Evidence for a GABAergic inhibitory nigrotectal pathway in the rat

The aim of the present study was to test the GABAergic nature of the inhibitory projection from substantia nigra, pars reticulata (SNr) to superior colliculus (SC) in the rat, through the use of extracellular recordings and microiontophoresis. The effect of SN stimulation on the spontaneous or glutamate-evoked firing of SC units was analyzed. Among 28 SC cells inhibited by SNr stimulation, 27 decreased their firing rate following iontophoretic application of either GABA or glycine. The effect of the iontophoretic administration of bicuculline on SN4-evoked inhibition was studied on 14 of these GABA- and glycine-sensitive neurons. Bicuculline reversibly blocked nigral inhibition on 12 neurons, with iontophoretic current which did not affect glycine depression. These results are consistent with the hypothesis that GABA is the inhibitory transmitter of the nigrotectal projection.

[1]  J. Deniau,et al.  Effect of substantia nigra stimulation on identified neurons in the VL-VA thalamic complex: Comparison between intact and chronically decorticated cats , 1978, Brain Research.

[2]  D. R. Curtis,et al.  Bicuculline, an antagonist of GABA and synaptic inhibition in the spinal cord of the cat. , 1971, Brain research.

[3]  J. E. Vaughn,et al.  Immunocytochemical localization of glutamate decarboxylase in rat substantia nigra , 1976, Brain Research.

[4]  E. Roberts,et al.  Elevation of γ-Aminobutyric Acid in Rat Brain with Hydroxylamine.∗ , 1959 .

[5]  J. E. Vaughn,et al.  The fine structural localization of glutamate decarboxylase in synaptic terminals of rodent cerebellum. , 1974, Brain research.

[6]  J. Deniau,et al.  Bilateral projection of nigro-collicular neurons: An electrophysiological analysis in the rat , 1977, Neuroscience Letters.

[7]  D. Albe-Fessard,et al.  Atlas stéréotaxique du diencéphale du rat blanc , 1966 .

[8]  J. Deniau,et al.  The nigro-tectal pathway. An electrophysiological reinvestigation in the rat , 1981, Brain Research.

[9]  S. Vincent,et al.  The nigrotectal projection: a biochemical and ultrastructural characterization , 1978, Brain Research.

[10]  M. L. Mulas,et al.  Evidence for a gabaergic projection from the substantia nigra to the ventromedial thalamus and to the superior colliculus of the rat , 1979, Brain Research.

[11]  David A. Hopkins,et al.  Substantia nigra projections to the reticular formation, superior colliculus and central gray in the rat, cat and monkey , 1976, Neuroscience Letters.

[12]  J. Deniau,et al.  Electrophysiological study of the nigro-tectal pathway in the rat , 1978, Neuroscience Letters.

[13]  Mitsuo Yoshida,et al.  Electrophysiological evidence for branching nigral projections to the thalamus and the superior colliculus , 1977, Brain Research.

[14]  H. Kuypers,et al.  The organization of the efferent projections of the substantia nigra in the rat. A retrograde fluorescent double labeling study , 1979, Brain Research.