Astroglia in CNS injury

Abstract

The astroglial response to CNS injury is considered in the context of neuron-glial relationships. Although previous models suggested that astroglial cells present in "scars" impede axon regrowth owing to irreversible changes in the glial cell following injury, recent in vivo and in vitro studies indicate that astroglial cells exhibit considerable plasticity, elevating expression of the glial filament protein and altering expression of properties which support axons, including extracellular matrix components and cell surface adhesion systems. Both in vivo and in vitro studies on neuron-glia interactions in different brain regions suggest that glia express region-specific properties, including ion channels, neurotransmitter uptake and receptor systems, and cell surface adhesion systems. Together these findings suggest that a more detailed analysis of glial response to injury in different brain regions will lead to an appreciation of the diversity of the astroglial response to injury, and its regulation by neuron-glia relationships.

The Metabotropic Glutamate Receptor mGluR5 Induces Calcium Oscillations in Cultured Astrocytes via Protein Kinase C Phosphorylation

“…These potential roles include neuron-glia communication through [Ca 2±j~waves following glutamate receptor activation (Cornell-Bell and Finkbeiner, 1991;Dani et al, 1992), stimulation of reactive gliosis (Hatten et al, 1991;Eng et al, 1992), alteration of glial morphology l990b), and control of the volume and ion balance in the microenvironment of the synapses via receptormediated modulation of ion channels (Cornell-Bell et al, 1992;Smith, 1992). The present identification of mGluRS in the mechanism of astrocyte [Ca2~J, oscillations will help further the understanding of the role of not only a specific mGluR subtype but also [Ca2~I 1 oscillations in brain function.…”

Electrophysiological Changes That Accompany Reactive GliosisIn Vitro

“…In the adult, proliferation-competent glial cells are thought to participate in glial scar formation (reactive gliosis). Gliosis may involve induction of formerly postmitotic cells to dedifferentiate and proliferate (Hatten et al, 1991) and can be associated with trauma (Reier, 1986), infarct lesions (Kraig and Jaeger, 1990), Alzheimer's plaques (Murphy et al, 1992), epileptic seizure foci (Pollen and Trachtenberg, 1970), neurotoxicity (Niquet et al, 1994), ischemic injury (Kraig and Jaeger, 1990), and mechanical injury (Reier, 1986). Thus, gliogenesis and gliosis are temporally and f unctionally distinct modes of glial proliferation, the former prevailing during early brain development and the latter an integral part of wound healing.…”

Olfactory ensheathing cells: Historical perspective and therapeutic potential

“…However, it is also clear that astrocytes are not always nonpermissive for axonal growth. In fact, there appear to be differences in the ability of astrocytes to support axonal growth, depending on the degree of differentiation of the cells (Baehr and Bunge, 1989;Hatten et al, 1991;Lucius et al, 1996); on whether the astrocytes have formed a two-or three-dimensional substratum for the growing axons (Fawcett et al, 1989); on the part of the CNS that is injured (Alonso and Privat, 1993a,b;Chauvet et al, 1998;Prieto et al, 2000); and on the presence or absence of macrophages (David et al, 1990), Schwann cells Dezawa et al, 1999) or OECs (Li et al, 1997(Li et al, , 1998.…”

“…The driving force behind these experiments was to manipulate the cellular environment of the lesion site in the brain or spinal cord so as to create one more conducive to supporting axonal growth across the lesion and into the tissue on the distal side. Even though, as mentioned above, macroglia of the CNS appear to play a major role in the abortive regeneration of axons in the brain and spinal cord (Liuzzi and Lasek, 1987;Reier and Houle, 1988;Reier et al, 1989;Fawcett, 1991;Hatten et al, 1991), it was hypothesized that the presence of OECS would create a more favourable and supportive environment for axonal growth (Doucette, 1990(Doucette, , 1995Wozniak, 1993;Ramon-Cueto and Valverde, 1995;Franklin and Barnett, 1997).…”

“…Schwann cells are good promoters of axonal growth, and under certain conditions, even astrocytes have been shown to possess growth-promoting properties Ard et al, 1987;Ard and Bunge, 1988;Neugebauer et al, 1988;Silver 1988;Bahr and Bunge, 1989;Hatten et al, 1991;Kawaja and Gage, 1991). However, promoting axonal growth in the injured spinal cord of adult mammals is only one of many problems that must be overcome in the treatment of spinal cord injury .…”