Target-specific projections of amygdala somatostatin-expressing neurons to the hypothalamus and brainstem.

Somatostatin neurons in the central nucleus of the amygdala (CeA/Sst) can be parsed into subpopulations that project either to the nucleus of the solitary tract (NST) or parabrachial nucleus (PBN). We have shown recently that inhibition of CeA/Sst-to-NST neurons increased the ingestion of a normally aversive taste stimulus, quinine HCl (QHCl). Because the CeA innervates other forebrain areas such as the lateral hypothalamus (LH) that also sends axonal projections to the NST, the effects on QHCl intake could be, in part, the result of CeA modulation of LH-to-NST neurons. To address these issues, the present study investigated whether CeA/Sst-to-NST neurons are distinct from CeA/Sst-to-LH neurons. For comparison purposes, additional experiments assessed divergent innervation of the LH by CeA/Sst-to-PBN neurons. In Sst-cre mice, two different retrograde transported flox viruses were injected into the NST and the ipsilateral LH or PBN and ipsilateral LH. The results showed that 90% or more of retrograde-labeled CeA/Sst neurons project either to the LH, NST, or PBN. Separate populations of CeA/Sst neurons projecting to these different regions suggest a highly heterogeneous population in terms of synaptic target and likely function.