Immunocytochemical and autoradiographic methods to demonstrate the coexistence of neuroactive substance: cerebellar Purkinje cells have glutamic acid decarboxylase, cysteine sulfinic acid decarboxylase, and motilin immunoreactivity.

Evidence is presented from immunocytochemical experiments that Purkinje cells in the mammalian cerebellum of a number of species contain gamma aminobutyric acid (GABA), taurine and the peptide motilin. Purkinje neurons show immunoreactivity to antibodies against glutamic acid decarboxylase (GAD), the synthetic enzyme for GABA, cysteine sulfinic acid decarboxylase (CSADC ase), the synthetic enzyme for taurine and motilin. Single neurons have either unique localization for GAD or motilin or CSADC ase or two substances in combination providing evidence for coexistence of these neuroactive agents. Functional studies with iontophoresis of GABA, taurine, and motilin into rabbit lateral vestibular nucleus elicited strong depressant effect on neuronal firing. The interactions of motilin and GABA were additive and inhibitory. Thus, Purkinje neurons of the cerebellum use multiple chemical messengers in their interactions. These chemical messengers coexist in single neurons. Their effects as far as our studies indicate are inhibitory and consistent with previous demonstrations of the physiological actions of Purkinje cells.