Memory consolidation in day-old chicks requires BDNF but not NGF or NT-3; an antisense study

Neurotrophins have been implicated in memory consolidation and recall as well as in other forms of neural plasticity. This study examined the effects of Brain-Derived Neurotrophic Factor (BDNF), Nerve Growth Factor (NGF) and Neurotrophin-3 (NT-3) on consolidation of memory for a one-trial passive avoidance task in day-old chicks. In this task chicks, having pecked once at a bitter tasting bead, avoid a similar but dry bead subsequently. Intracerebral administration of antisense ODNs to BDNF 6-12 h prior to training induced amnesia for the avoidance response by 3 h after training. Administration of a "control" scrambled sequence or saline had no effect on recall; chicks continued to avoid the bead. Treatment with BDNF-AS did not inhibit shorter-term recall; amnesia was not present 1 h after training, but prevented longer-term recall, as amnesia was still present 24 h after training. Treatment with BDNF-antisense reduced both BDNF mRNA and BDNF protein in the chick brain, but did not alter mRNA levels of glyceraldehyde-3-phosphate dehydrogenase. By contrast, no effect of antisense to NGF or NT-3 on behaviour was observed, even though administration reduced the mRNA for each. There were no significant effects of any antisense on other behavioural measures at the doses used. Thus we conclude that BDNF has a specific role in memory consolidation for the passive avoidance task.