Up-regulation of immunoglobulin G gene expression in the hippocampus of rats subjected to acute immobilization stress

Immunoglobulin G (IgG) is thought to be produced by matured B lymphocytes, however, it was recently found to be synthesized in neurons of the brain, especially showing higher expression level in the hippocampus. To study the possible effects of IgG in the hippocampus, we examined IgG protein and mRNA expressions in rat hippocampal neurons with immunohistochemistry, immunofluorescence, in situ hybridization and laser microdissection-assisted RT-PCR. Increased IgG expressions at both protein and mRNA levels were detected in the hippocampus of an acute immobilization stress model of rat. No change was observed in the cortex or the thalamus. Furthermore, the microtubule-associated protein 2 (MAP2) and β III tubulin proteins did not show significant changes. Based on these findings, we hypothesize that hippocampal IgG may play a key role in adverse circumstances such as stress. The finding of increased IgG expression in the hippocampus following stress may also provide possibilities for developing antidepressant medication.