Memory Processing in the Avian Hippocampus Involves Interactions between β-Adrenoceptors, Glutamate Receptors, and Metabolism

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Abstract
Noradrenaline is known to modulate memory formation in the mammalian hippocampus. We have examined how noradrenaline and selective β-adrenoceptor (AR) agonists affect memory consolidation and how antagonists inhibit memory consolidation in the avian hippocampus. Injection of selective β-AR agonists and antagonists at specific times within 30 min of a weakly or strongly reinforced, single-trial, bead discrimination learning test in 1-day-old chicks allowed us to determine the pattern of β-AR involvement in hippocampal memory processing. Different β-AR subtypes were recruited in temporal sequence after learning in the order β1, β3, and β2. We provide evidence that the effect of manipulation of β1-ARs by selective agonists and antagonists within 2.5 min of training parallels the action of NMDA receptor agonists and antagonists. Activation of β3- and β2-ARs facilitated memory but utilized different mechanisms: β3-ARs by stimulating glucose uptake and metabolism, and β2-ARs by increasing the breakdown of glycogen—with both metabolic events occurring in astrocytes and affecting intermediate memory. The different receptors are activated at different times within the lifetime of labile memory and within 30 min of learning. We have defined separate roles for the three β-ARs in memory and demonstrated that the avian hippocampus is involved in learning and memory in much the same way as the hippocampus in the mammalian brain.