The specific aims of the project are: 1. What is the role of propriospinal interneurons located rostral to the cervical enlargement in the control of primate arm and hand movements? 2. How are motoneuron and interneuron excitability regulated during normal movements by inhibitory mechanisms in the spinal cord? 3. Is the normal activity of spinal motoneurons during voluntary movement dependent on the action of monoamines? The activity of cervical neurons will be recorded during voluntary reaching, isolated wrist movements, and cocontraction of flexor and extensor muscles of the wrist in the awake monkey. Inhibitory and neuromodulator inputs to spinal neurons will be manipulated with local iontophoresis of pharmacological agents that activate or block serotonin, noradrenaline, GABA or glycine receptors. Input and output connections of interneurons will be identified with spike-triggered averages of EMG and natural and electrical stimulation of peripheral afferents and descending pathways. These studies will elucidate the mechanisms by which the excitability of interneurons and motoneurons are controlled during voluntary movements and lay the foundation for future studies on the mechanisms of motor dysfunction and recovery from injury.

Thesaurus Terms:
arm, limb movement, neural initiation, spinal cord, spinal cord injury
afferent nerve, electrostimulus, gamma aminobutyrate, glycine, hormone receptor, hormone regulation /control mechanism, interneuron, motor neuron, neural inhibition, norepinephrine, serotonin Macaca mulatta, Macaca nemestrina, electromyography, nontherapeutic iontophoresis

Institution: UNIVERSITY OF WASHINGTON
Office of Sponsored Programs, SEATTLE, WA 98105
Fiscal Year: 2006
Department: PHYSIOLOGY AND BIOPHYSICS
Project Start: 28-SEP-2000
Project End: 31-AUG-2010
ICD: NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE
IRG: SMI

The Journal of Neurophysiology Vol. 80 No. 5 November 1998, pp. 2475-2494 Copyright ©1998 by the American Physiological Society

Activity of Spinal Interneurons and Their Effects on Forearm Muscles During Voluntary Wrist Movements in the Monkey

Steve I. Perlmutter, Marc A. Maier, and Eberhard E. Fetz

During training and recording sessions, the monkeys sat upright in a primate chair adjusted for each animal. The working arm was restrained with the elbow bent at 90°. The hand was held with the fingers straight and the wrist in the midsupination/pronation position. The flexion/extension axis of the wrist was aligned with the shaft of a torque transducer. The other arm was restrained loosely.

Behavioral paradigm
The monkeys were trained to generate isometric, ramp-and-hold flexion and extension torques about the wrist. Torque controlled the position of a cursor on a video screen in front of the animal. To obtain a fruit juice or applesauce reward, the monkeys held the cursor for 1.5-2 s within a target window that specified a given flexion or extension torque 0.2 N-m. For animals B and R, the target windows alternated back and forth between fixed flexion and extension levels. These animals produced ramp-and-hold torques in each direction starting from a maintained torque in the opposite direction (Fig. 1A). Monkey W began each trial by positioning the cursor within a center target window, corresponding to zero torque, for 1-4 s. Then a target window appeared at one of six positions randomly selected from three flexion and three extension levels. Monkey W produced ramp-and-hold torques in each direction starting from rest

Surgical implants
All surgeries were performed with the use of aseptic techniques with the animals under 1-1.5% halothane or isoflurane anesthesia after training was completed. Atropine sulfate was administered preoperatively; antibiotics (cefazolin, 25 mg/kg) and analgesics (ketoprofen, 5 mg/kg) were given postoperatively. Head stabilization lugs were cemented to the exposed skull with dental acrylic, which was anchored to the bone with screws.

A stainless steel recording chamber was implanted over the lower cervical spine (Fig. 2). Following a midline incision, soft tissue was retracted to expose the lateral masses of the midcervical to upper thoracic vertebrae. The dorsal spinous processes of the C4-T2 vertebrae were removed and a unilateral laminectomy of C5-T1 was performed. Each lamina was removed with a rongeur from its junction with the facet to just past the midline. Bone screws were introduced into the vertebrae, and the recording chamber was positioned over the laminectomy and cemented in place with dental acrylic. The skin and underlying soft tissue were pulled tightly in layers around the chamber with purse-string sutures. The outer surface of the skin was held in contact with the underside of a small flange near the top of the chamber, protecting the exposed skin margin. The chamber was closed at all times with a protective cap except during recording sessions.

In monkeys B and R, vitalium screws were inserted into the intact C4-T2 laminae and the implant remained stable for ~2 mo. In monkey W, the stability of the implant was extended to 6 mo with the surgical technique of Anderson et al. (1991) (Fig. 2).
 
The implant procedure fused the C4-T2 vertebrae. After recovery from surgery, the monkeys exhibited a stiffened posture of the upper back, but showed no signs of discomfort nor any neurological symptoms. The animals' behavior in their home cages returned to near normal and their performance at the trained task quickly reached preoperative levels.

Bipolar electromyographic electrodes were implanted in 10-14 forearm muscles. In monkey W, patch electrodes (Microprobe, Clarksburg, MD) and multistranded stainless steel wires were sutured to surgically exposed muscles with the monkey under isoflurane anesthesia. Connecting wires were led subcutaneously to a multicontact socket connector cemented to the skull. In monkeys B and R, wire pairs were inserted transcutaneously with the animals under ketamine anesthesia; external wires and connectors were taped to the upper arm and concealed in a jacket worn by the monkey. Replacement of transcutaneous electrodes every 2-4 wk ensured recording quality.

Muscles were identified on the basis of their anatomic location and characteristic movements elicited by trains of low-intensity intramuscular stimuli. Pairs of electrodes were implanted in primary extensor and flexor muscles of the wrist: extensor carpi ulnaris (ECU), extensor carpi radialis (ECR), extensor digitorum communis (EDC), extensor digitorum-2,3 (ED-2,3), extensor digitorum-4,5 (ED-4,5), flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), flexor digitorum profundus (FDP), flexor digitorum superficialis (FDS), and palmaris longus (PL). Other muscles with secondary actions at the wrist were recorded frequently. Pronator teres (PT) was active primarily in flexion, abductor pollicis longus (APL) and supinator (SUP) were active primarily in extension, and brachioradialis (BR) was active in either or both directions for different animals.

Recording procedure
During recording sessions, the head and vertebral implants were secured to the primate chair with nylon screws. The implants were held firmly, but both restraints were somewhat flexible, allowing the animal to make small postural adjustments. Monkey B received occasional intramuscular injections of diazepam (2-4 mg) to eliminate excessive movements that jeopardized stable neuronal recordings. These procedures were well tolerated: all monkeys moved voluntarily from their home cages and seated themselves in the primate chair for each day's session.

An X-Y positioning stage and microdrive were mounted on the chamber (Fig. 2). Activity of neurons in the C6-T1 spinal segments was recorded extracellularly with glass-insulated tungsten or Elgiloy electrodes advanced through the dura mater under direct visual observation through a dissecting microscope. Neurons were isolated while the monkey performed the isometric wrist task for 2-5 h/day. Stable recordings of individual neurons could be maintained for >30 min when the monkey sat quietly. As many as 100 tracks were made in each animal during a period of 2-6 mo. None of the animals exhibited observable behavioral deficits at any time.