Nuclear origin of thalamic afferents of the ventral striatum determines their relation to patch/matrix configurations in enkephalin-immunoreactivity in the rat.

The relation of thalamic terminal fibers in the ventral striatum with patch and matrix compartments, as defined by enkephalin-immunohistochemistry, was studied in adjacent or double-stained sections of the rat brain by combining anterograde tracing of Phaseolus vulgaris-leucoagglutinin (PHA-L) and enkephalin staining. Experiments with small PHA-L injections in the dorsal thalamus show that the paraventricular thalamic nucleus projects to the medial nucleus accumbens and rather selectively to the patch compartment in more lateral parts of the nucleus. The central medial thalamic nucleus sends its fibers to more lateral parts of the nucleus accumbens and the ventral part of the caudate-putamen, where these fibers terminate in the matrix compartment.