Abstract
Pituitary adenylate cyclase-activating polypeptide (PACAP) is being studied to understand the endocrine regulation of energy balance and has been shown to be important in the regulation of the stress response (1,2). Specifically, PACAP has been shown to regulate thermogenesis, an energy burning process regulated by the sympathetic nervous system that contributes to achieving energy homeostasis in response to cold stress and overfeeding. PACAP is expressed in the sympathetic nervous system and is required at the adrenomedullary synapse to maintain epinephrine secretion from the adrenal medulla in response to physiological stress (3). Across the branches of the sympathetic nervous system, PACAP receptor expression is most well characterized in the superior cervical ganglia (SCG) (4). However, a detailed characterization of PACAP and its receptors has not been performed in ganglia whose postganglionic fibres innervate adipose tissues (stellate and celiac ganglia) in response to thermogenic stress. We hypothesized that PACAP is produced by preganglionic neurons innervating the stellate and celiac ganglia, and act on PACAP receptors expressed on the post-ganglionic neurons, and this expression will be upregulated in response to chronic cold stress. Due to their small and amorphous shape, we have developed a protocol to reliably isolate the stellate and celiac ganglia and validate their identity through the presence of tyrosine hydroxylase mRNA, using adrenal and SCG samples as positive controls. PACAP receptor expression (VPAC1, VPAC2, PAC1) was examined in the ganglia utilizing real-time PCR, and PACAP protein was visualized in the ganglia of transgenic mice that express eGFP under the control of the PACAP promoter (PACAP-eGFP mice) (5). This research demonstrates the expression of PACAP receptors in ganglia whose postganglionic fibres innervate adipose tissue, enhancing our understanding of PACAP’s role in the SNS, and its contribution to the regulation of adaptive thermogenesis. References: (1) Gray et al., Pacap: Regulator of the stress response. In: Fink G, ed. Stress: Physiology, biochemistry, and pathology. 2019:279-291. (2) Mustafa, Adv Pharmacol. San Diego, Calif:445-457. (3) Eiden et al., Pflungers Arch. 2018 Jan;470(1):79-88. (4) Braas et al., J Biol Chem. 1999 Sep 24;274(39):27702-27710. (5) Condro et al., J Comp Neurol. 2016 Dec 15; 524(18):3827-3848.
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