Reciprocal connections between the amygdala, hypothalamus and parabrachial nucleus are known to regulate the hypothalamic-pituitary-adrenal axis and autonomic responses to conditioned fear (Takeuchi et al., 1982; Gray et al., 1989). The amygdala also participates in stress- and reward-related behaviors through its connections to the PFC and NAc, respectively (Simpson et al., 2001; Myers-Schulz and Koenigs, 2012; Stuber et al., 2011). The basolateral nucleus of the amygdala is densely innervated by cholinergic projections arising from the basal forebrain (Sah et al., 2003), with cholinergic inputs synapsing on pyramidal neurons (89% of efferents) and GABAergic interneurons (Muller et al., 2011). Different pathways reside within the amygdala and are responsible for various functions regarding the acquisition, expression, and retrieval of fear memories as well as unconditioned behaviors (LeDoux, 2003).
