Spinothalamic and spinohypothalamic tract neurons in the cervical enlargement of rats. I. Locations of antidromically identified axons in the thalamus and hypothalamus

1994 ◽  
Vol 71 (3) ◽  
pp. 959-980 ◽  
Author(s):  
R. J. Dado ◽  
J. T. Katter ◽  
G. J. Giesler
Keyword(s):  
Dorsal Horn ◽  
Dynamic Range ◽  
Ventral Horn ◽  
Mechanical Stimuli ◽  
Spinothalamic Tract ◽  
Noxious Heat ◽  
Antidromic Activation ◽  
Posterior Thalamus ◽  
Electrolytic Lesions ◽  
Nociceptive Input

1. Seventy-seven neurons in the cervical enlargement of rats anesthetized with urethan were initially antidromically activated using currents < or = 30 microA from the contralateral posterior thalamus. A goal of these experiments was to determine the course of physiologically characterized spinal axons within the diencephalon. Therefore, in 38 cases, additional antidromic mapping was done throughout the mediolateral extent of the diencephalon at multiple anterior-posterior planes. 2. Electrolytic lesions marking the recording sites were recovered for 71 neurons. Thirty-one were located in the superficial dorsal horn (SDH); 39 were in nucleus proprius or the lateral reticulated area of the deep dorsal horn (DDH), and one was in the ventral horn. 3. Eight of 38 (21%) neurons that were tested for more anterior projections could only be antidromically activated with currents < or = 30 microA from sites in the contralateral posterior thalamus. Such neurons are referred to as spinothalamic tract (STT) neurons. Lesions marking the lowest threshold points for antidromic activation were located in or near the posterior thalamic group (Po). At more anterior levels, considerably higher currents were required for antidromic activation or it was not possible to activate the neurons with currents up to 500 microA. Four of these neurons were physiologically characterized and each responded preferentially to noxious mechanical stimuli (wide dynamic range, WDR). Each of the three neurons that were tested responded to noxious heat stimuli. These findings confirm anatomic studies that have shown that a number of STT axons terminate in Po and suggest that such axons that originate in the cervical enlargement carry nociceptive input from the upper extremity. 4. In 15 cases, electrode penetrations were made systematically throughout much of the contralateral ventrobasal complex (VbC). In 17 cases, penetrations were made throughout the intralaminar nuclei contralaterally, including the central lateral nucleus (CL). Surprisingly, only one of the examined axons was antidromically activated with low currents from CL and one from VbC, although both of these nuclei are known to receive sizeable inputs from the STT. 5. Many of the axons (27 of the 38 tested, 71%) that were initially antidromically activated from the contralateral posterior thalamus could also be antidromically activated with low currents (< or = 30 microA) and at increased latencies from sites located anteriorly in the contralateral hypothalamus. Such neurons are referred to as spinothalamic tract/spinohypothalamic tract (STT/SHT) neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

scholarly journals Neuronal hyperexcitability in the ventral posterior thalamus of neuropathic rats: modality selective effects of pregabalin

2016 ◽  
Vol 116 (1) ◽  
pp. 159-170 ◽  
Author(s):  
Ryan Patel ◽  
Anthony H. Dickenson
Keyword(s):  
Dynamic Range ◽  
Spinal Nerve ◽  
Population Coding ◽  
Mechanical Stimuli ◽  
Spinothalamic Tract ◽  
Noxious Heat ◽  
Posterior Thalamus ◽  
Central Processing ◽  
Wdr Neurons

Neuropathic pain represents a substantial clinical challenge; understanding the underlying neural mechanisms and back-translation of therapeutics could aid targeting of treatments more effectively. The ventral posterior thalamus (VP) is the major termination site for the spinothalamic tract and relays nociceptive activity to the somatosensory cortex; however, under neuropathic conditions, it is unclear how hyperexcitability of spinal neurons converges onto thalamic relays. This study aimed to identify neural substrates of hypersensitivity and the influence of pregabalin on central processing. In vivo electrophysiology was performed to record from VP wide dynamic range (WDR) and nociceptive-specific (NS) neurons in anesthetized spinal nerve-ligated (SNL), sham-operated, and naive rats. In neuropathic rats, WDR neurons had elevated evoked responses to low- and high-intensity punctate mechanical stimuli, dynamic brushing, and innocuous and noxious cooling, but less so to heat stimulation, of the receptive field. NS neurons in SNL rats also displayed increased responses to noxious punctate mechanical stimulation, dynamic brushing, noxious cooling, and noxious heat. Additionally, WDR, but not NS, neurons in SNL rats exhibited substantially higher rates of spontaneous firing, which may correlate with ongoing pain. The ratio of WDR-to-NS neurons was comparable between SNL and naive/sham groups, suggesting relatively few NS neurons gain sensitivity to low-intensity stimuli leading to a “WDR phenotype.” After neuropathy was induced, the proportion of cold-sensitive WDR and NS neurons increased, supporting the suggestion that changes in frequency-dependent firing and population coding underlie cold hypersensitivity. In SNL rats, pregabalin inhibited mechanical and heat responses but not cold-evoked or elevated spontaneous activity.

Spinothalamic and spinohypothalamic tract neurons in the cervical enlargement of rats. II. Responses to innocuous and noxious mechanical and thermal stimuli

1994 ◽  
Vol 71 (3) ◽  
pp. 981-1002 ◽  
Author(s):  
R. J. Dado ◽  
J. T. Katter ◽  
G. J. Giesler
Keyword(s):  
Dorsal Horn ◽  
Dynamic Range ◽  
Receptive Fields ◽  
Ventral Horn ◽  
Zona Incerta ◽  
High Threshold ◽  
Mechanical Stimuli ◽  
Spinothalamic Tract ◽  
Noxious Stimuli ◽  
Wdr Neurons

1. The goal of this study was to gather data that would increase our understanding of nociceptive processing by spinothalamic tract (STT) neurons that receive inputs from the hand and arm. Fifty neurons in the cervical enlargement of urethan-anesthetized rats were antidromically activated from the contralateral posterior thalamus. A stimulating electrode was moved systematically within an anterior-posterior plane in the thalamus until a point was located where the smallest amount of current antidromically activated the neuron. The antidromic thresholds at each of these lowest threshold points was < or = 30 microA; the mean antidromic threshold was 15.4 +/- 1.0 (SE) microA. Lowest threshold points were found primarily in the posterior thalamic group (Po), zona incerta, and in or near the supraoptic decussation. 2. The recording sites of 47 neurons were marked and recovered. Recording sites were located in the superficial dorsal horn (SDH, n = 15), deep dorsal horn (DDH, n = 31), and ventral horn (n = 1). Recording sites were located across the mediolateral extent of the SDH. Within the DDH, recording sites were concentrated laterally in nucleus proprius and dorsally in the lateral reticulated area. The locations of the recording points confirm previous anatomic descriptions of STT neurons in the cervical enlargement. 3. Cutaneous excitatory receptive fields were restricted to the ipsilateral forepaw or forelimb in 67% (10/15) of the neurons recorded in the SDH and 42% (13/31) of the neurons recorded in the DDH. Neurons having larger, more complex receptive fields were also commonly encountered. Thirty-three percent (5/15) of the neurons recorded in the SDH and 58% (18/31) recorded in the DDH had receptive fields that were often discontinuous and included areas of the ipsilateral shoulder, thorax, and head, including the face. 4. Innocuous and noxious mechanical stimuli were applied to the receptive field of each neuron. Fifty percent (25/50) responded to innocuous mechanical stimuli but responded at higher frequencies to noxious stimuli (wide dynamic range, WDR). Forty-four percent (22/50) responded only to noxious stimuli (high threshold, HT). Six percent (3/50) responded preferentially to innocuous stimuli (low threshold, LT). WDR and HT neurons were recorded in both the SDH and DDH, including nucleus proprius, an area not typically associated with nociceptive transmission at other levels of the cord. Sixty percent (9/15) of the units recorded in the SDH were classified as WDR neurons; the other 40% (6/15) were classified HT. Forty-eight percent (15/31) of the units recorded in the DDH were classified as WDR neurons and 42% (13/31) as HT.(ABSTRACT TRUNCATED AT 400 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.

Responses of monkey medullary dorsal horn neurons during the detection of noxious heat stimuli

1989 ◽  
Vol 62 (2) ◽  
pp. 437-449 ◽  
Author(s):  
W. Maixner ◽  
R. Dubner ◽  
D. R. Kenshalo ◽  
M. C. Bushnell ◽  
J. L. Oliveras
Keyword(s):  
Dorsal Horn ◽  
Stimulus Intensity ◽  
Dynamic Range ◽  
Thermal Stimulus ◽  
Mechanical Stimuli ◽  
Behavioral Task ◽  
Noxious Heat ◽  
Nociceptive Neurons ◽  
Medullary Dorsal Horn ◽  
Wdr Neurons

1. We examined the activity of thermally sensitive trigeminothalamic neurons and nonprojection neurons in the medullary dorsal horn (trigeminal nucleus caudalis) in three monkeys performing thermal and visual detection tasks. 2. An examination of neuronal stimulus-response functions, obtained during thermal-detection tasks in which noxious heat stimuli were applied to the face, indicated that wide-dynamic-range neurons (WDR, responsive to innocuous mechanical stimuli with greater responses to noxious mechanical stimuli) could be subclassified based on the slope values of linear regression lines. WDR1 neurons exhibited significantly greater sensitivity to noxious heat stimulation than WDR2 neurons or nociceptive-specific neurons (NS, responsive only to noxious stimuli). 3. In one behavioral task, the monkeys detected 1.0 degrees C increases in noxious heat from preceding noxious heat stimuli ranging from 44 to 48 degrees C. WDR1, WDR2, and NS neurons increased their discharge frequency as a function of the intensity of the first noxious heat temperature (T1) as well as the final temperature (T2). The responses of WDR1 neurons were greater than those produced by WDR2 or NS neurons across all the temperatures examined. The order of stimulus presentation affected the responses of WDR1 neurons to 1.0 degrees C increases in the noxious heat range but not those of WDR2 or NS neurons. 4. In a second behavioral task, the monkeys detected small increases in noxious heat (0.2-0.8 degrees C) from a first temperature of 46 degrees C. Although the responses of all three classes of neurons were monotonically related to stimulus intensity, WDR1 neurons exhibited greater sensitivity to small temperature increases than either WDR2 or NS neurons. 5. Subpopulations of all three classes of neurons exhibited responses that were independent of thermal stimulus parameters or sensory modality and that only occurred during the behavioral task. These task-related responses were time-locked to specific behavioral events associated with trial initiation and trial continuation. 6. These data provide evidence that a subpopulation of WDR neurons is the dorsal horn cell type most sensitive to small increases in noxious heat in the 45-49 degrees C temperature range and provides the most information about stimulus intensity. The findings support the view that nociceptive neurons have the capacity to precisely encode stimulus features in the noxious range and that WDR neurons are likely to participate in the monkeys' ability to perceive the intensity of such stimuli.

Responses of neurons in the gracile nucleus of cats to innocuous and noxious stimuli: basic characterization and antidromic activation from the thalamus

1992 ◽  
Vol 68 (3) ◽  
pp. 818-832 ◽  
Author(s):  
K. D. Cliffer ◽  
T. Hasegawa ◽  
W. D. Willis
Keyword(s):  
Background Activity ◽  
Dorsal Column ◽  
Mechanical Stimuli ◽  
Noxious Heat ◽  
Antidromic Activation ◽  
Low Intensity ◽  
Ventrobasal Thalamus ◽  
Gracile Nucleus ◽  
Nociceptive Input ◽  
Lateral Nucleus

1. Responses to innocuous and noxious mechanical and thermal stimuli were recorded from 90 neurons in the gracile nucleus of anesthetized cats. Cells were tested by antidromic activation for projections to the contralateral ventrobasal thalamus. 2. Cells were characterized broadly by their responses to mechanical stimuli as 1) responding only to tapping (16%), 2) fast-adapting to low-intensity mechanical stimuli (33%), or 3) slowly adapting (51%; most with a fast-adapting component to their responses). All fast-adapting cells and those slowly adapting cells that were tested with noxious heat were further categorized on the basis of their patterns of firing and responses to stimuli. These plus the tap-responsive cells comprised a more restricted sample of 76 categorized cells. 3. Many (22) slowly adapting cells responded to noxious heat (69% of tested slowly adapting cells; 29% of all categorized cells), either on the first application (9 cells) or after sensitization (13 cells), indicating input originating in nociceptors. Nearly all of these (21) responded more to intense pressure than to innocuous pressure. The majority of slowly adapting cells not responsive to noxious heat (5 of 8) or not tested with it (8 of 12) also responded more to intense than to innocuous pressure, suggesting possible input originating in nociceptors. Most cells that responded to noxious heat also had both rapidly and slowly adapting responses with low thresholds. Many were recorded in the range of the cluster region of the gracile nucleus. 4. Cells antidromically activated from the thalamus projected to the rostral part of the ventral posterior lateral nucleus, regardless of their physiological category, and included many with nociceptive input. Latencies of antidromic activation were shorter at more caudal locations in the gracile nucleus, indicating higher conduction velocities to the thalamus. Responses of antidromically activated cells to low-intensity phasic stimuli tended to be greater than those of cells not antidromically activated. 5. Background activity of the neurons was low, most firing at less than one spike/s. Antidromically activated cells had higher background activity than cells not antidromically activated. 6. The results indicate a greater proportion and more widespread distribution of cells with nociceptive input in the cat gracile nucleus than has been previously recognized. Many of these projected to the ventrobasal thalamus, showing that information originating in nociceptors can reach the thalamus through a dorsal column-medial lemniscal pathway in cats.

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.

The primate spinocervicothalamic pathway: responses of cells of the lateral cervical nucleus and spinocervical tract to innocuous and noxious stimuli

1988 ◽  
Vol 59 (3) ◽  
pp. 861-885 ◽  
Author(s):  
J. W. Downie ◽  
D. G. Ferrington ◽  
L. S. Sorkin ◽  
W. D. Willis
Keyword(s):  
Conduction Velocity ◽  
Dynamic Range ◽  
Receptive Fields ◽  
Glabrous Skin ◽  
Mechanical Stimuli ◽  
Spinothalamic Tract ◽  
Sinusoidal Vibration ◽  
Antidromic Activation ◽  
Lateral Cervical Nucleus ◽  
Stimulation Of

1. The response properties of neurons of the spinocervicothalamic pathway were studied in anesthetized macaque monkeys. Graded innocuous and noxious mechanical stimuli, including sinusoidal vibration and thermal pulses, were applied to the cutaneous receptive fields. 2. Forty-nine cells in the lateral cervical nucleus (LCN) were identified by antidromic activation from the ventral posterior lateral (VPL) nucleus of the contralateral thalamus. Twelve spinocervical tract (SCT) cells in the lumbosacral enlargement of the spinal cord were identified by antidromic activation from stimulation of the ipsilateral dorsolateral funiculus below C3 but not above C1. 3. Latencies for antidromic activation of LCN neurons averaged 2.3 ms, corresponding to a mean conduction velocity of approximately 17 m/s. Mean latency for orthodromic activation of LCN neurons following electrical stimulation of peripheral nerves was 12.6 ms. Overall mean conduction velocity for the monkey spinocervicothalamic pathway was estimated to be 29 m/s. 4. Most LCN cells had receptive fields on hairy skin, but some had input from glabrous skin and a few had subcutaneous fields. The receptive fields of most SCT cells had a glabrous skin component. Receptive fields tended to be smaller for SCT than LCN cells even for fields on a comparable part of the distal hindlimb. 5. Based on their responses to a series of mechanical stimuli (brushing, pressure, pinch, and squeeze), LCN and SCT cells were classified as low-threshold (LT), wide dynamic range (WDR), or high-threshold (HT) neurons. Most of the cells were in the LT or WDR classes. Thus the spinocervicothalamic pathway in the monkey differs from the spinothalamic tract (STT), in that STT cells are generally of the WDR or HT classes. 6. With the use of discriminant analysis, LCN and SCT neurons were allocated to categories determined from a k-means cluster analysis of the responses of 318 STT cells. The LCN and SCT neurons were in different proportions in the various categories than were STT cells, suggesting differences in the signaling properties of the spinocervicothalamic and spinothalamic paths. 7. Innocuous steady indentation of the skin failed to excite any of the neurons tested. Thus no positive evidence was obtained for an input to LCN neurons from slowly adapting mechanoreceptors. 8. Sinusoidal vibratory stimuli were used to test the ability of LCN and SCT neurons to follow repeated innocuous mechanical stimuli. Vibration at 10 Hz and an amplitude of 100 micron resulted in repetitive discharges in most LCN neurons and half the SCT neurons tested; many LCN neurons had thresholds below 25 micron.(ABSTRACT TRUNCATED AT 400 WORDS)

Location and properties of dorsal horn neurons at origin of spinoreticular tract in lumbar enlargement of the rat

1980 ◽  
Vol 44 (5) ◽  
pp. 862-877 ◽  
Author(s):  
D. Menetrey ◽  
A. Chaouch ◽  
J. M. Besson
Keyword(s):  
Dorsal Horn ◽  
Receptive Fields ◽  
Radiant Heat ◽  
Mechanical Stimuli ◽  
Spinothalamic Tract ◽  
Antidromic Activation ◽  
Electrophysiological Properties ◽  
Tactile Stimuli ◽  
Adjacent Structures ◽  
Conduction Velocities

1. Spinoreticular tract neurons at the rat lumbar cord level were identified by antidromic activation following stimulation at mainly pontine and mesencephalic levels. These units, which were found in the dorsal half of the cord, could be separated into two groups according to their spinal location, electrophysiological properties, and their central projections. 2. Units in the dorsolateral funiculus nucleus projected mainly to the cuneiformis area and adjacent structures with frequent bilateral projections. They had the slowest conduction velocities, sometimes in the unmyelinated range. Generally, they were driven only by stimulation of subcutaneous and/or deep structures. 3. Neurons located in the dorsal horn mainly projected contralaterally to pontine and mesencephalic levels. their conduction velocities and the electrophysiological properties were identical to those observed for the rat spinothalamic tract (22). Almost all (86%) had clear cutaneous sensitivity and generally large receptive fields: 40% responded to nonnoxious and noxious mechanical cutaneous stimuli and frequently to noxious radiant heat, 26% were exclusively excited by light tactile stimuli, and 20% required noxious cutaneous mechanical stimulation for activation. There was a good correlation between responses to natural and transcutaneous electrical stimulation: units driven by noxious mechanical stimuli received A-delta- and/or C-fiber inputs. The remaining units (14%) had more complex receptive fields associated with both excitatory and inhibitory inputs originating from a single peripheral area. 4. The functional heterogeneity of the rat spinoreticular tract is reminiscent of that demonstrated for the rat and monkey spinothalamic tracts. Similarly, the rat spinoreticular neurons are under the influence of descending inhibitory controls originating from the nucleus raphe magnus and bulbar reticular formation. 5. Responses of the rat spinoreticular tract neurons are consistent with the involvement of this pathway in the transmission of messages of both innocuous and noxious origins.

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