Anxiogenic-like consequences in animal models of complex partial seizures

Epilepsy and its neurobehavioral comorbidities: Insights gained from animal models

It is well established that epilepsy is associated with numerous neurobehavioral comorbidities, with a bidirectional relationship; people with epilepsy have an increased incidence of depression, anxiety, learning and memory difficulties, and numerous other psychosocial challenges, and the occurrence of epilepsy is higher in individuals with those comorbidities. Although the cause-and-effect relationship is uncertain, a fuller understanding of the mechanisms of comorbidities within the epilepsies could lead to improved therapeutics. Here, we review recent data on epilepsy and its neurobehavioral comorbidities, discussing mainly rodent models, which have been studied most extensively, and emphasize that clinically relevant information can be gained from preclinical models. Furthermore, we explore the numerous potential factors that may confound the interpretation of emerging data from animal models, such as the specific seizure induction method (e.g., chemical, electrical, traumatic, genetic), the role of species and strain, environmental factors (e.g., laboratory environment, handling, epigenetics), and the behavioral assays that are chosen to evaluate the various aspects of neural behavior and cognition. Overall, the interplay between epilepsy and its neurobehavioral comorbidities is undoubtedly multifactorial, involving brain structural changes, network-level differences, molecular signaling abnormalities, and other factors. Animal models are well poised to help dissect the shared pathophysiological mechanisms, neurological sequelae, and biomarkers of epilepsy and its comorbidities.

Classification of partial seizures based on functional connectivity: A MEG study with support vector machine

Temporal lobe epilepsy (TLE) is a chronic neurological disorder that is divided into two subtypes, complex partial seizures (CPS) and simple partial seizures (SPS), based on clinical phenotypes. Revealing differences among the functional networks of different types of TLE can lead to a better understanding of the symbology of epilepsy. Whereas Although most studies had focused on differences between epileptic patients and healthy controls, the neural mechanisms behind the differences in clinical representations of CPS and SPS were unclear. In the context of the era of precision, medicine makes precise classification of CPS and SPS, which is crucial. To address the above issues, we aimed to investigate the functional network differences between CPS and SPS by constructing support vector machine (SVM) models. They mainly include magnetoencephalography (MEG) data acquisition and processing, construction of functional connectivity matrix of the brain network, and the use of SVM to identify differences in the resting state functional connectivity (RSFC). The obtained results showed that classification was effective and accuracy could be up to 82.69% (training) and 81.37% (test). The differences in functional connectivity between CPS and SPS were smaller in temporal and insula. The differences between the two groups were concentrated in the parietal, occipital, frontal, and limbic systems. Loss of consciousness and behavioral disturbances in patients with CPS might be caused by abnormal functional connectivity in extratemporal regions produced by post-epileptic discharges. This study not only contributed to the understanding of the cognitive-behavioral comorbidity of epilepsy but also improved the accuracy of epilepsy classification.

Anticipatory anxiety of seizures is associated with ictal emotional distress and amygdala onset seizures

OBJECTIVE

Anxiety disorders are a frequent psychiatric condition in patients with epilepsy. Anticipatory Anxiety of Seizures (AAS) is described as a daily persistent fear, or excessive worry of having a seizure. AAS seems to be related to "subjective ictal anxiety" reported by patient. The current study aimed to assess the association between objective ictal features and the presence of AAS.

METHODS

Ninety-one patients with drug-resistant focal epilepsy underwent a standardized psychiatric assessment, specific for epilepsy, and a pre-surgical long term video-EEG or stereoelectroencephalography (SEEG). We compared seizures semiology and epilepsy features of patients with AAS (n=41), to those of patients without AAS (n=50). We analyzed emotional and motor behavior ictal signs as well as ictal consciousness. We further assessed amygdala ictal involvement in seizures recorded with SEEG (n=28).

RESULTS

AAS was significantly associated with the presence of ictal emotional distress: negative emotional behavior (p<0.01) and negative emotion, explicitly reported to examiner during record (p=0.015), regardless of the ictal level of consciousness. Among the patients recorded with SEEG, we found a significant involvement of amygdala within the seizure onset zone (p<0.01) for patients with AAS.

SIGNIFICANCE

Higher risk of developing AAS is associated with seizures expressing negative emotional symptoms, independently of ictal consciousness level. Persistent interictal fear of seizures might be viewed as the consequence of a reinforcement of the emotional networks secondary to amygdala involvement in seizures of temporal origin. Physicians should screen for AAS not only to assess the impact of epilepsy on daily life, but also as an interictal biomarker of ictal semiology and emotional network involvement at seizure onset.

Epilepsy-associated comorbidities among adults: A plausible therapeutic role of gut microbiota

Epilepsy is a debilitating disorder that affects about 70 million people in the world currently. Most patients with epilepsy (PWE) often reported at least one type of comorbid disorder. These may include neuropsychiatric disorders, cognitive deficits, migraine, cardiovascular dysfunction, systemic autoimmune disorders and others. Current treatment strategies against epilepsy-associated comorbidities have been based on targeting each disorder separately with either anti-seizure medications (ASMs), anti-inflammatories or anti-depressant drugs, which have often given inconsistent and ineffective results. Gut dysbiosis may be a common pathological pathway between epilepsy and its comorbid disorders, and thus may serve as a possible intervention target. Therefore, this narrative review aimed to elucidate the potential pathological and therapeutic role of the gut microbiota in adult epilepsy-associated comorbidities. This review noticed a scarcity in the current literature on studies investigating the direct role of the gut microbiota in relation to epilepsy-associated comorbidities. Nevertheless, gut dysbiosis have been implicated in both epilepsy and its associated comorbidities, with similarities seen in the imbalance of certain gut microbiota phyla (Firmicutes), but differences seen in the mechanism of action. Current gut-related interventions such as probiotics have been consistently reported across studies to provide beneficial effects in correcting gut dysbiosis and improving various disorders, independent of epilepsy. However, whether these beneficial effects may translate towards epilepsy-associated comorbidities have yet to be determined. Thus, future studies determining the therapeutic potential of gut microbiota interventions in PWE with epilepsy-associated comorbidities may effectively improve their quality of life.

Toward evidence-based severity assessment in mouse models with repeated seizures: I. Electrical kindling

OBJECTIVE

Ethical decisions about an allowance for animal experiments need to be based on scientifically sound information about the burden and distress associated with the experimental procedure and models. Thereby, species differences need to be considered for recommendations regarding evidence-based severity assessment and refinement measures.

METHODS

A comprehensive analysis of behavioral patterns and corticosterone or its metabolites in serum and feces was completed in kindled mice. The impact of kindling via two different stimulation sites in the amygdala and hippocampus was determined. Data were compared to those from naive and electrode-implanted groups.

RESULTS

Amygdala and hippocampus kindled mice exhibited comparable behavioral patterns with increased activity in the open field, reduced anxiety-associated behavior in the elevated-plus maze, and increased anhedonia-associated behavior in the saccharin preference test. In addition, repeated stimulation of the hippocampus caused a reduction in burrowing behavior and an increase in active social interaction. Levels of corticosterone and its metabolites were not altered in serum or feces, respectively. A comparison of mouse data with findings from amygdala kindled rats confirmed pronounced species differences in behavioral patterns associated with the kindling process.

SIGNIFICANCE

Taken together the findings suggest a severity classification for the mouse kindling paradigms as moderate regardless of the stimulation site. The outcome of the species comparison provides valuable guidance for species selection for studies exploring behavioral comorbidities. In this context, it is emphasized that the mouse kindling paradigms seem to be well suited for studies exploring the link between ictal events and network alterations on the one hand, and hyperactivity and anhedonia-associated behavior on the other hand. Moreover, the underlying pathophysiological mechanisms and the impact of therapeutic interventions on these behavioral alterations can be studied in these paradigms providing guidance for the clinical management of respective psychiatric comorbidities in patients.

Emotion and mood disorders associated with epilepsy

Epilepsy is a disorder characterized by recurrent seizures. Epilepsy can alter mood and emotions. Treatments for epilepsy can also alter mood and emotions. This chapter reviews the emotional changes that can occur before, during, and after a seizure, such as fear and anger, the interictal mood disorders associated with epilepsy, such as depression and anxiety, as well as alterations of emotional processing including comprehending and expressing emotional prosody and faces. The possible treatments of these emotional and mood disorders are also reviewed.

Assessment and Management of Depression and Anxiety in Children and Adolescents with Epilepsy

Anxiety and depression in children and adolescents with epilepsy are common comorbidities which place a significant burden on patients and families and complicate the clinical management of epilepsy. This paper presents a narrative review on the aetiology, phenomenology, assessment, and management of depression and anxiety among paediatric patients with epilepsy. The recognition of affective comorbidity in paediatric epilepsy is limited at present, and the contributory role of antiepileptic medication towards such comorbidity must be considered by clinicians.

Emotional asymmetries in refractory medial temporal and frontal lobe epilepsy: Their impact on predicting lateralization and localization of seizures

BACKGROUND

Emotional disturbances have been reported in patients with epilepsy. Although conflicting results emanate from relevant studies, depressive symptoms are seen more often in temporal lobe epilepsy (TLE) whereas, hypomanic/manic symptoms usually accompany frontal lobe epilepsy (FLE); the above psychiatric symptoms are especially seen in refractory epilepsy. However, neocortical TLE and medial TLE are considered as distinct epileptic syndromes, and there is limited literature on comparison of affective traits in medial TLE (MTLE) and FLE.

AIM

In the present study, we sought to investigate affective traits among epilepsy surgery candidates suffering refractory left medial TLE (LMTLE), right medial TLE (RMTLE), left FLE (LFLE), and right FLE (RFLE).

RESULTS

Our results revealed that patients with MTLE scored significantly higher than the ones with FLE in depression, anxiety, asthenia, and melancholia as measured by the Symptoms Rating Scale for Depression and Anxiety (SRSDA), while patients with FLE scored significantly higher in mania than those with MTLE. Moreover, patients with MTLE scored significantly higher than their FLE counterparts on the anxiety scale of the State Trait Personality Inventory (STPI)-trait version. When laterality of the seizure focus was taken into account, no differences were found among both patients with MTLE and patients with FLE, with exception for the Trail Making Test part B (TMT-B) in which patients with RMTLE performed significantly worse than patients with LMTLE. Seizure frequency was higher for FLE.

CONCLUSIONS

We provide evidence for an anterior-frontal versus a posterior-medial temporal cerebral functional asymmetry with regard to the manifestation of manic and depressive emotional traits in FLE and MTLE, respectively. Our results are mainly discussed within the frame of their contribution in localizing and to a lesser extent in lateralizing seizures foci in epilepsy surgery candidates. We suggest that this is of great importance in the context of preoperative monitoring of epilepsy surgery, especially when neuropsychologists are called upon to provide anatomical information in defining the functional deficit zone.

Tantrums, Emotion Reactions and Their EEG Correlates in Childhood Benign Rolandic Epilepsy vs. Complex Partial Seizures: Exploratory Observations

We explored associations between EEG pathophysiology and emotional/behavioral (E/B) problems of children with two types of epilepsy using standard parent questionnaires and two new indicators: tantrums recorded by parents at home and brief, emotion-eliciting situations in the laboratory. Children with Benign Rolandic epilepsy (BRE, N = 6) reportedly had shorter, more angry tantrums from which they recovered quickly. Children with Complex Partial Seizures (CPS, N = 13) had longer, sadder tantrums often followed by bad moods. More generally, BRE correlated with anger and aggression; CPS with sadness and withdrawal. Scores of a composite group of siblings (N = 11) were generally intermediate between the BRE and CPS groups. Across all children, high voltage theta and/or interictal epileptiform discharges (IEDs) correlated with negative emotional reactions. Such EEG abnormalities in left hemisphere correlated with greater social fear, right hemisphere EEG abnormalities with greater anger. Right hemisphere localization in CPS was also associated with parent-reported problems at home. If epilepsy alters neural circuitry thereby increasing negative emotions, additional assessment of anti-epileptic drug treatment of epilepsy-related E/B problems would be warranted.

Anxiety-related behavior in hyperhomocysteinemia induced by methionine nutritional overload in rats: role of the brain oxidative stress

The aim of this study was to examine the effects of a methionine-enriched diet on anxiety-related behavior in rats and to determine the role of the brain oxidative status in these alterations. Adult male Wistar rats were fed from the 30th to 60th postnatal day with standard or methionine-enriched diet (double content comparing with standard diet: 7.7 g/kg). Rats were tested in open field and light-dark tests and afterwards oxidative status in the different brain regions were determined. Hyperhomocysteinemia induced by methionine-enriched diet in this study decreased the number of rearings, as well as the time that these animals spent in the center of the open field, but increased index of thigmotaxy. Oxidative status was selectively altered in the examined regions. Lipid peroxidation was significantly increased in the cortex and nc. caudatus of rats developing hyperhomocysteinemia, but unaltered in the hippocampus and thalamus. Based on the results of this research, it could be concluded that hyperhomocysteinemia induced by methionine nutritional overload increased anxiety-related behavior in rats. These proanxiogenic effects could be, at least in part, a consequence of oxidative stress in the rat brain.

Expression of neuropeptide Y1 receptors in the amygdala and hippocampus and anxiety-like behavior associated with Ammon's horn sclerosis following intrahippocampal kainate injection in C57BL/6J mice

Damage to the amygdala is often linked to Ammon's horn sclerosis (AHS) in surgical specimens of patients suffering from temporal lobe epilepsy (TLE). Moreover, amygdalar pathology is thought to contribute to the development of anxiety symptoms frequently found in TLE. The neuropeptide Y (NPY) Y1 receptor is critical in the regulation of anxiety-related behavior and epileptiform activity in TLE. Therefore, intrahippocampal kainate (KA) injection was performed to induce AHS-associated TLE and to investigate behavioral and cytoarchitectural changes that occur in the amygdala related to Y1 receptor expression. Status epilepticus was induced by intrahippocampal KA injection in C57BL/6J mice. Anxiety-like behavior was assessed using the elevated plus maze (EPM). Pathology of hippocampus and amygdala (volume loss and gliosis) was examined in KA-injected and saline-injected controls. Y1 receptor expression was measured using immunohistochemistry and ELISA. Animal injected with KA showed increased anxiety-like behaviors and reduced risk assessment in the EPM test compared with saline-injected controls. In the ipsilateral hippocampus of KA-injected animals, CA1 ablation, granule cell dispersion, and volume reduction were accompanied by astrogliosis indicating the development of AHS. In the amygdala, a significant decrease in the volume of nuclei and numbers of neurons was observed in the ipsilateral lateral, basolateral, and central amygdalar nuclei, which was accompanied by astrogliosis. In addition, a decrease in Y1 receptor-expressing cells in the ipsilateral CA1 and CA3 sectors of the hippocampus, ipsilateral and contralateral granule cell layer of the dentate gyrus, and ipsilateral central nucleus of the amygdala was found, consistent with a reduction in Y1 receptor protein levels. Our results suggest that plastic changes in hippocampal and/or amygdalar Y1 receptor expression may negatively impact anxiety levels. Moreover, intrahippocampal KA injection can induce amygdalar damage suggesting that AHS-associated amygdala damage may contribute to behavioral alterations seen in patients with TLE.

Age-dependent decline in learning and memory performances of WAG/Rij rat model of absence epilepsy

Recent clinical studies revealed emotional and cognitive impairments associated with absence epilepsy. Preclinical research with genetic models of absence epilepsy however have primarily focused on dysfunctional emotional processes and paid relatively less attention to cognitive impairment. In order to bridge this gap, we investigated age-dependent changes in learning and memory performance, anxiety-like behavior, and locomotor activity of WAG/Rij rats (a valid model of generalized absence epilepsy) using passive avoidance, Morris water maze, elevated plus maze, and locomotor activity cage. We tested 5 month-old and 13 month-old WAG/Rij rats and compared their performance to age-matched Wistar rats. Results revealed a decline in emotional and spatial memory of WAG/Rij rats compared to age-matched Wistar rats only at 13 months of age. Importantly, there were no significant differences between WAG/Rij and Wistar rats in terms of anxiety-like behavior and locomotor activity at either age. Results pointed at age-dependent learning and memory deficits in the WAG/Rij rat model of absence epilepsy.

Neural and cellular mechanisms of fear and extinction memory formation

Over the course of natural history, countless animal species have evolved adaptive behavioral systems to cope with dangerous situations and promote survival. Emotional memories are central to these defense systems because they are rapidly acquired and prepare organisms for future threat. Unfortunately, the persistence and intrusion of memories of fearful experiences are quite common and can lead to pathogenic conditions, such as anxiety and phobias. Over the course of the last 30 years, neuroscientists and psychologists alike have attempted to understand the mechanisms by which the brain encodes and maintains these aversive memories. Of equal interest, though, is the neurobiology of extinction memory formation as this may shape current therapeutic techniques. Here we review the extant literature on the neurobiology of fear and extinction memory formation, with a strong focus on the cellular and molecular mechanisms underlying these processes.

Short- and long-term anxiogenic effects induced by a single injection of subconvulsant doses of pilocarpine in rats: investigation of the putative role of hippocampal pathways

RATIONALE

Behavioral consequences of convulsive episodes are well documented, but less attention was paid to changes that occur in response to subconvulsant doses of drugs.

OBJECTIVES

We investigated short- and long-term effects of a single systemic injection of a subconvulsant dose of pilocarpine on the behavior of rats as evaluated in the elevated plus maze.

METHODS AND RESULTS

Pilocarpine induced an anxiogenic-like profile 24 h later, and this effect persisted for up to 3 months (% of time spent on open arms at 24 h, control = 35.47 ± 3.23; pilocarpine 150 = 8.2 ± 2.6; 3 months, control = 31.9 ± 5.5; pilocarpine 150 = 9.3 ± 4.9). Temporary inactivation of fimbria-fornix with lidocaine 4% promoted an anxiolytic-like effect per se, suggesting a tonic control of this pathway on the modulation of anxiety-related behaviors. Lidocaine also reduced the anxiogenic-like profile of animals tested 1 month after pilocarpine treatment (% of time spent on open arms, saline + phosphate-buffered saline (PBS) = 31.7 + 3.7; saline + lidocaine = 54.4 + 4.7; pilocarpine + PBS = 10.3 + 4.1; pilocarpine + lidocaine = 40.1 + 9.1). To determine whether the anxiogenic-like effect was mediated by septal region or by direct hippocampal projections to the diencephalon, the neural transmission of post-commissural fornix was blocked, and a similar reduction in the anxiogenic-like effect of pilocarpine was observed.

CONCLUSIONS

Our findings suggest that a single systemic injection of pilocarpine may induce long-lasting anxiogenic-like behavior in rats, an effect that appears to be mediated, in part, through a direct path from hippocampus to medial hypothalamic sites involved in fear responses.

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.

Depression and anxiety in children and adolescents with epilepsy: prevalence, risk factors, and treatment

Among the psychiatric comorbid conditions in children and adolescents with epilepsy, depression and anxiety disorders require further attention because they carry the risk of reduced quality of life and life-threatening complications (e.g., suicide). Research in recent years has shed light on both the prevalence of emotional problems in youth with epilepsy and the safety and efficacy of treatment options. A number of challenges exist in treating patients with epilepsy. This is particularly true when seizures are difficult to control and medication regimens are more complex. Some pharmaceutical options may provide assistance with both seizures and emotional distress, but care is needed when considering such treatment approaches. In addition, integration of mental health professionals into the care of patients is necessary when cases are complicated and risk factors are high. Thorough methods to accurately diagnose emotional conditions and regular monitoring of symptoms can help prevent serious problems that can negatively affect the success of children and adolescents in everyday life. Collaboration between disciplines offers the best hope for early identification and treatment of these conditions.

Short-term full kindling of the amygdala dissociates natural and periaqueductal gray-evoked flight behaviors of the rat

Panic attacks present a high comorbidity with agoraphobia, separation anxiety and generalized anxiety disorder. Nevertheless, while panic attacks have been frequently equated to fear, the relationship of panic disorder with specific phobias remains uncertain. The combination of experimental models of panic and phobias could but afford valuable information about both the comorbidity and causation of these disorders. As it regards, while the defensive behaviors produced by stimulation of dorsal periaqueductal gray matter (DPAG) resemble a panic attack, resistance to capture (RC) behaviors that ensue the kindling of the amygdala (AMY) are reminiscent of a phobic reaction. Therefore, this study examined the thresholds of DPAG-evoked panic-like behaviors in rats showing RC behaviors. Rats bearing electrodes in the DPAG and right AMY were subjected to either the full- (Kin-F) or sham- (Kin-S) kindling of AMY. RC behaviors were evaluated throughout both kindling procedures. Thresholds of DPAG-evoked defensive behaviors were recorded before and after the kindling. Moreover, performances of Kin-F and Kin-S rats in the elevated plus-maze were compared to those of intact controls. Data showed that Kin-F and Kin-S rats perform similarly in the elevated plus-maze, thereby making AMY-kindled rats unlikely as a model of generalized anxiety disorder. On the other hand, whereas the RC is characterized by a marked facilitation of natural freezing and flight behaviors, DPAG-evoked freezing (immobility and exophthalmus) and flight (galloping) behaviors were unexpectedly attenuated. Data suggest that RC is mediated by circuits distinct from those of DPAG-evoked defensive behaviors. Consequently, panic and phobic attacks may be mediated by different mechanisms as well.

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.

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.

Which clinical and experimental data link temporal lobe epilepsy with depression?

The association of temporal lobe epilepsy with depression and other neuropsychiatric disorders has been known since the early beginnings of neurology and psychiatry. However, only recently have in vivo and ex vivo techniques such as Positron Emission Tomography, Magnetic Resonance Imaging and Magnetic Resonance Spectroscopy in combination with refined animal models and behavioral tests made it possible to identify an emerging pattern of common pathophysiological mechanisms. We now have growing evidence that in both disorders altered interaction of serotonergic and noradrenergic neurons with glutamatergic systems is associated with abnormal neuronal circuits and hyperexcitability. Neuronal hyperexcitability can possibly evoke seizure activity as well as disturbed emotions. Moreover, decreased synaptic levels of neurotransmitters and high glucocorticoid levels influence intracellular signaling pathways such as cAMP, causing disturbances of brain-derived and other neurotrophic factors. These may be associated with hippocampal atrophy seen on Magnetic Resonance Imaging and memory impairment as well as altered fear processing and transient hypertrophy of the amygdala. Positron Emission Tomography studies additionally suggest hypometabolism of glucose in temporal and frontal lobes. Last, but not least, in temporal lobe epilepsy and depression astrocytes play a role that reaches far beyond their involvement in hippocampal sclerosis and ultimately, therapeutic regulation of glial-neuronal interactions may be a target for future research. All these mechanisms are strongly intertwined and probably bidirectional such that the structural and functional alterations from one disease increase the risk for developing the other. This review provides an integrative update of the most relevant experimental and clinical data on temporal lobe epilepsy and its association with depression.

Depression and anxiety in epilepsy: the association with demographic and seizure-related variables

BACKGROUND

Depression and anxiety are common psychiatric symptoms in patients with epilepsy, exerting a profound negative effect on health-related quality of life. Several issues, however, pertaining to their association with psychosocial, seizure-related and medication factors, remain controversial. Accordingly, the present study was designed to investigate the association of interictal mood disorders with various demographic and seizure-related variables in patients with newly-diagnosed and chronic epilepsy.

METHODS

We investigated 201 patients with epilepsy (51.2% males, mean age 33.2 +/- 10.0 years, range 16-60) with a mean disease duration of 13.9 +/- 9.5 years. Depression and anxiety were assessed in the interictal state with the Beck Depression Inventory, 21-item version (BDI-21) and the state and trait subscales of the State-Trait Anxiety Inventory (STAI-S and STAI-T), respectively. The association of mood disorders with various variables was investigated with simple and multiple linear regression analyses.

RESULTS

High seizure frequency and symptomatic focal epilepsy (SFE) were independent determinants of depression, together accounting for 12.4% of the variation of the BDI-21. The STAI-S index was significantly associated with the type of epilepsy syndrome (SFE). Finally, high seizure frequency, SFE and female gender were independent determinants of trait anxiety accounting for 14.7% of the variation of the STAI-T.

CONCLUSION

Our results confirm the prevailing view that depression and anxiety are common psychological disorders in epileptics. It is additionally concluded that female gender, high seizure frequency and a symptomatic epilepsy syndrome are independent risk factors for the development of anxiety and/or depression.

Neural, endocrine and electroencephalographic hyperreactivity to human contact: a diathesis-stress model of seizure susceptibility in El mice

The El mouse strain provides a non-induced model of idiopathic, multifactorial epilepsy in which seizures are elicited in response to stressful environmental stimuli such as tail suspension handling. In the present studies, genetically seizure susceptible El and non-susceptible ddY control mice were exposed to tail suspension, foot-shock and social stressors in order to test the hypothesis that neural and physiological responses to such stimuli would be exaggerated in the El strain. The first experiment assessed neural cell density, stress neuropeptide (corticotropin releasing factor--CRF) levels, and plasma corticosterone activation in El and ddY mice in an unhandled control condition or following exposure to tail suspension or foot-shock stressors. The second experiment assessed brain electroencephalographic activity using telemetrically monitored skull surface electrodes in El and ddY mice exposed to tail suspension or social interaction stressors. Assessment of El mouse brains revealed higher cell counts in amygdala and elevated CRF peptide content in the paraventricular thalamic nucleus relative to ddY controls. El mice exhibited significantly elevated plasma corticosterone levels 60 min following exposure to tail suspension and foot-shock stressors relative to ddY controls. Finally, El mice exhibited significantly elevated brain electroencephalographic (1-4 Hz) activity in response to tail suspension, but not social interaction, relative to ddY controls. These results indicate that potentiated neural, endocrine and physiological activation arises in the El strain following exposure to a known seizure trigger stimulus, involuntary tail suspension handling. The findings support a diathesis-stress hypothesis in which genetically seizure susceptible El mice exhibit a multifaceted hyperreactivity to noxious environmental stimuli.

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.

Behavioral characteristics of WAG/Rij rats susceptible and non-susceptible to audiogenic seizures

Some rats of the WAG/Rij (Wistar Albino Glaxo from Rijswijk) and Wistar strain are susceptible for audiogenic (convulsive) seizures. In the present study, behavior of susceptible and non-susceptible rats from the WAG/Rij strain, genetically predisposed to absence epilepsy, and outbred Wistar strain, genetically not predisposed to absence epilepsy, was compared to assess the level of anxiety (in the open field, light-dark choice and elevated plus-maze tests) and the level of depression (in the sucrose consumption and forced swimming tests). Increased level of anxiety was found only in audiogenic susceptible rats both from WAG/Rij and Wistar strain, but increased level of depression was found only in WAG/Rij rats independently of their susceptibility to audiogenic seizures. The results suggest that enhanced level of depression in WAG/Rij strain rats is associated with absence epilepsy but enhanced level of anxiety with susceptibility to audiogenic seizures.

Anxiety in patients with epilepsy: systematic review and suggestions for clinical management

Up to 50 or 60% of patients with chronic epilepsy have various mood disorders including depression and anxiety. Whereas the relationship between epilepsy and depression has received much attention, less is known about anxiety disorders. It is now recognized that anxiety can have a profound influence on the quality of life of patients with epilepsy. The relationship between anxiety disorders and epilepsy is complex. It is necessary to distinguish between different manifestations of anxiety disorder: ictal, postictal, and interictal anxiety. Preexisting vulnerability factors, neurobiological factors, iatrogenic influences (antiepileptic drugs, epilepsy surgery), and psychosocial factors are all likely to play a role, but with considerable individual differences. Despite the high prevalence of anxiety disorders in patients with epilepsy, there are no systematic treatment studies or evidence-based guidelines for best treatment practice. Nevertheless, a practical approach based on the temporal relationship between anxiety and epileptic seizures allows clinicians to consider appropriate treatment strategies to reduce the psychiatric comorbidity in patients with epilepsy.

[Patients with epilepsy and anxiety disorders. Diagnosis and treatment]

Up to 50-60% of patients with epilepsy may develop psychiatric complications, in particular depression, anxiety, and psychotic disorders. Although this comorbidity has received a great deal of attention in recent years, the anxiety spectrum of psychiatric disturbances in epilepsy patients has not been extensively studied, although this comorbidity has a significant effect on the medical management and quality of life. The etiology is multifactorial, including neurobiological and shared pathophysiological mechanisms as well as psychosocial and iatrogenic factors (e.g., influence of antiepileptic drugs, epilepsy surgery). Despite the high prevalence of comorbid anxiety in epilepsy, very little is known about optimal treatment strategies. This article reviews the complex interrelationships between anxiety disorders and epilepsy from a clinical point of view. The evaluation of anxiety relative to ictal, peri-ictal, and postictal states is described, and medical treatment options for anxiety disorders in patients with epilepsy are discussed, illustrating that their treatment extends far beyond seizure control.

Environmental Enrichment Facilitates Amygdala Kindling but Reduces Kindling-Induced Fear in Male Rats

The purpose of this experiment was to determine the effect of prior environmental enrichment on the acquisition of kindling and the expression of kindling-induced fear. Sixty male rats were housed either in an enriched environment or in isolation, starting immediately after weaning. As adults, they were subjected to either 50 amygdala-kindling stimulations or sham stimulations, followed by testing in an unfamiliar open field. The kindled-enriched rats acquired the kindled state more quickly than did the kindled-isolated rats, but they also showed less fear in the open field than did the kindled-isolated rats. These results suggest that environmental enrichment has differential effects on kindling acquisition and its behavioral consequences.

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.

Epilepsy and anxiety

Studies in the general population demonstrate that anxiety disorders are associated with impaired quality of life and function. Available evidence suggests that comorbid anxiety disorders are frequent among patients with epilepsy but that neither the interrelationships between them nor the impact of anxiety disorders on functional outcome is well studied. The study and management of anxiety disorders are further complicated by the occurrence of seizures, the temporal relationship between seizures and anxiety symptoms/syndromes, and the influence of antiepileptic drugs. Increased recognition of anxiety disorders among patients with epilepsy and evaluation of the potential impact of these disorders on functional outcome and the beneficial and detrimental effects of antiepileptic drugs in clinical practice are needed.

Amygdala kindling increases fear responses and decreases glucocorticoid receptor mRNA expression in hippocampal regions

Amygdala kindling dramatically increases fearful behavior in rats. Because kindling-induced fear increases in magnitude as rats receive more stimulations, kindling provides an excellent model for studying the nature and neural mechanisms of fear sensitization. In the present experiment, we studied whether the development of kindling-induced fear is related to changes in glucocorticoid receptor (GR) mRNA expression in various brain regions. Rats received 20, 60 or 100 amygdala kindling stimulations or 100 sham stimulations. One day after the final stimulation, their fearful behavior was assessed in an unfamiliar open field. Then, the rats were sacrificed and their brains were processed for in situ hybridization of GR mRNA expression. We found that compared with the sham-stimulated rats, the rats that received 60 or 100 kindling stimulations were significantly more fearful in the open field and also had significantly less GR mRNA expression in the dentate gyrus and CA1 subfield of the hippocampus. Importantly, the changes in fearful behavior were significantly correlated with the changes in GR mRNA expression. These results suggest that alterations in GR mRNA expression in hippocampal regions may play a role in the development of kindling-induced fear.

Effects of etomidate, ketamine or propofol, and their combinations with conventional antiepileptic drugs on amygdala-kindled convulsions in rats

Ketamine, etomidate and propofol modified behavioral and electrographic correlates of kindled seizures in rats. In detail, ketamine (5 mg/kg) and propofol (15 mg/kg) significantly increased afterdischarge threshold, reduced seizure severity and shortened seizure and afterdischarge durations. Etomidate (7.5 mg/kg) was effective in terms of seizure and afterdischarge durations. Moreover, the combinations of ketamine (2.5 mg/kg) with carbamazepine (15 mg/kg) or valproate (50 mg/kg; all drugs at their subeffective doses), reduced the severity and duration of kindled seizures. The antiseizure potency of the ketamine/carbamazepine combination was comparable to that of carbamazepine alone administered at 20 mg/kg, while the effect of ketamine/valproate was comparable to the efficacy of valproate alone at 100 mg/kg. However, the combinations of ketamine with phenobarbital or diphenylhydantoin did not exert any protective action. Propofol and etomidate entirely failed to interact with conventional antiepileptics. The combinations of ketamine with carbamazepine or valproate did not induce any significant motor impairment in the chimney test or memory deficit in the passive avoidance task. A pharmacokinetic interaction, at least in plasma, can be excluded, because ketamine (2.5 mg/kg) did not affect the free plasma concentrations of carbamazepine or valproate. Results of the present study may suggest that there may be no risk of negative interactions between injectable anesthetics and antiepileptics in cases of partial epilepsy.

Kindling-induced emotional behavior in male and female rats

Modeling fear in animals is a critical approach for identifying the neural mechanisms involved in human disorders such as generalized anxiety and panic. Amygdala kindling has proven useful in this regard because it produces dramatic increases in fearful behavior. The purpose of this experiment was to compare the behavioral effects of kindling in male and female rats. Compared with the sham-stimulated rats, the kindled male and female rats showed similar increases in fearful behavior, with some sex differences in fear-related open-field activity. They also showed decreased immobility in the forced-swim test and increased sucrose consumption. These results suggest that kindling-induced fear is generally similar in male and female rats and that kindling does not appear to induce depression-like behavior.

Altered conditioned fear behavior in glutamate decarboxylase 65 null mutant mice

We investigated the involvement of the 65 kDa isoform of glutamic acid decarboxylase (GAD65) and GAD65-mediated gamma-aminobutyric acid (GABA) synthesis in the formation and expression of Pavlovian fear memory. To this end, behavioral, endocrine and autonomic parameters were examined during conditioned fear retrieval of mice with targeted ablation of the GAD65 gene (GAD65-/- mice). These mutant mice were found to display specific fear behavior (freezing, escape), as well as autonomic (increased defecation) and endocrine activation (increased plasma corticosterone) during fear memory retrieval. However, freezing was reduced and flight and escape behavior were increased in GAD65-/- mice compared to their wild type and heterozygous littermates, while corticosterone levels and defecation rates did not differ between genotypes. Active defensive behavior of GAD65-/- mice was observed during both auditory cued and contextual retrieval of fear memory, as well as immediately after conditioning. These data indicate a selectively altered behavioral fear response in GAD65-/- mice, most likely due to deficits in threat estimation or the elicitation of appropriate conditioned fear behavior, and suggest that GAD65 is a genetic determinant of conditioned fear behavior. GAD65-/- mice provide a valuable tool to further dissect the GABAergic mechanisms involved in fear and anxiety and to model GABA-related neurological and psychiatric disorders.

Persistent behavioral and autonomic supersensitivity to stress following prenatal stress exposure in rats

Prenatal restraint stress (PS) has been suggested as an attractive chronic model of anxiety. Here, we characterized the behavioral and autonomic responsivity to acute stress exposure in adult PS subjects. In Wistar rats, locomotor activity, as well as spontaneous behavior in an established animal model of anxiety, the elevated plus-maze, was unaffected by PS. However, the anxiogenic-like response normally seen on the plus-maze following a restraint stress was markedly potentiated in adult PS subjects, despite indistinguishable corticosterone responses. In addition, we assessed the tail skin temperature response to a mild social stressor, transient social mixing. The diazepam-sensitive, late phase of the temperature response was markedly potentiated in adult PS subjects. In summary, PS induces a persistent phenotype of increased behavioral and autonomic sensitivity to stress. This paradigm might serve as an attractive screening model for anti-anxiety compounds.

Use of epileptic animals for adverse effect testing

A crucial parameter deciding the clinical utility of new antiepileptic drugs (AEDs) is the therapeutic index expressing the margin between anticonvulsant and adverse effects. The latter is commonly quantified during preclinical testing in the rotarod test in normal, healthy rodents. However, the validity of using normal animals for adverse effect predictions in epilepsy patients is questionable. Limbic kindling of rodents induced by corneal kindling of mice and amygdala kindling of rats confirm that epileptic animals are more susceptible to the behavioral and cognitive alterations following acute administration of NMDA antagonists and certain established AEDs. This appears to represent a permanent reactivity specific for limbic kindling since it is absent in rats after chemical kindling with pentylenetetrazole. Animal species with inborn epilepsy, including audiogenic and photosensitive animals, are not revealing an enhanced susceptibility to the behavioral alterations induced by NMDA antagonists. In contrast, these induce severe adverse effects in genetic absence epilepsy rats where certain AEDs also are associated with a more marked deterioration of motor function than in normal animals. This appears in line with several complications with AED use in man being linked to an interaction with the dysfunction of the brain imposed by the epileptic condition. Thus, it is important to involve epileptic animals in preclinical adverse effect testing, in particular when evaluating new AED candidates with novel or unknown mechanisms. In that respect, limbic kindling appears to represent a sensitive and relevant approach.

Dorsal hippocampal kindling selectively impairs spatial learning/short-term memory

Kindling with electrical stimulation of the dorsal hippocampus has been shown to disrupt spatial task performance in rats. The present study investigated the specificity of this effect in terms of the possible contribution of nonmnemonic effects, the presence of a more general mnemonic deficit, and the involvement of learning/short-term memory and/or long-term memory processes. Rats were fully kindled with stimulation of the dorsal hippocampus and subsequently tested for acquisition, 7-day retention, and 28-day retention of a hidden platform (HP) location in the Morris water maze and an object discrimination problem in a modified water maze. To control for nonmnemonic behavioral impairments, testing on both tasks was preceded by training on visible platform control tasks. Kindling impaired acquisition of the HP location but spared performance on all other aspects of testing, indicating a specific impairment of spatial learning/short-term memory. These results suggest that epileptogenesis induced by hippocampal stimulation is indeed associated with a selective disruption of the mechanisms mediating spatial learning/short-term memory.

Clobazam shows a different antiepileptic action profile from clonazepam and zonisamide in Ihara epileptic rats

PURPOSE

Clobazam (CLB, 1,5-benzodiazepine, 1,5-BZP) has been reported to show unique antiepileptic action profile distinguishing from standard 1,4-BZPs. To further elucidate the action profile of CLB, its effects on the abnormal circling fits (ACFs) and generalized tonic-clonic convulsions (GTCs) in Ihara epileptic rats (IERs), a genetically epileptic mutant, were examined in comparison with conventional antiepileptic drugs (AEDs), a 1,4-BZP, clonazepam (CZP) and a non-BZP, zonisamide (ZNS).

METHODS

The incidence of ACFs or GTCs in IERs was recorded automatically by the computer-assisted behavior monitoring system (COBAS N-IV) before, during and after the drug treatment period for 5 days in each. The drugs were orally administered twice daily. The daily and total incidences of ACFs or GTCs were calculated every each period in each dose group. The incidences of various behaviors such as feeding, gnawing and scratching recorded simultaneously were used for evaluating the behavioral activity (BA).

RESULTS

CLB (30 and 60 mg/kg) prevented the appearance of ACFs and GTCs without affecting BAs. CZP (1 and 3 mg/kg) suppressed the occurrence of ACFs but induced no effect on the incidence of GTCs. Furthermore, it inhibited BAs at the same doses. ZNS (15 mg/kg) suppressed GTCs but little ACFs without affecting BA.

CONCLUSION

CLB exhibited a different action profile from CZP and ZNS in a novel epileptic mutant, IERs, and was expected to be a useful AED superior to 1,4-BZPs in clinical practice.

Hippocampal involvement in the expression of kindling-induced fear in rats

Kindling dramatically increases fearful behavior in rats. Because kindling-induced fear increases in magnitude as rats receive more stimulations, kindling provides a superb opportunity to study the nature and neural mechanisms of fear sensitization. Interestingly, these changes in behavior are accompanied by increased binding to inhibitory receptors and decreased binding to excitatory receptors in the CA1 and dentate gyrus regions of the hippocampus. This led us to hypothesize that kindling-induced fear may result from an increased inhibitory tone within hippocampal circuits. To test this hypothesis, we investigated FOS protein immunoreactivity in hippocampal and amygdalar regions of kindled rats that were exposed to an unfamiliar open field. We found that FOS immunoreactivity was significantly decreased in the CA1 region, dentate gyrus, and perirhinal cortex of kindled rats compared to sham-stimulated rats. These results support our hypothesis that kindling-induced fear may be produced by inhibition within hippocampal circuits. They also suggest that neural changes within the hippocampus may be important for the sensitization of fear.

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.

Does the kindling model of epilepsy contribute to our understanding of multiple chemical sensitivity?

Multiple chemical sensitivity (MCS) is a phenomenon whereby individuals report an increased sensitivity to low levels of chemicals in the environment. Kindling is a model of synaptic plasticity whereby repeated low-level electrical stimulation to a number of brain sites leads to permanent increases in seizure susceptibility. Stimulation that is initially subthreshold for subclinical seizure provocation comes, over time, to elicit full-blown motor seizures. Kindling can also be induced by chemical stimulation, and repeated exposures to some pesticides have been shown to induce signs of behavioral seizure, facilitate subsequent electrical kindling, and induce subclinical electrographic signs of hyperexcitability in the amygdala. Many of the symptoms of MCS suggest that CNS limbic pathways involved in anxiety are altered in individuals reporting MCS. Limbic structures are among the most susceptible to kindling-induced seizures, and persistent cognitive and emotional sequelae have been associated with temporal lobe epilepsy (TLE) in humans and kindling in animals. Thus, a number of parallels exist between kindling and MCS phenomena, leading to initial speculations that MCS may occur via a kindling-like mechanism. However, kindling requires the activation of electrographic seizure discharge and has thus been primarily examined as a model for TLE. Events leading to the initial evocation of a subclinical electrographic seizure have been much less well studied. It is perhaps these events that may serve as a more appropriate model for the enhanced chemical responsiveness characteristic of MCS. Alternatively, kindling may be useful as a tool to selectively increase sensitivity in subcomponents of the neural fear circuit to address questions relating the role of anxiety in the development and expression of MCS.

Long-term amygdala kindling in rats as a model for the study of interictal emotionality in temporal lobe epilepsy

Temporal lobe epileptics often experience profound interictal (i.e. between seizure) emotional disturbances, such as fear, anxiety, and depression. Although the presence of this interictal emotionality has been well documented, little progress has been made in identifying its precise nature and cause because it is not amenable to experimental analysis in clinical populations. Accordingly, there is much to gain by studying the fundamental nature and neural basis of interictal emotionality using animal models. Kindling is a widely studied animal model of temporal lobe epilepsy in which daily electrical stimulation of certain brain regions results in the gradual progression and intensification of limbic motor seizures. Several investigators have found that partial and short-term kindling produce robust changes in emotional behavior in both cats and rats. Recently, our laboratory has developed a new model to study interictal emotionality using long-term kindling in rats. These long-term kindled rats display profound changes in fearful and defensive behavior which last for at least two months after the final stimulation. We are now beginning to use this model to study the neural mechanisms underlying the development and expression of interictal emotionality.

The mnemonic effects of kindling

Kindling produces enduring changes in the brain that are evident in not only enhanced susceptibility to seizure-evoking stimuli but also alterations in non-epileptic behaviors or functions. The present review examines the effects of kindling on one class of non-epileptic functions, learning and memory, and explores the dependence of these effects on variables such as the site of kindling, extent of kindling, and interval between kindling and testing. Current research shows that kindling is capable of altering performance on a variety of tasks including those that require spatial cognition, aversive conditioning, and object-related cognition and that non-mnemonic effects are unlikely, in at least some cases, to underlie these effects. Consideration of the conditions under which these effects are observed indicates a distinct relation between specific mnemonic effects and both the site and extent of kindling. Continued characterization of the mnemonic effects of kindling should provide a theoretical framework to guide discovery of their underlying mechanisms, which, in turn, may lead to rational therapy for mnemonic dysfunction associated with epilepsy and insights into the mechanisms of learning and memory.

Consequences of Pentylenetetrazole Kindling on Spatial Memory and Emotional Responding in the Rat

We investigated the consequences of pentylenetetrazole (PTZ) kindling on cognitive capacities of rats in a Morris water maze assessing spatial reference memory and in the spontaneous alternation test used as an index of working memory. The emotional consequences of PTZ kindling were also evaluated in an elevated plus maze test. Results indicated that PTZ kindled rats were not different from controls in mastering the water maze. However, PTZ kindled rats did not persist in searching the platform when evaluated at the end of learning. This suggests an altered place memory, although alternative explanations, like reduced anxiety, may be involved. Indeed, such anxiolytic activity was observed in a separate group of kindled rats evaluated in the plus maze test. No significant effect of PTZ kindling was noted in the spontaneous alternation test. These results question the generalization of previous results obtained in learning tests using electric shocks and illustrate the complexity of the PTZ model for the study of the behavioral consequences of kindling.

Behavioral, psychotic, and anxiety disorders in epilepsy: etiology, clinical features, and therapeutic implications

This chapter deals with some aspects of psychiatric disturbances in people with epilepsy. Because depression and its treatment are extensively described later in this issue, they are not discussed here. The same pertains to forced normalization.

Persistence of the interictal emotionality produced by long-term amygdala kindling in rats

Long-term amygdala kindling in rats results in large and reliable increases in emotional behaviour that model the interictal emotionality often observed in temporal lobe epileptics [Kalynchuk L. E. et al. (1997) Biol. Psychiat. 41, 438-451; Pinel J. P. J. et al. (1977) Science 197, 1088-1089]. These experiments investigated the persistence of these kindling-induced increases in emotional behaviour after the cessation of the kindling stimulations. In Experiment 1, rats received 99 amygdala or sham stimulations. Then, they were tested on three tests of emotionality (i.e. activity in an unfamiliar open field, resistance to capture from the open field, and activity in an elevated-plus maze) either one day, one week, or one month after the final stimulation. The rats tested one day after the last stimulation displayed substantial decreases in open-field activity, increases in resistance to capture and increases in open-arm activity on the elevated-plus maze; these effects decreased, but not to control levels, in the rats tested one month after the final stimulation. In Experiment 2, rats received 99 amygdala or sham stimulations, and their resistance to capture was assessed one day later. Then, after a 60-day stimulation-free period, the rats received another zero, one, 10, or 30 amygdala stimulations and their resistance to capture was reassessed one day later. The high levels of resistance to capture observed in the rats tested one day after the 99 stimulations declined significantly during the 60-day stimulation-free period, but it remained significantly above control levels. However, the administration of 30 additional stimulations reinstated asymptotic levels of resistance to capture. These results provide the first systematic evidence that kindling-induced increases in emotional behaviour persist at significant levels for at least two months following the termination of kindling stimulations. Thus, they suggest that the neural changes underlying the genesis of interictal emotionality may be closely related to those mediating epileptogenesis itself.

Long-term kindling and interictal emotionality in rats: effect of stimulation site

Long-term amygdala kindling in rats produces increases in emotionality (Kalynchuk et al., Biol. Psychiatry, 41 (1997) 438-451). The present experiment was conducted to investigate whether this hyperemotionality is specific to amygdala kindling or whether it can be produced by kindling other structures. Rats received 99 convulsive or sham stimulations of either the amygdala, the hippocampus, or the caudate nucleus. One day after the stimulation phase, each rat's open-field activity and resistance to capture were assessed; the following day, each rat was tested on an elevated plus maze. The site of stimulation had a significant effect on the results of each of these tests. The amygdala-kindled and hippocampal-kindled rats explored less in the open field, were more resistant to capture from the open field, and engaged in a greater percentage of open-arm activity in the elevated plus maze than did the caudate-kindled rats or the sham-stimulated controls. The caudate-kindled rats were more active in the open field than their sham-stimulated controls, but they did not significantly differ from them in terms of the other measures. These results suggest that kindling-induced emotionality is produced by limbic kindling but not nonlimbic kindling.