A re-examination of the striatal input from the mediodorsal thalamic nucleus in the rat

The projection from the mediodorsal thalamic nucleus to the striatum in the rat was studied by placing injections of the retrograde tracer Fluoro-Gold into the caudate putamen and small deposits of biotinylated dextran amine (BDA) into the mediodorsal thalamic nucleus. The relationship of thalamic afferent fibers with the compartmental organization of the striatum was studied by combining (BDA) tracing and enkephalin immunohistochemistry. The medial segment of the mediodorsal thalamic nucleus projects to the nucleus accumbens whereas the lateral segment projects sparsely to the medial regions of the caudate putamen. The caudal pole of the mediodorsal thalamic nucleus was found to project abundantly to ventrolateral regions of the precommissural caudate putamen, reaching areas of strong enkephalin immunoreactivity. The dorsolateral and caudal regions of the striatum did not receive projections from the mediodorsal thalamic nucleus. The present findings demonstrate a topographical organization of the thalamostriatal projections originating in the mediodorsal thalamic nucleus of the rat