Contrasting roles for β1, β2 and β3-adrenoceptors in memory formation in the chick

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Abstract

Noradrenaline plays distinct roles in the modulation and consolidation of memory for one-trial, discriminated, avoidance learning in the chick. We have previously shown that activation of β2-, β3- and α1-adrenoceptors (ARs) by injection into the multimodal forebrain association region (intermediate medial hyperstriatum ventrale [IMHV] or intermediate medial mesopallium [IMM]) is involved in the consolidation of memory 30 min after training and that activation of α2-ARs in the caudate putamen plays a role in the reinforcement of memory leading to consolidation in the IMM (IMHV). In this paper we provide evidence that noradrenaline acts at β1-ARs in the basal ganglia (lobus parolfactorius or medial striatum) in short-term memory processing immediately post-training and demonstrate inhibition of memory by selective AR antagonists at particular times in the sequential memory processing sequence after training. These results support separate roles for β2- and β3-ARs in memory consolidation. Our studies suggest that, as a consequence of the learning experience, noradrenaline acts in different brain regions and at different times in memory processing, to enhance memory through distinct populations of ARs.

Section snippets

Learning paradigm

Up to 240 1- to 2-day old Black-Australorp×White Leghorn or Rhode Island Red×New Hampshire male chicks (body weight 34.98±0.58 g brain weight 0.84±0.01 g; forebrain 0.44±0.01 g) were delivered from a local poultry farm (Research Poultry, Pty Ltd, Victoria, Australia) on the morning of each experiment. It might be expected that the chicks could be stressed because of the relocation from the hatchery. Our source of chicks is located relatively close to the University and care is taken during

Effect on STM of the selective β1-AR agonist RO363 injected into the MSt (LPO)

Injection of the selective β1-AR agonist RO363 into the MSt at times from −5 min to +5 min after weakly reinforced training showed that there was a very limited time period in which the AR agonist caused memory enhancement (Fig. 2A). RO363 significantly enhanced memory formation when given immediately (+0 min) or +2.5 min after training (F4,83=8.755, P<0.001). Injection at −5 and +5 min after training produced retention levels similar to those of saline injected chicks. RO363 injected 2.5 min

Discussion

Inhibition of β-ARs reveals discrete temporal and spatial roles of these receptors in the action of noradrenaline in memory processing. Inhibition of any of the three β-AR subtypes results in memory deficits and demonstrates that activation of all these ARs is necessary for normal memory processing. β1-ARs have a role in the caudate putamen within the time frame of STM, whereas in the mesopallium (IMM/IMHV) β3- and β2-ARs are involved in ITM consolidation of memory 30 min after training.

The

Conclusion

There are clearly different roles for noradrenaline at each of the three β-ARs in memory processing. Their roles depend on the time relative to learning and their location in the brain. Activation of β1-ARs is important in the basal ganglia at the time of learning and STM and is likely to be involved in attention and arousal, whereas activation of β3-ARs in the multimodal association area of the mesopallium is important for maintaining ITM A and β2-ARs are important for ITM B and the

Acknowledgments

This work was supported by a grant from the National Health and Medical Research Council of Australia.

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