Behavioral and Neurochemical Characteristics of Two Months Old WAG/Rij Rats with Genetic Absence Epilepsy

Abstract

WAG/Rij rats are genetic animal model of absence epilepsy with comorbidity of depression. The first spike-wave discharges (SWDs) in WAG/Rij rats begin to appear at the age of 2-3 months and are fully manifested by 5-6 months. Occurrence of SWDs in the EEG is the main index of absence epilepsy. Previously it has been shown that the extensive absence epilepsy in 5-6 months old WAG/Rij rats is accompanied by decrease of dopamine and its metabolites concentrations in the meso-cortico-limbic and nigro-striatal dopaminergic brain systems, resulting in the expression of depression-like behavioral symptoms, and impairments of the learning and memory processes. In 36 days old WAG/Rij rats, SWDs are not manifested, deficiency of the mesolimbic dopamine is not revealed, and symptoms of depression-like behavior are not expressed. In this study, behavior in the open field, light-dark choice, forced swimming tests, monoamines and their metabolites concentrations in 5 brain structures (prefrontal cortex, nucleus accumbens, hypothalamus, striatum, hippocampus) were investigated in two months old WAG/Rij rats in comparison with age-matched Wistar rats. Reduced concentration of the dopamine and its metabolites, and increased concentration of the serotonin was found in WAG/Rij rats compared with Wistar rats only in the prefrontal cortex, indicating that the prefrontal cortex is the brain structure where neurochemical abnormalities appear first. No substantial changes in the monoamine and their metabolites concentrations have been revealed in other brain structures. Two months old WAG/Rij rats didn’t exhibit depression-like behavior in the forced swimming test, and learning/memory deficits in the passive avoidance test, but they showed behavioral changes, indicating increase anxiety/stress-reactivity, and alterations in learning/memory in the active avoidance test. Results suggest that two month-old WAG/Rij rats are at the stage of so called “pre-pathology” (increased anxiety and stress reactivity) preceding the development of depression-like behavior and substantial cognitive impairments which are co-morbid to fully expressed absence epilepsy in 5-6 months old rats of this strain.