Table 1.
Summary of the arguments in favor or against some key controversial aspects of the putative role of the vagus nerve mediating some actions of ghrelin.
Controversial notion | Key observations in favor | Key observations against |
---|---|---|
Ghrelin-induced food intake in humans involves the vagus nerve. | -IV-injected ghrelin does not increase eating in 7 patients with total subdiaphragmatic vagotomy (le Roux et al., 2005). | -IV-injected ghrelin increases food intake and appetite in ten patients with total gastrectomy (Adachi et al., 2010). |
Ghrelin-induced food intake in rats involves the sensory neurons of the vagus nerve. | -IV-injected ghrelin does not increase food intake in rats 7 days after total subdiaphragmatic vagotomy or in rats with capsaicin-induced or surgical gastric vagotomy (Date et al., 2002). -IP-injected ghrelin does not increase food intake in 16-h food deprived rats receiving perivagal treatment with capsaicin at the cervical level (Chen et al., 2005). - IP-injected ghrelin does not increase food intake during the nocturnal phase in rats tested ~3 months after a total subdiaphragmatic vagotomy (Davis et al., 2020). |
-IP-injected ghrelin fully increases food intake in rats with either subdiaphragmatic vagal deafferentation or total subdiaphragmatic vagotomy (Arnold et al., 2006). |
Ghrelin-induced GH release in rats involves the vagus nerve. | -IV-injected ghrelin does not increase GH release in rats 7 days after total subdiaphragmatic vagotomy or in rats with capsaicin-induced or surgical gastric vagotomy (Date et al., 2002). -IV- or ICV-injected ghrelin display an attenuated effect on plasma GH secretion in rats 7 days after total subdiaphragmatic vagotomy (Al-Massadi et al., 2011). |
-A great body of evidence indicates that ghrelin controls GH secretion in rats acting at hypothalamic and pituitary levels (Steyn et al., 2016). |
GHSR is expressed in sensory neurons of the vagus nerve of mice. | -Widespread GHSR was detected in the mouse NG using IHC, ISH, fluorescent ISH, reverse transcription PCR (Christie et al., 2020, Davis et al., 2020, Kentish et al., 2012, Page et al., 2007, Zhang et al., 2020). | -GHSR mRNA undetectable or detected in a small subset of JG neurons in mice using qPCR, single-cell RNA sequencing or multiplex ISH (Bob-Manuel and Gautron, 2021, Egerod et al., 2018, Kupari et al., 2019). |