SPATIOTEMPORAL SELECTIVE EFFECTS ON BRAIN-DERIVED NEUROTROPHIC FACTOR AND TRKB MESSENGER-RNA IN RAT HIPPOCAMPUS BY ELECTROCONVULSIVE SHOCK

Electroconvulsive therapy is used in the treatment of affective disorders and schizophrenia and experimental electroconvulsive shock may serve as an animal model for this treatment. The aim of this study was to investigate a possible role for neurotrophins in the mechanism of action of experimental electroconvulsive shock and thus in clinical electroconvulsive therapy. The effect of electroconvulsive shock on levels of messenger RNAs encoding the neurotrophin brain-derived neurotrophic factor and the receptor trkB in rat hippocampus was determined by in situ hybridization with RNA probes 1, 3, 9 and 27 h following the shock. Brain-derived neurotrophic factor messenger RNA levels were increased at 1, 3 and 9 h following the shock and normalized after 27 h. Granule cells of the dentate gyrus showed a more rapid response as compared to hilar cells and pyramidal cells of CAI. Total trkB messenger RNA levels, including the transcripts for both the truncated and full length trkB receptor protein (gp95(trkB) and gp145(trkB), respectively), showed a pattern of increase very similar to that of the brain-derived neurotrophic factor messenger RNA. However, using a probe selective for the full length (gp145(trkB)) trkB messenger RNA, we determined a delayed pattern of activation with significant increase only at 3 and 9 h after the shock. In hippocampus total trkB messenger RNA was found to consist of approximately one-quarter of mRNA encoding gp145(trkB) and three-quarters encoding gp95(trkB) as revealed by RNAase protection. While brain-derived neurotrophic factor and the truncated trkB messenger RNAs appear to increase with a similar pattern, suggesting a similar mechanism of activation by electroconvulsive shock, full length receptor trkB messenger RNA appears to increase with a delayed pattern suggesting a separate mechanism of activation. Electroconvulsive shock-induced seizures seem to include activation of a brain neurotrophin known to be important for neuronal plasticity.