Energy metabolism and memory processing: Role of glucose transport and glycogen in responses to adrenoceptor activation in the chicken

From experiments using a discriminated bead task in young chicks, we have defined when and where adrenoceptors (ARs) are involved in memory modulation. All three ARs subtypes (α1-, α2- and β-ARs) are found in the chick brain and in regions associated with memory. Glucose and glycogen are important in the role of memory consolidation in the chick since increasing glucose levels improves memory consolidation while inhibiting glucose transporters (GLUTs) or glycogen breakdown inhibits memory consolidation. The selective β3-AR agonist CL316243 enhances memory consolidation by a glucose-dependent mechanism and the administration of the non-metabolized glucose analogue 2-deoxyglucose reduces the ability of CL316243 to enhance memory. Agents that reduce glucose uptake by GLUTs and its incorporation into the glycolytic pathway also reduce the effectiveness of CL316243, but do not alter the dose–response relationship to the β2-AR agonist zinterol. However, β2-ARs do have a role in memory related to glycogen breakdown and inhibition of glycogenolysis reduces the ability of zinterol to enhance memory. Both β2- and β3-ARs are found on astrocytes from chick forebrain, and the actions of β3-ARs on glucose uptake, and β2-ARs on the breakdown of glycogen is consistent with an effect on astrocytic metabolism at the time of memory consolidation 30 min after training. We have shown that both β2- and β3-ARs can increase glucose uptake in chick astrocytes but do so by different mechanisms. This review will focus on the role of ARs on memory consolidation and specifically the role of energy metabolism on AR modulation of memory.