transmitter substances found in autonomic nervous system, enteric nervous system, and nonadrenergic, noncholinergic neurons.

Acetylcholine

The primary transmitter at ANS ganglia, at the somatic neuromuscular junction, and at parasympathetic postganglionic nerve endings. A primary excitatory transmitter to smooth muscle and secretory cells in the ENS. Probably also the major neuron-to-neuron (“ganglionic”) transmitter in the ENS.

Adenosine triphosphate (ATP)

Acts as a transmitter or cotransmitter at many ANS-effector synapses

Calcitonin gene-related peptide (CGRP)

Found with substance P in cardiovascular sensory nerve fibers. Present in some secretomotor ENS neurons and interneurons. A cardiac stimulant.

Cholecystokinin (CCK)

May act as a cotransmitter in some excitatory neuromuscular ENS neurons.

Dopamine

A modulatory transmitter in some ganglia and the ENS. Possibly a postganglionic sympathetic transmitter in renal blood vessels.

Enkephalin and related opioid peptides

Present in some secretomotor and interneurons in the ENS. Appear to inhibit ACh release and thereby inhibit peristalsis. May stimulate secretion.

Galanin

Present in secretomotor neurons; may play a role in appetite-satiety mechanisms

GABA

May have presynaptic effects on excitatory ENS nerve terminals. Has some relaxant effect on the gut. Probably not a major transmitter in the ENS

Gastrin-releasing peptide (GRP)

Extremely potent excitatory transmitter to gastrin cells. Also known as mammalian bombesin.

Neuropeptide Y (NPY)

Found in many noradrenergic neurons. Present in some secretomotor neurons in the ENS and may inhibit secretion of water and electrolytes by the gut. Causes long-lasting vasoconstriction. It is also a cotransmitter in some parasympathetic postganglionic neurons

Nitric oxide (NO)

A cotransmitter at inhibitory ENS and other neuromuscular junctions; may be especially important at sphincters.

Cholinergic nerves innervating blood vessels appear to activate the synthesis of NO by vascular endothelium.

NO is not stored, it is synthesized on demand by nitric oxide synthase,

Norepinephrine (NE)

The primary transmitter at most sympathetic postganglionic nerve endings.

Serotonin (5-HT)

An important transmitter or cotransmitter at excitatory neuron-to-neuron junctions in the ENS.

Vasoactive intestinal peptide (VIP)

Excitatory secretomotor transmitter in the ENS; may also be an inhibitory ENS neuromuscular cotransmitter.

A probable cotransmitter in many cholinergic neurons. A vasodilator (found in many perivascular neurons)

and cardiac stimulant

Substance P

an important sensory neurotransmitter in the ENS and elsewhere. Tachykinins appear to be

excitatory cotransmitters with ACh at ENS neuromuscular junctions. Found with CGRP in cardiovascular sensory

neurons. Substance P is a vasodilator (probably via release of nitric oxide).