Spinothalamic Tract Neurons Research Articles

Effects of stimulation in nucleus reticularis gigantocellularis on the activity of spinothalamic tract neurons in the monkey

Effects of stimulation in nucleus reticularis gigantocellularis on the activity of spinothalamic tract neurons in the monkey

Depression of primate spinothalamic tract neurons by iontophoretic application of 5-hydroxytryptamine

The effects of iontophoretic applications of 5-hydroxytryptamine (5-HT) were tested upon primate spinothalamic tract neurons recorded extracellularly in the spinal cord of anesthetized monkeys. The activity of most high threshold and wide dynamic range spinothalamic tract cells was depressed. 5-HT also reduced the responses of the cells to glutamate pulses which by themselves had a powerful excitatory action. It is concluded that 5-HT has a depressant action upon the postsynaptic membranes of spinothalamic tract cells, although the action has a slow time course. The observations are consistent with, but by no means prove, the hypothesis that serotonergic pathways descending from the brain stem produce a postsynaptic inhibition of spinothalamic tract neurons.

Spatial and temporal transformations of input to spinothalamic tract neurons and their relation to somatic sensations.

Spatial and temporal transformations of input to spinothalamic tract neurons and their relation to somatic sensations.

MECHANISMS OF FIRST AND SECOND PAIN IN THE PERIPHERAL AND CENTRAL NERVOUS SYSTEMS

Brief (< 2.0 sec) noxious heat pulses (peak temp = 51.5°C) programmed by a computer and generated by a contact thermode produced first and second pain in human subjects. Measurements of reaction time confirmed that these first and second pains were related to the conduction of impulses in A heat nociceptive and C polymodal nociceptive afferents respectively. Estimates of psychophysical magnitude showed that when four identical heat pulses were applied to the same spot on the hand (interstimulus interval 80 sec), the first pain progressively decreased in perceived intensity whereas the second pain increased with interstimulus intervals of 3 sec or less. The first pain did not decrease if the location of the thermode was changed between each stimulus whereas the summation of the second pain increased under these conditions. Identical trains of noxious heat pulses partially suppressed the responses of A and of C nociceptive afferents. These psychophysical observations and physiologic records indicate that the temporal suppression of heat-induced first pain is related to the suppression of A heat nociceptors and that prolonged temporal summation of second pain is related to summation within the central nervous system. A heat nociceptive afferents and C polymodal nociceptive afferents converge on two types of spinothalamic tract neurons: (1) wide dynamic-range neurons that receive input from non-nociceptive and nociceptive afferents. and (2) nociceptive-specific neurons. Since both types show summation of responses to repeated C fiber stimulation, they can account for summation of second pain.

Convergence of muscle and cutaneous input onto primate spinothalamic tract neurons

Convergence of muscle and cutaneous input onto primate spinothalamic tract neurons

Spinal cord potentials evoked by cutaneous afferents in the monkey

1. Negative intermediary cord potentials and the equivalent field potentials were recorded from the surface or within the monkey lumbosacral spinal cord in response to stimulation of myelinated afferent fibers in cutaneous or mixed nerves of the hindlimb. 2. Cord potentials resembling the N1 and N2 potentials described in the cat spinal cord were found but, in addition, activation of small myelinated fibers produced a later potential named here the N3-wave. By use of a subtraction technique, it is estimated that the N3-wave has a latency of 11.4 (+/- 3.5 SD) ms from the time of arrival of the volley in the largest affs at 9 (+/- 3) ms after its onset, and the wave lasts 23 (+/- 5.7) ms. 3. The N3-wave is not lost following spinal cord transection, but may instead be enhanced. It is thus due to neural circuitry intrinsic to the lumbosacral spinal cord. 4. The longitudinal distribution of the N3-wave is similar to that of the N1- and N2-waves. 5. The field potential associated with the N3-wave and recorded from within the spinal cord has two negative foci in some animals: near the dorsalmost part of the dorsal horn and in an area equivalent to Rexed's laminae IV-VI. The field potential reverses in sign in the ventral horn. 6. The N3-wave is evoked by Adelta fibers. This was shown by grading the stimulus strength, by measuring the conduction delay for producing the wave when stimuli are applied either proximally or distally on the sural nerve, and by showing that the N3-wave persists when the Aalphabeta fibers are anodally blocked. 7. There is often a late burst discharge in spinal neurons, including spinothalamic tract neurons, which can be attributed to Adelta fibers and which corresponds in time to the N3-wave. 8. It is proposed that the N3-wave can be used as a monitor of the central effects of Adelta fibers in the spinal cord.

Inhibition of primate spinothalamic tract neurons by stimulation in the region of the nucleus raphe magnus

Inhibition of primate spinothalamic tract neurons by stimulation in the region of the nucleus raphe magnus

Effects of dorsal column stimulation on primate spinothalamic tract neurons.

The effect of dorsal column stimulation on spinothalamic tract cells was investigated in anesthetized monkeys. The dorsal column stimuli were applied at midthoracic or at cervical levels of the cord, while the responses of spinothalamic tract cells of the lumbosacral enlargement were examined. A dorsal column volley depressed the activity of spinothalamic tract cells for about 150 ms. A similar depression was observed whether the spinothalamic tract cell was classified as hair activated, low, or high threshold, based on its response properties to cutaneous stimulation. The hair-activated and low-threshold spinothalamic tract cells were initially excited by the dorsal column volley, but often it was possible to demonstrate that a depression could be produced by stimuli which were too weak to cause excitation of these cells. Depression was produced both of the responses of spinothalamic tract cells to electrical stimulation of peripheral nerves and to mechanical stimulation of cutaneous nociceptors. A similar depression was produced by electrical stimulation of large afferents in peripheral nerves. The pathway mediating the depression of spinothalamic tract cells was shown to involve antidromic invasion of collaterals of dorsal column fibers. The best points for stimulation of the cord to produce a depression were over the ipsilateral dorsal column. A lesion interrupting the dorsal column eliminated the depression of cells below the lesion, whereas a lesion of much of the lateral column had no effect. The mechanism of the depression is likely to be complex. Apart from interactions at an interneuronal level, dorsal column volleys can be presumed to collide with sensory input from afferents which project up the dorsal column; collision would interfere chiefly with the responses of hair-activated and low-threshold spinothalamic tract cells. In addition, dorsal column volleys were shown to evoke inhibitory postsynaptic potentials in some spinothalamic tract neurons, and they also produced primary afferent depolarization, at least of large cutaneous afferemts. The excitation of hair-activated and low-threshold spinothalamic tract cells argues against their participation in signaling pain, since dorsal column stimulation in humans does not produce pain at stimulus intensities and frequencies which should activate such neurons. Alternatively, an ascending volley in the dorsal column or in other pathways may interfere with pain transmission in the brain.

Responses of primate spinothalamic tract neurons to natural stimulation of hindlimb

Responses of primate spinothalamic tract neurons to natural stimulation of hindlimb

Static and dynamic responses of spinothalamic tract neurons to mechanical stimuli.

The activity of primate spinothalamic tract neurons was investigated. Units were identified by antidromic activation from the diencephalon. Most had a spontaneous discharge. The fastest spontaneous discharge rates were from neurons activated by receptors in muscles or joints. However, such activity could be decreased by repositioning the hindlimb. Spontaneous activity was also altered by changes in anesthetic level. Time-interval histograms demonstrated the patterns of spontaneous discharge. Many units could be excited by noxious stimulation. Graded step displacements of the skin often evoked a slowly adapting discharge which was a function of pressure (or displacements above a threshold of some hundreds of microns). Responses continued to increase as pressures became noxious. Rapidly adapting responses of hair-activated and low-threshold spinothalamic tract neurons were tested with ramp stimuli and found to signal acceleration (or a higher derivative of position), velocity, or a combination of these. Responses to stimulus acceleration were prominent when hairs were displaced, while responses to stimulus velocity were seen with displacement of the skin. Possible receptor types which might account for the observations are discussed.

Organization and receptive fields of primate spinothalamic tract neurons.

A technique is described for recording from axons belonging to the spinothalamic tract of the monkey. The axons arose from cell bodies located within the spinal cord since the latency of orthodromic activation by afferents within the dorsal funiculus was short. The axons were antidromically activated from the ipsilateral diencephalon. The spectrum of conduction velocities indicates that the recordings favored large-diamter axons. However, all of the classes of spinothalamic tract units described from soma-dendritic recordings were represented in the sample. When the locations of the axons in the ventrolateral white matter were mapped, there was virtually complete overlap in the distributions of hair-activated, low-, and high-threshold spinothalamic tract axons, suggesting that the "lateral spinothalamic tract" conveys tactile, as well as pain and temperature, information. The only segregated population of axons were those belonging to units activated by receptors in deep tissues, including muscle. These were in a band along the ventral surface of the cord. The stimulus points for antidromically activating spinothalamic cells of axons were in the known diencephalic course of the spinothalamic tract, including the ventral posterior lateral nucleus. Stimulus point locations were similar for high-threshold and other categories of units. Receptive-field sizes were smaller for high-threshold spinothalamic cells or axons than for hair-activated or low-threshold units. Receptive-field size was correlated with position on the hindlimb. The smallest fields belonged to cells in lamina I, with progressively larger sizes for cells in laminae IV and V. Receptive-field shape was evaluated by the length/width ratio, which was smallest for high-threshold units and progressively larger for low-threshold and hair-activated units. The receptive-field positions of spinothalamic tract axons were related to the locations of the axons. There was a rough somatotopic representation in the tract, with the most caudal dermatomes represented dorsolaterally, and the most rostral ventromedially.

Responses of primate spinothalamic tract neurons to electrical stimulation of hindlimb peripheral nerves

The responses of spinothalamic tract neurons were studied by extra- and intracellular recordings from the lumbosacral spinal cord in anesthetized rhesus monkeys (Macaca mulatta). The neurons were identified by antidromic activation from the contralateral diencephalon. They were then classified by the mildest form of mechanical stimulation applied to the ipsilateral hindlimb. The effects of electrical stimulation of the nerve(s) supplying the receptive field were investigated. Graded electrical stimulation revealed that the threshold responses of spinothalamic tract neurons excited by weak mechanical stimuli occurred when the largest afferent fibers were activated. On the other hand, neurons that required intense mechanical stimulation for their excitation tended to have higher thresholds to electrical stimulation. Some spinothalamic tract cells were shown to receive monosynaptic excitatory connections from peripheral nerve fibers, although polysynaptic connections may generally be more important. An input from unmyelinated afferent fibers was demonstrated. It is concluded the primate spinothalamic tract neurons receive a rich convergent input from a variety of cutaneous receptors. The experiments provide some evidence for the most likely types of receptors.

Responses of primate spinothalamic tract neurons to natural stimulation of hindlimb.

Responses of primate spinothalamic tract neurons to natural stimulation of hindlimb.

Location of cells of origin of spinothalamic tract in lumbar enlargement of the monkey.

Location of cells of origin of spinothalamic tract in lumbar enlargement of the monkey.

Location of cells of origin of the spinothalamic tract in the lumbar enlargement of cat

Electrical stimulation was applied through a concentric bipolar electrode in the area of entry of the medial lemniscus into the thalamus to produce antidromic volleys in axons of spinothalamic tract neurons. The lumbar spinal cord was then searched systematically with a glass microelectrode in order to determine the location of the antidromically activated cells. The small size of many of the antidromic potentials necessitated the use of an averaging computer, which improved the signal-to-noise ratio by a factor of ten. Over 100 cells have been found in 25 cats at the level of L6. Most of these were located in lamina VIII and medial lamina VII of Rexed contralateral to the stimulating electrode in the brain. Cells were also found in a comparable position at higher and lower levels of the lumbosacral cord. The conduction velocities observed were 9–97 m/sec with a median of 33 m/sec. Commissural neurons are located in laminae VI to VIII. Some of these neurons thus give rise to the spinothalamic tract in the cat.

Integrative neural cardiovascular control.

Integrative neural cardiovascular control.

Spinal neurons specifically excited by noxious or thermal stimuli: marginal zone of the dorsal horn.

HIGH-THRESHOLD MECHANORECEPTORS and their centrally projecting myelinated fibers make up a functionally distinct group of cutaneous sensory units that have been suggested as part of the afferent apparatus for pain resulting from mechanical damage to the skin (3, 17). The argument for their relation to pain was based on two points: 1) the ability of such afferent elements, unique among those with medullated fibers, to provide signals differentiating noxious from innocuous mechanical events affecting the skin; and 2) the well-established correlation between pain and activity in thin myelinated afferent fibers

Responses of dorsal horn cells of M. mulatta to cutaneous and sural nerve A and C fiber stimuli.

Responses of dorsal horn cells of M. mulatta to cutaneous and sural nerve A and C fiber stimuli.

Inhibitory of glycine on spinal neurons in the cat.

Inhibitory of glycine on spinal neurons in the cat.

Unit analysis of nociceptive mechanisms in the thalamus of the awake squirrel monkey.

THE PREVAILING CONCEPT of pain sensation has arisen from von Frey’s (14) extension of Miiller’s (37) doctrine of specific nerve energies. According to this view, there are cutaneous receptors which, when stimulated, generate impulses which are transmitted via central pathways anatomically distinct from those subserving other forms of somatic sensation. Evidence from animal (8, 20, 33, 46, 48, 57) and human (9, 25) experiments has indicated that activity in small diameter peripheral fibers is associated with pain responses and sensation. The pain-specificity concept is further supported by the work of Poggio and Mountcastle (43) in which it was found that, in the anesthetized cat, nearly 60yo of the units recorded from a posterolateral thalamic region responded only to noxious stimuli. The cortical projection of this thalamic area has subsequently been found to contain neurons which are apparently exclusively nociceptive (7). Other electrophysiological work (2, 22, 41) has suggested that certain of the medial and intralaminar thalamic nuclei may also contain exclusively nociceptive units. However, the concept of pain-specific elements has been challenged (23, 35, 39, 47, 51, 52) for a number of reasons; among these is the lack of evidence for morphologically distinct “pain receptors” (26, 52), the paucity of specifically high threshold mechanoreceptive neurons (23, 50) or fibers, (10, 19, 20, 46, 57) and the failure to account for clinical phenomena such as congenital abnormalities in pain perception and the persistence of pain following spinothalamic tractotomy (5,29,31,39,40). One alternative view has been that pain results from a unique patterning of impulses from nonspecific cutaneous receptors (51). bines certain elements of ‘ Still another concept of cutaneous sensation com‘specificity” and “pattern” theory (35) . The purpose of this study was to test the hypothesis that, in the awake animal, there are thalamic neurons which respond only to noxious stimuli. An additional purpose was to explore the possibility that certain thalamic neurons, responsive to innocuous stimuli, may show a quantitatively distinct response to noxious stimuli. Awake animals were used because there is evidence that anesthetics may profoundly influence the response properties