Astrocytes and presynaptic plasticity in the striatum: Evidence and unanswered questions

One of the main functions of astrocytes is to ensure glutamate homeostasis by glutamate uptake and glutamine synthesis. However, during the past ten years it has become clear that astrocytes may also induce changes in synaptic glutamate release when respective pathways must cope with the consequences of brain damage or other alterations in their functional requirements. The loss of glutamatergic synapses in Parkinson's and Huntington's disease is likely to associate with a continuous redistribution of presynaptic activity within the pool of surviving synapses, and astrocytes may have a role in the maintenance of independent control at individual glutamate release sites. The rodent striatum should be a good model structure to analyse astrocyte-synapse interactions underlying disease-related plasticity, because it does not itself contain any glutamatergic neurons. Here we examine recent results that may shed light on the mechanisms underlying pathway-specific alterations in the corticostriatal or thalamostriatal synaptic transmission with a possible involvement of astrocytic release or uptake of glutamate. The conclusions emphasize the need of exploring the highly compartmentalised and presumably heterogeneous synapse astrocyte-interactions at a single synapse level.