Fragile X Mental Retardation protein (FMRP), which is not produced in victims of Fragile X Syndrome, is a mRNA binding protein that seems to be involved in transport and translational regulation of a subset of mRNAs. We have continued our investigations into the FMRP-containing stress granules (Mazroui et al., 2002) which form in response to in vivo electrical stimulation of hippocampal neurons (Weiler et al, SfN 2003). Since the granule fraction defined by centrifugation yields a motley collection of mRNP and transport granules, we have chosen to use TIA-1 as a marker to select stress granules. Hippocampi from rats before and at defined intervals after in vivo perforant path stimulation are rapidly removed and frozen on dry ice. After cell lysis, granules are rapidly and gently purified using antibody to TIA-1 that is conjugated to magnetic beads. The protein content of stress granules can then be directly compared to the proteins associated with a polyribosomal pellet isolated from the same lysate throug...