Neural activity triggers Ca waves in hippocampal astrocyte networks

Abstract

Recent findings that the neurotransmitter glutamate can trigger cytoplasmic Ca waves in networks of cultured astrocytes suggest a new range of possible mechanisms for neural-glial interaction and for signalling over distance within the brain. To explore some of these possibilities, we have used confocal microscopy and the Ca indicator fluo-3 to study organotypically cultured slices of rat hippocampus where astrocytes and neurons are intermingled in their normal tissue relationships. We observe that electrical stimulation of the dentate gyrus induces Ca signals in astrocytes of region CA3, acting via a TTX-sensitive neuronal fiber projection that releases glutamate as its major neurotransmitter. Astrocyte Ca transients can occur within two seconds of the onset of neural stimulation, and waves and oscillations result from sustained stimulation at frequencies as low as 2 Hz. Neurally-evoked astrocyte Ca waves propagate both within and between individual hippocampal astrocytes at velocities of 10 - 20 um/sec, while the oscillations have periods of approximately 20 sec (at 21 °C).