Immunohistochemical evaluation of the protein expression of nerve growth factor and its TrkA receptor in rat limbic regions following electroshock seizures

Repeated (but not acute) exposure to brief, non-injurious seizures evoked by minimal electroconvulsive shock (ECS) decreases neuronal death in limbic system and increases mRNA levels for nerve growth factor (NGF). Thus, the induction of NGF is a potential mechanism for the neuroprotection evoked by repeated ECS. The neuroprotective action of NGF is mediated by the TrkA receptor. This study determined whether repeated ECS exposure increased TrkA and NGF protein levels. To determine the functional significance of changes in these proteins, we compared the effects of ECS given daily either for 7 days (chronic ECS) or for 1 day (acute ECS). After chronic ECS, upregulation of both NGF and TrkA was found in perirhinal cortex, thalamus, and amygdala. In hippocampus, TrkA was upregulated in CA2, CA3 and CA4. NGF increase in hippocampus was found in CA1 and dentate gyrus. In frontal cortex and substantia innominata, an increase in NGF (but not in TrkA) was found. In most brain regions, TrkA and NGF remained unchanged after acute ECS. Our results demonstrate that repeated exposure to ECS causes an upregulation of TrkA and NGF proteins in several limbic areas in which neuroprotective effects are observed suggesting that NGF contributes to ECS-evoked neuroprotection.