Principles of motor organization of the monkey cervical spinal cord

Abstract

The organization of spinal cord motor columns innervating 18 selected macaque forelimb muscles was studied with the technique of retrograde transport of horseradish peroxidase. The reliability of the method was evaluated in the cat hindlimb.Motor columns innervating forearm muscles with similar actions on the hand appear to overlap in the anterior horn. Extensor motoneurons are generally positioned ventral and/or lateral to flexor motoneurons. Motoneurons controlling hand movement are located primarily in segments C8 and Tl.Motoneurons that innervate individual muscles are arranged in rostrocaudal columns in the anterior horn of the spinal cord. The segmental localization of motor columns innervating primate forelimb muscles was originally described by Sherrington (1898) in studies involving stimulation of individual ventral nerve roots. Although the somatotopic organization of motor columns in the anterior horn has been reported for the cat lumbosacral cord (Romanes, 1951;Burke et al., 1977;Sato et al., 1978), the only topographical data available for the monkey cervical cord relate to the distribution of motoneurons that contribute to individual ventral roots (Sprague, 1948) and major peripheral nerves (Reed, 1940).In the present study we sought to determine both the segmental and topographical organization of individual motor columns involved in controlling hand movement in the monkey. The retrograde transport of horseradish peroxidase (HRP) from selected muscles to motoneurons was used (Burke et al., 1977;Sato et al., 1978;Richmond et al., 1978; Matusda et al., 1978;Landmesser, 1978). Materials and MethodsThe studies were carried out in 10 Macaca mulatta and 4 M. fuscicularis monkeys of both sexes (2.9 to 4.2 kg). The reliability of the method was first evaluated in the cat.Injection barbiturate anesthesia the desired muscle was exposed and, with the use of an operating microscope, was carefully dissected from surrounding muscles. Care was taken to preserve the neurovascular pedicle. Muscles were identified by anatomic position, tendinous insertion, and when necessary, by electrical stimulation of the muscle (Hartman and Straus, 1933). The muscles were injected from a 27 gauge needle over 15 min at multiple sites with a saline solution of HRP (25,000 units/ml, Sigma HRP type VI, St. Louis, MO). Sufficient HRP was injected to render each muscle a dark brown color. To prevent the spread of HRP to adjacent muscles, Silastic and cotton barriers were positioned between the muscle to be injected and the surrounding muscle groups. The tissues surrounding the injected muscle were irrigated frequently with normal saline after the injection. By 3 hr, the injected muscle had returned to a more normal appearance and visible HRP leakage had stopped. Less frequent irrigation was continued for approximately 12 hr postinjection and the Silastic and cotton barriers remained in place for the duration of the experiment. Study of the spinal cord. After 48 hr under anesthesia, each animal was heparinized and perfused th...

Tension Distribution of Single Motor Units in Multitendoned Muscles: Comparison of a Homologous Digit Muscle in Cats and Monkeys

“…Because of conduction block, 34 MUs were stimulated in the radial nerve in the upper arm or forearm. Of the 23 MUs stimulated in the ventral roots, 1 was in spinal segment C7, 18 were in C8, and 4 were in T1, consistent with segmental location of motoneuron columns for other macaque extrinsic finger muscles (Jenny and Inukai, 1983). Data from the one cynomologous monkey were similar to data from the three rhesus monkeys, and data from both species, therefore, were pooled for analysis.…”

Motoneuron Death after Human Spinal Cord Injury

“…Multi-segmental destruction of motor axons will denervate some muscles completely and irreparably because motor pools typically span 1-3 spinal levels in humans, 38 as they do in the macaque. 39 Complete, chronic denervation is consistent with the inability to excite various muscles after injury using peripheral nerve stimulation.…”

Progressive plastic changes in the hand representation of the primary motor cortex parallel incomplete recovery from a unilateral section of the corticospinal tract at cervical level in monkeys

“…From previously available anatomical material, the rostro-caudal level where the dorsal rootlets entering respectively the 7 th and the 8 th cervical spinal segments meet was determined, corresponding to the rostral zone of the spinal portion covered by the 6 th cervical lamina. The aimed lesion was located caudal with respect to the pool of biceps motoneurones but rostral to the pool of triceps, forearm and hand muscle motoneurones [18]. The muscles and the skin were sutured.…”