Functional morphology of excitable glial nets associated with sensory nerve endings-calcium image analysis.

点击翻译按钮获取中文摘要

Recent studies have shown that glial cells respond to various stimuli by a transient elevation in the intracellular Ca^<2+> concentration, and that these signals mediate glial activities to regulate neuronal functions. In cutaneous sensory devices, glial elements connect with each other by branched processes to form a network extending among different axon terminals. In order to define spatiotemporal dynamics and physiological properties of the cell signals in these glial nets, calcium images of isolated lanceolate endings, motion receptors of rat vibrissae, were monitored by time-lapse confocal microscopy while the cells were stimulated by application of the neurotransmitter adenosine 5'-triphosphate (ATP), or by touching with a micromanipulator-driven glass needle. Morphological backgrounds of the glial signaling were observed electron microscopically. Stimulation with ATP evoked an oscillatory elevation in the intracellular Ca^<2+> concentration in the glial cells. Responses in thei … More r lamellar processes covering axon terminals always proceeded to those in their cell bodies. In each lamella, the initial wave evoked by a given trial of the stimulant arose from a specific locus within the cell process. Touching with a glass needle on lanceolates triggered a Ca^<2+> spike in the affected glial lamellae. The Ca^<2+> waves occasionally traveled within, and between the glial cells, to enter other glial processes enveloping neighboring lanceolates. These findings imply subcellular compartmentalization that may enable each glial lamella to modulate the activity of its accompanying lanceolate terminal through its own Ca signal as well as to regulate neighboring lanceolates through interlamellar signal propagation. Pharmacological experiments have shown that the ATP-evoked responses of the glia are mediated by the purinoceptor subtype P2Y_2, activation of which induces Ca^<2+> release from an intracellular store. Gliai lamellae of lanceolate endings examined by electron microscopy revealed smooth endoplasmic reticulum which would store Ca^<2+> in the lumen, and gap junctions which maybe involved in the intercellular signal propagation. Less