Platelets and neurons share many similarities. The top panel shows the communication between a presynaptic and a postsynaptic neuron. Neurons are activated by calcium signaling, which triggers the release of neurotransmitters such as serotonin, dopamine, epinephrine, histamine, glutamate, and GABA. The neurotransmitters then bind to the corresponding receptors on the postsynaptic neuron to complete neurotransmission. The lower panel shows an activated platelet with dense granules containing neurotransmitters, adenosine triphosphate, adenosine diphosphate, and calcium, and α-granules containing growth factors, cytokines, antioxidants, and adhesion molecules. Similar to the mechanism which occurs at the presynapse of neurons, calcium-dependent activation of platelets triggers the fusion of the granules with the plasma membrane via highly conserved docking molecules called SNAREs. This results in the rapid release of neurotransmitters, which bind to corresponding receptors expressed on the surface of T cells.