Efferents of the pretectal complex: separate populations of neurons project to lateral thalamus and to inferior olive.

The efferent projections of the pretectal complex were studied in the rat with the retrograde transport method. Injections of nuclear yellow or a mixture of true blue and granular blue placed in the thalamic lateral dorsal nucleus resulted in retrogradely labeled neurons in all pretectal nuclei, including the anterior, posterior, medial, olivary, and optic tract nuclei. Injections in the inferior olive complex resulted in labeled cells in the anterior, posterior, and optic tract nuclei. In no case were individual pretectal neurons seen to contain both fluorescent markers. These results indicate that ascending and descending projections from the pretectal complex arise from distinctly separate populations of neurons.