Cerebellar cortical and nuclear afferents from the feline locus coeruleus complex

The origin and distribution of cerebellar cortical and nuclear afferents from the locus coeruleus complex (the nucleus locus coeruleus, the nucleus subcoeruleus, the medial and lateral subdivisions of the parabrachial nucleus and the Kölliker-Fuse nucleus) have been studied by means of retrograde transport of the wheat germ agglutinin-horseradish peroxidase complex in the cat. Cerebellar cortical depositions of the tracer were made by pressure injections, while nuclear depositions were made by implanting the tracer in crystalline form. The projection is bilateral with an ipsilateral preponderance. It reaches all the cerebellar nuclei as well as vermal, intermediate and lateral parts of the cerebellar cortex. The highest cell counts were made after tracer depositions in vermal and intermediate parts of the cerebellum. The projection in the cat has a more widespread origin than previously reported. It originates mainly within the nucleus locus coeruleus and the parabrachial nucleus (especially in its lateral subdivision), but retrogradely labelled neurons were also found in nucleus subcoeruleus, the Kölliker-Fuse nucleus and the A4 cell group. The cells of origin were of different shapes, but usually had a maximum diameter of the cell body between 15 and 30 micron. Cerebellar efferent axons passing through the locus coeruleus complex were anterogradely labelled following implants in all the cerebellar nuclei, but definite terminal labelling was not observed within the nuclei of the locus coeruleus complex.