Iontophoretic studies on pallidal neurones and the projection from the subthalamic nucleus

The predominant response of pallidal neurones to gamma-aminobutyric acid (GABA), glycine and dopamine when applied iontophoretically, was inhibition of firing rate. With dopamine some excitatory responses were observed, this never being the case with GABA or glycine. Picrotoxin reversibly blocked neuronal responses to GABA but not glycine in fourteen cases. Strychnine abolished glycine evoked inhibitions in seventeen cells while not affecting GABA responses. A number of cells were responsive to a stimulus delivered to the subthalamic nucleus (s.t.n.), an electrode array being used to establish the specificity of response to s.t.n. stimulation. In eight out of fourteen cases there was a reduction of 40% or more in the inhibitory responses following stimulation, with picrotoxin applied iontophoretically. Strychnine, conversely, had no effect on the synaptically evoked inhibition at doses that exceeded those required to antagonize iontophoretically applied glycine. Similarly, fluphenazine and naloxone administered iontophoretically or intraperitoneally (I.P.) had no effect on eight cells. The results indicate the existence of a 'GABA-ergic' link in the projection from the subthalamic nucleus to the globus pallidus, though other transmitters, but not glycine or dopamine, may contribute to the observed synaptic responses.