Philippe Pierret

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Astrocytes from the ventral mesencephalon and from the striatum respectively promote the dendritic and axonal arborization of dopamine (DA) neurons in vitro. To test this response in vivo, astrocytes in primary cultures from the neonatal cerebral cortex, ventral mesencephalon, or striatum were coimplanted with fetal ventral mesencephalic tissue into the(More)
Ras signal transduction pathways have been implicated as key regulators in neuroplasticity and synaptic transmission in the brain. These pathways can be modulated by Ras guanyl nucleotide exchange factors, (GEF) which activate Ras proteins by catalysing the exchange of GDP for GTP. Ras guanyl nucleotide-releasing protein (RasGRP), a recently discovered Ras(More)
This study investigated the potential of immature and adult serotonin (5-HT) neurons for axonal growth into intrastriatal grafts of ventral mesencephalic tissue. Implantation of dissociated fetal (embryonic days 14-15) ventral mesencephalic tissue was carried out in immature [postnatal days (P) 5-14] and adult rat neostriatum. The brains were processed 2-6(More)
We previously showed that grafts of fetal ventral mesencephalic tissue are practically not innervated by host serotonin (5-HT) axons after implantation into the striatum of rats aged more than 14 days, at variance with transplants of cortical or striatal tissue into the adult striatum, which are well innervated by these axons. Using 5-HT(More)
Estrogens can influence the survival, plasticity and function of many adult neurons. Many of these effects, such as neurite outgrowth and increased dendritic spine density, are mediated by changes in neuronal cytoskeletal architecture. Since neurofilament proteins play a key role in the maintenance and remodeling of the neuronal cytoskeleton, we postulated(More)
Serotoninergic (5-HT) neurons of adult recipients provide a much denser innervation of striatal than ventral mesencephalic grafts implanted into the neostriatum of the rat. Moreover, grafts from both brain regions are more innervated by host 5-HT axons after implantation in neonatal than adult hosts. To test the hypothesis that differences in glial scarring(More)
The identification of axon growth inhibitory molecules offers new hopes for repair of the injured CNS. However, the navigational ability of adult CNS axons and the guidance cues they can recognize are still essentially unknown. Astrocytes may express guidance molecules and are known to have different regional phenotypes. To evaluate their influence on the(More)
Ras guanyl nucleotide-releasing protein (RasGRP) is a recently discovered Ras guanyl nucleotide exchange factor that is expressed in selected regions of the rodent CNS, with high levels of expression in the hippocampus. Biochemical studies suggest that RasGRP can activate the Ras signal pathway in response to changes in diacylglycerol and possibly calcium.(More)
In the nervous system, Ras signal transduction pathways are involved in cellular differentiation, neuronal survival and synaptic plasticity. These pathways can be modulated by Ras guanyl nucleotide exchange factors (Ras GEFs), which activate Ras protein by catalyzing the exchange of GDP for GTP. RasGRP, a recently discovered Ras GEF is expressed in brain as(More)