Schwann cell-induced loss of synapses in the central nervous system

Schwann cells exhibit excitotoxicity consistent with release of NMDA receptor agonists

Neurodegenerative effects of Schwann cells transplanted into the central nervous system have been observed previously. We report here that conditioned medium from Schwann cell cultures exhibit degenerative influences on hippocampal neurons. Aliquots of Schwann cell-conditioned medium compromised the morphologic integrity of the neurons, markedly elevated their intracellular calcium concentrations, and decreased their viability. The degenerative effects of Schwann cell medium on neuronal morphology and viability were blocked by N-methyl-D-aspartate (NMDA) receptor antagonists D-(-)-2-amino-5-phosphonopentanoic acid (D-APV) and 5,7-dicholorokynurenic acid (DCKA). Glutamate was detected in Schwann cell-conditioned medium at a concentration on the order of 10(-5) M. D-Amino acid oxidase (DAAOx) also attenuated the neurotoxicity exhibited by Schwann cells. These data suggest that Schwann cells release biologically relevant concentrations of excitotoxins that include glutamate and D-serine.

New roles for astrocytes: regulation of CNS synaptogenesis

The notion that astrocytes have a profound influence on the function of synapses between CNS neurons implies that the development of synaptic connections and their glial neighbors are controlled by reciprocally acting signals. Currently, however, synaptogenesis is considered a purely neuronal affair. This article summarizes recent experimental evidence suggesting that this may not be the case. Astrocytes may indeed regulate the formation, maturation and maintenance of synapses. The recent advances caution that synapses cannot develop correctly without astrocytes. Further progress on this issue requires new experimental models to identify signaling pathways and to scrutinize the relevance of glia-synapse interactions in vivo.