Summary
Extracellular microelectrodes were used to record the activity of reticulospinal neurons within the medial ponto-medullary reticular formation in the cat. In one series of experiments reticulospinal neurons were activated from electrodes in the ventro-medial reticulospinal tract (RSTm) and in the ipsiand contralateral lateral reticulospinal tracts (RSTi, RSTC) at spinal levels C1–2, C4, Th1 and L1. RSTm neurons were found primarily in n.r. pontis caudalis and the rostro-dorsal part of n.r. gigantocellularis. 71% of these neurons projected as far as the lumbar spinal cord. RSTi neurons projecting to C4 and beyond were clustered in the caudo-ventral part of n.r. gigantocellularis, but those RSTi neurons projecting to the first three cervical segments were located more rostro-dorsally. In all, 63% of the RSTi neurons projected to the lumbar spinal cord. RSTc neurons, which comprised only 5% of the reticulospinal population, were found throughout n.r. gigantocellularis. RSTm neurons had a median conduction velocity of 101 m/sec whereas RSTi and RSTc had median conduction velocities on the order of 70 m/sec.
In a second series of experiments microstimulation was used to activate branches of reticulospinal neurons within the gray matter of the cervical enlargement. Twenty-two of thirty-three neurons found to project to the cervical ventral horn were branching neurons that also sent axons to the lumbar spinal cord. Thus much of the reticulospinal activity reaching the cervical enlargement also acts at one or more other spinal levels. Detailed investigation of the course of reticulospinal axons within the cervical gray matter indicated that a single axon may traverse wide areas of the ventral horn including regions on both sides of the spinal cord.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Abzug, C., Maeda, M., Peterson, B.W., Wilson, V.J.: Cervical branching of lumbar vestibulospinal axons. J. Physiol. (Lond.) 243, 499–522 (1974)
Bement, S.L., Ranck, J.B.: A quantitative study of electrical stimulation of central myelinated fibers. Exp. Neurol. 24, 147–170 (1969)
Eccles, J.C., Nicoll, R.A., Schwarz, W.P., Táboříková, H., Willey, T.J.: Reticulospinal neurones with and without monosynaptic inputs from cerebellar nuclei. J. Neurophysiol. 38, 513–530 (1975)
Engberg, I., Lundberg, A., Ryall, R.W.: Reticulospinal inhibition of interneurones. J. Physiol. (Lond.) 194, 225–236 (1968)
Grillner, S., Hongo, T., Lund, S.: Convergent effects on alpha motoneurones from the vestibulospinal tract and a pathway descending in the medial longitudinal fasciculus. Exp. Brain Res. 12, 457–479 (1971)
Grillner, S., Lund, S.: The origin of a descending pathway with monosynaptic action on flexor motoneurones. Acta physiol. scand. 74, 274–284 (1968)
Ito, M., Udo, M., Mano, N.: Long inhibitory and excitatory pathways converging onto cat reticular and Deiters' neurons and their relevance to reticulofugal axons. J. Neurophysiol. 33, 210–226 (1970)
Jankowska, E., Lund, S., Lundberg, A., Pompeiano, O.: Inhibitory effects evoked through ventral reticulospinal pathways. Arch. ital. Biol. 106, 124–140 (1968)
Jankowska, E., Lundberg, A., Roberts, W.J., Stuart, D.: A long propriospinal system with direct effect on motoneurones and on interneurones in the cat lumbosacral cord. Exp. Brain Res. 21, 169–194 (1974)
Jankowska, E., Roberts, W.J.: An electrophysiological demonstration of the axonal projections of single spinal interneurones in the cat. J. Physiol. (Lond.) 222, 597–622 (1972)
Klüver, H., Barrera, E.: A method for the combined staining of cells and fibers in the nervous system. J. Neuropath. exp. Neurol. 12, 400–403 (1953)
Llinás, R., Terzuolo, C.A.: Mechanisms of supraspinal actions upon cord activities. Reticular inhibitory mechanisms on alpha-extensor motoneurons. J. Neurophysiol. 27, 579–591 (1964)
Lundberg, A., Vyklický, L.: Inhibition of transmission to primary afferents by electrical stimulation of the brain stem. Arch. ital. Biol. 104, 86–97 (1966)
Magni, F., Willis, W.D.: Cortical control of brain stem reticular neurons. Arch. ital. Biol. 102, 418–433 (1964a)
Magni, F., Willis, W.D.: Subcortical and peripheral control of brain stem reticular neurons. Arch. ital. Biol. 102, 434–448 (1964b)
Magoun, H.W., Rhines, R.: An inhibitory mechanism in the bulbar reticular formation. J. Neurophysiol. 9, 165–171 (1946)
Nyberg-Hansen, R.: Functional organization of descending supraspinal fibre systems to the spinal cord. Anatomical observations and physiological correlations. Ergebn. Anat. Entwickl.-Gesch. 39, Heft 2, 1–48 (1966)
Peterson, B.W., Anderson, M.E., Filion, M.: Responses of ponto-medullary reticular neurons to cortical, tectal and cutaneous stimuli. Exp. Brain Res. 21, 19–44 (1974)
Peterson, B.W., Filion, M., Felpel, L.P., Abzug, C.: Responses of medial reticular neurons to stimulation of the vestibular nerve. Exp. Brain Res. 22, 335–350 (1975)
Petras, J.M.: Cortical, tectal and tegmental fiber connections in the spinal cord of the cat. Brain Res. 6, 275–324 (1967)
Pompeiano, O., Swett, J.E.: Actions of graded cutaneous and muscular afferent volleys on brain stem units in the decerebrate, cerebellectomized cat. Arch. ital. Biol. 101, 552–582 (1963)
Rexed, B.: A cytoarchitectonic atlas of the spinal cord in the cat. J. comp. Neurol. 100, 297–379 (1954)
Rhines, R., Magoun, H.W.: Brain stem facilitation of cortical motor response. J. Neurophysiol. 9, 219–229 (1946)
Roberts, W.J., Smith, D.O.: Analysis of threshold currents during microstimulation of fibres in the spinal cord. Acta physiol. scand. 89, 384–394 (1973)
Smirnov, K.A., Potekhina, I.L.: Localization and properties of reticulospinal neurons with axons descending in the dorsolateral parts of the lateral funiculi. Neurophysiology 6, 208–213 (1974)
Thomas, R.C., Wilson, V.J.: Precise localization of Renshaw cells with a new marking technique. Nature (Lond.) 206, 211–213 (1965)
Torvik, A., Brodal, A.: The origin of reticulospinal fibers in the cat. An experimental study. Anat. Rec. 128, 113–137 (1957)
Udo, M., Mano, N.: Discrimination of different spinal monosynaptic pathways converging onto reticular neurons. J. Neurophysiol. 33, 227–238 (1970)
Wilson, V.J., Yoshida, M.: Comparison of effects of stimulation of Deiters' nucleus and the medial longitudinal fasciculus on neck, forelimb and hindlimb motoneurons. J. Neurophysiol. 32, 743–758 (1969)
Wilson, V.J., Yoshida, M., Schor, H.H.: Supraspinal monosynaptic excitation and inhibition of thoracic back motoneurons. Exp. Brain Res. 11, 282–295 (1970)
Author information
Authors and Affiliations
Additional information
Supported in part by grant NSF GB 36927 from the National Science Foundation and grants NS 02619 and NS 05463 from the National Institutes of Health.
NINDS Fellow.
NINDS Training Fellow.
Rights and permissions
About this article
Cite this article
Peterson, B.W., Maunz, R.A., Pitts, N.G. et al. Patterns of projection and branching of reticulospinal neurons. Exp Brain Res 23, 333–351 (1975). https://doi.org/10.1007/BF00238019
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00238019