The glia-neuronal interaction: Some observations

Despite intensive investigation into the mechanisms underlying the memory process, the physical bases for this superior cognitive function remain elusive. Neuronal activity-associated magnetic fields (NAAMFs) hypothesis of memory suggests that items of information are stored as three-dimensional bundles of magnetic fields associated to the complex but extremely organised cerebral cortex. The present paper proposes a plausible architectural organisation of neuronal activity-associated magnetic fields that may explain how information could be stored in the human cerebral cortex. Magnetic fields generated as consequence of neuronal minicolumns activation could modify the basal “electromagnetic status” of the closest astrocytes allowing codification and storage of information.

This chapter focuses on studies of neuron-glia interactions. Glial cells actively participate in several aspects of neuronal growth and differentiation both by providing cell-cell contact interactions and by secreting neuronal growth-promoting factors. In turn, neurons influence the cellular behavior of both astrocytes and oligodendrocytes, primarily by secreting substances into the microenvironment. Such substances as neurohormones and neurotransmitters are shown to affect several glial functions including electrophysiological responses, energy metabolism, and ionic homeostasis. In several instances, these effects appear to be mediated through receptors on glial cells. The role of glial cells in the aging process of the neuron is only beginning to be appreciated. If glial cells are actively involved in the regulation of the microenvironment, then it follows that any changes in the behavior of glial cells with aging will ultimately affect neuronal function. It is clear from in vitro studies that glial cells are pluripotential cells with several functional capabilities. Their responsiveness to an environment in which neurons are maturing as compared to an environment where neurons are injured or aging clearly portrays the multifunctional role of the astrocyte.

This chapter provides an overview of the physiology of neuroglia. The glialneuronal relationship begins during the embryonic development of the organism and continues throughout its life. Pertinent aspects of glial pathophysiology and its consequences for neural function and dysfunction are discussed in the chapter for understanding the normal physiology. The blood-brain barrier appears to be more a function of vascular endothelial cells than glial cells. The chapter focuses on the functional glial-neuronal interactions and suggests that glia are active, rather than passive partners, in the ongoing glial-neuronal relationship and are critical for sustained and efficient neuronal functioning. Neurons and glial cells may interact by a reciprocal influencing of differentiation. The level of potassium in the extracellular space surrounding the neuron appears to be regulated by glia. The membrane potential of glia is primarily dependent on the extracellular and intracellular distribution of potassium. Glial cells contribute to neuronal functioning by extraneuronal regulation of neurotransmitters in the CNS and, possibly, more directly, as in the glutamate-glutamine cycle.