Description of a large projection from the mesodiencephalic junction to the rostral red nucleus. An anatomical study in the rat and in the cat.

Horseradish peroxidase (HRP) or wheat germ agglutinin conjugated to HRP (WGA-HRP) were deposited in the rostral pole (Rpc) of the red nucleus in 6 rats and 5 cats. In the rat, a zone of dense retrograde cell labeling and of diffuse axonal labeling occurred in the sub-pretectal area, a region which corresponds to the posterior thalamic nucleus (PT) of Bold et al. (Brain Research, 12 (1984) 521-527). In the cat, a similar retrograde and anterograde pattern of labeling was observed. The labeled area extended from the deep pretectum up to the diencephalon above the dorsomedial aspect of the ventral posterior thalamic nucleus. In a second set of experiments, 14 rats received a tracer injection (HRP, WGA-HRP or Phaseolus vulgaris-leucoagglutinin) in the sub-pretectal area. The resultant pattern of labeling consisted in a heavy anterograde terminal labeling within the Rpc of the red nucleus. Sparse retrograde cell labeling also occurred in the Rpc.