Screening for neurotransmitters: A rapid radiochemical procedure

Among the known or suspected neurotransmitter compounds are: acetylcholine, norepinephrine, γ‐aminobutyric acid, epinephrine, 5‐hydroxytryptamine, dopamine, and octopamine. This communication describes a rapid screening procedure for identifying which of these substances are likely candidates for neurotransmitters in a particular tissue. The method is based on the selective synthesis and localization of transmitters in those cells which are presumed to release them. The procedural steps are: (1) incubation of tissue in a physiological medium containing one or more radiochemical precursors of suspected transmitters; (2) acidic extraction of all or selected parts (e.g., single cells) of the incubated tissue; (3) high‐voltage paper electrophoresis of the extract under conditions which separate most of the compounds of interest; and (4) quantification of isotope in each transmitter candidate. The effectiveness and sensitivity of the method have been shown with several preparations whose transmitters are known. In certain cases the sensitivity can extend to a single cell level. Preliminary results are also reported on the application of the technique to a lobster sensory system of unknown transmitter chemistry, the abdominal muscle receptor organ.