Recent studies suggest that brain-derived neurotrophic factor (BDNF) plays a critical role in long-term synaptic plasticity in the adult brain. Previous studies on the insular cortex (IC), a region of the temporal cortex implicated in the acquisition and storage of different aversive learning tasks, have demonstrated that tetanic stimulation of the basolateral nucleus of the amygdala (Bla) induces an N-methyl-D-aspartate (NMDA)-dependent form of long-term potentiation (LTP) in the IC of adult rats in vivo. Here, we show that acute intracortical microinfusion of BDNF induces a lasting potentiation of synaptic efficacy in the Bla-IC projection of anesthetized adult rats. This constitutes an in vivo demonstration of neurotrophin-induced potentiation of synaptic transmission in the neocortex. These findings support the concept that BDNF could be a synaptic messenger involved in activity-dependent synaptic plasticity.