Abstracts

OBJECTIVE: Attendees will learn that calcium waves propagate through neuronal stem cells of the developing cerebral cortex, and are triggered embryonically by mild trauma as well by endogenous levels of ATP.
In the developing embryonic neocortex, newborn neurons migrate along radial glial fibers from the proliferative ventricular zone (VZ) into the postmitotic cortical plate where specific cortical layers are established. Radial glial cells span the width of the cortex during early development and provide a scaffold for migration. In addition to their role as migratory guides, radial glial cells have recently been shown to function as neuronal stem cells. Immature neurons climb along their own parental radial glial fibers into the developing cortex. Radial glial cells then transform into astrocytes during the first postnatal week, and may therefore be considered a part of the astrocytic lineage. While a key role for radial glia in neuronal production and migration has been demonstrated, radial glial signaling has not been explored in detail. Since the radial glial cell is crucial to neurogenesis and migration, potential signaling pathways could be important in the establishment of the laminated cortex.
METHODS: To begin to investigate radial glial signaling, we have used calcium imaging to monitor activity throughout the ventricular zone. Acute coronal slices from E16 rat brain were loaded with the calcium indicator Fluo-3 for 1-2 hours. Calcium activity within cortical slices was then monitored using an epifluorescence microscope and digital camera. Slices were stimulated using an extracellular electrode. Drugs were applied either focally or via bath perfusion. In some experiments, whole-cell recording, immunohistochemistry, and western blotting techniques were used.
RESULTS: We find that electrical or mechanical stimulation triggers a robust, slowly propagating calcium wave that travels throughout the VZ at a rate of 5.8 +/- 2.0 mm/sec. Dye-filling experiments show that radial glial cells participate in the waves. The calcium wave is mediated, at least in part, by a diffusible signal, because a wave can be elicited in a separate cortical slice located up to 150 mm away. The wave is not dependent upon extracellular calcium but does require the ATP receptor subtype P2Y1 and calcium release from IP3-sensitive intracellular calcium stores.
CONCLUSIONS: These findings show that robust calcium waves propagate through radial glial cells of the embryonic cortical ventricular zone. Similar to calcium waves in astrocytes, these waves rely on ATP signaling and calcium release from IP3-mediated intracellular stores. We propose that release and signaling via metabotropic ATP receptors triggers and sustains this propagating wave throughout radial glial cells of the VZ. Currently we are examining whether VZ calcium increases triggered by ATP can cause changes in gene expression or rates of proliferation, migration, or secretion. Since radial glial cells are involved in neurogenesis and neuronal migration, these calcium waves may be involved in the establishment of the laminated cortex.
[Supported by: This work is supported by grants from the NINDS and the March of Dimes Birth Defects Foundation.]