Transmitter mediated regulation of energy metabolism in nervous tissue at the cellular level

The Monoamines 5-hydroxytryptamine (5-HT), noradrenaline (NA) and histamine, and the peptide Vasoactive Intestinal Polypeptide (VIP), regulate energy metabolism in nervous tissue, in addition to producing excitation and/or inhibition. These transmitters induce glycogen hydrolysis in a concentration dependent manner. The glycogen breakdown is brought about by increased cyclic AMP formation, or translocation of calcium ions to activate phosphorylase, and is partially localized in glial cells. Data from a diversity of nervous systems, including leech and snail ganglia, and rodent cortex, point towards important roles for neurons containing these transmitters in the regulation of the glycogen turnover. It is proposed that energy metabolism may be controlled within domains defined by the geometric arrangements of the neurons releasing these transmitters. The different domains may overlap temporally and spatially to coordinate energy metabolism in relation to increases in neuronal activity. The non-myelin forming glial cells, which contain glycogen whose turnover rate is altered by the transmitters, appear to be important in the local supply of energy substrate to neurons.