliminated the extensor reflex of maximal electric-induced seizures test in 50% of the experimental animals. In addition, it showed protection in the PTZ test by diminishing the death rate.

The effect of the acute administration of various selective 5-HT receptor antagonists on focal hippocampal seizures in freely-moving rats

In this study, we assessed the effects of the acute administration of various 5-HT receptor antagonists on hippocampal partial seizures generated by low-frequency electrical stimulation in male Wistar rats. The seizure threshold and severity were determined by measuring the pulse number threshold and primary and secondary afterdischarges, respectively, and the latency of secondary discharge was also determined. The administration of either the selective 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazineyl]ethyl]-N-(pyridinyl)-c yclohe xanecarboximimde 3 HCl (WAY 100635, 0.1-1 mg/kg i.p.), the selective 5-HT(3) receptor antagonist granisetron (0.3-3 mg/kg i.p.), the selective 5-HT(2A) receptor antagonist R-(+)-a-(2, 3-dimethoxyphenyl)-1-[2-(4-fluorophenyl) ethyl]-4-piperidine-methanol (MDL 100907, 0.3-3 mg/kg i.p.) or the 5-HT(2B,C) receptor antagonist antagonist N-(1-methyl-5-indolyl)-N'-(3-pyridyl) urea HCl (SKB 200646A, 5-50 mg/kg i.p.) did not alter the pulse number threshold compared to vehicle-treated animals. However, the acute administration of WAY 100635 (0.3 mg/kg) and M100907 (1 mg/kg) significantly increased, whereas granisetron (1 mg/kg) decreased, the primary afterdischarge duration compared to vehicle-treated animals. The latency of secondary after discharge was significantly decreased by WAY 100635 (1 mg/kg) and granisetron (3 mg/kg) compared to vehicle-treated animals. These results suggest that in this model, the antagonism of 5-HT(1A), 5-HT(2A), 5-HT(3) or 5-HT(2B,C) receptors do not lower or raise seizure threshold. However, the antagonism of 5-HT(1A) receptors may increase or augment seizure severity.

Studies on the role of 5-HT2C and 5-HT2B receptors in regulating generalised seizure threshold in rodents

The present studies were conducted to investigate the role of 5-HT2C and 5-HT2B receptors in the generation of pentylenetetrazol and electroshock-evoked seizures. The 5-HT2C/2B receptor-preferring agonist 1-(m-chlorophenyl)-piperazine (mCPP; 2.5-7 mg/kg i.p.) weakly elevated seizure threshold in the mouse (but not the rat) electroshock test and also provided appreciable protection against pentylenetetrazol-induced myoclonic and/or tonic seizures in mice and rats, an action that was inhibited by the 5-HT2C/2B receptor antagonist 5-methyl-1-(3-pyridylcarbomoyl)-1,2,3,5-tetrahydropyrrolo[2, 3-f]indole (SB-206553; 10-20 mg/kg p.o.). In contrast, the 5-HT2B receptor agonist 1-[5-(2-thienylmethoxy)-1H-3-indoyl]propan-2-amine hydrochloride (BW-723C86; 3-30 mg/kg s.c.) had no effect on the threshold for generalised seizures in any of the models employed. These results indicate that the observed anticonvulsant effects of mCPP are likely to be mediated by activation of 5-HT2C receptors. However, blockade of these receptors in mice (or rats) by SB-206553 (5-20 mg/kg p.o.) did not result in the reduced seizure threshold characteristic of mutant mice deficient of 5-HT2C receptors, suggesting that in normal adult animals this receptor subtype may usually be subjected to only a low level of 5-hydroxytryptamine tone.

Endogenous serotonin inhibits epileptiform activity in rat hippocampal CA1 neurons via 5-hydroxytryptamine1A receptor activation

The modulatory effects of endogenous serotonin on the synaptic transmission and epileptiform activity were studied in the rat hippocampus with the use of extracellular and intracellular recording techniques. Field excitatory postsynaptic potential was reversibly depressed by serotonin in a concentration-dependent manner. Intracellular recordings revealed that serotonin-mediated synaptic depression was unaffected by extracellular Ba2+ or intracellular application of Cs+ while the postsynaptic hyperpolarizing effect was completely blocked. Epileptiform activity induced by picrotoxin (50 microM), a GABA(A) receptor antagonist, was also dose-dependently suppressed by serotonin. The antiepileptic effect was mimicked by 5-hydroxytryptamine1A agonist and was blocked by 5-hydroxytryptamine1A antagonists. 5-Hydroxytryptamine2 antagonist had no effect on the modulation. Similarly, fluoxetine, a selective serotonin re-uptake blocker, potently inhibited the epileptiform activity and this effect was blocked by 5-hydroxytryptamine1A receptor antagonist. Depletion of endogenous serotonin by pretreating the slices with p-chloroamphetamine completely prevented the antiepileptic action of fluoxetine, without modifying the action of serotonin in the same cells. These results suggest that the antiepileptic action of fluoxetine is due to an enhancement of endogenous serotonin which in turn is mediated by 5-hydroxytryptamine1A receptor. Endogenous serotonin transmission in the hippocampus is therefore capable of limiting the development and propagation of seizure activity.

Effect of acute administration of various 5-HT receptor agonists on focal hippocampal seizures in freely moving rats

In this study, we assessed the effects of the acute administration of various 5-HT receptor agonists on hippocampal partial seizures generated by low-frequency electrical stimulation in male Wistar rats. The seizure threshold and severity were determined by measuring the pulse number threshold and primary and secondary afterdischarges and the latency of secondary discharge was also determined. The administration (0.1-1 mg/kg, i.p.) of either the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-aminopropyl)tetralin (8-OH-DPAT), or the selective 5-HT3 receptor agonist, 4-amino-(6-chloro-2-pyridyl)-1-piperidine (SR 57227A, 0.3-3 mg/kg, i.p.), did not alter any of the seizure parameters compared to those in vehicle-treated animals. Similarly, the administration of 0.3 and 1 mg/kg, i.p., of the 5-HT2A,C receptor agonist, (+/-)-2,5-dimethoxy-4-iodophenyl-2-aminopropane (DOI), did not alter any of the seizure parameters, whereas 3 mg/kg significantly decreased the latency of the secondary afterdischarge compared to that in vehicle-treated animals. The selective serotonin reuptake inhibitor, (+/-)-fluoxetine (2 mg/kg, i.p.), significantly increased the pulse number threshold and decreased the primary afterdischarge duration compared to those in vehicle-treated animals. In contrast, higher doses (6 or 20 mg/kg, i.p.) of fluoxetine did not significantly alter any of the seizure parameters measured. These results suggest that, in this model, stimulation of 5-HT1A, 5-HT2A,C and 5-HT3 receptors does not alter seizure threshold or severity and that the blockade of 5-HT uptake produced by a low dose of fluoxetine appears to increase seizure threshold and decrease seizure severity.

Serotonin inhibits epileptiform discharge by activation of 5-HT1A receptors in CA1 pyramidal neurons

The anti-epileptiform effect of serotonin was characterized in cellular models of epilepsy using electrophysiological recording techniques. In the bicuculline model, both serotonin (20 microM) and its 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 10 microM) completely blocked the epileptiform discharge and caused membrane hyperpolarization and reduction in input resistance. These effects were completely antagonized by the 5-HT1A receptor antagonist N-t-butyl-3(4-[2-methoxyphenyl]piperazin-1-yl)-2-phenyl-propanamid e(WAY 100135) (10 microM). Epileptiform discharge induced by positive current injection was also blocked by serotonin. The presence of WAY 100135 renders serotonin ineffective in the same model. In the bicuculline model, epileptiform discharge blocked by serotonin reappeared and was also intensified when BaCl2 was added to the medium. To rule out the possibility of serotonin-induced hyperpolarization strengthening the inhibitory effect of endogenous Mg2+ on glutamate N-methyl-D-aspartic acid (NMDA) receptor we studied the antiepileptic effect of serotonin in the 0 Mg2+ model. Spontaneous activity and evoked bursts seen with the 0 Mg2+ model were completely blocked by serotonin. WAY 100135 completely antagonized serotonin effects in this model as well. This study provides evidence suggesting that in rat CA1 pyramidal neurons, serotonin can inhibit epileptiform activity in a variety of accepted epilepsy cellular models and that inhibition of epileptiform bursts by serotonin may be mediated by activation of the 5-HT1A receptor subtype.

Enhancement of the anticonvulsant effect of fluoxetine following blockade of 5-HT1A receptors

Serotonin reuptake inhibitors, such as fluoxetine, have been shown to exert anticonvulsant effects in several animal models of epilepsy. In view of recent studies showing that 5-HT1A receptor antagonists (somatodendritic autoreceptor antagonists) enhance the increase in extracellular 5-hydroxytryptamine (5-HT, serotonin) produced by serotonin reuptake inhibitors, it was of interest to determine if these antagonists also enhance the anticonvulsant effect of fluoxetine in Genetically Epilepsy-Prone Rats (GEPRs). The 5-HT1A receptor antagonists (-)-pindolol and LY 206130 (1-[1-H-indol-4-yloxy]-3-[cyclohexylamino]-2-propanol maleate) were examined in the present study and both enhanced the anticonvulsant action of fluoxetine in severe seizure GEPRs (GEPR-9s). The latter effect of LY 206130 was found to be dose- and 5-HT-dependent. These findings provide further evidence that the increase in extracellular serotonin observed after administering fluoxetine in combination with a 5-HT1A receptor antagonist is physiologically important and that the anticonvulsant effect of fluoxetine in the GEPR is mediated through an increase in extracellular 5-HT.

Effects of serotonin on induced epileptiform activity in CA1 pyramidal neurons of genetically epilepsy prone rats

The seizure susceptibility in genetically epilepsy prone rats (GEPRs) is reported to be caused by abnormalities in several neurotransmitter systems including the serotonergic system. Among the reported abnormalities is a decrease in brain serotonin content. Therefore, we examined the effects of exogenous serotonin on brain slices from the severe seizure strain of GEPRs (GEPR-9s). We employed conventional electrophysiological techniques to record from CA1 pyramidal neurons of hippocampi of GEPR-9s. The membrane resting potential and input resistance of the GEPR-9 CA1 pyramidal neurons were not different from those of the Sprague-Dawley rats. Serotonin (20 microM) inhibited the directly and synaptically evoked action potentials in GEPR-9 CA1 neurons, as it did in the Sprague Dawley neurons, but only in some and not all of the neurons tested (blocked the directly evoked potentials in 57% and synaptically evoked potentials in 33.3% of the total neurons). This inhibition was also accompanied by hyperpolarization and reduction of membrane input resistance. In the bicuculline-treated brain slices of the GEPR-9, serotonin inhibited the epileptiform bursts causing concurrent hyperpolarization and reduction in membrane input resistance. The effects of the selective serotonin 5-HT1A receptor agonist, 8-OH-DPAT (20 microM) on GEPR-9 pyramidal CA1 neurons were similar to those of serotonin, except the magnitude of hyperpolarization and reduction of membrane input resistance were less than those produced by serotonin. We conclude that the apparent decrease in sensitivity of the GEPR-9 CA1 pyramidal neurons to serotonin may represent a deficiency of serotonin 5-HT1A receptor.

Antidepressants and seizures: clinical anecdotes overshadow neuroscience

Pharmacological treatment of depression in persons with epilepsy has been an area of controversy because some drugs commonly are perceived specifically to induce or exacerbate seizures in patients with seizure disorders. This prevailing misconception is unjustified by scientific studies, yet it continues to prevent afflicted persons from receiving appropriate therapy. The scientific literature shows that tricyclic antidepressant drugs cause seizures in overdose in both animals and humans. In lower doses, these drugs have anticonvulsant activity in humans and animals. Thus, the antidepressant drugs are like several antiepileptic drugs that can both prevent and cause seizures. The anticonvulsant activity of antidepressant drugs has been studied extensively in animals and almost certainly stems from their capacity to block norepinephrine and/or serotonin reuptake. The pharmacodynamic action responsible for their convulsant effects has not been well studied but may be due to their local anesthetic, antihistaminic, or antimuscarinic activity. The newer, more selective monoamine uptake blockers have very low convulsant liability, and it is suggested that their anticonvulsant activity, which is well documented in animals, be investigated further in humans. If their effects in humans are analogous to those in animals, these drugs can be used safely in epileptic patients with depression, and it is possible that their anticonvulsant activity can be exploited for use in the treatment of epilepsy.