Table 2. List of receptors and the molecules that activate them.

Summary of the receptors known to be relevant to the gut-brain axis including inhibitors, agonists, and the locations in which the receptors may be found.

Receptor	Inhibitors	Agonists	Location	References
α1 - adrenoreceptors	Prazosin Phentolamine	Epinephrine Norepinephrine Phenylephrine Methoxamine Midodrine Oxymetazoline	Mesenteric arterioles	Luo et al., 2016, Kim and Jwa, 2015, Manoharan et al., 2016, Hirst and Silinsky, 1975, Grayson and Oyebola, 1983
α2- adrenoreceptors	N/A	Epinephrine Norepinephrine Clonidine Oxymetazoline	Postsynaptic CNS neurons adrenergic and cholinergic nerve terminals vascular smooth muscle	Shelkar et al., 2016
β1-adrenoreceptors	Propranolol	Epinephrine Norepinephrine Isoprenaline Dopamine Dobutamine	Mesenteric arterioles	Manivasagam et al., 2016, Grayson and Oyebola, 1983
β2-adrenoreceptors	Propranolol	Epinephrine Isoprenaline Salbutamol Albuterol Terbutaline Salmeterol Formoterol Pirbuterol Albuterol Mirabegron	Mesenteric arterioles	Edgell et al., 2016, Arcaro et al., 2016, Cortese et al., 2016, Blais et al., 2016, Grayson and Oyebola, 1983
D1	Haloperidol	Dopamine Fenoldopam	Nerve endings of intestinal wall mucosal layer	Borcherding et al., 2015, Sclafani, 2001
D2	Haloperidol Doperidone	Dopamine Aripiparazole Quinpirole Ketamine Phencyclidine Bromocriptine	Nerve endings of intestinal wall	##Ji and Wu, 2016, Jiang et al., 2016, Li et al., 2015, Lladó-Pelfort et al., 2016, Sclafani, 2001
D3	Haloperidol Doperidone	Dopamine Quinpirole Cariprazine	Nerve endings of intestinal wall mucosal layer	Watson et al., 2015, Sander et al., 2016, Sclafani, 2001
D4	Haloperidol	Dopamine	Mucosal layer	Sclafani, 2001
D5	Haloperidol	Dopamine	Nerve endings of intestinal wall mucosal layer	Sclafani, 2001
5 - HT1	Atypical Antipsychotics	Serotonin (5-HT1A) Azapirones (5-HT1A)) Triptans (5-HT1B and 5-HT1D)	Pre-synaptic enteric nerves gastrointestinal smooth muscle	Kishi et al., 2013, Araldi et al., 2016, Gershon et al., 1990
5-HT2	Trazadone Atypical Antipsychotics	LSD (5-HT2A) Lisuride (5-HT2A) Mescaline (5-HT2A) Lorcaserin (5-HT2C)	Gastrointestinal smooth muscle	Karaki et al., 2014, Higgins et al., 2016, Gershon et al., 1990
5-HT3	• Ondansentron	N/A	Myenteric neurons	Neal and Bornstein, 2006
5-HT4	N/A	Cisapride Tegaserod	Myenteric neurons, muscularis mucosa	Lefebvre et al., 2016, Neal and Bornstein, 2006