Heterogeneity of expression of neuropeptide genes by astrocytes: functional implications.

A specific subset of neuropeptides are expressed in astrocytes, with specificity in terms of both brain region and gene, as well as with specific developmental patterns: the overall pattern of expression is thus heterogeneous. These neuropeptides have been demonstrated to have a number of trophic effects, including regulation of cell number, of length of axons and dendrites, and of neuronal phenotype. The developmental regulation of expression of neuropeptides in astrocytes further supports functional roles for the neuropeptides as trophic modeling factors. Not all the trophic effects have to be stimulatory and evidence suggests that opioid peptides may function to prune dendrites or decrease cell numbers in order to modulate or shape the nervous system. In addition to roles during development, preliminary experiments suggest that astrocyte neuropeptide expression turns back on in the adult brain following injury, suggesting that the neuropeptides may play a role in supporting survival or recovery of damaged neurons. The heterogeneity of neuropeptide expression in astrocytes must therefore contribute to the establishment and maintenance of the network of communication among neurons and glia in the nervous system in ways we have yet to understand fully.