The Effects of Adrenergic Antagonists on Spatial Memory in the Zebra Finch (taeniopygia guttata)

The adrenergic system appears to be involved in the consolidation and reconsolidation of hippocampally dependent spatial memories in mammals. Based on connectivity, cell types, ontogeny and receptor distribution, the avian hippocampus is thought to be a homolog to the mammalian hippocampus. The adrenergic system appears to be fairly conserved but may show some species specializations. To determine if the adrenergic system plays a role in spatial learning and memory in birds, we used a series of experiments to investigate the role of α- and β-adrenergic receptors on spatial navigation and memory in an avian species, zebra finches, using the Day Escape Maze, a dry maze analog of the Morris Water Maze. Experiment 1 investigated the role of the β-adrenergic receptor antagonist, propranolol (20 and 40 mg/kg) and saline on interference with reconsolidation and long term recall of spatial learning when drugs were given immediately after memory reactivation. Experiment 2 analyzed the role of propranolol in spatial memory when drug delivery was given at two time points after memory reactivation. Birds were injected with 60 mg/kg of propranolol or saline immediately following reactivation or 25 min after reactivation and spatial memory was assessed using specific probe trials. Experiment 3 assessed the role of α-adrenergic receptors in spatial memory using a receptor antagonist, Phentolamine. Birds were injected with 45 mg/kg either immediately after memory reactivation or 25 min after reactivation. Collectively, these three studies suggest that, in contrast to mammals, neither propranolol nor Phentolamine given at various doses and time points after reactivation of spatial memory impairs spatial recall or spatial memory in the zebra finch. Thus, across vertebrate taxa, the effects of norepinephrine on spatial memory reconsolidation may not be conserved or the distribution of adrenergic receptors in the hippocampus may not be conserved