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PubMed1995

Substance P is a possible neurotransmitter in the rat spinothalamic tract.

In order to shed some light on the neurotransmitters in the spinothalamic tract (STT), we examined, biochemically and immunohistochemically, the contents of various neurotransmitter candidates in the terminal field of the STT after cervical hemi-chordotomy (HC) and dorsal quadrant-chordotomy (dQC) in the rat. Substance P (SP), calcitonin gene-related peptide (CGRP), enkephalin, neuropeptide Y, neurotensin, oxytocin and dynorphin A were analyzed immunohistochemically. The contents of neuropeptides (SP, CGRP and cholecystokinin octapeptide) were measured by radioimmunoassay and those of amino acids (aspartic acid, glutamic acid, gamma-aminobutyric acid (GABA) and glycine) and noradrenaline were determined using high-performance liquid chromatography. Cervical hemi-chordotomy, but not dQC, caused significant decreases of the SP-like immunoreactivity in and SP content of the ventral thalamus on the ipsilateral side, compared with that on the contralateral side and of rats subjected to sham-operation. However, neither HC nor dQC resulted in any changes in the ventral thalamic contents of other putative neurotransmitters examined. These results suggest that, in rats, the STT contains SP and that SP-positive fibers run in the ventral half of the ascending spinal tract at the cervical level.

Amino Acids↗

PubMed1986

Actions of opioids on primate spinothalamic tract neurons.

The effects of iontophoretically applied opiates were tested on 24 spinothalamic tract cells in 12 anesthetized monkeys. The drugs used were chosen because of their agonist actions on different classes of opiate receptors (mu, morphine; kappa, dynorphin; delta, methionine enkephalinamide; sigma, N-allylnormetazocine or SKF 10047 and phencyclidine). The actions of the opiate drugs were generally inhibitory, although excitatory or mixed effects were sometimes seen, especially with morphine and dynorphin. Drug effects could change, depending on the position of the iontophoretic electrode array or on the current employed. Naloxone sometimes antagonized the action of the opiate drugs used, but naloxone did not seem to be a drug suited for iontophoretic application. A number of explanations are discussed to explain the variable actions of the opiate drugs.

Animals↗

PubMed1995

Glutamatergic and GABAergic input to rat spinothalamic tract cells in the superficial dorsal horn.

The distribution of synaptic terminals onto spinothalamic tract cells (types I and II) of the superficial dorsal horn was determined with special reference to the amino acid transmitters glutamate and gamma-aminobutyric acid. Fifteen spinothalamic cells retrogradely labeled from the thalamus with the neuroanatomical tracer wheatgerm agglutinin conjugated to horseradish peroxidase were sectioned for electron microscopy. Serial sections from several levels through each cell were immunostained for glutamate and gamma-aminobutyric acid using a postembedding immunogold technique. Perimeter measurements of spinothalamic cell somata and dendrites and the lengths of apposition for all terminal profiles in contact with the spinothalamic cells were obtained from electron micrographs using a digitizing tablet. These data were used to determine the density of terminals on the soma and dendrites. In addition, the terminal population on these cells was categorized by transmitter content (glutamate, gamma-aminobutyric acid, or unlabeled). The results demonstrate that terminal density increased on dendrites relative to their distance from the soma. Glutamatergic and GABAergic input composed 37% and 20% of the terminal population, respectively, and these percentages remained uniform for the soma and dendrites. There were no significant differences among the 15 cells analyzed for this study. The results, therefore, suggest that both type I and type II STT cells of the superficial DH have similar synaptic organizations.

Animals↗

PubMed2000

A simple method for estimating conduction velocity of the spinothalamic tract in healthy humans.

OBJECTIVES: The object of this study was to establish a method for estimating the conduction velocity (CV) of the spinothalamic tract (STT) in relation to clinical application. METHODS: The CV of the STT was estimated by an indirect method based on that reported by Kakigi and Shibasaki in 1991 (Kakigi R, Shibasaki H. Electroenceph clin Neurophysiol 80 (1991) 39). Laser-evoked potentials (LEP) were measured in 8 subjects following hand (LEPH) and foot (LEPF) laser stimulation. The conduction times recorded at the scalp (P340, P400 and N150 potentials) were considered as the summation of peripheral and central components. The peripheral conduction times were calculated by measuring the latency of the electrical cutaneous silent period (from the same stimulus site of LEPs), corrected for F- and M-wave latency values. RESULTS: The CV of the STT ranged between 8.3 and 11.01 m/s and its mean value was found to be approximately 9.87+/-1.24 m/s. The CV of the STT obtained by the N150 latencies overlapped that obtained by the P340/P400 latencies. CONCLUSIONS: Our data suggest that our method appears appropriate and useful for practical clinical purposes, furnishing an additional tool for investigating the physiological function of small-fiber pathways.

Brain↗

PubMed1982

The responses to somatic stimuli of deep spinothalamic tract cells in the lumbar spinal cord of the cat.

1. The responses to natural somatic stimuli of thirty-seven antidromically identified spinothalamic tract (s.t.t.) cells in Rexed's laminae VII and VIII of the lumbar spinal cord of the cat have been studied. A further twenty-eight s.t.t. cells were identified antidromically.2. Cells were activated from sites in, or close to, one of the following locations: nucleus (n.) parafascicularis or n. centrum medianum, magnocellular part of the medial geniculate or the medial leminiscus, n. ventralis posterior medialis, n. lateralis posterior.3. The majority (84%) of s.t.t. cells showed spontaneous discharge at 1-67 Hz.4. Somatic stimuli excited 81% of s.t.t. cells but gave rise to inhibition of spontaneous discharge in 54% of cells. Only 8.1% of cells gave only inhibitory responses while 35.1% gave only excitatory responses and 45.9% gave both inhibitory and excitatory responses. No response could be elicited in 10.8% of cells.5. The proportion of s.t.t. cells giving inhibitory and excitatory responses to hair movement, light touch or tap, innocuous pinch, noxious pinch, joint movement, twisting of and intense pressure on joints, flicking, palpation or deflexion of large muscles, skin cooling and warming and noxious heat are documented. Of these stimuli, only skin cooling and warming failed to produce a response in any cell.6. Many cells showed convergence from receptors in muscles, joint and skin although 29.7% responded exclusively to innocuous cutaneous stimuli.7. Convergence from receptors on wide, and sometimes quite separate, areas of the hind quarters was common but exclusively contralateral receptive fields were not found and for none of the above stimuli was the contralateral side more effective than the ipsilateral side.

Action Potentials↗

PubMed1986

Loss of spinothalamic tract neurons following neonatal treatment of rats with the neurotoxin capsaicin.

The purpose of the present experiments was to determine whether the organization of spinothalamic tract (STT) cells of adult rats was altered following the loss of most of their small-diameter peripheral afferent fibers, resulting from the neonatal administration of capsaicin. Rat pups were randomly assigned to serve as normal controls, to serve as vehicle controls, or to receive subcutaneous injections of capsaicin (50 mg/kg) on postnatal day (PND) 1, 2, 7, or 15; or an injection on PND 1, 3, and 5. When 60 days old, they were anesthetized and received 0.1-microliter thalamic injections of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) in the area of the central lateral nucleus (CL), the posterior group (PO), and the ventrobasal complex (VB), or the area of CL or VB. Following a survival time of 48 hr, the animals were perfused, and neuronal HRP reaction product was visualized with tetramethylbenzidine. The number and distribution of WGA:HRP-labeled STT neurons varied in treated animals with the time of capsaicin injection. Rats injected with capsaicin on or before PND 7 demonstrated a significant reduction of labeled STT neurons from the superficial laminae of the spinal cord. Additionally, lamina I neurons were unlabeled in animals treated before PND 7 even with large thalamic injections. Differences in the distribution of labeled STT neurons could not be demonstrated for animals injected with capsaicin on PND 7 or PND 15, though there was a decrement in the number of labeled neurons in PND 7 animals. In order to make certain that absence of labeled STT neurons was not due to some technical error or to insufficient spread of WGA:HRP at the site of injection, six injections of WGA:HRP were placed in the thalamus of PND 1 and normal adult animals. Where the dense core of reaction product did not extend caudal to the posterior commissure, WGA:HRP-positive neurons were located and distributed similarly to those cases described for large thalamic injections. Neurons in superficial laminae of the nucleus proprius and lamina I of the contralateral spinal cord were labeled where the dense core of the thalamic injection extended into the mesencephalon of PND 1 animals. These studies indicate that the number and distribution of the cells of origin of the STT are altered in adult rats following their neonatal treatment with the neurotoxin capsaicin, and that this effect is limited to a critical postnatal period.

Age Factors↗

PubMed1989

Cells of origin of spinothalamic tract projections to the medial and lateral thalamus in the cat.

The double fluorescent retrograde labeling method was used to examine the distribution of spinothalamic tract (STT) cells that project to the medial and lateral thalamus in the cat. Injections of one fluorescent tracer (Fast Blue or Diamidino Yellow) were made throughout the lateral thalamus and injections of the other tracer were made in the medial thalamus at sites extrapolated from recording track coordinates. Survival times were successively extended (up to 5 weeks) in order to maximize labeling in both the cervical and lumbosacral spinal cord. On average, over 2,000 labeled contralateral STT cells were counted in serial sections from segments C5-7 and L5-S2. Numerical variability of the order of a factor of two was attributable to inherent differences between individual animals. The total number of cells labeled with fluorescent tracers was comparable to the number labeled with horseradish peroxidase in control cases, although there were significant differences between the laminar distributions of labeling produced by the two methods. Injections made anterior to the thalamus to control for labeling due to leakage or passing fibers did not produce substantial spinal labeling. The laminar distribution of fluorescent dye-labeled STT cells was consistent; about half (47%) were located in lamina I, 8% were in lamina V, 5% in lamina VI, 20% in lamina VII, and 20% in lamina VIII. The proportions of STT cells in laminae I and V were higher in cervical segments (57% and 12%, respectively) than in lumbosacral segments (38% and 6%). The dominant contribution of lamina I cells to the STT thus revealed by the fluorescent tracers is striking. The proportions of STT cells labeled from the medial and the lateral thalamus varied with segmental and laminar location and with injection placement. The majority (62%) of STT cells in most cases projected only to the medial thalamus, 25% projected only to the lateral thalamus, and 13% projected to both. The STT cell populations in laminae I, VII, and VIII each displayed this common projection pattern. In contrast, cells in laminae V and VI projected predominantly to the lateral thalamus. Twice as many STT cells in lamina I (19%) projected to both the medial and the lateral thalamus as from other laminae. A greater proportion of laminae V-VIII STT cells in segments L5-6 projected to the lateral thalamus, and in S1-2, more projected to the medial thalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

Amidines↗

PubMed1982

The effects of serotonin antagonists on the inhibition of primate spinothalamic tract cells produced by stimulation in nucleus raphe magnus or periaqueductal gray.

The effects of serotonin antagonists were examined on the inhibition and excitation of nociceptive spinothalamic tract cells produced by brainstem stimulation with short (200 msec) or long (2 sec) stimulus trains. The inhibitory effects resulting from stimulation in either nucleus raphe magnus (NRM) or in the periaqueductal gray with short stimulus trains were significantly reduced after the administration of serotonin receptor blockers. Reductions in periaqueductal gray inhibition were also observed on inhibition produced by long duration trains, whereas the effects of NRM inhibition were dependent on stimulus duration, current strength and dose of antagonist. The rare excitatory effect of NRM stimulation was also found to be relatively reduced after the administration of a serotonin antagonist. The relatively weak effects of serotonin antagonists on NRM inhibition are discussed in relation to three hypotheses: 1) parallel pathways; 2) multiple receptors; or 3) corelease of serotonin and another transmitter from raphe-spinal neurons.

Animals↗

PubMed2001

Conduction velocity of the spinothalamic tract in humans as assessed by CO(2) laser stimulation of C-fibers.

We measured the conduction velocity (CV) of C-fibers in the spinothalamic tract (STT) following stimulation with a CO(2) laser using a new method. We delivered non-painful laser pulses to tiny areas of the skin overlying the vertebral spinous processes at different levels from the 7(th) cervical (C7) to the 12(th) thoracic (T12), and recorded cerebral evoked potentials in 11 healthy men. We used the term "ultra-late laser evoked potentials" (ultra-late LEPs), since the peak latency was much longer than that for conventional LEPs related to Adelta-fibers following painful laser stimulation (late LEPs). The mean CV of C-fibers in the STT was 2.2+/-0.6 m/s, which was significantly lower than the CV of the Adelta-fibers (10.0+/-4.5 m/s). This technique is novel and simple, and should be useful as a diagnostic tool for assessing the level of spinal cord lesions.

Adult↗

PubMed1984

Effects of iontophoretically released peptides on primate spinothalamic tract cells.

The peptides substance P (SP), methionine-enkephalin (M-ENK), leucine-enkephalin (L-ENK), and cholecystokinin (CCK) were released iontophoretically near spinothalamic tract (STT) cells in anesthetized monkeys and STT-like cells in decorticate, spinalized monkeys. Peptide effects were observed on background discharges, firing induced by release of glutamate, and activity evoked by pinching the skin. SP could have any of several actions on STT cells, including excitation, inhibition, or biphasic effects. Multiple effects often resulted while recording from an individual cell when the dose or the electrode position was changed. M-ENK and L-ENK generally inhibited STT cells, and in some cases it was possible to demonstrate a reversal of the inhibition by naloxone. CCK also caused an inhibition that was additive with that produced by L-ENK. The multiple actions of SP on STT cells suggests the possibility that there may be more than one type of SP receptor on STT cells, although alternative explanations should be considered. Inhibition of STT cells by M- and L-ENK is consistent with the known analgesic action of opiates through spinal cord mechanisms. CCK has an action on STT cells similar to that of the enkephalins.

Action Potentials↗

PubMed1990

Collaterals of primate spinothalamic tract neurons to the periaqueductal gray.

Collateral projections are an important feature of the organization of ascending projections from the spinal cord to the brain. Primate spinothalamic tract (STT) neurons with collaterals to the periaqueductal gray (PAG) were studied by means of a fluorescent double-labeling method. Granular Blue and rhodamine-labeled latex microspheres were placed in the ventral posterior lateral (VPL) nucleus of the thalamus and the periaqueductal gray, respectively. Single and double labeled neurons were studied in the upper cervical cord, cervical enlargement, thoracic cord, lumbar enlargement, and sacral segments. The laminar distribution of double labeled neurons was similar to that of spinomesencephalic tract (SMT) neurons. Most double labeled (STT-SMT) neurons were located in contralateral laminae I, V, VII, and X. Relatively more lamina I STT-SMT neurons were found in the cervical enlargement and more lamina V STT-SMT neurons in the lumbar enlargement. The density of STT-SMT neurons in the upper cervical segments and cervical enlargement was almost equal. The density of STT-SMT neurons in the lumbar enlargement was 40% of that in the cervical enlargement. The thoracic and sacral segments had the lowest density of STT-SMT neurons, about 10% of that in the cervical enlargement. STT-SMT neurons constituted 14.7% of SMT neurons and 6% of STT neurons in the cervical enlargement and 15.3% of SMT neurons and 2.9% of STT neurons in the lumbar enlargement. The branch points of eight STT-SMT axons were studied electrophysiologically. The average percentage of conduction time spent in the parent axon was more than 85% for an antidromic action potential from the VPL nucleus and 91% from the PAG. Branch points of STT-SMT axons were calculated to be 9-13 mm caudal to the PAG, in the pons or rostral medulla.

Action Potentials↗

PubMed1987

Effects of stimulating the subcoeruleus-parabrachial region on the non-noxious and noxious responses of T1-T5 spinothalamic tract neurons in the primate.

The effects of electrical stimulation of the subcoeruleus-parabrachial (SC-PB) region on the discharge rate of upper thoracic spinothalamic tract (STT) neurons were investigated in 21 monkeys anesthetized with alpha-chloralose. STT cells were antidromically activated from the medial thalamus (MT) and the ventral posterior lateral nucleus (VPL) and received viscerosomatic convergent input from the cardiopulmonary sympathetic afferents and the left chest-forearm region. Stimulation of the SC-PB region inhibited the activity of all 30 STT neurons studied in the T1-T5 regions of the spinal cord. The minimum average current required to decrease the discharge rate of 22 cells exhibiting spontaneous activity was 89 +/- 10 microA (100 Hz, 100 microseconds duration). Currents as high as 300 microA completely inhibited the activity of most cells. Examination of the importance of frequency of stimulation from the SC-PB area on 8 cells revealed that impulses of at least 40 Hz (208 +/- 37 microA, 100 microseconds duration) were necessary to inhibit the spontaneous activity by 60%. Higher frequencies produced greater degrees of inhibition. Stimulation of the SC-PB region also inhibited the response of 23 of 23 neurons excited by noxious pinch and 11 of 11 wide dynamic range cells stimulated by innocuous input such as blowing or brushing hair. No differences in the inhibition produced by SC-PB stimulation on cells projecting to VPL (n = 20), MT (n = 5), or both VPL and MT (n = 5) were observed. These results demonstrate that the SC-PB region may be an important brainstem site for descending inhibition of both noxious and innocuous somatic input to upper thoracic STT cells in the primate.

Animals↗

PubMed2000

Enhanced phosphorylation of NMDA receptor 1 subunits in spinal cord dorsal horn and spinothalamic tract neurons after intradermal injection of capsaicin in rats.

The functional enhancement of NMDA receptors after peripheral tissue injury is proposed to contribute to the sensitization of spinothalamic tract (STT) cells and hyperalgesia. Protein phosphorylation is a major mechanism for the regulation of NMDA receptor function. In this study, Western blots, immunofluorescence double labeling, and the retrograde tracing method were used to examine whether phosphorylation of NMDA receptor 1 (NR1) subunits increases in spinal cord tissue and spinal dorsal horn neurons, especially in STT cells, after injection of capsaicin (CAP) into the glabrous skin of one hindpaw of anesthetized rats. Western blots showed that phosphorylated NR1 protein in spinal cord tissue was increased 30 min after CAP injection. Immunofluorescence double-labeling staining showed no significant difference in the number of the NR1-like immunoreactive neurons in laminae I-VII in the lumbosacral segments (L(4)-S(1)) on the ipsilateral and the contralateral sides 30 min after CAP or vehicle injection. However, the numbers of phospho-NR1-like immunoreactive neurons were significantly increased on the ipsilateral side compared with the vehicle injection group. STT cells were labeled by bilateral microinjections of the retrograde tracer fluorogold into the lateral thalamus, including the ventral-posterior lateral nucleus. Immunofluorescence staining was performed at 30, 60, and 120 min after CAP injection or at 30 min after vehicle injection. There was a significant increase in the proportion of STT cells with phosphorylated NR1 subunits compared either with the contralateral side 30 and 60 min after CAP injection or either side of animals after intradermal injection of vehicle. These results provide direct evidence that NMDA receptors in STT cells are phosphorylated after CAP injection.

Animals↗

PubMed1980

Inhibition and excitation of primate spinothalamic tract neurons by stimulation in region of nucleus reticularis gigantocellularis.

1. Electrical stimulation in the region of the nucleus reticularis gigantocellularis (NGc) in anesthetized monkeys inhibited or excited spinothalamic tract neurons in the lumbosacral and cervical enlargements. 2. The descending effects were generally more pronounced for activity evoked by cutaneous A-delta-fibers than for activity produced by large myelinated cutaneous afferents. Nevertheless, the responses to all types of natural stimuli used could be inhibited or facilitated. 3. The excitation from repeated brief stimulus trains to the NGc sometimes increased progressively, suggesting the existence of a positive feedback system. Occasionally, repeated stimulation of the NGc produced a progressively greater inhibition. 4. The threshold stimulus strength to elicit the inhibitory and excitatory actions was usually less than 50 microA, and in some cases less than 25 microA. The inhibition and excitation increased as the stimulus intensity was raised above the threshold value, or as the number and/or frequency of pulses in the stimulus train was increased. 5. The strongest inhibition and excitation was produced by stimulation within the NGc on either side of the brain stem. There was no obvious topographic organization of inhibitory and excitatory zones. 6. Dorsolateral tractotomies in the high cervical spinal cord did not prevent the effects of NGc stimulation, indicating that the inhibitory and excitatory pathways descend in the ventral parts of the white matter. 7. It is suggested that the inhibition and excitation are mediated by the medullary reticulospinal system.

Animals↗

PubMed1988

Inhibition of rat spinothalamic tract neuronal responses to noxious skin heating by stimulation in midbrain periaqueductal gray or lateral reticular formation.

The descending inhibitory effects of electrical midbrain stimulation on identified lumbar spinothalamic tract (STT) neurons were investigated in rats anesthetized with sodium pentobarbital. STT units were identified by their antidromic response to stimulation in the contralateral ventrobasal thalamus or medial lemniscus (mean conduction velocity: 18-20 m/sec). Thirty-two of 43 dorsal horn multireceptive STT units gave reproducible responses to noxious heat stimuli (42-56 degrees C, 10 sec) applied to the ventral hind paw. All STT units' responses were suppressed during stimulation (100 msec trains at 100 Hz, 3/sec, 15-300 microA) in PAG or LRF bilaterally. On- and offset of inhibition was rapid (less than 1 sec). STT unit responses to noxious heat were more effectively suppressed by LRF than PAG stimulation, based on statistically significant differences in mean thresholds for inhibition, slopes of current-inhibition plots, and mean current intensities evoking 50% inhibition. Mapping experiments revealed lowest-threshold (less than 25 microA) sites for inhibition to be in ventral PAG, subjacent tegmentum, and LRF bilaterally. STT unit responses increased with graded increases in stimulus temperature from threshold (mean: 46 degrees C) to 56 degrees C. Slopes of temperature-response functions were significantly reduced with little change in threshold during PAG stimulation, whereas these functions were shifted in a parallel manner toward higher temperatures during LRF stimulation. The serotonin antagonist methysergide reduced or blocked PAG- or LRF-evoked inhibition in 3/5 and 5/12 STT units, respectively. These results indicate that STT units are subject to different inhibitory controls from PAG and LRF.

Animals↗

PubMed1995

Evidence for glutamate as neurotransmitter in trigemino-and spinothalamic tract terminals in the nucleus submedius of cats.

The nucleus submedius in the medial thalamus of cats is an important termination site for lamina I trigemino-and spinothalamic tract (TSTT) neurons, many of which are nociceptive-specific, and the nucleus submedius has been proposed to be a dedicated nociceptive substrate involved in the affective aspect of pain. In the present study, the distribution of glutamate was examined by immunocytochemical methods in order to evaluate the possible role of this amino acid as a neurotransmitter in TSTT terminals in the nucleus submedius. TSTT terminals were identified by anterograde transport of horseradish peroxidase and wheatgerm agglutinin-horseradish peroxidase conjugate from the spinal cord or the medullary dorsal horn. Quantitative analysis of immunogold labelling revealed that TSTT terminals contain about twice the tissue average of glutamate-like immunoreactivity. A strong positive correlation was found between the density of synaptic vesicles and the density of gold particles in these terminals, whereas no relationship was seen between these variables in GABAergic presynaptic dendrites. Enrichment of glutamate-like immunoreactivity (approximately 250% of the tissue average) was also observed in terminals of presumed cortical origin. Presynaptic dendrites and neuron cell bodies in the nucleus submedius were found to contain relatively low levels of glutamate-like immunoreactivity, at or below the tissue average. These observations provide evidence that glutamate is a neurotransmitter in lamina I TSTT terminals in the nucleus submedius. The findings also suggest glutamatergic neurotransmission between cortical afferents and nucleus submedius neurons. Glutamate is therefore likely to be an important mediator of nociceptive processing in the medial thalamus.

Animals↗

PubMed1985

Inhibition of primate spinothalamic tract cells by TENS.

Transcutaneous electrical nerve stimulation (TENS) was applied in an experimental animal model to investigate the underlying mechanisms of this treatment. Recordings were made from identified spinothalamic tract (STT) neurons in the lumbosacral spinal cords of seven anesthetized monkeys. The STT cells were activated by stimulating the common peroneal nerve at a suprathreshold intensity for C-fibers. Evoked responses of C-fibers were compared before, during, and after application of TENS for 5 minutes from a commercially available TENS unit. The current delivered by the TENS unit was monitored. In 14 STT cells, some degree of inhibition of C-fiber evoked responses occurred only when the intensity of TENS exceeded the threshold of A delta fibers. At a given stimulus intensity, bursts of pulses repeated at a low rate were more effective than high-rate pulses. When TENS was applied to an area of the skin within a cell's receptive field, it was more effective than when it was applied outside the receptive field. The C-fiber volley recorded from a peripheral nerve was not reduced in size, and there were no substantial changes in its latency due to TENS. The inhibition of the activity of STT cells was not altered appreciably after intravenous injection of naloxone hydrochloride. These results suggest that TENS produces central nervous system inhibition by activating A delta afferent fibers. The inhibitory effects of TENS on STT cells appear to be due to a mechanism that does not involve release of endogenous opioid substances.

Animals↗

PubMed1999

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.

Animals↗