Segmental Spinal Cord Potentials Research Articles

Somatosensory evoked potentials recorded from the posterior pharynx to stimulation of the median nerve and cauda equina

Somatosensory evoked potentials (ppSEPs) in response to stimulation of the median nerve at the wrist and the cauda equina at the epidural space (the L4 level) were recorded from the posterior wall of the pharynx in 15 patients who underwent spinal surgery under general anesthesia, using disc electrodes attached to the endotracheal tube, and compared with segmental spinal cord potentials (seg-SCPs) that were recorded simultaneously from the posterior epidural space (PES). ppSEPs consisted of the initially positive spike (P9) followed by slow positive (P13) and negative (N22) waves. The P13 and N22 of ppSEPs had phase reversal relationship with the P2 and N2 recorded from the PES, respectively. The peak latencies of P9 (9.40 ± 0.7 ms) (mean ± SD), P13 (13.1 ± 0.9 ms), and N22 (22.0 ± 2.1 ms) of ppSEPs coincided with those of P1, N1 and P2 of seg-SCPs, respectively. ppSEPs were recorded more clearly with a reference electrode on the dorsal surface of the neck than with the reference electrode at the earlobe or back of the hand. The threshold and maximal stimulus intensities were also similar between the ppSEPs and seg-SCPs. Thus, the P9, P13, and N22 components of ppSEPs were thought to have the same origin as the P1, N1 and P2 of seg-SCPs, respectively. Therefore, the P9, P13 and N22 of ppSEPs may reflect incoming volleys through the root, synchronized activities of the interneurons and primary afferent depolarizations (PAD), respectively. ppSEPs in response to cauda equina stimulation showed that the latencies of the two initial components (4.6 ± 0.4 and 6.4 ± 0.6 ms) corresponded to those of the SCPs recorded from the PES (4.6 ± 0.3 and 6.3 ± 0.5 ms), suggesting that these potentials reflect impulses conducting through the spinal cord, similar to epidurally recorded SCPs.

Somatosensory evoked potentials recorded from the posterior pharynx to stimulation of the median nerve and cauda equina

Somatosensory evoked potentials (ppSEPs) in response to stimulation of the median nerve at the wrist and the cauda equina at the epidural space (the L4 level) were recorded from the posterior wall of the pharynx in 15 patients who underwent spinal surgery under general anesthesia, using disc electrodes attached to the endotracheal tube, and compared with segmental spinal cord potentials (seg-SCPs) that were recorded simultaneously from the posterior epidural space (PES). ppSEPs consisted of the initially positive spike (P9) followed by slow positive (P13) and negative (N22) waves. The P13 and N22 of ppSEPs had phase reversal relationship with the P2 and N2 recorded from the PES, respectively. The peak latencies of P9 (9.40 ± 0.7 ms) (mean ± SD), P13 (13.1 ± 0.9 ms), and N22 (22.0 ± 2.1 ms) of ppSEPs coincided with those of P1, N1 and P2 of seg-SCPs, respectively. ppSEPs were recorded more clearly with a reference electrode on the dorsal surface of the neck than with the reference electrode at the earlobe or back of the hand. The threshold and maximal stimulus intensities were also similar between the ppSEPs and seg-SCPs. Thus, the P9, P13, and N22 components of ppSEPs were thought to have the same origin as the P1, N1 and P2 of seg-SCPs, respectively. Therefore, the P9, P13 and N22 of ppSEPs may reflect incoming volleys through the root, synchronized activities of the interneurons and primary afferent depolarizations (PAD), respectively. ppSEPs in response to cauda equina stimulation showed that the latencies of the two initial components (4.6 ± 0.4 and 6.4 ± 0.6 ms) corresponded to those of the SCPs recorded from the PES (4.6 ± 0.3 and 6.3 ± 0.5 ms), suggesting that these potentials reflect impulses conducting through the spinal cord, similar to epidurally recorded SCPs.

Erb's point stimulation produces slow positive potentials in the human lumbar spinal cord.

Evoked spinal cord potentials (SCPs) were recorded from the posterior epidural space (PES) at the cervical and lumbrosacral enlargements in response to electrical stimulation of the brachial plexus at Erb's point in 17 chronic pain patients. Erb's point stimulation produced slow positive potentials (heterosegmental slow positive potentials, HSPs) in the PES at the lumbrosacral enlargement in all 13 subjects without spinal cord lesions but not in 4 subjects with spinal cord lesions. The HSP1 with a central peak latency of 21 +/- 2 ms (mean +/- SE) was recorded at the stimulus intensity up to two to three times the threshold strength (T) of the initially positive spike (P1) of the segmental SCP, which was simultaneously recorded from the PES at the cervical enlargement. At the stimulus intensity of more than 3T, another slow positive potential (HSP2) with central peak latency of 71 +/- 6 ms was recorded. These slow positive potentials (HSP1 and HSP2) might be produced by a feedback loop via supraspinal structures, presumably primary afferent depolarizations, in comparison to the HSPs of our previous studies in the rat. Slow negative potentials were sometimes noted before (5 of 13) and/or after (2 of 13) the HSP1. These slow negative potentials probably reflect the activities of dorsal horn neurons producing the HSP1 and HSP2, respectively, also elicited by a feedback loop via supraspinal structures.

Effects of dorsal root entry zone lesion on spinal cord potentials evoked by segmental, ascending and descending volleys.

The spinal cord potentials (SCPs) were recorded from the dorsal root entry zone (DREZ) and posterior epidural space in patients before and after dorsal root entry zone lesion (DREZL) during general anaesthesia. The SCPs from the DREZ activated by segmental, ascending and descending volleys were basically the same in fundamental waveform as those recorded from the posterior epidural space. Segmentally activated slow negative (N1) wave, reflecting synchronized activities of dorsal horn neurones, and positive (P2) wave, thought to indicate primary afferent depolarization, were affected by DREZL in all 4 subjects tested, even by contralateral stimulation, suggesting that these components of the segmental SCPs in man partly reflect the activities of the contralateral dorsal horn. The spike-like potentials activated by ascending volleys were not affected by DREZL, while the subsequent slow components were decreased in the lesioned level. This may indicate that ascending spinal cord tracts are not affected by the operation, and suggests that the origin of the slow components by ascending volleys lies at least in part in the segmental dorsal horn. The slow negative and positive components, recorded at a remote segment from DREZL, in response to the descending volleys, were augmented after DREZL, suggesting that activation of ascending or descending inhibition through a feedback loop via the supraspinal structures might occur at least transiently following DREZL. All components of the SCPs activated by descending volleys were decreased or disappeared in recording from the lesioned level, as expected. Thus, intra-operative recording of the SCPs during DREZL might be beneficial for monitoring and studying human spinal cord function.

Slow positive dorsal cord potentials activated by heterosegmental stimuli

Heterosegmental slow positive waves (HSPs) and segmental spinal cord potentials were recorded from the cord dorsum in ketamine-anesthetized rats. Forepaw stimulation produced HSPs in the lumbo-sacral enlargement (lumbar HSPs), whereas hind paw stimulation evoked HSPs in the cervical cord (cervical HSP). Both the HSP and the secondary component of the slow positive wave (P 2s) in the segmental spinal cord potential were highly vulnerable to anesthetics and completely disappeared after spinal cord transection at the C 1 2 level, indicating that both the HSP and P 2s are produced by a long feedback loop via supraspinal structures. The lumbar HSP evoked by forepaw stimulation was maximal in amplitude at the L 5 level and more dominant in the ipsilateral cord dorsum than in the contralateral one, but widely distributed in the lumbo-sacral cord. A variability of onset (7–18 msec for cervical and 5–17 msec for lumbar HSPs) and peak (22–35 msec for cervical and 12–50 msec for lumbar HSPs) suggests the existence of several nuclei to form the feedback loops for descending impulses to produce the HSPs. There were no peak latency differences between the HSP and P 2s. Since there were several similar characteristics between the P 2s and HSP such as high vulnerability to anesthetic, a complete disappearance after high spinal transection and similar response curves to graded intensities of stimulation, there may be a close relationship between their feedback nuclei and the pathways mediating them. All wide dynamic range (WDR) neurons ( 12 12 ) in lamina V of Rexed responded to heterosegmental stimulation with inhibition of firing. The time-course of inhibitio of WDR neurons was similar to that of the HSP from the same segment. These results suggest that the HSP reflects an inhibitory process, such as primary afferent depolarization, activated by a feedback loop via supraspinal structures.

Electrophysiological phenomena recorded from spinal cord slice preparation in the adult rat

The dorsal root potential (DRP-V) is believed to have the same origin as the slow positive potential of the segmental spinal cord potential. Furthermore it is also thought to be a reflection of primary afferent depolarization (PAD) which is an index of presynaptic inhibition1. It is believed that primary afferent terminals are depolarized by GABAergic neurons in the substantia gelatinosa (lamina-II). However, intracellular recording from substantia gelatinosa (SG) neurons has been impossible in vivo and very difficult in vitro, because of the high vulnerability of SG neurons to anoxic and mechanical damage in adult rat together with their small size. An in vitro spinal preparation has been developed in the newborn rat. However, it is known that the mode of synaptic transmissions in the adult rat is not the same as in the newborn rat2,3. We therefore developed an in vitro adult rat spinal cord slice preparation to achieve stable intracellular recordings from SG neurons simultaneously with electrotonic potentials from the dorsal root for studying the relationship between them.

Effects of Isoflurane on Spinal Inhibitory Potentials

The effects of isoflurane on segmental spinal cord potentials and heterosegmental slow positive potentials in response to fore- and hindpaw stimulation were studied in the rat. The heterosegmental slow positive potential and late (second) component of the slow positive wave (P2) of segmental spinal cord potential, thought to be primary afferent depolarization, an agent of presynaptic inhibition activated by a feedback loop via supraspinal structures, were greatly suppressed by the anesthetic. In contrast the negative wave (N1) of segmental spinal cord potential, believed to be synchronized activity of dorsal horn neurons, was only minimally affected. No differential effects of isoflurane on spinal cord potentials activated by fore- and hindpaws were found. Thus, the inhibitory activities of the spinal cord, particularly those produced by a feedback loop via supraspinal structures, are suggested to be highly vulnerable to isoflurane.

Epidural recording of root and segmental spinal cord potentials

Epidural recording of root and segmental spinal cord potentials

Comparison of the human evoked electrospinogram recorded from the intrathecal, epidural and cutaneous levels

In 30 patients (17 of whom had a clinically normal spinal cord) spinal cord potentials evoked by peripheral nerve stimulation were studied with computer averaging techniques in order to compare the intrathecal, epidural and skin records. In epidural and skin records, segmental spinal cord potentials either recorded from lower cervical or lower thoracic intervertebral levels often had similar shapes and latencies, especially with regard to the first component of the intrathecally recorded responses. The second slow component became less significant and was even absent in some cases. The amplitude of the first component was on average 33% of that recorded intrathecally when recorded epidurally and only 10% when recorded from the skin. In three cases potentials of very prolonged onset latency were recorded epidurally or cutaneously while in the same cases intrathecal records resulted in potentials with normal latencies. Cervical tract responses at the C6–C7 intervertebral level after stimulation of the posterior tibial nerve were studied by the 3 recording methods. Epidural and skin records failed to reveal such a response regularly, while intrathecal recording invariably provided the cervical tract response. The 3 recording methods were discussed with respect to clinical applications and research. It can be stated with some reservation that epidural and skin surface recording techniques could be exploited if one could know the time of arrival of segmental afferent inputs at the spinal cord.

Evoked electrospinogram in spinal cord and peripheral nerve disorders.

Spinal cord evoked potentials have been studied by means of intrathecal application in 80 patients with various spinal cord and peripheral nerve disorders. The segmental spinal cord potentials are normal in acute motor polyneuropathy, generalized anterior horn cell disease and in discrete lesions of dorso-lumbar segments. On the other hand, the first component of the segmental response is delayed, reduced and sometimes dispersed or lost in chronic sensory-motor polyneuropathy and in hereditary spinocerebellar degeneration. the reduction in amplitude is also present in multiple sclerosis with clinical signs of dorsal funiculus involvement. In compressive lesions of the cauda-conus, recordings of lower thoracic intervertebral level show that the segmental responses are delayed with marked amplitude reduction. The potentials recorded from lumbo-sacral segments show a greater the amplitude of the second component proportionally to the first one as the duration of second component is longer in spastic paraplegia regardless of its etiology. The cervical tractus response is seen to be markedly slowed with a reduction of amplitude or is often absent in chronic polyneuropathy, spinocerebellar degeneration and in multiple sclerosis. The primary sensory neurones lying both in periphery and in the dorsal column are assumed to be responsible for the segmental evoked potentials especially for the first component. the late slow component is related to the activation of interneurones situated within the segmental gray matter and segmental collaterals of the dorsal root fibres carrying impulses to those cells. Cervical tractus responses are mostly formed by the dorsal column fibres and their physiological action upon demyelination is similar to that of the peripheral nerves.