DIRECT SIGNALING FROM ASTROCYTES TO NEURONS IN CULTURES OF MAMMALIAN BRAIN-CELLS

Although astrocytes have been considered to be supportive, rather than transmissive, in the adult nervous system, recent studies have challe nged this assumption by demonstrating that astrocytes possess function al neurotransmitter receptors. Astrocytes are now shown to directly mo dulate the free cytosolic calcium, and hence transmission characterist ics, of neighboring neurons. When a focal electric field potential was applied to single astrocytes in mixed cultures of rat forebrain astro cytes and neurons, a prompt elevation of calcium occurred in the targe t cell. This in turn triggered a wave of calcium increase, which propa gated from astrocyte to astrocyte. Neurons resting on these astrocytes responded with large increases in their concentration of cytosolic ca lcium. The gap junction blocker octanol attenuated the neuronal respon se, which suggests that the astrocytic-neuronal signaling is mediated through intercellular connections rather than synaptically. This neuro nal response to local astrocytic stimulation may mediate local interce llular communication within the brain.