Organization of Projections of the Rostromedial Tegmental Nucleus to the Striatum in the Dog Brain

Abstract

The organization of the projections of the rostromedial tegmental nucleus (RMTg) to functionally diverse areas of striatal structures in dogs (n = 26) was studied by a method based on retrograde axonal transport of horseradish peroxidase and fluorochromes. Projection fibers from neurons in the limbic medial part of the RMTg were found to be directed only to the limbic segments of the caudate nucleus, putamen, and nucleus accumbens. However, most segments of striatal structures showed convergence of projection fibers running from neurons in functionally diverse parts of the RMTg. Thus, the motor dorsolateral segment of the caudate nucleus, as well as striatal segments innervated by fibers from neurons in functionally diverse structures (the ventrolateral segment of the caudate nucleus and the lateral segment of the nucleus accumbens) received fibers from neurons in the motor lateral part of the RMTg and limbic medial part of the RMTg. The possible pathways conducting functionally diverse information and integrating it in the projection systems studied here are assessed.