Membrane Potentials

Receptor

Receptor

Distribution

General Function

Notes

Receptor

Agonist/Antagonist

Acetylcholine (ACh)

Nicotinic receptors

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Muscarinic receptors

Throughout body, esp. neuromuscular junction and brain

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PNS receptors:  lungs, CV system, GI tract

Excitatory

------------

Excitatory (GI) or

Inhibitory (CV)

Activates contraction of skeletal muscles;

------------

Target of some anti-asthmatic, anti-diarrheal drugs

Ag – nicotine (low conc.)

Antag – nicotine (high conc.)

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Ag – muscarine

Antag – atropine

Dopamine

Mainly CNS

Excitatory

or

inhibitory

Dopamine plays a key role in Parkinsonism and in development of addictions

Ag – Provigil

Antag – Hadol (anti-psychotic)

γ-amino Butyric Acid (GABA)

CNS

THE inhibitory neurotransmitter in the CNS, especially in the brain

GABA receptors mediate effects of ethanol and many hypnotics (barbiturates, Valium, Librium, Versed, etc.)

Ag – Valium, etc.

Antag – picrotoxin

Glycine

CNS

Inhibitory, especially important in spinal cord

Release blocked by tetanus toxin (destroys SNARE)

Ag – taurine

Antag – strychnine

Glutamate & aspartate

Throughout CNS

THE excitatory neurotransmitters in the CNS

Involved in excitotoxicity following a stroke

Ag – domoic acid

Antag – PCP

Serotonin

Throughout CNS, esp. in medulla, higher brain centers; spinal cord

Excitatory

or

Inhibitory

Drugs targeting serotonin synapses (SSRIs) are used to treat depression,  bulimia, etc.

Ag – LSD, mescaline, psylocibin

Antag – palonostron (anti-nausea in chemo.)

Catecholamines

(epinephrine, norepinephrine, dopamine)

Brain; sympathetic nervous system & adrenal glands

Excitatory

or

Inhibitory

Essential in brain’s regulation of CV, GI, and respiratory systems

Ag – Albuterol (asthma)

Antag – β-blockers (e.g., Inderol)

Peptides

(e.g., endorphins, Substance P)

Throughout body, esp. in CNS and GI tract

Excitatory

or

Inhibitory

Regulate sleep-awake cycles in brain, release of hormones, endogenous analgesics

Chronic pain (Substance P)

 Ag – opioids (in the case of endorphin receptors)

Antag – synthetic anti-hypertensives(?)

Nitric oxide (NO)

Throughout body

Inhibitory

Inhibits vasoconstriction → enhanced blood flow

Nitroglycerine (alleviates angina pain) is bioactivated → unstable intermediate → NO

None known

Carbon monoxide (CO)

Retina; brain, esp. hippocampus; GI tract

Excitatory

or

Inhibitory

Required for long-term memory formation?  NO often doesn’t work without CO.

None known

Cannabinoid

(really Anandemide)

Throughout brain, body

Macrophages

Excitatory

or

Inhibitory

Agonists → analgesia, ↑ appetite, ↓leukocyte recruitment in inflammation

Ag – THC, many synthetics

Antag – rimonabant (anti-obesity drug)

Adenosine

(a neuromodulator, meaning it alters responses to ‘real’ neurotransmitters)

Throughout CNS, esp. in brain

Usually Inhibitory

Contributes to alcohol’s effects on coordination and development of alcohol tolerance, also important in opioid analgesia.

Ag – many synthetic

Antag –caffeine, theophylline

Vanilloid

Endings of peripheral nerves – especially pain receptors

Excitatory

Ag – capsaicin

Antag – capsazepine (synthetic topical analgesic)