Noradrenergic pre vs. postreceptors
Receptors can also be found pre-synaptically to regulate the output of a cell (feedback loop). A good example that shows how the same agonist (adrenaline) can act both pre- and postsynaptically is shown below. The α2 receptor is a Gi coupled protein receptor, thus inhibitory. The β2 receptor (as well as the β1) is stimulatory (Gs-protein).