Neurotransmitters that are released from neurons can interact in a receptor-mediated manner with nonneuronal cells, such as astrocytes, choroid plexus cells, or cells of the vasculature. Nonneuronal cells—in particular, astrocytes and the microglia—can release molecules, such as interleukins and prostanoids, known to play a role in cell–cell communication in the immune system and in inflammatory processes, respectively. This chapter focuses on the evidence indicating that the neurotransmitters vasoactive intestinal peptide (VIP) and noradrenaline (NA) act on astrocytes to regulate energy metabolism in the cerebral cortex. Observations reviewed in the chapter show that VIP and NA participate in the regulation of brain energy metabolism by tightly regulating the glycogen content and the glucose uptake in astrocytes for NA. In addition, cytological and pharmacological evidence strongly suggest that VIP- and NA-containing neurons interact with intraparenchymal blood vessels. The demonstration of homeostatic functions regulated by the neurotransmitters contained in discrete neuronal circuits supports the concept that such circuits may represent, within the brain, the counterpart of the autonomic nervous system that regulates, among other functions, blood flow, energy metabolism, and local homeostasis in peripheral tissues.
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