ABSTRACT
HRP solution was injected into the right subnucleus caudalis of the trigeminal nerve in the cat, and the labeled cells in the nucleus raphe dorsalis of six cases were examined and analyzed. The labeled cells appeared more in the middle portion and its rostral adjacent parts of the nucleus raphe dorsalis, decreased in number rostrally and caudally, and were entirely absont in the caudal end of the nucleus. In the ventral part and the ventral areas of the lateral parts of the nucleus labeled cells were more than in the other areas of the nucleus, no difference was found between the two sides. In the dorsal part and the dorsal regions of the lateral parts of the nucleus only a few labeled cells were seen. The labeled cells varied in forms, but in the ventral part and the ventral regions of the lateral parts they were mainly fusiform in shape. In addition, in nucleus raphe magnus, nucleus raphe pallidus, and nucleus raphe obscurus, small numbers of neurones were labeled as well.As the nucleus raphe magnus takes part in the inhibition of the response to noxious stimuli in the spinal dorsal horn, and as both the nucleus raphe magnus and nucleus raphe dorsalis belong to the more developed raphe nuclei and contain more 5-HT neurones, it seems that there might be somatotopic relations between the nucleus raphe dorsalis which projects mainly to subnucleus caudalis and the nucleus raphe magnus which projects mainly to the spinal dorsal horn.
ABSTRACT
1. The subnucleus caudalis of the spinal trigeminal nucleus of cat was injected with 30% HRP (Sigma, type Ⅵ). Well localized groups of labeled neurons were observed in the dorsolateral horn of the contralateral red nucleus. This dorsolateral horn, being present in the rostral and middle thirds of the nucleus, consisted mainly of middle-sized and small neurons.2. Injections were also made into the second and third segments of the cervical spinal cord and the caudal part of the bulbar reticular formation. The labeled neurons appearing in these experiments were diffusely distributed in the red nucleus, yet limited in the rostral third of it.3. Summarizing our findings and the data from the literature, we got the impression that the rostral two thirds of the red nucleus gave projections to the central structures rostral to the upper cervical spinal cord, and the caudal two thirds of it to those caudal to the lower cervical cord, which indicating a somatotopic organization of the red nucleus neurons giving descending projection fibers.