Rapid Turnover of Glycogen in Memory Formation

The influence of noradrenaline acting at alpha(2)-AR and beta(2)-ARs on the turnover of glycogen after learning has been investigated. The role of glycogen turnover in memory formation was examined using weakly-reinforced, single trial bead discrimination training in day-old domestic chickens. This study follows our previous work that focused on the need for glycogen breakdown (glycogenolysis) during learning. Inhibition of glycogenolysis by 1,4-dideoxy-1,4-imino-d-arabinitol (DAB) prevented the consolidation of strongly-reinforced learning and inhibited memory. The action of DAB could be prevented by stimulating glycogenolysis with the selective beta(2)-AR agonist, zinterol. Stimulation of alpha(2)-ARs has been shown to lead to an increase in the turnover and synthesis of glycogen. In the present study, we examined the effect of inhibition of alpha(2)-AR stimulated glycogen turnover (measured as(14)C-glucose incorporation into glycogen) on the ability of zinterol to promote the consolidation of weakly reinforced memory. In astrocytes, the selective alpha(2)-AR agonist clonidine stimulated C-14-glucose incorporation into glycogen in chick astrocytes and this was inhibited by the selective alpha(2)-AR antagonist, ARC239. The critical importance of the timing of ARC239 injection relative to training and intracerebral administration of zinterol was examined. It is concluded that our data provides evidence for a readily accessible labile pool of glycogen in brain astrocytes. If glycogen synthesis is inhibited, the can be depleted within 10 min, thus preventing zinterol from promoting consolidation.