Modulation of glial glycogen metabolism by 5-hydroxytryptamine in leech segmental ganglia

Leech segmental ganglia (16 out of 23 per animal) were divided into experimental and control groups (4 ganglia per group). The amounts of glycogen in the ganglia were assayed by a specific extraction procedure and fluorimetry, or by liquid scintillation counting following labelling of the glycogen by [(3)H]glucose. Within any individual animal the amounts of glycogen in the ganglia were relatively constant (max. variation 16%). 5-HT (10(?6)-10(?4) M) reduced in a dose-dependent manner the endogenous glycogen (max. 20% reduction), and the [(3)H]glycogen (max. 60% reduction). The glycogenolytic effect was studied by light-microscope autoradiography in serial sections of segmental ganglia previously exposed to [(3)H]glucose. The 5-HT-mediated glycogenolysis was localized principally in the glial cells surrounding the neuron perikarya. 5-HT, in addition to its conventional transmitter role, may regulate the supply of energy substrate from glial cells to neurons within domains defined by the projections of the neurons from which it is released.