Background: 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). Methods: 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. Results: 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 (n=8) 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. Conclusion: The identified neuron classes raise interesting questions about differential integration of visceral information to the amygdala in complex behaviours.
Disclosure: Authors declare no conflicts of interest and work supported by the NHMRC of Australia (SJM - C. J. Martin fellowship) and the NIH of the United States (MCA, HL-041119).