Synaptic control of hindlimb motoneurones during three forms of the fictive scratch reflex in the turtle.

1. The turtle spinal cord produces three forms of the fictive scratch reflex in response to tactile stimulation of sites on the body surface. Common to all three forms is the rhythmic alternation of activity between hip protractor and hip retractor motoneurones. Hip protractor motoneurone activity is monitored via nerves innervating the hip protractor muscle puboischiofemoralis internus pars anteroventralis (VP‐HP). Hip retractor activity is monitored via nerves innervating several monoarticular hip retractor muscles, one hip adductor muscle, and several biarticular hip retractor‐knee flexor muscles (HR‐KF). Each form is characterized by the timing of activity of motoneurones innervating femorotibialis (FT‐KE), a monoarticular knee extensor muscle, within this alternating cycle (Robertson, Mortin, Keifer & Stein, 1985). In the present study, intracellular recordings revealed a corresponding regulation of synaptic drive to knee extensor motoneurones with respect to the synaptic drive to the motoneurones innervating antagonist muscles of the hip. These patterns of synaptic activation give rise to the distinct motor pattern underlying each form of the scratch reflex. 2. VP‐HP, HR‐KF and FT‐KE motoneurones all exhibited phasic depolarizing and hyperpolarizing changes in membrane voltage during the production of the rhythmic motor patterns underlying each stratch form. Membrane depolarization is caused by synaptic excitation (EPSPs) and gives rise to motoneurone discharge. Hyperpolarization is primarily the result of postsynaptic inhibition (IPSPs) mediated by an increased conductance of chloride ions (Cl‐) and ensures motor pool quiescence during antagonist activation. 3. VP‐HP motoneurones depolarized during activation of the VP‐HP motor pool and hyperpolarized during activation of the HR‐KF motor pool. HR‐KF motoneurones depolarized during activation of the HR‐KF motor pool and hyperpolarized during activation of the VP‐HP motor pool. In many cases, the amplitude of hyperpolarization was directly related to the intensity of the antagonist motor pool burst. During the rostral scratch, HR‐KF motor pool activity was sometimes deleted, along with the depolarizing wave in HR‐KF motoneurones and the hyperpolarizing wave in VP‐HP motoneurones. The interneurones providing the synaptic drive to these antagonist motoneurones appear, therefore, to have reciprocal activation patterns. 4. FT‐KE motoneurones depolarized during FT‐KE motor pool activation and hyperpolarized during FT‐KE motor pool quiescence. This alternation of opposing synaptic drive underlies the rhythmic activation of the FT‐KE motor pool during all scratch forms.(ABSTRACT TRUNCATED AT 400 WORDS)

[1]  C. Sherrington Observations on the scratch‐reflex in the spinal dog , 1906, The Journal of physiology.

[2]  W. Smith The Integrative Action of the Nervous System , 1907, Nature.

[3]  ANESTHESIA AND SURGERY. , 1936, Annals of surgery.

[4]  K. Koketsu,et al.  Cholinergic and inhibitory synapses in a pathway from motor‐axon collaterals to motoneurones , 1954, The Journal of physiology.

[5]  [Respiratory rhythm]. , 1955, Acta medica Scandinavica. Supplementum.

[6]  J. Eccles,et al.  The specific ionic conductances and the ionic movements across the motoneuronal membrane that produce the inhibitory post‐synaptic potential , 1955, The Journal of physiology.

[7]  M. Ito,et al.  Anion permeability of the synaptic and non‐synaptic motoneurone membrane , 1961, The Journal of physiology.

[8]  L. M. Ashley,et al.  Laboratory anatomy of the turtle , 1962 .

[9]  T. Sears,et al.  The slow potentials of thoracic respiratory motoneurones and their relation to breathing , 1964, The Journal of physiology.

[10]  W. Willis The case for the Renshaw cell. , 1971, Brain, behavior and evolution.

[11]  Warren F. Walker,et al.  The locomotor apparatus of Testudines , 1973 .

[12]  G. Orlovsky,et al.  Activity of interneurons mediating reciprocal 1a inhibition during locomotion , 1975, Brain Research.

[13]  S. Grillner,et al.  Central Generation of Locomotion in Vertebrates , 1976 .

[14]  E. Barrett,et al.  Separation of two voltage‐sensitive potassium currents, and demonstration of a tetrodotoxin‐resistant calcium current in frog motoneurones. , 1976, The Journal of physiology.

[15]  G. Orlovsky,et al.  Activity of motoneurons during fictitious scratch reflex in the cat , 1980, Brain Research.

[16]  G. Orlovsky,et al.  Activity of Ia inhibitory interneurons during fictitious scratch reflex in the cat , 1980, Brain Research.

[17]  H. E. Desnedt,et al.  Spinal motoneuron recruitment in man: rank deordering with direction but not with speed of voluntary movement. , 1981, Science.

[18]  S. Grillner Control of Locomotion in Bipeds, Tetrapods, and Fish , 1981 .

[19]  S. Soffe,et al.  Tonic and phasic synaptic input to spinal cord motoneurons during fictive locomotion in frog embryos. , 1982, Journal of neurophysiology.

[20]  C. Perret Centrally generated pattern of motoneuron activity during locomotion in the cat. , 1983, Symposia of the Society for Experimental Biology.

[21]  L. Jordan Factors determining motoneuron rhythmicity during fictive locomotion. , 1983, Symposia of the Society for Experimental Biology.

[22]  P. Stein The vertebrate scratch reflex. , 1983, Symposia of the Society for Experimental Biology.

[23]  T. Ruigrok,et al.  Morphology of lumbar motoneurons innervating hindlimb muscles in the turtle Pseudemys scripta elegans: An intracellular horseradish peroxidase study , 1984, The Journal of comparative neurology.

[24]  D. Richter,et al.  Post‐synaptic inhibition of bulbar inspiratory neurones in the cat. , 1984, The Journal of physiology.

[25]  T. Ruigrok,et al.  The organization of motoneurons in the turtle lumbar spinal cord , 1984, The Journal of comparative neurology.

[26]  G. A. Robertson,et al.  Three forms of the scratch reflex in the spinal turtle: central generation of motor patterns. , 1985, Journal of neurophysiology.

[27]  P. Stein,et al.  Three forms of the scratch reflex in the spinal turtle: movement analyses. , 1985, Journal of neurophysiology.

[28]  Peter Wallén,et al.  Phasic Control of Vertebrate Motoneurones During Rhythmic Motor Acts, with Special Reference to Fictive Locomotion in the Lamprey , 1986 .

[29]  S. Soffe,et al.  Spinal Interneurones and Swimming in Frog Embryos , 1986 .

[30]  C. Perret Synaptic Influences Contributing to the Pattern of Limb Motoneuron Activity during Fictive Locomotion in the Cat , 1986 .

[31]  D. Richter,et al.  How Is the Respiratory Rhythm Generated? A Model , 1986 .

[32]  Paul S. G. Stein,et al.  The Forms of a Task and Their Blends , 1986 .