Comparative effects of stimulation of the trigeminal ganglion and the superior sagittal sinus on cerebral blood flow and evoked potentials in the cat

The superior sagittal sinus (SSS) and the trigeminal ganglion (Vg) of anesthetized cats were stimulated electrically and field potentials in the upper cervical spinal cord and regional cerebral blood flow were recorded. Stimulation of the entire ganglion produced smaller field potential changes in two regions (medioventral area (MVA); dorsolateral area (DLA] of the upper spinal cord than did stimulation of the sagittal sinus (Vg/SSS response ratio = 17% for the MVA and 48% for the DLA). Stimulation of the trigeminal ganglion increased blood flow in only the frontal and parietal cortices (+93% and +33%), whereas stimulation of the sinus produced both larger changes in these areas (+137% and +139%) and also produced changes in regional cerebral blood flow in the thalamus (+122%).     

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.     

Responses and afferent pathways of C(1)-C(2) spinal neurons to gastric distension in rats

Some evidence shows that the upper cervical spinal cord might play an important role in propriospinal processing as a sensory filter and modulator for visceral afferents. The aims of this study were to determine (1). the responses of C(1)-C(2) spinal neurons to gastric distension and (2). the relative contribution of vagal and spinal visceral afferent pathways for transmission of gastric input to the upper cervical spinal cord. Extracellular potentials of single C(1)-C(2) spinal neurons were recorded in pentobarbital anesthetized male rats. Graded gastric distension (20-80 mm Hg) was produced by air inflation of a latex balloon surgically placed in the stomach. Sixteen percent of the neurons (32/198) responded to gastric distension; 17 neurons were excited and 15 neurons were inhibited by gastric distension. Spontaneous activity of neurons with inhibitory responses was higher than those neurons with excitatory responses (18.1+/-2.7 vs. 3.8+/-1.7 impulses s(-1), p<0.001). Twenty-eight of thirty-two (87.5%) neurons responded to mechanical stimulation of somatic fields on head, neck, ears or shoulder. Most lesion sites of neurons with excitatory responses were found in laminae V, VII; however, neurons with inhibitory responses were in laminae III, IV. Bilateral cervical vagotomy abolished responses of 4/8 neurons tested. Spinal transection at C(6)-C(7) abolished responses of the other four neurons that still responded to gastric distension after bilateral vagotomy. Results of these data supported the concept that a group of C(1)-C(2) spinal neurons might play a role in processing sensory information from the stomach that travels in vagal and spinal visceral afferent fibers.     

Synaptic inhibition of accessory motoneurons evoked by stimulation of the trigeminal nerve in the cat.

Stimulation of the trigeminal nerve produced polysynaptic inhibitory postsynaptic potentials (IPSPs) in accessory motoneurons of the cat. This contrasts with the observation that dorsal cervical motoneurons responded with EPSPs to trigeminal stimulus. Stimulation of the rostral part of spinal trigeminal nucleus elicited di- or polysynaptic IPSPs in accessory motoneurons. Transection of the anterior funiculus at the upper cervical cord selectively abolished the IPSPs. The IPSPs were antagonized by systematically administrated strychnine but not bicuculline.     

Cortical potentials evoked by epidural stimulation of the cervical and thoracic spinal cord in man

Scalp somatosensory evoked potentials (SEPs) were recorded after electrical stimulation of the spinal cord in humans. Stimulating electrodes were placed at different vertebral levels of the epidural space over the midline of the posterior aspect of the spinal cord. The wave form of the response differed according to the level of the stimulating epidural electrodes. Cervical stimulation elicited an SEP very similar to that produced by stimulation of upper extremity nerves, e.g., bilateral median nerve SEP, but with a shorter latency. Epidural stimulation of the lower thoracic cord elicited an SEP similar to that produced by stimulation of lower extremity nerves. The results of upper thoracic stimulation appeared as a mixed upper and lower extremity type of SEP. The overall amplitudes of SEPs elicited by the epidural stimulation were higher than SEPs elicited by peripheral nerve stimulation. In 4 patients the CV along the spinal cord was calculated from the difference in latencies of the cortical responses to stimulation at two different vertebral levels. The CVs were in the range of 45-65 m/sec. The method was shown to be promising for future study of spinal cord dysfunctions.     

Spinal evoked potential in the cat: effects of asphyxia, strychnine, cord section and compression.

Averaged evoked potentials to sciatic nerve stimulation and to direct stimulation of the cervical spinal cord were recorded from the dura and skin over the spinal cord and cauda equina in bipolar and common reference leads in cats and compared. Response waveform and conduction characteristics are described. The effects of increasing stimulus intensity, asphyxia and strychnine on these potentials are related. Alterations in these potentials produced by spinal cord at one or two levels are also described. These potentials are compared to similar potentials which have been recorded in man and the possible clinical application of some of these methods is discussed.     

Expression of c-Fos-like immunoreactivity in the caudal medulla and upper cervical spinal cord following stimulation of the superior sagittal sinus in the cat

Migraine is an episodic vascular headache with a well-recognized clinical picture but a poorly understood pathogenesis. Stimulation of a pain-sensitive trigeminally innervated intracranial structure, the superior sagittal sinus (SSS), was undertaken to map the higher-order neurons potentially involved in the processing of vascular head pain. The animals were prepared for stimulation by exposure of the sinus and then maintained under α-chloralose anaesthesia for 24 h before SSS stimulation, perfusion and immunohistochemical processing for the detection ofFosprotein. Examination of the medulla and upper cervical cord revealed marked increases inFos-like immunoreactivity in laminae I and IIo of the trigeminal nucleus caudalis and the dorsal horn of the upper cervical spinal cord. In addition,Fos-like immunoreactivity was observed in lamina X of the upper cervical spinal cord, in the commissural and medial nuclei of the solitary tract and in the nucleus retroambigualis. The use of immunohistochemical detection ofFos has allowed visualization of several populations of neurons likely to be involved in the central neural processing of vascular headache syndromes, particularly migraine.     

An intraspinal sympathetic preganglionic pathway: Physiologic evidence in the cat

Electrical stimulation of the zona intermedia of the lower thoracic/upper lumbar cat spinal cord resulted in increases of heart rate (HR), blood pressure (BP) and cardiac contractility (dp/dt). Sites of maximal cardiovascular response (SMCR) were localized histologically to the intermediolateral nucleus (ILN). The inotropic and chronotropic responses were abolished by spinal cord transection or hemisection two to three segments rostral to the site of stimulation. Discrete electrolytic lesions in the white matter adjacent to the ILN were also shown to markedly decrease or abolish the chronotropic and inotropic responses elicited by stimulation of a more caudal SMCR. Longitudinal spinal section resulted in decreased cardiovascular responses from an SMCR; these changes were larger on the left side and greatest for BP as compared to HR and dp/dt. These findings indicate the existence of an ascending intraspinal cardiovascular pathway located in the deep white matter adjacent to the ILN. They further suggest that this is the intraspinal sympathetic preganglionic pathway recently described anatomically.     

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--7 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 it one could know the time of arrival segmental afferent inputs at the spinal cord.     

Supraspinal regulation of spinal reflex discharge into cardiac sympathetic nerves

(1) In chloralose anaesthetized cats, reflex responses were recorded in inferior cardiac nerves following stimulation of intercostal nerves and hind limb afferent nerves. (2) In 80% of cats, a long latency reflex response alone was recorded, whereas, in the others, a short and long latency response was present to intercostal nerve stimulation. (3) In cats displaying only a long latency somatocardiac reflex response, damage to the ventral quadrant of the ipsilateral cervical spinal cord, through which runs a bulbospinal inhibitory pathway, resulted in the appearance of shorter latency reflexes to intercostal nerve stimulation. Lesions elsewhere in the cervical cord did not do this. (4) The characteristics of the early responses indicated that they were somatosympathetic reflexes and not dorsal root reflexes. (5) The early reflexes remained and the late reflex disappeared on subsequent complete transection of the spinal cord. The early reflexes were therefore spinal reflexes, and suppressed in the animal with cord intact. (6) Lesions at C4, which included a contralateral hemisection and a section of dorsal columns extending into the dorsal part of the lateral funiculus, abolished the inhibition of a sympathetic reflex that followed stimulation of some somatic afferent nerve fibres. These sections did not release the spinal reflex. Therefore, this reflex inhibition was not responsible for the suppression of the spinal somatosympathetic reflex. (7) The descending inhibitory influence on the segmental reflex pathway was not antagonized by strychnine, bicuculline or picrotoxin. (8) The possibility is discussed that the spinal reflex pathway into cardiac sympathetic nerves is tonically inhibited by a bulbospinal pathway originating from the classical depressor region of the ventromedial reticular formation.     

Spinal cord potentials evoked by peripheral nerve stimulation.

Lumbar, thoracic, and cervical spinal cord responses evoked by sciatic nerve stimulation were measured in 20 cats at the skin level and directly from the dorsal surface of the cord. Computer averaging techniques were used for both skin level recordings and cord surface recordings at all levels. Recordings made directly from the cord surface at lumbar levels were large and were characterized by a large, initial, negative transient, followed by a more complicated and variable waveform. As recording electrodes were moved rostrally, the initial large spike decreased in amplitude and the duration and latency of the response increased. At cervical levels were large and were characterized by a large, initial, negative transient, followed by a more complicated and variable waveform. As recording electrodes were moved rostrally, the initial large spike decreased in amplitude and the duration and latency of the response increased. At cervical levels the responses were polyphasic, of long duration and small amplitude. Deafferentation by posterior rhizotomy of all lumbar and sacral roots ipsilateral to sciatic nerve stimulation abolished the response at all levels. Thoracic cord section also abolished the response over the cervical cord. Skin level recordings were of shorter latency than direct recordings, especially at cervical levels. Response configurations were similar for both recording techniques at lumbar levels, but had different waveforms at both thoracic and cervical levels. Clinical implications of the techniques and possible explanations of the waveforms recorded are discussed.     

Peripheral and segmental spinal abnormalities of median and ulnar somatosensory evoked potentials in Hirayama's disease

OBJECTIVES: To investigate the origin of juvenile muscle atrophy of the upper limbs (Hirayama's disease, a type of cervical myelopathy of unknown origin). SUBJECTS: Eight male patients were studied; data from 10 normal men were used as control. METHODS: Median and ulnar nerve somatosensory evoked potentials (SEP) were recorded. Brachial plexus potentials at Erb's point (EP), dorsal horn responses (N13), and subcortical (P14) and cortical potentials (N20) were evaluated. Tibial nerve SEP and motor evoked potentials (MEP) were also recorded from scalp and spinal sites to assess posterior column and pyramidal tract conduction, respectively. RESULTS: The most important SEP findings were: a very substantial attenuation of both the EP potentials and the N13 spinal responses; normal amplitude of the scalp N20; and normal latency of the individual peaks (EP-N9-N13-P14-N20). Although both nerves were involved, abnormalities in response to median nerve stimulation were more significant than those in response to ulnar nerve stimulation. There was little correlation between the degree of alterations observed and the clinical state. Latencies of both spinal and cortical potentials were normal following tibial nerve stimulation. The mean latency of cervical MEP and the central conduction time from the thenar eminence were slightly but significantly longer in patients than in controls. CONCLUSIONS: The findings support the hypothesis that this disease, which is clinically defined as a focal spinal muscle atrophy of the upper limb, may also involve the sensory system; if traumatic injury caused by stretching plays a role in the pathogenesis, the damage cannot be confined to the anterior horn of the spinal cord.     

Central nervous system plasticity after spinal cord injury in man: interlimb reflexes and the influence of cutaneous stimulation

In persons who have sustained severe injuries to the cervical spinal cord, electrical stimulation of mixed peripheral nerves in a lower limb can evoke short-latency, bilateral motor responses in muscles of the distal upper limbs; such motor responses have been termed interlimb reflexes. In the present study, we investigated the role that cutaneous stimulation plays in evoking interlimb reflexes. Fifteen subjects with chronic injury (>1 year) to the cervical spinal cord were investigated. Single motor unit activity was recorded from a number of distal upper limb muscles. The lower limb cutaneous area within which stimulation recruited a given motor unit of the upper limb was defined as that motor unit's ‘receptive field’. Activity from a total of 48 single motor units was analyzed. The majority of motor units responded to light touch, individual hair movement, and thermal (hot and cold) stimulation. Excitatory responses were observed bilaterally, although contralateral responses predominated. Stimulation occasionally resulted in inhibition of a spontaneously active motor unit. Receptive fields varied a great deal in size, with proximal locations being larger than those encountered in more distal lower limb locations (i.e. the toes). The spinocervical tract is a possible candidate for mediating some portion of these interlimb reflexes, the origin of which may be due to new growth (regenerative sprouting) in the spinal cord caudal to a severe injury.     

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.     

Short-latency somatosensory evoked potentials in brain death

Summary Simultaneous recording of somatosensory evoked potentials to median nerve stimulation above the upper and lower neck in brain-dead patients revealed that all cervical responses were preserved in 10%, whereas a marked reduction in amplitude or even loss of N 13b at the level of the C2 spinous process was observed in 90%. Of the patients, 55% revealed an additional loss of N 13a, recorded at the level of the C7 spinous process; in 15% all cortical and spinal evoked potentials were missing, but Erb's point waves were still normal. These results suggest two different origins of the main negative waves (N 13a and N 13b), recorded above the upper and lower cervical spinal cord. N 13a (C7) is supposed to arise in the dorsal horn at the C6/7 level, N 13b (C2) in the cervicomedullary junction.     

Evoked potentials and contingent negative variation during treatment of multiple sclerosis with spinal cord stimulation.

Cervical somatosensory evoked potentials, brainstem evoked potentials, visual evoked potentials, and the cerebral contingent negative variation were recorded in patients with definite multiple sclerosis before, during, and after spinal cord stimulation. Improvements were seen in the cervical somatosensory and brainstem evoked potentials but neither the visual evoked potential nor the contingent negative variation changed in association with spinal cord stimulation. The results indicate that spinal cord stimulation acts at spinal and brainstem levels and that the clinical improvements seen in patients are caused by an action at these levels rather than by any cerebral arousal or motivational effect. The evoked potentials were not useful in predicting which patients were likely to respond to stimulation.     

Convergence of trigeminal input with visceral and phrenic inputs on primate C1-C2 spinothalamic tract neurons.

Trigeminal, spinal and vagal afferent fibers overlap in C1-C2 segments. We hypothesized that trigeminal input from the superior sagittal sinus (SSS) can excite C1-C2 spinothalamic tract (STT) neurons receiving thoracic visceral or phrenic inputs. Effects of SSS stimulation were evenly divided among cells responding to each nerve stimulus; magnitude of responses to ipsilateral vagal input was greater in neurons excited by SSS input. Somatic fields of 80% of neurons responding to SSS stimulation included face areas innervated by the trigeminal nerve, whereas somatic fields of 89% of neurons unaffected by SSS stimulation were located only on areas innervated by cervical spinal nerves. Results are consistent with the idea that pain referred to trigeminal areas could originate in thoracic organs.     

Convergence of trigeminal input with visceral and phrenic inputs on primate C1–C2 spinothalamic tract neurons

Trigeminal, spinal and vagal afferent fibers overlap in C1–C2 segments. We hypothesized that trigeminal input from the superior sagittal sinus (SSS) can excite C1–C2 spinothalamic tract (STT) neurons receiving thoracic visceral or phrenic inputs. Effects of SSS stimulation were evenly divided among cells responding to each nerve stimulus; magnitude of responses to ipsilateral vagal input was greater in neurons excited by SSS input. Somatic fields of 80% of neurons responding to SSS stimulation included face areas innervated by the trigeminal nerve, whereas somatic fields of 89% of neurons unaffected by SSS stimulation were located only on areas innervated by cervical spinal nerves. Results are consistent with the idea that pain referred to trigeminal areas could originate in thoracic organs.     

Influence of isoflurane anesthesia on motor evoked potentials elicited by transcortical,brainstem, and spinal root stimulation

Abstract

Electrical stimulation over the motor cortexl base ofthe skulll and cervical spine motor roots was performed in 9 male rats (41 0 ± 86 g) before and after induction with isoflurane at 7 MAC concentration. The mean latency and amplitude of descending spinal evoked potential (OSEP) from spinal cord and motor evoked potentials (MEPs) from forearm muscles obtained after motor cortexl brainsteml and cervical root stimulations were calculated and compared. The electrical current intensity to elicit the MEPs after corticall brainsteml and spinal roots stimulation were 23.4 ± 7.61 7.0 ± 3.71 and 7.4 ± 0.8 mAl respectively. The brainstem stimulation activated descending motor pathways with a latency midway between that produced by electrical stimulation over the motor cOrtexI and by electrical stimulation over the cervical enlargements. The latency difference between cortical (8.8 ± 3.2 msec) and brainstem (5.7 ± 7.2 msec) stimulation was 3.7 ± 2.3 msec in all forearm extensor muscles. The latency difference between cervical (3.6 ± 0.9 msec) and brainstem stimulation (5.7 ± 7.2 msec) was 2.3 ± 7.7 msec for the same musclesl suggesting the brainstem stimulation activates the descending motor neurons at the level of cervicalmedullary junction. The amplitudes were 789 ± 7471 672 ± 3541 and 765 ± 389 µV for corticall brainsteml and cervical root stimulations. The inhalation anesthesia isoflurane at 7MAC (7.2%) completely abolished the cortical and brainstem MEPs within minutesl while the MEPs elicited by direct stimulation of the cervical spinal roots remained unchanged. Our results indicate synaptic-dependent MEPs elicited at motor cortex or brainstem levels are highly sensitive to isoflurane anesthesia. [Neural Res 1998; 20: 555-558]     

Postnatal development of descending motor pathways studied in man by percutaneous stimulation of the motor cortex and the spinal cord

Using the percutaneous electrical stimulation of the brain and spinal cord, we have determined central motor pathway conduction velocities in a group of 19 healthy fullterm newborns (average post-conceptional age 39.8 weeks) and in 19 infants between 2 months and 8 years of age. The newborns were examined during the first postnatal week. The percutaneous stimulation of the motor cortex and of the cervical and lumbar enlargements of the spinal cord was made by means of bipolar electrodes. The evoked compound muscle action potentials were recorded by bipolar surface electrodes fixed on the skin overlying the thenar eminence muscles and the tibialis anterior muscle. In fullterm newborns, the responses of lower limb muscles to cortical stimulation were more difficult to obtain than those of upper limb muscles. Conduction velocities of central motor fibres along the spinal cord (between vertebrae C7 and L4) were around 10 m/sec in fullterm newborns and 38 m/sec at the age of 4 years. These values are considerably lower than those described for adult man (48-60 m/sec). The adult values are established around the age of 8 years.