Anatomical evidence of a reciprocal connection between the posterior thalamic nucleus and the parvocellular division of the red nucleus in the rat. A combined retrograde and anterograde study.

The functional and anatomical organizations of the magnocellular part of the red nucleus are now well established. Our knowledge of the parvocellular part is, however, more limited. Using both anterograde and retrograde tracing methods, the present study suggests in the rat the existence of a large projection from the posterior thalamic nucleus to the parvocellular part of the red nucleus. In turn, the parvocellular part of the red nucleus sends a weaker projection to the posterior thalamic nucleus. Three different tracers were utilized (horseradish peroxidase alone, horseradish peroxidase conjugated to wheat germ agglutinin and Phaseolus vulgaris leucoagglutinin), all of which gave similar results. The posterior thalamic nucleus is known to receive a large proportion of somatosensory afferents. It is suggested, therefore, that in addition to receiving cerebellar and cortical inputs, the parvocellular part of the red nucleus has access to highly integrated somatosensory and/or nociceptive information delivered by the posterior thalamic nucleus.