Noradrenaline involvement in the memory-enhancing effects of exposure to a complex rhythm stimulus following discriminated passive avoidance training in the young chick.

Previous research in our laboratory has demonstrated a significant memory-enhancing effect of exposure to a complex rhythm stimulus following weakly-reinforced passive avoidance learning in chicks. The aim of this study was to explore whether noradrenaline mediates this process. Chicks were trained on a strongly-reinforced single-trial passive avoidance task involving discrimination between two coloured beads. Intracerebral administration of the protein synthesis blocker, anisomycin, revealed that a phase of memory formation sensitive to arousal levels was extended by approximately 35 min following exposure to the complex rhythm stimulus. Administration of 2,4-dinitrophenol showed that this extension occurred during phase B of intermediate-term memory. Finally, a higher dose of the beta-adrenergic receptor antagonist, propranolol, was required to inhibit long-term memory in the presence of the auditory stimulus than in its absence. These findings suggest that the memory-enhancing effects of the complex rhythm stimulus may be mediated by noradrenaline, possibly via an increase in physiological arousal.