[Study of the neurons of the supraspinal systems of the cat brain using the method of retrograde axonal transport of horseradish peroxidase].

Horseradish peroxidase (HRP) was injected into cervical, thoracic, lumbar and sacral segments of 18 cats. In all the cases HRP was transported retrogradely to the brain stem neurons in the medial reticular formation, vestibular complex and the red nucleus. The present findings demonstrate that, in addition to the above mentioned groups, there exist several other groups of neurons. Many labelled neurons are present in the locus coeruleus and the nucleus subcoeruleus, ipsilaterally. These neurons seem to be located in the same position as the monoaminergic (catecholamine-containing) neurons. Labelled HPR-positive neurons are present in the retroambiguous nucleus and in the upper pontine tegmentum adjoining the rubrospinal tract, mainly contralaterally, in the bulbar raphe, the mesencephalic central gray and the hypothalamus, mainly ipsilaterally. The occurrence of retrograde-labelled neurons in the locus coeruleus and the dorsal hypothalamus after HRP injections as far caudally as the lumbar segments, indicates that these cell groups give rise to descending fibres which pass almost the entire length of the spinal cord.