What does Dale's principle state regarding neurotransmitter release?

Dale's principle, which originates from the work of neuroscientist Dale, asserts that a neuron typically releases only one type of neurotransmitter. This principle suggests a level of consistency and specialization in neurotransmitter release, which has implications for how neural communication works. For example, if a neuron is identified as a dopaminergic neuron, it primarily releases dopamine and not other neurotransmitters like serotonin or norepinephrine. This singularity supports predictable patterns of signaling in neural circuits and helps to establish specific roles for different types of neurons in the nervous system.

This principle is not suggesting that neurons cannot have distinct effects when acting on different receptors, nor does it negate the existence of co-release mechanisms where certain neurons can release more than one neurotransmitter under specific circumstances. However, the core assertion is that under standard operational conditions, each neuron is typically tied to one main neurotransmitter.