Descending projections from brainstem and sensorimotor cortex to spinal enlargements in the cat

Summary Single and double retrograde tracer techniques were employed in cats to investigate: (1) the topographical relationships between supraspinal neurons projecting to either the brachial or lumbosacral enlargement, (2) the distribution and relative frequency of single supraspinal neurons which project to both enlargements by means of axonal branching.In one group of cats large injections of horseradish peroxidase (HRP) were made throughout either the brachial or lumbosacral enlargement. The results from these experiments support recent observations on the multiplicity of brainstem centers giving origin to descending spinal pathways and provide evidence for a population of corticospinal neurons in area 6.In a second set of experiments, HRP was injected in one enlargement, and ³H-apo-HRP (enzymatically inactive) was injected in the other enlargement. Relatively large numbers of neurons with collateral projections to both enlargements (double-labeled) were observed in the medullary and pontine reticular formation, the medial and inferior vestibular nuclei bilaterally, the ipsilateral lateral vestibular nucleus, Edinger-Westphal nucleus, caudal midline raphe nuclei and nuclear regions surrounding the brachium conjunctivum. By contrast, double-labeled neurons were infrequently observed in the red nucleus and sensorimotor cortex, contralateral to the injections.In the red nucleus, lateral vestibular nucleus and sensorimotor cortex, neurons projecting to the brachial enlargement were largely segregated topographically from neurons projecting to the lumbosacral enlargement. However, there was some overlap, and double-labeled neurons were consistently observed within the region of overlap. In the sensorimotor cortex, the overlap between brachial- and lumbar-projecting neurons was most prominent in areas 4 and 3a, along the cruciate sulcus, but also involved other cytoarchitectonic regions in the medial aspect of the hemisphere.Abbreviations AM nucleus ambiguus - ap area postrema - aq aqueduct - BC brachium conjunctivum - ci central inferior nucleus of the raphe - cs central superior nucleus of the raphe - Cun cuneate nucleus - EC external cuneate nucleus - EW Edinger-Westphal nucleus - ETC central tegmental field - FTG gigantocellular tegmental field - FTL lateral tegmental field - FTM magnocellular tegmental field - FTP paralemniscal tegmental field - Gr gracile nucleus - IO inferior olive - K-F Kölliker-Fuse nucleus - LC nucleus locus coeruleus - li rostral linear nucleus of the raphe - LR lateral reticular nucleus - mlf medial longitudinal fasciculus - PAG periaqueductal gray - PbL lateral parabrachial nucleus - PG pontine gray - PON preolivary nucleus - ppr post-pyramidal nucleus of the raphe - RB restiform body - RNm red nucleus, magnocellular division - RNp red nucleus, parvocellular division - SC superior colliculus - SN substantia nigra - SOl lateral nucleus of the superior olive - SOm medial nucleus of the superior olive - Spin V spinal trigeminal nucleus - SubC nucleus subcoeruleus - TB trapezoid body - tb nucleus of the trapezoid body - trm tegmental reticular nucleus - VInf inferior vestibular nucleus - VLd lateral vestibular nucleus, dorsal division - VLv lateral vestibular nucleus, ventral division - VM medial vestibular nucleus - VSm superior vestibular nucleus, medial divisionCranial Nerves and their Nuclei III oculomotor nucleus or nerve - V sensory nucleus of the trigeminal nerve - VI abducens nucleus - VII I facial nucleus, lateral part - VII m facial nucleus, medial part - X vagus nucleus - XII hypoglossal nucleusThe research was supported by USPHS grants NS 12440 and MH 14277. ³H-apo-HRP was generously provided by New England Nuclear