Reticulospinal connections with limb and axial motoneurons

SummaryResponses of motoneurons supplying muscles of the forelimbs, hindlimbs, back, and neck to stimulation of the medial pontomedullary reticular formation were studied with intracellular recording in cere-bellectomized cats under chloralose anesthesia.Stimulation of the midline or of a reticular region consisting of nucleus reticularis (n.r.) pontis caudalis and the dorsorostral part of n.r. gigantocellularis produced monosynaptic excitation of ipsilateral motoneurons supplying axial muscles and flexor and extensor muscles in both proximal and distal parts of the limbs. This widespread excitation appears to have been produced by rapidly conducting medial reticulospinal fibers.Stimulation of a second region consisting of n.r. ventralis and the ventrocaudal part of n. r. gigantocellularis produced monosynaptic excitation of ipsilateral neck and back motoneurons but only longer latency, apparently multisynaptic excitation of limb motoneurons. Collision tests indicated that this monosynaptic excitation did not involve fibers descending along the midline. It therefore appears to have been produced by lateral reticulospinal fibers.Reticular stimulation also produced short latency, monosynaptic inhibition of neck motoneurons, long latency, apparently polysynaptic inhibition of limb motoneurons and intermediate latency inhibition of back motoneurons. The latencies and properties of inhibitory responses of back motoneurons indicated that they were produced either disynaptically by fast fibers or monosynaptically by slower fibers.The data indicate that the medial pontomedullary reticular formation can be divided into a number of different zones each with a distinct pattern of connections with somatic motoneurons. These include the dorsorostrally located medial reticulospinal projection area, from which direct excitation of a wide variety of motoneurons can be evoked, the ventrocaudally located lateral reticulospinal projection area from which direct excitation of neck and back and direct inhibition of neck motoneurons can be evoked and the dorsal strip of n.r. gigantocellularis which has direct excitatory and inhibitory actions only on neck motoneurons.

[1]  A. Brodal,et al.  The projection of the superior colliculus onto the reticular formation of the brain stem an experimental anatomical study in the cat , 1974, Experimental Brain Research.

[2]  O. Pompeiano,et al.  Fastigioreticular fibers in the cat. An experimental study with silver methods , 1962, The Journal of comparative neurology.

[3]  S. Grillner,et al.  Convergent effects on alpha motoneurones from the vestibulospinal tract and a pathway descending in the medial longitudinal fasciculus , 1971, Experimental Brain Research.

[4]  A. Brodal,et al.  Experimental studies of commissural and reticular formation projections from the vestibular nuclei in the cat. , 1968, Brain research.

[5]  M. Ito,et al.  Electrophysiological analysis of the vestibulospinal reflex pathway of rabbit. II. Synaptic actions upon spinal neurones , 1973, Experimental Brain Research.

[6]  A. Brodal,et al.  Terminal distribution of spinoreticular fibers in the cat. , 1957, A.M.A. archives of neurology and psychiatry.

[7]  H. Kuypers,et al.  THE DESCENDING PATHWAYS TO THE SPINAL CORD, THEIR ANATOMY AND FUNCTION. , 1964, Progress in brain research.

[8]  A. Lundberg,et al.  Inhibitory effects evoked through ventral reticulospinal pathways. , 1968, Archives italiennes de biologie.

[9]  J. Eccles,et al.  Topographic studies on medial reticular nucleus. , 1976, Journal of Neurophysiology.

[10]  J. D. Coulter,et al.  A new long spinal projection from the vestibular nuclei in the cat , 1977, Brain Research.

[11]  R. Nyberg‐hansen.  Functional Organization of Descending Supraspinal Fibre Systems to the Spinal Cord , 1966, Ergebnisse der Anatomie und Entwicklungsgeschichte / Reviews of Anatomy, Embryology and Cell Biology / Revues d’anatomie et de morphologie expérimentale.

[12]  H. Klüver,et al.  A method for the combined staining of cells and fibers in the nervous system. , 1953, Journal of neuropathology and experimental neurology.

[13]  David P. C. Lloyd,et al.  ACTIVITY IN NEURONS OF THE BULBOSPINAL CORRELATION SYSTEM , 1941 .

[14]  M. Ito,et al.  Long inhibitory and excitatory pathways converging onto cat reticular and Deiters' neurons and their relevance to reticulofugal axons. , 1970, Journal of neurophysiology.

[15]  A. Brodal.  THE RETICULAR FORMATION OF THE BRAIN STEM , 1957 .

[16]  R. Mackel,et al.  Reticulospinal excitation and inhibition of neck motoneurons , 1978, Experimental Brain Research.

[17]  H. Magoun,et al.  Brain stem facilitation of cortical motor response. , 1946, Journal of neurophysiology.

[18]  C. Terzuolo,et al.  MECHANISMS OF SUPRASPINAL ACTIONS UPON SPINAL CORD ACTIVITIES. RETICULAR INHIBITORY MECHANISMS ON ALPHA-EXTENSOR MOTONEURONS. , 1964, Journal of neurophysiology.

[19]  V. J. Wilson,et al.  Comparison of effects of stimulation of Deiters' nucleus and medial longitudinal fasciculus on neck, forelimb, and hindlimb motoneurons. , 1969, Journal of neurophysiology.

[20]  V. J. Wilson,et al.  Connections between semicircular canals and neck motorneurons in the cat. , 1974, Journal of neurophysiology.

[21]  H. Kuypers,et al.  Retrograde axonal transport of horseradish peroxidase from spinal cord to brain stem cell groups in the cat , 1975, Neuroscience Letters.

[22]  B. W. Peterson,et al.  Patterns of projection and branching of reticulospinal neurons , 1975, Experimental Brain Research.

[23]  B. Peterson,et al.  Properties of projections from vestibular nuclei to medial reticular formation in the cat. , 1975, Journal of neurophysiology.

[24]  H. Magoun,et al.  An inhibitory mechanism in the bulbar reticular formation. , 1946, Journal of neurophysiology.

[25]  J. Petras.  Cortical, tectal and tegmental fiber connections in the spinal cord of the cat. , 1967, Brain research.

[26]  S Grillner,et al.  The origin of a descending pathway with monosynaptic action on flexor motoneurones. , 1968, Acta physiologica Scandinavica.

[27]  M. Filion,et al.  Responses of ponto-medullary reticular neurons to cortical, tectal and cutaneous stimuli , 1974, Experimental Brain Research.

[28]  D. Stuart,et al.  A long propriospinal system with direct effect on motoneurones and on interneurones in the cat lumbosacral cord , 2004, Experimental Brain Research.

[29]  V. J. Wilson,et al.  Supraspinal monosynaptic excitation and inhibition of thoracic back motoneurons , 2005, Experimental Brain Research.