TRIMETHYLTIN-INDUCED PLASTIC NEURONAL CHANGES IN RAT HIPPOCAMPUS ARE ACCOMPANIED BY ASTROCYTIC TROPHIC ACTIVITY

Partial deafferentation of the hippocampus due to trimethyltin (TMT) i ntoxication has been reported to induce plastic rearrangements of neur onal elements but the factors that direct these responses are unknown. To assess the possible involvement of nerve growth factor (NGF) in th e phenomenon we evaluated the presumable changes in the expression pat tern of NGF immunoreactivity (NGF-IR) in rat hippocampus 21 days after administration of TMT (8 mg/kg, i.p.) when reactive changes are fully developed. Immunolabelling for TrkA known to mediate biological effec ts of NGF and for GFAP to identify astroglial cells as a one of presum ed source of postinjury produced factors was carried out on adjacent s ections to establish the relation between expression of these proteins . In control hippocampus NGF- IR and TrkA-IR were localized in neurons and/or neuropil. After exposure to TMT remarkable non-neuronal expres sion of both proteins was observed. The distribution pattern of NGF, T rkA and GFAP overlapped suggesting that reactive astrocytes may not on ly produce NGF but also may become responsive to this neurotrophin. Zo nes of extensive NGF and TrkA astroglial expression corresponded to ar eas of axonal-dendritic rearrangements reported earlier. The data sugg est that astroglia-derived trophic activity may be involved in neurona l plastic events associated with treatment with TMT.