α4β2 Receptors of ventral hippocampus and memory consolidation

It is known that neuronal nicotinic receptors are involved in memory processes[1]. Dihydro-β-erythroidine (DHBE) is an agent that has been used to study the function of the α4β2 receptor, although it also has affinity for the α7 and α3β2 receptors[2]. We now studied the alkaloid erysodine, which has a higher (7-fold) affinity for the α4β2 receptor than its analog DHBE, to characterize the participation of this receptor in memory consolidation. Cannulae were implanted into the ventral hippocampus of rats. Eight days later they were trained in inhibitory avoidance. Immediately after training nicotine (2µg/µL/min), DHBE (2.0µg/µL/min), erysodine (2.0 or 6.0µg/µL/min) or isotonic saline (1.0µL/min) were administered though the cannulae to independent groups, and retention of the task was evaluated 24h later. Training, escape, and retention latencies were analyzed with the non-parametric Kruskal-Wallis and Mann-Whitney U tests. Nicotine had no effect on memory consolidation, while the antagonists DHBE and erysodine impaired it. Even though erysodine has a higher affinity for the α4β2 receptor, the memory deficiency was significantly greater with DHBE. These results suggest that blockade of the other receptors to which DHBE show affinity (α7 and α3β2), produce an additional interference with memory consolidation; this hypothesis must be put to the experimental test. To conclude, this work indicates that nicotinic receptors located in the ventral hippocampus have an important role in the process of memory consolidation.

Acknowledgements: The authors thank Angel Méndez and Martín García for their excellent technical assistance. Supported by PAPCA-FES Iztacala 2007–2008, PAPIIT-IN212906, and PAPIIT-211608).

References: 1. Levin, E.D., et al. (2006) Psychopharmacology 184:523–539. 2. Tucci, S.A., et al. (2003) Neuropharmacology 44:367–373.