Radial Nerve Stimulation Research Articles

Caudate unit activity and somal diameters in intact and nigral lesioned cats

In a search for morphofunctional relationships in the head of the caudate nucleus (CN), we recorded extracellular unit activity in intact cats and in cats that had received bilateral injections of 6-OHDA into the substantia nigra (SN) 30 days previously. Only units firing spontaneously and continuously for 2 min were studied. In dorsal regions, potentials were small and iterative at almost constant intervals; the somal diameters were relatively small. In the ventrolateral region, potentials were bigger and appeared in bursts; somal diameters were significantly larger ( p < 0.05). For the centromedial region a histogram of numbers of neurons as a function of diameters revealed a Gaussian distribution extending from small to large neurons. Most dorsal neurons increased their firing rate to radial nerve, visual, SN, and/or nucleus centralis medialis (NCM) stimulation. Ventral neurons usually responded with excitation followed by long lasting inhibition, particularly to SN and NCM stimulation. A few neurons responded to all four inputs and some showed long-lasting potentiation in response to low frequency stimulation, suggesting a more general function. Greatest convergence (65%) was found for NCM and SN inputs. In lesioned cats, there was no SN driving, NCM's inhibitory actions almost disappeared, and the excitatory action of the other stimuli was reduced.

Somatosensory evoked potentials from musculocutaneous nerve in the diagnosis of brachial plexus injuries

A technique for recording somatosensory evoked potentials using stimulation of musculocutaneous sensory nerve fibers proximal to the wrist has been used in 10 normal subjects and in 8 patients with traumatic lesions of proximal parts of the brachial plexus. The technique gave satisfactory evoked potentials in all normal subjects and provided useful information in patients with avulsion of the 5th and 6th cervical roots. The results were similar to those obtained by radial nerve stimulation. The results in 3 patients with upper trunk injuries and in 1 patient with avulsion of the 5th cervical root were unhelpful. In 2 patients with multiple cervical root avulsions the evoked potentials from cervical cord and contralateral scalp were absent and were attenuated at Erb's point. This is the first report where musculocutaneous nerve evoked potentials have been applied to a group of patients.

DEPRESSION OF NOCICEPTIVE SYMPATHETIC REFLEXES BY THE INTRATHECAL ADMINISTRATION OF MIDAZOLAM

The effect of the intrathecal administration of midazolam 0.5-1.0 mg in 1-2 ml of physiological saline solution, has been observed on responses evoked in renal sympathetic nerves by supramaximal electrical stimulation of radial and tibial nerves. In artificially ventilated dogs anaesthetized with alpha-chloralose, the intrathecal administration of midazolam caused a marked depression of reflexes evoked from the tibial nerve but had no effect on either spontaneous sympathetic activity or reflexes evoked by radial nerve stimulation. Neither the small amount (1-2 microliters) of benzyl alcohol, present as a preservative (administered intrathecally), nor midazolam 1 mg kg-1 i.v. caused any significant depression of the evoked somato--sympathetic reflexes. The effects of intrathecal midazolam were reversed by the benzodiazepine antagonists Ro 15-1788 1 mg kg-1 i.v. and Ro 15-3505 1-2 mg kg-1 i.v. but not by naloxone 2 mg i.v. It is suggested that the antinociceptive effect of locally applied midazolam could be the result of a non-opioid GABA-mediated system which may have implications in the management of pain.

Influence of drugs on evoked potentials in the cat cerebellum: III. Effects of morphine hydrochloride (2).

In intact cats, morphine hydrochloride (2.0 mg/kg, i.v.) depressed spontaneous discharge of the Purkinje cell in 8 of the 15 neurons tested. These effects of morphine were antagonized by naloxone hydrochloride (0.4 mg/kg, i.v.). This opiate significantly decreased the evoked potentials produced by superficial radial nerve (SR) stimulation in the molecular layer of the cerebellar cortex. Although morphine decreased the potentials evoked by SR or tooth pulp stimulation in the nucleus fastigii and nucleus interpositus, this drug hardly influenced them in the nucleus dentatus. In the decerebrated cats, morphine significantly increased the potentials evoked in the cerebellar cortices by SR stimulation. In the somatosensory area I (SSA-I)- or motor area (MA)-lesioned cats, morphine decreased the cerebellar potentials evoked by SR stimulation, but increased them in the SSA-I- and MA-lesioned cats. Naloxone antagonized these effects of morphine. From our results, it appears that the decreasing effects of morphine on the cerebellar potentials evoked by SR stimulation may be affected by the functions of the SSA-I and MA of the cerebral cortex and that morphine may influence the cerebellum.

INFLUENCE OF DRUGS ON EVOKED POTENTIALS IN THE CAT CEREBELLUM: III. EFFECTS OF MORPHINE HYDROCHLORIDE (2)

In intact cats, morphine hydrochloride (2.0 mg/kg, i.v.) depressed spontaneous discharge of the Purkinje cell in 8 of the 15 neurons tested. These effects of morphine were antagonized by naloxone hydrochloride (0.4 mg/kg, i.v.). This opiate significantly decreased the evoked potentials produced by superficial radial nerve (SR)stimulation in the molecular layer of the cerebellar cortex. Although morphine decreased the potentials evoked by SR or tooth pulp stimulation in the nucleus fastigii and nucleus interpositus, this drug hardly influenced them in the nucleus dentatus. In the decerebrated cats, morphine significantly increased the potentials evoked in the cerebellar cortices by SR stimulation. In the somatosensory area I (SSA-I)- or motor area (MA)-lesioned cats, morphine decreased the cerebellar potentials evoked by SR stimulation, but increased them in the SSA-I- and MA-lesioned cats. Naloxone antagonized these effects of morphine. From our results, it appears that the decreasing effects of morphine on the cerebellar potentials evoked by SR stimulation may be affected by the functions of the SSA-I and MA of the cerebral cortex and that morphine may influence the cerebellum.

Convergence of central and peripheral signals on vestibular cells.

Nerve and cortical input convergence patterns, representing the fore- and hindlimb, were studied in single cells located in the lateral vestibular nucleus of the cat. Deitersian cells responded with excitation to cortical stimulation with a latency ranging from 4 to 14 msec, while responses ranged from 9 to 12 msec to radial nerve stimulation and from 14 to 18 msec to sciatic nerve stimulation. Lateral vestibular nuclear neurons responding to radial nerve stimulation also receive the main cortical input from the sensorimotor cortical area concerned with the forelimb. Neurons responding to sciatic nerve stimulation receive an equal cortical input from both fore- and hindlimb areas of the sensorimotor cortex. In a few cells different combinations of convergence of cortical and peripheral inputs were also observed.

Somatosensory evoked potentials in patients with supraclavicular brachial plexus injuries.

In 12 patients with traumatic lesions of brachial plexus, we studied somatosensory evoked potentials by stimulation of median, radial, and ulnar nerves at the wrist and by recording at the arm, Erb point, cervical spinal cord, and contralateral cortex. Results after median nerve stimulation in patients with upper trunk lesions were normal. Patients with C5/6 root avulsion had either normal, delayed, or absent responses at the cervical cord and cortex, depending on the presence of complicating distal lesions. In patients with particular involvement of C7 root, results were normal after median and ulnar stimulation but were abnormal after radial nerve stimulation. In patients with multiple root avulsions and flail anesthetic arm, no potentials could be recorded from the cervical cord or contralateral cortex, regardless of which nerve was stimulated. For relevant information, it was important to stimulate nerves having roots near the anatomic site of the lesion as determined clinically and electromyographically.

Non-Opioid Pathways Suppress Pain in Humans

Subcutaneous electrical stimulation (SCNS) of median, radial, and saphenous nerves produces prolonged analgesia. The effect of subcutaneous nerve stimulation (SCNS) is not mediated by opiate receptors. (1) There is no cross-tolerance with opiates, and SCNS suppresses pain in patients under chronic meperidine medication. (2) Patients unresponsive to morphine benefit from SCNS. (3) There is no development of tolerance to SCNS. (4) SCNS analgesia is not naloxone-reversible. (5) SCNS can be administered with oral analgesics, either opiate or non-opiate, increasing patient comfort. These observations suggest that non-endorphinergic pathways produce powerful analgesia.

Selective augmentation of visual pathways by morphine in α-chloralose-anesthetized cats

Morphine sulfate, 0.1 to 5.0 mg/kg, was tested for effects on afferent sensory activity in acutely prepared α-chloralose-anesthetized cats. Morphine increased the responsiveness of the primary projection tracts of the visual system to electrical stimulation of the optic chiasm but did not augment responses in the primary somatosensory system to stimulation of the radial nerve. Preferential sensory augmentation was observed in cortical areas which exhibited responses to both sensory modalities. Anterior marginal association activity evoked by stimulation of the optic chiasm was augmented by morphine but activity elicited by radial nerve stimulation was not. In cats anesthetized with dial-urethane or midcollicularly transected, morphine was without significant effect on the visual afferent pathways. A possible brain stem site for morphine facilitation of visual tract responsiveness is discussed.

Slowing of cortical somatosensory evoked activity by Δ 9-tetrahydrocannabinol and dimethylheptylpyran in alpha-chloralose-anesthetized cats

Somatosensory and visual evoked potentials in the classical afferent primary pathways in cats anesthetized with α-chloralose were studied in order to characterize the effects of Δ 9-tetrahydrocannabinol (THC) and the synthetic analog, dimethylheptylpyran (DMHP) on central sensory processing. THC and DMHP slowed primary cortical responses to radial nerve or ventralis posterolateralis (VPL) stimulation in a dose dependent manner. THC did not alter VPL activity evoked by radial nerve stimulation. Amplitude of the primary somatic response was depressed at the 4 mg/kg dose. Responses of visual cortex and lateral geniculate nucleus, evoked by stimulation of optic chiasm, were unchanged at the doses studied However, the nonmodality-specific response of the anterior marginal association cortex to stimulation of either modality was depressed by THC. Data suggest the association cortex which exhibits sensory convergence was most sensitive to the effects of THC. Findings were consistent with a thalamocortical site of action for THC. DMHP produced similar effects and was more potent.

Effect of superficial radial nerve stimulation on the activity of nigro-striatal dopaminergic neurons in the cat: role of cutaneous sensory input.

The release of 3H-dopamine (DA) continuously synthesized from 3H-tyrosine was measured in the caudate nucleus (CN) and in the substantia nigra (SN) in both sides of the brain during electrical stimulation of the superficial radial nerve in cats lightly anaesthetized with halothane. Use of appropriate electrophysiologically controlled stimulation led to selective activation of low threshold afferent fibers whereas high stimulation activated all cutaneous afferents. Results showed that low threshold fiber activation induced a decreased dopaminergic activity in CN contralateral to nerve stimulation and a concomitant increase in dopaminergic activity on the ipsilateral side. Stimulation of group I and threshold stimulation of group II afferent fibers induced changes in the release of 3H-DA mainly on the contralateral CN and SN and in the ipsilateral CH. High stimulation was followed by a general increase of the neurotransmitter release in the four structures. This shows that the nigro-striatal dopaminergic neurons are mainly--if not exclusively--controlled by cutaneous sensory inputs. This control, primarily inhibitory in the side contralateral to the stimulation, seems rather non-specific when high threshold cutaneous fibers are also activated. Such activations could contribute to reestablish sufficient release of DA when the dopaminergic function is impaired as in Parkinson's disease.

Peripheral nerve stimulation for producing the suppressive effect on the tooth pulp-evoked jaw opening reflex in rat: Relation between stimulus intensity and degree of suppression

To reveal the peripheral physiologic mechanisms involved in local electrical stimulation, effects of conditioning radial nerve stimulation (0.1-ms duration, 45-Hz frequency, for 15 min) on the tooth pulp-evoked jaw opening reflex, which was monitored by the digastric electromyogram (dEMG), were investigated in Wistar albino rats. The activity of the dEMG was gradually decreased after the onset of the conditioning stimulation and after its cessation, the activity slowly recovered to the control value. A good suppressive effect was observed with a conditioning stimulus intensity of only four or six times the Aα threshold of the radial nerve compound action potential. When the jaw opening reflex was evoked with the supramaximum intensity of tooth-pulp stimulation, radial-induced suppression was rarely observed. The present study showed that direct peripheral nerve stimulation produced the suppressive effect similar to acupuncture or transcutaneous electrical nerve stimulation and that the effect was presumably elicited by the impulses of large-diameter A fibers, not by those of small-diameter ones.

Modulation of spasticity: prolonged suppression of a spinal reflex by electrical stimulation.

Electrical subcutaneous nerve stimulation of radial, median, and saphenous nerves has been shown to produce prolonged analgesia. In a double blind study, such stimulation also suppressed clonus for 3 hours after stimulation ceased in subjects with spasticity. Since the effect is contralateral, each subject was his own control. Because stimulation of the nerve in the wrist suppressed ankle clonus, the mechanism mediating the effect must be centrifugal inhibition. These results suggest that subcutaneous nerve stimulation may also be a tool in the management of spasticity.

Non-opioid pathways suppress pain in humans

Subcutaneous electrical stimulation (SCNS) of median, radial, and saphenous nerves produces prolonged analgesia. The effect of subcutaneous nerve stimulation (SCNS) is not mediated by opiate receptors. (1) There is no cross-tolerance with opiates, and SCNS suppresses pain in patients under chronic meperidine medication. (2) Patients unresponsive to morphine benefit from SCNS. (3) There is no development of tolerance to SCNS. (4) SCNS analgesia is not naloxone-reversible. (5) SCNS can be administered with oral analgesics, either opiate or non-opiate, increasing patient comfort. These observations suggest that non-endorphinergic pathways produce powerful analgesia.

Peripheral nerve stimulation in the management of dysmenorrhea

Electrical stimulation of radial, median, and saphenous nerves produces analgesia in patients with dysmenorrhea, whereas control stimulation in adjacent points does not. Pain relief is not reversed by naloxone, and patients experience permanent analgesia after 10 consecutive daily treatments.A follow-up of patients treated for surgically documented gynecological pain due to endometriosis shows them to be pain-free 5 years after cessation of treatment, as measured by verbal report, attendance at work, and analgesic abstinence. To our knowledge this represents the first such long-term follow-up in the clinical pain literature, and suggests that peripheral nerve stimulation may be useful in the treatment of dysmenorrhea.

Control of sensory transmission by electrical stimulation within the caudal raphe nuclei of the cat

These experiments used evoked potential techniques to define further the role of neurons in the caudal raphe nuclei (CRN) in the control of sensory transmission. In each experiment, single-pulse, low-intensity stimuli were tested for the ability to change the amplitude of potentials in the spinothalamic tract (ST) and medial lemniscus (ML) evoked by superficial radial nerve stimulation. It was shown that the effect of CRN stimulation was directed specifically to neurons of the ST because only a small and variable effect was seen on the sensory-evoked potential in the ML. Also, CRN sites were located in two discontinuous regions where electrical stimulation was most effective in inhibiting sensory-evoked activity in the ST. Finally, it was shown that the effect on inhibition of the ST included activity carried by both large-diameter and small-diameter primary afferent fibers.

Electrophysiological correlates among the radial nerve, the caudate and the entopeduncular nuclei in cats

The entopeduncular nucleus (EPN), as the medial part of the globus pallidum, has been considered the efferent structure of the striatum. Based on this, we decided to study its possible somatosensory projections and the electrophysiological relationship with the caudate nucleus (CN). Radial nerve stimulation produced evoked responses (ER) in CN and EPN. The ERs recorded in EPN are of shorter latencies (11 msec) than those in CN (23 msec). Electrical stimulation of CN elicited ERs in EPN. These ERs are bigger when the stimulation sites coincide with the regions of CN where somatic stimulation also elicited ERs. The same regions of CN yielding ERs by somatic stimulation respond to EPN stimulation. The ERs recorded in EPN by radial nerve stimulation diminished when the CN was stimulated 7 msec after the radial nerve, while other intervals were less effective. The results show that the radial nerve probably has direct ipsi and contralateral projections to the EPN and a bidirectional connection between EPN and CN. We suggest a feedback response of EPN to CN stimulation, an arrangement which would be the functional basis for the central motor regulation.

Short latency somatosensory evoked potentials from radial, median and ulnar nerve stimulation in man

Short latency somatosensory evoked potentials (SEPs) were elicited by stimulation at the wrist of median, radial, and ulnar nerves, singly or in combination, using normal subjects. Amplitude of P10 was strikingly lower with radial stimulation than with median stimulation, while ulnar-derived P10 was intermediate in amplitude. This difference probably reflects the antidromic firing of motor fibers contained in median nerves as compared with the superficial branch of radial nerve, which is entirely sensory. Beyond P10, there appear to be no significant differences between median, radial and ulnar-derived SEPs. With simulateneous stimulation of several nerves within one arm, larger potentials were sometimes achieved but with poorer definition of P12 and P14. The clinical utility of radial, ulnar, and median stimulation for localizing peripheral lesions derives from the distinct anatomical pathways of the stimulated fibers through the brachial plexus and from the separable motor and sensory components of P10. SEP is less invasive than EMG; this fact, plus its freedom from sampling error, make it potentially more suitable than conventional EMG for sequentially following a patient's clinical course.

The effects of low spinal injury on the latencies of cortical evoked responses from forelimb stimulation.

A previous report showed that following spinal cord transaction well below the C7 level in cats, later components of the cortical somatic evoked potential (SEP) (40 msec or longer) produced in response to median or radial nerve stimulation were abnormal (Katz et al., 1977). Evidence presented here shows that early components of the radial nerve SEP are also altered following spinal cord transection. Latencies of both early and late components were increased as higher functional transections of the spinal cord were made. This monotonic increase in latency of the primary components supports the hypothesis that the results may be due to increasing loss of excitatory input. Correlation of latency change with level of injury may serve as a useful diagnostic tool.

Thalamic projections to the feline motor cortex studied with horseradish peroxidase

Cells in the thalamus projecting to the distal forelimb regions of the motor cortex, area 3a, and the sensory cortex were identified with horseradish peroxidase (HRP). These cortical areas were defined by mapping evoked potentials from superficial and deep radial nerve stimulation. Following injections into the motor cortex, the labelled cells were distributed throughout a large region (>2 mm wide) in the ventral portion of the ventral lateral nucleus (VL). The border area between VL and the ventral posterolateral nucleus (VPL) also contained labelled cells. The region containing labelled cells following injections into area 3a was in the rostral, dorsal VPL, and overlapped with the region containing cells labelled by injections into the motor cortex. Cells labelled by injections into the sensory cortex were near the center of VPL distinctly separated from those labelled after injections into either area 3a or the motor cortex.