An excitatory input to nucleus raphe magnus from the red nucleus in the cat

In chloralose-anaesthetized cats, with the cerebellum removed, stimulation in the red nucleus excited the majority (60-65%) of neurones in nucleus raphe magnus (NRM), including raphespinal neurones. Evidence was obtained for both monosynaptic and polysynaptic excitation. The projection was confirmed by recording antidromic responses in the red nucleus to stimulation in NRM. It is suggested that the role of NRM in motor control is to inhibit spinal flexion responses to peripheral stimuli so that commands from the red nucleus and other motor control regions may take place without interruption.