Glia:neuron index: review and hypothesis to account for different values in various mammals.

The present paper proposes a hypothesis to account for different values of the glia:neuron index in comparable central nervous system tissues of various mammals. This hypothesis assumes that K+ ions released by active neurons are a mitogenic signal for glial cells. The thicker the tissue (for example, the brain wall), the more difficult is efficient K+ clearance, and more perinatal glial cell proliferation should occur. Thus, this hypothesis accounts for higher glia:neuron indices in mammals with thicker brain walls.