Responses of primate T1-T5 spinothalamic neurons to gallbladder distension

1984 ◽  
Vol 247 (6) ◽  
pp. R995-R1002 ◽  
Author(s):  
W. S. Ammons ◽  
R. W. Blair ◽  
R. D. Foreman
Keyword(s):  
Chest Pain ◽  
Dynamic Range ◽  
Discharge Rate ◽  
Gallbladder Disease ◽  
High Rate ◽  
High Threshold ◽  
Spinothalamic Tract ◽  
Left Chest ◽  
Afferent Fibers ◽  
Upper Thoracic

Extracellular unit recordings were obtained from 44 spinothalamic tract (STT) neurons in the T1-T5 segments of 15 alpha-chloralose anesthesized monkeys (Macaca fascicularis). Each cell had a somatic receptive field in the left chest region and was excited by electrical stimulation of cardiopulmonary sympathetic afferent fibers. Gallbladder distension to pressures between 20 and 100 mmHg increased activity in 16 of 44 neurons. Responses usually consisted of bursts of activity associated with increased gallbladder pressure (phasic responses) followed by maintained activity during the distension (tonic responses). Magnitude of phasic responses was linearly related to the distending pressure and was consistently greater than magnitude of tonic responses. The gallbladder-responsive and nonresponsive groups included similar proportions of wide dynamic range, high threshold, and high-threshold inhibitory cells. Nine of 10 gallbladder-responsive cells and 11 of 21 gallbladder-nonresponsive cells increased their discharge rate after injection of 2 micrograms/kg bradykinin into left atrium. Activity of cells with gallbladder input increased from 14 +/- 4 to 33 +/- 4 spikes/s. Cells without gallbladder input increased their discharge rate to a significantly less degree (10 +/- 3-23 +/- 4 spikes/s). These results indicate that upper thoracic STT neurons may increase their activity during gallbladder distension. Convergence of afferent information from the chest and gallbladder may explain chest pain occurring during gallbladder disease. Furthermore the tendency of gallbladder-responsive cells to respond to bradykinin injections with a high rate of discharge could explain how this chest pain of gallbladder origin may closely mimic pain of angina pectoris.

Primate nucleus gracilis neurons: responses to innocuous and noxious stimuli

1988 ◽  
Vol 59 (3) ◽  
pp. 886-907 ◽  
Author(s):  
D. G. Ferrington ◽  
J. W. Downie ◽  
W. D. Willis
Keyword(s):  
Conduction Velocity ◽  
Dynamic Range ◽  
Subcutaneous Tissue ◽  
Receptive Fields ◽  
High Threshold ◽  
Spinothalamic Tract ◽  
Sinusoidal Vibration ◽  
Nucleus Gracilis ◽  
Pressure Sensitive ◽  
Stimulation Of

1. Recordings were made from 67 neurons in the nucleus gracilis (NG) of anesthetized macaque monkeys. All of the cells were activated antidromically from the ventral posterior lateral (VPL) nucleus of the contralateral thalamus. Stimuli used to activate the cells orthodromically were graded innocuous and noxious mechanical stimuli, including sinusoidal vibration and thermal pulses. 2. The latencies of antidromic action potentials following stimulation in the VPL nucleus were significantly shorter for cells in the caudal compared with the rostral NG. The mean minimum afferent conduction velocity of the afferent conduction velocity of the afferent fibers exciting the NG cells was 52 m/s, as judged from the latencies of the cells to orthodromic volleys evoked by electrical stimulation of peripheral nerves. The overall conduction velocity of the pathway from peripheral nerve to thalamus was approximately 40 m/s. 3. Cutaneous receptive fields on the distal hindlimb usually occupied an area equivalent to much less than a single digit. However, a few cells had receptive fields up to or exceeding the area of the foot. 4. NG cells were classified by their responses to graded mechanical stimulation of the skin as low threshold (LT) or wide dynamic range (WDR). No high-threshold NG cells were found. A special subcategory of pressure-sensitive LT (SA) neurons was recognized. Many of these cells were maximally responsive to maintained indentation of the skin. The sample of NG cells differed from the population of primate spinothalamic and spinocervicothalamic pathways so far examined, in having a larger proportion of LT neurons and a smaller proportion of WDR cells. A few NG cells responded best to manipulation of subcutaneous tissue. 5. Discriminant analysis permitted the NG cells to be assigned to classes determined by a k-means cluster analysis of the responses of a reference set of 318 primate spinothalamic tract (STT) cells. There were four classes of cells based on normalized responses of individual neurons and another four classes based upon responses compared across the population of cells. The NG cells were allocated to the various categories in different proportions than either primate STT cells or spinocervicothalamic neurons, consistent with the view that the functional roles of these somatosensory pathways differ. 6. Some of the pressure-sensitive NG cells were excited when the skin was stretched, suggesting an input from type II slowly adapting (Ruffini) mechanoreceptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Grouping of somatosensory neurons in the spinal cord and the gracile nucleus of the rat by cluster analysis

1994 ◽  
Vol 72 (6) ◽  
pp. 2590-2597 ◽  
Author(s):  
J. W. Leem ◽  
B. H. Lee ◽  
W. D. Willis ◽  
J. M. Chung
Keyword(s):  
Cluster Analysis ◽  
Dorsal Horn ◽  
Dynamic Range ◽  
High Threshold ◽  
Spinothalamic Tract ◽  
Wide Dynamic Range ◽  
Gracile Nucleus ◽  
Noxious Stimuli ◽  
Thermal Stimuli ◽  
Wide Dynamic Range Neurons

1. A set of 11 cutaneous stimuli defined previously to differentiate among different types of cutaneous sensory receptors in the rat hindpaw was also effective in differentially activating second-order sensory neurons in the dorsal horn and the gracile nucleus of rats. 2. All sampled units were responsive to more than 1 of the 11 stimuli. However, none responded to innocuous warming or cooling stimuli. Therefore further analysis was restricted to responses to nine of the selected stimuli. 3. Cluster analysis of the responses to nine selected innocuous and noxious mechanical stimuli and noxious thermal stimuli yielded seven classes that seemed functionally distinct from each other: a class of high-threshold neurons, three classes of convergent (wide dynamic range) neurons, a class of a mixture of poorly responsive neurons and neurons receiving Pacinian inputs, and two classes of low-threshold neurons. 4. High-threshold neurons responded predominantly to noxious mechanical and thermal stimuli and presumably received an input from both mechanically and thermally sensitive nociceptors. These cells were located in the dorsal horn, and some were spinothalamic tract cells. Wide dynamic range neurons were excited by innocuous and noxious stimuli, but better by noxious stimuli. These classes of cells were either in the dorsal horn (some were spinothalamic tract cells) or in the nucleus gracilis.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatosensory response properties of contralaterally projecting spinothalamic and nonspinothalamic neurons in the second cervical segment of the cat

1991 ◽  
Vol 66 (1) ◽  
pp. 83-102 ◽  
Author(s):  
M. V. Smith ◽  
A. V. Apkarian ◽  
C. J. Hodge
Keyword(s):  
Dynamic Range ◽  
Cervical Spinal Cord ◽  
Average Distance ◽  
Whole Body ◽  
High Threshold ◽  
Average Depth ◽  
Spinothalamic Tract ◽  
Antidromic Activation ◽  
Response Properties ◽  
Electrolytic Lesions

1. The upper cervical spinal cord contains over one-third of the cells of the spinothalamic tract (STT). This study investigated response properties of contralaterally projecting STT neurons in C2 of the cat by the use of single-unit, microelectrode recordings. Standard antidromic stimulation and collision techniques were used to identify STT units projecting to the contralateral thalamus. Once an STT unit was found, its receptive field (RF) and responses to cutaneous stimuli such as touch, pressure, deep muscle squeeze, tap, noxious pinch, and heat were characterized. C2 units that were not activated from the contralateral thalamus (non-STT units) were also characterized. The locations of thalamic stimulation electrodes and spinal recording sites were reconstructed from electrolytic lesions. 2. A total of 48 STT and 68 non-STT units were well characterized. RF sizes were classified as small, intermediate, large, or whole body. Each unit was also classified as having one of two possible response types: simple units were those with homogeneous responses within the RF and were classified as low threshold (LT), high threshold (HT), wide dynamic range (WDR), deep, or tap. Complex units were those that responded differently in different regions of the RF. 3. The average depth of non-STT units subdivided by RF size was 2.1 +/- 0.6 (SD) mm for cells with small RFs, 2.4 +/- 0.8 mm for cells with intermediate RFs, 2.8 +/- 0.3 mm for cells with large RFs, and 2.7 +/- 0.5 mm for cells with whole-body RFs. The average depth of non-STT units based on response type was 2.0 +/- 0.5 mm for LT, 2.3 +/- 0.7 mm for HT, 2.1 +/- 0.7 mm for WDR, 2.6 +/- 0.9 mm for deep, 2.6 +/- 0.5 mm for tap, and 2.4 +/- 0.2 mm for complex. 4. A somatotopic organization along the rostrocaudal length of C2 and upper C3 was observed for non-STT units with small- and intermediate-size RFs. The average distance of the recording sites from the rostralmost dorsal rootlet of C2 was 3.8 +/- 2.1 mm for units with RFs on the face, 7.1 +/- 4.3 mm for units with RFs on the neck, and 11.9 +/- 5.1 mm for units with RFs on the forelimb. 5. The average threshold for antidromic activation of STT units was 175 +/- 120 microA. Most C2 STT units were activated from the ventroposterior region of the thalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of Responses of Primate Spinothalamic Tract Neurons to Pruritic and Algogenic Stimuli

2004 ◽  
Vol 91 (1) ◽  
pp. 213-222 ◽  
Author(s):  
Donald A. Simone ◽  
Xijing Zhang ◽  
Jun Li ◽  
Jun-Ming Zhang ◽  
Christopher N. Honda ◽  
...  
Keyword(s):  
Dynamic Range ◽  
Intradermal Injection ◽  
High Threshold ◽  
Mechanical Stimuli ◽  
Spinothalamic Tract ◽  
Wide Dynamic Range ◽  
Antidromic Activation ◽  
Lateral Nucleus ◽  
Maximal Time

We investigated the role of mechanosensitive spinothalamic tract (STT) neurons in mediating 1) the itch evoked by intradermal injection of histamine, 2) the enhanced sense of itch evoked by innocuous stroking (alloknesis), and 3) the enhanced pain evoked by punctate stimulation (hyperalgesia) of the skin surrounding the injection site. Responses to intradermal injections of histamine and capsaicin were compared in STT neurons recorded in either the superficial or the deep dorsal horn of the anesthetized monkey. Each neuron was identified by antidromic activation from the ventral posterior lateral nucleus of thalamus and classified by its initial responses to mechanical stimuli as wide dynamic range (WDR) or high-threshold (HT). Approximately half of the WDRs and one of the HTs responded weakly to histamine, some with a duration > 5 min, the maximal time allotted. WDRs but not HTs exhibited a significant increase in response to punctate stimulation after histamine consistent with their possible role in mediating histamine-induced hyperalgesia. Neither type of neuron exhibited significant changes in response to stroking, consistent with their unlikely role in mediating alloknesis. Furthermore, nearly all STT neurons exhibited vigorous and persistent responses to capsaicin, after which they became sensitized to stroking and to punctate stimulation. We conclude that the STT neurons in our sample are more likely to contribute to pain, allodynia, and hyperalgesia than to itch and alloknesis.

Position of Spinothalamic Tract Axons in Upper Cervical Spinal Cord of Monkeys

2000 ◽  
Vol 84 (3) ◽  
pp. 1180-1185 ◽  
Author(s):  
Xijing Zhang ◽  
Christopher N. Honda ◽  
Glenn J. Giesler
Keyword(s):  
Spinal Cord ◽  
Dorsal Horn ◽  
Dynamic Range ◽  
Cervical Spinal Cord ◽  
High Threshold ◽  
Spinothalamic Tract ◽  
Antidromic Activation ◽  
Lateral Funiculus ◽  
Upper Cervical ◽  
Low Threshold

Percutaneous upper cervical cordotomy continues to be performed on patients suffering from several types of severe chronic pain. It is believed that the operation is effective because it cuts the spinothalamic tract (STT), a primary pathway carrying nociceptive information from the spinal cord to the brain in humans. In recent years, there has been controversy regarding the location of STT axons within the spinal cord. The aim of this study was to determine the locations of STT axons within the spinal cord white matter of C2 segment in monkeys using methods of antidromic activation. Twenty lumbar STT cells were isolated. Eleven were classified as wide dynamic range neurons, six as high-threshold cells, and three as low-threshold cells. Eleven STT neurons were recorded in the deep dorsal horn and nine in superficial dorsal horn. The axons of the examined neurons were located at antidromic low-threshold points (<30 μA) within the contralateral lateral funiculus of C2. All low-threshold points were located ventral to the denticulate ligament, within the lateral half of the ventral lateral funiculus (VLF). None were found in the dorsal half of the lateral funiculus. The present findings support our previous suggestion that STT axons migrate ventrally as they ascend the length of the spinal cord. Also, the present findings indicate that surgical cordotomies that interrupt the VLF in C2 likely disrupt the entire lumbar STT.

Electrophysiological characteristics of primate spinothalamic neurons with renal and somatic inputs

1989 ◽  
Vol 61 (6) ◽  
pp. 1121-1130 ◽  
Author(s):  
W. S. Ammons
Keyword(s):  
Nerve Stimulation ◽  
Receptive Fields ◽  
High Threshold ◽  
Spinothalamic Tract ◽  
Renal Nerve ◽  
C Fibers ◽  
Afferent Fibers ◽  
Renal Nerve Stimulation ◽  
Somatic Receptive Fields ◽  
Stimulation Of

1. Spinothalamic tract (STT) neurons in the T10-L3 segments were studied for responses to renal and somatic stimuli. A total of 90 neurons was studied in 25 alpha-chloralose anesthetized monkeys (Macaca fascicularis). All neurons were antidromically activated from the ventral posterior lateral nucleus of the thalamus. 2. Sixty-two cells were excited by renal nerve stimulation and six inhibited. Probability of locating cells with renal input was greatest in T11-L1. Cells were located in laminae I and IV-VII; however, most were located in laminae V-VII. Antidromic latencies averaged 4.61 +/- 0.32 (SE) ms, whereas antidromic conduction velocities averaged 43.23 +/- 9.03 m/s. 3. Cells with excitatory renal input received A delta input only (36 cells) or A delta- and C-fiber inputs (26 cells). Stimulation of A delta renal afferent fibers evoked bursts of 1-10 spikes/stimulus [mean 3.6 +/- 0.9 spikes/stimulus] with onset latencies of 10.7 +/- 0.5 ms. Stimulation of C-fibers evoked 1.3 +/- 0.5 spikes/stimulus with onset latencies of 61.7 +/- 11.1 ms. Magnitude of responses to A delta-fiber stimulation was greatest in T12 and decreased both rostrally and caudally. Inhibitory responses to renal nerve stimulation required activation of renal C-fibers. 4. All cells that responded to stimulation of renal afferent fibers received convergent inputs from somatic structures. Forty-four cells were classified as wide dynamic range, 10 were high threshold, 12 were high-threshold cells with inhibitory input from hair, 2 were deep, and 2 were low threshold. Somatic receptive fields were large and located on the flank and abdomen and/or the upper hindlimb. Fourteen cells had inhibitory receptive fields located on the contralateral hindlimb or one of the forearms. 5. It is concluded that T11-L1 STT cells in the monkey respond reliably to renal nerve stimulation. Thoracolumbar STT cells may thus play a role in pain that results from renal disease. The locations of the somatic receptive fields of the cells suggest that they are responsible for the referral of renal pain to the flank and abdomen.

Inhibition of Primate Spinothalamic Tract Neurons by Spinal Glycine and GABA Is Modulated by Guanosine 3′,5′-Cyclic Monophosphate

1999 ◽  
Vol 81 (3) ◽  
pp. 1095-1103 ◽  
Author(s):  
Qing Lin ◽  
Jing Wu ◽  
Yuan Bo Peng ◽  
Minglei Cui ◽  
William D. Willis
Keyword(s):  
Signal Transduction ◽  
Dorsal Horn ◽  
Central Sensitization ◽  
Dynamic Range ◽  
Cgmp Level ◽  
High Threshold ◽  
Descending Inhibition ◽  
Spinothalamic Tract ◽  
Cyclic Monophosphate ◽  
Deep Layers

Inhibition of primate spinothalamic tract neurons by spinal glycine and GABA is modulated by guanosine 3′,5′-cyclic monophosphate. Our recent work has suggested that the nitric oxide/guanosine 3′,5′-cyclic monophosphate (NO/cGMP) signal transduction system contributes to central sensitization of spinothalamic tract (STT) neurons in part by influencing the descending inhibition of nociception resulting from stimulation in the periaqueductal gray. This study was designed to examine further whether activation of the NO/cGMP cascade reduces the inhibition of the activity of STT neurons mediated by spinal inhibitory amino acid (IAA) receptors. Responses of STT cells to noxious cutaneous stimuli were inhibited by iontophoresis of glycine and GABA agonists in anesthetized monkeys. Administration of 8-bromoguanosine-3′,5′-cyclophosphate sodium (8-bromo-cGMP), a membrane permeable analogue of cGMP, either by microdialysis or by iontophoresis reduced significantly the IAA-induced inhibition of wide dynamic range (WDR) STT cells in the deep layers of the dorsal horn. The reduction in inhibition lasted for up to 1–1.5 h after the cessation of drug infusion. In contrast, IAA-induced inhibition of WDR STT cells in the superficial dorsal horn and high-threshold (HT) cells in superficial or deep layers was not significantly changed during 8-bromo-cGMP infusion. Iontophoresis of 8-bromo-cGMP onto STT cells produced the same actions as produced by microdialysis of this agent, but the effect was not as long-lasting nor as potent. Finally, an attenuation of the IAA receptor–mediated inhibition of STT cells produced by iontophoretic release of a NO donor, 3-morpholinosydnonimine, could be blocked by pretreatment of the spinal cord with a guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. These results suggest that an increased spinal cGMP level contributes to the sensitization of WDR STT neurons in the deep dorsal horn in part by down-regulating spinal IAA receptors. However, no evidence is provided in this study that the NO/cGMP cascade regulates IAA receptors on HT and superficial WDR neurons. Combined with the preceding studies, our data support the view that NO and cGMP function in the same signal transduction cascade and play an important role in central sensitization.

A further examination of effects of cortical stimulation on primate spinothalamic tract cells

1983 ◽  
Vol 49 (2) ◽  
pp. 424-441 ◽  
Author(s):  
R. P. Yezierski ◽  
K. D. Gerhart ◽  
B. J. Schrock ◽  
W. D. Willis
Keyword(s):  
Motor Cortex ◽  
Sensorimotor Cortex ◽  
Dynamic Range ◽  
Cortical Stimulation ◽  
Cortical Inhibition ◽  
Sensory Cortex ◽  
High Threshold ◽  
Spinothalamic Tract ◽  
Average Latency ◽  
Stimulation Of

1. Stimulation of the sensorimotor cortex was found to excite and/or inhibit nociceptive spinothalamic tract cells. Thirteen wide dynamic range cells were inhibited by cortical stimulation, 6 were excited and 14 were both excited and inhibited. Four of six high-threshold cells were excited and one was inhibited. 2. Intermediate (200 ms) or long (2 s) duration conditioning trains were effective in reducing responses of spinothalamic cells evoked by noxious mechanical or thermal stimuli and by A- and C-fiber volleys in the sural nerve. Preferential inhibition of low-threshold responses with little or no effect on high-threshold discharges was observed in some cases. 3. Inhibitory actions were obtained primarily from stimulation of the SI sensory cortex and area 5, while excitation or excitation followed by inhibition was the dominant effect from motor cortex (area 4). Spinothalamic cells were also excited by stimulation of the medullary pyramid. 4. In eight animals extensive mapping of the sensorimotor cortex showed that for a given cell, stimulation of the sensory cortex produced inhibition while stimulation of motor cortex resulted in excitation. 5. The average latency of inhibition from sensory cortex was 29.8 +/- 10 ms, while the average latency of excitation from motor cortex was significantly shorter, 13.5 +/- 9 ms. The shortest latencies for excitation from pyramidal stimulation in the cases evaluated ranged from 2 to 9 ms. 6. Spinal cord lesions were made in five animals to determine the descending pathway(s) mediating corticofugal effects. Cortical and pyramidal effects were eliminated or considerably reduced by lesions involving the dorsal part of the lateral funiculus. This observation combined with latency data suggest that the corticospinal tract may be involved in the mediation of cortical excitation, while both pyramidal and extrapyramidal pathways are likely to be involved in cortical inhibition.

scholarly journals Termination Zones of Functionally Characterized Spinothalamic Tract Neurons Within the Primate Posterior Thalamus

2008 ◽  
Vol 100 (4) ◽  
pp. 2026-2037 ◽  
Author(s):  
Steve Davidson ◽  
Xijing Zhang ◽  
Sergey G. Khasabov ◽  
Donald A. Simone ◽  
Glenn J. Giesler
Keyword(s):  
Dynamic Range ◽  
Lumbar Spinal Cord ◽  
High Threshold ◽  
Chemical Information ◽  
Thalamic Nuclei ◽  
Spinothalamic Tract ◽  
Noxious Heat ◽  
Antidromic Activation ◽  
Posterior Thalamus ◽  
Medial Geniculate

The primate posterior thalamus has been proposed to contribute to pain sensation, but its precise role is unclear. This is in part because spinothalamic tract (STT) neurons that project to the posterior thalamus have received little attention. In this study, antidromic mapping was used to identify individual STT neurons with axons that projected specifically to the posterior thalamus in Macaca fascicularis. Each axon was located by antidromic activation at low stimulus amplitudes (<30 μA) and was then surrounded distally by a grid of stimulating points in which 500-μA stimuli were unable to activate the axon antidromically, thereby indicating the termination zone. Several nuclei within the posterior thalamus were targets of STT neurons: the posterior nucleus, suprageniculate nucleus, magnocellular part of the medial geniculate nucleus, and limitans nucleus. STT neurons projecting to the ventral posterior inferior nucleus were also studied. Twenty-five posterior thalamus-projecting STT neurons recorded in lumbar spinal cord were characterized by their responses to mechanical, thermal, and chemical stimuli. Sixteen of 25 neurons were recorded in the marginal zone and the balance was located within the deep dorsal horn. Thirteen neurons were classified as wide dynamic range and 12 as high threshold. One-third of STT neurons projecting to posterior thalamus responded to noxious heat (50°C). Two-thirds of those tested responded to cooling. Seventy-one percent responded to an intradermal injection of capsaicin. These data indicate that the primate STT transmits noxious and innocuous mechanical, thermal, and chemical information to multiple posterior thalamic nuclei.

Excitation of primate spinothalamic neurons by cutaneous C-fiber volleys

1979 ◽  
Vol 42 (5) ◽  
pp. 1354-1369 ◽  
Author(s):  
J. M. Chung ◽  
D. R. Kenshalo ◽  
K. D. Gerhart ◽  
W. D. Willis
Keyword(s):  
Dynamic Range ◽  
High Threshold ◽  
Mechanical Stimuli ◽  
Spinothalamic Tract ◽  
Noxious Heat ◽  
C Fibers ◽  
C Fiber ◽  
Excitatory Action ◽  
Low Threshold ◽  
Lateral Nucleus

1. The responses of spinothalamic tract cells in the lumbosacral spinal cords of anesthetized monkeys were examined following electrical stimulation of the sural nerve or the application of noxious thermal and mechanical stimuli to the skin on the lateral aspect of the foot. 2. The spinothalamic tract neurons were classified as wide dynamic range (WDR), high-threshold (HT), or low-threshold (LT) cells on the basis of their responses to mechanical stimuli. 3. All of the WDR and HT spinothalamic tract cells tested responded to volleys in A- and C-fibers. However, strong C-fiber responses were more common in HT than in WDR cells. 4. The responses atributed to C-fibers were graded with the size of the C-fiber volley. The latencies of the responses attributed to C-fibers indicated that the fastest afferents involved had a mean conduction velocity of 0.9 m/s. The responses remained after anodal blockade of conduction in A-fibers. 5. Temporal summation of the responses of spinothalamic tract cells was demonstrated both to brief trains of stimuli at 33 Hz and to single stimuli repeated at 1- to 2-s intervals. The latter phenomenon is often called "windup." 6. The responses of several spinothalamic tract cells to noxious heat pulses could still be elicited during anodal blockade of conduction in A-fibers. Similarly, it was possible to demonstrate an excitatory action of noxious mechanical stimuli despite interference with conduction in A-fibers by anodal current. 7. The cells investigated were located either in the marginal zone or in the layers of the dorsal horn equivalent to Rexed's laminae IV-VI in the cat. The cells were generally activated antidromically from the caudal part of the ventral posterior lateral nucleus of the thalamus.

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