Cell-specific expression of calcineurin immunoreactivity within the rat basolateral amygdala complex and colocalization with the neuropeptide Y Y1 receptor.

Neuropeptide Y (NPY) produces potent anxiolytic effects via activation of NPY Y1 receptors (Y1r) within the basolateral amygdaloid complex (BLA). The role of NPY in the BLA was recently expanded to include the ability to produce stress resilience and long-lasting reductions in anxiety-like behavior. These persistent behavioral effects are dependent upon activity of the protein phosphatase, calcineurin (CaN), which has long been associated with shaping long-term synaptic signaling. Furthermore, NPY-induced reductions in anxiety-like behavior persist months after intra-BLA delivery, which together indicate a form of neuronal plasticity had likely occurred. To define a site of action for NPY-induced CaN signaling within the BLA, we employed multi-label immunohistochemistry to determine which cell types express CaN and if CaN colocalizes with the Y1r. We have previously reported that both major neuronal cell populations in the BLA, pyramidal projection neurons and GABAergic interneurons, express the Y1r. Therefore, this current study evaluated CaN immunoreactivity in these cell types, along with Y1r immunoreactivity. Antibodies against calcium-calmodulin kinase II (CaMKII) and GABA were used to identify pyramidal neurons and GABAergic interneurons, respectively. A large population of CaN immunoreactive cells displayed Y1r immunoreactivity (90%). Nearly all (98%) pyramidal neurons displayed CaN immunoreactivity, while only a small percentage of interneurons (10%) contained CaN immunoreactivity. Overall, these anatomical findings provide a model whereby NPY could directly regulate CaN activity in the BLA via activation of the Y1r on CaN-expressing, pyramidal neurons. Importantly, they support BLA pyramidal neurons as prime targets for neuronal plasticity associated with the long-term reductions in anxiety-like behavior produced by NPY injections into the BLA.