Hippocampal neurotrophins after stimulation of the basolateral amygdala, and memory improvement in lesioned rats

Purpose: To investigate a possible role of neurotrophins in the memory improving effect of stimulating the basolateral amygdala. Methods: The BDNF and NGF levels were measured in the hippocampus of fimbria-fornix lesioned male rats after four days of training in the water maze and stimulation of the basolateral amygdala. Results: The behavioral results confirm that daily post-training stimulation of the amygdala improves the learning abilities of the lesioned animals. BDNF increased in lesioned and trained animals, but stimulating the basolateral amygdala induces a significantly greater increase. NGF showed a slight (but significant) increase in fimbria-fornix lesioned and trained animals, but stimulating the amygdala does not produce a further increase. In separate groups of animals we measured the levels of both neurotrophins in acute experiments, after 2 and 24 hours of stimulating the amygdala. BDNF was significantly increased at both times, while NGF showed again only slight increases (significant at 24 h). Conclusions: These results suggest that the BDNF response to amygdala stimulation might be of functional importance in the observed learning improvement. The changes in NGF are most likely due to the accumulation of this protein after removal of the septal axons.