THE ORIGIN AND TERMINATION OF THE RETICULOSPINAL TRACT IN THE CAT——HRP METHOD / 解剖学报

ABSTRACT

The origin and termination of the reticulospinal tract were studied with HRP technique in ten cats by injecting HRP into the spinai dorsal horn or gray matter on one side of the cervical or lumbar enlargement, It was discovered that the reticulospinal neurons were located not only in the medial part of the medullopontal tegmentum, but also in its lateral part. There were also a few scattered labeled neurons in the reticular formation of midbrain. The reticulospinal tract ended in the spinal dorsal horn as well as in the ventral horn. The reticulospinal tract mainly originated from the ventromedial part of the medulla and pons. In this region the labeled cells were most numerous in the nucleus gigantocellularis, less in the nucleus medulla oblongatae centralis subnucleus ventralis and the nucleus pontis centralis caudalis, and much less in the nucleus pontis centralis oralis, the nucleus paragigantocellularis laterlris and the paramedium reticularis subnucleus ventralis. Occasionally a few scattered abeled cells could be seen in the nucleus cuneiformis. The reticulospinal fibers from these nuclei projected bilaterally to both cervical and lumbar enlargments of the spinal cord except that the nucleus cuneiformis projected bilaterally to the cervical enlargement only.Two groups of labeled cells were found in the ventrolateral part of the medullary and pontal reticular formation, corresponding to the position of group A 1 and A 7 of noradrenergic neurons respectively.The reticulospinal tract derived from the medial part of the brain stem terminated predominately in the gray matter ventral to the spinal dorsal horn, but a few of them ended in the dorsal horn. These connections provide direct pathways for the control of motor and sensory functions of the spinal cord by medial reticular formation.It has been proved by Brodal with chromatolysis techenique that every cell in the nucleus paramedium reticularis sends its efferent fiber to the spinal area of cerebellum, but in this study labeled cells were found in e nucleus paramedium reticularis subnucleus ventralis. We suppose that the axons of these labeled neurons may be divided into two branches, one projecting to the cerebellum and the other to the spinal cord.It is noteworthy that we also found some labeled neurons in the nucleus medullae oblongatae centralis subnucleus dorsalis and nucleus parvocellularis, the so called "receptive region" of the reticular formation. The fibers originating from this region terminated in the spinal dorsal horn mainly, suggesting that this tract probably influences the sensory function of the spinal cord. It seems that the conception of the lateral reticular formation of the brain stem as a pure "receptive area" of the reticular formation may have be modified.