Go back to John Kiernan's home page.
Back to Anatomical Foundations of Neuroscience
| Table 3. Known and suspected neurotransmitters of vertebrate animals | ||
| Name | Biochemistry and inactivation | Some functions |
| Acetylcholine (ACh) | A quaternary ammonium ion. Synthesized in bouton from choline and acetylcoenzyme A (choline acetyltransferase). Hydrolysis in synaptic cleft yields acetate and choline (acetylcholinesterase). Choline reabsorbed into presynaptic terminal | Neurons using ACh are cholinergic. Known transmitter of motor neurons, all preganglionic and some postganglionic visceral neurons. Strong evidence for cholinergic neurons in several parts of brain |
| Dopamine (DA) | Primary amine, derivative of dihydroxyphenylalanine (DOPA). Formed by DOPA decarboxylase in presynaptic parts of axon. Reuptake by axon; also inactivation catalyzed by monoamine oxidase and catechol O-methyl transferase | Neurons using DA are dopaminergic. Transmitter in nigrostriatal pathway of mammalian brain. Also in many other neurons, including some interneurons of autonomic ganglia and retina |
| Noradrenaline (= norepinephrine or levarterenol; NA or NE) | Primary amine formed from dopamine in presynaptic parts of axon (dopamine beta-hydroxylase). Inactivation mechanisms, as for dopamine | Neurons using NA are noradrenergic (also often called "adrenergic"). Transmitter to most structures supplied by sympathetic ganglia. A hormone of the adrenal medulla. NA-containing neurons in brain stem (locus coeruleus) have axons that go to most parts of brain and spinal cord; probably modulates other synapses |
| Adrenaline (= epinephrine) | Secondary amine formed by N-methylation of noradrenaline. Inactivation as for dopamine and noradrenaline | Hormone of the adrenal medulla. Also produced by some neurons in brain stem |
| Serotonin (= 5-hydroxytryptamine, 5HT) | Primary amine derived from tryptophan (synthesis by a decarboxylase in axon). Inactivation by reuptake into neuron and by monoamine oxidase | Neurons using 5HT are serotonergic. Cells in midline of brain stem (raphe nuclei) have axons that send branches to most parts of brain and spinal cord. Raphespinal fibers inhibit transmission of pain signals |
| Histamine | A heterocyclic amine derived from histidine (histidine decarboxylase). Several catabolic enzymes | Evidence for an excitatory function in the hypothalamus. Histamine from non-neural sources excites pain-sensitive axons in injured tissues, along with other mediators |
| Gamma-aminobutyrate (GABA) | Amino acid anion. Formed from glutamate by decarboxylation in the presynaptic terminal (glutamate decarboxylase). Uptake by postsynaptic cell and by neuroglia | Neurons using GABA are GABAergic. Always an inhibitory transmitter, in many parts of central nervous system including retina, spinal cord, and cerebellum |
| Glutamate | Anion of a common amino acid. Synthesis in neuron. Reuptake by presynaptic terminal from synaptic cleft | Excitatory action at synapses in most parts of the central nervous system. |
| Aspartate | Anion of a common amino acid. Synthesis and inactivation as for glutamate. properties | Glutamate and aspartate have similar physiological and pharmacological |
| Glycine | Common amino acid. Synthesis in neuron. Reuptake by presynaptic terminal | Inhibitory action at some synapses in spinal cord, including those of the Renshaw cells |
| Adenosine triphosphate (ATP) | A purine nucleotide. It is released together with ACh, DA and NA, but is principal transmitter of some neurons. Several relevant metabolic pathways are recognized | Neurons thought to use ATP are said to be purinergic (an unfortunate term because the purine adenine is not a putative transmitter). Inhibitory to intestinal smooth muscle supplied by enteric nervous system; possibly also in the brain |
| Nitric oxide (NO) | Inorganic compound that diffuses quickly through cell membranes and cytoplasm, influencing second messenger systems. Inactivated after a few seconds, by reaction with oxygen | May be the principal transmitter of some neurons in the enteric nervous system. Also produced by some neurons in the brain |
| Peptides (Only a few are listed here) | Some are synthesized directly on ribosomes. Many are split off from larger precursor protein molecules. Catabolism rather slow, by proteolytic enzymes. The names of peptides bear little relevance to functions. | Most peptides of nervous tissue occur in alimentary tract, either in enteric neurons or in epithelial cells. Neuropeptides occur also in several parts of the central nervous system. Sites listed below are not necessarily the most important ones | Number of amino acids |
| Carnosine | 2 | Olfactory bulb (excitatory) |
| Thyrotrophin releasing hormone (TRH) | 3 | Hypothalamus |
| Enkephalins (leu-ENK and met-ENK) | 5 | Brain stem, spinal cord. Transient morphine-like action on cells with opiate receptors |
| Oxytocin | 8 | Hypothalamus and neurohypophysis; hypothalamospinal fibers |
| Vasopressin | 8 | Hypothalamus and neurohypophysis |
| Luteinizing hormone releasing hormone (LHRH) | 10 | Hypothalamus |
| Substance P | 11 | Small neurons of dorsal root ganglia (excitatory); involved in pain and axon reflex vasodilation |
| Somatostatin | 13 | Hypothalamus; enteric nervous system (inhibitory) |
| Vasoactive intestinal polypeptide (VIP) | 28 | system (inhibitory); some autonomic ganglia |
| Beta-endorphin | 31 | Adenohypophysis. Morphine like action on cells with opiate receptors; longer duration of action than enkephalins |
Back to Anatomical Foundations of Neuroscience
Go back to John Kiernan's home page.
--------------------------------
Last updated: January 2003