Amygdala‐projecting solitary tract nucleus (NTS) neurons are predominately higher order

The amygdala receives visceral information via the solitary tract nucleus (NTS). Although previous studies suggest broad interaction between visceral, NTS and other central information, little is known about amygdala‐projecting NTS neurons (e.g. 2nd order or higher). Here, we examined interactions between solitary tract (ST) afferents and NTS neurons projecting to the central nucleus of the amygdala (NTS‐CeA). To identify NTS‐CeA projection neurons, fluorescent retrograde tracers were injected into CeA. Later in 250 μM horizontal slices, we recorded from tracer filled NTS‐CeA neurons. Graded intensity ST shocks evoked postsynaptic currents (PSC) whose responses became more complex with increasing shock intensity indicating multiple convergent inputs. Analysis of ST‐PSC amplitude, synaptic jitter and failure rates identified two populations of neurons. Some NTS‐CeA neurons received low jitter ST‐EPSCs identifying them as 2nd order neurons with direct ST afferent input. However, most NTS‐CeA neurons (10 of 18) were higher order exhibiting no low jitter ST‐EPSCs, rather, multiple high jitter EPSCs and IPSCs with frequent failures. Higher order neurons received afferent information through highly convergent polysynaptic pathways. The identified neuron classes raise interesting questions about differential integration of visceral information to the amygdala in complex behaviors.