Amino acids: glutamate,[4] aspartate, D-serine, γ-aminobutyric acid (GABA), glycine
Gasotransmitters: nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H2S)
Monoamines: dopamine (DA), norepinephrine (noradrenaline; NE, NA), epinephrine (adrenaline), histamine, serotonin (SER, 5-HT)
Trace amines: phenethylamine, N-methylphenethylamine, tyramine, 3-iodothyronamine, octopamine, tryptamine, etc.
Peptides: somatostatin, substance P, cocaine and amphetamine regulated transcript, opioid peptides[9]
Purines: adenosine triphosphate (ATP), adenosine
Others: acetylcholine (ACh), anandamide, etc