| Abstract: | Following coagulation of either the substantia nigra or the caudate nucleus and fundus caudati of the cat, the distribution of degenerating terminals in the sections of the striatum has been determined especially in the fundus caudati on one side and in the various cell groups of the substantia nigra compacta on the other side; and the types of synapses have been described. There are reverberating circuits between the fundus caudati and the medial groups of the nigra characterized by their small cells, between the putamen and the postero-lateral cell groups of the nigra, between the caudatum and the rostral cell groups of the nigra, presumably with the specialization that the lateral caudatum is in two-way connection with the rostro-lateral cell groups of the nigra as is the medial caudatum with the rostro-medial cell group. The transmitter for the striatofugal terminals in the nigra which have pleomorphic synapses is probably GABA. Dopamine is the transmitter of the axo-spinous synapses of the nigrostriatal neurons with the small striatal nerve cells for which the transmitter seems to be Acetylcholine. The nigro-striatal reverberating circuits have three outputs available; 1. from parts of the striatum to the entopeduncular nucleus (internal segment of pallidum) and from there through the H2 and H1 fields of Forel to the oral ventral nucleus of the thalamus (V.o.a) which directly projects to the area 6 a alpha of motor cortex; 2. also from parts of the striatum to the pallidum (outer segment) and continuing through the descending pallido-reticulospinal pathway and 3. from the postero-lateral cell groups of the nigra probably through descending fibers which cross the midline in the commissura colliculi superioris and extend through the reticular formation directly or indirectly to the spinal cord. |
