Origin, course and termination of dopaminergic substantia nigra neurons projecting to the amygdaloid complex in the cat

The organization of dopaminergic neurons projecting to the amygdala was examined using retrograde (horseradish peroxidase histochemistry) and anterograde ([ 3H]leucine autoradiography) transport methods and Falck-Hillarp histofluorescence techniques combined with microspectrofluorometry and radiofrequency lesions. Cell bodies located within the pars lateralis and pars compacta of the substantia nigra were found to project to the lateral and central amygdaloid nuclei, respectively. Both of these areas within the substantia nigra contained dopaminergic perikarya, while the central and lateral amygdaloid nuclei contained fluorescent varicosities with features indicative of dopaminergic neurons. Lesions restricted to the pars lateralis of the substantia nigra resulted in a loss of fluorescence in the lateral amygdaloid nucleus. Autoradiographic experiments revealed that the projections from the pars lateralis did not run with fibers originating from the pars compacta in the nigrostriatal tract but rather had their own course occupying a lateral position adjacent to the cerebral peduncle and joining the ventral amygdalo-fugal bundle. The data indicate that, in the cat, there are two separate dopaminergic projections to the amygdala arising from the substantia nigra.