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

Impaired Spatial Learning and Memory in Middle-Aged Mice with Kindling-Induced Spontaneous Recurrent Seizures

Temporal lobe epilepsy is the most common and often drug-resistant type of epilepsy in the adult and aging populations and has great diversity in etiology, electro-clinical manifestations, and comorbidities. Kindling through repeated brief stimulation of limbic structures is a commonly used model of temporal lobe epilepsy. Particularly, extended kindling can induce spontaneous recurrent seizures in several animal species. However, kindling studies in middle-aged, aging, or aged animals remain scarce, and currently, little is known about kindling-induced behavioral changes in middle-aged/aging animals. We therefore attempted to provide more information in this area using a mouse model of extended hippocampal kindling. We conducted experiments in middle-aged mice (C57BL/6, male, 12-14 months of age) to model new-onset epilepsy in adult/aging populations. Mice experienced twice daily hippocampal stimulations or handling manipulations for 60-70 days and then underwent continuous electroencephalogram (EEG)-video monitoring to detect spontaneous recurrent seizures. Extended kindled mice consistently exhibited spontaneous recurrent seizures with mean incidences of 6-7 events per day, and these seizures featured EEG discharges and corresponding convulsions. The handling control mice showed neither seizure nor aberrant EEG activity. The two groups of mice underwent the Morris water maze test of spatial learning and memory 1-2 weeks after termination of the kindling stimulation or handling manipulation. During visible platform trials, the kindled mice took a longer distance and required more time than the control mice to find the platform. During hidden platform trials, the kindled mice showed no improvement over 5-day trials in finding the platform whereas the control mice improved significantly. During probe tests in which the hidden platform was removed, the kindled mice spent less time than the controls searching in the correct platform location. There were no significant differences between the kindled and control mice with respect to swim speed or total locomotor activity in an open-field test. Together, these observations indicate that the extended kindled mice with spontaneous recurrent seizures are impaired in spatial learning and memory as assessed by the Morris water maze test. We postulate that the extended hippocampal kindling in middle-aged mice may help explore epileptogenic mechanisms and comorbidities potentially relevant to new-onset temporal lobe epilepsy in adult and aging patients. Limitations and confounds of our present experiments are discussed to improve future examinations of epileptic comorbidities in extended kindled mice.

A companion to the preclinical common data elements for pharmacologic studies in animal models of seizures and epilepsy. A Report of the TASK3 Pharmacology Working Group of the ILAE/AES Joint Translational Task Force

Preclinical pharmacology studies in animal models of seizures and epilepsy have provided a platform to identify more than 20 antiseizure drugs in recent decades. To minimize variability in lab‐to‐lab studies and to harmonize approaches to data collection and reporting methodology in pharmacologic evaluations of the next generation of therapies, we present common data elements (CDEs), case report forms (CRFs), and this companion manuscript to help with the implementation of methods for studies in established preclinical seizure and epilepsy models in adult rodents. The development of and advocacy for CDEs in preclinical research has been encouraged previously by both clinical and preclinical groups. It is anticipated that adoption and implementation of these CDEs in preclinical studies may help standardize approaches to minimize variability and increase the reproducibility of preclinical studies. Moreover, they may provide a methodologic framework for pharmacology studies in atypical animal models or models in development, which may ultimately promote novel therapy development. In the present document, we refer selectively to animal models that have a long history of preclinical use, and in some cases, are clinically validated.

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.

Specific disruption of contextual memory recall by sparse additional activity in the dentate gyrus

The dentate gyrus (DG) of the hippocampus is essential for contextual and spatial memory processing. While lesion or silencing of the DG impairs contextual memory encoding and recall, overly activated DG also prevents proper memory retrieval. Abnormally elevated activity in the DG is repeatedly reported in amnesic mild cognitive impairment (aMCI) patients or aged adults. Although the correlation between memory failure and abnormally active hippocampus is clear, their causal relationship or the underlying nature of such interfering activity is not well understood. Using optogenetics aided by a carefully controlled adeno-associated virus infection system, we were able to examine the differential effects of abnormally activated hippocampus on mice motor behavior and memory function, depending on the extent of the stimulation. Optogenetic stimulation of massive proportion of dorsal DG cells resulted in memory retrieval impairment, but also induced increase in general locomotion. Random additional activity in a sparse population of dorsal DG neurons, however, interfered with contextual memory recall without inducing hyperactivity. Our findings thus establish the causal role of elevated DG activity on memory recall failure, suggesting such aberrant DG activity may contribute to amnesic symptoms in aMCI patients and aged adults.

Corneal kindled C57BL/6 mice exhibit saturated dentate gyrus long-term potentiation and associated memory deficits in the absence of overt neuron loss

Memory deficits have a significant impact on the quality of life of patients with epilepsy and currently no effective treatments exist to mitigate this comorbidity. While these cognitive comorbidities can be associated with varying degrees of hippocampal cell death and hippocampal sclerosis, more subtle changes in hippocampal physiology independent of cell loss may underlie memory dysfunction in many epilepsy patients. Accordingly, animal models of epilepsy or epileptic processes exhibiting memory deficits in the absence of cell loss could facilitate novel therapy discovery. Mouse corneal kindling is a cost-effective and non-invasive model of focal to bilateral tonic-clonic seizures that may exhibit memory deficits in the absence of cell loss. Therefore, we tested the hypothesis that corneal kindled C57BL/6 mice exhibit spatial pattern processing and memory deficits in a task reliant on DG function and that these impairments would be concurrent with physiological remodeling of the DG as opposed to overt neuron loss. Following corneal kindling, C57BL/6 mice exhibited deficits in a DG-associated spatial memory test - the metric task. Compatible with this finding, we also discovered saturated, and subsequently impaired, LTP of excitatory synaptic transmission at the perforant path to DGC synapse. This saturation of LTP was consistent with evidence suggesting that perforant path to DGC synapses in kindled mice had previously experienced LTP-like changes to their synaptic weights: increased postsynaptic depolarizations in response to equivalent presynaptic input and significantly larger amplitude AMPA receptor mediated spontaneous EPSCs. Additionally, there was evidence for kindling-induced changes in the intrinsic excitability of DGCs: reduced threshold to population spikes under extracellular recording conditions and significantly increased membrane resistances observed in DGCs. Importantly, quantitative immunohistochemical analysis revealed hippocampal astrogliosis in the absence of overt neuron loss. These changes in spatial pattern processing and memory deficits in corneal kindled mice represent a novel model of seizure-induced cognitive dysfunction associated with pathophysiological remodeling of excitatory synaptic transmission and granule cell excitability in the absence of overt cell loss.

The PTZ kindling mouse model of epilepsy exhibits exploratory drive deficits and aberrant activity amongst VTA dopamine neurons in both familiar and novel space

Recurrent seizures that define epilepsy are often accompanied by psychosocial problems and cognitive deficits with incompletely understood aetiology. We therefore used the pentylenetetrazol (PTZ) kindling model of epilepsy in mice to examine potential seizure-associated neuropathologies, focusing on motivation, memory and novel-environment-induced activation of midbrain dopaminergic neurons. In addition to recurrent seizures, we found that PTZ kindling led to a strong suppression of novelty-driven exploration while largely sparing fear-driven exploration. The deficits in exploratory drive may be relevant for other cognitive impairments since reduced unassisted rearing in a learning arena correlated with poorer spatial memory of object location. Using c-Fos immunofluorescence as a marker of neuronal activity, we observed that dopamine neurons within the ventral tegmental area (VTA) of PTZ kindled mice demonstrate hyperactivity at baseline and hypoactivity in response to a novel environment compared to saline-injected cagemate controls. These data extend previous findings of PTZ kindling-mediated disruptions of hippocampal processes important for novel environment recognition and learning by demonstrating PTZ kindling also induces motivational deficits that are associated with reduced stimulus-evoked activation of VTA dopamine neurons. More broadly, these data help understand the aetiology of complex behavioural changes in the PTZ kindling model, and may assist in the development of superior diagnoses and treatments for epilepsy.

Acute cognitive impact of antiseizure drugs in naive rodents and corneal-kindled mice

OBJECTIVE

Some antiseizure drugs (ASDs) are associated with cognitive liability in patients with epilepsy, thus ASDs without this risk would be preferred. Little comparative pharmacology exists with ASDs in preclinical models of cognition. Few pharmacologic studies exist on the acute effects in rodents with chronic seizures. Predicting risk for cognitive impact with preclinical models may supply valuable ASD differentiation data.

METHODS

ASDs (phenytoin [PHT]; carbamazepine [CBZ]; valproic acid [VPA]; lamotrigine [LTG]; phenobarbital [PB]; tiagabine [TGB]; retigabine [RTG]; topiramate [TPM]; and levetiracetam [LEV]) were administered equivalent to maximal electroshock median effective dose ([ED50]; mice, rats), or median dose necessary to elicit minimal motor impairment (median toxic dose [TD50]; rats). Cognition models with naive adult rodents were novel object/place recognition (NOPR) task with CF-1 mice, and Morris water maze (MWM) with Sprague-Dawley rats. Selected ASDs were also administered to rats prior to testing in an open field. The effect of chronic seizures and ASD administration on cognitive performance in NOPR was also determined with corneal-kindled mice. Mice that did not achieve kindling criterion (partially kindled) were included to examine the effect of electrical stimulation on cognitive performance. Sham-kindled and age-matched mice were also tested.

RESULTS

No ASD (ED50) affected latency to locate the MWM platform; TD50 of PB, RTG, TPM, and VPA reduced this latency. In naive mice, CBZ and VPA (ED50) reduced time with the novel object. Of interest, no ASD (ED50) affected performance of fully kindled mice in NOPR, whereas CBZ and LEV improved cognitive performance of partially kindled mice.

SIGNIFICANCE

Standardized approaches to the preclinical evaluation of an ASD's potential cognitive impact are needed to inform drug development. This study demonstrated acute, dose- and model-dependent effects of therapeutically relevant doses of ASDs on cognitive performance of naive mice and rats, and corneal-kindled mice. This study highlights the challenge of predicting clinical adverse effects with preclinical models.

The α4β2 nicotinic acetylcholine receptor modulates autism-like behavioral and motor abnormalities in pentylenetetrazol-kindled mice

Epilepsy is associated with several psychiatric disorders, including cognitive impairment, autism and attention deficit/hyperactivity disorder (ADHD). However, the psychopathology of epilepsy is frequently unrecognized and untreated in patients. In the present study, we investigated the effects of ABT-418, a neuronal nicotinic acetylcholine receptor agonist, on pentylenetetrazol (PTZ)-kindled mice with behavioral and motor abnormalities. PTZ-kindled mice displayed impaired motor coordination (in the rotarod test), anxiety (in the elevated plus maze test) and social approach impairment (in the three-chamber social test) compared with control mice. ABT-418 treatment (0.05 mg/kg, intraperitoneally) alleviated these behavioral abnormalities in PTZ-kindled mice. Immunolabeling of tissue sections demonstrated that expression of the α4 nicotinic acetylcholine receptor subunit in the medial habenula was similar in control and PTZ-kindled mice. However, expression was significantly decreased in the piriform cortex in PTZ-kindled mice. In addition, we examined the expression of the synaptic adhesion molecule neuroligin 3 (NLG3). NLG3 expression in the piriform cortex was significantly higher in PTZ-kindled mice compared with control mice. Collectively, our findings suggest that ADHD-like or autistic-like behavioral abnormalities associated with epilepsy are closely related to the downregulation of the α4 nicotinic receptor and the upregulation of NLG3 in the piriform cortex. In summary, this study indicates that ABT-418 might have therapeutic potential for attentional impairment in epileptic patients with psychiatric disorders such as autism and ADHD.

Effects of an acute seizure on associative learning and memory

Past studies have demonstrated that inducing several seizures or continuous seizures in neonatal or adult rats results in impairments in learning and memory. The impact of a single acute seizure on learning and memory has not been investigated in mice. In this study, we exposed adult 129SvEvTac mice to the inhalant flurothyl until a behavioral seizure was induced. Our study consisted of 4 experiments where we examined the effect of one seizure before or after delay fear conditioning. We also included a separate cohort of animals that was tested in the open field after a seizure to rule out changes in locomotor activity influencing the results of memory tests. Mice that had experienced a single seizure 1h, but not 6h, prior to training showed a significant impairment in associative conditioning to the conditioned stimulus when compared with controls 24h later. There were no differences in freezing one day later for animals that experienced a single seizure 1h after associative learning. We also found that an acute seizure reduced activity levels in an open-field test 2h but not 24h later. These findings suggest that an acute seizure occurring immediately before learning can have an effect on the recall of events occurring shortly after that seizure. In contrast, an acute seizure occurring shortly after learning appears to have little or no effect on long-term memory. These findings have implications for understanding the acute effects of seizures on the acquisition of new knowledge.

Analysis of radiation therapy in a model of triple-negative breast cancer brain metastasis

Most cancer patients with brain metastases are treated with radiation therapy, yet this modality has not yet been meaningfully incorporated into preclinical experimental brain metastasis models. We applied two forms of whole brain radiation therapy (WBRT) to the brain-tropic 231-BR experimental brain metastasis model of triple-negative breast cancer. When compared to sham controls, WBRT as 3 Gy × 10 fractions (3 × 10) reduced the number of micrometastases and large metastases by 87.7 and 54.5 %, respectively (both p < 0.01); whereas a single radiation dose of 15 Gy × 1 (15 × 1) was less effective, reducing metastases by 58.4 % (p < 0.01) and 47.1 % (p = 0.41), respectively. Neuroinflammation in the adjacent brain parenchyma was due solely to a reaction from metastases, and not radiotherapy, while adult neurogenesis in brains was adversely affected following both radiation regimens. The nature of radiation resistance was investigated by ex vivo culture of tumor cells that survived initial WBRT ("Surviving" cultures). The Surviving cultures surprisingly demonstrated increased radiosensitivity ex vivo. In contrast, re-injection of Surviving cultures and re-treatment with a 3 × 10 WBRT regimen significantly reduced the number of large and micrometastases that developed in vivo, suggesting a role for the microenvironment. Micrometastases derived from tumor cells surviving initial 3 × 10 WBRT demonstrated a trend toward radioresistance upon repeat treatment (p = 0.09). The data confirm the potency of a fractionated 3 × 10 WBRT regimen and identify the brain microenvironment as a potential determinant of radiation efficacy. The data also nominate the Surviving cultures as a potential new translational model for radiotherapy.

The effects of Nigella sativa on neural damage after pentylenetetrazole induced seizures in rats

Nigella sativa (NS) has been suggested to have neuroprotective and anti-seizures properties. The aim of current study was to investigate the effects of NS hydro-alcoholic extract on neural damage after pentylenetetrazole (PTZ) - induced repeated seizures. The rats were divided into five groups: (1) control (saline), (2) PTZ (50 mg/kg, i.p.), (3-5) PTZ-NS 100, PTZ-NS 200 and PTZ-NS 400 (100, 200 and 400 mg/kg of NS extract respectively, 30 min prior to each PTZ injection on 5 consecutive days). The passive avoidance (PA) test was done and the brains were then removed for histological measurements. The PTZ-NS 100, PTZ-NS 200 and PTZ-NS 400 groups had lower seizure scores than PTZ group (P < 0.01 and P < 0.001). The latency to enter the dark compartment by the animals of PTZ group was lower than control in PA test (P < 0.01). Pre-treatment by 400 mg/kg of the extract increased the latency to enter the dark compartment (P < 0.05). Meanwhile, different doses of the extract inhibited production of dark neurons in different regions of hippocampus (P < 0.001). The present study allows us to suggest that the NS possesses a potential ability to prevent hippocampal neural damage which is accompanied with improving effects on memory.

Aberrant hippocampal neurogenesis after limbic kindling: Relationship to BDNF and hippocampal-dependent memory

Seizures dramatically increase the number of adult generated neurons in the hippocampus. However, it is not known whether this effect depends on seizures that originate in specific brain regions or whether it is nonspecific to seizure activity regardless of origin. We used kindling of different brain sites to address this question. Rats received 99 kindling stimulations of the basolateral amygdala, dorsal hippocampus, or caudate nucleus over a 6-week period. After kindling, we counted the number of adult generated hippocampal neurons that were birth-dated with the proliferative marker bromodeoxyuridine (BrdU) to evaluate cell proliferation and survival under conditions of repeated seizures. Next, we counted the number of doublecortin immunoreactive (DCX-ir) cells and evaluated their dendritic complexity to determine if limbic and nonlimbic seizures have differential effects on neuronal maturation. We also quantified hippocampal brain-derived neurotrophin factor (BDNF) protein levels using an ELISA kit and assessed memory performance using a hippocampal-dependent fear conditioning paradigm. We found that limbic, but not nonlimbic, seizures dramatically increased hippocampal cell proliferation and the number of hilar-CA3 ectopic granule cells. Further, limbic kindling promoted dendritic outgrowth of DCX-ir cells and the number of DCX-ir cells containing basal dendrites. Limbic kindling also enhanced BDNF protein levels throughout the entire hippocampus and impaired the retrieval of fear memories. Collectively, our results suggest a relationship between limbic seizures, neurogenesis, BDNF protein, and cognition.

Limbic but not non-limbic kindling impairs conditioned fear and promotes plasticity of NPY and its Y2 receptor

Epileptic seizures negatively affect cognition. However, the mechanisms that contribute to cognitive impairments after seizures are largely unknown. Here, we examined the effects of long-term kindling (i.e., 99 stimulations) of limbic (basolateral amygdala, dorsal hippocampus) and non-limbic (caudate nucleus) brain sites on conditioned fear and hippocampal plasticity. We first showed that kindling had no effect on acquisition of a hippocampal-dependent trace fear-conditioning task but limbic kindling impaired the retrieval of these fear memories. To determine the relationship between memory and hippocampal neuronal activity, we examined the expression of Fos protein 90 min after memory retrieval (i.e., 4 days after the last kindling stimulation). We found that limbic kindling, but not non-limbic kindling, decreased Fos expression in the granule cell layer, hilus, CA3 pyramidal cell layer, and CA1 pyramidal cell layer. Next, to investigate a mechanism that could contribute to dampen hippocampal neuronal activity in limbic-kindled rats, we focused on the endogenous anticonvulsant neuropeptide Y (NPY), which is expressed in a subset of GABAergic interneurons and can prevent glutamate release through interactions with its Y2 receptor. We found that limbic kindling significantly decreased the number of NPY-immunoreactive cells in several hippocampal subfields despite minimal staining of the neurodegenerative marker Fluoro-Jade B. However, we also noted that limbic kindling enhanced NPY immunoreactivity throughout the mossy fiber pathway. In these same regions, we observed limbic kindling-induced de novo expression of the NPY Y2 receptor. These novel findings demonstrate the site-specific effects of kindling on cognition and NPY plasticity, and they provide evidence that altered hippocampal NPY after limbic seizures coincides with dampened neural activity and cognitive impairments.

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.

Different emotional disturbances in two experimental models of temporal lobe epilepsy in rats

Affective symptoms such as anxiety and depression are frequently observed in patients with epilepsy. The mechanisms of comorbidity of epilepsy and affective disorders, however, remain unclear. Diverse models are traditionally used in epilepsy research, including the status epilepticus (SE) model in rats, which are aimed at generating chronic epileptic animals; however, the implications of different SE models and rat strains in emotional behaviors has not been reported. To address this issue, we examined the emotional sequelae of two SE models of temporal lobe epilepsy (TLE)--the lithium-pilocarpine (LIP) model and the kainic acid (KA) model--in two different rat strains (Wistar and Sprague-Dawley), which differ significantly in the pattern and extent of TLE-associated brain lesions. We found differences between LIP- and KA-treated animals in tests for depression-like and anxiety-like behaviors, as well as differences in plasma corticosterone levels. Whereas only LIP-treated rats displayed increased motivation to consume saccharin, both SE models led to reduced motivation for social contact, with LIP-treated animals being particularly affected. Evaluation of behavior in the open field test indicated very low levels of anxiety in LIP-treated rats and a mild decrease in KA-treated rats compared to controls. After exposure to a battery of behavioral tests, plasma corticosterone levels were increased only in LIP-treated animals. This hyperactivity in the hypothalamus-pituitary-adrenocortical (HPA) axis was highly correlated with performance in the open field test and the social interaction test, suggesting that comorbidity of epilepsy and emotional behaviors might also be related to other factors such as HPA axis function. Our results indicate that altered emotional behaviors are not inherent to the epileptic condition in experimental TLE; instead, they likely reflect alterations in anxiety levels related to model-dependent dysregulation of the HPA axis.

Hippocampal-dependent spatial memory in the water maze is preserved in an experimental model of temporal lobe epilepsy in rats

Cognitive impairment is a major concern in temporal lobe epilepsy (TLE). While different experimental models have been used to characterize TLE-related cognitive deficits, little is known on whether a particular deficit is more associated with the underlying brain injuries than with the epileptic condition per se. Here, we look at the relationship between the pattern of brain damage and spatial memory deficits in two chronic models of TLE (lithium-pilocarpine, LIP and kainic acid, KA) from two different rat strains (Wistar and Sprague-Dawley) using the Morris water maze and the elevated plus maze in combination with MRI imaging and post-morten neuronal immunostaining. We found fundamental differences between LIP- and KA-treated epileptic rats regarding spatial memory deficits and anxiety. LIP-treated animals from both strains showed significant impairment in the acquisition and retention of spatial memory, and were unable to learn a cued version of the task. In contrast, KA-treated rats were differently affected. Sprague-Dawley KA-treated rats learned less efficiently than Wistar KA-treated animals, which performed similar to control rats in the acquisition and in a probe trial testing for spatial memory. Different anxiety levels and the extension of brain lesions affecting the hippocampus and the amydgala concur with spatial memory deficits observed in epileptic rats. Hence, our results suggest that hippocampal-dependent spatial memory is not necessarily affected in TLE and that comorbidity between spatial deficits and anxiety is more related with the underlying brain lesions than with the epileptic condition per se.

Kindling of the lateral septum and the amygdala: effects on anxiety in rats

Long-term kindling of limbic system structures may produce substantial changes in emotional behavior in rats. This study examined long-term changes in two kindled structures that have opposite effects on anxiety, the lateral septum and the central nucleus of the amygdala. The purpose of the experiment was to examine the specificity of the emotional effects of kindling by employing a double dissociation design. Animals were tested in two common animal models of anxiety, the water-lick conflict test and the elevated plus-maze. In the conflict test amygdala-kindled animals demonstrated a significant anxiolytic effect when compared with sham-kindled animals. This effect was potentiated by chlordiazepoxide. Septally-kindled animals exhibited a significant anticonflict effect when compared to sham-kindled animals in the first session. Septally-kindled animals spent significantly more time on the open arms of the elevated plus-maze than did sham-kindled animals. Observed changes persisted 6weeks after the termination of 150 kindling sessions. The effects of long-term kindling were highly consistent with those of disruption rather than facilitation.

Regional changes in gene expression after limbic kindling

Repeated electrical stimulation results in development of seizures and a permanent increase in seizure susceptibility (kindling). The permanence of kindling suggests that chronic changes in gene expression are involved. Kindling at different sites produces specific effects on interictal behaviors such as spatial cognition and anxiety, suggesting that causal changes in gene expression might be restricted to the stimulated site. We employed focused microarray analysis to characterize changes in gene expression associated with amygdaloid and hippocampal kindling. Male Long-Evans rats received 1 s trains of electrical stimulation to either the amygdala or hippocampus once daily until five generalized seizures had been kindled. Yoked control rats carried electrodes but were not stimulated. Rats were euthanized 14 days after the last seizures, both amygdala and hippocampus dissected, and transcriptome profiles compared. Of the 1,200 rat brain-associated genes evaluated, 39 genes exhibited statistically significant expression differences between the kindled and non-kindled amygdala and 106 genes exhibited statistically significant differences between the kindled and non-kindled hippocampus. In the amygdala, subsequent ontological analyses using the GOMiner algorithm demonstrated significant enrichment in categories related to cytoskeletal reorganization and cation transport, as well as in gene families related to synaptic transmission and neurogenesis. In the hippocampus, significant enrichment in gene expression within categories related to cytoskeletal reorganization and cation transport was similarly observed. Furthermore, unique to the hippocampus, enrichment in transcription factor activity and GTPase-mediated signal transduction was identified. Overall, these data identify specific and unique neurochemical pathways chronically altered following kindling in the two sites, and provide a platform for defining the molecular basis for the differential behaviors observed in the interictal period.

Neurobehavioral consequences of stressor exposure in rodent models of epilepsy

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

Cortical kindling induces elevated levels of AMPA and GABA receptor subunit mRNA within the amygdala/piriform region and is associated with behavioral changes in the rat

Cortical kindling causes alterations within the motor cortex and results in long-standing motor deficits. Less attention has been directed to other regions that also participate in the epileptiform activity. We examined if cortical kindling could induce changes in excitatory and inhibitory receptor subunit mRNA in the amygdala/piriform regions and if such changes are associated with behavioral deficits. After cortical kindling, amygdala/piriform regions were dissected to analyze mRNA levels of NMDA, AMPA, and GABA receptor subunits using reverse transcription polymerase chain reaction, or rats were subjected to a series of behavioral tests. Kindled rats had significantly greater amounts of GluR1 and GluR2 AMPA receptor mRNA, and alpha1 and alpha2 GABA receptor subunit mRNA, compared with sham controls, which was associated with greater anxiety-like behaviors in the elevated plus maze and reduced freezing behaviors in the fear conditioning task. In summary, cortical kindling produces dynamic receptor subunit changes in regions in addition to the seizure focus.

Effects of pentylenetetrazol-induced brief convulsive seizures on spatial memory and fear memory

Previous studies have demonstrated that in the pentylenetetrazol (PTZ) kindling model, recurrent seizures either impair or have no effect on learning and memory. However, the effects of brief seizures on learning and memory remain unknown. Here, we found that a single injection of a convulsive dose of PTZ (50 mg/kg, ip) induced brief seizures in Sprague-Dawley rats. Administration of PTZ before training impaired the acquisition of spatial memory in the Morris water maze (MWM) and fear memory in contextual fear conditioning. However, the administration of PTZ immediately after training did not affect memory consolidation in either task. These findings suggest that brief seizures have different effects on acquisition and consolidation of spatial and fear memory.

Effects of repeated electroconvulsive shock seizures and pilocarpine-induced status epilepticus on emotional behavior in the rat

Affective symptoms are frequently observed in patients with epilepsy. Although the etiology of these behavioral complications remains unknown, it is possible that brain damage associated with frequent or prolonged seizures may contribute to their development. To address this issue, we examined the behavioral sequelae of repeated brief seizures evoked by electroconvulsive shock (ECS) and compared them with those resulting from prolonged status epilepticus (SE) induced with pilocarpine. Using the open-field and elevated plus-maze tests, we detected the presence of behavioral alterations indicative of elevated levels of anxiety in rats that were administered a course of ECS seizures. Fear conditioning was also enhanced in these animals. However, the rats that had experienced SE exhibited less anxiety-like behavior than controls and were severely impaired in fear conditioning. These results support the notion that brain lesions caused by either brief repeated seizures or SE is sufficient to induce some affective disturbances.

Changes in midline thalamic recruiting responses in the prefrontal cortex of the rat during the development of chronic limbic seizures

PURPOSE

Mesial temporal lobe epilepsy (MTLE) is a common form of epilepsy that affects the limbic system and is associated with decreases in memory and cognitive performance. The medial prefrontal cortex (PC) in rats, which has a role in memory, is associated with and linked anatomically to the limbic system, but it is unknown if and how MTLE affects the PC.

METHODS

We evoked responses in vivo in the PC by electrical stimulation of the mediodorsal (MD) and reuniens (RE) nuclei of the thalamus at several time points following status epilepticus, before and after onset of spontaneous seizures. Kindled animals were used as additional controls for the effect of seizures that were independent of epilepsy.

RESULTS

Epileptic animals had decreased response amplitudes and significantly reduced recruiting compared to controls, whereas kindled animals showed an increase in both measures. These changes were not associated with neuronal loss in the PC, although there was significant loss in both the MD and RE in the epileptic animals.

CONCLUSIONS

There is a significant reduction in the thalamically induced evoked responses in the PCs of epileptic animals. This finding suggests that physiologic dysfunction in MTLE extends beyond primary limbic circuits into areas without overt neuronal injury.

Amygdaloid kindling is anxiogenic but fails to alter object recognition or spatial working memory in rats

Kindling in rats produces enduring behavioral changes that parallel the psychobehavioral disturbances frequently accompanying temporal lobe epilepsy. Some evidence suggests that the site of kindling is an important determinant of the type of behavioral changes observed following kindling, although this variable has not been systematically investigated. In the present experiments, the effects of amygdaloid kindling were assessed on a battery of behavioral tests we used previously to assess the effects of kindling in dorsal hippocampus or perirhinal cortex. Three generalized seizures were kindled with stimulation in or near the basolateral amygdala. One week later, rats were tested successively on measures of anxiety, activity, object recognition memory, and spatial working memory over a period of 3 weeks. Amygdaloid kindling produced increased anxiety, but spared all other behaviors assessed. This pattern of results is partially distinct from the previously described effects of perirhinal cortical kindling, which increases anxiety but also impairs object recognition memory, and is completely distinct from dorsal hippocampal kindling, which selectively increases activity and impairs spatial working memory. The observations suggest that kindling of distinct highly interconnected temporal lobe sites produces distinct patterns of behavioral comorbidity. The underlying mechanisms are thus most likely localized to intrinsic circuits at the site of seizure origination.

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.

Kindling of basolateral amygdala but not ventral hippocampus or perirhinal cortex disrupts sensorimotor gating in rats

The neural mechanisms mediating prepulse inhibition (PPI) appear to have relevance to neurological and psychiatric disorders. Patients with temporal lobe epilepsy exhibit psychotic symptoms and disrupted PPI, therefore the present experiments examined the consequences of seizures induced by kindling on PPI. Rats were chronically implanted with an electrode into the basolateral amygdala, perirhinal cortex, or ventral hippocampus and stimulated twice daily until 3 fully generalized, class 5 seizures were elicited. Kindling of basolateral amygdala, but not perirhinal cortex or ventral hippocampus, disrupted PPI when testing began 2min, but not 48h, following the elicitation of the third class 5 seizure. Startle amplitudes were unaffected by kindling. These results suggest that the anatomical origin of seizures is an important factor in determining their potentially disruptive effects on PPI.

Disruption of PTEN coupling with 5-HT2C receptors suppresses behavioral responses induced by drugs of abuse

The widespread distribution of the tumor suppressor PTEN (phosphatase and tensin homolog deleted on chromosome 10) in the adult brain suggests its role in a broad range of brain functions. Here we show evidence supporting a physical interaction of PTEN with a region in the third intracellular loop (3L4F) of the serotonin 5-HT2C receptor (5-HT2cR, formerly 5-HT1c receptor) in cell cultures. PTEN limits agonist-induced phosphorylation of 5-HT2cR through its protein phosphatase activity. We showed the probable existence of PTEN:5-HT2cR complexes in putative dopaminergic neurons in the rat ventral tegmental area (VTA), a brain region in which virtually all abused drugs exert rewarding effects by activating its dopamine neurons. We synthesized the interfering peptide Tat-3L4F, which is able to disrupt PTEN coupling with 5-HT2cR. Systemic application of Tat-3L4F or the 5-HT2cR agonist Ro600175 suppressed the increased firing rate of VTA dopaminergic neurons induced by delta9-tetrahydrocannabinol (THC), the psychoactive ingredient of marijuana. Using behavioral tests, we found that Tat-3L4F or Ro600175 blocks conditioned place preference of THC or nicotine, and that Ro600175, but not Tat-3L4F, produces anxiogenic effects, penile erection, hypophagia and motor functional suppression. These results suggest a potential strategy for treating drug addiction with the Tat-3L4F peptide.

Models of epilepsy in the developing and adult brain: implications for neuroprotection

Repeated seizures cause a sequence of molecular and cellular changes in both the developing and adult brain, which may lead to intractable epilepsy. This article reviews this sequence of neuronal alterations, with emphasis on the kindling model. At each step, the opportunity exists for strategic intervention to prevent or reduce the downstream consequences of epileptogenesis and seizure-induced adverse plasticity. The concept of seizure-induced brain damage must be expanded to include behavioral and cognitive deficits, as well as structural neuronal damage and increased predisposition to seizures.

Behavioral differences between subgroups of rats with high and low threshold to clonic convulsions induced by DMCM, a benzodiazepine inverse agonist

In epileptic patients, there is a high incidence of psychiatric comorbidities, such as anxiety. Gamma-aminobutyric acid (GABA) ionotropic receptor GABA(A)/benzodiazepine allosteric site is involved in both epilepsy and anxiety. This involvement is based on the fact that benzodiazepine allosteric site agonists are anticonvulsant and anxiolytic drugs; on the other hand, benzodiazepine inverse agonists are potent convulsant and anxiogenic drugs. The aim of this work was to determine if subgroups of rats selected according to their susceptibility to clonic convulsions induced by a convulsant dose 50% (CD50) of DMCM, a benzodiazepine inverse agonist, would differ in behavioral tests commonly used to measure anxiety (elevated plus-maze, open field) and depression (forced swimming test). In the first experiment, subgroups of adult male Wistar rats were selected after a single dose of DMCM and in the second experiment they were selected after two injections of DMCM given after an interval of 1 week. Those rats presenting full clonic convulsions were termed Low Threshold rats to DMCM-induced clonic convulsions (LTR) and those not having clonic convulsions High Threshold rats to DMCM-induced clonic convulsions (HTR). In both experiments, only those rats presenting full clonic convulsions induced by DMCM and those not showing any signs of motor disturbances were used in the behavioral tests. The results showed that the LTR subgroup selected after two injections of a CD50 of DMCM spent a significantly lower time in the open arms of the elevated plus-maze and in the off the walls area of the open field; moreover, this group also presented a higher number of rearings in the open field. There were no significant differences between HTR and LTR subgroups in the forced swimming test. LTR and HTR subgroups selected after only one injection of DMCM did not differ in the three behavioral tests. To verify if the behavioral differences between HTR and LTR subgroups of rats selected after two injections of DMCM were due to the clonic convulsion, another experiment was carried out in which subgroups of rats susceptible and nonsusceptible to clonic convulsions induced by a CD50 of picrotoxin, a GABA(A) receptor channel blocker, were selected and submitted to the elevated plus-maze and open field tests. The results obtained did not show any significant differences between these two subgroups in the elevated plus-maze and open field tests. In another approach to determine the relation between fear/anxiety and susceptibility to clonic convulsions, subgroups of rats were selected in the elevated plus-maze as more or less fearful/anxious. The CD50 for clonic convulsions induced by DMCM was determined for each of these two subgroups. The results showed a significantly lower CD50 for the more fearful/anxious subgroup, which means a higher susceptibility to clonic convulsions induced by DMCM. The present findings show a relation between susceptibility to clonic convulsions and fear/anxiety and vice versa which may be due to differences in the assembly of GABA(A)/allosteric benzodiazepine site receptors in regions of the brain.

The importance of housing conditions on behavioral sensitization and tolerance to ethanol

The differential outcomes of social isolation and crowding environment on the effects of single or repeated administration of ethanol on open-field behavior were examined in female mice. Whereas housing conditions did not alter the increase in locomotor activity induced by ethanol single administration, behavioral sensitization (a progressive increase of a drug effect following repeated drug administration) to the locomotor activating effect of ethanol was significantly greater in crowded mice as compared to isolated and control groups. Single administration of ethanol significantly decreased rearing frequency and increased immobility duration, there being tolerance to these ethanol behavior effects after repeated treatment. Social isolation attenuated the increase in immobility behavior induced by single administration of ethanol and potentiated the tolerance of ethanol-induced rearing decrease, verified after repeated treatment. These results point out that both sensitization and tolerance to the behavioral effects of ethanol can be critically influenced by housing conditions.

Chronic administration of quetiapine alleviates the anxiety-like behavioural changes induced by a neurotoxic regimen of dl-amphetamine in rats

We have demonstrated that the atypical antipsychotic drugs prevent cell death in PC12 cells induced by various cytotoxins and have protective effects on methamphetamine-induced neurotoxcity in rats. The present study was designed to examine the possible effects of chronic administration of quetiapine, an atypical antipsychotic drug, on the anxiety-like behavioural consequences of a neurotoxic regimen of dl-amphetamine. Rats were treated with quetiapine (10 mg/kg/day; i.p.) for 33 days. During days 15-19 of this period, the animals were given dl-amphetamine (20 mg/kg/day; s.c.) 1 h after the administration of quetiapine. The repeated administration of dl-amphetamine resulted in a decrease of tyrosine hydroxylase (TH) immunostaining in the caudate putamen, hyperthermia, and anxiety-like behavioural changes. The behavioural changes were indicated by a significant increase in the time spent in the light box in the light/dark box test, an increase in the ratios of ambulation distance inside the inner circle over the total ambulation distance and rearings inside the inner circle over the total rearings in the open field test, and an increase in the time spent in open arms in the elevated plus-maze test. Chronic administration of quetiapine significantly attenuated the dl-amphetamine-induced hyperthermia, and the anxiety-like behavioural changes in the light/dark box and in the open field tests. These results suggest that quetiapine can normalize the dl-amphetamine-induced anxiety-like behavioural changes, and might be helpful in the treatment for amphetamine-induced emotional changes.

Anterior perirhinal cortex kindling produces long-lasting effects on anxiety and object recognition memory

Temporal lobe epilepsy (TLE) is frequently accompanied by memory impairments and, although their bases are unknown, most research has focused on the hippocampus. The present study investigated the importance of another medial temporal lobe structure, the perirhinal cortex (Prh), in changes in memory in TLE using kindling as a model. Rats were kindled twice daily with anterior Prh stimulation until three fully generalized seizures were evoked. Beginning 7 days 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 task in a water maze in order to assess anxiety-related and exploratory behaviour, object recognition memory and spatial cognition. Kindling increased anxiety-related behaviour in both the elevated plus and open field mazes and disrupted spontaneous object recognition but spared all other behaviours tested. These results are consistent with other findings indicating a greater role for the Prh in object memory and emotional behaviour than in spatial memory and contrast with the selective disruption of spatial memory produced by dorsal hippocampal kindling. The site-selectivity of the behavioural disruptions produced by kindling indicates that such effects are probably mediated by changes particular to the site of seizure initiation rather than to changes in the characteristic circuitry activated by limbic seizure generalization. Further investigation of the behavioural effects of Prh kindling may be useful for studying the mechanisms of mnemonic and affective dysfunction associated with TLE and offer insights into bases for variability in such dysfunction across patients.

Conditioned effects of kindling three different sites in the hippocampal complex of the rat

Rats received kindling stimulations to the perirhinal cortex (PRh), ventral hippocampus (VH), or dorsal hippocampus (DH) in 1 environment and an equivalent number of sham stimulations in a 2nd environment. The PRh-kindled rats displayed rapid kindling and a swift emergence of conditioned interictal defensiveness. In contrast, the VH- and DH-kindled rats displayed much slower kindling and slow or no conditioning, respectively. No effects of conditioning on the convulsions, comparable with those associated with amygdala kindling, were observed. These results establish the generality of some of the previously reported kindling-related conditioned effects, confirm the site specificity of some of these effects, and suggest that the convulsions, rather than the stimulations, function as the unconditioned stimuli for the conditioning of interictal behavior.

Medial prefrontal cortex is involved in spatial temporal order memory but not spatial recognition memory in tests relying on spontaneous exploration in rats

The present study describes two novel tasks relying on spontaneous patterns of exploration in a radial-arm maze that can be used to assess spatial recognition memory and spatial temporal order memory (i.e. memory for the order in which places have been visited) in the rat. In the recognition memory task, rats were permitted to freely explore two arms in the maze on a first trial and one 'familiar' arm and one novelly located arm on a second trial 105 min later. In the temporal order memory task, rats were permitted to explore two arms in the maze on a first trial, two novel arms on a second trial 60 min later, and one 'older familiar' arm and one 'more recent familiar' arm on a third trial 45 min later. Using these tasks, we found that rats direct greater exploration at a novel than a familiar arm location, thus showing long-term spatial recognition memory, and at an older familiar arm than a more recent familiar arm, thus showing long-term spatial temporal order memory. Lidocaine inactivation of the mPFC prior to the final trial in each task disrupted performance on the temporal order but not the recognition memory task, thereby demonstrating a role for the mPFC in the retrieval and/or use of temporal order information but not in spatial memory per se. These findings highlight the specific involvement of the rat mPFC in temporal order memory and have important implications for a broader understanding of mPFC function.

Mechanisms of epilepsy progression: current theories and perspectives from neuroplasticity in adulthood and development

Clinical and epidemiological studies have repeatedly demonstrated that a subset of patients with epilepsy have progressive syndromes with increasing seizure frequency and cumulative adverse effects despite optimal anticonvulsant therapy. Recent longitudinal imaging studies and long-term neuropsychological studies have confirmed that a substantial subset of people with epilepsy undergo progressive brain atrophy accompanied by functional declines that worsen with duration of epilepsy. As further evidence of the progressive and adverse effects of inadequately controlled epilepsy, chronic experimental models of epilepsy and the phenomenon of kindling have provided abundant evidence that neural circuits undergo long-term progressive structural and functional alterations in response to seizures. This long-term seizure-induced plasticity in neural circuits appears to be "bidirectional", inducing progressive damage while also inducing resistance to additional damage, as a function of timing or inter-seizure interval. Seizure-induced plasticity has pronounced age-dependence, and influences long-term cognitive consequences of seizures during early life and acquired susceptibility to epilepsy in adulthood. While it is clear from clinical and epidemiological studies that human epilepsy is a heterogeneous disorder and that not all epileptic syndromes are progressive, emerging results from studies of activity-dependent and seizure-induced plasticity and perspectives from "complex systems" analysis are providing new insights into systematic neurobiological processes that are likely to influence the progressive features of epileptic syndromes and patterns of progression in individual patients. The emerging perspective is that phenomena of plasticity and genetic background exert powerful effects in development and adulthood through regulation of activity-dependent structural and functional remodeling of neural circuitry, and that these effects not only influence progression and consequences of seizures, but also offer new opportunities for therapeutic intervention.

The relation between extent of dorsal hippocampal kindling and delayed-match-to-place performance in the Morris water maze

Dorsal hippocampal kindling impairs subsequent performance on spatial tasks. The relation between this effect and the extent of kindling achieved prior to testing has not been clearly established. Thus, the present study investigated the effects of dorsal hippocampal kindling on performance of a delayed-match-to-place (DMTP) task in the Morris water maze by assessing performance after each of series of different points in the kindling process including 1, 6, 11, and 16 afterdischarges, 1 stage 1 seizure, and 1 stage 5 seizure. We found that kindling produced a deficit that was apparent very early into kindling in terms of both direct swim (by 1 AD) and escape distance (by 6 ADs) measures but that did not clearly change in severity with further kindling. These results illustrate that kindling of even a few localized hippocampal seizures can disrupt spatial cognition and suggest that the mechanisms mediating memory disruption either do not change substantially as kindling progresses or that compensatory processes are engaged across training that mitigate any further kindling-related deteriorations in performance.

Do seizures cause irreversible cognitive damage? Evidence from animal studies

Data from experimental models provide evidence that both prolonged and brief seizures can cause irreversible impairment in spatial and emotional learning and memory. Factors related to the severity of the behavioral impairments include genetic background, age at the time of the epileptogenic insult, extent of brain lesion, location of seizure focus, seizure duration, seizure number, brain reserve, and environmental and social living conditions. Further, as in humans, the interval between the last seizure and behavioral testing as well as treatment with antiepileptic drugs can affect the test results.

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.

Anticipating the Attack: Temporal Conditioning During Amygdala Kindling in Rats

The present study showed that amygdala-kindled rats use short-interval timing superimposed on phase or ordinal timing to predict when a convulsion will occur. In 2 experiments, rats received 1 stimulation and 1 sham stimulation each day, always at the same times (conditioned stimulus [CS]+ and CS- times, respectively) and 150 s after rats had been placed in the testing chamber (the preadministration interval). As kindling progressed, the rats displayed more defensive behavior at the CS+ time than at the CS- time. Then, a stimulation-free peak-procedure test was conducted: At the CS+ time, but not at the CS- time, defensive behavior increased progressively as the 150-s preadministration interval elapsed, and then it gradually declined.

The effect of kindled seizures on the locomotory behavior of Long-Evans rats

The incidence of attention deficit hyperactivity disorder (ADHD) is higher in children with epilepsy than in the general childhood population. The origin of the symptoms of ADHD seen in children with epilepsy is unknown. This experiment used an animal model to investigate whether seizures could be a cause of the hyperactivity sometimes associated with epilepsy. Sixteen male Long-Evans rats were implanted with electrodes, and 8 of them were kindled until generalized stage 5 seizures were elicited. Eight subjects were handled, but not kindled. The behavior of the rats in the two groups was compared in an open field test. The time spent in four behaviors was measured: exploratory behavior, immobility, eating, and grooming. Rats were tested after 5 stage 5 seizures, after 10 stage 5 seizures, after 15 stage 5 seizures, after a 2-week rest period, and after 5 more stage 5 seizures. Data were analyzed using the Mann-Whitney rank sum test. Twenty-four hours after a seizure, the kindled rats displayed a greater level of exploratory behavior than did the controls. They were not found to differ on any other measure. After a 2-week rest period, the group difference in behavior disappeared. When kindling was reinitiated, the kindled rats again showed increased exploratory behavior. The findings suggest that the increased exploratory behavior found in the kindled rats resulted from recent seizure activity. It may be that the hyperactivity seen in some children with epilepsy also results from recent seizure activity.