Monosynaptic raphespinal and reticulospinal projection to forelimb motoneurones in cats

Wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) was injected in the nerve branches to the spino- and acromiodeltoid muscles. After injection, the cats were awake for a period of 100 h during which they performed target-reaching and/or walking movements. Transneuronally labelled neurones were found in the nucleus raphe pallidus, in the magno- and gigantocellular parts of the medial reticular formation. All neurones were located between the level of the obex and 6 mm rostrally of the obex. These results demonstrate that medullary raphespinal and reticulospinal neurones have monosynaptic connexions with deltoid motoneurones. The raphespinal projection is partly from neurones with large cell bodies assumed to be non-monoaminergic.