In addition to CCK, ghrelin is also known to regulate food intake via AgRP neurons (Chen et al., 2015; Cowley et al., 2003; Hewson and Dickson, 2000; Kamegai et al., 2001; Nakazato et al., 2001; Tang-Christensen et al., 2004; van den Top et al., 2004; Wang et al., 2014; Zigman et al., 2005) and obesity is thought to cause ghrelin resistance in AgRP neurons as measured by Fos staining and ex vivo recordings (Briggs et al., 2010; Briggs et al., 2014). Here, FOS is linked to obesity due to melanocortin 4 receptor deficiency.