Amygdala electrical stimulation inducing spatial memory recovery produces an increase of hippocampal bdnf and arc gene expression.

Amygdala seems to promote the consolidation of plastic modification in different brain areas and these long-term brain changes require a rapid de novo RNA and protein synthesis. We have previously shown that basolateral amygdala electrical stimulation produces a partial recovery of spatial memory in fimbria-fornix lesioned animals and it is also able to increase the BDNF protein content in the hippocampus. The emerging question is whether these increased BDNF protein content arises from previously synthesized RNA or from de novo RNA expression. Now we address the question if amygdala electrical stimulation 15min after daily water maze training produces a rapid de novo RNA synthesis in the hippocampus, a critical brain area for spatial memory recovery in fimbria-fornix lesioned animals. In addition, we also study RNA arc expression, a gene which is essential for memory and neural plasticity processes. To this purpose, we study amygdala stimulation effects on the expression of plasticity related-early-genes bdnf and arc in the hippocampus of fimbria-fornix lesioned animals trained in a water-maze for 4days. We also checked on the expression of both genes in non-lesioned, untrained animals (acute condition) at 0.5, 1, 2 and 24h after basolateral amygdala electrical stimulation. Our data from trained animals confirm that daily amygdala electrical stimulation 15min after water maze training produces a partial memory recovery and that is coupled to an increase of bdnf and arc genes expression in the hippocampus. Additionally, the acute study shows that a single session of amygdala stimulation induces a transient increase of both genes (peaking at 30min). These results confirm the memory improving effect of amygdala stimulation in fimbria-fornix-lesioned animals and sustain the assumption that the memory improving effect is mediated by newly synthetized BDNF acting on a memory relevant structure like the hippocampus. The increased amount of BDNF within the hippocampus seems to be locally synthetized by mechanisms activated by the amygdala stimulation.