Table 1.

Summary of the Major Types of Myenteric and Submucosal Neurons in the Mammalian Gastrointestinal Tract^*

Main functional groups (% of total, guinea-pig*)	Projections to target cells (morphological classification)	Major neurotransmitter/s modulator/s (additional neurochemical markers)
Myenteric plexus
Intrinsic sensory neurons (26%)	Mucosal epithelium	Tachykinins/Acetylcholine (calbindin)
Motor neurons that stimulate smooth muscle relaxation (18%)	Anal, to smooth muscle	Nitric oxide/vasoactive intestinal peptide/pituitary adenylate cyclase-activating polypeptide/ATP
Motor neurons that stimulate smooth muscle contraction (37%)	Oral, to smooth muscle	Acetylcholine/tachykinins
Interneurons (various types) (16%)	Oral and anal to other neurons	Acetylcholine/tachykinins/serotonin/neuropeptide Y/somatostatin
Neurons that project out of the gut (<1%)	Other autonomic ganglia	Acetylcholine
Submucosal plexus
Secreto-motor/vasodilator neurons (non-cholinergic) (45%)	Mucosal epithelium and intestinal blood vessels	Vasoactive intestinal peptide
Secreto-motor/vasodilator neurons (44%)	Mucosal epithelium and blood vessels	Acetylcholine
Intrinsic sensory neurons (11%)	Myenteric and submucosal neurons, and epithelium	Thought to be tachykinin (express calbindin)

^*Broadly similar proportions of the main neuronal types have been found in all species studied to date

Adapted from Saffrey MJ. Ageing of the enteric nervous system. Mechanisms of ageing and development. 2004; 125(12): 899–906.