Projections from the substantia nigra pars reticulata to the motor thalamus of the rat: Single axon reconstructions and immunohistochemical study

This is a study in the rat of the distribution of specific neurotransmitter s in neurones projecting from the substantia nigra reticulata (SNR) to the ventrolateral (VL) and ventromedial (VM) thalamic nuclei. Individual axons projecting from the SNR to these thalamic nuclei have also been reconstruct ed following small injection of the anterograde tracer dextran biotin into the the SNR. Analysis of reconstructions revealed two populations of SNR ne urones projecting onto the VL and VM thalamic nuclei. One group projects di rectly onto the VM and VL, and the other projects to the VM/VL and to the p arafascicular nucleus. In another set of experiments Fluoro-Gold was inject ed into the VL/VM to label SNR projection neurones retrogradely, and immuno histochemistry was performed to determine the distribution of choline acety ltransferase (ChAT), vesicular acetylcholine transporter (VAChT), gamma -am inobutyric acid (GABA), and glutamate in Fluoro-Gold-labelled SNR projectio n neurones. Most SNR-VL/VM thalamic projection neurones were immunoreactive to acetylcholine or glutamate, whereas only 25% of the projection neurones were found to be immunoreactive to GABA. (C) 2001 Wiley-Liss, Inc.