Lower Cervical Levels Research Articles

Changes in sensorimotor sleep spindle activity and seizure susceptibility after somatosensory deafferentation

This investigation examined the effects of dorsal column transections on susceptibility to monomethylhydrazine (MMH)-induced seizures and sensorimotor EEG sleep spindle activity in the cat. Eleven animals, prepared with indwelling cortical electrodes over hind limb and forelimb projection areas of somatosensory cortex, received bilateral lesions of the dorsal columns at either high (C 1–C 3) or low (C 5-T 1) cervical spinal levels. After a 3-week recovery period, each animal was administered a convulsive dose of MMH. Seizure susceptibility was measured in terms of latency to onset of tonic-clonic convulsions. Sensorimotor 12- to 15-Hz sleep spindle activity was assessed in comparable segments of the pre- and postlesion EEG. Results showed a progressive and significant decrease in seizure susceptibility with successively more encephalad dorsal column transections. The EEG data showed significant postlesion enhancements of sleep spindle activity over cortical sites roughly corresponding to peripheral receptive fields below the level of the lesions. Results suggested an association between the extent of spindle enhancement and the magnitude of MMH seizure response attenuation. This finding was consistent with previous reports indicating a relationship between rhythmic 12- to 15-Hz sensorimotor EEG activity and central inhibitory processes.

External nucleus of inferior colliculus: auditory and spinal somatosensory afferents and their interactions.

1. The discharges of 129 units were studied in the external nucleus of the inferior colliculus of 11 anesthetised and paralyzed cats. This region is known to receive fibers from auditory nuclei and the dorsal column nuclei. 2. Stimuli used were pure tone bursts, monaural or binaural, tactile stimulation of the body surface, and electrical stimulation of the dorsal columns (DC) at a low cervical level and of the contralateral and ipsilateral tibial nerves. 3. Forty-six percent of units were only influenced by one type of stimulation (26% auditory, 20% DC). Of the remaining bimodally influenced units, the majority was excited by pure tone stimuli and inhibited by DC stimulation. 4. A small proportion of the total population (18%) was excited by both DC and auditory input, and units sensitive to both tones and tactile stimulation of the skin were rare (4%). 5. Auditory tuning curves were generally very broad compared with those of units in the central nucleus of the inferior colliculus. Similarly, somatic receptive fields were large and usually extended over a whole limb. 6. The majority of tone-responsive units were influenced binaurally (70%); most somatic receptive fields were located on the contralateral fore- or hindlimb (16/18). 7. The results indicate that both auditory and somatosensory information is contained in the discharges of units in the external nucleus of the inferior colliculus. 8. Speculations are made about the role of this nucleus in descending auditory input to the spinal cord and in the comparison of auditory and cutaneous information during sound-evoked coordinated body movements.

Effects of various lesions on crossed and uncrossed descending inspiratory pathways in the cervical spinal cord of the cat.

✓ Various cervical spinal cord lesions interrupting portions of the descending respiratory pathways were made in 12 cats. Results suggest: 1) that the descending inspiratory pathways lie in the ventrolateral portion of the high cervical spinal cord; 2) that a decussation of these pathways exists between the low medullary and high cervical level; 3) that fibers descend via both crossed and uncrossed pathways along the length of the cervical cord to innervate phrenic nuclei bilaterally; 4) that activity in the crossed pathway running along the length of the cervical cord is related to the level of PaCO2.

Direction of blood flow in the primate cervical spinal cord.

✓ The direction of blood flow in the cervical spinal cord of monkeys was studied by direct cinematic observation of the results of dye injections, plus separate angiographic studies. The studies indicated that in monkeys blood enters the cervical spinal cord mainly from radicular arteries that are usually derived from branches of the costo-cervical trunk. Although some blood entering at the low cervical level flows toward the thoracic cord, the major component flows up to the C-2 level. The findings cast doubt on the established assumption that the vertebral arteries provide the main blood supply of the cervical cord.

HUMAN SPINAL CORD IMPEDANCE: ITS APPLICATION IN NEUROSURGICAL STEREOTAXIC CORDOTOMY

INTRODUCTION Surgical access to the central nervous system has, for the most part, been obtained through operations that provide wide exposure and direct visualization of the target area. However, the application of radiologic and electrophysiologic techniques to neurosurgery permit reduction of the magnitude of the operative exposure without sacrifice of any of the surgical goals. Operations to relieve pain are based on our knowledge of “pain pathways,” which is admittedly imperfect. The relief of suffering remains one of the first responsibilities of the physician. While acute pain may act as a warning signal, chronic pain serves no such useful purpose and may lead to total incapacitation of the patient. This is true whether the pain is caused by malignancy or by an otherwise harmless condition. Surgical destruction by cordotomy of the pain pathway in the spinal cord (the lateral spinothalamic tract) has been used for more than 50 years to treat intractable pain states.ls2 The recent conversion of a cordotomy from an open visual procedure to a closed stereotaxic procedure has extended the benefits of cordotomy to many more patients,3 but to reduce the hazard of this technique it is necessary that the four steps of stereotaxic surgery be followed: 1) definition of the radiologic coordinates of the target; 2) the use of a precision apparatus to approach the target; 3) physiologic confirmation of the target; and 4) precise destruction of the target. To eliminate any one of these steps is to increase the hazard to the patient. THE TARGET Destruction of the lateral spinothalamic tract of the second cervical cord segment usually results in a contralateral loss of superficial pain, temperature, deep pain, and visceral pain below a level of C3 or C4. The hazards of cordotomy at this level are chiefly due to anatomic variation and the proximity of other important pathways as well as the variation in the position of the tracts with the size and position of the motor decussation (FIGURES 1 & 2). A descending respiratory pathway, the ventrolateral reticulospinal tract, is probably intermingled with and deep to the fibers of the anterior part of the lateral spinothalamic tract. Unilateral destruction of this pathway results in little functional respiratory loss unless contralateral respiratory function is poor. Bilateral lesions involving the anterior portion of the lateral spinothalamic tract have been extremely dangerous in that patients may lose their ability to breathe while sleeping. For bilateral pain relief, a stereotaxic cordotomy may be performed at C2 and 7-10 days later at a lower cervical level by the anterior technique of Lin and co-workers.6 A variation in the level of the motor decussation that usually extends from the obex to the C1 level and the presence of aberrant corticospinal tracts may pose additional hazards.