Glutamate and GABA imbalance promotes neuronal apoptosis in hippocampus after stress

People who experience traumatic events have an increased risk of post-traumatic stress disorder (PTSD). However, PTSD-related pathological changes in the hippocampus and prefrontal cortex remain poorly understood.

We investigated the effect of a PTSD-like animal model induced by severe stress. The experimental rats received 20 inescapable electric foot shocks in an enclosed box for a total of 6 times in 3 days. The physiological state (body weight and plasma corticosterone concentrations), emotion, cognitive behavior, brain morphology, apoptosis, and balance of gamma-aminobutyric acid (GABA) and glutamate in the hippocampus and prefrontal cortex were observed. Cell damages were examined with histological staining (HE, Nissl, and silver impregnation), while apoptosis was analyzed with flow cytometry using an Annexin V and propidium iodide (PI) binding and terminal deoxynucleotidyl transferase mediated-dUTP nick end labeling (TUNEL) method.

In comparison with the sham litter-mates, the stressed rats showed decreased body weight, inhibition of hypothalamic-pituitary-adrenal (HPA) axis activation, increase in freezing response to trauma reminder, hypoactivity and anxiety-like behaviors in elevated plus maze and open field test, poor learning in Morris water maze, and shortened latency in hot-plate test. There were significant damages in the hippocampus but not in the prefrontal cortex. Imbalance between glutamate and GABA was more evident in the hippocampus than in the prefrontal cortex.

These results suggest that neuronal apoptosis in the hippocampus after severe traumatic stress is related to the imbalance between glutamate and GABA. Such modifications may resemble the profound changes observed in PTSD patients.