INTRACELLULAR CALCIUM OSCILLATIONS IN ASTROCYTES - A HIGHLY PLASTIC, BIDIRECTIONAL FORM OF COMMUNICATION BETWEEN NEURONS AND ASTROCYTES IN-SITU

The spatial-temporal characteristics of intracellular calcium ([Ca2+]( i)) changes elicited in neurons and astrocytes by Various types of sti muli were investigated by means of confocal fluorescent microscopy in acute rat brain slices loaded with the Ca2+ indicator indo-1. Neurons and astrocytes from the visual cortex and CA1 hippocampal region were identified in situ on the basis of their morphological, electrophysiol ogical, and pharmacological features. We show here that stimulation of neuronal afferents triggered periodic [Ca2+](i) oscillations in astro cytes. The frequency of these oscillations was under a dynamic control by neuronal activity as it changed according to the pattern of stimul ation. After repetitive episodes of neuronal stimulation as well as re petitive stimulation with a metabotropic glutamate receptor agonist, a strocytes displayed a long-lasting increase in [Ca2+](i) oscillation f requency. Oscillating astrocytes were accompanied by repetitive [Ca2+] (i) elevations in adjacent neurons, most likely because of the release of glutamate via a tetanus toxin-resistant process. These results rev eal that [Ca2+](i) oscillations in astrocytes represent a highly plast ic signaling system that underlies the reciprocal communication betwee n neurons and astrocytes.