Electrical Root Stimulation Research Articles

The Results of Intraoperative Direct Electrical Stimulation of Roots and Placode During Myelomeningocele Repair

The Results of Intraoperative Direct Electrical Stimulation of Roots and Placode During Myelomeningocele Repair

Evaluation of proximal and distal motor nerve conduction using the electrical root stimulation technique in the femoral and obturator nerves.

This study aimed to investigate the adaptability of the electrical root stimulation technique by achieving normative data from the obturator and femoral nerves of healthy dogs. For this purpose, two stimulations and recordings were performed on both the obturator and femoral nerves in 40 dogs (22 males and 18 females). Electrical root stimulation was applied via monopolar needle electrodes between the sixth to seventh and fifth to sixth lumbar interarcuate spaces to the obturator and femoral nerves, respectively. Muscle waves were recorded from the gracilis and sartorius muscles of the left and right pelvic limb. The proximal motor nerve conduction velocity was 60.89 ± 3.93 m/s and 59.87 ± 4.83 m/s in the obturator and femoral nerves, respectively. Our results showed that electrical root stimulation could be a useful method to test the integrity of the roots of obturator and femoral nerves and their proximal parts.

Electrical stimulation of lumbar spinal nerve roots in dogs.

The aim of this study was to test the applicability of electrical stimulation of lumbar spinal nerve roots and obtain normative electrical root stimulation (ERS) data for L7 nerve root and sciatic nerve in dogs. For that purpose ERS and sciatic nerve stimulations were performed consecutively, in totally 40 healthy dogs. ERS was applied in the L7/S1 intervertebral space via monopolar needle electrodes. Muscle responses were recorded from the gastrocnemius muscles on the left and right hind limbs. Sciatic nerve stimulation was performed at the greater trochanter level on the left hind limb, with records obtained from the left gastrocnemius muscle. Mean root latencies of the left and right side were 5.22 ± 0.49 ms and 5.29 ± 0.53 ms, respectively. There was no significant difference in root latency between the right and left sides. The mean terminal latency was 3.82 ± 0.46 ms. The proximal motor nerve conduction velocity of the sciatic nerve was 63.15 ± 3.43 m/s. The results of this study show that ERS provides objective data about the integrity of lumbar spinal nerve roots by evaluating the entire population of motor fibres and total length of the motor axon in dogs. ERS can be considered a useful diagnostic method for confirmation of diagnoses of lumbosacral diseases.

Basic methodological principles of multimodal intraoperative monitoring during spine surgeries.

In the very early stages of development Intraoperative Neurophysiology (ION), somatosensory evoked potentials (SEPs) was the only available modality for monitoring functional integrity of the spinal cord and was used for many years in USA, Europe and Japan. This uni-modality approach very soon showed many disadvantages: it was nonspecific for the motor tracts, sensitive to inhalation anesthetics, needed relatively long time to update data, and patients with spinal cord pathology would sometimes have low quality of SEPs. Neuroanesthesia at that time, 30 years ago, was mainly based on inhalational anesthetics, the “deadly enemy” for SEPs when used with a higher amount of minimal alveolar concentration. An early report by Lesser et al. [10], showed that injury to the motor tracts of the spinal cord can happen with no changes within the parameters of SEPs. This first observation is later on confirmed by excellent and very well documented examples by Pelosi et al. [16], Minahan et al.[ 12], Jones et al. [9]. To avoid the influence of anesthetics and to show other advantages of direct recordings of traveling and stationary waves of SEPs, a team led by Dr. S. Jones from the UK, introduced monitoring of SEPs by the catheter-electrode in Europe placed in the epidural space of the spinal cord [7]. As highly and reliable this technique was it didn’t gain popularity as an intraoperative monitoring method of SEPs because of the relative invasiveness. During the process of developing different methods for spinal cord monitoring, there were many trials and errors, but probably the most challenging one was when the intraoperative monitoring method of “neurogenic motor evoked potentials” (NMEPS) was introduced [13]. This method was based on the translaminar electrical stimulation of the spinal cord and recording time locked electrical activity over peripheral nerves, mainly of the low extremities. The author of this method claimed that activity recorded from limb muscles represented motor evoked potentials. Later on, collision studies [21] and unfortunate postoperative paraplegic patients with preserved NMEPS showed that this activity was mostly an antidromic stimulation of the dorsal columns. Therefore, it might be used for monitoring the functional integrity of the dorsal, but not for lateral columns [5, 12]. In search of a more specific monitoring method for the functional integrity of the spinal cord’s motor tracts, Machida et al. [11] introduced a method of electrical stimulation of the spinal cord and recording activity over the limb muscles. The breakthrough in ION of the spinal cord took place by introducing methods of intraoperative monitoring of the motor evoked potentials (MEPs), eliciting them by applying single transcranial electrical stimulus and recording D wave from the vicinity of the spinal cord [1]. Using a technique of short train of stimuli, instead of single stimulus, Taniguchi and colleagues, elicited MEPs by direct stimulation of the exposed motor cortex [20] or transcranially and recording them from the limb muscles [15]. An important milestone in the preservation of spinal roots is the development of methodology for electrical stimulation of roots during placement of pedicle screws [2, for review see 22]. In this paper we will describe the methodological aspects of: (a) motor evoked potentials (MEPs) elicited by transcranial electrical stimulation (TES), (b) muscle activity after electrical stimulation of the spinal cord and (c) pedicle screw stimulation. The methodological aspect of intraoperative monitoring with somato-sensory evoked potentials is described in this issue by MacDonald. The importance of combining the use of multimodal evoked potentials during spinal cord surgeries has been addressed by Sala et al., in this issue as well.

Brain-derived neurotrophic factor induces NMDA receptor subunit one phosphorylation via ERK and PKC in the rat spinal cord.

Brain-derived neurotrophic factor (BDNF) is involved in the modulation of synaptic transmission in the spinal cord, and several circumstantial lines of evidence suggest that it has the ability to modulate the activity of the NMDA receptor. Here we dissect the signalling mechanisms by which BDNF exerts its neuromodulatory role on the NMDA receptor subunit 1 (NR1). Using a preparation of adult isolated dorsal horn with dorsal roots attached, we found that electrical stimulation of roots induced a concomitant release of BDNF and an increased phosphorylation of NR1, which was partly prevented by the BDNF sequestering molecule, TrkB-IgG. Using a second approach in vitro, we confirmed that both exogenous glutamate and BDNF (but not other neurotrophins) were able to induce NR1 phosphorylation, in particular at residue Ser-897. NR1 phosphorylation induced by BDNF was blocked by a TrkB inhibitor, an ERK inhibitor and a PKC inhibitor but not a PKA inhibitor. Activation of PKC using exogenous PMA also led to NR1 phosphorylation. Together these data suggest that BDNF modulates the activity of the receptor by phosphorylation via the kinases ERK and PKC.

The relation between conduction velocity and axonal length.

Motor evoked potentials (MEPs) obtained by electrical root stimulation and F waves were used to examine the proximal nerve conduction velocity (CV) to tibialis anterior (TA), extensor digitorum brevis (EDB), flexor carpi radialis (FCR), and abductor pollicis brevis (APB) muscles in 40 humans. By subtracting motor latencies obtained by stimulating the peripheral nerve at the same point from the F-wave and MEP latencies, we could measure the CV over identical proximal segments. It was found that proximal CV to TA and FCR was significantly higher than to EDB and APB, respectively. Combining the data of the proximal CV to all four muscles in relation with axonal length resulted in a highly significant inverse relationship (r2 = 0.77). Thus the axonal length explained to a large extent the higher CV of the arm nerves and also the inverse relation between body height and CV. The distal CV was always lower than proximal CV; however, there was no support for an additional effect of this gradient in explaining the relationship between CV and height since it was constant for all body heights.

C2 and C3 Pain Dermatomes in Man

This report defines the C2 and C3 pain dermatomes by the distribution of: the hypalgesia clearing after surgical root decompression; the dysaesthesias produced by electrical root stimulation; and the hypalgesia produced by anaesthetic root block. The C2 pain dermatome, so defined, consists of an occipital parietal area 6-8 cm wide, ascending paramedially from the subocciput to the vertex. The C3 pain dermatome is a craniofacial area including the scalp around the ear, the pinna, the lateral cheek over the angle of the jaw, the submental region and the lateral and anterior aspects of the upper neck. These C2 and C3 pain dermatomes do not overlap and are smaller than the C2 and C3 tactile dermatomes described in the literature.

Spinal cord stimulation in patients with a battered root syndrome.

Sixteen patients suffering from pain due to a "battered" root syndrome (BRS) [1] were treated with spinal cord stimulation (SCS). All patients had undergone spinal surgery and complained of severe intractable radicular pain. The myelograms revealed an amputated root, the computerized tomograms showed periradicular scar tissues, electromyograms and/or sensory evoked potentials showed pathological changes. Electrical root stimulation via an indwelling, Teflon-coated needle reduced pain significantly within 30 min (80-100 Hz, 0.2-0.3 V). Root blocks with 1 ml bupivacaine (0.5%) abolished the patient's pain completely. No patient revealed major psychosomatic or psychosocial problems. Employing this patient selection schedule, 75% of the patients were pain-free after a mean follow-up period of 16 months range 6-30.

Intrasegmental inhibition of the displacement-sensitive pathway in the crayfish (Procambarus clarkii)

1. Inhibition across the body median ofProcambarus was investigated using fluid movement as stimulus. The medially cut tailfan with connected isolated ventral cord was mounted in two compartments of the dissection dish in order to stimulate selectively each side of the fan (Fig. 1). 2. Higher order interneurons (as inferred by latency of response to electrical root stimulation and response behavior) of the fluid-movementmonitoring pathway are subject to much stronger inhibitory influences than are lower order interneurons. 3. Among the interneurons strongly inhibited by contralateral stimuli two groups are established: fibers that receive unilateral input and others that receive excitatory input from both sides of the body. The group of ‘bilaterals’ receives stronger inhibition than do fibers with unilateral excitation. 4. Inhibitory circuits crossing the median line of the body are functionally subdivided so as to convey inhibition only between interneurons of the same vector polarity. 5. The strong inhibitory influence (in the average 80% reduction of a response to an exclusively ipsilateral stimulus of comparable strength) observed in fibers with bilateral input suggests that the function of such interneurons in this system of orientation to the signal source is the indication of fluid movement parallel to the long axis of the body using a method comparable to the balancing of a bridge circuit.