A genetic epilepsy rat model displays endophenotypes of psychosis

A quantitative and T-pattern analysis of anxiety-like behavior in male GAERS, NEC, and Wistar rats bred under the same conditions, against a commercially available Wistar control group in the hole board and elevated plus maze tests

AIM

The Genetic Absence Epilepsy Rats from Strasbourg (GAERS) are an inbred polygenic model of childhood absence epilepsy (CAE), which, as their non-epileptic control (NEC) rats, are derived from Wistar rats. While the validity of GAERS in reproducing absence seizures is well established, its use as a model for CAE psychiatric comorbidities has been subject to conflicting findings. Differences in colonies, experimental procedures, and the use of diverse controls from different breeders may account for these disparities. Therefore, in this study, we compared GAERS, NEC, and Wistar bred in the same animal facility with commercially available Wistar (Cm Wistar) as a third control.

METHODS

We performed hole board (HB) and elevated plus maze (EPM) tests that were analyzed with standard quantitative and T-pattern analysis in male, age-matched Cm Wistar and GAERS, NEC, and Wistar, bred under the same conditions, to rule out the influence of different housing factors and provide extra information on the structure of anxiety-like behavior of GAERS rats.

RESULTS

Quantitative analysis showed that GAERS and NEC had similar low anxiety-like behavior when compared to Cm Wistar but not to Wistar rats, although a higher hole-focused exploration was revealed in NEC. T-pattern analysis showed that GAERS, NEC, and Wistar had a similar anxiety status, whereas GAERS and NEC exhibited major differences with Cm Wistar but not Wistar rats. EPM results indicated that GAERS and NEC also have similar low anxiety compared to Cm Wistar and/or Wistar rats. Nevertheless, the analysis of the T-pattern containing open-arm entry showed GAERS and Wistar to be less anxious than NEC and Cm Wistar rats.

CONCLUSION

To summarize, comorbid anxiety may not be present in male GAERS rats. This study also highlighted the importance of including a control Wistar group bred under the same conditions when evaluating their behavior, as using Wistar rats from commercial breeders can lead to misleading results.

Accelerated high frequency rTMS induces time-dependent dopaminergic alterations: a DaTSCAN brain imaging study in healthy beagle dogs

Aim

The neurobiological effects of repetitive transcranial magnetic stimulation are believed to run in part through the dopaminergic system. Accelerated high frequency rTMS (aHF-rTMS), a new form of stimuli delivery, is currently being tested for its usefulness in treating human and canine mental disorders. However, the short-and long-term neurobiological effects are still unclear, including the effects on the dopaminergic system. In aHF-rTMS, multiple sessions are delivered within 1 day instead of one session per day, not only to accelerate the time to response but also to increase clinical efficacy. To gain more insight into the neurobiology of aHF-rTMS, we investigated whether applying five sessions in 1 day has direct and/or delayed effects on the dopamine transporter (DAT), and on dopamine metabolites of cerebrospinal fluid (CSF) in beagles.

Materials and methods

Thirteen beagles were randomly divided into two groups: five active stimulation sessions (n = 9), and 5 sham stimulation sessions (n = 4). Using DaTSCAN, DAT binding indices (BI) were obtained at baseline, after 1 day, 1 month, and 3 months post stimulation. CSF samples were collected after each scan.

Results

Active aHF-rTMS significantly reduced striatal DAT BI 1 day post-active stimulation session (p < 0.01), and the effect lasted to 1 month (p < 0.01). No significant DAT BI change was found in sham group. No significant changes in dopamine metabolites of CSF were found.

Conclusion

Although no significant effects on CSF dopamine metabolites were observed, five sessions of active aHF-rTMS significantly decreased striatal DAT BI after 1 day and up to 1 month post stimulation, indicating immediate and delayed effects on the brain dopaminergic system. Our findings in healthy beagles further substantiate the assumption that (a)HF-rTMS affects the brain dopaminergic system and it may pave the way to apply (a)HF-rTMS treatment in behaviorally disturbed dogs.

Metyrapone abolishes spike-wave discharge seizures in genetic absence epilepsy rats from Strasbourg by reducing stress hormones

OBJECTIVE

Stress is one of the most commonly reported triggers for seizures in patients with epilepsy, although the mechanisms that mediate this effect are not established. The clinical evidence supporting this is derived from patients' subjective experience of stress, and how this influences their own seizures. Animal models can be used to explore this phenomenon in controlled environments, free from subjective bias. Here, we used genetic absence epilepsy rats from Strasbourg (GAERS), a genetic rat model of absence epilepsy, to explore the influence of stress and stress hormones on spontaneous seizures.

METHODS

Adult male GAERS (n = 38) and nonepileptic control (NEC) rats (n = 4) were used. First, rats were subjected to 30-min restraint stress to assess hypothalamic-pituitary-adrenal axis function. Next, we assessed the effects of 30-min noise stress, and cage tilt stress, on spike-wave discharge seizures in GAERS. We then performed pharmacological experiments to assess the direct effects of stress hormones on seizures, including corticosterone, metyrapone, and deoxycorticosterone.

RESULTS

GAERS exhibited elevated baseline corticosterone levels, compared to NEC rats. Noise stress and cage tilt stress significantly enhanced seizure incidence (p < .05), but only during stress periods. Exogenous corticosterone administration also significantly increased seizure occurrence (p < .05). Metyrapone, an inhibitor of corticosterone synthesis, completely abolished seizures in GAERS, and seizures remained suppressed for >2 h. However, deoxycorticosterone, the precursor of corticosterone, increased seizures.

SIGNIFICANCE

These results suggest that GAERS exhibit elevations in stress hormones, and this may contribute to seizures. Inhibiting corticosterone synthesis with metyrapone prevents seizures in GAERS, and shows potential for repurposing this drug as a future antiseizure medication.

Cannabinoid 1/2 Receptor Activation Induces Strain-Dependent Behavioral and Neurochemical Changes in Genetic Absence Epilepsy Rats From Strasbourg and Non-epileptic Control Rats

Childhood absence epilepsy (CAE) is characterized by absence seizures, which are episodes of lack of consciousness accompanied by electrographic spike-wave discharges. About 60% of children and adolescents with absence seizures are affected by major neuropsychological comorbidities, including anxiety. Endocannabinoids and monoamines are likely involved in the pathophysiology of these CAE psychiatric comorbidities. Here, we show that the synthetic cannabinoid receptor type 1/2 (CB1/2R) agonist WIN 55,212-2 (2 mg/kg) has a strain-dependent effect on anxiety-like and motor behavior when assess in the hole board test and cerebral monoaminergic levels in Genetic Absence Epilepsy Rats from Strasbourg (GAERS) and their non-epileptic control (NEC) rat strain. Using quantitative and Temporal pattern (T-pattern) analyses, we found that WIN 55,212-2 did not affect the emotional status of GAERS, but it was anxiolytic in NEC. Conversely, WIN 55,212-2 had a sedative effect in GAERS but was ineffective in NEC. Moreover, vehicle-treated GAERS more motivated to explore by implementing more complex and articulated strategies. These behavioral changes correlate with the reduction of 5-HT in the hippocampus and substantia nigra (SN) and noradrenaline (NA) in the entopeduncular nucleus (EPN) in vehicle-treated GAERS compared to NEC rats, which could contribute to their low anxiety status and hypermotility, respectively. On the other hand, the increased level of NA in the EPN and 5-HT in the SN is consistent with an activation of the basal ganglia output-mediated motor suppression observed in WIN 55,212-2-treated GAERS rats. These data support the view of a strain-dependent alteration of the endocannabinoid system in absence epilepsy by adding evidence of a lower emotional responsiveness and a basal ganglia hypersensitivity to cannabinoids in GAERS compared to NEC rats.

Retrosplenial Cortex Contributes to Network Changes during Seizures in the GAERS Absence Epilepsy Rat Model

Resting state-fMRI was performed to explore brain networks in Genetic Absence Epilepsy Rats from Strasbourg and in nonepileptic controls (NEC) during monitoring of the brain state by simultaneous optical Ca2+-recordings. Graph theoretical analysis allowed for the identification of acute and chronic network changes and revealed preserved small world topology before and after seizure onset. The most prominent acute change in network organization during seizures was the segregation of cortical regions from the remaining brain. Stronger connections between thalamic with limbic regions compared with preseizure state indicated network regularization during seizures. When comparing between strains, intrathalamic connections were prominent in NEC, on local level represented by higher thalamic strengths and hub scores. Subtle differences were observed for retrosplenial cortex (RS), forming more connections beyond cortex in epileptic rats, and showing a tendency to lateralization during seizures. A potential role of RS as hub between subcortical and cortical regions in epilepsy was supported by increased numbers of parvalbumin-positive (PV+) interneurons together with enhanced inhibitory synaptic activity and neuronal excitability in pyramidal neurons. By combining multimodal fMRI data, graph theoretical methods, and electrophysiological recordings, we identified the RS as promising target for modulation of seizure activity and/or comorbidities.

Genetically Epilepsy-Prone Rats Display Anxiety-Like Behaviors and Neuropsychiatric Comorbidities of Epilepsy

Epilepsy is associated with a variety of neuropsychiatric comorbidities, including both anxiety and depression. Despite high occurrences of depression and anxiety seen in human epilepsy populations, little is known about the etiology of these comorbidities. Experimental models of epilepsy provide a platform to disentangle the contribution of acute seizures, genetic predisposition, and underlying circuit pathologies to anxious and depressive phenotypes. Most studies to date have focused on comorbidities in acquired epilepsies; genetic models, however, allow for the assessment of affective phenotypes that occur prior to onset of recurrent seizures. Here, we tested male and female genetically epilepsy-prone rats (GEPR-3s) and Sprague-Dawley controls in a battery of tests sensitive to anxiety-like and depressive-like phenotypes. GEPR-3s showed increased anxiety-like behavior in the open field test, elevated plus maze, light-dark transition test, and looming threat test. Moreover, GEPR-3s showed impaired prepulse inhibition of the acoustic startle reflex, decreased sucrose preference index, and impaired novel object recognition memory. We also characterized defense behaviors in response to stimulation thresholds of deep and intermediate layers of the superior colliculus (DLSC), but found no difference between strains. In sum, GEPR-3s showed inherited anxiety, an effect that did not differ significantly between sexes. The anxiety phenotype in adult GEPR-3s suggests strong genetic influences that may underlie both the seizure disorder and the comorbidities seen in epilepsy.

T-type calcium channels in the orbitofrontal cortex mediate sensory integration as measured using a spontaneous oddity task in rats

The roles of low-voltage-activated (T-type) calcium channels in brain diseases have been studied extensively. Less is known regarding the involvement of T-type channels in cognition and behavior. Sensory integration (SI) is a cognitive process whereby the brain uses unimodal or multimodal sensory features to create a comprehensive representation of the environment. The multisensory object oddity (MSO) task assesses SI using combinations of sensory features of objects, either in the same or different sensory modalities. The regulation of SI involves the orbitofrontal cortex (OFC), an area which shows high levels of T-type calcium channel expression. We tested the effects of blocking T-type calcium channels on the MSO task with the selective T-type antagonist, Z944 (5 mg/kg; i.p. systemic; 100 or 500 µM OFC infusion), in male Long Evans rats. With systemic treatment, Z944 impaired the visual and visual-olfactory versions of the task. Infusion of 100 and 500 µM Z944 produced deficits in the olfactory version of the task. In addition, only vehicle-infused, but not Z944-infused, rats showed significant performance above chance for all task variants. Thus, the present results suggest that T-type calcium channels in OFC are involved in SI of features in an oddity task. Given that unimodal SI was disrupted by OFC infusions of Z944, the deficits in the multimodal task must be interpreted with caution. As SI is disrupted in psychiatric disorders, further investigations elucidating the brain regions implicated in SI regulation by T-type calcium channels may help inform therapeutic development for those suffering from SI impairments.

Neurocognitive Comorbidities in Pediatric Epilepsy: Lessons in the Laboratory and Clinical Profile

Children with epilepsy are at risk for a variety of neurocognitive comorbidities. Animal models have increased our understanding about the neurobiological mechanisms underlying the association between seizures and these comorbidities. This article starts with an overview of the current data on animal model research, studying the influence of early-life seizures, followed by a summary of potential cellular and molecular mechanisms by which seizures can affect cognitive development. We then describe specific abnormal neuropsychological profiles that accompany specific pediatric epilepsy syndromes. Finally, we offer a potential guideline to the treatment and management of children with epilepsy and its neurocognitive comorbidities.

Dissociable effects of the d- and l- enantiomers of govadine on the disruption of prepulse inhibition by MK-801 and apomorphine in male Long-Evans rats

RATIONALE

The search for novel antipsychotic drugs to treat schizophrenia is driven by the poor treatment efficacy, serious side effects, and poor patient compliance of current medications. Recently, a class of compounds known as tetrahydroprotoberberines, which includes the compound _d,l-govadine, have shown promise in preclinical rodent tests relevant to schizophrenia. To date, the effect of govadine on prepulse inhibition (PPI), a test for sensorimotor gating commonly used to assess the effects of putative treatments for schizophrenia, has not been determined.

OBJECTIVES

The objective of the present study was to determine the effects of each enantiomer of govadine (_d- and _l-govadine) on PPI alone and its disruption by the distinct pharmacological compounds apomorphine and MK-801.

METHODS

Male Long-Evans rats were treated systemically with _d- or _l-govadine and apomorphine or MK-801 prior to PPI. The PPI paradigm employed here included parametric manipulations of the prepulse intensity and the interval between the prepulse and pulse.

RESULTS

Acute MK-801 (0.15 mg/kg) significantly increased the startle response to startle pulses alone, while both MK-801 and apomorphine (0.2 mg/kg) significantly increased reactivity to prepulse-alone trials. Both MK-801 and apomorphine disrupted PPI. In addition, _d-govadine alone significantly disrupted PPI in the apomorphine experiment. Pretreatment with _l-, but not _d-, govadine (1.0 mg/kg) blocked the effect of apomorphine and MK-801 on PPI. Treatment of rats with _l-govadine alone (0.3, 1.0, 3.0 mg/kg) also dose-dependently increased PPI.

CONCLUSIONS

Given the high affinity of _l-govadine for dopamine D2 receptors, these results suggest that further testing of _l-govadine as an antipsychotic is warranted.

Persistent Interictal Musical Hallucination in a Patient With Mesial Temporal Sclerosis-Related Epilepsy: First Case Report and Etiopathological Hypothesis

Musical hallucination is a disorder of complex sound processing of instrumental music, songs, choirs, chants, etc. The underlying pathologies include moderate to severe acquired hearing loss (the auditory equivalent of Charles Bonnet syndrome), psychiatric illnesses (depression, schizophrenia), drug intoxication (benzodiazepines, salicylate, pentoxifylline, propranolol), traumatic lesions along the acoustic pathways, and epilepsy. The hallucinations are most likely to begin late in life; 70% of patients are women. Musical hallucination has no known specific therapy. Treating the underlying cause is the most effective approach; neuroleptic and antidepressant medications have only rarely succeeded.Musical hallucination in epilepsy typically presents as simple partial seizures originating in the lateral temporal cortex. To our knowledge, no formal report of musical hallucination in the interictal state has been published before. In contrast, other interictal psychotic features are a relatively common complication, especially in patients with long-standing drug-resistant epilepsy.We describe a 62-year-old woman with a long history of mesial temporal lobe epilepsy whose musical hallucination was solely interictal. We speculate on the possible link between temporal epilepsy and her hallucination. We hypothesize that, as a result of her epileptic activity-induced damage, an imbalance developed between the excitatory and inhibitory projections connecting the mesial temporal cortex to the other auditory structures. These structures may have generated hyperactivity in the lateral temporal cortex through a "release" mechanism that eventually resulted in musical hallucination.

WONOEP appraisal: Biomarkers of epilepsy-associated comorbidities

Neurologic and psychiatric comorbidities are common in patients with epilepsy. Diagnostic, predictive, and pharmacodynamic biomarkers of such comorbidities do not exist. They may share pathogenetic mechanisms with epileptogenesis/ictogenesis, and as such are an unmet clinical need. The objectives of the subgroup on biomarkers of comorbidities at the XIII Workshop on the Neurobiology of Epilepsy (WONOEP) were to present the state-of-the-art recent research findings in the field that highlighting potential biomarkers for comorbidities in epilepsy. We review recent progress in the field, including molecular, imaging, and genetic biomarkers of comorbidities as discussed during the WONOEP meeting on August 31-September 4, 2015, in Heybeliada Island (Istanbul, Turkey). We further highlight new directions and concepts from studies on comorbidities and potential new biomarkers for the prediction, diagnosis, and treatment of epilepsy-associated comorbidities. The activation of various molecular signaling pathways such as the "Janus Kinase/Signal Transducer and Activator of Transcription," "mammalian Target of Rapamycin," and oxidative stress have been shown to correlate with the presence and severity of subsequent cognitive abnormalities. Furthermore, dysfunction in serotonergic transmission, hyperactivity of the hypothalamic-pituitary-adrenocortical axis, the role of the inflammatory cytokines, and the contributions of genetic factors have all recently been regarded as relevant for understanding epilepsy-associated depression and cognitive deficits. Recent evidence supports the utility of imaging studies as potential biomarkers. The role of such biomarker may be far beyond the diagnosis of comorbidities, as accumulating clinical data indicate that comorbidities can predict epilepsy outcomes. Future research is required to reveal whether molecular changes in specific signaling pathways or advanced imaging techniques could be detected in the clinical settings and correlate with epilepsy-associated comorbidities. A reliable biomarker will allow a more accurate diagnosis and improved treatment of epilepsy-associated comorbidities.

Monoaminergic Mechanisms in Epilepsy May Offer Innovative Therapeutic Opportunity for Monoaminergic Multi-Target Drugs

A large body of experimental and clinical evidence has strongly suggested that monoamines play an important role in regulating epileptogenesis, seizure susceptibility, convulsions, and comorbid psychiatric disorders commonly seen in people with epilepsy (PWE). However, neither the relative significance of individual monoamines nor their interaction has yet been fully clarified due to the complexity of these neurotransmitter systems. In addition, epilepsy is diverse, with many different seizure types and epilepsy syndromes, and the role played by monoamines may vary from one condition to another. In this review, we will focus on the role of serotonin, dopamine, noradrenaline, histamine, and melatonin in epilepsy. Recent experimental, clinical, and genetic evidence will be reviewed in consideration of the mutual relationship of monoamines with the other putative neurotransmitters. The complexity of epileptic pathogenesis may explain why the currently available drugs, developed according to the classic drug discovery paradigm of "one-molecule-one-target," have turned out to be effective only in a percentage of PWE. Although, no antiepileptic drugs currently target specifically monoaminergic systems, multi-target directed ligands acting on different monoaminergic proteins, present on both neurons and glia cells, may represent a new approach in the management of seizures, and their generation as well as comorbid neuropsychiatric disorders.

Integrative properties and transfer function of cortical neurons initiating absence seizures in a rat genetic model

KEY POINTS

Absence seizures are accompanied by spike-and-wave discharges in cortical electroencephalograms. These complex paroxysmal activities, affecting the thalamocortical networks, profoundly alter cognitive performances and preclude conscious perception. Here, using a well-recognized genetic model of absence epilepsy, we investigated in vivo how information processing was impaired in the ictogenic neurons, i.e. the population of cortical neurons responsible for seizure initiation. In between seizures, ictogenic neurons were more prone to generate bursting activity and their firing response to weak depolarizing events was considerably facilitated compared to control neurons. In the course of seizures, information processing became unstable in ictogenic cells, alternating between an increased and a decreased responsiveness to excitatory inputs, depending on the spike and wave patterns. The state-dependent modulation in the excitability of ictogenic neurons affects their inter-seizure transfer function and their time-to-time responsiveness to incoming inputs during absences.

ABSTRACT

Epileptic seizures result from aberrant cellular and/or synaptic properties that can alter the capacity of neurons to integrate and relay information. During absence seizures, spike-and-wave discharges (SWDs) interfere with incoming sensory inputs and preclude conscious experience. The Genetic Absence Epilepsy Rats from Strasbourg (GAERS), a well-established animal model of absence epilepsy, allows exploration of the cellular basis of this impaired information processing. Here, by combining in vivo electrocorticographic and intracellular recordings from GAERS and control animals, we investigated how the pro-ictogenic properties of seizure-initiating cortical neurons modify their integrative properties and input-output operation during inter-ictal periods and during the spike (S-) and wave (W-) cortical patterns alternating during seizures. In addition to a sustained depolarization and an excessive firing rate in between seizures, ictogenic neurons exhibited a pronounced hyperpolarization-activated depolarization compared to homotypic control neurons. Firing frequency versus injected current relations indicated an increased sensitivity of GAERS cells to weak excitatory inputs, without modifications in the trial-to-trial variability of current-induced firing. During SWDs, the W-component resulted in paradoxical effects in ictogenic neurons, associating an increased membrane input resistance with a reduction in the current-evoked firing responses. Conversely, the collapse of cell membrane resistance during the S-component was accompanied by an elevated current-evoked firing relative to W-sequences, which remained, however, lower compared to inter-ictal periods. These findings show a dynamic modulation of ictogenic neurons' intrinsic properties that may alter inter-seizure cortical function and participate in compromising information processing in cortical networks during absences.

The T-type calcium channel antagonist Z944 rescues impairments in crossmodal and visual recognition memory in Genetic Absence Epilepsy Rats from Strasbourg

Childhood absence epilepsy (CAE) is often comorbid with behavioral and cognitive symptoms, including impaired visual memory. Genetic Absence Epilepsy Rats from Strasbourg (GAERS) is an animal model closely resembling CAE; however, cognition in GAERS is poorly understood. Crossmodal object recognition (CMOR) is a recently developed memory task that examines not only purely visual and tactile memory, but also requires rodents to integrate sensory information about objects gained from tactile exploration to enable visual recognition. Both the visual and crossmodal variations of the CMOR task rely on the perirhinal cortex, an area with dense expression of T-type calcium channels. GAERS express a gain-in-function missense mutation in the Cav3.2 T-type calcium channel gene. Therefore, we tested whether the T-type calcium channel blocker Z944 dose dependently (1, 3, 10mg/kg; i.p.) altered CMOR memory in GAERS compared to the non-epileptic control (NEC) strain. GAERS demonstrated recognition memory deficits in the visual and crossmodal variations of the CMOR task that were reversed by the highest dose of Z944. Electroencephalogram recordings determined that deficits in CMOR memory in GAERS were not the result of seizures during task performance. In contrast, NEC showed a decrease in CMOR memory following Z944 treatment. These findings suggest that T-type calcium channels mediate CMOR in both the GAERS and NEC strains. Future research into the therapeutic potential of T-type calcium channel regulation may be particularly fruitful for the treatment of CAE and other disorders characterized by visual memory deficits.

Environmental enrichment imparts disease-modifying and transgenerational effects on genetically-determined epilepsy and anxiety

INTRODUCTION

The absence epilepsies are presumed to be caused by genetic factors, but the influence of environmental exposures on epilepsy development and severity, and whether this influence is transmitted to subsequent generations, is not well known. We assessed the effects of environmental enrichment on epilepsy and anxiety outcomes in multiple generations of GAERS - a genetic rat model of absence epilepsy that manifests comorbid elevated anxiety-like behaviour.

METHODS

GAERS were exposed to environmental enrichment or standard housing beginning either prior to, or after epilepsy onset, and underwent EEG recordings and anxiety testing. Then, we exposed male GAERS to early enrichment or standard housing and generated F1 progeny, which also underwent EEG recordings. Hippocampal CRH mRNA expression and DNA methylation were assessed using RT-PCR and pyrosequencing, respectively.

RESULTS

Early environmental enrichment delayed the onset of epilepsy in GAERS, and resulted in fewer seizures in adulthood, compared with standard housed GAERS. Enrichment also reduced the frequency of seizures when initiated in adulthood. Anxiety levels were reduced by enrichment, and these anti-epileptogenic and anxiolytic effects were heritable into the next generation. We also found reduced expression of CRH mRNA in GAERS exposed to enrichment, but this was not due to changes in DNA methylation.

CONCLUSIONS

Environmental enrichment produces disease-modifying effects on genetically determined absence epilepsy and anxiety, and these beneficial effects are transferable to the subsequent generation. Reduced CRH expression was associated with these phenotypic improvements. Environmental stimulation holds promise as a naturalistic therapy for genetically determined epilepsy which may benefit subsequent generations.

Cognitive deficits and brain myo-Inositol are early biomarkers of epileptogenesis in a rat model of epilepsy

One major unmet clinical need in epilepsy is the identification of therapies to prevent or arrest epilepsy development in patients exposed to a potential epileptogenic insult. The development of such treatments has been hampered by the lack of non-invasive biomarkers that could be used to identify the patients at-risk, thereby allowing to design affordable clinical studies. Our goal was to test the predictive value of cognitive deficits and brain astrocyte activation for the development of epilepsy following a potential epileptogenic injury. We used a model of epilepsy induced by pilocarpine-evoked status epilepticus (SE) in 21-day old rats where 60-70% of animals develop spontaneous seizures after around 70days, although SE is similar in all rats. Learning was evaluated in the Morris water-maze at days 15 and 65 post-SE, each time followed by proton magnetic resonance spectroscopy for measuring hippocampal myo-Inositol levels, a marker of astrocyte activation. Rats were video-EEG monitored for two weeks at seven months post-SE to detect spontaneous seizures, then brain histology was done. Behavioral and imaging data were retrospectively analysed in epileptic rats and compared with non-epileptic and control animals. Rats displayed spatial learning deficits within three weeks from SE. However, only epilepsy-prone rats showed accelerated forgetting and reduced learning rate compared to both rats not developing epilepsy and controls. These deficits were associated with reduced hippocampal neurogenesis. myo-Inositol levels increased transiently in the hippocampus of SE-rats not developing epilepsy while this increase persisted until spontaneous seizures onset in epilepsy-prone rats, being associated with a local increase in S100β-positive astrocytes. Neuronal cell loss was similar in all SE-rats. Our data show that behavioral deficits, together with a non-invasive marker of astrocyte activation, predict which rats develop epilepsy after an acute injury. These measures have potential clinical relevance for identifying individuals at-risk for developing epilepsy following exposure to epileptogenic insults, and consequently, for designing adequately powered antiepileptogenesis trials.

Shift in interictal relative gamma power as a novel biomarker for drug response in two mouse models of absence epilepsy

OBJECTIVE

Two monogenic mouse models of childhood absence epilepsy, stargazer and tottering, differ strikingly in their response to N-methyl-d-aspartate (NMDA) receptor blockade. We sought to evaluate the change in interictal relative gamma power as a reliable biomarker for this gene-linked antiepileptic drug (AED) response.

METHODS

The effects of AEDs on absolute and relative (to the total) power of frequencies between 2 and 300 Hz were analyzed within the interictal electroencephalogram (EEG) and correlated with antiseizure efficacy in awake behaving stargazer, tottering, and wild-type (WT) littermate control mice.

RESULTS

At baseline, we found a significant absolute as well as relative augmentation of 16-41 Hz power in stargazer compared to both tottering and WT mice. In stargazer, the NMDA receptor-antagonist MK-801 (0.5 mg/kg) paradoxically exacerbates absence seizures but normalizes the augmented beta/gamma band of power to WT levels, suggesting that the elevation in 16- to 41-Hz power is an NMDA receptor-mediated network property. In contrast, ethosuximide (200 mg/kg) and 4-aminopyridine (2.5 mg/kg) reduce seizure activity and increase relative power within the gamma range in both stargazer and tottering mice. Intraperitoneal saline injection had no significant effect on either seizure frequency or relative gamma power. Along with results using carbamazepine and flupirtine, there was a strong inverse relationship between relative change in seizure duration and change in peak relative gamma power (r(2) = 0.726).

SIGNIFICANCE

In these two models of absence epilepsy, drugs that reduce relative gamma power are associated with an increase in seizures, whereas drugs that augment relative gamma power reduce seizures. Therefore, drug-induced modulation of relative gamma power may serve as a biomarker for AED efficacy in absence epilepsy. Given the relationship between gamma power and fast-spiking interneurons, these results also suggest that a drug's effect may in part be determined by its impact on specific inhibitory networks.

Neuregulin 1 expression and electrophysiological abnormalities in the Neuregulin 1 transmembrane domain heterozygous mutant mouse

Background

The Neuregulin 1 transmembrane domain heterozygous mutant (Nrg1 TM HET) mouse is used to investigate the role of Nrg1 in brain function and schizophrenia-like behavioural phenotypes. However, the molecular alterations in brain Nrg1 expression that underpin the behavioural observations have been assumed, but not directly determined. Here we comprehensively characterise mRNA Nrg1 transcripts throughout development of the Nrg1 TM HET mouse. In addition, we investigate the regulation of high-frequency (gamma) electrophysiological oscillations in this mutant mouse to associate molecular changes in Nrg1 with a schizophrenia-relevant neurophysiological profile.

Methods

Using exonic probes spanning the cysteine-rich, epidermal growth factor (EGF)-like, transmembrane and intracellular domain encoding regions of Nrg1, mRNA levels were measured using qPCR in hippocampus and frontal cortex from male and female Nrg1 TM HET and wild type-like (WT) mice throughout development. We also performed electrophysiological recordings in adult mice and analysed gamma oscillatory at baseline, in responses to auditory stimuli and to ketamine.

Results

In both hippocampus and cortex, Nrg1 TM HET mice show significantly reduced expression of the exon encoding the transmembrane domain of Nrg1 compared with WT, but unaltered mRNA expression encoding the extracellular bioactive EGF-like and the cysteine-rich (type III) domains, and development-specific and region-specific reductions in the mRNA encoding the intracellular domain. Hippocampal Nrg1 protein expression was not altered, but NMDA receptor NR2B subunit phosphorylation was lower in Nrg1 TM HET mice. We identified elevated ongoing and reduced sensory-evoked gamma power in Nrg1 TM HET mice.

Interpretation

We found no evidence to support the claim that the Nrg1 TM HET mouse represents a simple haploinsufficient model. Further research is required to explore the possibility that mutation results in a gain of Nrg1 function.

Assessing Susceptibility to Epilepsy in Three Rat Strains Using Brain Metabolic Profiling Based on HRMAS NMR Spectroscopy and Chemometrics

The possibility that a metabolomic approach can inform about the pathophysiology of a given form of epilepsy was addressed. Using chemometric analyses of HRMAS NMR data, we compared several brain structures in three rat strains with different susceptibilities to absence epilepsy: Genetic Absence Epilepsy Rats from Strasbourg (GAERS), Non Epileptic Control rats (NEC), and Wistar rats. Two ages were investigated: 14 days postnatal (P14) before the onset of seizures and 5 month old adults with fully developed seizures (Adults). The relative concentrations of 19 metabolites were assessed using (1)H HRMAS NMR experiments. Univariate and multivariate analyses including multiblock models were used to identify the most discriminant metabolites. A strain-dependent evolution of glutamate, glutamine, scyllo-inositol, alanine, and glutathione was highlighted during cerebral maturation. In Adults, data from somatosensory and motor cortices allowed discrimination between GAERS and NEC rats with higher levels of scyllo-inositol, taurine, and phosphoethanolamine in NEC. This epileptic metabolic phenotype was in accordance with current pathophysiological hypothesis of absence epilepsy (i.e., seizure-generating and control networks) and putative resistance of NEC rats and was observed before seizure onset. This methodology could be very efficient in a clinical context.

The prevalence of psychosis in epilepsy; a systematic review and meta-analysis

BACKGROUND

Epilepsy has long been considered to be a risk factor for psychosis. However there is a lack of consistency in findings across studies on the effect size of this risk which reflects methodological differences in studies and changing diagnostic classifications within neurology and psychiatry. The aim of this study was to assess the prevalence of psychosis in epilepsy and to estimate the risk of psychosis among individuals with epilepsy compared with controls.

METHODS

A systematic review and meta-analysis was conducted of all published literature pertaining to prevalence rates of psychosis in epilepsy using electronic databases PUBMED, OVIDMEDLINE, PsychINFO and Embase from their inception until September 2010 with the following search terms: prevalence, incidence, rate, rates, psychosis, schizophrenia, schizophreniform illness, epilepsy, seizures, temporal lobe epilepsy.

RESULTS

The literature search and search of reference lists yielded 215 papers. Of these, 58 (27%) had data relevant to the review and 157 were excluded following a more detailed assessment. 10% of the included studies were population based studies. The pooled odds ratio for risk of psychosis among people with epilepsy compared with controls was 7.8. The pooled estimate of prevalence of psychosis in epilepsy was found to be 5.6% (95% CI: 4.8-6.4). There was a high level of heterogeneity. The prevalence of psychosis in temporal lobe epilepsy was 7% (95% CI: 4.9-9.1). The prevalence of interictal psychosis in epilepsy was 5.2% (95% CI: 3.3-7.2). The prevalence of postictal psychosis in epilepsy was 2% (95% CI: 1.2-2.8).

CONCLUSIONS

Our systematic review found that up to 6% of individuals with epilepsy have a co-morbid psychotic illness and that patients have an almost eight fold increased risk of psychosis. The prevalence rate of psychosis is higher in temporal lobe epilepsy (7%). We suggest that further investigation of this association could give clues to the aetiology of psychosis.

The role of dopamine signaling in epileptogenesis

Clinical and experimental studies implicate most neuromodulatory systems in epileptogenesis. The dopaminergic system has a seizure-modulating effect that crucially depends on the different subtypes of dopamine (DA) receptors involved and the brain regions in which they are activated. Specifically, DA plays a major role in the control of seizures arising in the limbic system. Studies performed in a wide variety of animal models contributed to illustrate the opposite actions of D1-like and D2-like receptor signaling in limbic epileptogenesis. Indeed, signaling from D1-like receptors is generally pro-epileptogenic, whereas D2-like receptor signaling exerts an anti-epileptogenic effect. However, this view might appear quite simplistic as the complex neuromodulatory action of DA in the control of epileptogenesis likely requires a physiological balance in the activation of circuits modulated by these two major DA receptor subtypes, which determines the response to seizure-promoting stimuli. Here we will review recent evidences on the identification of molecules activated by DA transduction pathways in the generation and spread of seizures in the limbic system. We will discuss the intracellular signaling pathways triggered by activation of different DA receptors in relation to their role in limbic epileptogenesis, which lead to the activation of neuronal death/survival cascades. A deep understanding of the signaling pathways involved in epileptogenesis is crucial for the identification of novel targets for the treatment of epilepsy.

Issues related to symptomatic and disease-modifying treatments affecting cognitive and neuropsychiatric comorbidities of epilepsy

Many symptoms of neurologic or psychiatric illness--such as cognitive impairment, depression, anxiety, attention deficits, and migraine--occur more frequently in people with epilepsy than in the general population. These diverse comorbidities present an underappreciated problem for people with epilepsy and their caregivers because they decrease quality of life, complicate treatment, and increase mortality. In fact, it has been suggested that comorbidities can have a greater effect on quality of life in people with epilepsy than the seizures themselves. There is increasing recognition of the frequency and impact of cognitive and behavioral comorbidities of epilepsy, highlighted in the 2012 Institute of Medicine report on epilepsy. Comorbidities have also been acknowledged, as a National Institutes of Health (NIH) Benchmark area for research in epilepsy. However, relatively little progress has been made in developing new therapies directed specifically at comorbidities. On the other hand, there have been many advances in understanding underlying mechanisms. These advances have made it possible to identify novel targets for therapy and prevention. As part of the International League Against Epilepsy/American Epilepsy Society workshop on preclinical therapy development for epilepsy, our working group considered the current state of understanding related to terminology, models, and strategies for therapy development for the comorbidities of epilepsy. Herein we summarize our findings and suggest ways to accelerate development of new therapies. We also consider important issues to improve research including those related to methodology, nonpharmacologic therapies, biomarkers, and infrastructure.

Characterization of a dopamine transporter polymorphism and behavior in Belgian Malinois

BACKGROUND

The Belgian Malinois dog breed (MAL) is frequently used in law enforcement and military environments. Owners have reported seizures and unpredictable behavioral changes including dogs' eyes "glazing over," dogs' lack of response to environmental stimuli, and loss of behavioral inhibition including owner-directed biting behavior. Dogs with severe behavioral changes may be euthanized as they can represent a danger to humans and other dogs. In the dog, the dopamine transporter gene (DAT) contains a 38-base pair variable number tandem repeat (DAT-VNTR); alleles have either one or two copies of the 38-base pair sequence. The objective of this study was to assess frequency of DAT-VNTR alleles, and characterize the association between DAT-VNTR alleles and behavior in MAL and other breeds.

RESULTS

In an American sample of 280 dogs comprising 26 breeds, most breeds are predominantly homozygous for the DAT-VNTR two-tandem-repeat allele (2/2). The one-tandem-repeat allele is over-represented in American MAL (AM-MAL) (n = 144), both as heterozygotes (1/2) and homozygotes (1/1). All AM-MAL with reported seizures (n = 5) were 1/1 genotype. For AM-MAL with at least one "1" allele (1/1 or 1/2 genotype, n = 121), owners reported higher levels of attention, increased frequency of episodic aggression, and increased frequency of loss of responsiveness to environmental stimuli. In behavior observations, Belgian Military Working Dogs (MWD) with 1/1 or 1/2 genotypes displayed fewer distracted behaviors and more stress-related behaviors such as lower posture and increased yawning. Handlers' treatment of MWD varied with DAT-VNTR genotype as did dogs' responses to handlers' behavior. For 1/1 or 1/2 genotype MWD, 1) lower posture after the first aversive stimulus given by handlers was associated with poorer obedience performance; 2) increased aversive stimuli during protection exercises were associated with decreased performance; 3) more aversive stimuli during obedience were associated with more aversive stimuli during protection; and 4) handlers used more aversive stimuli in protection compared with obedience exercises.

CONCLUSIONS

The single copy allele of DAT-VNTR is associated with owner-reported seizures, loss of responsiveness to environmental stimuli, episodic aggression, and hyper-vigilance in MAL. Behavioral changes are associated with differential treatment by handlers. Findings should be considered preliminary until replicated in a larger sample.

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.

Ethosuximide reduces epileptogenesis and behavioral comorbidity in the GAERS model of genetic generalized epilepsy

PURPOSE

Ethosuximide (ESX) is a drug of choice for the symptomatic treatment of absence seizures. Chronic treatment with ESX has been reported to have disease-modifying antiepileptogenic activity in the WAG/Rij rat model of genetic generalized epilepsy (GGE) with absence seizures. Here we examined whether chronic treatment with ESX (1) possesses antiepileptogenic effects in the genetic absence epilepsy rats from Strasbourg (GAERS) model of GGE, (2) is associated with a mitigation of behavioral comorbidities, and (3) influences gene expression in the somatosensory cortex region where seizures are thought to originate.

METHODS

GAERS and nonepileptic control (NEC) rats were chronically treated with ESX (in drinking water) or control (tap water) from 3 to 22 weeks of age. Subsequently, all animals received tap water only for another 12 weeks to assess enduring effects of treatment. Seizure frequency and anxiety-like behaviors were serially assessed throughout the experimental paradigm. Treatment effects on the expression of key components of the epigenetic molecular machinery, the DNA methyltransferase enzymes, were assessed using quantitative polymerase chain reaction (qPCR).

KEY FINDINGS

ESX treatment significantly reduced seizures in GAERS during the treatment phase, and this effect was maintained during the 12-week posttreatment phase (p < 0.05). Furthermore, the anxiety-like behaviors present in GAERS were reduced by ESX treatment (p < 0.05). Molecular analysis revealed that ESX treatment was associated with increased expression of DNA methyltransferase enzyme messenger RNA (mRNA) in cortex.

SIGNIFICANCE

Chronic ESX treatment has disease-modifying effects in the GAERS model of GGE, with antiepileptogenic effects against absence seizures and mitigation of behavioral comorbidities. The cellular mechanism for these effects may involve epigenetic modifications.

Stress, epilepsy, and psychiatric comorbidity: how can animal models inform the clinic?

Psychiatric complaints afflict many patients with epilepsy, and these contribute significantly to the impaired quality of life experienced by sufferers of this common group of neurological conditions. Psychiatric disorders in epilepsy patients are under-diagnosed and under-treated. Moreover, evidence suggests that the psychiatric disorders may act as risk factors for some types of epilepsy and exacerbate disease progression in established cases, promoting the case for a bidirectional relationship between epilepsy and psychopathology. While cause and effect relationships can be difficult to establish in human studies, appropriate animal models provide valuable tools with which to study the interactions between epilepsy and stress-related disorders. Indeed, many epilepsy models exhibit behavioral phenotypes which are reflective of psychiatric disorders, and, conversely, stressful environments appear to promote a vulnerability to developing epilepsy. This review summarizes this research area, exploring the behavioral phenotypes in animal models of epilepsy and then examining the influence of stressful environments on susceptibility to seizures and epilepsy. The ultimate goal of this line of research is to be able to translate these findings to humans. Understanding the relationships between epilepsy and associated psychiatric disorders will facilitate effective treatment of mood disorders in epilepsy, inform about the pathophysiology of each individually, and potentially open up novel therapeutic disease-modifying strategies for patients with epilepsy.

Repeatedly stressed rats have enhanced vulnerability to amygdala kindling epileptogenesis

Psychiatric disorders associated with elevated stress levels, such as depression, are present in many epilepsy patients, including those with mesial Temporal Lobe Epilepsy (mTLE). Evidence suggests that these psychiatric disorders can predate the onset of epilepsy, suggesting a causal/contributory role. Prolonged exposure to elevated corticosterone, used as a model of chronic stress/depression, accelerates limbic epileptogenesis in the amygdala kindling model. The current study examined whether exposure to repeated stress could similarly accelerate experimental epileptogenesis. Female adult non-epileptic Wistar rats were implanted with a bipolar electrode into the left amygdala, and were randomly assigned into stressed (n=18) or non-stressed (n=19) groups. Rats underwent conventional amygdala kindling (two electrical stimulations per day) until 5 Class V seizures had been experienced ('the fully kindled state'). Stressed rats were exposed to 30min restraint immediately prior to each kindling stimulation, whereas non-stressed rats received control handling. Restraint stress increased circulating corticosterone levels (pre-stress: 122±17ng/ml; post-stress: 632±33ng/ml), with no habituation observed over the experiment. Stressed rats reached the 'fully kindled state' in significantly fewer stimulations than non-stressed rats (21±1 vs 33±3 stimulations; p=0.022; ANOVA), indicative of a vulnerability to epileptogenesis. Further, seizure durations were significantly longer in stressed rats (p<0.001; ANOVA). These data demonstrate that exposure to repeated experimental stress accelerates the development of limbic epileptogenesis, an effect which may be related to elevated corticosterone levels. This may have implications for understanding the effects of chronic stress and depression in disease onset and progression of mTLE in humans.

Pilocarpine-induced temporal lobe epilepsy in the rat is associated with increased dopamine neuron activity

Temporal lobe epilepsy (TLE) is defined as the occurrence of spontaneous seizures that involve the limbic system, with the hippocampal formation and associated structures being central to the most prevalent refractory form of adult focal epilepsy. TLE is often associated with psychotic features resembling the hallucinations and delusions that occur with schizophrenia. Given evidence that the ventral hippocampus plays an important role in the maintenance of temporal lobe seizures, we investigated whether an animal model of TLE using intrahippocampal injection of pilocarpine induces alterations in mesolimbic dopamine neuron activity. We found that in 60% of rats in which pilocarpine induced seizure activity, there was a significant increase in the number of dopamine neurons firing per electrode track. Furthermore, this occurred in concert with an increase in amphetamine-stimulated locomotor activity. Both observations are similar to those observed in a rodent developmental model of psychosis. Therefore, as in animal models of schizophrenia, TLE-associated psychosis is probably due to abnormal hippocampal overdrive of dopamine neuron activity.

Evidence for shared susceptibility to epilepsy and psychosis: a population-based family study

BACKGROUND

There is emerging evidence of an etiological overlap between a range of neurodevelopmental disorders, including schizophrenia and epilepsy. Here we investigate shared familial vulnerability to psychotic illness and epilepsy in a family-based study.

METHODS

The study population consisted of parents and their children born in Helsinki between 1947 and 1990. The Finnish Hospital Discharge Register was used to determine psychiatric and neurological outcomes in adulthood for all offspring. Parental history of psychosis and epilepsy was determined by linking the Hospital Discharge Register and the Finnish Population Register.

RESULTS

Our total sample comprised 9653 families and 23,404 offspring. Individuals with epilepsy had a 5.5-fold increase in the risk of having a broadly defined psychotic disorder, an almost 8.5-fold increase in the risk of having schizophrenia, and a 6.3-fold increase in the risk of having bipolar disorder. There was strong evidence of clustering of the association between epilepsy and psychosis within families. Individuals with a parental history of epilepsy had a 2-fold increase in the risk of developing psychosis, compared with individuals without a parental history of epilepsy. Individuals with a parental history of psychosis had, reciprocally, a 2.7-fold increase in the risk of having a diagnosis of generalized epilepsy, compared with individuals without a parental history of psychosis. Post hoc analyses showed that these associations were not driven by the comorbidity of epilepsy and psychosis in the parents.

CONCLUSIONS

These findings support recent evidence of overlapping etiological factors between epilepsy and schizophrenia, especially recent evidence of a genetic overlap between these disorders.

The WAG/Rij strain: a genetic animal model of absence epilepsy with comorbidity of depression [corrected]

A great number of clinical observations show a relationship between epilepsy and depression. Idiopathic generalized epilepsy, including absence epilepsy, has a genetic basis. The review provides evidence that WAG/Rij rats can be regarded as a valid genetic animal model of absence epilepsy with comorbidity of depression. WAG/Rij rats, originally developed as an animal model of human absence epilepsy, share many EEG and behavioral characteristics resembling absence epilepsy in humans, including the similarity of action of various antiepileptic drugs. Behavioral studies indicate that WAG/Rij rats exhibit depression-like symptoms: decreased investigative activity in the open field test, increased immobility in the forced swimming test, and decreased sucrose consumption and preference (anhedonia). In addition, WAG/Rij rats adopt passive strategies in stressful situations, express some cognitive disturbances (reduced long-term memory), helplessness, and submissiveness, inability to make choice and overcome obstacles, which are typical for depressed patients. Elevated anxiety is not a characteristic (specific) feature of WAG/Rij rats; it is a characteristic for only a sub-strain of WAG/Rij rats susceptible to audiogenic seizures. Interestingly, WAG/Rij rats display a hyper-response to amphetamine similar to anhedonic depressed patients. WAG/Rij rats are sensitive only to chronic, but not acute, antidepressant treatments, suggesting that WAG/Rij rats fulfill a criterion of predictive validity for a putative animal model of depression. However, more and different antidepressant drugs still await evaluation. Depression-like behavioral symptoms in WAG/Rij rats are evident at baseline conditions, not exclusively after stress. Experiments with foot-shock stress do not point towards higher stress sensitivity at both behavioral and hormonal levels. However, freezing behavior (coping deficits) and blunted response of 5HT in the frontal cortex to uncontrollable sound stress, increased c-fos expression in the terminal regions of the meso-cortico-limbic brain systems and greater DA response of the mesolimbic system to forced swim stress suggest that WAG/Rij rats are vulnerable to some, but not to all types of stressors. We propose that genetic absence epileptic WAG/Rij rats have behavioral depression-like symptoms, are vulnerable to stress and might represent a model of chronic low-grade depression (dysthymia). Both 5HT and DAergic abnormalities detected in the brain of WAG/Rij rats are involved in modulation of vulnerability to stress and provocation of behavioral depression-like symptoms. The same neurotransmitter systems modulate SWDs as well. Recent studies suggest that the occurrence and repetition of absence seizures are a precipitant of depression-like behavior. Whether the neurochemical changes are primary to depression-like behavioral alterations remains to be determined. In conclusion, the WAG/Rij rats can be considered as a genetic animal model for absence epilepsy with comorbidity of dysthymia. This model can be used to investigate etiology, pathogenic mechanisms and treatment of a psychiatric comorbidity, such as depression in absence epilepsy, to reveal putative genes contributing to comorbid depressive disorder, and to screen novel psychotropic drugs with a selective and/or complex (dual) action on both pathologies.

Acute administration of typical and atypical antipsychotics reduces EEG γ power, but only the preclinical compound LY379268 reduces the ketamine-induced rise in γ power

A single non-anaesthetic dose of ketamine, a non-competitive NMDA receptor (NMDAR) antagonist with hallucinogenic properties, induces cognitive impairment and psychosis, and aggravates schizophrenia symptoms in patients. In conscious rats an equivalent dose of ketamine induces key features of animal models of acute psychosis, including hyperlocomotor activity, deficits in prepulse inhibition and gating of auditory evoked potentials, and concomitantly increases the power of ongoing spontaneously occurring gamma (30-80 Hz) oscillations in the neocortex. This study investigated whether NMDAR antagonist-induced aberrant gamma oscillations could be modulated by acute treatment with typical and atypical antipsychotic drugs. Extradural electrodes were surgically implanted into the skull of adult male Wistar rats. After recovery, rats were subcutaneously administered either clozapine (1-5 mg/kg, n=7), haloperidol (0.05-0.25 mg/kg; n=8), LY379268 (a preclinical agonist at mGluR2/3 receptors: 0.3-3 mg/kg; n=5) or the appropriate vehicles, and 30 min later received ketamine (5 mg/kg s.c.). Quantitative measures of EEG gamma power and locomotor activity were assessed throughout the experiment. All three drugs significantly reduced the power of baseline EEG gamma oscillations by 30-50%, an effect most prominent after LY379268, and all inhibited ketamine-induced hyperlocomotor activity. However, only pretreatment with LY379268 attenuated trough-to-peak ketamine-induced gamma hyperactivity. These results demonstrate that typical and atypical antipsychotic drugs acutely reduce cortical gamma oscillations, an effect that may be related to their clinical efficacy.