Behavioral seizure correlates in animal models of epilepsy: a road map for assay selection, data interpretation, and the search for causal mechanisms

Role of P2Y receptors in astrocyte physiology and pathophysiology

Astrocytes are active constituents of the brain that manage ion homeostasis and metabolic support of neurons and directly tune synaptic transmission and plasticity. Astrocytes express all known P2Y receptors. These regulate a multitude of physiological functions such as cell proliferation, Ca²⁺ signalling, gliotransmitter release and neurovascular coupling. In addition, P2Y receptors are fundamental in the transition of astrocytes into reactive astrocytes, as occurring in many brain disorders such as neurodegenerative diseases, neuroinflammation and epilepsy. This review summarizes the current literature addressing the function of P2Y receptors in astrocytes in the healthy brain as well as in brain diseases.

Neuropharmacological potentials of β-carboline alkaloids for neuropsychiatric disorders

Neuropsychiatric disorders are diseases of the central nervous system (CNS) which are characterised by complex pathomechanisms that including homeostatic failure, malfunction, atrophy, pathology remodelling and reactivity anomaly of the neuronal system where treatment options remain challenging. β-Carboline (βC) alkaloids are scaffolds of structurally diverse tricyclic pyrido[3,4-b]indole alkaloid with vast occurrence in nature. Their unique structural features which favour interactions with enzymes and protein receptor targets account for their potent neuropharmacological properties. However, our current understanding of their biological mechanisms for these beneficial effects, especially for neuropsychiatric disorders is sparse. Therefore, we present a comprehensive review of the scientific progress in the last two decades on the prospective pharmacology and physiology of the βC alkaloids in the treatment of some neuropsychiatric conditions such as depression, anxiety, Alzheimer's disease, Parkinson's disease, brain tumour, essential tremor, epilepsy and seizure, licking behaviour, dystonia, agnosia, spasm, positive ingestive response as demonstrated in non-clinical models. The current evidence supports that βC alkaloids offer potential therapeutic agents against most of these disorders and amenable for further drug design.

In vivo CRISPRa decreases seizures and rescues cognitive deficits in a rodent model of epilepsy

Epilepsy is a major health burden, calling for new mechanistic insights and therapies. CRISPR-mediated gene editing shows promise to cure genetic pathologies, although hitherto it has mostly been applied ex vivo. Its translational potential for treating non-genetic pathologies is still unexplored. Furthermore, neurological diseases represent an important challenge for the application of CRISPR, because of the need in many cases to manipulate gene function of neurons in situ. A variant of CRISPR, CRISPRa, offers the possibility to modulate the expression of endogenous genes by directly targeting their promoters. We asked if this strategy can effectively treat acquired focal epilepsy, focusing on ion channels because their manipulation is known be effective in changing network hyperactivity and hypersynchronziation. We applied a doxycycline-inducible CRISPRa technology to increase the expression of the potassium channel gene Kcna1 (encoding K_v1.1) in mouse hippocampal excitatory neurons. CRISPRa-mediated K_v1.1 upregulation led to a substantial decrease in neuronal excitability. Continuous video-EEG telemetry showed that AAV9-mediated delivery of CRISPRa, upon doxycycline administration, decreased spontaneous generalized tonic-clonic seizures in a model of temporal lobe epilepsy, and rescued cognitive impairment and transcriptomic alterations associated with chronic epilepsy. The focal treatment minimizes concerns about off-target effects in other organs and brain areas. This study provides the proof-of-principle for a translational CRISPR-based approach to treat neurological diseases characterized by abnormal circuit excitability.

Investigating the potential for seizure prediction in dogs with idiopathic epilepsy: owner-reported prodromal changes and seizure triggers

BACKGROUND

Canine idiopathic epilepsy (IE) is characterised by recurrent seizure activity, which can appear unpredictable and uncontrollable. The purpose of this study was to investigate the potential for seizure prediction in dogs by exploring owner-perceived seizure prediction abilities and identifying owner-reported prodromal changes (long-term changes in disposition that indicate forthcoming seizures) and seizure triggers (stimuli that precipitate seizures) in dogs with IE.

METHODS

This is an online, international, cross-sectional survey of 229 owners of dogs diagnosed with IE, meeting the International Veterinary Epilepsy Task Force tier I diagnostic criteria.

RESULTS

Over half (59.6 per cent) of owners believed they were able to predict an upcoming seizure in their dog, of whom nearly half (45.5 per cent) were able to do so at least 30 minutes before the seizure commenced. The most common 'seizure predictors' were preseizure behavioural changes including increased clinginess (25.4 per cent), restlessness (23.1 per cent) and fearful behaviour (19.4 per cent). Nearly two-thirds of owners reported prodromal changes (64.9 per cent), most commonly restlessness (29.2 per cent), and nearly half (43.1 per cent) reported seizure triggers, most commonly stress (39.1 per cent).

CONCLUSIONS

The relatively high prevalence of owner-reported prodromal changes and seizure triggers shows promise for utilising these methods to aid seizure prediction in dogs, which could open a window of time for pre-emptive, individualised drug interventions to abort impending seizure activity.

A Review of Medical Conditions and Behavioral Problems in Dogs and Cats

Not all animals behave identically when faced with the same situation. These individual differences in the expression of their behavior could be due to many factors, including medical conditions. These medical problems can change behavior directly or indirectly. The aims of this review are to describe the state of the art of the relationship among some medical and behavioral problems, and to propose new lines of investigation. The revision is focused on the relation between behavioral problems and pain, endocrine diseases, neurological problems, vomeronasal organ alterations, and cardiac disorders. These problems represent a diagnostic challenge from a practical point of view. The most common sign of pain in animals is a change in behavior. Although the relation of pain to behavioral problems has been widely studied, it is not absolutely clear. As an example, the relation between sleep disorders and pain is poorly known in veterinary medicine. New studies in humans and laboratory animals show that a reciprocal relationship does, in fact, exist. More specifically, the literature suggests that the temporal effect of sleep deprivation on pain may be stronger than that of pain on sleep. Some behavioral problems could modify the sleep-awake cycle (e.g., cognitive dysfunction). The impact of these behavioral problems on pain perception is completely unknown in dogs and cats. Thyroid hormones play an important role, regarding behavioral control. Both hypothyroidism and hyperthyroidism have been related to behavioral changes. Concerning hypothyroidism, this relationship remains controversial. Nonetheless, new neuro-imaging studies provide objective evidence that brain structure and function are altered in hypothyroid patients, both in laboratory animals and in humans. There are many neurological problems that could potentially change behavior. This paper reviews those neurological problems that could lead to behavioral changes without modifying neurological examination. The most common problems are tumors that affect central nervous system silent zones, mild traumatic brain injury, ischemic attacks, and epilepsy. Most of these diseases and their relationship to behavior are poorly studied in dogs and cats. To better understand the pathophysiology of all of these problems, and their relation to behavioral problems, may change the diagnostic protocol of behavioral problems.

Modeling of Focal Seizures with Automatisms in Rats with Pendulum Movements

Phenotypical study was carried out in rats with pendulum movements. The animals exhibited a high level of abortive seizures in response to audiogenic stimuli and longer postictal catalepsy in comparison with those in Wistar population. Seizure severity positively correlated with the duration of poststimulus catalepsy (r=0.90). High aggressiveness towards humans, the absence of BP elevation in stress, lower body weights, and lower weights of the kidneys and spleen in PM rats are considered concomitant traits. Correlations were detected between startle-1 and BP in rats with pendulum movements (r=0.70) and between startle-10 and BP in narcotized Wistar rats (r=-0.0.71). The newly described signs in rats with pendulum movements did not contradict the signs of the focal seizure model with typical automatisms in humans.

Hippocampal GAD67 Transduction Using rAAV8 Regulates Epileptogenesis in EL Mice

Gene therapy has been employed as a therapeutic approach for intractable focal epilepsies. Considering the potential of focal GABAergic neuromodulation in regulating epileptogenesis, the GABA-producing enzyme, γ-aminobutyric acid decarboxylase 67 (GAD67), is highly suitable for epilepsy therapy. The EL/Suz (EL) mouse is a model of multifactorial temporal lobe epilepsy. In the present study, we examined focal gene transduction in epileptic EL mice using recombinant adeno-associated virus serotype 8 (rAAV8) expressing human GAD67 to enhance GABA-mediated neural inhibition. Eight-week-old mice were bilaterally injected with rAAV8-GFP or rAAV8-GAD67 in the hippocampal CA3 region. After four weeks, the GAD67-transduced EL mice, but not the rAAV-GFP-treated EL mice, exhibited a significant reduction in seizure generation. The GAD67-mediated depression became stable after 14 weeks. The excitability of the CA3 region was markedly reduced in the GAD67-transduced EL mice, consistent with the results of the Ca²⁺ imaging using hippocampal slices. In addition, downregulation of c-Fos expression was observed in GAD67-transduced hippocampi. Our findings showed that rAAV8-GAD67 induced significant changes in the GABAergic system in the EL hippocampus. Thus, rAAV8-mediated GAD67 gene transfer is a promising therapeutic strategy for the treatment of epilepsies.

Modulation of the intrinsic neuronal excitability by multifunctional liposomes tailored for the treatment of Alzheimer's disease

Purpose

Nanotechnologies turned out to be promising in the development of diagnostic and therapeutic approaches toward neurodegenerative disorders. However, only a very scant number of nanodevices until now proved to be effective on preclinical animal models. Although specific tests in vivo are available to assess the potential toxicity of these nanodevices on cognitive functions, those to evaluate their biosafety in vitro on neurons are still to be improved.

Materials and methods

We utilized the patch-clamp technique on primary cultures of cortical neural cells isolated from neonatal rats, aiming to evaluate their electrical properties after the incubation with liposomes (mApoE-PA-LIPs), previously proved able to cross the blood–brain barrier and to be effective on mouse models of Alzheimer’s disease (AD), both in the absence and in the presence of β-amyloid peptide oligomers.

Results

Data show a high degree of biocompatibility, evaluated by lactate dehydrogenase (LDH) release and MTT assay, and the lack of cellular internalization. After the incubation with mApoE-PA-LIPs, neuronal membranes show an increase in the input resistance (from 724.14±76 MΩ in untreated population to 886.06±86 MΩ in the treated one), a reduction in the rheobase current (from 29.6±3 to 24.2±3 pA in untreated and treated, respectively), and an increase of the firing frequency, consistent with an ultimate increase in intrinsic excitability. Data obtained after co-incubation of mApoE-PA-LIPs with β-amyloid peptide oligomers suggest a retention of liposome efficacy.

Conclusion

These data suggest the ability of liposomes to modulate neuronal electrical properties and are compatible with the previously demonstrated amelioration of cognitive functions induced by treatment of AD mice with liposomes. We conclude that this electrophysiological approach could represent a useful tool for nanomedicine to evaluate the effect of nanoparticles on intrinsic neuronal excitability.

Time course evaluation of behavioral impairments in the pilocarpine model of epilepsy

Epilepsy is a brain function disorder characterized by unpredictable and recurrent seizures. The majority of patients with temporal lobe epilepsy (TLE), which is the most common type of epilepsy, have to live not only with seizures but also with behavioral alterations, including anxiety, psychosis, depression, and impaired cognitive functioning. The pilocarpine model has been recognized as an animal model of TLE. However, there are few studies addressing behavioral alterations in the maturation phase when evaluating the time course of the epileptogenic process after pilocarpine administration. Therefore, the present work was designed to analyze the neurobehavioral impairments of male adult Wistar rats during maturation and chronic phases in the pilocarpine model of epilepsy. Behavioral tests included: open-field tasks, olfactory discrimination, social recognition, elevated plus maze, and the forced swimming test. The main behavioral alterations observed in both maturation and chronic phases of the pilocarpine model were olfactory and short-term social memory deficits and decrease in the immobility time in the forced swimming test. Moreover, increased anxiety-like responses were only observed in the maturation phase. These findings indicate that early behavioral impairments can be observed in the pilocarpine model during the maturation phase, and these behavioral deficits also occur during the acquired epilepsy (chronic phase). Several of the neurobehavioral impairments that are associated with epilepsy in humans were observed in the pilocarpine-treated rats, thus, rendering this animal model a useful tool to study neuroprotective strategies as well as neurobiological and psychopathological mechanisms associated with epileptogenesis.

Opportunities for improving animal welfare in rodent models of epilepsy and seizures

Animal models of epilepsy and seizures, mostly involving mice and rats, are used to understand the pathophysiology of the different forms of epilepsy and their comorbidities, to identify biomarkers, and to discover new antiepileptic drugs and treatments for comorbidities. Such models represent an important area for application of the 3Rs (replacement, reduction and refinement of animal use). This report provides background information and recommendations aimed at minimising pain, suffering and distress in rodent models of epilepsy and seizures in order to improve animal welfare and optimise the quality of studies in this area. The report includes practical guidance on principles of choosing a model, induction procedures, in vivo recordings, perioperative care, welfare assessment, humane endpoints, social housing, environmental enrichment, reporting of studies and data sharing. In addition, some model-specific welfare considerations are discussed, and data gaps and areas for further research are identified. The guidance is based upon a systematic review of the scientific literature, survey of the international epilepsy research community, consultation with veterinarians and animal care and welfare officers, and the expert opinion and practical experience of the members of a Working Group convened by the United Kingdom's National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs).

Domoic acid induced status epilepticus promotes aggressive behavior in rats

Domoic acid (DA), a naturally occurring environmental toxin, has been observed to induce status epilepticus in humans, sea lions and pelicans. In a recent Sprague Dawley rat model, domoic acid dosing induced a state of status epilepticus which, after a symptom-free latent period without further dosing, progressed to recurrent spontaneous seizures, a hallmark of epilepsy. Certain individuals in this study also developed unusual behavioral changes, in particular an atypical aggression towards conspecifics. In this report we characterized the progression of aggressive behaviors after DA-induced status epilepticus and explored the relationship between aggressive behavior and recurrent spontaneous seizures. Experimental studies in this laboratory rat model are particularly relevant to California sea lions (Zapholus californianus), which show a spectrum of both epileptic and unusual behaviors, including aggression towards conspecifics in rehabilitation facilities, weeks to months after suspected exposure to domoic acid in the wild.

Behavioral changes in dogs associated with the development of idiopathic epilepsy

OBJECTIVES

The aim of the study was to demonstrate behavioral changes with the development of epilepsy in dogs, a species proposed as a naturally occurring animal model for human epilepsy.

METHODS

Owners of dogs diagnosed with idiopathic epilepsy (n=80) completed a modified, previously-validated behavioral and seizure questionnaire. Principal axis factor analysis identified behavioral factors, the scores for which were compared before and after the development of epilepsy.

RESULTS

Drug-naïve dogs showed an increase in the behavior factors Fear/Anxiety, Defensive Aggression, and Abnormal Perception. In dogs receiving antiepileptic medication, there were still increases in Fear/Anxiety and Abnormal Perception, but no longer in Defensive Aggression. Additional increases were observed in Abnormal Reactivity, Attachment Disorder, Demented Behavior, and Apathetic Behavior. Pharmacoresistant dogs had larger increases in Controlling Aggression, Abnormal Perception, and Demented Behavior than drug responders.

CONCLUSION

Our data suggest that dogs, like humans and rodents, exhibit neurobehavioral comorbidities with the development of epilepsy.

Neurobehavioral consequences of stressor exposure in rodent models of epilepsy

Both normal, non-epileptic as well as seizure-prone rodents exhibit a spectrum of anxiogenic-like behaviors in response to stressor exposure. Comparative analysis reveals that the same set of emotionality dependent measures is sensitive to both stress reactivity in normal rodents as well as stress hyperreactivity typically seen in seizure-prone rodents. A variety of unconditioned, exploratory tasks reflect global sensitivity to stressor exposure in the form of behavioral inhibition of locomotor output. Moreover, well chosen stressors can trigger de novo seizures with or without a history of seizure incidence. Seizures may be elicited in response to stressful environmental stimuli such as noxious noises, tail suspension handling, or home cage disturbance. Stress reactivity studies in rodents with a genetic predisposition to seizures have yielded important clues regarding brain substrates that mediate seizure ontogeny and modulate ictogenesis. Brains of seizure susceptible rodents reflect elevated content of the stress-related neuropeptide, corticotropin-releasing factor (CRF) in several nuclei relative to non-susceptible controls and neutralization of brain CRF attenuates seizure sensitivity. Findings outlined in this review support a diathesis-stress hypothesis in which behavioral- and neuro-pathologies of genetically seizure susceptible rodents arise in part due to multifaceted hyperreactivity to noxious environmental stimuli.

An integrated system for video and telemetric electroencephalographic recording to measure behavioural and physiological parameters

INTRODUCTION

The combined evaluation of physiology and behaviour allows a complete and more comprehensive pre-clinical assessment of central nervous system (CNS) function. An integrated video-telemetric electroencephalography (Video-tEEG) system, which allows the simultaneous and continuous recording of EEG and video images for long periods, was developed.

METHODS

This study focuses on the refinement of the surgical methodology for the combined recording of cortical, hippocampal EEG and electromyogram (EMG) waveforms in freely moving rats. The post-operative recovery of animals was monitored by recording EEGs by telemetry and the general activity by video, on days 1, 6 and 15 after surgery, for approximately 24h, on each occasion.

RESULTS

The results suggested that the applied surgical technique for the implantation of the telemetric transmitter, allowed for a gradual recovery of the animals within 15days. During the recovery period the behavioural and locomotor parameters measured, indicated that there were no changes to the light-dark circadian cycle, and these parameters gradually tended to reach background levels within a 15-day period. Using a mechanical connection between the deep and the telemetric electrodes, 15days after surgical implantation the recording system was able to acquire cortical and hippocampal EEG traces of good quality.

DISCUSSION

This present study is concerned with the refinement of the surgical technique, as well as the integration and synchronisation of the commercially available Dataquest telemetry system and the Noldus video system, in order to study cortical, hippocampal EEG waveforms, in combination with behaviour and locomotion. The application of this integrated Video-tEEG system could provide advantages in the ethical use of animals in different pre-clinical research areas.

Behavioral and cognitive alterations, spontaneous seizures, and neuropathology developing after a pilocarpine-induced status epilepticus in C57BL/6 mice

Many patients with epilepsy suffer from psychiatric comorbidities including depression, anxiety, psychotic disorders, cognitive, and personality changes, but the mechanisms underlying the association between epilepsy and psychopathology are only incompletely understood. Animal models of epilepsy, such as the pilocarpine model of acquired temporal lobe epilepsy (TLE), are useful to study the relationship between epilepsy and behavioral dysfunctions. In the present study, we examined behavioral and cognitive alterations, spontaneous seizures, and neuropathology developing after a pilocarpine-induced status epilepticus in the C57BL/6 (B6) inbred strain of mice, which is commonly used as background strain for genetically modified mice. For this study, we used the same pilocarpine ramping-up dosing protocol and behavioral test battery than in a previous study in NMRI mice, thus allowing direct comparison between these two mouse strains. All B6 mice that survived SE developed epilepsy with spontaneous recurrent seizures. Epileptic B6 mice exhibited significant increases of anxiety-related behavior in the open field and light-dark box, increased locomotor activity in the open field, elevated plus maze, hole board, and novel object exploration tests, and decreased immobility in the forced swimming and tail suspension tests. Furthermore, spatial learning and memory were severely impaired in the Morris water maze, although hippocampal damage was much less severe than previously determined in NMRI mice. B6 mice in which pilocarpine did not induce SE but only single seizures did not exhibit any detectable neurodegeneration, but differed behaviorally from sham controls in several tests of the test battery used. Our data indicate that the pilocarpine model of TLE in B6 mice is ideally suited to study the neurobiological mechanisms underlying the association between seizures, brain damage and psychopathology.

Quality of rearing guides expression of behavioral and neural seizure phenotypes in EL mice

The present studies employed behavioral and neural markers of seizure-related plasticity to examine the relative contributions of genetic predisposition versus rearing environment in generating adult phenotypes in EL mice, a stress-induced animal model of epilepsy. Early environment was manipulated by cross-fostering pups of the EL strain to a seizure-resistant CD-1 control strain of mouse. The impact of changes in rearing quality on growth,exploratory and stress-reactivity phenotypes were examined, with a focus on the role of maternal care in shaping seizure susceptibility and neural cF os activation. Improvement in maternal care imposed by replacing biological EL dams with foster CD-1 mothers was sufficient to decrease pup mortality, to increase body weight gain (+0.1 g/day) and to delay the onset of seizure susceptibility in EL offspring beyond post-natal day 80–90. Moreover,hypoactivity in hippocampus and cortex among EL offspring cross-fostered to EL, but not CD-1 control, dams suggests that changes in rearing environment were accompanied by enduring changes in brain plasticity. Thus, neural and behavioral phenotypes of EL mice are dependent upon post-partum maternal care which if systematically enhanced can postpone seizure expression.

Application of experimental stressors in laboratory rodents

This unit presents eight separate stressor protocols for laboratory rodents. Stress induction is a critical element in the study of neural and neuroendocrine mechanisms involved in establishing and maintaining a state of stress. The first four procedures, immobilization, footshock, swimming, and noise, involve acute exposure to noxious stimuli. The next three procedures, social isolation, resident/intruder aggression, and maternal deprivation, induce social disruption by withdrawal from a group housing condition, attack within the unfamiliar territory of a dominant male, or segregation of a preweanling pup from its mother, respectively. The final procedure, sleep deprivation, involves passive denial of the opportunity to sleep. Support protocols are provided to address the need for environmental acclimation and calming procedures prior to any stress-related studies (including, for rats, handling of the animals as a calming measure) and to detail a simple method of quantifying the response to a given stressor by direct measurement of levels of the stress hormones adrenocorticotropic hormone (ACTH) and corticosterone.

Paternal care paradoxically increases offspring seizure susceptibility in the El mouse model of epilepsy

The El mouse is a model of idiopathic epilepsy in which seizures emerge on Postnatal Days (PNDs) 80-90, although time to first seizure can be modified by experiential factors including handling during development and history of past seizures. This study tested the hypothesis that a significant increase in the amount of parental investment would impact seizure susceptibility in adult El offspring. The study used a single dam control, in which the litter was reared by a female biological parent, and a biparental experimental group, in which both biological parents reared the litter. Components of parental care and pup body weights were quantified on PNDs 2-21, and adult offspring were examined using a handling-induced seizure susceptibility (HISS) test on PNDs 80-90 to assess the long-term impact of alterations in the perinatal environment. As expected, presence of both parents did increase parental/pup contact time by 350% relative to single-mother parenting and also reduced body weight, an index of perinatal stressor exposure, in already underweight El offspring. Accordingly, HISS testing of adult El offspring revealed a deleterious effect of biparental rearing, which increased seizure incidence to 30% relative to 0% for the single dam condition. These results suggest that the presence of a second care provider in addition to the dam constitutes a form of stressor exposure in El pups and, as a consequence, reduces the time to first seizure in genetically susceptible offspring.

Seizure susceptibility and locus ceruleus activation are reduced following environmental enrichment in an animal model of epilepsy

Alterations in the complexity of social and physical housing environments modulate seizure susceptibility in animal models of epilepsy. The studies described here tested the hypothesis that environmental enrichment would delay seizure onset in the epileptic (El) mouse. Neural activation measured via cFos expression, accumulation of the stress neuropeptide corticotropin-releasing factor (CRF), and behavioral seizure susceptibility were quantified in El mice to better understand the mechanisms of ictogenesis. Enrichment housing of El mice from Postnatal Days 21 to 49 produced a 100% decrease in seizure susceptibility relative to El controls. cFos expression increased in the primary motor cortex, locus ceruleus, and hippocampus of El mice relative to ddY controls, an effect attenuated by enrichment housing. CRF levels were elevated by enrichment in the hippocampus of ddY mice only. This study provides evidence that enrichment housing delays the onset of seizure susceptibility in El mice while altering the neuronal and stress-related responses in seizure-associated regions of the El brain.

Cognitive and magnetic resonance volumetric abnormalities in new-onset pediatric epilepsy

This paper addresses the issue of cognitive morbidity and abnormalities in quantitative MR volumetric in children with new and recent onset idiopathic epilepsy. The available literature suggests that mild diffuse cognitive problems are evident in children with new onset epilepsy in the context of intact whole brain and lobar volumetrics. Subsets of children can be identified with salient academic and volumetric abnormalities. These findings represent the baseline upon which any subsequent effects of chronic epilepsy may accrue.

Behavioral alterations in the pilocarpine model of temporal lobe epilepsy in mice

Psychiatric disorders frequently occur in patients with epilepsy, but the relationship between epilepsy and psychopathology is poorly understood. Frequent comorbidities in epilepsy patients comprise major depression, anxiety disorders, psychosis and cognitive dysfunction. Animal models of epilepsy, such as the pilocarpine model of acquired epilepsy, are useful to study the relationship between epilepsy and behavioral dysfunctions. However, despite the advantages of mice in studying the genetic underpinning of behavioral alterations in epilepsy, mice have only rarely been used to characterize behavioral correlates of epilepsy. This prompted us to study the behavioral and cognitive alterations developing in NMRI mice in the pilocarpine model of epilepsy, using an anxiety test battery as well as tests for depression, drug-induced psychosis, spatial memory, and motor functions. In order to ensure the occurrence of status epilepticus (SE) and decrease mortality, individual dosing of pilocarpine was performed by ramping up the dose until onset of SE. This protocol was used for studying the consequences of SE, i.e. hippocampal damage, incidence of epilepsy with spontaneous recurrent seizures, and behavioral alterations. SE was terminated by diazepam after either 60, 90 or 120 min. All mice that survived SE developed epilepsy, but the severity of hippocampal damage varied depending on SE length. In all anxiety tests, except the elevated plus maze test, epileptic mice exhibited significant increases of anxiety-related behavior. Surprisingly, a decrease in depression-like behavior was observed in the forced swimming and tail suspension tests. Furthermore, epileptic mice were less sensitive than controls to most of the behavioral effects induced by MK-801 (dizocilpine). Learning and memory were impaired in epileptic mice irrespective of SE duration. Thus, the pilocarpine-treated mice seem to reflect several of the behavioral and cognitive disturbances that are associated with epilepsy in humans. This makes these animals an ideal model to study the neurobiological mechanisms underlying the association between epilepsy and psychopathology.

Epilepsy

PURPOSE OF REVIEW

To provide a critical review of studies published between December 2005 and November 2006, and detect the advances of basic and clinical research in epilepsy.

RECENT FINDINGS

The complexity of the mechanisms underlying epileptogenesis and drug resistance was repeatedly highlighted. Seizure diagnosis and classification are still difficult, despite the use of valid and reliable instruments. Even well defined epilepsy syndromes may exhibit complex genetic patterns and atypical electroencephalogram features. Low prevalence rates of active epilepsy have been reported from several countries, suggesting underreporting for sociocultural reasons. Several pregnancy and neonatal factors can be found to increase the risk of epilepsy when accurate data are available from well defined populations. Early remission of seizures does not always predict terminal remission after prolonged follow-up. Cognitive regression may be associated with the presence of interictal electroencephalographic epileptiform abnormalities. A Cochrane review showed lamotrigine to be less frequently withdrawn than carbamazepine. However, these findings are contrasted by clinical practice, which showed no individual drug to be more likely to confer seizure freedom than any other.

SUMMARY

Recent research highlights the complexity of the mechanisms of epileptogenesis and drug response, and the difficulties with the classification of epilepsy into separate phenotypic categories.

Seizure prophylaxis in an animal model of epilepsy by dietary fluoxetine supplementation

Clinical and animal model evidence suggests that selective serotonin reuptake inhibitors (SSRIs) act as anticonvulsants. The present studies tested the possibility that the El mouse model of genetically predisposed/handling-triggered epilepsy would exhibit fewer seizures following SSRI treatment via dietary fluoxetine adulteration. In particular, potential bioenergetic and neural mechanisms for anticonvulsant efficacy of fluoxetine were explored using food intake/body weight monitoring and quantification of brain serotonin transporter protein. El mice consuming a chow diet ad libitum or yoked in quantity to fluoxetine diet intake exhibited seizure incidence of 40% in response to tail-suspension handling, whereas seizures were abolished (0%) among El mice consuming a fluoxetine-adultered diet over 7 days. A 3 day period of fluoxetine administration was insufficient to exert anticonvulsant efficacy and all treatment groups exhibited the same circadian locomotor activity patterns at the time of seizure susceptibility testing. Bioenergetic factors could not account for the anticonvulsant efficacy of fluoxetine since yoked diet controls with matched food intake, body weight change and blood glucose levels exhibited the same 40% seizure incidence as ad libitum chow controls. Importantly, the 7 day period of dietary fluoxetine exposure was effective in selectively reducing cell density in the parietal cortex and increasing serotonin transporter protein content in the nucleus accumbens. Taken together, these results suggest that dietary fluoxetine supplementation abolishes handling-induced seizure susceptibility in El mice via a neural remodeling mechanism independent of energy balance.

Short-term social recognition memory deficit and atypical social and physiological stressor reactivity in seizure-susceptible El mice

The present studies characterize working memory capabilities in the El mouse model of epilepsy using a species-typical social recognition memory task. As the El mouse exhibits a stress hyper-reactivity phenotype, the impact of hypertonic saline consumption, a memory modulatory treatment, upon social recognition performance was also examined. The hypotheses under test were: (1) that seizure susceptible El mice would perform poorly in the short-term working memory task relative to seizure resistant ddY controls, and (2) that the behavioral and neural responses to stressor exposure would be atypical in El mice. Results revealed a short-term working memory deficit and altered reactivity to social, environmental, and physiological stressors in El mice. In Experiment 1, El mice exhibited poor sociability and decreased olfactory investigation times, both anxiogenic-like traits, compared to ddY controls. In Experiment 2, El mice exhibited poor working memory performance compared to capable performance in ddY controls. Social recognition memory in ddY mice was abolished, however, by salt-loading whereas El mice were unaffected by exposure to this physiological stressor. In Experiment 3, all salt-loaded mice exhibited enhanced brain stress neuropeptide (corticotropin releasing factor-CRF) content, and salt-loaded El mice exhibited a 70% reduction in handling-induced seizures. These findings suggest that El mice exhibit high emotionality as well as atypical reactions to stressor exposure, and that these characteristics impact social working memory performance and seizure susceptibility.

Routine tail suspension husbandry facilitates onset of seizure susceptibility in EL mice

PURPOSE

Tail suspension can elicit seizures in susceptible EL mice, a model of idiopathic, multifactorial epilepsy. Further, repeated tail suspension hastens the lifetime onset of seizure susceptibility in these mice. The present study tested the hypothesis that curtailing human handling during development would delay the onset of seizure susceptibility relative to EL mice handled regularly by using tail suspension for standard laboratory husbandry.

METHODS

Control mice were handled by the tail for bedding changes, whereas unhandled mice bedding was changed by using specially designed connector cages that allowed mice to transfer without handling to a cage containing clean bedding. Seizure susceptibility was tested beginning at 70, 80, 90, 100, or 140 days of age by using a handling-induced seizure-susceptibility paradigm.

RESULTS

Among handled mice, more than half of the sample exhibited seizures by age 80 days relative to fewer than one fourth of unhandled mice. In addition, each group was tested a second time 10 days after the initial seizure-susceptibility test to detect potential experience-induced increases in seizure susceptibility. Once again, a higher frequency of handled mice expressed seizures at significantly younger ages relative to unhandled mice.

CONCLUSIONS

Although it was already known that repeated tail suspension could speed the onset of seizure susceptibility in EL mice, the present results are the first to demonstrate the converse finding that decreasing routine human handling can delay significantly the onset of seizure susceptibility. This suggests that removal of nonconsensual aspects of human-animal contact may delay or prevent the onset of seizure susceptibility.