Effects of Red Nucleus Microstimulation on the Locomotor Pattern and Timing in the Intact Cat: A Comparison With the Motor Cortex

Abstract

Effects of red nucleus microstimulation on the locomotor pattern and timing in the intact cat: a comparison with the motor cortex. To determine the extent to which the rubrospinal tract is capable of modifying locomotion in the intact cat, we applied microstimulation (cathodal current, 330 Hz; pulse duration 0.2 ms; maximal current, 25 microA) to the red nucleus during locomotion. The stimuli were applied either as short trains (33 ms) of impulses to determine the capacity of the rubrospinal tract to modify the level of electromyographic (EMG) activity in different flexors and extensors at different phases of the step cycle or as long trains (200 ms) of pulses to determine the effect of the red nucleus on cycle timing. Stimuli were also applied with the cat at rest (33-ms train). This latter stimulation evoked short-latency (average = 11.8-19.0 ms) facilitatory responses in all of the physiological flexor muscles of the forelimb that were recorded; facilitatory responses were also common in the elbow extensor, lateral head of triceps but were rare in the physiological wrist and digit extensor, palmaris longus. Responses were still evoked in most muscles when the current was decreased to near threshold (3-10 microA). Stimulation during locomotion with the short trains of stimuli evoked shorter-latency (average = 6.0-12.5 ms) facilitatory responses in flexor muscles during the swing phase of locomotion and, except in the case of the extensor digitorum communis, evoked substantially smaller responses in stance. The same stimuli also evoked facilitatory responses in the extensor muscles during swing and produced more complex effects involving both facilitation and suppression in stance. Increasing the duration of the train to 200 ms modified the amplitude and duration of the EMG activity of both flexors and extensors but had little significant effect on the cycle duration. In contrast, whereas stimulation of the motor cortex with short trains of stimuli during locomotion had very similar effects to that of the red nucleus, increasing the train duration to 200 ms frequently produced a marked reset of the step cycle by curtailing stance and initiating a new period of swing. The results suggest that whereas both the motor cortex and the red nucleus have access to the interneuronal circuits responsible for controlling the structure of the EMG activity in the step cycle, only the motor cortex has access to the circuits responsible for controlling cycle timing.

Contribution of the Motor Cortex to the Structure and the Timing of Hindlimb Locomotion in the Cat: A Microstimulation Study

“…Data were analyzed as previously described (Rho et al 1999). In brief, the data obtained with the cat at rest were computer-rectified and averaged.…”

“…There is abundant evidence from lesion (Adkins et al 1971;Chambers and Liu 1957;Liddell and Phillips 1944;Kuypers 1963), single-unit recording (Amos et al 1990;Armstrong 1986;Beloozerova and Sirota 1993;Drew 1988Drew , 1993, and intracortical microstimulation (ICMS) (Armstrong and Drew 1985b; Rho et al 1999) studies that the motor cortex makes an important contribution to the control of the forelimb during locomotion in cats, particularly in situations that require a fine control over paw placement or limb trajectory.…”

“…For instance, although several studies suggest a differential contribution to the control of the proximal and distal hindlimb in non-human primates (Hatanaka et al 2001;Wise and Tanji 1981) and rats (Donoghue and Wise 1982;Neafsey et al 1986), one of the major studies in the cat reports that the motor cortex exerts a global influence on the hindlimb in its entirety (Nieoullon and Rispal-Padel 1976). Moreover, although stimulation of the motor cortex has been demonstrated to reset the locomotor rhythm in reduced preparations (Degtyarenko et al 1993;Leblond et al 2001;Orlovsky 1972), there is little indication whether this is so in the intact animal or whether the nature of the resetting is similar to that observed during stimulation of the forelimb representation of the motor cortex (Rho et al 1999).…”

Individual Premotor Drive Pulses, Not Time-Varying Synergies, Are the Units of Adjustment for Limb Trajectories Constructed in Spinal Cord

“…Separable rhythmogenic circuits and pattern forming circuits have been proposed for respiration (Feldman et al, 1988), turtle scratch (Lennard, 1985), cat-paw shake (Koshland and Smith, 1989), and cat locomotion (Prochazka, 1996;Rho et al, 1999;Quevado et al, 2005;Stecina et al, 2005;McCrea and Rybak, 2007). Timed synergies have been identified in locomotion in cats (Krouchev et al, 2006) and in human studies (Cappellini et al, 2006).…”

Spatial Segregation of Different Modes of Movement Control in the Whisker Representation of Rat Primary Motor Cortex

“…A closer look to the mammalian motor system suggests that this question is reasonable, because the use of the same motor periphery using presumptively different access routes is the rule rather than an exception. For instance, most of so-called "semiautomatic" movements (e.g., defense, righting, licking, mastication, and locomotion) are speculated to use CPGs downstream from M1 (Orlovsky, 1972;Lund and Lamarre, 1974;Armstrong and Drew, 1984;Moriyama, 1987;Huang et al, 1989;Zhang and Sasamoto, 1990;Rho et al, 1999;Cooke and Graziano, 2004). However, the very same body parts involved in semiautomatic movements can be moved in a nonautomatic, "arbitrary" way, most likely using different signaling routes.…”