Strong induction of activin expression after hippocampal lesion.

We studied the temporal and spatial mRNA expression pattern of activin/inhibin beta A, beta B and alpha subunits after unilateral kainic acid lesions of the hippocampal CA3 region. We found a strikingly increased expression of beta A mRNA in the ipsilateral hippocampus 6-24 h after injury. By contrast, the beta B and alpha mRNAs were expressed at equally low levels in normal and injured hippocampi, suggesting that the beta A transcripts give rise to activin A, but not to activin AB or inhibin. In situ hybridization demonstrated the presence of beta A mRNA in neurones near the site of lesion. Expression of all known types of activin receptors could be demonstrated in normal and injured hippocampi by RT-PCR. These findings suggest a role of activin in brain injury.