Anatomy of Cortical Amygdala Circuits that Support Innate Olfactory Valence

The posterolateral cortical amygdala (plCoA) is known to be involved in innate, odor-driven behavioral responses. There are 2 currently debated models in which the plCoA is involved with these behaviors. In one model, the plCoA encodes valence with hardwired circuits capable of driving innate aversive behaviors and the another for innate attractive behaviors, reminiscent of labeled line coding; an opposing model suggests the plCoA uses a population code, whereby valence emerges in downstream areas. Little is known about the connectivity of plCoA, and deciphering the anatomy should help to distinguish between these circuit motifs. To accomplish this, we used anterograde and retrograde tracing experiments to show that the plCoA is topographically organized on an anterior-posterior (AP) axis based on its outputs, and contains molecularly distinct neuronal populations (Vglut1 and Vglut2) that are also spatially segregated on an anterior-posterior axis. This bifurcating circuitry ultimately reveals the Vglut1 neurons in the posterior plCoA (p-plCoA) project primarily to the nucleus accumbens (NAc), and the Vglut2 neurons in the anterior plCoA (a-plCoA) projects primarily to the medial amygdala (MeA). These data reveal a neuronal substrate for valence encoding that is consistent with the plCoA operating with molecularly determined circuitry, ultimately most similar to a labeled line system