Long-term microglial and astroglial activation in the hippocampus of trimethyltin-intoxicated rat: stimulation of NGF and TrkA immunoreactivities in astroglia but not in microglia.
In the present study we investigated the microglial and astroglial response after trimethyltin (TMT) exposure over a prolonged period of time. Male Wistar rats were given a single dose of TMT (8 mg/kg, i.p.) and survived 4, 7, 21, 60 and 180 days after the administration of the toxin. Histochemistry (Griffonia simplicifolia lectin staining) and immunocytochemistry for GFAP were applied to identify micro- and astroglial cells, respectively. To assess the trophic response of glial cells (NGF and TrkA expression), single or double staining experiments were performed. In addition, the biochemical evaluation of GFAP and NGF were carried out at chosen timepoints using immunoblotting technique and ELISA, respectively. The main findings of our study were as follows. (1) A protracted activation of microglia (at least up to 2 months posttreatment). (2) A long-lasting expression of GFAP immunoreactivity (at least up to 6 months posttreatment) and a steady increase in GFAP content (at least up to 2 months posttreatment). (3) The appearance of enormously enlarged, round-shape astrocytes exclusively localized to CA1 and observed 2 months posttreatment. (4) The stimulation of NGF and TrkA expression in reactive astrocytes. (5) The strongest activation of micro- and astroglia coincided with the most prominent neurodegeneration in the hippocampus, i.e., in CA4/CA3c and CA1. It is tempting to assume that the activation of glial cells in the hippocampal areas particularly vulnerable to TMT may affect neuronal fate after neurotoxic insult.