Resumen:
It is well known that emotionally arousing experiences usually result in a robust and persistent
memory trace and the expression of enhanced anxiety. Extensive data in humans and rodents
have demonstrated that the stress effects on emotional processing and memory formation are
largely mediated by the amygdala complex. It is well documented that the ERK pathway plays a
major role in synaptic plasticity, learning and memory formation (Sweatt 2001; Thomas and
Huganir 2004), and several reports indicated that ERK activation in amygdala after fear
conditioning is required for fear memory consolidation (Schafe, Nadel et al. 1999; Schafe, Swank
et al. 2008). In line with these evidence, recent findings showed a consistent enhancement of p-
ERK in the BLA in the consolidation of contextual fear memory in stressed animals (Maldonado,
Martijena et al. 2011). In addition, several studies reported that acute stress results in the
activation of the ERK signaling cascade in brain regions that are essential components of the
neural circuitry orchestrating environmental challenges induced emotional responses (Ailing, Fan
et al. 2008; Todorovic, Sherrin et al. 2009). Given the importance of the ERK cascade in stress
effects and in the formation of fear memory, the present study investigated the potential
involvement of the ERK pathway in amygdala subnuclei in the influence of a prior stressful event
on the consolidation of a contextual fear memory and on the onset of anxiety-like behavior. A
robust and persistent ERK2 activation was evident in the basolateral amygdala which lasts at
least one day after the stressful experience. Moreover, such environmental challenge facilitated
fear memory formation and increased anxiety-like behavior in the elevated plus maze. In
addition, pretreatment with the intra-BLA infusion, but not into the central nucleus of the
amygdala, with UO126 (MEK inhibitor), prevented the stress induced facilitating influence on
fear memory formation and anxiety-like behavior. Given that the activation of ERK1/2 pathway is
essential for associative memory and for stress-induced emotional reactions, we propose that
the activation of ERK2 in BLA following stress exposure is an important mechanism for the
promoting influence of stress on both processes.