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

PET imaging identifies anti-inflammatory effects of fluoxetine and a correlation of glucose metabolism during epileptogenesis with chronic seizure frequency

The serotonergic system has shown to be altered during epileptogenesis and in chronic epilepsy, making selective serotonin reuptake inhibitors interesting candidates for antiepileptogenic therapy. In this study, we aimed to evaluate disease-modifying effects of fluoxetine during experimental epileptogenesis. Status epilepticus (SE) was induced by lithium-pilocarpine, and female rats were treated either with vehicle or fluoxetine over 15 days. Animals were subjected to 18F-FDG (7 days post-SE), 18F-GE180 (15 days post-SE) and 18F-flumazenil positron emission tomography (PET, 21 days post-SE). Uptake (18F-FDG), volume of distribution (18F-GE180) and binding potential (18F-flumazenil) were calculated. In addition, hyperexcitability testing and video-EEG monitoring were performed. Fluoxetine treatment did not alter brain glucose metabolism. 18F-GE180 PET indicated lower neuroinflammation in the hippocampus of treated animals (-22.6%, p=0.042), but no differences were found in GABAA receptor density. Video-EEG monitoring did not reveal a treatment effect on seizure frequency. However, independently of the treatment, hippocampal FDG uptake 7 days after SE correlated with seizure frequency during the chronic phase (r=-0.58; p=0.015). Fluoxetine treatment exerted anti-inflammatory effects in rats during epileptogenesis. However, this effect did not alter disease outcome. Importantly, FDG-PET in early epileptogenesis showed biomarker potential as higher glucose metabolism correlated to lower seizure frequency in the chronic phase.

Cannabidiol Exerts Anticonvulsant Effects Alone and in Combination with Δ9-THC through the 5-HT1A Receptor in the Neocortex of Mice

Cannabinoids have shown potential in drug-resistant epilepsy treatment; however, we lack knowledge on which cannabinoid(s) to use, dosing, and their pharmacological targets. This study investigated (i) the anticonvulsant effect of Cannabidiol (CBD) alone and (ii) in combination with Delta-9 Tetrahydrocannabinol (Δ9-THC), as well as (iii) the serotonin (5-HT)1A receptor's role in CBD's mechanism of action. Seizure activity, induced by 4-aminopyridine, was measured by extracellular field recordings in cortex layer 2/3 of mouse brain slices. The anticonvulsant effect of 10, 30, and 100 µM CBD alone and combined with Δ9-THC was evaluated. To examine CBD's mechanism of action, slices were pre-treated with a 5-HT1A receptor antagonist before CBD's effect was evaluated. An amount of ≥30 µM CBD alone exerted significant anticonvulsant effects while 10 µM CBD did not. However, 10 µM CBD combined with low-dose Δ9-THC (20:3 ratio) displayed significantly greater anticonvulsant effects than either phytocannabinoid alone. Furthermore, blocking 5-HT1A receptors before CBD application significantly abolished CBD's effects. Thus, our results demonstrate the efficacy of low-dose CBD and Δ9-THC combined and that CBD exerts its effects, at least in part, through 5-HT1A receptors. These results could address drug-resistance while providing insight into CBD's mechanism of action, laying the groundwork for further testing of cannabinoids as anticonvulsants.

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.

Antidepressant Drugs for Seizures and Epilepsy: Where do we Stand?

People with epilepsy (PWE) are more likely to develop depression and both these complex chronic diseases greatly affect health-related quality of life (QOL). This comorbidity contributes to the deterioration of the QOL further than increasing the severity of epilepsy worsening prognosis. Strong scientific evidence suggests the presence of shared pathogenic mechanisms. The correct identification and management of these factors are crucial in order to improve patients' QOL. This review article discusses recent original research on the most common pathogenic mechanisms of depression in PWE and highlights the effects of antidepressant drugs (ADs) against seizures in PWE and animal models of seizures and epilepsy. Newer ADs, such as selective serotonin reuptake inhibitors (SRRI) or serotonin-noradrenaline reuptake inhibitors (SNRI), particularly sertraline, citalopram, mirtazapine, reboxetine, paroxetine, fluoxetine, escitalopram, fluvoxamine, venlafaxine, duloxetine may lead to improvements in epilepsy severity whereas the use of older tricyclic antidepressant (TCAs) can increase the occurrence of seizures. Most of the data demonstrate the acute effects of ADs in animal models of epilepsy while there is a limited number of studies about the chronic antidepressant effects in epilepsy and epileptogenesis or on clinical efficacy. Much longer treatments are needed in order to validate the effectiveness of these new alternatives in the treatment and the development of epilepsy, while further clinical studies with appropriate protocols are warranted in order to understand the real potential contribution of these drugs in the management of PWE (besides their effects on mood).

Effect of ramosetron, a 5-HT3 receptor antagonist on the severity of seizures and memory impairment in electrical amygdala kindled rats

The entorhinal cortex (EC) plays a pivotal role in epileptogenesis and seizures. EC expresses high density of serotonergic receptors, especially 5-HT3 receptors. Cognitive impairment is common among people with epilepsy. The present study investigated the role of 5-HT3 receptor on the severity of seizures and learning and memory impairment by electrical kindling of amygdala in rats. The amygdala kindling was conducted in a chronic kindling manner in male Wistar rats. In fully kindled animals, ramosetron (as a potent and selective 5-HT3 receptor antagonist) was microinjected unilaterally (ad doses of 1, 10 or 100 µg/0.5 µl) into the EC 5 min before the novel object recognition (NOR) and Y-maze tests or kindling stimulations. Applying ramosetron at the concentration of 100 μg/0.5 µl (but not at 1 and 10 µg/0.5 µl) reduced afterdischarge (AD) duration and increased stage 4 latency in the kindled rats. Moreover, the obtained data from the NOR test showed that treatment by ramosetron (10 and 100 µg/0.5 µl) increased the discrimination index in the fully kindled animals. Microinjection of ramosetron (10 and 100 µg/0.5 µl) in fully kindled animals reversed the kindling induced changes in the percentage of spontaneous alternation in Y-maze task. The findings demonstrated an anticonvulsant role for a selective 5-HT3 receptor antagonist microinjected into the EC, therefore, suggesting an excitatory role for the EC 5-HT3 receptors in the amygdala kindling model of epilepsy. This anticonvulsive effect was accompanied with a restoring effect on cognitive behavior in NOR and Y-maze tests.

Endogenous and exogenous serotonin, but not sumatriptan, ameliorate seizures and neuroinflammation in the pentylenetetrazole-induced seizure model in rats

ABSTRACT Background: Epilepsy has neuropsychiatric comorbidities such as depression, bipolar disorder, and anxiety. Drugs that target epilepsy may also be useful for its neuropsychiatric comorbidities. Objective: To investigate the effects of serotonergic modulation on pro-inflammatory cytokines and the seizures in pentylenetetrazole (PTZ)-induced seizure model in rats. Methods: Male Wistar rats were injected intraperitoneally with serotonin, selective serotonin reuptake inhibitor fluoxetine, 5-HT1B/D receptor agonist sumatriptan, or saline 30 min prior to PTZ treatment. Behavioral seizures were assessed by the Racine's scale. Concentrations of IL-1β, IL-6, and TNF-α in serum and brain tissue were determined by ELISA. Results: Serotonin and fluoxetine, but not sumatriptan, alleviated PTZ-induced seizures by prolonging onset times of myoclonic-jerk and generalized tonic-clonic seizures. The anti-seizure effect of fluoxetine was greater than that of serotonin. Likewise, serotonin and fluoxetine, but not sumatriptan, reduced PTZ-induced increases in the levels of IL-1β and IL-6 in both serum and brain tissue. None of the administered drugs including PTZ affected TNF-α concentrations. Conclusions: Our findings suggest that endogenous and exogenous serotonin exhibits anticonvulsant effects by suppressing the neuroinflammation. It seems that 5-HT1B/D receptors do not mediate anticonvulsant and anti-neuroinflammatory effects of serotonin.

Sudden unexpected death in epilepsy: Respiratory mechanisms

Epilepsy is one of the most common chronic neurologic diseases, with a prevalence of 1% in the US population. Many people with epilepsy live normal lives, but are at risk of sudden unexpected death in epilepsy (SUDEP). This mysterious comorbidity of epilepsy causes premature death in 17%-50% of those with epilepsy. Most SUDEP occurs after a generalized seizure, and patients are typically found in bed in the prone position. Until recently, it was thought that SUDEP was due to cardiovascular failure, but patients who died while being monitored in hospital epilepsy units revealed that most SUDEP is due to postictal central apnea. Some cases may occur when seizures invade the amygdala and activate projections to the brainstem. Evidence suggests that the pathophysiology is linked to defects in the serotonin system and central CO₂ chemoreception, and that there is considerable overlap with mechanisms thought to be involved in sudden infant death syndrome (SIDS). Future work is needed to identify biomarkers for patients at highest risk, improve ascertainment, develop methods to alert caregivers when SUDEP is imminent, and find effective approaches to prevent these fatal events.

Bidirectional Relations Among Depression, Migraine, and Epilepsy: Do They Have an Impact on Their Response to Treatment?

The evaluation and treatment of patients with epilepsy is not limited to the type of epilepsy, but it must incorporate the common comorbid neurologic, psychiatric, and medical disorders, as the latter can bare an impact on the course and response to treatment of the seizure disorder and vice versa. In this article we review the bidirectional relations among epilepsy and two of its most common comorbidities, mood disorders and migraine and examine the implications of these relations on the selection of therapies of these three disorders and their response to treatment. We also review the most salient common pathogenic mechanisms that may explain such relations.

Serotonergic therapy in epilepsy

PURPOSE OF REVIEW

The serotonergic system is implicated in multiple aspects of epilepsy, including seizure susceptibility, sudden unexpected death in epilepsy (SUDEP), and comorbid depression. Despite the complexity of serotonin's effects on various neuronal networks, ongoing research provides considerable insight into the role of serotonin in human epilepsy. This review explores the potential roles of serotonergic therapies to improve clinical outcomes in epilepsy.

RECENT FINDINGS

In recent decades, research has markedly increased our knowledge of the diverse effects of serotonin on brain function. Animal models of epilepsy have identified the influence of serotonin on seizure threshold in specific brain regions, serotoninergic augmentation's protective effects on terminal apnea and mortality in SUDEP, and mechanisms underlying behavioral improvement in some models of comorbid depression. Human clinical studies are largely consistent with animal data but the translation into definitive treatment decisions has moved less rapidly.

SUMMARY

Evidence for serotonergic therapy is promising for improvement in seizure control and prevention of SUDEP. For some epilepsies, such as Dravet syndrome, basic research on serotonin receptor agonists has translated into a positive clinical trial for fenfluramine. The cumulative results of safety and efficacy studies support the routine use of SSRIs for comorbid depression in epilepsy.

Epilepsy Associated Depression: An Update on Current Scenario, Suggested Mechanisms, and Opportunities

Depression is one of the most frequent psychiatric comorbidities associated with epilepsy having a major impact on the patient's quality of life. Several screening tools are available to identify and follow up psychiatric disorders in epilepsy. Out of various psychiatric disorders, people with epilepsy (PWE) are at greater risk of developing depression. This bidirectional relationship further hinders pharmacotherapy of comorbid depression in PWE as some antiepileptic drugs (AEDs) worsen associated depression and coadministration of existing antidepressants (ADs) to alleviate comorbid depression has been reported to worsen seizures. Selective serotonin reuptake inhibitors (SSRIs) and selective serotonin and norepinephrine reuptake inhibitors (SNRIs) are first choice of ADs and are considered safe in PWE, but there are no high-quality evidences. Similar to observations in people with depression, PWE also showed pharmacoresistant to available SSRI/SNRIs, which further complicates the disease prognosis. Randomized double-blind placebo-controlled clinical trials are necessary to report efficacy and safety of available ADs in PWE. We should also move beyond ADs, and therefore, we reviewed common pathological mechanisms such as neuroinflammation, dysregulated hypothalamus pituitary adrenal (HPA) axis, altered neurogenesis, and altered tryptophan metabolism responsible for coexistent relationship of epilepsy and depression. Based on these common pertinent pathways involved in the genesis of epilepsy and depression, we suggested novel targets and therapeutic approaches for safe management of comorbid depression in epilepsy.

Mast cell activation ameliorates pentylenetetrazole-induced seizures in rats: The potential role for serotonin

Neuroinflammation plays a key role in the pathogenesis of epilepsy, but the underlying mechanisms are not well understood. Mast cells are multifunctional immune cells that are also activated by stress. The effects of activated mast cells on epileptogenesis are not yet known. This study investigated the effects and mechanisms of compound 48/80-stimulated mast cell activation on pentylenetetrazole-induced epileptic seizures in rats. Male Wistar rats were separated into seven groups (n = 12). Group-1(NS+PTZ) received intraperitoneal saline solution, while groups 2(C-48/80+PTZ-1), 3(C-48/80+PTZ-2), and 4(C-48/80+PTZ-3) received compound-48/80 at doses of 0.5, 1, and 2 mg/kg, respectively, 30 min before 45 mg/kg pentylenetetrazole administration. Similarly, Group-5(Cr+C-48/80+PTZ) received 10 mg/kg cromolyn plus 2 mg/kg compound-48/80 before pentylenetetrazole, and Group-6(MC Dep+C-48/80+PTZ) was exposed to a mast cell-depletion process, and then received 2 mg/kg compound-48/80. Group-7(5-HT+PTZ) received 10 mg/kg serotonin. Seizure stages were evaluated using Racine's scale. Compound-48/80 at 2 mg/kg induced anticonvulsive effects against pentylenetetrazole-induced seizures by extending onset-times of both myoclonic-jerk and generalized tonic-clonic seizures (p = 0.0001), and by shortening the duration of generalized tonic-clonic seizure (p = 0.008). These effects were reversed by cromolyn (p = 0.0001). These effects were not observed in mast cell-depleted rats. Similarly to compound 48/80, serotonin also exhibited anticonvulsive effects against seizures (p < 0.05). Compound 48/80 acts as an anticonvulsant by activating mast cells in a dose-dependent manner. The anticonvulsive effects of mast cell activation may be mediated by serotonin. Mast cell activation may therefore provide protective activity against seizures under appropriate circumstances.

Endocannabinoid-serotonin systems interaction in health and disease

Endocannabinoid (eCB) and serotonin (5-HT) neuromodulatory systems work both independently and together to finely orchestrate neuronal activity throughout the brain to strongly sculpt behavioral functions. Surprising parallelism between the behavioral effects of 5-HT and eCB activity has been widely reported, including the regulation of emotional states, stress homeostasis, cognitive functions, food intake and sleep. The distribution pattern of the 5-HT system and the eCB molecular elements in the brain display a strong overlap and several studies report a functional interplay and even a tight interdependence between eCB/5-HT signaling. In this review, we examine the available evidence of the interaction between the eCB and 5-HT systems. We first introduce the eCB system, then we describe the eCB/5-HT crosstalk at the neuronal and synaptic levels. Finally, we explore the potential eCB/5-HT interaction at the behavioral level with the implication for psychiatric and neurological disorders. The precise elucidation of how this neuromodulatory interaction dynamically regulates biological functions may lead to the development of more targeted therapeutic strategies for the treatment of depressive and anxiety disorders, psychosis and epilepsy.

Interactions of antiepileptic drugs with drugs approved for the treatment of indications other than epilepsy

Introduction: Comorbidities of epilepsy may significantly interfere with its treatment as diseases in the general population are also encountered in epilepsy patients and some of them even more frequently (for instance, depression, anxiety, or heart disease). Obviously, some drugs approved for other than epilepsy indications can modify the anticonvulsant activity of antiepileptics. Areas covered: This review highlights the drug-drug interactions between antiepileptics and aminophylline, some antidepressant, antiarrhythmic (class I-IV), selected antihypertensive drugs and non-barbiturate injectable anesthetics (ketamine, propofol, etomidate, and alphaxalone). The data were reviewed mainly from experimental models of seizures. Whenever possible, clinical data were provided. PUBMED data base was the main search source.Expert opinion: Aminophylline generally reduced the protective activity of antiepileptics, which, to a certain degree, was consistent with scarce clinical data on methylxanthine derivatives and worse seizure control. The only antiarrhythmic with this profile of action was mexiletine when co-administered with VPA. Among antidepressants and non-barbiturate injectable anesthetics, trazodone, mianserin and etomidate or alphaxalone, respectively, negatively affected the anticonvulsant action of some antiepileptic drugs. Clinical data indicate that only amoxapine, bupropion, clomipramine and maprotiline should be used with caution. Possibly, drugs reducing the anticonvulsant potential of antiepileptics should be avoided in epilepsy patients.

Serotonin and sudden unexpected death in epilepsy

Epilepsy is a highly prevalent disease characterized by recurrent, spontaneous seizures. Approximately one-third of epilepsy patients will not achieve seizure freedom with medical management and become refractory to conventional treatments. These patients are at greatest risk for sudden unexpected death in epilepsy (SUDEP). The exact etiology of SUDEP is unknown, but a combination of respiratory, cardiac, neuronal electrographic dysfunction, and arousal impairment is thought to underlie SUDEP. Serotonin (5-HT) is involved in regulation of breathing, sleep/wake states, arousal, and seizure modulation and has been implicated in the pathophysiology of SUDEP. This review explores the current state of understanding of the relationship between 5-HT, epilepsy, and respiratory and autonomic control processes relevant to SUDEP in epilepsy patients and in animal models.

Trazodone increases seizures in a genetic WAG/Rij rat model of absence epilepsy while decreasing them in penicillin-evoked focal seizure model

AIM

Psychiatric disorders, especially depression and anxiety, are among the most disabling comorbidities in patients with epilepsy, and they are difficult to treat because many antidepressants cause proconvulsive effects. Thus, it is important to identify the seizure risks associated with antidepressants. Trazodone is one of the most frequently prescribed selective serotonin reuptake inhibitor (SSRI) antidepressant drugs for the treatment of depression and anxiety. The aim of the present study was to evaluate the effects of trazodone on epileptiform activity in a penicillin-evoked focal seizure model in Wistar rats and in a genetic absence epilepsy model in Wistar Albino Glaxo/Rijswijk strain (WAG/Rij) rats.

METHODS

Trazodone at 5-, 10-, and 30-mg/kg doses was injected intraperitoneally in Wistar rats 30 min after penicillin injection, and spike frequency and amplitude of penicillin-induced epileptiform activity were evaluated. In a separate experimental model, the same trazodone doses were injected in WAG/Rij rats to elucidate their effects on number, duration, and amplitude of spike-and-wave discharges (SWDs) and on depression-anxiety like behavior. In both experimental groups, after trazodone injections recordings were made for 3 h. Depression-anxiety like behaviors in WAG/Rij rats were examined using forced swim test and open-field test.

RESULTS

Trazodone at 10- and 30-mg/kg doses significantly reduced the frequency of penicillin-induced epileptiform activity without changing the amplitude. Trazodone at a 5-mg/kg dose had no effect on either frequency or amplitude of epileptiform activity. Trazodone at all doses significantly increased number and duration of SWDs without changing the amplitude. In addition, all doses of trazodone decreased the number of squares crossed and duration of grooming in open-field test, and reduced swimming time activity and increased immobility time in forced swim test.

CONCLUSION

Our results suggest that depending on the dose used, trazodone had an anticonvulsant effect or no effect on penicillin-evoked focal seizure model, but all trazodone doses resulted in proconvulsant and depression-anxiety like behavior in WAG/Rij rats, which represent a genetic absence model of epilepsy.

The effect of vortioxetine on penicillin-induced epileptiform activity in rats

Vortioxetine is a multimodal antidepressant agent that modulates 5-HT receptors and inhibits the serotonin transporter. It is indicated especially in cases of major depressive disorder related to cognitive dysfunction. There are many studies investigating the effects of antidepressants on the seizure threshold and short-term epileptic activity. However, the effect of vortioxetine on epileptic seizures is not exactly known. Our aim was to investigate the effects of vortioxetine on penicillin-induced epileptiform activity. Twenty-seven Wistar rats were divided into three groups: sham-control group, positive control group (diazepam), and vortioxetine group. After a penicillin-induced epilepsy model was formed in each of the three groups of animals, 0.1 ml of saline was administered to the control group, 0.1 ml (10 mg/kg) vortioxetine was administered in the vortioxetine group, and 0.1 mL (5 mg/kg) of diazepam was administered in the positive control group, intraperitoneally. The epileptic activity records were obtained for 120 minutes after the onset of seizure. There was no significant difference in spike wave activity between the vortioxetine and diazepam groups, whereas this was significantly reduced in the vortioxetine group compared with the controls. The administration of vortioxetine at a dose of 10 mg/kg immediately after the seizure induction significantly decreased the spike frequencies of epileptiform activity compared with the control group. No significant difference was found between the vortioxetine and positive controls. This study showed that vortioxetine reduces the number of acutely-induced epileptic discharges. Vortioxetine may be an important alternative for epileptic patients with major depressive disorder-related cognitive dysfunction.

The effect of fluoxetine on penicillin-induced epileptiform activity

AIM

Depression is the most frequent psychiatric comorbidity in patients with epilepsy. Fluoxetine is the most widely used selective serotonin reuptake inhibitor (SSRI) in depression. The aim of the present study was to evaluate the dose-dependent effect of fluoxetine on penicillin-induced seizure by electrocorticogram (ECoG), a model for simple partial epilepsy.

METHOD

The epileptiform activity was induced by intracortical (i.c.) microinjection of penicillin into the left sensorimotor cortex. Thirty minutes after penicillin injection, 5, 10, or 20 mg/kg doses of fluoxetine were administered intraperitoneally (i.p.). An ECoG recording was performed for 180 min using the data acquisition system. The frequency and the amplitude of the epileptiform activity were analyzed.

RESULTS

Penicillin induced bilateral spikes and spike-wave complexes within 2-5 min. The 5 and 10 mg/kg doses of fluoxetine significantly reduced the frequency (58%, p < 0.05 and 69%, p < 0.01, 40 and 50 min after fluoxetine injection, respectively) and amplitude (60%, p < 0.01 and 73%, p < 0.05, 40 and 120 min after fluoxetine injection, respectively) of epileptiform activity compared with penicillin-induced seizure group (control). Five-milligram fluoxetine (i.p.) was the most effective dose to decrease frequency and amplitude on penicillin-induced epileptiform activity. However, a higher fluoxetine dose (20 mg/kg) significantly increased frequency (147%, p < 0.01) and amplitude (123%, p < 0.05) of epileptiform activity 40 and 120 min after fluoxetine administration compared with control group. Also, bursts of population spikes were seen in 20 mg/kg fluoxetine doses.

CONCLUSION

Results of the present study indicate that low and moderate fluoxetine doses have an anticonvulsant effect while high doses have proconvulsant effect on penicillin-induced epileptic activity.

Bidirectional relations among common psychiatric and neurologic comorbidities and epilepsy: Do they have an impact on the course of the seizure disorder?

The treatment of epilepsy is not limited to the achievement of a seizure‐free state. It must also incorporate the management of common psychiatric and neurologic comorbidities, affecting on average between 30 and 50% of patients with epilepsy, which have a significant impact on their lives at various levels, including quality of life and the prognosis of the seizure disorder. Mood and anxiety disorders are the most frequent psychiatric comorbidities, whereas stroke and migraine are among the more common neurologic comorbidities, migraine among the younger patients and stroke among the older patients. Not only do these psychiatric and neurologic comorbidities each have a bidirectional relation with epilepsy, but primary mood disorders have a bidirectional relation with these 2 neurologic disorders. Furthermore, depression and migraine have been each associated with a more severe epilepsy course, whereas depression has been associated with a more severe course of stroke and migraines. The purpose of this article is to review the clinical implications of the complex relations among epilepsy and these 3 comorbid disorders, and to identify any clinical and/or experimental evidence that may suggest that having more than one of these comorbid disorders may increase the risk of and course of epilepsy.

A review of treatment options for behavioural manifestations of clinical anxiety as a comorbidity in dogs with idiopathic epilepsy

Psychiatric comorbidities affect a large percentage of people with epilepsy and have a detrimental impact on their quality of life. Recently, behavioural comorbidities, with similar characteristics to human psychiatric diseases, have been identified in dogs with idiopathic epilepsy. In particular, behaviours motivated by the fear-anxiety emotional system have been found to be associated with the occurrence of idiopathic epilepsy in both dogs receiving anti-epileptic drugs, and drug-naïve dogs. There has been little research into the relationship between epilepsy and behavioural signs, and even less into potential treatment protocols. The following article will review available literature from human medicine to describe the current state of knowledge about the bi-directional relationship between anxiety and epilepsy, draw parallels from reported anxiogenic and anxiolytic properties of anti-epileptic drugs and attempt to provide pharmaceutical and behavioural guidance for veterinary patients with epilepsy and comorbid anxiety.

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.

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).

Managing epilepsy-associated depression: Serotonin enhancers or serotonin producers?

Depression is one of the major psychiatric comorbidities having a major impact on the quality of life in people with epilepsy (PWE). Selective serotonin reuptake inhibitors (SSRIs) are considered as safest therapy for the treatment of depression in PWE. Although administration of SSRIs increases the synaptic serotonin levels, it decreases the overall serotonin synthesis in the brain. Long-term therapy with SSRIs has been reported to decrease serotonin synthesis, which may be the possible reason for lessening of their antidepressant effect over time as well as elevated seizure outcomes observed in PWE. Thus the present scenario warrants streamlined studies to explore the safety and efficacy of SSRIs as well as approaches beyond SSRIs for treatment of depression in epilepsy. In this review, we outline the approaches which may restore serotonin levels rather than a pseudo enhancement of serotonin with SSRIs. The potential of various anti-inflammatory approaches such as selective cyclooxygenase-2 inhibitors, inflammatory cytokine inhibitors, and indoleamine 2,3-dioxygenase inhibitors pertaining to their serotonin restoring effects is discussed as possible therapy for treatment of depression in epilepsy.

Common Mechanisms Underlying Epileptogenesis and the Comorbidities of Epilepsy

The importance of comorbidities in determining the quality of life of individuals with epilepsy and their families has received increasing attention in the past decade. Along with it has come a recognition that in some individuals, certain comorbidities may have preexisted, and may have contributed to their developing epilepsy. Many mechanisms are capable of interconnecting different dysfunctions that manifest as distinct disorders, often diagnosed and managed by different specialists. We review the human data from the perspective of epidemiology as well as insights gathered from neurodiagnostic and endocrine studies. Animal studies are reviewed to refine our mechanistic understanding of the connections, because they permit the narrowing of variables, which is not possible when studying humans.

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.

Effects of selective serotonin and norepinephrine reuptake inhibitors on depressive- and impulsive-like behaviors and on monoamine transmission in experimental temporal lobe epilepsy

OBJECTIVE

Examine therapeutic potential of a selective serotonin reuptake inhibitor (SSRI) and a norepinephrine reuptake inhibitor (NERI) in an animal model of comorbidity between epilepsy, depression-like, and impulsive-like impairments.

METHODS

Epilepsy was induced in male Wistar rats by LiCl and pilocarpine. An SSRI fluoxetine (FLX), and an NERI reboxetine (RBX) were administered either alone or as a combination over 1 week. Depressive-like and impulsive-like behaviors were examined using the forced swim test. Fast scan cyclic voltammetry was used to analyze serotonergic transmission in the raphe nucleus (RN)-prefrontal cortex (PFC) pathway, and noradrenergic transmission in locus coeruleus (LC)-PFC, and LC-RN projections. Monoamine levels in PFC were measured using high-performance liquid chromatography (HPLC). Functional capacities of 5-HT1A receptors and α2A adrenoreceptors in PFC were analyzed by autoradiography.

RESULTS

Epileptic rats showed behavioral signs of depression and hyperimpulsivity, suppressed serotonergic and noradrenergic tones, decreased levels of serotonin (5-HT), and norepinephrine (NE); 5-HT1A receptor and α2A adrenoreceptors functions remained intact. FLX failed to improve behavioral deficits, but effectively raised 5-HT level and marginally improved RN-PFC serotonergic transmission. RBX reversed impulsive-like behavior, normalized content of NE and noradrenergic tone in LC-PFC and LC-RN. FLX-RBX combination fully reversed depressive-like behavior, and normalized RN-PFC serotonergic transmission. None of the treatment modified the function of 5-HT and NE receptors.

SIGNIFICANCE

Depressive- and impulsive-like behaviors in the pilocarpine model of epilepsy stem respectively from dysfunctions of serotonergic and noradrenergic ascending pathways. At the same time, epilepsy-associated depression is SSRI resistant. The finding that an SSRI-NERI combination exerts antidepressant effect, along with RBX-induced improvement of LC-RN noradrenergic transmission point toward the involvement of LC-RN noradrenergic input in enabling therapeutic potential of FLX. Medications that improve serotonergic and noradrenergic transmission, such as serotonin-norepinephrine reuptake inhibitors may be effective in treating epilepsy-associated SSRI-resistant depression, as well as concurrent depression and attention-deficit/hyperactivity disorder (ADHD).

Brain serotonin content regulates the manifestation of tramadol-induced seizures in rats: disparity between tramadol-induced seizure and serotonin syndrome

BACKGROUND

Tramadol-induced seizures might be pathologically associated with serotonin syndrome. Here, the authors investigated the relationship between serotonin and the seizure-inducing potential of tramadol.

METHODS

Two groups of rats received pretreatment to modulate brain levels of serotonin and one group was treated as a sham control (n = 6 per group). Serotonin modulation groups received either para-chlorophenylalanine or benserazide + 5-hydroxytryptophan. Serotonin, dopamine, and histamine levels in the posterior hypothalamus were then measured by microdialysis, while simultaneously infusing tramadol until seizure onset. In another experiment, seizure threshold with tramadol was investigated in rats intracerebroventricularly administered with either a serotonin receptor antagonist (methysergide) or saline (n = 6).

RESULTS

Pretreatment significantly affected seizure threshold and serotonin fluctuations. The threshold was lowered in para-chlorophenylalanine group and raised in benserazide + 5-hydroxytryptophan group (The mean ± SEM amount of tramadol needed to induce seizures; sham: 43.1 ± 4.2 mg/kg, para-chlorophenylalanine: 23.2 ± 2.8 mg/kg, benserazide + 5-hydroxytryptophan: 59.4 ± 16.5 mg/kg). Levels of serotonin at baseline, and their augmentation with tramadol infusion, were less in the para-chlorophenylalanine group and greater in the benserazide + 5-hydroxytryptophan group. Furthermore, seizure thresholds were negatively correlated with serotonin levels (correlation coefficient; 0.71, P < 0.01), while intracerebroventricular methysergide lowered the seizure threshold (P < 0.05 vs. saline).

CONCLUSIONS

The authors determined that serotonin-reduced rats were predisposed to tramadol-induced seizures, and that serotonin concentrations were negatively associated with seizure thresholds. Moreover, serotonin receptor antagonism precipitated seizure manifestation, indicating that tramadol-induced seizures are distinct from serotonin syndrome.

Biomarkers of epileptogenesis: psychiatric comorbidities (?)

The last decade has witnessed a significant shift on our understanding of the relationship between psychiatric disorders and epilepsy. While traditionally psychiatric disorders were considered as a complication of the underlying seizure disorder, new epidemiologic data, supported by clinical and experimental research, have suggested the existence of a bidirectional relation between the two types of conditions: not only are patients with epilepsy at greater risk of experiencing a psychiatric disorder, but patients with primary psychiatric disorders are at greater risk of developing epilepsy. Do these data suggest that some of the pathogenic mechanisms operant in psychiatric comorbidities play a role in epileptogenesis? The aim of this article is to review the epidemiologic data that demonstrate that primary psychiatric disorders are more frequent in people who develop epilepsy, before the onset of the seizure disorder than among controls. The next question looks at the available data of pathogenic mechanisms of primary mood disorders and their potential for facilitating the development and/or exacerbation in the severity of epileptic seizures. Finally, we review data derived from experimental studies in animal models of depression and epilepsy that support a potential role of pathogenic mechanisms of mood disorders in the development of epileptic seizures and epileptogenesis. The data presented in this article do not yet establish conclusive evidence of a pathogenic role of psychiatric comorbidities in epileptogenesis, but raise important research questions that need to be investigated in experimental, clinical, and population-based epidemiologic research studies.

Chronic antidepressant treatment accelerates kindling epileptogenesis in rats

OBJECTIVES

Due to the high comorbidity of epilepsy and depression, antidepressant treatment is commonly indicated for patients with epilepsy. Studies in humans and animal models suggest that selective serotonin reuptake inhibitors (SSRIs) may reduce seizure frequency and severity, and these drugs are generally considered safe for use in epilepsy. No studies have investigated the effects of SSRIs on epileptogenesis, the neurobiological process underlying the development of the epileptic state.

METHODS

The effect of continuous infusion of the SSRI, fluoxetine (10mg/kg/day sc), versus vehicle control on amygdala kindling was examined in adult male Wistar rats. Seizure threshold and kindling rates were compared between SSRI-treated rats and controls. The study was then repeated examining the effect of a different SSRI, citalopram (10mg/kg/day sc), versus vehicle control. Hippocampal mRNA expression of the serotonin transporter (SERT) and the 5-HT1A receptor was examined in the brains of the rats post-mortem.

RESULTS

Treatment with either fluoxetine or citalopram significantly accelerated kindling epileptogenesis, as evidenced by fewer stimulations to reach Class V seizures compared to their respective vehicle-treated group (p<0.01 for both drugs). Seizure duration was also increased in fluoxetine-treated rats. No differences in seizure threshold were observed between treatments (p>0.05). mRNA analysis did not reveal any molecular changes which were common to both treatments.

CONCLUSIONS

The rate of epileptogenesis in rats is enhanced by chronic treatment with SSRIs. This could potentially have implications regarding the effect of SSRIs on the development or progression of human epilepsy.

Antidepressant therapy in epilepsy: can treating the comorbidities affect the underlying disorder?

There is a high incidence of psychiatric comorbidity in people with epilepsy (PWE), particularly depression. The manifold adverse consequences of comorbid depression have been more clearly mapped in recent years. Accordingly, considerable efforts have been made to improve detection and diagnosis, with the result that many PWE are treated with antidepressant drugs, medications with the potential to influence both epilepsy and depression. Exposure to older generations of antidepressants (notably tricyclic antidepressants and bupropion) can increase seizure frequency. However, a growing body of evidence suggests that newer ('second generation') antidepressants, such as selective serotonin reuptake inhibitors or serotonin-noradrenaline reuptake inhibitors, have markedly less effect on excitability and may lead to improvements in epilepsy severity. Although a great deal is known about how antidepressants affect excitability on short time scales in experimental models, little is known about the effects of chronic antidepressant exposure on the underlying processes subsumed under the term 'epileptogenesis': the progressive neurobiological processes by which the non-epileptic brain changes so that it generates spontaneous, recurrent seizures. This paper reviews the literature concerning the influences of antidepressants in PWE and in animal models. The second section describes neurobiological mechanisms implicated in both antidepressant actions and in epileptogenesis, highlighting potential substrates that may mediate any effects of antidepressants on the development and progression of epilepsy. Although much indirect evidence suggests the overall clinical effects of antidepressants on epilepsy itself are beneficial, there are reasons for caution and the need for further research, discussed in the concluding section.

Stress, seizures, and hypothalamic-pituitary-adrenal axis targets for the treatment of epilepsy

Epilepsy is a heterogeneous condition with varying etiologies including genetics, infection, trauma, vascular, neoplasms, and toxic exposures. The overlap of psychiatric comorbidity adds to the challenge of optimal treatment for people with epilepsy. Seizure episodes themselves may have varying triggers; however, for decades, stress has been commonly and consistently suspected to be a trigger for seizure events. This paper explores the relationship between stress and seizures and reviews clinical data as well as animal studies that increasingly corroborate the impact of stress hormones on neuronal excitability and seizure susceptibility. The basis for enthusiasm for targeting glucocorticoid receptors for the treatment of epilepsy and the mixed results of such treatment efforts are reviewed. In addition, this paper will highlight recent findings identifying a regulatory pathway controlling the body's physiological response to stress which represents a novel therapeutic target for modulation of the hypothalamic-pituitary-adrenal (HPA) axis. Thus, the HPA axis may have important clinical implications for seizure control and imply use of anticonvulsants that influence this neuronal pathway.

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.

Impaired maturation of serotonergic function in the dentate gyrus associated with epilepsy

Temporal lobe epilepsy is believed to develop after an initial precipitating injury, usually suffered in childhood or adolescence, and aspects include impaired maturation of the hippocampus, and specifically the dentate gyrus. The dentate gyrus receives a major serotonergic input from the brainstem raphe nuclei, and the serotonergic system may regulate neurogenesis in the developing and mature hippocampus. The aim of this work was to investigate changes which may be associated with abnormal functioning of the serotonergic system in the pilocarpine model of epilepsy, where spontaneous seizures are induced by administration of pilocarpine at 6 weeks of age. Application of serotonin (100 μM) led to a transient hyperpolarization of the resting membrane potential and decrease of the input resistance mediated by the 5-HT(1A) receptor that was similar between control and pilocarpine-treated animals and unaffected by the age of the animal. In the younger, but not in older control animals, serotonin led to a 5-HT(2) receptor-mediated long-term depression of evoked postsynaptic currents, a normal functional shift in the early adulthood of the Wistar rat. In pilocarpine-treated animals, this long-term depression persisted in older animals, indicating impaired maturation of the dentate gyrus. These data may indicate 5-HT(2) receptor function to be affected by the pathology of temporal lobe epilepsy.

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 antidepressants citalopram and reboxetine reduce seizure frequency in rats with chronic epilepsy

PURPOSE

  For a long time, antidepressants have been thought to possess proconvulsant properties. This assumption, however, remains controversial, since anticonvulsant effects have been attributed to certain antidepressants. To date, it remains unclear which antidepressants can be used for the treatment of depression in patients with epilepsy. In this respect, studies investigating the convulsant liability of antidepressants in a chronic epilepsy model can give valuable information. The present study was designed to determine the seizure liability of citalopram and reboxetine in the kainic acid-induced post-status epilepticus model for temporal lobe epilepsy.

METHODS

  Two months after the induction of status epilepticus, chronic epileptic rats (n = 16) were video-electroencephalography (EEG) monitored during seven consecutive weeks. Weeks 1, 3, 5, and 7 served as sham weeks during which the rats received intraperitoneal saline injections for four consecutive days, followed by a 3-day sham washout period during which no injections were given. During weeks 2, 4, and 6, rats received intraperitoneal injections with either citalopram (5, 10, and 15 mg/kg, once daily, n = 8) or reboxetine (10, 20, and 30 mg/kg, twice daily, n = 8) for 4 days, again followed by a washout period of 3 days. Drugs were administered in a randomly assigned fixed-dose regimen per week. Each rat served as its own control. The drug doses were selected based on the doses reported to have antidepressant effects in rats.

KEY FINDINGS

  Citalopram significantly decreased the spontaneous seizure frequency at the highest dose tested, that is, the mean number of seizures decreased from 12.8 seizures to 8.8 seizures per week (31%) after treatment with 15 mg/kg citalopram. This dose also significantly decreased the cumulative seizure duration. Administration of 5 and 10 mg/kg citalopram did not alter the seizure frequency. The two highest doses of reboxetine significantly decreased the spontaneous seizure frequency, that is, 20 mg/kg reboxetine decreased the seizure frequency from 14.1 to 7.9 (44%) and 30 mg/kg reboxetine decreased the seizure frequency from 11.8 to 7.2 (39%). In addition, both doses significantly decreased the cumulative seizure duration. Administration of 10 mg/kg reboxetine did not alter seizure frequency. Citalopram and reboxetine had no effect on seizure severity and seizure duration in any of the doses tested.

SIGNIFICANCE

  In general we can conclude that antidepressant doses of citalopram and reboxetine have, depending on the dose, an anticonvulsant effect or no effect on spontaneous seizures in the kainic acid-induced post-status epilepticus rat model.

Preclinical antiepileptic actions of selective serotonin reuptake inhibitors--implications for clinical trial design

Selective serotonin reuptake inhibitors (SSRIs) can reduce seizure frequency in humans, but no large-scale clinical trials have been done to test the utility of SSRIs as potential antiepileptic drugs. This may be caused in part by a small number of reports on seizures triggered by SSRI treatment. The preclinical literature on SSRIs is somewhat conflicting, which is likely to contribute to the hesitance in accepting SSRIs as possible anticonvulsant drug therapy. A careful review of preclinical studies reveals that SSRIs appear to have region-specific and seizure subtype-specific effects, with models of chronic partial epilepsy being more likely to respond than models of acute generalized seizures. Moreover, this preclinical profile is similar to that of clinical antiepileptic drugs. These observations suggest that SSRIs are promising antiepileptic agents, and that clinical trials may benefit from defining patient groups according to the underlying pathology.

Depression, stress, epilepsy and adult neurogenesis

Epilepsy and depression share an unusually high coincidence suggestive of a common etiology. Disrupted production of adult-born hippocampal granule cells in both disorders may contribute to this high coincidence. Chronic stress and depression are associated with decreased granule cell neurogenesis. Epilepsy is associated with increased production - but aberrant integration - of new cells early in the disease and decreased production late in the disease. In both cases, the literature suggests these changes in neurogenesis play important roles in their respective diseases. Aberrant integration of adult-generated cells during the development of epilepsy may impair the ability of the dentate gyrus to prevent excess excitatory activity from reaching hippocampal pyramidal cells, thereby promoting seizures. Effective treatment of a subset of depressive symptoms, on the other hand, may require increased granule cell neurogenesis, indicating that adult-generated granule cells can modulate mood and affect. Given the robust changes in adult neurogenesis evident in both disorders, competing effects on brain structure are likely. Changes in relative risk, disease course or response to treatment seem probable, but complex and changing patterns of neurogenesis in both conditions will require sophisticated experimental designs to test these ideas. Despite the challenges, this area of research is critical for understanding and improving treatment for patients suffering from these disorders.

A novel telemetry system for recording EEG in small animals

It has become increasingly evident that continuous EEG monitoring is necessary to observe the development of epilepsy in animals, and to determine the effect of drugs on spontaneous seizures. Telemetric recording systems have been increasingly used to monitor EEG in freely moving animals. One challenge faced by such systems is to monitor frequencies above 80Hz continuously for weeks. We present an implantable, 2.4-ml, telemetric sensor that can monitor EEG at 512 samples per second for eight weeks in a freely moving animal. With minor modifications, the same transmitter can operate at higher sample rates with a proportional decrease in operating life. Signal transmission is through bursts of 915-MHz radio power. The burst transmission and several other novel techniques reduce the transmitter's power consumption by two orders of magnitude while allowing 8 transmitters to share the same recording system. The use of radio-frequency transmission permits digitization within the sensor to sixteen-bit resolution, thus eliminating transmission-generated signal noise. The result is a signal with dynamic range 9mV, bandwidth 160Hz, input noise 12μV, and AC power interference less than 1μV. All circuit diagrams are open-source. Data acquisition takes place over the Internet using open-source software that works on multiple operating systems. The resulting system permits long-term, continuous, monitoring of EEG signals, therefore providing continuous and reliable data upon which to base studies of epilepsy in freely moving animals.

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.