neuromodulator

noun

neu·​ro·​mod·​u·​la·​tor -ˈmäj-ə-ˌlāt-ər 

: something (as a polypeptide) that potentiates or inhibits the transmission of a nerve impulse but is not the actual means of transmission itself

neuromodulatory

-lə-ˌtōr-ē, -ˌtȯr- 

adjective