Description These are intrinsic compounds or molecules that pass or transmit a signal or impulse from a presynaptic neuron to a postsynaptic neuron at a synapse. Outside media Molecular entities - Choose - acetylcholine anandamide aspartic acid beta endorphin dopamine epinephrine gamma-aminobutyric acid glutamic acid glycine N-Methyl-D-aspartic acid orexin serotonin