Anhedonia and cognitive function in adults with MDD: results from the International Mood Disorders Collaborative Project.

BACKGROUND: Cognitive dysfunction is common in major depressive disorder (MDD) and a critical determinant of health outcome. Anhedonia is a criterion item toward the diagnosis of a major depressive episode (MDE) and a well-characterized domain in MDD. We sought to determine the extent to which variability in self-reported cognitive function correlates with anhedonia. METHOD: A post hoc analysis was conducted using data from (N=369) participants with a Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision (DSM-IV-TR)-defined diagnosis of MDD who were enrolled in the International Mood Disorders Collaborative Project (IMDCP) between January 2008 and July 2013. The IMDCP is a collaborative research platform at the Mood Disorders Psychopharmacology Unit, University of Toronto, Toronto, Canada, and the Cleveland Clinic, Cleveland, Ohio. Measures of cognitive function, anhedonia, and depression severity were analyzed using linear regression equations. RESULTS: A total of 369 adults with DSM-IV-TR-defined MDD were included in this analysis. Self-rated cognitive impairment [ie, as measured by the Adult ADHD Self-Report Scale (ASRS)] was significantly correlated with a proxy measure of anhedonia (r=0.131, p=0.012). Moreover, total depression symptom severity, as measured by the total Montgomery-Åsberg Depression Rating Scale (MADRS) score, was also significantly correlated with self-rated measures of cognitive dysfunction (r=0.147, p=0.005). The association between anhedonia and self-rated cognitive dysfunction remained significant after adjusting for illness severity (r=0.162, p=0.007). CONCLUSIONS: These preliminary results provide empirical data for the testable hypothesis that anhedonia and self-reported cognitive function in MDD are correlated yet dissociable domains. The foregoing observation supports the hypothesis of overlapping yet discrete neurobiological substrates for these domains.

The impact of cognitive impairment on perceived workforce performance: results from the International Mood Disorders Collaborative Project.

BACKGROUND: Cognitive dysfunction and depression severity are key mediators of workplace adjustment in adults with major depressive disorder (MDD). Herein, we sought to determine the extent to which measures of depression severity and cognitive dysfunction were associated with perceived global disability, workplace performance and quality of life. METHOD: A post hoc analysis was conducted using data from 260 participants with a diagnosis of DSM-IV-TR-defined MDD who were enrolled in the International Mood Disorders Collaborative Project (IMDCP) between January 2008 and July 2013. Measures of workplace function, global disability, depression severity, cognitive function, and quality of life were employed. These data were analyzed using a multiple variable linear regression equations. RESULTS: Perceived global disability was significantly predicted by clinical ratings of depression severity (ß=0.54), and perceived inattention (ß=0.24), accounting for 37% of the variance. In addition, perceived inattention (ß=0.58) and clinical ratings of depression severity (ß=0.18), were also significant predictors of perceived workplace productivity/performance, accounting for 38% of the variance. Finally, both clinical ratings of depression severity (ß=-0.54), and perceived inattention (ß=-0.18) were significant inverse predictors of perceived quality of life, accounting for 34% of the variance. CONCLUSION: The overarching finding in the analysis herein is that workplace performance variability is explained by subjective measures of cognitive dysfunction to a greater extent than total depression symptom severity. Conversely, total depression symptom severity accounts for a greater degree of variability in global measures of disability relative to cognitive measures. Treatment strategies for adults with major depressive disorder should address issues of cognitive dysfunction to improve workforce participation and performance.

Cognitive deficits and functional outcomes in major depressive disorder: determinants, substrates, and treatment interventions.

BACKGROUND: Few reports have aimed to describe the mediational effect of cognitive deficits on functional outcomes in major depressive disorder (MDD), and relatively few interventions are demonstrated to mitigate cognitive deficits in MDD. METHODS: Studies enrolling subjects between the ages of 18-65 were selected for review. Bibliographies from identified articles were reviewed to identify additional original reports aligned with our objectives. RESULTS: Cognitive deficits in MDD are consistent, replicable, nonspecific, and clinically significant. The aggregated estimated effect size of cognitive deficits in MDD is small to medium. Pronounced deficits in executive function (≥1 SD below the normative mean) are evident in ∼20-30% of individuals with MDD). Other replicated abnormalities are in the domains of working memory, attention, and psychomotor processing speed. Mediational studies indicate that cognitive deficits may account for the largest percentage of variance with respect to the link between psychosocial dysfunction (notably workforce performance) and MDD. No conventional antidepressant has been sufficiently studied and/or demonstrated robust procognitive effects in MDD. CONCLUSIONS: Cognitive deficits in MDD are a principal mediator of psychosocial impairment, notably workforce performance. The hazards posed by cognitive deficits in MDD underscore the need to identify a consensus-based neurocognitive battery for research and clinical purposes. Interventions (pharmacological, behavioral, neuromodulatory) that engage multiple physiological systems implicated in cognitive deficits hold promise to reduce, reverse, and prevent cognitive deficits.

The effect of lisdexamfetamine dimesylate on body weight, metabolic parameters, and attention deficit hyperactivity disorder symptomatology in adults with bipolar I/II disorder.

OBJECTIVES: We primarily sought to determine the effect of adjunctive lisdexamfetamine dimesylate (LDX) on anthropometric and metabolic parameters. Our secondary aim was to evaluate the effect of LDX on attention deficit hyperactivity disorder (ADHD) symptom severity in adults with bipolar I/II disorder. METHODS: Forty-five stable adults (i.e., non-rapid cycling, absence of clinically significant hypo/manic symptoms) with bipolar I/II disorder and comorbid ADHD were enrolled in a phase IV, 4-week, flexible dose, open-label study of adjunctive LDX. All subjects were initiated at 30 mg/day of adjunctive LDX for the first week with flexible dosing (i.e., 30-70 mg/day) between weeks 2 and 4. RESULTS: Of the 45 subjects enrolled, 40 received adjunctive LDX (mean dose = 60 ± 10 mg/day). A statistically significant decrease from baseline to endpoint was evident in weight (p < 0.001), body mass index (p < 0.001), fasting total cholesterol (p = 0.011), low density lipoprotein cholesterol (p = 0.044), high density lipoprotein cholesterol (p = 0.015) but not triglycerides, or blood glucose. Significant reductions were also observed in leptin (p = 0.047), but not in ghrelin, adiponectin, or resistin levels. Diastolic blood pressure and pulse increased significantly over time but on average remained within the normal range (p < 0.001). There was a significant reduction from baseline to endpoint in the total score of the ADHD Self-Report Scale. Significant improvement from baseline to endpoint was also observed in the Montgomery-Åsberg Depression Rating Scale total score as well as the Clinical Global Impression Severity and Improvement score. CONCLUSIONS: Short-term adjunctive LDX treatment was well tolerated by this sample of adults with stable bipolar I/II disorder. Lisdexamfetamine dimesylate offered beneficial effects on body weight, body mass index and several metabolic parameters. In addition to demonstrating short-term (i.e., 4 weeks) safety and tolerability, beneficial effects of LDX were also observed in mitigating depressive and ADHD symptom severity.

Sleep-related epilepsy in the A/J mouse.

RATIONALE: Evident seizures during sleep are common in clinical practice but are uncommonly considered in animal models of epilepsy. A previous observation of spontaneous spike-and-wave activity during sleep in several A/J mice (A/J JAX) from Jackson Laboratory (Bar Harbor, ME) prompted this description of the inheritance of epileptic activity. METHODS: Mice from A/J, C57BI/6J (B6), and chromosomal substitutions strains were instrumented to record EEG and EMG activity over time without and with anti-epileptic drugs. Intercrosses were performed using linkage analysis to localize sub-chromosomal regions. RESULTS: Spike-discharge patterns (n = 12 mice) were of average duration of 1.9 seconds at a rate per hour of 17, with an intrinsic frequency of 6.41 Hz and an amplitude of 634.8 microV. Clonic movements were observed in < 10% of the episodes. Episodes were expressed (> 75%) either in slow-wave sleep or in transitions to and from slow-wave sleep. Events were rare in paradoxical sleep. Compared with vehicle, intraperitoneal administration of ethosuximide (150 mg/kg) or diazepam (5 mg/kg) inhibited or eliminated seizure activity, respectively. In contrast, spontaneous spike-and-wave activity was not observed in A/J mice from Harlan National Laboratories (Indianapolis, Ind) or in B6 mice from Jackson Laboratory. In an intercross between A/J JAX and B6 mice, the trait was not present in the first generation. The trait was observed in 2 chromosome-substitution strains, B6.A4 and B6.A7. In the intercross second generation of these chromosome-substitution strains (n = 113), significant linkage was observed to loci on chromosome 4. CONCLUSIONS: This is a sleep-related epilepsy phenotype that exhibits an oligogenic pattern of allelic inheritance.

A randomized, double-blind, placebo-controlled, crossover trial evaluating the effect of intranasal insulin on cognition and mood in individuals with treatment-resistant major depressive disorder.

BACKGROUND: Cognitive dysfunction in major depressive disorder (MDD) is identified as a primary therapeutic target; no current treatment is approved for the treatment of cognitive dysfunction in MDD. We examined whether intranasal insulin offered a beneficial effect across measures of cognitive function in adults with MDD. METHODS: Thirty-five adults (18-65 years of age: 47.09±9.89) meeting criteria for a major depressive episode as per the Diagnostic and Statistical Manual (DSM)-IV-Treatment Revised were included in this randomized, double blind, placebo-controlled, crossover design study. Subjects were not stratified based on baseline cognitive deficit. Subjects were randomized to 4 weeks of either intranasal insulin 40 International Units (IU) taken four times a day (i.e., morning, afternoon, evening, and before bed) (QID) (n=19) or placebo (n=16). RESULTS: No between group differences were observed in change from baseline on total Montgomery Åsberg Depression Rating Scale (MADRS) score (25.98±2.81), in either of the Positive or Negative subscales of the Positive and Negative Affect Schedule (PANAS), or on a global index of neurocognition. The possibility of practice and/or carry over effect could not be excluded. Methodological refinement (e.g., stratification of subjects based on baseline cognitive deficit) may have augmented assay sensitivity. CONCLUSION: Intranasal insulin did not demonstrate statistically significant improvements on overall mood, aspects of emotional processing, neurocognitive function, or self-reported quality of life patient reported outcomes.

The prevalence and clinical characteristics associated with Diagnostic and Statistical Manual Version-5-defined anxious distress specifier in adults with major depressive disorder: results from the International Mood Disorders Collaborative Project.

OBJECTIVES: The aim of the study was to evaluate the prevalence of and illness characteristics in adults with major depressive disorder (MDD) with anxious distress specifier (ADS) enrolled in the International Mood Disorders Collaborative Project, which is a collaborative research platform at the Mood Disorders Psychopharmacology Unit, University of Toronto, Canada and the Cleveland Clinic, Cleveland, Ohio, USA. METHODS: Data from participants who met criteria for a current major depressive episode as part of MDD (n = 830) were included in this post hoc analysis. Diagnostic and Statistical Manual Version-5-defined ADS was operationalized as the presence of at least two out of three proxy items instead of two out of five specifiers. RESULTS: A total of 464 individuals (i.e. 56%) met criteria for ADS. There were no between-group differences in sociodemographic variables (e.g. gender, employment, marital status). Greater severity of illness was observed in adults with ADS as evidenced by a higher number of hospitalizations, higher rates of suicidal ideation, greater depressive symptom severity, greater workplace impairment, decreased quality of life, and greater self-reported cognitive impairment. CONCLUSIONS: Our findings underscore the importance of evaluating ADS in adults with MDD as its presence identifies a subpopulation with greater illness-associated burden and hazards.

Binge eating in adults with mood disorders: Results from the International Mood Disorders Collaborative Project.

A post hoc analysis was conducted using data from participants (N=631) with a DSM-IV-TR defined diagnosis of major depressive disorder (MDD) or bipolar disorder (BD) who were enrolled in the International Mood Disorders Collaborative Project (IMDCP) between January 2008 and July 2013. It was determined that 20.6% of adults with mood disorders as part of the IMDCP fulfilled criteria for binge eating behaviour (BE). A higher percentage of individuals with BD met criteria for BE when compared to MDD (25.4% vs. 16%; p=0.004) Univariate analyses indicated that individuals with a mood disorder (i.e., MDD or BD) and BE had greater scores on measures of anxiety severity (p=0.013) and higher rates of lifetime and current substance dependence, lifetime alcohol abuse (p=0.007, p=0.006, and p=0.015, respectively), Attention Deficit Hyperactivity Disorder (ADHD) (p=0.018) and measures of neuroticism (p=0.019). Individuals with a mood disorder and concurrent BE had lower scores on measures of conscientiousness (p=0.019). Individuals meeting criteria for BE were also significantly more likely to be obese (i.e., BMI≥30kg/m2) (50% vs. 25.5%; p<0.001). Binge eating is common amongst adults utilising tertiary care services principally for a mood disorder. The presence of BE identifies a subset of adults with mood disorders who have greater illness complexity as evidenced by course of illness variables and comorbidity. Screening for BE amongst individuals with mood disorders is warranted; parsing neurobiological substrates subserving non-homeostatic eating behaviour amongst individuals with mood disorders is a future research vista.

Correlates of benzodiazepine use in major depressive disorder: The effect of anhedonia.

BACKGROUND: Current treatment guidelines emphasize the limited role of benzodiazepines in Major Depressive Disorder (MDD), mainly due to the absence of long-term data, risk of abuse and potential adverse effects. However, benzodiazepines continue to be prescribed for long-term use in a significant number of patients. This study sought to evaluate benzodiazepine use in a large sample of MDD patients seen at a tertiary care clinic, and determine whether use is related to illness severity or complexity, as well as to identify the clinical predictors of benzodiazepine use. METHODS: This was a naturalistic cross-sectional study conducted in MDD patients seen at the Mood Disorders Pyschopharmacology Unit at the University Health Network (N=326). Detailed information on current medication regimens was collected. A structured diagnostic interview, in addition to measures of symptom severity, quality of life, and personality were administered. Participants were grouped according to the presence or absence of prescribed benzodiazepines for daily use. RESULTS: The prevalence of regular benzodiazepine use was 25%. Benzodiazepine users were more likely to be female, unemployed, have a history of child abuse, and have comorbid panic disorder. Depression and anxiety scores were not significantly different between groups, although anhedonia was greater in the benzodiazepine group. A logistic regression revealed anhedonia was the strongest predictor of regular benzodiazepine use. CONCLUSION: The groups were similar in clinical profile suggesting benzodiazepine use is not necessarily linked to greater illness complexity or severity. Benzodiazepine use appears to be associated with specific diagnostic and symptom characteristics, possibly providing insight into the potential pharmacodynamic and neurobiological effects of frequent use.

Depression and employment status in primary and tertiary care settings.

OBJECTIVE: Major depressive disorder (MDD) is a leading cause of disability. Impairment in work function considerably adds to symptom burden and increases the economic impact of this disorder. Our study aimed to investigate the factors associated with work status in MDD within primary and tertiary care. METHOD: We used data from 2 large databases for our analysis--Study 1: the InSight database, a chart review of MDD patients treated by primary care physicians across Canada (n=986); and Study 2: the International Mood Disorders Collaborative Project, a cross-sectional study of mood disorder patients (Canadian data only: n=274). RESULTS: Both studies demonstrated high rates of unemployment and disability (30.3% to 42.1%). Quebec showed the highest rate of unemployment (21%) and British Columbia had the greatest percentage of patients on disability (15%). Employed and unemployed groups were similar based on clinical characteristics; however, unemployed people may have higher age, prevalence of medical comorbidity, and greater likelihood of receiving a benzodiazepine. Increased disability rates were associated with history of childhood abuse, duration of current major depressive episode, comorbidity, benzodiazepine use, as well as greater depression and anxiety severity. The unemployed-disability groups had greater somatic symptoms and anhedonia. In keeping with this, anhedonia was the strongest predictor of disability. Absenteeism was also high across both studies. CONCLUSIONS: Unemployment and disability rates in MDD are high. The presence of anhedonia and medical comorbidity significantly influenced work status, emphasizing the need for treatment strategies to alleviate the additional symptom burden in this subpopulation.

The prevalence and illness characteristics of DSM-5-defined "mixed feature specifier" in adults with major depressive disorder and bipolar disorder: Results from the International Mood Disorders Collaborative Project.

BACKGROUND: A substantial proportion of individuals with mood disorders present with sub-syndromal hypo/manic features. The objective of this analysis was to evaluate the prevalence and illness characteristics of the Diagnostic and Statistical Manual Version-5 (DSM-5) - defined mixed features specifier (MFS) in adults with major depressive disorder (MDD) and bipolar disorder (BD). METHOD: Data from participants who met criteria for a current mood episode as part of MDD (n=506) or BD (BD-I: n=216, BD-II: n=130) were included in this post-hoc analysis. All participants were enrolled in the International Mood Disorders Collaborative Project (IMDCP): a collaborative research platform at the Mood Disorders Psychopharmacology Unit, University of Toronto and the Cleveland Clinic, Cleveland, Ohio. Mixed features specifier was operationalized as a score ≥ 1 on 3 or more select items on the Young Mania Rating Scale (YMRS) or ≥ 1 on 3 select items of the Montgomery Åsberg Depression Rating Scale (MADRS) or Hamilton Depression Rating Scale (HAMD-17) during an index major depressive episode (MDE) or hypo/manic episode, respectively. RESULTS: A total of 26.0% (n=149), 34.0% (n=65), and 33.8% (n=49) of individuals met criteria for MFS during an index MDE as part of MDD, BD-I and BD-II, respectively. Mixed features specifier during a hypo/manic episode was identified in 20.4% (n=52) and 5.1% (n=8) in BD-I and BD-II participants, respectively. Individuals with MDE-MFS as part of BD or MDD exhibited a more severe depressive phenotype (p=0.0002 and p<0.0002, respectively) and reported a higher rate of alcohol/substance use disorder in the context of BD but not MDD (p=0.002). Individuals with MFS were more likely to have co-existing heart disease suggestive of a distinct pattern of comorbidity and neurobiology. LIMITATIONS: Data were post-hoc and obtained from individuals utilizing a university-based mood disorder centre which may affect generalizability. CONCLUSIONS: Diagnostic and Statistical Manual Version-5-defined MFS is common during an MDE as part of MDD and BD. The presence of MFS identifies a subgroup of individuals with greater illness complexity and possibly a higher rate of cardiovascular comorbidity. The results herein underscore the common occurrence of MFS in adults with either BD or MDD. Moreover, the results of our analysis indicate that adults with mood disorders and MFS have distinct clinical characteristics and comorbidity patterns.

Ventilatory behavior during sleep among A/J and C57BL/6J mouse strains.

The pattern of breathing during sleep could be a heritable trait. Our intent was to test this genetic hypothesis in inbred mouse strains known to vary in breathing patterns during wakefulness (Han F, Subramanian S, Dick TE, Dreshaj IA, and Strohl KP. J Appl Physiol 91: 1962-1970, 2001; Han F, Subramanian S, Price ER, Nadeau J, and Strohl KP, J Appl Physiol 92: 1133-1140, 2002) to determine whether such differences persisted into non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. Measures assessed in C57BL/6J (B6; Jackson Laboratory) and two A/J strains (A/J Jackson and A/J Harlan) included ventilatory behavior [respiratory frequency, tidal volume, minute ventilation, mean inspiratory flow, and duty cycle (inspiratory time/total breath time)], and metabolism, as performed by the plethsmography method with animals instrumented to record EEG, electromyogram, and heart rate. In all strains, there were reductions in minute ventilation and CO2 production in NREM compared with wakefulness (P < 0.001) and a further reduction in REM compared with NREM (P < 0.001), but no state-by-stain interactions. Frequency showed strain (P < 0.0001) and state-by-strain interactions (P < 0.0001). The A/J Jackson did not change frequency in REM vs. NREM [141 +/- 15 (SD) vs. 139 +/- 14 breaths/min; P = 0.92], whereas, in the A/J Harlan, it was lower in REM vs. NREM (168 +/- 14 vs. 179 +/- 12 breaths/min; P = 0.0005), and, in the B6, it was higher in REM vs. NREM (209 +/- 12 vs. 188 +/- 13 breaths/min; P < 0.0001). Heart rate exhibited strain (P = 0.003), state (P < 0.0001), and state-by-strain interaction (P = 0.017) and was lower in NREM sleep in the A/J Harlan (P = 0.035) and B6 (P < 0.0001). We conclude that genetic background affects features of breathing during NREM and REM sleep, despite broad changes in state, metabolism, and heart rate.

The effect of personality dimensions on functional outcomes in mood disorders.

INTRODUCTION: Functional impairment associated with mood disorders may be related to a characteristic "profile" of normative personality dimensions. METHODS: Individuals (age ≥ 18 years) with MDD (n = 400) or BD (n = 317), as defined by the Diagnostic and Statistical Manual of Mental Disorders, fourth edition, text revision (DSM-IV-TR), were enrolled in the IMDCP. Personality was evaluated with the Neuroticism-Extraversion-Openness Five-Factor Inventory (NEO-FFI), and functionality with the Sheehan Disability Scale and Endicott Work Productivity Scale. Path analysis using linear multiple regressions was performed to identify direct and indirect effects of personality on functional impairment. RESULTS: Lower conscientiousness exerted a significant direct effect on global (p = 0.017) and family life dysfunction in individuals with MDD (p = 0.002), as well as lower work productivity in both MDD (p = 0.020) and BD (p = 0.018). Lower extraversion exerted a significant direct effect on social impairment in individuals with BD (p = 0.017). Higher neuroticism and agreeableness as well as lower extraversion exerted indirect effects on global and social dysfunction in individuals with MDD via their effects on depression severity. In BD, higher neuroticism and openness indirectly affected global dysfunction. Family dysfunction was indirectly affected by higher neuroticism and openness as well as lower extraversion in MDD and BD. CONCLUSION: The results suggest that discrete personality dimensions may exert direct and indirect effects on functional outcomes in individuals with mood disorders. Personalizing disease management approaches in mood disorders with emphasis on vocational rehabilitation may benefit from measurement and intervention targeting personality.

Admixture analysis of age at onset in major depressive disorder.

OBJECTIVES: This study aimed to determine the distributions of the age at onset (AAO) in patients with major depressive disorder (MDD) using admixture analysis and to determine the clinical differences between subgroups with different AAO. METHODS: Participants were administered the Mini-International Neuropsychiatric Interview to obtain clinical data. Admixture analysis was performed using the STATA module DENORMIX to identify subgroups characterized by differences in AAO. RESULTS: The best fit model was the three-component model with the following means, standard deviations and proportions: 14.60 (3.75) years (49.1%), 29.15 (6.75) years (34.1%) and 46.96 (6.06) years (16.8%) (χ(2)=3.64, 2 df, P=.162). The three subgroups were divided by AAO of 22 and 40. After controlling for duration of illness, there were no significant differences between the three AAO subgroups in terms of gender and psychiatric family history. However, the early-onset subgroup was significantly more likely to report being single compared to the intermediate- and late-onset groups. The proportion of individuals meeting criteria for lifetime comorbid panic disorders and obsessive-compulsive disorder did not differ significantly between the AAO groups. However, the early-onset group reported a higher incidence of attention-deficit/hyperactivity disorder (5.1% vs. 1.7% and 1.2%, P=.086), although this was not statistically significant. CONCLUSIONS: Our study identified three characteristically different AAO subgroups in individuals suffering from MDD. The subgroups may reflect different underlying neurobiological mechanisms involved.

Ribonucleotide reductase inhibitors reduce atherosclerosis in a double-injury rabbit model.

Atheroproliferative disorders such as atherosclerosis are an important health problem and one of the leading causes of morbidity and mortality in the United States. Minimally invasive therapeutic procedures, including angioplasty with stent deployment, are used frequently for obstructive coronary artery disease. However, restenosis, a proliferative vascular response, is a common sequela to this procedure. The current study investigated the effect of inhibiting ribonucleotide reductase (RR), an enzyme necessary for cellular proliferation, in an attempt to ameliorate the proliferative response. Two RR inhibitors, didox and hydroxyurea, were chosen for their potent antiproliferative properties. Studies were carried out by using a double-injury rabbit model, in which endothelial denudation was followed by the administration of a high-fat diet. At 4 wk after initial endothelial denudation, the developing atherosclerotic lesion was subjected to transluminal balloon dilation to simulate clinical intervention with percutaneous transluminal angioplasty. The degree of restenosis and atheroproliferation was assessed at 8 wk. Histologic evaluation of the lesion demonstrated that treatment with didox and hydroxyurea significantly decreased lesion area and lumen loss. These results suggest that RR inhibition may be an effective new tool for the treatment of atheroproliferative disorders.

Genetic and phenotypic analysis of seizure susceptibility in PL/J mice.

Epilepsy is one of the most common but genetically complex neurological disorders in humans. Identifying animal models that recapitulate human epilepsies is important for pharmacological studies of anticonvulsants, dissection of molecular and biochemical pathogenesis of epilepsy, and discovery of epilepsy susceptibility genes. We discovered that the PL/J inbred mouse strain is susceptible to handling- and rhythmic tossing-induced seizure. The tonic-clonic and generalized seizures observed after induction were accompanied by abnormal EEGs, similar to seizures observed in EL and SWXL-4 mice. PL/J mice also had an extremely low threshold to electroconvulsive seizures compared to other strains and showed variable sensitivity to pentylenetetrazole-induced seizures. Gross neurostructural abnormalities were not found in PL/J mice. Crosses with the seizure-resistant C57BL/6 J strain revealed semidominant inheritance of the rhythmic tossing seizure trait with low penetrance. F2 progeny indicated that the genetic inheritance of seizure susceptibility in PL/J is non-Mendelian. We crossed DBA/2 J mice, which are resistant to rhythmic tossing seizure but susceptible to audiogenic seizures, to PL/J. We found that seizure penetrance in (DBA/2 J x PL/J)F1 mice was similar to the penetrance in (C57BL/6 J x PL/J)F1 mice but the severity and frequency of seizure were higher in (DBA/2 J x PL/J)F1 mice. The PL/J strain serves as an interesting new model for studying the genetics, neurobiology, and pharmacology of epilepsy.