α 2 ‐Adrenoceptors increase glycogen synthesis in chick astrocytes: possible mechanism to increase memory formation

From experiments using a discriminated bead task in chicks, we have defined when and where adrenoceptors (ARs) are involved in memory modulation. All 3 AR subtypes (α 1 ‐, α 2 ‐ and β‐ARs) are found in the chick brain and in regions associated with memory formation. Glucose and glycogen are important in memory formation since an increase in glucose levels improves while inhibiting glucose transporters (GLUTs) or glycogen breakdown inhibits memory consolidation. α 2 ‐ARs are expressed on chick astrocytes (B max 66.3 ± 17.7 fmol/mg protein) and stimulation with clonidine increases glycogen synthesis in a concentration‐dependent manner, whereas stimulation of β‐ or α 1 ‐ARs has no effect on increases in glycogen synthesis. The effect of clonidine was sensitive to inhibition by both pertussis toxin (Gi) and inhibitors of PI3K. With respect to memory, injection of α 2 ‐AR agonists into the medial striatum (MSt), but not the intermediate medial mesopallium (IMM) of chicks, increased memory consolidation. Injection of the postsynaptic α 2 ‐AR antagonist ARC239 decreased memory consolidation when injected into either the MSt or IMM. These results show that α 2 ‐ARs increase glycogen synthesis in chick astrocytes and are involved in memory consolidation in the chick. This research was supported by National Health and Medical Research Council Project Grants 236884 and 491169.