Kainate-evoked changes in dystrophin messenger RNA levels in the rat hippocampus

Dystrophin and dystroglycan messenger RNAs are expressed in specific brain areas, including regions of the cortex and the hippocampus, and in such neurons dystrophin has been localized to postsynaptic densities. In the present study we examined by in situ hybridization the effect of neuronal activation and neurotoxicity induced by kainate and pentylenetetrazole administered in vivo on dystrophin and dystroglycan expression in the rat brain. Kainate injection resulted in a transient but dramatic decrease in dystrophin transcript levels in the dentate gyrus granule cells, neurons not affected by kainate neurotoxicity, 6 h after injection. There was also a strong, concomitant increase in dystrophin messenger RNA levels in the CA3 subfield. At 24-72 h after kainate injection, the dystrophin transcript in the dentate granule cells returned to control levels, while it decreased gradually in the CA subfields, coinciding with the neurodegeneration observed in these areas. Comparable results were obtained with pan-dystrophin probes and probes specific to the short, G-dystrophin (Dp71) isoform that predominates in the dentate gyrus. This indicates that any dystrophin transcript that might be expressed in these areas responds to kainate in the same manner. In contrast, kainate insult had no significant effect on the dystroglycan messenger RNA levels in these hippocampal areas at 6 h post-injection. At later times. however, there was a gradual decrease in the dystroglycan messenger RNA in those areas which respond to the kainate insult with extensive neuronal death. For comparison, seizures which are not associated with progressive neurodegeneration were induced by pentylenetetrazole: in this situation the dystrophin and dystroglycan messenger RNA levels remained unchanged in all areas of the hippocampal formation. Since activation of glutamate receptors is thought to be involved in some forms of synaptic plasticity in the adult hippocampus, our data indicate that the dystrophin gene behaves as a candidate plasticity-related gene responding to glutamate.