STUDIES ON the HUMAN EVOKED ELECTROSPINOGRAM

Evoked potentials from the human spinal cord were studied in 39 normal volunteers. Intrathecal recordings from lower cervical and lower thoracic intervertebral levels were made after the supramaximal stimulation of the median, ulnar and posterior tibial nerves, respectively. It was shown that the segmental cord potentials varied in shape and size according to the spatial relationship between the position of the electrode tip and the spinal cord and roots within the vertebral canal. Three main types of segmental evoked responses were obtained. One of them was recorded behind the cord dorsum and around the midline, and was composed of fast, sharp early, and slow, late components. This was called a CD potential and its first component was related to the activity of the ascending dorsal funiculus fibres. The second evoked response was the DR potential, and this triphasic compound action potential of very high amplitude and longer duration had no remarkable late component. It was recorded when the tip of the intrathecal electrode was lateral to the midline within the vertebral canal, and was then related mostly to activity of the spinal roots. Another kind of potential was called PH potential. It had a very small triphasic spike and two later components with prominent negativities being higher than the first spike. This potential might be related to the electrode tip position facing, and close to, the posterior horn of the spinal gray matter. Late components of the segmental evoked potentials were related to the pre- and post synaptic activity of the horizontally oriented fibre within the segmental gray matter of the posterior horn.     

Proprioceptive pathways of the spinal cord.

In the Macaque, surgical lesions were made in the dorsal funiculus, in the dorsolateral funiculus, and through half of the spinal cord. The somatosensory and motor capacity of the animal were examined neurologically and electrophysiologically. The exact lesion was then confirmed pathologically in detail. The results of these experiments indicate that limb position information from the distal limb and proximal limb are relayed to the brain in two different fashions. Distal limb position information, especially the cortical representation of the limbs' volar surface as it moves in space, is drastically impaired by dorsal funiculus or posterior white column lesions. Proximal limb position may or may not be impaired by similar lesions, for this information while initially in the dorsal or posterior white columns is sorted out (as it ascends in the spinal cord) to the dorsolateral funiculus or white columns. For example, in the lower thoracic spinal cord, both distal and proximal hind limb sensation are impaired by posterior white column damage; in the cervical cord, only distal sensation is impaired by the same lesion, and proximal information is spared. We refer to this neuroanatomic rearranging as "fibre sorting", and we believe that it is clinically significant in spinal cord disease.     

Brainstem influences on transmission of somatosensory information in the spinocervicothalamic pathway

The inhibition of somatosensory responses of lateral cervical nucleus neurons resulting from stimulation of the brainstem has been investigated. Single unit extracellular recordings were obtained from neurons in the lateral cervical nucleus of chloralose-anesthetized cats. Electrical stimulation of the periaqueductal gray, nucleus raphe magnus, nucleus cuneiformis, and nuclei reticularis gigantocellularis and magnocellularis was found to be very effective in inhibiting the responses of lateral cervical nucleus neurons evoked by electrical or tactile stimulation of the skin. Additional experiments were performed to determine whether the inhibitory effects were mediated in the spinal cord dorsal horn or in the lateral cervical nucleus. These experiments which examined the effect of brainstem stimulation on the responses induced by stimulation of the dorsolateral funiculus or on the antidromic latency of activation of lateral cervical nucleus neurons from thalamus, revealed that most and possibly all the inhibition could be accounted for by an action on the spinal cord. These results are consistent with other studies showing that spinocervical tract cells in the spinal cord can be inhibited by stimulation of the same brainstem regions.     

Epidurally recorded cervical somatosensory evoked potential in humans

Three slow wave components, P10, N13 and P18, can be seen in the cervical somatosensory evoked potential (CSEP) in response to median nerve stimulation recorded by an electrode in the epidural space at the dorsal aspect of the cervical spinal cord referenced to an electrode at the suprasternal notch. In the region of high CSEP amplitude, which extends over several cervical segments, the peak-to-peak amplitude is more than 10 microV, permitting observation of the CSEP slow waves in single, unaveraged records. The CSEP to finger nerve stimulation had a similar wave form and the same latencies (referred to the Erb's potential) as the CSEP to median nerve stimulation. The P10 activity is of presynaptic origin; it is generated in the brachial plexus, spinal roots and terminal branches of the primary sensory fibers. The N13 slow wave is of postsynaptic origin; however, the small wave on the ascending phase of this main postsynaptic component represents superimposed presynaptic activity. In bipolar epidural recordings, 3-5 fast waves are superimposed on the slow CSEP waves, which are of lower amplitude than the slow waves in unipolar recordings. The fast waves show a slight but progressive delay at the more rostral recording sites and are present even with high frequency stimulation, presumably reflecting activity in long ascending tracts. The surface recorded CSEP to median nerve stimulation is 4-7 times lower in amplitude than the CSEP in unipolar epidural recordings. The small wave on the ascending phase of N13 and the N13 peak of the unipolar epidural recordings had the same latencies as the surface N11 and N13 peaks.     

Spinal evoked potential in the monkey

Computer-averaged evoked potential responses (EPs) to stimulation of the sciatic nerve and cervical spinal cord were recorded from the dura and skin over the cauda equina and spinal cord in seven monkeys, three with chronic spinal cord lesions. Sciatic EPs consisted of predominantly negative triphasic propagated potentials recorded at all spinal levels and greatest in amplitude over the cauda equina and caudal spinal cord. The conduction velocity of this EP was faster over the cauda equina and rostral spinal cord than over caudal cord segments. Triphasic potentials were succeeded by small negative potentials over the cauda equina and larger negative potentials over the lumbar enlargement. Sciatic EPs over the upper lumbar and thoracic cord were more sensitive to asphyxia than the initial triphasic potentials recorded over cauda equina and caudal cord but resisted changes from increasing the rate of stimulation up to 100 per second. Propagated thoracic EPs were preceded by nonpropagated potentials. The longer latency negative potentials occurring locally over the cauda equina and lower lumbar enlargement were abolished at levels of asphyxia and were attenuated at rates of stimulation that did not affect the preceding triphasic potentials. Following complete spinal cord transection, nonpropagated sciatic EPs were recorded in leads rostral to the section. In preparations with chronic partial cord hemisection involving dorsal and lateral quadrants, ipsilateral sciatic EPs had increased latency, reduced amplitude, and poor definition in the vicinity of and rostral to the lesion. Direct cervical cord stimulation elicited caudally propagated potentials which were followed by large, broad potentials over the lumbar enlargement.     

Fluoro-ruby retrograde tracing and three- dimensional visualization of the corticospinal tract in the guinea pig

Fluoro-ruby was injected into the posterior funiculus of the spinal cord in the cervical(C5-T2) and lumbar(L3-6) segments of adult guinea pigs.The spinal cord was cut into serial frozen sections.The Fluoro-ruby labeling was clearly delineated from the surrounding structure.The labeling traversed the cervical,thoracic and lumbar segments,and was located on the ventral portion of the posterior funiculus on the injected side,proximal to the intermediate zone of the dorsal gray matter.The fluorescence area narrowed rostro-caudally.The spinal cord,spinal cord gray matter and corticospinal tract were reconstructed using 3D-DOCTOR 4.0 software,resulting in a robust three-dimensional profile.Using functionality provided by the reconstruction software,free multi-angle observation and sectioning could be conducted on the spinal cord and corticospinal tract.Our experimental findings indicate that the Fluoro-ruby retrograde fluorescent tracing technique can accurately display the anatomical location of corticospinal tract in the guinea pig and that three-dimensional reconstruction software can be used to provide a three-dimensional image of the corticospinal tract.     

Evidence for an Anuran Homologue of the Mammalian Spinocervicothalamic System: An In Vitro Tract-tracing Study in Xenopus laevis

Evidence is presented for an anuran homologue of the mammalian spinocervicothalamic system. In vitro tract-tracing experiments with biotinylated dextran amine in Xenopus laevis show that ascending spinal fibres from all levels of the spinal cord, passing via the dorsolateral funiculus, terminate in a cell area ventrolateral to the dorsal column nucleus. This cell area can be considered a possible homologue of the mammalian lateral cervical nucleus. After tracer applications to the ventral thalamus or to the torus semicircularis (both targets for somatosensory projections), the anuran lateral cervical nucleus was retrogradely labelled contralateral to the application sites. Tracer applications to the dorsolateral funiculus at the obex level and rostral spinal cord resulted in labelling of the cells of origin of the spinocervical tract. These were found, mainly ipsilaterally, in the ventral part of the dorsal horn, and were rather evenly distributed throughout the spinal cord. These data suggest the presence of an anuran homologue of the mammalian spinocervicothalamic system. A brief survey of the literature shows that such a system is much more common in vertebrates than previously thought.     

False negative intraoperative somatosensory evoked potentials with simultaneous bilateral stimulation

A 43 year old man underwent spinal cord surgery for removal of filum terminale lipoma. Intraoperative somatosensory evoked potentials (SSEP) monitoring showed a transient loss of response on simultaneous bilateral posterior tibial nerve (PTN) stimulation that recovered within 20 minutes. The patients exhibited paralysis and abnormal proprioceptive perception in the right leg postoperatively, when SSEP recordings revealed abnormal response to right PTN and normal response to bilateral PTN stimulation. In order to avoid false negative intraoperative responses, stimulation of each leg independently in an alternative fashion is recommended.     

Spinal sources of noxious visceral and noxious deep somatic afferent drive onto the ventrolateral periaqueductal gray of the rat

Studies utilizing the expression of Fos protein as a marker of neuronal activation have revealed that pain of deep somatic or visceral origin selectively activates the ventrolateral periaqueductal gray (vlPAG). Previous anatomical tracing studies revealed that spinal afferents to the vlPAG arose from the superficial and deep dorsal horn and nucleus of the dorsolateral funiculus at all spinal segmental levels, with approximately 50% of vlPAG-projecting spinal neurons found within the upper cervical spinal cord. This study utilized detection of Fos protein to determine the specific populations of vlPAG-projecting spinal neurons activated by noxious deep somatic or noxious visceral stimulation. Pain of cardiac or peritoneal (i.e., visceral) origin activated neurons in the superficial and deep dorsal horn and nucleus of the dorsolateral funiculus of the thoracic cord, whereas pain of hindlimb (i.e., deep somatic) origin activated neurons in the same laminar regions but in the lumbosacral cord. Each of these deep noxious manipulations also activated neurons in the superficial and deep dorsal horn and nucleus of the dorsolateral funiculus of the upper cervical spinal cord. In a second set of experiments, the combination of retrograde tracing and Fos immunohistochemistry revealed that vlPAG-projecting spinal neurons activated by deep somatic pain were located in both the upper cervical and lumbosacral cord, whereas those activated by visceral pain were restricted to the thoracic spinal cord. Thus pain arising from visceral versus deep somatic body regions influences neural activity within the vlPAG via distinct spinal pathways. The findings also highlight the potential significance of the upper cervical cord in integrating pain arising from deep structures throughout the body.     

Spinal ascending pathways in amphibians: Cells of origin and main targets

As part of a research program on the evolution of somatosensory systems in vertebrates, the various components of ascending spinal projections were studied with in vivo and in vitro tract-tracing techniques in representative species of amphibians (the large green frog, Rana perezi, the clawed toad, Xenopus laevis and the ribbed newt, Pleurodeles waltl). Three main ascending sensory channels, each with largely separate targets, were demonstrated: 1. Ascending projections via the dorsal funiculus include primary and nonprimary projections that ascend to terminate mainly in the dorsal column nucleus at obex levels. A small component ascends farther rostralwards to terminate in the reticular formation, the octavolateral area, the trigeminal nuclear complex, and in the granular layer of the cerebellum. 2. Projections ascending via the dorsolateral funiculus reach other spinal and supraspinal targets than the dorsal funicular fibers, mainly ipsilaterally. At upper cervical cord and obex levels, many fibers innervate a region considered the amphibian homologue of the lateral cervical nucleus of mammals. In the medulla, these fibers ascend ventral to the descending trigeminal tract to terminate in the dorsal column and the solitary tract nuclei, and more rostrally, in the reticular formation, the descending trigeminal nucleus and the medial aspect of the ventral octaval nucleus. Major projections reach the area between the facial motor nucleus and the ventral octaval nucleus, and a mediolateral subcerebellar band. These projections arise in neurons located mainly in the ipsilateral deep dorsal and lateral fields throughout the spinal cord. 3. Ascending spinal projections via the ventral quadrant of the spinal cord (the ventral and ventrolateral funiculi) ascend throughout the brainstem up to the diencephalon. Along its course, this component innervates various parts of the reticular formation, the octavolateral area, the granular layer of the cerebellum, the region ventromedial and ventrolateral to the isthmic nucleus, and the subcerebellar region. In the mesencephalon, the torus semicircularis, the midbrain tegmentum and, sparsely, the tectum mesencephali are innervated. Beyond the midbrain, various dorsal and particularly ventral thalamic nuclei and the posterior tubercle are innervated by this ascending sensory channel. The cells of origin of some of these projections were observed in the dorsal, and to a lesser extent, in the lateral and ventral spinal fields of the spinal cord. Evidence for the presence of these three main ascending sensory channels throughout vertebrates will be discussed. The presence of such channels appears to be a shared character in the brain of both amniotes and anamniotes. J. Comp. Neurol. 378:205–228, 1997. © 1997 Wiley-Liss, Inc.     

The human cervical and lumbo-sacral evoked electrospinogram. Data from intra-operative spinal cord surface recordings.

We have undertaken the analysis of the human 'evoked electrospinogram' during intra-dural surgical explorations in 20 patients. Averaged spinal cord surface evoked potentials to peripheral nerve electrical stimulation were obtained from various restricted loci on the pial surface of the cervical and lumbo-sacral spinal cord. The brachial plexus P9 potential and its lumbo-sacral counterpart P17 were recorded as ubiquitous initial far-field positivities. The pre-synaptic compound action potentials N11 and N21 dwelt on the ascending slope of N13 and N24 respectively. They were composed of 1-5 sharp peaks and collected from the dorsal and dorso-lateral positions mainly, on the cervical and lumbo-sacral cord respectively. They are thought to be generated in the proximal portion of the dorsal root, the dorsal funiculus and the afferent collaterals to the dorsal horn. Compound action potentials could also be gathered from the surface of the dorsal roots, the cervical N10 and lumbo-sacral N19 potentials. The large cervical N13 and lumbo-sacral N24 waves originate from a dorso-ventral post-synaptic dipole, generated in deep laminae of the dorsal horn during the activation of large diameter afferent fibers. These waves were maximal on the main entry cord segments of the stimulated nerves and fell off on the 1-4 more rostral and caudal segments. The N2 wave is the dorsal component of another post-synaptic dorso-ventral dipole generated in deep laminae of the dorsal horn but activated by medium diameter afferent fibers. The latest event was the N3 wave, also possibly part of a dorso-ventral post-synaptic dipole, and generated by cells in the dorsalmost and deep dorsal horn laminae during the activation of small diameter afferent fibers. The P wave was a prolonged positive deflection which carried the N2 and N3 waves. It is the manifestation of pre-synaptic inhibition on primary afferent fibers. A supra-segmental ascending spinal cord volley was also described, composed of a long succession of sharp and low voltage peaks.     

The lateral cervical nucleus of the Japanese monkey (Macaca fuscata)

Based on the normal histological findings and the organization of the spinal afferents revealed by the Nauta and the Marchi methods, a cell group corresponding to the lateral cervical nucleus (NCL) of the cat was identified in the first and the second cervical segments of the spinal cord of the Japanese monkey (Macaca fuscata). The nucleus begins to appear at the level of the caudal end of the gracile nucleus and gradually disappears within the caudal half of the second cervical segment of the cord. The nucleus consists of medium-sized and small-sized nerve cells and receives spinal afferents ascending through the lateral funiculus, probably chiefly through the posterior spino-cerebellar tract, from lower levels of the spinal cord. The spinal afferents seem to take origin entirely, or at least chiefly, from the ipsilateral spinal gray and to terminate in the nucleus without any localization. Some problems concerning the lateral cervical nucleus as the site of the spino-thalamic tract have also been discussed from the point of view of comparative anatomy.     

Functional deficits of central sensory and motor pathways in patients with cervical spinal stenosis: a study of SEPs and EMG responses to non-invasive brain stimulation

The central conduction time of the descending and ascending fibers of the spinal cord were examined in patients with radiologically defined cervical spinal stenosis (antero-posterior diameter of the spinal canal less than 13 mm). Nineteen patients were examined, only 4 of whom showed clinical signs of spastic weakness or ataxia. The electromyographic response after non-invasive stimulation of the leg area of the motor cortex was delayed in 13 of the 15 clinically unaffected patients. The central latency (N21-P39) of the somatosensory evoked response after stimulation of the tibial nerve (tibialis SEP) was increased in 12 of the 15 individuals. The 4 patients with clinical signs showed abnormal latencies with both methods. The use of both techniques for the examination of the function of the spinal cord revealed increased latencies in the central motor and/or sensory pathways in all patients. The technique of non-invasive stimulation of the corticospinal system therefore provides an additional tool to detect and quantify subclinical and clinically apparent lesions in patients with defined cervical spinal stenosis.     

The origins of lumbosacral spinal evoked potentials in humans using a surface electrode recording technique.

Somatosensory evoked potentials were recorded over the lumbar spine and scalp in 12 normal subjects after stimulating the posterior tibial nerve at the knee and ankle and the sural nerve at the ankle. The H-reflex from the soleus muscle was recorded at the same time. The effects of stimulus intensity, frequency of stimulation and vibration were assessed. It was concluded that when the posterior tibial nerve was stimulated in the popliteal fossa, three negative peaks were recorded over the lumbosacral area. They arose from activity in the dorsal roots, the dorsal horn of the spinal cord (SD) and the ventral roots. In contrast when the posterior tibial nerve and the sural nerve were stimulated at the ankle only two negative peaks were recorded, a dorsal root potential and a spinal cord dorsum potential. In addition the data suggested that the peripheral nerve fibres that are involved with generating the surface recorded spinal potential with mixed nerve stimulation are primarily muscle afferents.     

Supraspinal nocifensive responses of cats: spinal cord pathways, monoamines, and modulation

These experiments were conducted to determine (1) whether dorsal and ventral ascending spinal pathways can each mediate unlearned supraspinal nocifensive responses of cats to noxious thermal stimuli and (2) whether interrupting the spinal projection of supraspinal monoaminergic neurons alters the excitability and natural modulation of these responses. In partially restrained cats, thermal pulses (greater than or equal to 47 degrees C) delivered to the hindlimbs of intact cats or rostral to lesions of the thoracic spinal cord elicited abrupt body movements and interruption of eating (or of exploring for) liquified food. These electronically monitored responses automatically terminated the stimulus. Natural modulation of responsiveness was produced by delivering food and thermal stimuli simultaneously; this reduced response probability by an average of 41%. Complete transection of the thoracic spinal cord eliminated both thermally elicited responses and orienting responses to noxious and tactile mechanical stimulation of the hindlimbs. Ventral bilateral thoracic spinal cord lesions that spared only the dorsal funiculus and portions of the dorsolateral funiculus (three cats) significantly reduced orienting responses to all mechanical hindlimb stimuli and reduced, but did not eliminate, movement and interrupt responses to noxious thermal hindlimb stimuli. Response latency was unaffected. Food-induced response suppression persisted although lumbar spinal cord concentrations of serotonin (5HT) and norepinephrine (NE) were markedly reduced. A bilateral lesion of the dorsal funiculi and dorsal portions of the dorsolateral funiculi (one cat) also reduced nocifensive responsiveness, but only the NE concentration in lumbar spinal cord was reduced significantly relative to a matched cervical sample. In contrast, deep bilateral lesions of the dorsolateral funiculi (two cats) produced an increase in the probability of movement and interrupt responses without affecting either response latency or food-induced response suppression. Lumbar spinal cord concentrations of NE and, in one cat, 5HT were reduced. We conclude that (1) the dorsal and ventral spinal funiculi are each sufficient to initiate and necessary to maintain normal supraspinally organized nocifensive behavior in the cat; (2) descending monoaminergic pathways are not necessary for the phasic modulation of these responses; and (3) the tonic excitability, but not the phasic modulation, of these responses is determined in part by fibers in the dorsolateral funiculus.     

Unmasking of presynaptic and postsynaptic high-frequency oscillations in epidural cervical somatosensory evoked potentials during voluntary movement.

OBJECTIVE: To investigate the effect of the voluntary movement on the amplitude of the somatosensory evoked potentials (SEPs) recorded by an epidural electrode at level of the cervical spinal cord (CSC). METHODS: Fourteen patients underwent an epidural electrode implant at CSC level for pain relief. After the median nerve stimulation, SEPs were recorded from the epidural electrode and from 4 surface electrodes (in frontal and parietal regions contralateral to the stimulated side, over the 6th cervical vertebra, and on the Erb's point). SEPs were recorded at rest and during a voluntary flexo-extension movement of the stimulated wrist. Beyond the low-frequency SEPs, also the high-frequency oscillations (HFOs) were analysed. RESULTS: The epidural electrode contacts recorded a triphasic potential (P1-N1-P2), whose negative peak showed the same latency as the cervical N13 response. The epidural potential amplitude was significantly decreased during the voluntary movement, as compared to the rest. Two main HFOs were identifiable: (1) the 1200 Hz HFO which was significantly lower in amplitude during movement than at rest, and (2) the 500 Hz HFO which was not modified by the voluntary movement. CONCLUSIONS: The low-frequency cervical SEP component is subtended by HFOs probably generated by: (1) postsynaptic potentials in the dorsal horn neurones (1200 Hz), and (2) presynaptic ascending somatosensory inputs (500 Hz). SIGNIFICANCE: Our findings show that the voluntary movement may affect the somatosensory input processing also at CSC level.     

Spinally elicited peripheral nerve responses are sensory rather than motor.

OBJECTIVES: Spinally elicited peripheral nerve responses, commonly called neurogenic motor evoked potentials (NMEPs), are widely used to monitor spinal cord motor function during surgery. However, numerous evidence suggests that these responses are primarily sensory rather than motor. The collision technique was utilized to address this issue.METHODS: Collision studies were performed in 7 patients during surgery. An ascending volley of sensory (AS) and motor activity (AM) was elicited by posterior tibial nerve stimulation at the popliteal fossa. After a short time delay, high cervical spinal stimulation produced a descending volley of sensory (DS) and motor (DM) activity. The AM volley ascended only to the anterior horn cells whereas the AS and DS volleys collided in the spinal cord. The inter-stimulus delays were varied so as to affect the degree of spinal cord collision. The DS and DM activity which remained after collision was recorded from the posterior tibial nerves at the ankle.RESULTS: Inter-stimulus delays of 18 ms or less resulted in no apparent peripheral descending volleys. These findings were consistent for all the patients studied.CONCLUSIONS: Spinally elicited peripheral nerve responses are primarily sensory rather than motor and are mediated by the same neural pathways as SEPs.     

Responses from dorsal column nuclei (DCN) in the monkey to stimulation of upper and lower limbs and spinal cord

Responses from the dorsal surface of the exposed dorsal column nuclei (DCN) in baboons and a monkey (Macaca fascicularis) were recorded in response to electrical stimulation of the posterior tibial nerve at the ankle, the common peroneal nerve at the knee, the sciatic nerve, the spinal cord at T10, and the median nerve at the wrist. Recordings of far-field potentials from the vertex with a non-cephalic reference were made before exposing the DCN and simultaneously with recordings from the DCN. The response recorded from the DCN using a monopolar electrode to median nerve stimulation was a negative deflection (N wave) followed by a large and slow positive wave (P wave). The N wave was often preceded by a small positive deflection. The response from the median nerve to electrical stimulation of the DCN had the same latency as the initial positive peak and the initial portion of the N wave in the response from the DCN to stimulation of the median nerve, indicating that the initial positive peak was generated by presynaptic events in the DCN. The response recorded from the surface of the DCN to stimulation of the lower limbs consisted of many irregular waves followed by a large, positive deflection. Sometimes these irregular waves were superimposed on a small negative peak, and they were preceded by a positive deflection. The response from the tibial nerve to stimulation of the DCN consisted of a series of waves that had the same latency as the waves of the response from the DCN to stimulation of the tibial nerve.(ABSTRACT TRUNCATED AT 250 WORDS)     

The human posterior tibial somatosensory evoked potential: synapse dependent and synapse independent spinal components

Evidence has been obtained for the existence of two separate events occurring in the human spinal cord following posterior tibial nerve (PTN) stimulation. These events can be recorded on the surface in unanesthetized individuals. The first is an ascending wave which is conducted up to the cord at constant velocity and has a relatively short refractory period consistent with a compound nerve action potential. This represents the afferent volley traversing the lumbosacral plexus and the ascending dorsal columns. A second event, the N22/P22 complex, is surface negative on the back and surface positive anteriorly; its amplitude is maximal 5-15 cm above the level of the L4 spine and its peak latency remains constant at all levels. This activity has a relatively long refractory period. These characteristics of N22/P22 indicate that it is a localized synaptically dependent event conforming to a transverse dipole with dorsal negativity and a simultaneous anterior positivity. The N22/P22 is probably generated in the dorsal grey at the root entry zone. The N22/P22 is analogous to the stationary N13/P13 recorded over the neck following median nerve stimulation.     

Central neuromechanisms underlying control of intragastric pressure through acupuncture atZusanli (ST36) in rats：the upper cervical cord is the key link between the ascending and descending pathways

Sensory inputs stimulated byZusanli (ST36) acupuncture in the abdomen are known to converge in the upper cervical cord. However, it is unclear whether these inputs are subsequently conveyed to the hypothalamic paraventricular nucleus and what kind of afferent ifbers are involved. We focused on the upper cervical cord, where afferent inputs converge, and detected c-fos expression in oxytocinergic neurons. We found thatZusanli acupuncture therapy effectively elevated intragastric pressure, but inhibited expression of c-fos in oxytocinergic neurons of the paraventricular nucleus in upper cervical cord injured rats. TheseZusanli acupuncture effects remained even after complete dorsal cord transection. However, after complete transection of the spinal cord or dorsolateral funiculus, the effects were signiifcantly at-tenuated and even disappeared. These ifndings suggest that the paraventricular nucleus is responsible for pooling and integrating signals from theZusanli acupuncture and sensory information from the intragastric pressure variation, thereby contributing to the regulation of intragastric pressure. The upper cervical cord serves as the key link between ascending and descending pathways, which conveys afferent inputs to the paraventricular nucleus through the dorsolateral funiculus.