Neuronal responses to iontophoretically applied dopamine, glutamate, and GABA of identified dopaminergic cells in the rat substantia nigra after kainic acid-induced destruction of the striatum.

Kainic acid (KA 1.2-1.5 micrograms) was injected unilaterally into the rat striatum (ST). Fifteen to 30 days later neurons of the substantia nigra (SN) were identified by antidromic stimulation from the ST or medial forebrain bundle (MFB). The projecting axons had conduction velocity similar to that recorded in unlesioned animals. REsponses to iontophoretically applied dopamine (DA), glutamate (GLU), and GABA (5-100 nA) were recorded from neurons of the dopaminergic pars compacta-striatal projection. Control experiments were performed in intact rats. GABA and DA inhibited neurons tested in controls while GLU had an excitatory effect. Changes in firing rate induced by GABA and GLU developed 1-5 s after the beginning of their ejection while the action of DA appeared after a delay of 20-40 s. Neurons in lesioned animals showed a net decrease in sensitivity to all three neurotransmitters. The highest current tested gave responses 50-70% lower than in controls. The data suggest that destruction of striatal efferents with KA does not induce hypersensitivity in the pars compacta of the SN.