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

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".

The Wistar Audiogenic Rat (WAR) strain and its contributions to epileptology and related comorbidities: History and perspectives

In the context of modeling epilepsy and neuropsychiatric comorbidities, we review the Wistar Audiogenic Rat (WAR), first introduced to the neuroscience international community more than 25years ago. The WAR strain is a genetically selected reflex model susceptible to audiogenic seizures (AS), acutely mimicking brainstem-dependent tonic-clonic seizures and chronically (by audiogenic kindling), temporal lobe epilepsy (TLE). Seminal neuroethological, electrophysiological, cellular, and molecular protocols support the WAR strain as a suitable and reliable animal model to study the complexity and emergent functions typical of epileptogenic networks. Furthermore, since epilepsy comorbidities have emerged as a hot topic in epilepsy research, we discuss the use of WARs in fields such as neuropsychiatry, memory and learning, neuroplasticity, neuroendocrinology, and cardio-respiratory autonomic regulation. Last, but not least, we propose that this strain be used in "omics" studies, as well as with the most advanced molecular and computational modeling techniques. Collectively, pioneering and recent findings reinforce the complexity associated with WAR alterations, consequent to the combination of their genetically-dependent background and seizure profile. To add to previous studies, we are currently developing more powerful behavioral, EEG, and molecular methods, combined with computational neuroscience/network modeling tools, to further increase the WAR strain's contributions to contemporary neuroscience in addition to increasing knowledge in a wide array of neuropsychiatric and other comorbidities, given shared neural networks. During the many years that the WAR strain has been studied, a constantly expanding network of multidisciplinary collaborators has generated a growing research and knowledge network. Our current and major wish is to make the WARs available internationally to share our knowledge and to facilitate the planning and execution of multi-institutional projects, eagerly needed to contribute to paradigm shifts in epileptology. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

Screening of anxiety and quality of life in people with epilepsy

PURPOSE

Up to 60% of people with epilepsy (PwE) have psychiatric comorbidity including anxiety. Anxiety remains under recognized in PwE. This study investigates if screening tools validated for depression could be used to detect anxiety disorders in PWE. Additionally it analyses the effect of anxiety on QoL.

METHOD

261 participants with a confirmed diagnosis of epilepsy were included. Neurological Disorders Depression Inventory for Epilepsy (NDDI-E) and Emotional Thermometers (ET), both validated to screen for depression were used. Hospital Anxiety and Depression Scale-Anxiety (HADS-A) with a cut off for moderate and severe anxiety was used as the reference standard. QoL was measured with EQ5-D. Sensitivity, specificity, positive and negative predictive value and ROC analysis as well as multivariate regression analysis were performed.

RESULTS

Patients with depression (n=46) were excluded as multivariate regression analysis showed that depression was the only significant determinant of having anxiety in the group. Against HADS-A, NDDI-E and ET-7 showed highest level of accuracy in recognizing anxiety with ET7 being the most effective tool. QoL was significantly reduced in PwE and anxiety.

CONCLUSION

Our study showed that reliable screening for moderate to severe anxiety in PwE without co-morbid depression is feasible with screening tools for depression. The cut off values for anxiety are different from those for depression in ET7 but very similar in NDDI-E. ET7 can be applied to screen simultaneously for depression and "pure" anxiety. Anxiety reduces significantly QoL. We recommend screening as an initial first step to rule out patients who are unlikely to have anxiety.

Topiramate for the treatment of epilepsy and other nervous system disorders

Initially synthesized as an oral hypoglycemic agent, topiramate was approved for use as an anticonvulsant in 1996. Its broad spectrum efficacy in epilepsy, including as monotherapy and in children, is well established. Topiramate has also been used in the management of nonepileptic neurologic and psychiatric conditions, including migraine prophylaxis (with firmly established efficacy), obesity (with some evidence of long-term maintenance of weight loss), substance dependence, bipolar disorder and neuropathic pain, and it has been investigated as a possible neuroprotective agent. Paresthesias and cognitive side effects are the most common troublesome adverse effects. Recent trends towards lower doses may help achieve the best combination of efficacy and tolerability.

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

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

The role of the central noradrenergic system in behavioral inhibition

Although the central noradrenergic system has been shown to be involved in a number of behavioral and neurophysiological processes, the relation of these to its role in depressive illness has been difficult to define. The present review discusses the hypothesis that one of its chief functions that may be related to affective illness is the inhibition of behavioral activation, a prominent symptom of the disorder. This hypothesis is found to be consistent with most previous neuropsychopharmacological and immunohistochemical experiments on active behavior in rodents in a variety of experimental conditions using manipulation of neurotransmission at both locus coeruleus and forebrain adrenergic receptors. The findings support a mechanism in which high rates of noradrenergic neural activity suppress the neural activity of principal neurons in forebrain regions mediating active behavior. The suppression may be mediated through postsynaptic galaninergic and adrenergic receptors, and via the release of corticotrophin-releasing hormone. The hypothesis is consistent with clinical evidence for central noradrenergic system hyperactivity in depressives and with the view that this hyperactivity is a contributing etiological factor in the disorder. A similar mechanism may underlie the ability of the noradrenergic system to suppress seizure activity suggesting that inhibition of the spread of neural activation may be a unifying function.

Psychiatric comorbidity in patients with epilepsy: a population-based study

PURPOSE

Patients with epilepsy often suffer from concomitant psychiatric disorders. Treatment patterns and the extent of comorbidity are insufficiently investigated and appropriate methods are scarce. The purpose of the study was to estimate the prevalence of psychiatric comorbidity in patients with epilepsy and to investigate prescription patterns of drugs prescribed for psychiatric disorders in epilepsy.

METHODS

Prescription data from the Norwegian Prescription Database (NorPD) regarding the use of CNS-active drugs included anonymous data from almost 190,000 patients and 1.1-1.3 million prescriptions per year (2004-2007). Searches were based upon use of specific drugs, defined daily doses, number of patients, prescriptions, gender, and age. Reimbursement codes related to psychiatric diagnosis were used as indicators for clinical use.

RESULTS

The prevalence of psychiatric comorbidity in patients with epilepsy was estimated to be 32%. There were 56% women and 44% men participating in the study. Among patients using antidepressants two thirds were women, but no gender differences were seen with antipsychotic medication. Antidepressants and antipsychotics were used 3.4 (20.9%) and 5.8 (13.4%) times more frequently than in the general population, accounting for 7.88 and 1.99 defined daily doses (DDDs)/1,000 inhabitants/day/year respectively. Lamotrigine was the most commonly used antiepileptic drug (AED) in epilepsy, accounting for 33% of the use of AEDs (in total 5.65 DDDs/1,000 inhabitants/day/year). The use of benzodiazepines was 9.55 DDDs/1,000 inhabitants/day/year. The patients had complex pharmacotherapy with two to eight concomitant drugs.

CONCLUSION

The present study gives an estimate of psychiatric comorbidity of 32% in patients with epilepsy in a nation-wide population. The pharmacotherapy in this patient population is complex. The results provide valuable data on prescription patterns that contribute to pharmacovigilance on a national scale.

Antiepileptic drugs in epilepsy and other disorders--a population-based study of prescriptions

PURPOSE

The aim of the study was to quantify the use of antiepileptic drugs (AEDs) in epilepsy and other indications in a nation-wide population using a prescription database.

MATERIALS AND METHODS

Prescription data of AEDs were collected from the Norwegian Prescription Database for the period 2004-2007, including 5.1 million prescriptions from 144,653 patients, all having at least one prescribed and dispensed AED. Diagnosis-related reimbursement codes were used as indicators for clinical use.

RESULTS

Of the AEDs used, 71% was in epilepsy, 15% in psychiatry, 13% in neuropathic pain, and <1% in migraine, trigeminus neuralgia and cancer adjuvance. The use in epilepsy increased steadily from 7.0 to 7.5 DDDs/1000 inhabitants/day (7%) from 2004 to 2007. The use of AEDs in other indications increased considerably more from 2004 to 2007: Neuropathic pain to 1.40 DDDs/1000 inhabitants/day (360%), psychiatry to 1.59 (200%), and migraine to 0.005 (642%). The prevalence of AED users increased and in 2007 it was 0.97% in epilepsy, 0.8% in neuropathic pain, 0.33% in psychiatry and 0.001% in migraine. In 2007, 49% of the AEDs used in epilepsy were a new drug, carbamazepine, lamotrigine and valproate being most frequently used. New AEDs were used in 96% in migraine prophylaxis, 94% in neuropathic pain, and 64% in psychiatry.

CONCLUSIONS

Based on a nation-wide prescription database, this study quantifies the wide and increasing use of AEDs, in particular the newer drugs.

Antiepileptic drugs in non-epilepsy disorders: relations between mechanisms of action and clinical efficacy

Antiepileptic drugs (AEDs) are used extensively to treat multiple non-epilepsy disorders, both in neurology and psychiatry. This article provides a review of the clinical efficacy of AEDs in non-epilepsy disorders based on recently published preclinical and clinical studies, and attempts to relate this efficacy to the mechanism of action of AEDs and pathophysiological processes associated with the disorders. Some newer indications for AEDs have been established, while others are under investigation. The disorders where AEDs have been demonstrated to be of clinical importance include neurological disorders, such as essential tremor, neuropathic pain and migraine, and psychiatric disorders, including anxiety, schizophrenia and bipolar disorder. Many of the AEDs have various targets of action in the synapse and have several proposed relevant mechanisms of action in epilepsy and in other disorders. Pathophysiological processes disturb neuronal excitability by modulating ion channels, receptors and intracellular signalling pathways, and these are targets for the pharmacological action of various AEDs. Attention is focused on the glutamatergic and GABAergic synapses. In psychiatric conditions such as schizophrenia and bipolar disorder, AEDs such as valproate, carbamazepine and lamotrigine appear to have clear roles based on their effect on intracellular pathways. On the other hand, some AEDs, e.g. topiramate, have efficacy for nonpsychiatric disorders including migraine, possibly by enhancing GABAergic and reducing glutamatergic neurotransmission. AEDs that seem to enhance GABAergic neurotransmission, e.g. tiagabine, valproate, gabapentin and possibly levetiracetam, may have a role in treating neurological disorders such as essential tremor, or anxiety disorders. AEDs with effects on voltage-gated sodium or calcium channels may be advantageous in treating neuropathic pain, e.g. gabapentin, pregabalin, carbamazepine, oxcarbazepine, lamotrigine and valproate. Co-morbid conditions associated with epilepsy, such as mood disorders and migraine, may often respond to treatment with AEDs. Other possible disorders where AEDs may be of clinical importance include cancer, HIV infection, drug and alcohol abuse, and also in neuroprotection. A future challenge is to evaluate the second-generation AEDs in non-epilepsy disorders and to design clinical trials to study their effects in such disorders in paediatric patients. Differentiation between the main mechanisms of action of the AEDs needs more consideration in drug selection for tailored treatment of the various non-epilepsy disorders.

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.

AEDs and psychotropic drugs in children with autism and epilepsy

The efficacy of antiepileptic drugs (AEDs) and psychotropic medications in children with autism is limited to the treatment of seizures or to specific behaviors such as irritability, impulsivity, hyperactivity, repetitive behaviors, or aggression. The reliability and value of the available data--to determine the efficacy of these medications in autism--are limited by lack of controlled clinical trials, the small number of subjects, the heterogeneity of the population studied, and the brief duration of most drug trials. Indeed, few controlled clinical trials using AEDs in autism, with or without seizures, have been conducted. Because some AEDs also have a positive effect on mood, the benefits that children with autism sometimes obtain from these medications may not be due to the treatment of the abnormal electrical activity or the seizures per se but to an effect on common neuronal systems responsible for both behavior and epilepsy. The relationship between epilepsy and autism, and specifically the effects that abnormal electrical activity may have on the developing brain, may provide some valuable insights into the type of studies that are needed to help us understand the pathophysiology of autism.

Neurochemical underpinnings in bipolar disorder and epilepsy

In this article, we discuss and highlight some of the potential neurochemical underpinnings of bipolar disorder (BD) and epilepsy. Some similarities are found in both disorders, such as the episodic course of the illnesses, the possible mechanism of kindling, and the efficacy of some antiepileptic drugs (AEDs) in treatment, all pointing to a common underlying pathophysiology. Common mechanisms at the level of ion channels might include the antikindling and the calcium-antagonistic and potassium outward current-modulating properties of AEDs. However, future research on intracellular mechanisms might become decisive for a better understanding of the similarities between the disorders.