Morphometric abnormalities and hyperanxiety in genetically epileptic rats: a model of psychiatric comorbidity?

Imaging studies of epilepsy patients with comorbid affective disturbance demonstrate morphometric changes in limbic brain regions implicated in psychiatric disease. Genetic Absence Epilepsy Rats from Strasbourg (GAERS), specifically bred for their epilepsy phenotype, also exhibit elevated anxiety-like behaviors suggesting a common causality. Here we examined whether relevant cerebral morphological alterations exist in this rat strain using volumetric measurements and large deformation high dimensional mapping (HDM-LD), a tool recently validated to produce accurate three-dimensional surface representations of the hippocampus.

Volumetric MRI and the Open Field test of anxiety were performed in adult female GAERS (n=12) and Non-Epileptic Controls (NEC; n=11). The volumes of selected brain regions, including cortex, hippocampus, amygdala, thalamus, hypothalamus and lateral ventricles, were measured using Region-Of-Interest analysis from the MRI data and total volumes compared between the two strains.

GAERS had increased amygdala (right: p=0.003; left p<0.001), cortices (right: p=0.006; left p=0.012) and ventricular volumes (p=0.002) when compared with NEC rats. Further, HDM-LD showed GAERS to have hippocampal volume loss in two regions: the medial hippocampal surface immediately caudal to the hippocampal commissure, and the lateral hippocampal surface over the mid-portion of the septotemporal axis. GAERS exhibited increased anxiety in the Open Field compared with NEC rats: reduced distance traveled (p<0.001) and reduced time in the centre area (p=0.042).

Morphometric brain changes in GAERS could be relevant to their hyperanxious and epileptic phenotypes. This model may be useful in illuminating the pathogenesis of affective disorders generally, as well as modeling psychiatric comorbidities of epilepsy.