User:Rob Hurt/Retrograde neurotransmission

In neuroscience, retrograde neurotransmission is the process by which a retrograde neurotransmitter is released by a postsynaptic dendrite or cell body, and travels backwards across a chemical synapse to bind to the presynaptic neuron. The primary purpose of retrograde neurotransmission is regulation of neurotransmission. For this reason, retrograde neurotransmission allows neural circuits to create feedback loops.

Formal definition of a retrograde neurotransmitter
In 2009, Regehr et al. proposed criteria for defining retrograde neurotransmitters. According to their work, a signaling molecule can be considered a retrograde neurotransmitter if it satisfies all of the following criteria:


 * The appropriate machinery for synthesizing and releasing the retrograde messenger must be located in the postsynaptic neuron


 * Disrupting the synthesis and/or release of the messenger from the postsynaptic neuron must prevent retrograde signaling


 * The appropriate targets for the retrograde messenger must be located in the presynaptic bouton


 * Disrupting the targets for the retrograde messenger in the presynaptic boutons must eliminate retrograde signaling


 * Exposing the presynaptic bouton to the messenger should mimic retrograde signaling provided the presence of the retrograde messenger is sufficient for retrograde signaling to occur


 * In cases where the retrograde messenger is not sufficient, pairing the other factor(s) with the retrograde signal should mimic the phenomenon

Types of retrograde neurotransmitters
The most prevalent endogenous retrograde neurotransmitters are nitric oxide and various cannabinoids.