Phorbol ester-stimulated stellation in primary cultures of astrocytes from different brain regions.

Stellation is the process by which astrocytes change from epithelial-like to process-bearing cells. Stellation occurs following activation of either cyclic AMP-dependent protein kinase or protein kinase C. This process occurs through tubulin-dependent rearrangement of the cytoskeleton. We have evaluated the ability of phorbol, 12-myristate, 13-acetate (PMA) to induce astrocyte stellation. Astrocytes from five brain regions (cerebellum, cerebral cortex, hippocampus, diencephalon, and brain-stem) were examined to determine if all astrocytes would exhibit similar responses to this activator of protein kinase C. Stellation was evaluated following cell fixation by either phase optics using conventional light microscopy, or scanning laser confocal light microscopy of cultures prepared using immunocytochemistry for tubulin and glial fibrillary acidic protein. Both the number of cells responding to PMA and the sensitivity to PMA varied for astrocytes from each brain region. PMA-induced stellation was most robust in cerebellar and brainstem astrocytes, with greater than 70% responding. Less than 40% of hippocampal and diencephalic astrocytes responded to PMA at the maximum dose (10(-5) M). PMA also induced different numbers of processes or branching patterns of processes on astrocytes from different brain regions. The protein kinase C induced stellation response in astrocytes supports the hypothesis that astrocytes contribute to neural plasticity.

Three-day exposure to low-dose ethanol alters guanine nucleotide binding protein expression in the developing rat hippocampus.

Alcohol-related birth defects result from acute and chronic insults that perturb sequential developmental programs. The molecular targets of EtOH include G-protein coupled signal transduction pathways. In order to test the hypothesis that G-proteins are involved in EtOH-induced hippocampal teratogenesis, rat pups were administered 3.3 g/kg.day of EtOH on postnatal days (PN) 5 to 7 using the pup-in-a-cup model of third trimester "binge" exposure. This exposure paradigm produced a selective 40% decrease in the 52 kDa isoform of the stimulatory form of the heterotrimeric guanine nucleotide binding protein (G alpha s) in the hippocampus on PN 7 with no significant changes in the levels of G alpha i or G alpha o. Immunohistochemistry demonstrated that this decrease occurred in the somas of both hippocampal pyramidal cells and granule cells of the dentate gyrus. Computer-assisted cell counting indicates that this decrease was not due to pyramidal cell death on PN 7. Northern and slot blot analysis demonstrated a 30% decrease in G alpha s messenger RNA in the hippocampus. These results suggest that EtOHs teratogenic effects in the hippocampus may involve disruption of G alpha s-coupled signal transduction pathways, which are critical for normal synaptogenesis, neurotransmitter signaling and the integration of these signals with growth factor signaling pathways.