Behaviors induced or disrupted by complex partial seizures

Repeated hippocampal seizures lead to brain-wide reorganization of circuits and seizure propagation pathways

Repeated seizure activity can lead to long-term changes in seizure dynamics and behavior. However, resulting changes in brain-wide dynamics remain poorly understood. This is due partly to technical challenges in precise seizure control and in vivo whole-brain mapping of circuit dynamics. Here, we developed an optogenetic kindling model through repeated stimulation of ventral hippocampal CaMKII neurons in adult rats. We then combined fMRI with electrophysiology to track brain-wide circuit dynamics resulting from non-afterdischarge (AD)-generating stimulations and individual convulsive seizures. Kindling induced widespread increases in non-AD-generating stimulation response and ipsilateral functional connectivity and elevated anxiety. Individual seizures in kindled animals showed more significant increases in brain-wide activity and bilateral functional connectivity. Onset time quantification provided evidence for kindled seizure propagation from the ipsilateral to the contralateral hemisphere. Furthermore, a core of slow-migrating hippocampal activity was identified in both non-kindled and kindled seizures, revealing a novel mechanism of seizure sustainment and propagation.

Functional connectivity changes of nucleus Accumbens Shell portion in left mesial temporal lobe epilepsy patients

Growing evidence has supported that the nucleus accumbens (NAc), especially its shell portion, has been involved in epileptogenesis. However, relevant studies on vivo human brain are quite limited. In this study, we investigated left mesial temporal lobe epilepsy (MTLE) related function connectivity (FC) changes of NAc subregions using resting-state functional magnetic resonance imaging. We calculated functional connectivity from two NAc subregions to both whole brain and 16 related targets. Two-sample t-test (Alphasim multiple comparisons corrected) was performed to identify the effect of the disease on each seed's whole brain network. Repeated-measures ANOVA and Post hoc pairwise t test (Bonferroni corrections) were performed to visualize the seed to target FC group differences in each subdivision. In whole brain FC networks, neither the left or right core show different FC changes. The left shell showed decreased FC with a cluster located around the right inferior frontal gyrus. The right shell portion showed increased FC with a cluster located around the left inferior temporal gyrus. The seed to targets results showed that the left shell of LTLE group exhibited lower FC with left posterior-parahippocampal gyrus and right caudate, putamen, thalamus, paracingulate gyrus but higher FC with right subcallosal cortex. The right core of LTLE group exhibited higher FC with right frontal pole and the right shell exhibited lower FC with left thalamus and left anterior-parahippocampal gyrus. This is the first study to investigate the functional connectivity changes of NAc subdivisions of epilepsy in vivo human brain. Our results showed that the left MTLE related FC changes on NAc are mainly on shell portion rather than core. The decrease FC between the left shell and right frontal area and the decrease FC between the right shell and left temporal area suggested they serve vital roles for MTLE.

Seizures elevate gliovascular unit Ca2+ and cause sustained vasoconstriction

Seizures can result in a severe hypoperfusion/hypoxic attack that causes postictal memory and behavioral impairments. However, neither postictal changes to microvasculature nor Ca²⁺ changes in key cell types controlling blood perfusion have been visualized in vivo, leaving essential components of the underlying cellular mechanisms unclear. Here, we use 2-photon microvascular and Ca²⁺ imaging in awake mice to show that seizures result in a robust vasoconstriction of cortical penetrating arterioles, which temporally mirrors the prolonged postictal hypoxia. The vascular effect was dependent on cyclooxygenase 2, as pretreatment with ibuprofen prevented postictal vasoconstriction. Moreover, seizures caused a rapid elevation in astrocyte endfoot Ca²⁺ that was confined to the seizure period, and vascular smooth muscle cells displayed a significant increase in Ca²⁺ both during and following seizures, lasting up to 75 minutes. Our data show enduring postictal vasoconstriction and temporal activities of 2 cell types within the neurovascular unit that are associated with seizure-induced hypoperfusion/hypoxia. These findings support prevention of this event may be a novel and tractable treatment strategy in patients with epilepsy who experience extended postseizure impairments.

Seizures cause enduring microvascular constriction via long lasting calcium elevations in vascular smooth muscle cells.

Localizing and lateralizing values of postictal behavioral impairments in epileptic rats

Transient postictal behavioral impairments in patients with epilepsy provide clues to seizure localization, but no attempt has been made previously to study the localization/lateralization value of postseizure motor disturbances in experimental models of epilepsy. The present study investigated relation of postictal motor deficit to seizure localization in the rat model of sound-induced reflex epilepsy. Sound-induced motor seizures started with a focal brainstem seizure (running) and progressed to a secondarily generalized seizure. Depending on innate or acquired seizure susceptibility of rats, focal brainstem seizures secondarily generalized within the brainstem (brainstem-generalized seizures) or spread to the forebrain (focal or generalized forebrain seizures). All sound-induced seizures were followed by catalepsy and abnormal limb posturing. The duration of the postictal catalepsy and the pattern of the posture abnormality depended on brainstem or forebrain localization of secondarily generalized seizures. Brainstem-driven seizures induced long-lasting whole-body catalepsy and cataleptic limb posture in the postictal period. Secondary seizure generalization to the forebrain led to shortening postictal catalepsy and development of rigid limb posturing. Asymmetric limb posturing was always observed after focal forebrain seizures, and the postictal asymmetry was closely linked to ictal asymmetry of the earliest running seizure phase, predicting lateralization of the seizure-onset side. This is the first demonstration of circuit-specific postictal behavioral impairments and their localization and lateralization values in epileptic rats.

Neurodegeneration and Pathology in Epilepsy: Clinical and Basic Perspectives

Epilepsy is commonly associated with a number of neurodegenerative and pathological alterations in those areas of the brain that are involved in repeated electrographic seizures. These most prominently include neuron loss and an increase in astrocyte number and size but may also include enhanced blood-brain barrier permeability, the formation of new capillaries, axonal sprouting, and central inflammation. In animal models in which seizures are either repeatedly elicited or are self-generated, a similar set of neurodegenerative and pathological alterations in brain anatomy are observed. The primary causal agent responsible for these alterations may be the cascade of events that follow a seizure and lead to an hypoperfusion/hypoxic episode. While epilepsy has long and correctly been considered an electrical disorder, the vascular system likely plays an important causal role in the neurodegeneration and pathology that occur as a consequence of repeated seizures.

Accelerated cognitive decline in a rodent model for temporal lobe epilepsy

OBJECTIVE

Cognitive impairment is frequently observed in patients with temporal lobe epilepsy. It is hypothesized that cumulative seizure exposure causes accelerated cognitive decline in patients with epilepsy. We investigated the influence of seizure frequency on cognitive decline in a rodent model for temporal lobe epilepsy.

METHODS

Neurobehavioral assessment was performed before and after surgery, after the induction of self-sustaining limbic status epilepticus (SSLSE), and in the chronic phase in which rats experienced recurrent seizures. Furthermore, we assessed potential confounders of memory performance.

RESULTS

Rats showed a deficit in spatial working memory after the induction of the SSLSE, which endured in the chronic phase. A progressive decline in recognition memory developed in SSLSE rats. Confounding factors were absent. Seizure frequency and also the severity of the status epilepticus were not correlated with the severity of cognitive deficits.

SIGNIFICANCE

The effect of the seizure frequency on cognitive comorbidity in epilepsy has long been debated, possibly because of confounders such as antiepileptic medication and the heterogeneity of epileptic etiologies. In an animal model of temporal lobe epilepsy, we showed that a decrease in spatial working memory does not relate to the seizure frequency. This suggests for other mechanisms are responsible for memory decline and potentially a common pathophysiology of cognitive deterioration and the occurrence and development of epileptic seizures. Identifying this common denominator will allow development of more targeted interventions treating cognitive decline in patients with epilepsy. The treatment of interictal symptoms will increase the quality of life of many patients with epilepsy.

Postictal behavioural impairments are due to a severe prolonged hypoperfusion/hypoxia event that is COX-2 dependent

Seizures are often followed by sensory, cognitive or motor impairments during the postictal phase that show striking similarity to transient hypoxic/ischemic attacks. Here we show that seizures result in a severe hypoxic attack confined to the postictal period. We measured brain oxygenation in localized areas from freely-moving rodents and discovered a severe hypoxic event (pO2 < 10 mmHg) after the termination of seizures. This event lasted over an hour, is mediated by hypoperfusion, generalizes to people with epilepsy, and is attenuated by inhibiting cyclooxygenase-2 or L-type calcium channels. Using inhibitors of these targets we separated the seizure from the resulting severe hypoxia and show that structure specific postictal memory and behavioral impairments are the consequence of this severe hypoperfusion/hypoxic event. Thus, epilepsy is much more than a disease hallmarked by seizures, since the occurrence of postictal hypoperfusion/hypoxia results in a separate set of neurological consequences that are currently not being treated and are preventable.

Resting state functional network disruptions in a kainic acid model of temporal lobe epilepsy

We studied the graph topological properties of brain networks derived from resting-state functional magnetic resonance imaging in a kainic acid induced model of temporal lobe epilepsy (TLE) in rats. Functional connectivity was determined by temporal correlation of the resting-state Blood Oxygen Level Dependent (BOLD) signals between two brain regions during 1.5% and 2% isoflurane, and analyzed as networks in epileptic and control rats. Graph theoretical analysis revealed a significant increase in functional connectivity between brain areas in epileptic than control rats, and the connected brain areas could be categorized as a limbic network and a default mode network (DMN). The limbic network includes the hippocampus, amygdala, piriform cortex, nucleus accumbens, and mediodorsal thalamus, whereas DMN involves the medial prefrontal cortex, anterior and posterior cingulate cortex, auditory and temporal association cortex, and posterior parietal cortex. The TLE model manifested a higher clustering coefficient, increased global and local efficiency, and increased small-worldness as compared to controls, despite having a similar characteristic path length. These results suggest extensive disruptions in the functional brain networks, which may be the basis of altered cognitive, emotional and psychiatric symptoms in TLE.

Dual Effects of Limbic Seizures on Psychosis-Relevant Behaviors Shown by Nucleus Accumbens Kindling in Rats

BACKGROUND

A paradox in epilepsy and psychiatry is that temporal lobe epilepsy is often predisposed to schizophrenic-like psychosis, whereas convulsive therapy can relieve schizophrenic symptoms. We have previously demonstrated that the nucleus accumbens is a key structure in mediating postictal psychosis induced by a hippocampal electrographic seizure.

OBJECTIVE/HYPOTHESIS

The purpose of this study is to test a hypothesis that accumbens kindling cumulating in a single (1-time) or repeated (5-times) convulsive seizures have different effects on animal models of psychosis.

METHODS

Electrical stimulation at 60 Hz was applied to nucleus accumbens to evoke afterdischarges until one, or five, convulsive seizures that involved the hind limbs (stage 5 seizures) were attained. Behavioral tests, performed at 3 days after the last seizure, included gating of hippocampal auditory evoked potentials (AEP) and prepulse inhibition to an acoustic startle response (PPI), tested without drug injection or after ketamine (3 mg/kg s.c.) injection, as well as locomotion induced by ketamine or methamphetamine (1 mg/kg i.p.).

RESULTS

Compared to non-kindled control rats, 1-time, but not 5-times, convulsive seizures induced PPI deficit and decreased gating of hippocampal AEP, without drug injection. Compared to non-kindled rats, 5-times, but not 1-time, convulsive seizures antagonized ketamine-induced hyperlocomotion, ketamine-induced PPI deficit and AEP gating decrease. However, both 1- and 5-times convulsive seizures significantly enhanced methamphetamine-induced locomotion as compared to non-kindled rats.

CONCLUSIONS

Accumbens kindling ending with 1 convulsive seizure may induce schizophrenic-like behaviors, while repeated (≥5) convulsive seizures induced by accumbens kindling may have therapeutic effects on dopamine independent psychosis.

Effects of hippocampal partial kindling on sensory and sensorimotor gating and methamphetamine-induced locomotion in kindling-prone and kindling-resistant rats

The effects of hippocampal partial kindling on gating of hippocampal auditory-evoked potentials (AEPs), prepulse inhibition (PPI) to an acoustic startle response, and methamphetamine-induced locomotion were examined in selectively bred kindling-prone (Fast) and kindling-resistant (Slow) rats. Ten electrographic seizures (afterdischarges, ADs) induced by high-frequency stimulation of the hippocampal CA1 region resulted in deficits in gating of hippocampal AEP and PPI in Fast, but not Slow, rats. The increase in AD duration with kindling was similar in Fast and Slow rats. Kindling-induced changes in hippocampal AEP and PPI in Fast rats were abolished by pretest injection of CGP7930 (1mg/kg i.p.), a positive allosteric modulator of GABAB receptors. Injection of haloperidol (0.1mg/kg i.p.) daily before kindling also prevented kindling-induced changes in PPI and hippocampal AEP in Fast rats. Interestingly, methamphetamine-induced hyperlocomotion was enhanced by kindling in Slow, but not Fast, rats. However, the methamphetamine-induced hyperlocomotion in Slow rats was not suppressed by daily injection of 0.1mg/kg i.p. haloperidol before kindling, as compared with kindling without haloperidol. It is concluded that genetic disposition affected the behavioral consequences of repeated seizures. Fast rats required fewer hippocampal ADs to induce sensory (AEP) and sensorimotor (PPI) deficits, while Slow kindled rats were more sensitive to methamphetamine-induced locomotion. Dopaminergic blockade by haloperidol during kindling, or acute injection of CGP7930 before testing, attenuated some of the behavioral deficits induced by repeated hippocampal seizures, suggesting possible therapeutic strategies to treat the schizophrenic-like symptoms associated with temporal lobe epilepsy.

Looking for complexity in quantitative semiology of frontal and temporal lobe seizures using neuroethology and graph theory

Epileptic syndromes and seizures are the expression of complex brain systems. Because no analysis of complexity has been applied to epileptic seizure semiology, our goal was to apply neuroethology and graph analysis to the study of the complexity of behavioral manifestations of epileptic seizures in human frontal lobe epilepsy (FLE) and temporal lobe epilepsy (TLE). We analyzed the video recordings of 120 seizures of 18 patients with FLE and 28 seizures of 28 patients with TLE. All patients were seizure-free >1 year after surgery (Engel Class I). All patients' behavioral sequences were analyzed by means of a glossary containing all behaviors and analyzed for neuroethology (Ethomatic software). The same series were used for graph analysis (CYTOSCAPE). Behaviors, displayed as nodes, were connected by edges to other nodes according to their temporal sequence of appearance. Using neuroethology analysis, we confirmed data in the literature such as in FLE: brief/frequent seizures, complex motor behaviors, head and eye version, unilateral/bilateral tonic posturing, speech arrest, vocalization, and rapid postictal recovery and in the case of TLE: presence of epigastric aura, lateralized dystonias, impairment of consciousness/speech during ictal and postictal periods, and development of secondary generalization. Using graph analysis metrics of FLE and TLE confirmed data from flowcharts. However, because of the algorithms we used, they highlighted more powerfully the connectivity and complex associations among behaviors in a quite selective manner, depending on the origin of the seizures. The algorithms we used are commonly employed to track brain connectivity from EEG and MRI sources, which makes our study very promising for future studies of complexity in this field.

Animal models of epilepsy: use and limitations

Epilepsy is a chronic neurological condition characterized by recurrent seizures that affects millions of people worldwide. Comprehension of the complex mechanisms underlying epileptogenesis and seizure generation in temporal lobe epilepsy and other forms of epilepsy cannot be fully acquired in clinical studies with humans. As a result, the use of appropriate animal models is essential. Some of these models replicate the natural history of symptomatic focal epilepsy with an initial epileptogenic insult, which is followed by an apparent latent period and by a subsequent period of chronic spontaneous seizures. Seizures are a combination of electrical and behavioral events that are able to induce chemical, molecular, and anatomic alterations. In this review, we summarize the most frequently used models of chronic epilepsy and models of acute seizures induced by chemoconvulsants, traumatic brain injury, and electrical or sound stimuli. Genetic models of absence seizures and models of seizures and status epilepticus in the immature brain were also examined. Major uses and limitations were highlighted, and neuropathological, behavioral, and neurophysiological similarities and differences between the model and the human equivalent were considered. The quest for seizure mechanisms can provide insights into overall brain functions and consciousness, and animal models of epilepsy will continue to promote the progress of both epilepsy and neurophysiology research.

Alzheimer's disease and epilepsy: insight from animal models

Alzheimer's disease (AD) and epilepsy are separated in the medical community, but seizures occur in some patients with AD, and AD is a risk factor for epilepsy. Furthermore, memory impairment is common in patients with epilepsy. The relationship between AD and epilepsy remains an important question because ideas for therapeutic approaches could be shared between AD and epilepsy research laboratories if AD and epilepsy were related. Here we focus on one of the many types of epilepsy, temporal lobe epilepsy (TLE), because patients with TLE often exhibit memory impairment, depression and other comorbidities that occur in AD. Moreover, the seizures that occur in patients with AD may be nonconvulsive, which occur in patients with TLE. Here we first compare neuropathology in TLE and AD with an emphasis on the hippocampus, which is central to both AD and TLE research. Then we compare animal models of AD pathology with animal models of TLE. Although many aspects of the comparisons are still controversial, there is one conclusion that we suggest is clear: some animal models of TLE could be used to help address questions in AD research, and some animal models of AD pathology are bona fide animal models of epilepsy.

Consciousness and epilepsy: why are complex-partial seizures complex?

Why do complex-partial seizures in temporal lobe epilepsy (TLE) cause a loss of consciousness? Abnormal function of the medial temporal lobe is expected to cause memory loss, but it is unclear why profoundly impaired consciousness is so common in temporal lobe seizures. Recent exciting advances in behavioral, electrophysiological, and neuroimaging techniques spanning both human patients and animal models may allow new insights into this old question. While behavioral automatisms are often associated with diminished consciousness during temporal lobe seizures, impaired consciousness without ictal motor activity has also been described. Some have argued that electrographic lateralization of seizure activity to the left temporal lobe is most likely to cause impaired consciousness, but the evidence remains equivocal. Other data correlates ictal consciousness in TLE with bilateral temporal lobe involvement of seizure spiking. Nevertheless, it remains unclear why bilateral temporal seizures should impair responsiveness. Recent evidence has shown that impaired consciousness during temporal lobe seizures is correlated with large-amplitude slow EEG activity and neuroimaging signal decreases in the frontal and parietal association cortices. This abnormal decreased function in the neocortex contrasts with fast polyspike activity and elevated cerebral blood flow in limbic and other subcortical structures ictally. Our laboratory has thus proposed the "network inhibition hypothesis," in which seizure activity propagates to subcortical regions necessary for cortical activation, allowing the cortex to descend into an inhibited state of unconsciousness during complex-partial temporal lobe seizures. Supporting this hypothesis, recent rat studies during partial limbic seizures have shown that behavioral arrest is associated with frontal cortical slow waves, decreased neuronal firing, and hypometabolism. Animal studies further demonstrate that cortical deactivation and behavioral changes depend on seizure spread to subcortical structures including the lateral septum. Understanding the contributions of network inhibition to impaired consciousness in TLE is an important goal, as recurrent limbic seizures often result in cortical dysfunction during and between epileptic events that adversely affects patients' quality of life.

Repeated seizures lead to altered skilled behaviour and are associated with more highly efficacious excitatory synapses

People with epilepsy have a high incidence of interictal behavioural problems that appear to be related to the location of their seizure focus. This study investigated a novel test of the hypotheses that repeated seizures result in behavioural deficits and altered performance during the interictal state, and that those behaviours are related to the presence of more highly efficacious excitatory synapses. We tested these hypotheses by first repeatedly eliciting seizures with electric current through indwelling electrodes in the corpus callosum at the level of the caudal forelimb area of sensorimotor neocortex in the rat. We then assessed learned skilled behaviours that primarily utilize the forelimbs on tasks that are sensitive to the functional integrity of that structure. We observed both behavioural deficits and altered kinematic performance in rats that experienced repeated neocortical seizures relative to an electrode-implanted control group. From a separate set of rats, tissue was prepared for quantification of thickness and excitatory synaptic subtypes from neocortical layer V. We observed significantly increased numbers of perforated synapses that make their connections directly onto the dendritic shaft at 3 weeks following the last seizure. Altered reaching behaviours are likely due to neural reorganization in the neocortex including more efficacious synapses.

Behavioral measures in animal studies: relevance to patients with epilepsy

The relevance of behavioral endpoints in animal seizure models to clinical epilepsy is outlined and enhanced in the present review by linking specific preclinical dependent measures with a quality-of-life scale that serves as an index of the health and welfare of patients with epilepsy (Quality of Life in Epilepsy inventory). This preclinical-to-clinical translation is possible based on existing literature within at least three behavioral domains: (1) physical and motor actions, (2) affective and emotional responses to environmental challenge, and (3) social, sexual, and parental functions. Face valid commonalities in observable behaviors are emphasized with the goal of engaging basic and applied researchers in collaborative research projects to accelerate the pace of discovery in the behavioral phenotyping of epilepsy field.

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

A broad spectrum of learning/memory, social interaction, and affective behavioral measures serve as functional correlates for neurobiological changes in seizure-prone animals as well as in epileptic clinical populations. The utility of such measures is demonstrated by their ability to distinguish anomalous characteristics in developing organisms predisposed to seizure onset, as well as to discriminate prior seizure history in organisms with established pathology. For instance, typical findings that generalize across species suggest that seizure-experienced organisms exhibit a variety of deficits in cognitive function as well as inappropriate social neglect and aggression. Behavioral testing batteries have also proven useful in assessing neural mechanisms for seizure induction, subcortical neural circuits, and neuropeptide modulators, for example, as well as in identifying neural pathology resulting from prior seizure activity. However, the wanton application of behavioral tests can also produce false positives in the identification of seizure-related disorders unless alternative performance and motivational hypotheses are discounted effectively. Accordingly, the present review attempts to provide the reader interested in behavioral phenotyping and characterization of seizure-prone rats and mice with a roadmap for rational selection, implementation, and interpretation of data from behavior assays while highlighting potential successes and pitfalls inherent in employing functional correlates of brain activity using animal models of epilepsy.

Hippocampal CA1 kindling but not long-term potentiation disrupts spatial memory performance

Long-term synaptic enhancement in the hippocampus has been suggested to cause deficits in spatial performance. Synaptic enhancement has been reported after hippocampal kindling that induced repeated electrographic seizures or afterdischarges (ADs) and after long-term potentiation (LTP) defined as synaptic enhancement without ADs. We studied whether repeated stimulations that gave LTP or ADs resulted in spatial performance deficits on the radial arm maze (RAM) and investigated the minimal number of ADs required for such deficits. Three experimental groups were run as follows: (1) 5 hippocampal ADs in 1 d (5-AD group), (2) 10 hippocampal ADs in 2 d (10-AD group), and (3) 12 -frequency primed-burst stimulations (PBSs) in 2 d in order to induce LTP without ADs (LTP group). Each experimental group was run together with a control group during the same time period. Rats were first trained in a spatial task on a radial arm maze with four of the eight arms baited, then given control or experimental treatment, and maze performance was tested in the first week (1-4 d) and fourth week (22-25 d) after treatment. Basal dendritic population excitatory postsynaptic potentials (pEPSPs) and medial perforant path (MPP)-evoked dentate gyrus population spike and polysynaptic CA1 excitation were recorded before and after experimental and control treatment. Spatial memory errors, in particular reference memory errors, were significantly higher in the 10-AD kindled group than any other group on the first and fourth week after treatment. Spatial memory errors were not significantly different in the 5-AD and LTP groups as compared with any control groups at any time. Basal dendritic pEPSP in CA1 was enhanced for about 1 wk after 12 PBSs, 10 ADs, or 5 ADs, while the dentate gyrus population spike and CA1 polysynaptic excitation evoked by MPP was increased for up to 4 wk after 10 ADs, but not 12 PBSs. Thus, distributed alteration of multiple synaptic transmission in the entorhinal-hippocampal circuit, but not LTP at the basal dendritic synapses in CA1, may disrupt spatial performance after 10 hippocampal ADs.

Intraseptal tacrine-induced disruptions of spatial memory performance

The medial septal nucleus regulates the physiology and emergent functions (e.g., memory formation) of the hippocampal formation. This nucleus is particularly rich in cholinergic receptors and is a putative target for the development of cholinomimetic cognitive enhancing drugs. Several studies have examined the direct effects of intraseptal cholinomimetic treatments and the results have been somewhat conflicting with both promnestic and amnestic effects. Several variables (e.g., age, task difficulty, timing of drug administration) may influence treatment outcome. The present study examined the effects of intraseptal infusion of the acetylcholinesterase inhibitor tacrine (0-25 microg/0.5 microl) on spatial memory performance. Tacrine was infused into the medial septum just prior to testing. Tacrine infusions did not significantly affect the number of correct choices in the first eight entries, or the number of correct choices until an error. This treatment did not alter the angle of arm entries, or impair the animals' ability to complete the task (enter all baited arms). However, tacrine produced a linear dose-dependent increase in errors, doubling (12.5 microg) and tripling (25.0 microg) the number of errors made before rats completed the task. The deficit demonstrates that activation of intraseptal cholinergic receptors can disrupt spatial memory performance. These findings are discussed with regards to septohippocampal-dependent memory processes and the development of therapeutic strategies in the treatment of age-related memory disorders.

Phenotyping the untouchables: environmental enhancement of behavioral and physiological activation in seizure-prone El mice

The onset and frequency of spontaneous and tail suspension-induced seizures in El mice appear to be influenced strongly by developmental and experiential factors over the first 3 months of life. To assess the impact of social factors on behavioral characteristics of El mice prior to the age of seizure susceptibility, locomotor activity and exploratory measures of arousal were recorded in 40-day-old El and control DDY mice exposed to group and isolation housing conditions. Once mice reached maturity, physiological reactivity to a tail suspension stressor was evaluated. The locomotor activity measure revealed circadian entrainment in both strains, nocturnal hyperactivity in El mice, and a locomotor activity-attenuating effect of group housing in El mice. In the two-compartment model of exploration, latency to enter, transitions to and from, and rearing in a brightly lit compartment were 50% higher in El relative to DDY mice, again suggesting a hyperactive phenotype. Finally, an acute 2-minute tail suspension stressor applied to 75-day-old mice implanted with radiotelemetry transmitters revealed a reactive tachycardia in El, but not DDY, mice. No seizures were observed during any of the experimental manipulations. Taken together, these results suggest that spontaneously occurring deviations in behavioral and cardiovascular measures of arousal characterize preseizure El mice and that motor features of hyperarousal can be exaggerated by the environmental manipulation of isolation housing.

Enhancement of central dopaminergic activity in the kainate model of temporal lobe epilepsy: implication for the mechanism of epileptic psychosis

There is an increased incidence of schizophrenia-like psychosis in temporal lobe epilepsy (TLE), and several risk factors have been implicated, including the duration of epilepsy and temporal lobe neuropathology. To investigate the biological mechanism of epileptic psychosis, we examined alterations of central dopaminergic systems in the kainate model of TLE. In adult rats, kainate was microinjected into the left amygdala to induce status epilepticus. An indirect dopamine agonist methamphetamine (MAP, 2 mg/kg, i.p.) was administered before and 1 month after the kainate treatment. MAP-induced locomotor activity was significantly enhanced in the kainate group compared with the baseline (pre-kainate) level, which was antagonized by pretreatment with haloperidol. The enhancement of locomotor activity in the kainate group was significantly correlated with the density of hippocampal CA1 neurons. Although the basal extracellular dopamine concentration was significantly lower in the striatum in the kainate group than in the control group (5.5 vs 39.2 fmol/20-min sample), the maximal concentration following MAP administration did not differ between the two groups. These results clearly demonstrate that hypersensitivity of the dopamine systems develops in the chronic phase of the kainate-induced TLE model, which may be responsible for the mechanism of epileptic psychosis.

Kindling of the ventral tegmental area induces supersensitivity in the central dopamine system

Kindling of the ventral tegmental area (VTA), a major source of the mesolimbic dopamine pathway, was examined in rats. We applied two quantitative measurements of dopamine sensitivity before and 2 weeks after VTA kindling (20 times electrical stimulations (100 microA at 1 min intervals) delivered once per day for 14 consecutive days): behavioral responses induced by test VTA stimulation and methamphetamine (MAP)-induced locomotor activity. The total amount of MAP-induced locomotor activity was significantly increased after VTA kindling, while the responses to electrical stimulation were unchanged. These results indicate that repeated activation of the mesolimbic dopamine system can produce a neuroplastic change, which results in dopamine supersensitivity.

Perspectives for the development of animal models of bipolar disorder

Bipolar disorder (BD) has been a particularly challenging illness for the development of adequate animal models for neurobiological studies. These difficulties are largely related to the peculiar clinical characteristics of this illness, with an intriguing alternation of mania, depression, euthymia, and mixed states. The etiology and brain mechanisms involved in this several mental illness remain unknown. Preclinical studies with animal models of mania or depression have been developed to evaluate the potential efficacy of new psychotropic drugs and generate information concerning the biochemical effects of these drugs on specific targets. These models try to mimic the behavioral components of mania and depression in human subjects and examine the pharmacological responses and mechanisms of action of potentially new therapeutic agents. The main limitation is that there is currently no model that would mimic mood cyclicity, which is a hallmark feature of BD. Thus, these models do not represent valid paradigms for the study of this illness, because they do not address key questions regarding cyclicity. In this review, we propose that new genetics approaches involving potential animal models of BD are a promising new area for further development.

Working and Reference Memory in Seizure-Prone and Seizure-Resistant Rats: Impact of Amygdala Kindling

In rat selectively bred for different amygdala kindling rates (Fast vs. Slow), comorbid differences in learning were detected. Here, performance was tested in a delayed alternation task before, during, and after kindling. Although similar reference memory was evident, Fast rats showed working memory deficits with increasing delays between information and choice trials. Further, seizures shortly before learning disrupted both reference and working memory in Fast, but not Slow, rats. Weeks after kindling, progressive delays further disrupted Fast rats, but only longer delays disrupted Slow rats. Clearly relevant to individual differences in human epilepsy, a temporal lobe, seizure-prone genetic background in rats provides poorer original learning and easier disruption of new learning by recent and past seizures than a seizure-resistant background.

Dorsal hippocampus and classical fear conditioning to tone and context in rats: effects of local NMDA-receptor blockade and stimulation

Consistent with the importance of the hippocampus in learning more complex stimulus relations, but not in simple associative learning, the dorsal hippocampus has commonly been implicated in classical fear conditioning to context, but not to discrete stimuli, such as a tone. In particular, a specific and central role in contextual fear conditioning has been attributed to mechanisms mediated by dorsal hippocampal N-methyl-D-aspartate (NMDA)-type glutamate receptors. The present study characterized the effects of blockade or tonic stimulation of dorsal hippocampal NMDA receptors by bilateral local infusion of the noncompetitive NMDA receptor antagonist MK-801 (dizocilpine maleate; 6.25 microg/side) or of NMDA (0.7 microg/side), respectively, on classical fear conditioning to tone and context in Wistar rats. Freezing was used to measure conditioned fear. Regardless of whether conditioning was conducted with tone-shock pairings or unsignaled footshocks (background or foreground contextual conditioning), both NMDA and MK-801 infusion before conditioning resulted in reduced freezing during subsequent exposure to the conditioning context. Freezing during subsequent tone presentation in a new context, normally resulting from conditioning with tone-shock pairings, was not impaired by MK-801 but was strongly reduced by NMDA infusion before conditioning; this freezing was also reduced by NMDA infusion before tone presentation (in an experiment involving NMDA infusions before conditioning and subsequent tone presentation to assess the role of state-dependent learning). It was assessed whether unspecific infusion effects (altered sensorimotor functions, state dependency) or infusion-induced dorsal hippocampal damage contributed to the observed reductions in conditioned freezing. Our data suggest that formation of fear conditioning to context, but not tone, requires NMDA receptor-mediated mechanisms in the dorsal hippocampus. As indicated by the effects of NMDA, some dorsal hippocampal processes may also contribute to fear conditioning to tone. The role of the dorsal hippocampus and local NMDA receptor-mediated processes in fear conditioning to tone and context is discussed in comparison with ventral hippocampal processes.

The expression of interictal, preictal, and postictal facial-wiping behavior in temporal lobe epilepsy: a neuro-ethological analysis and interpretation

By videotape recordings analysis we investigated the frequencies of interictal, preictal, and postictal wiping or rubbing movements targeting the face region (face wiping, FW) in 17 right and 13 left mesial temporal lobe epilepsy (MTLE) patients. Patients' data were compared with FW frequencies obtained in 22 healthy controls listening to a presentation. Results showed that: (1) FW movements were present in both controls and patients; however, the patient groups showed lower interictal and preictal FW rates relative than controls; (2) right and left temporal lobe seizures were followed by a marked increase in the expression of wiping activities directed to the nose as well as to other face regions with respect to the interictal-preictal period; (3) during the first 5min postictal FW was performed preferentially with the hand ipsilateral to the seizure focus; (4) postictal examination of the patient by an observer, especially if of the opposite sex, resulted in a higher incidence of FW acts. After temporal lobe seizures there is an exaggerated expression of movements targeting the face region, and not exclusively directed to the nose. According to an ethological interpretation of the FW behavior as a motor behavior present throughout the phylogenetic scale, from rodents to primates, we suggest the postictal emergence of an innate action pattern modulated by external emotional-cognitive stimuli.

Partial hippocampal kindling increases GABAB receptor-mediated postsynaptic currents in CA1 pyramidal cells

In previous studies, we showed that partial hippocampal kindling decreased the efficacy of the presynaptic GABAB receptors on both GABAergic and glutamatergic terminals of CA1 neurons in hippocampal slices in vitro. In this study, GABAB receptor-mediated inhibitory postsynaptic currents (GABAB-IPSCs) were assessed by whole-cell recordings in CA1 pyramidal neurons in hippocampal slices of male Long-Evans rats. The peak GABAB-IPSC evoked by a brief train of supramaximal stratum radiatum stimuli (20 pulses of 300 Hz) in the presence of picrotoxin (0.1 mM) and kynurenic acid (1 mM) was larger in neurons of kindled (65.9 +/- 5.2 pA, N=42 cells) than control (45.8 +/- 4.8 pA, N=32 cells) rats (P<0.01). Adding GABA uptake blocker nipecotic acid (1 mM) or GABAB receptor agonist baclofen (0.01 mM) in the perfusate induced outward currents that were blocked by GABAB receptor antagonist CGP 55845A (1 microM). The peak outward current induced by nipecotic acid was larger in neurons of the kindled (55.4 +/- 5.7 pA, N=30) than the control group (39.8 +/- 4.5 pA, N=28) (P<0.05). However, the magnitude of the baclofen-induced current was not different between kindled (90.8 +/- 6.9 pA, N=29) and control (87.2 +/- 5.9 pA, N=21) groups (P>0.05). We concluded that partial hippocampal kindling increased GABAB-IPSCs in hippocampal CA1 pyramidal cells via multiple presynaptic mechanisms.

Complex partial seizures and depression

A long-recognized association exists between epilepsy and affective disturbance, especially depression. People with complex partial seizures that result from temporal lobe seizure foci are highly vulnerable to psychiatric disorders. Accurate diagnosis of such disorders is an important key to treatment. Interictal depression or dysphoria is the most clinically significant problem of this type. Pharmacotherapeutic treatments that have positive effects in other types of depressive illness are also effective for depression associated with epilepsy. Electroconvulsive therapy is helpful to some patients with depression that is refractory to drug treatment or psychotherapy. Surgical resection of seizure foci may lead to psychiatric improvement for some individuals, but can also have psychiatric complications.

Is complete seizure control imperative?

Is complete control imperative? The answer depends on whether complete control is indeed possible, on the possibility of achieving modifications of lifestyle, and on the type of epilepsy, with particular reference to the presence of progressive dysfunction. This may be seen in patients with temporal lobe or other forms of focal epilepsy, in the epileptic encephalopathies such as West and Lennox Gastaut Syndromes and even in some patients with idiopathic generalized epilepsy. Progressive memory changes and global cognitive problems are examples. Progressive language deterioration, secondary epileptogenesis and phenomena analogous to kindling are also important issues. How long treatment should be continued depends on many factors, not least the preference of the patient and of the family. Weighing the benefits of complete control versus the side effects and risks of medication or surgery is crucial. There are obvious benefits to complete control; it is imperative if these benefits are greater than the cost.

Metabotropic glutamate receptors in the hippocampus and nucleus accumbens are involved in generating seizure-induced hippocampal gamma waves and behavioral hyperactivity

The involvement of metabotropic glutamate receptor (mGluR) subtypes in the generation of hippocampal EEG (30-100 Hz) and behaviors induced by a hippocampal afterdischarge (AD) was examined in freely behaving rats. A hippocampal AD induced an increase in gamma waves (30-100 Hz) for 20 min, accompanied by behavioral hyperactivity. Bilateral intracerebroventricular (i.c.v.) infusion of (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG), a group I and II mGluR antagonist, 30 min before a hippocampal AD, significantly suppressed both the increase in gamma waves and the behavioral hyperactivity. The hippocampal theta rhythm, the spontaneous hippocampal gamma waves, and evoked field potential oscillations of approximately 40 Hz were not affected by MCPG. Pre-infusion (i.c.v.) of (2S)-alpha-ethylglutamic acid (EGLU; a group II mGluR antagonist), but not (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA; a group I mGluR antagonist), suppressed the postictal increase of both hippocampal gamma waves and behaviors. MCPG was infused locally into different brain structures in order to specify its target sites. Intra-hippocampal infusion of MCPG, or EGLU, blocked the increase in both gamma waves and behaviors. Infusion of MCPG into the nucleus accumbens suppressed the postictal behavioral hyperactivity without affecting the increase in hippocampal gamma waves. MCPG injected into the medial septum blocked neither postictal gamma activity nor behavioral hyperactivity. It is suggested that the group II mGluRs in the hippocampus are involved in generation of the postictal hippocampal gamma waves, while behavioral hyperactivity is partly mediated by mGluRs in the nucleus accumbens. However, spontaneous gamma and theta waves in the normal hippocampus are not mediated by mGluRs.

Peri-Ictal Behavioral and Cognitive Changes

Peri-ictal behavioral and cognitive changes contribute substantially to disability and distress among people with epilepsy. Psychosis, depression, and suicide may all occur as complications of seizures. Greater appreciation and understanding of the peri-ictal period is clinically important and might open novel therapeutic windows. At the same time this period provides a model for understanding basic mechanisms underlying mood and thought disorders and the substrates of cognition, volition, emotion, and consciousness. This review will discuss behavioral and cognitive antecedents of seizures, including the preictal milieu, reflex seizures, and self-induced seizures. Behavioral and cognitive treatment approaches that have been undertaken are reviewed. Both acute and delayed postictal emotional, behavioral, and cognitive changes will be discussed. Finally, possible mechanisms by which epileptic brain activity and behavior may modify each other are considered.

Conditioned effects of kindling

Mild periodic electrical stimulation to any one of many brain sites leads to the development and progressive intensification of elicited motor seizures. Since its discovery in 1969, this kindling phenomenon has been widely studied both as a model of epileptogenesis and as a form of neuroplasticity, and recently there has been increasing interest in kindling as a model of the interictal (i.e. between-seizures) changes in emotionality that accompany certain forms of epilepsy. Despite the extensive use of the kindling model, little consideration has been given to the role played by the cues regularly associated with the delivery of the kindling stimulations. However, we have recently demonstrated that cues associated with the standard kindling protocol (e.g. the stimulation environment) produce conditioned effects on both the motor seizures and interictal behavior of rats and that some kindling sites, such as the amygdala, produce conditioned interictal behaviors that are defensive in nature. The implications that these findings have for the study of interictal behavioral changes in particular and to kindling research in general are discussed.

Dorsal hippocampal kindling produces a selective and enduring disruption of hippocampally mediated behavior

Kindling produces enduring neural changes that are subsequently manifest in enhanced susceptibility to seizure-evoking stimuli and alterations in some types of behavior. The present study investigated the effects of dorsal hippocampal (dHPC) kindling on a variety of behaviors to clarify the nature of previously reported effects on spatial task performance. Rats were kindled twice daily with dHPC stimulation until three fully generalized seizures were evoked. Beginning 7 d later and on successive days, rats were tested in an elevated plus maze, a large circular open field, an open field object exploration task, and a delayed-match-to-place (DMTP) task in a water maze to assess anxiety-related and activity-related behavior (tasks 1 and 2), object recognition memory (task 3), and spatial cognition (task 4). Kindling disrupted performance on the DMTP task in a manner that was not delay dependent and produced a mild enhancement of activity-related behaviors in the open field task but not the elevated plus maze. All other aspects of testing were spared. These findings indicate that dHPC kindling produces enduring and selective effects on behavior that are consistent with a restricted disruption of hippocampally mediated functions. Possible bases for these effects are changes in local NMDA receptor function and/or changes in local inhibition, which might alter the optimal conditions for experience-dependent induction of intrahippocampal plasticity. This preparation may be useful for studying the mechanisms of mnemonic dysfunction associated with temporal lobe epilepsy and may offer unique insights into the mechanisms underlying normal hippocampal function.