Competition among model lateral amygdala principal cells during Pavlovian fear conditioning

Inputs about the conditioned (CS) and unconditioned (US) stimuli converge in the lateral amygdala (LA) during classical fear conditioning (FC). This leads to potentiation of CS inputs to LA neurons, and consequent increases in the firing of central medial amygdala (CeM) cells. In turn, CeM cells drive conditioned fear responses via their projections to fear effector neurons. However, transmission of information from LA to CeM neurons is indirect, involving a multilayered intra-amygdaloid network that includes basal amygdala (BA), the central lateral (CeL) nucleus, and intercalated cells (ITC), all of which project to CeM. Although consensus is emerging that CeM is the main fear output station of the amygdala for conditioned fear responses, the details of connectivity within Ce are not well understood. LA axons contact CeL but not CeM cells, and it is not clear how LA influences CeM through CeL. Also, CeL contains two types of CeM-projecting cells, with inhibitory (CeL-Off; PKCδ+) and excitatory (CeL-On; PKCδ-) responses to the CS. These two cell types are reciprocally connected by GABAergic synapses and it was hypothesized that the inhibition of CeL-Off cells by Cel-On cells leads to the disinhibition of CeM cells. However, it is not clear whether LA inputs connect differently to the two CeL cell subtypes and whether intrinsic and afferent synapses to Ce can undergo activitydependent plasticity. For instance, it has been suggested that the connections between the CeL sub-types could potentiate as a result of FC.