Dale's principle

Dale's Principle (or Dale's Law) was postulated by the English neuroscientist Henry Hallett Dale and it states that, although different neurotransmitters can be produced at different synapses within the brain, individual neurons are capable of releasing only one neurotransmitter from its axonal terminal. Although Dale's Principle has been shown to be false in many cases, it none the less remains correct for the vast majority of neurons forming the human brain.

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Exceptions are composed of neuron types releasing two or more neurotransmitters at the same time and include:

• GABA-gylcine co-release.
• Acetylcholine-glutamate co-release.
• Dopamine-glutamate co-release.

Some types of neurons are also known to co-release classical neurotransmitters with a signaling peptide hormone. Examples include:

• Acetylcholine (ACh) and vasoactive intestinal peptide (VIP) co-release.
• Acetylcholine (ACh) and calcitonin gene-related peptide (CGRP) co-release.
• Glutamate and dynorphin co-release (in the hippocampal synapses).

Dale stated that a neurotransmitter must:

• be synthesised in nerve terminals;
• be stored in synaptic vesicles;
• be released in response to neuronal stimulations;
• act on a postsynaptic receptor; and
• undergo transmitter reuptake