Date on Master's Thesis/Doctoral Dissertation

8-2023

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Anatomical Sciences and Neurobiology

Degree Program

Anatomical Sciences and Neurobiology, PhD

Committee Chair

Lundy, Robert

Committee Co-Chair (if applicable)

Samuelsen, Chad

Committee Member

Samuelsen, Chad

Committee Member

Bickford, Martha

Committee Member

Krimm, Robin

Committee Member

Corbitt, Cynthia

Author's Keywords

Gustatory system; somatostatin neurons; central amygdala; nucleus of solitary tract; parabrachial nucleus; lateral hypothalamus

Abstract

The nucleus of solitary tract (NST) and parabrachial nucleus (PBN) represent the first and second central synapses of ascending gustatory information. Neural processing in these nuclei is influenced by descending input from forebrain regions such as the central nucleus of the amygdala (CeA). In mice, we have shown that somatostatin (Sst) expressing neurons of CeA that project to NST and PBN are largely distinct cell populations and optogenetic inhibition of the CeA/Sst-to-NST subpopulation increases the intake of high concentrations of quinine with no apparent effect on sucrose intake. Synaptic connectivity of these cells is needed to understand the possible mechanisms underlying these behavioral responses. Our lab has previously demonstrated that CeA/Sst terminals within the PBN expressed GABA and made synaptic contacts largely with non-GABAergic neural elements. To determine whether CeA/sst terminals within the NST also express GABA, we used electron microscopy combined with cre-dependent anterograde transported virus injections (AAV9-DIO-dApex2) into the CeA of Sst-cre mice and post-embedding immunogold labelling for GABA. We found that majority of CeA/sst terminals in NST express GABA and synapsed with non-GABAergic targets. These results suggest that CeA/Sst cells provide monosynaptic input to second order NST projection neurons (non-GABAergic) and that this direct feedback inhibition is necessary for appropriate responding to bitter taste quality

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