neurotransmitter

https://doi.org/10.1351/goldbook.11955
Biochemical that is released upon excitation from a presynaptic membrane, crosses the synaptic space and binds to a receptor on the postsynaptic membrane, where it induces a signal that may be either stimulatory or inhibitory.
Source:
PAC, 2015, 87, 841. (IUPAC Glossary of terms used in neurotoxicology (IUPAC Recommendations 2015)) on page 890 [Terms] [Paper]