Fig. 2. Plasticity of glycogen metabolism in astrocytes. Activation of c-AMP-dependent intracellular signaling by a restricted set of neurotransmitters (noradrenaline, vasoactive intestinal peptide, adenosine) results in a short-term (seconds to minutes) effect, i.e. glycogenolysis, and in a delayed (hours) transcriptionally regulated action, i.e. glycogen resynthesis. This long-term plastic response triggers the induction of expression of a coordinated set of genes involved in glycogen resynthesis such as the transcription factors C/EBP, and the genes encoding for the enzymes glycogen synthase and protein targeting to glycogen.