Quick and Dirty Guide to Neurotransmitters

* Acetylcholine: neurotransmitter of the neuromuscular junction. Also important as a transmitter in the peripheral nervous system (affecting heart, stomach, liver, sweat glands, blood vessels and other organs). Affects two kinds of receptors - nicotinic acetocholine receptors (nACRs) and muscarinic receptors.

Formed from choline and lecithin. Vitamin C, B vitamins, calcium, and zinc are also important in its formation.

Affects vasopressin (aka antidiuretic hormone).

After release into the synaptic gap it gets broken down into choline and acetic acid.

nACRs are ion channel receptors. When acetylcholine binds to the receptor, a conformational change in the receptor opens an ion channel that allows the influx of a positively charged molecule. In the neuromuscular junction this is Ca++.

Why are these called "nicotinic"? Does nicotine affect them? Yes - nicotine seems to modulate/enhance acetylcholine transmission.

* Catecholamines

o Dopamine - Monoamine neurotransmitter. Formed from the amino acid l-tyrosine. Important in muscular control and movement. Parkinson's disease results from inadequate levels of dopamine. Also important in the limbic system and cerebral cortex - deficiencies in these areas have been linked to schizophrenia. Plays a role in digestive and cardiovascular systems as well. G protein receptors (D1, D2).

(schizophrenics self-medicate with nicotine ~90+%)

o Norepinephrine (NE) - same as noradrenaline. produced by adrenal medulla. found in brain, esp hypothalamus. affects mood and attention. functions as hormone and neurotransmitter. primary neurotransmitter of the PNS (peripheral nervous system) Monoamine neurotransmitter. Formed from the amino acid l-tyrosine.

o Epinephrine - same as adrenaline. functions as both a hormone and neurotransmitters. produced by adrenal medulla. increases heart rate and speeds breakdown of glycogen to glucose via cAMP secondary messenger system. Monoamine neurotransmitter. Formed from the amino acid l-tyrosine.

* Serotonin: 5HT, 5 Hydroxytryptamine. Monoamine neurotransmitter. Formed from the amino acid l-tryptophan. Some receptors are ion channels, others are G proteins linked to adenylate cyclase (both positively and negatively). Linked with mood, sleep, consciousness, as well as digestion. Precursor to melatonin.

Prozac, Ecstacy are selective serotonin reuptake inhibitors.

MAO Inhibitors: antidepressant medications that slow monoamine oxidase, the enzyme which breaks down monoamine neurotransmitters like serotonin and dopamine.

* Histamine:

* Amino Acids

o Glutamate - Excitory amino acid neurotransmitter. Formed from glutamic acid. Receptors: G-protein (adenylate cyclase), NMDA, AMPA. Ketamine blocks glutamate receptors in the brain.

o Aspartate - Excitory amino acid neurotransmitter.

o GABA - Gamma-aminobutyric acid. Inhibitory amino acid neurotransmitter. NMDA, N-methyl d-aspartatic acid (ion channel) receptor. Induces sleep (?). Barbituates + benzodiaprenes enhance GABA receptors.

(describe NMDA receptors. Mg+ ion "plug")

o Glycine - Inhibitory amino acid neurotransmitter. NMDA, N-methyl d-aspartatic acid (ion channel) receptor. Strychnine blocks glycine receptors.

* Neuropeptides - over 30 identified

o Substance P - a small protein composed of 11 amino acids which seems to function as a neurotransmitter among pain fibers. Acts on G protein receptors (adenylate cyclase). Can cause (smooth) muscle contraction. May cause local tissue inflammation.

o Enkephalins, Endorphins - Opioid peptides. Not exactly neurotransmitters. Hormones? Neural hormones? Longer "prohormone" version gets absorbed into cell (how?) and then gets "digested" into active form. Inhibit neuronal activity in CNS by interacting with opioid receptors (mu, delta, and kappa). Seems to happen by affecting ion transmission (K+ or Ca++) or maybe G proteins

Seem to act "locally" on affected tissues rather than on the brain. May function as enhancers or modulators of neurotransmission signals.

Morphine affects the mu receptor.

Paul
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"Consciousness is the knowing, with each other, by two or more participants in a relation."
- Gordon Pask

Copyright notice: The entire contents of this document are Copyright 1997 Paul L. Moses. Redistribution for personal, noncommercial use is permissible, so long as the document is distributed in its entirety, including this notice. Any other use requires an express written request and consent from the listowner. All rights reserved.