Calcium signaling in invertebrate glial cells

Abstract

Calcium signaling studies in invertebrate glial cells have been performed mainly in the nervous systems of the medicinal leech (Hirudo medicinalis) and the sphinx moth Manduca sexta. The main advantages of studing glial cells in invertebrate nervous systems are the large size of invertebrate glial cells and their easy accessibility for optical and electrophysiological recordings. Glial cells in both insects and annelids express voltage-gated calcium channels and, in the case of leech glial cells, calcium-permeable neurotransmitter receptors, which allow calcium influx as one major source for cytosolic calcium transients. Calcium release from intracellular stores can be induced by metabotropic receptor activation in leech glial cells, but appears to play a minor role in calcium signaling. In glial cells of the antennal lobe of Manduca, voltage-gated calcium signaling changes during postembryonic development and is essential for the migration of the glial cells, a key step in axon guidance and in stabilization of the glomerular structures that are characteristic of primary olfactory centers.

Glial cells in neuronal network function

“…Because of their relative simplicity, invertebrate system studies have proved to be extremely useful in elucidating many aspects of neurophysiology and neuronal network function. Although invertebrate and vertebrate glial cells may share similar features (Freeman & Doherty 2006;Lohr & Deitmer 2006;Shaham 2006;Murai & Van Meyel 2007;Jackson & Haydon 2008), the phylogenetic differences between vertebrates and invertebrates of the phenotype and function of glial cells may make it difficult to extrapolate and generalize the conclusions obtained in invertebrate systems. Additionally, glial cells are more numerous, display higher morphological complexity and probably have more complex functions in mammals (Ramón y Cajal 1899; Nedergaard et al 2003).…”

G protein activation by uncaging of GTP-γ-S in the leech giant glial cell

“…A second UV pulse, or UV illumination to a cell not injected with caged GTP-␥-S, had no effect on the cytosolic Ca , which depolarized the cell to near -30·mV, evoked a Ca 2+ transient in all cells injected and not injected with GTP-␥-S (Fig.·4A-C). This Ca 2+ rise had been shown to be due to voltage-dependent Ca 2+ influx (Lohr and Deitmer, 2006;Munsch and Deitmer, 1992). The amplitude of the Ca 2+ transients amounted to about 30% fluorescence change for both stimuli (Fig.·4C).…”

“…One of the most prevalent pathways initiated by activation of G proteins is the activation of phospholipase C (PLC), which leads to the formation of inositol-trisphosphate (IP 3 ) and the release of Ca 2+ from intracellular stores (Berridge et al, 2000). As electrically inexcitable cells, glial cells use this pathway in response to many kinds of stimuli, including neurotransmitters, neuromodulators, growth factors and cytokines (Lohr and Deitmer, 2006;Fiacco and McCarthy, 2006). In the nervous system, glial cells often respond to active neurons releasing neurotransmitters, which activate metabotropic receptors in the glial cells.…”

Development of a glial network in the olfactory nerve: role of calcium and neuronal activity

“…Calcium transients in glial cells have been reported many systems, including olfactory ensheathing cells in the mammalian olfactory bulb (Reiger et al, 2007), astrocytes in the cortex (van den Pol et al, 1992), and neuropil glial cells in the olfactory (antennal) lobe of the moth and in the giant glial cells of medicinal leech ganglia (Lohr et al, 2005;Lohr and Deitmer, 2006).…”

“…In the latter, calcium transients begin to appear at stage 6, and are present in all NP glial cells by stage 7; stage 6 is the stage at which NP glial cells begin to migrate to surround and stabilize developing glomeruli (Lohr et al, 2005;Lohr and Deitmer, 2006;Bauman et al, 1996).…”