Ultrastructure of neuroglial contacts in crayfish stretch receptor

Abstract

In order to explore neuroglial relationships in a simple nervous system, we have studied the ultrastructure of the crayfish stretch receptor, which consists of only two mechanoreceptor neurons enwrapped by glial cells. The glial envelope comprises 10-30 glial layers separated by collagen sheets. The intercellular space between the neuronal and glial membranes is generally less than 10-15 nm in width. This facilitates diffusion between neurons and glia but restricts neuron communication with the environment. Microtubule bundles passing from the dendrites to the axon through the neuron body limit vesicular transport between the perikaryon and the neuronal membrane. Numerous invaginations into the neuron cytoplasm strengthen glia binding to the neuron and shorten the diffusion pathway between them. Double-membrane vesicles containing fragments of glial, but not neuronal cytoplasm, represent the captured tips of invaginations. Specific triads, viz., "flat submembrane cisterns - vesicles - mitochondria", are presumably involved in the formation of the invaginations and double-membrane vesicles and in neuroglial exchange. The tubular lattice in the glial cytoplasm might transfer ions and metabolites between the glial layers. The integrity of the neuronal and glial membranes is impaired in some places. However, free neuroglial passage might be prevented or limited by the dense diffuse material accumulated in these regions. Thus, neuroglial exchange with cellular components might be mediated by transmembrane diffusion, especially in the invaginations and submembrane cisterns, by the formation of double-walled vesicles in which large glial masses are captured and by transfer through tubular lattices.

Dynamics of ultrastructural alterations in photosensitized crayfish glial and neuronal cells: Structures involved in transport processes and neuroglial interactions

“…2A) and glial protrusions into the neuronal cytoplasm (Figs. 1, 3A, 4B), this provides robust attachment of the glial envelope to the neuron (Fedorenko and Uzdensky, 2009a). Flattened and elongated glial nuclei are fewer than those in SN.…”

“…Small hydrophobic and amphiphilic metabolites cross the plasma membrane, but how are macromolecules and supramolecular structures transferred between cells? The vesicular transport between the SN perikarion and the plasma membrane and further to the satellite glial cells is limited by the fibrillar microtubular basket surrounding the neuronal soma (Fig1-3; Fedorenko and Uzdensky, 2009a). However, glial protrusions penetrate into the neuronal cytoplasm up to 0.5-1 lm (Figs.…”

“…Mitochondria, vesicles of smooth ER, and dictyosomes are often present in the vicinity of SC. These may be involved in energy supply and in metabolite and ion exchange (Fedorenko and Uzdensky, 2009a). Transport structures in glial cells.…”

“…It consists of a single sensory neuron (SN) enwrapped by the multilayer glial envelope. Its ultrastructure is well characterized (Fischer et al, 1975;Tao-Cheng et al, 1981;Fedorenko et al, 1995;Fedorenko and Uzdensky, 2008, 2009a,b, 2010. PDT-induced inactivation and death of this neuron and surrounding glial cells as well as involvement of diverse signaling pathways in their damage have been recently explored (Uzdensky et al, 2002(Uzdensky et al, , 2005(Uzdensky et al, , 2007.…”

Photodynamic therapy: a review of applications in neurooncology and neuropathology

“…In this object, neuroglial interactions are clearly indentified. 75 In the stationary state, this neuron fires regularly with a constant rate for several hours. Photosens-mediated PDT induced elimination of neuronal activity, necrosis of neuron and surrounding glial cells, and apoptosis of glia.…”