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.

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)

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)

Physiological properties of sensory trigeminal neurons projecting to mesencephalic parabrachial area in the cat

1989 ◽  
Vol 61 (6) ◽  
pp. 1153-1160 ◽  
Author(s):  
H. Hayashi ◽  
T. Tabata
Keyword(s):  
Dynamic Range ◽  
Receptive Fields ◽  
Radiant Heat ◽  
Tooth Pulp ◽  
Mechanical Stimuli ◽  
Head Region ◽  
Facial Region ◽  
Tactile Stimuli ◽  
Wdr Neurons ◽  
Stimulation Of

1. One hundred forty-one trigeminomesencephalic neurons in the sensory trigeminal nucleus of cats anesthetized with alpha-chloralose were identified by antidromic stimulation of the mesencephalic parabrachial area (PBA) which includes the nucleus cuneiformis, lateral periaqueductal gray matter, and the region between the inferior colliculus and brachium conjunctivum. 2. Neurons were categorized based on their responses to non-noxious and noxious mechanical and heat stimuli delivered to their peripheral receptive fields (RFs) including skin, mucosa, guard hairs, vibrissae, cornea, and tooth pulps. They were classified into three types: 48 nociceptive-specific (NS) neurons which responded to heavy pressure and/or noxious mechanical stimuli, and/or noxious radiant heat; 19 wide dynamic range (WDR) neurons which had a graded response to light tactile stimuli, noxious pinch, and/or noxious radiant heat; and 36 low-threshold mechanoreceptive (LTM) neurons which responded maximally to innocuous tactile stimuli. In subnucleus caudalis (Vc), NS and WDR neurons were the majority (75%) among the three types, while in the rostral subnuclei they were about one-half (54%) of the population. 3. The RFs were distributed over the orofacial and head region but mainly in the facial region. Twelve neurons (33% of the LTM neurons) responded to deflection of vibrissae and only 1 NS neuron out of 52 NS and WDR neurons tested responded to electrical stimulation of a tooth pulp. 4. A contralateral projection was dominant (57%), 30% projected ipsilaterally and 13% projected bilaterally.(ABSTRACT TRUNCATED AT 250 WORDS)

Properties of deep spinothalamic tract cells in the rat, with special reference to ventromedial zone of lumbar dorsal horn

1984 ◽  
Vol 52 (4) ◽  
pp. 612-624 ◽  
Author(s):  
D. Menetrey ◽  
J. de Pommery ◽  
F. Roudier
Keyword(s):  
Dorsal Horn ◽  
Receptive Fields ◽  
Lumbar Spinal Cord ◽  
Proprioceptive Information ◽  
Step Cycle ◽  
Spinothalamic Tract ◽  
Ongoing Activity ◽  
Homogeneous Population ◽  
Electrophysiological Properties ◽  
Postural Changes

Spinothalamic tract cells lying at the base of the dorsal horn or in deeper areas were identified in the rat at the lumbar spinal cord level by injecting horseradish peroxidase or stimulating posterior thalamic areas. Two groups of neurons were delineated; each constituted a homogeneous population of cells in terms of electrophysiological properties. Ventromedial dorsal horn cells lay at the base of the dorsal horn in its most medial aspect. They constitute a densely packed formation, which in the rat's ascending pathway system is restricted to the spinothalamic tract. Their main characteristics were a) ongoing activity, which consisted of small groups of spikes occurring at regular intervals, with a maximal discharge during ankle extension; b) unilateral receptive fields, which were restricted to the distal parts of the limb and involved both proprioceptive (ankle, joint digits) and exteroceptive (foot skin) structures; c) input of innocuous origin (midrange articular movement, touch, pressure) that was excitatory and input of noxious cutaneous origin (radiant heat) that was inhibitory; the same areas of foot skin were thus potentially either excitatory or inhibitory, depending on the nature of the stimulus applied; d) ankle flexion could differentially modulate both ongoing activity and excitatory responses from distal parts of the limb, inhibiting the former and potentiating the latter. In consequence, the ability of these cells to be driven by both proprioceptive and cutaneous inputs from limb extremities as well as by interactions of these inputs would appear to be very favorable for informing the central nervous system about limb position in both passive postural changes and the step cycle. It is suggested that they supply the thalamus with integrated information about locomotion. Lamina VII cells also constituted a subpopulation of neurons with very homogeneous electrophysiological properties. They were characterized by widespread inhibitory receptive fields, possibly spanning both hindlimbs and the ipsilateral forelimb. Inhibition was most effective when the stimulus (pressure, pinch) was intense and applied to proximal parts of the hindlimb. Ongoing activity consisted of spikes set at regular intervals and sometimes related to midrange movements of the knee. Although the significance of the widespread inhibitory receptive fields remains unclear, it has been suggested that these neurons are involved in the transmission of proprioceptive information.(ABSTRACT TRUNCATED AT 400 WORDS)

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)

A comparative study of the changes in receptive-field properties of multireceptive and nocireceptive rat dorsal horn neurons following noxious mechanical stimulation

1989 ◽  
Vol 62 (4) ◽  
pp. 854-863 ◽  
Author(s):  
J. M. Laird ◽  
F. Cervero
Keyword(s):  
Dorsal Horn ◽  
Mechanical Stimulation ◽  
Receptive Fields ◽  
Mechanical Stimulus ◽  
Mechanical Stimuli ◽  
Dorsal Horn Neurons ◽  
Mechanical Threshold ◽  
Before And After ◽  
Low Threshold ◽  
Noxious Mechanical Stimulation

1. Single-unit electrical activity has been recorded from 42 dorsal horn neurons in the sacral segments of the rat's spinal cord. The sample consisted of 20 multireceptive (class 2) cells with both A- and C-fiber inputs and 22 nocireceptive (class 3) cells. All neurons had cutaneous receptive fields (RFs) on the tail. 2. The RF sizes of the cells and their response thresholds to mechanical stimulation of the skin were determined before and after each of a series of 2-min noxious mechanical stimuli. Up to five such stimuli were delivered at intervals ranging from 10 to 60 min. In most cases, only one cell per animal was tested. 3. The majority of neurons were tested in barbiturate-anesthetized animals. However, to test whether or not this anesthetic influenced the results obtained, experiments were also performed in halothane-anesthetized and decerebrate-spinal preparations. The results from these experiments are considered separately. 4. All of the neurons responded vigorously to the first noxious pinch stimulus and all but one to the rest of the stimuli in the series. The responses of the neurons varied from stimulus to stimulus, but there were no detectable trends in the two groups of cells. 5. The RFs of the class 2 cells showed large increases (624.3 +/- 175.8 mm2, mean +/- SE) after the application of the pinch stimuli. The RFs of the class 3 neurons, which were initially smaller than those of the class 2 cells, either did not increase in size or showed very small increases after the pinch stimuli (38.3 +/- 11.95 mm2, mean +/- SE). 6. Some cells in both groups (6/10 class 2 cells and 7/16 class 3 cells) showed a decrease in mechanical threshold as a result of the noxious mechanical stimulus, but none of the class 3 cells' thresholds dropped below 20 mN into the low-threshold range. 7. The results obtained in the halothane-anesthetized and decerebrate-spinal animals were very similar to those seen in the barbiturate-anesthetized experiments, with the exception that in the decerebrate-spinal animals, the RFs of the class 2 cells were initially larger and showed only small increases.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional properties of retinal ganglion cells during optic nerve regeneration in the goldfish

1998 ◽  
Vol 15 (6) ◽  
pp. 1145-1155 ◽  
Author(s):  
D.-J. OH ◽  
D.P.M. NORTHMORE
Keyword(s):  
Receptive Field ◽  
Ganglion Cells ◽  
Receptive Fields ◽  
Optic Tract ◽  
Evoked Responses ◽  
Antidromic Activation ◽  
Discharge Rates ◽  
Conduction Velocities ◽  
Maintained Discharge ◽  
Retinotectal System

After being severed, optic axons in goldfish regenerate and eventually restore the retinotectal map; refinement of the map depends upon impulse activity generated by the ganglion cells. Because little is known about the changes in activity and receptive-field properties of ganglion cells during regeneration, we made extracellular recordings from them in the intact eye up to 95 days after sectioning their axons in the optic tract. Their receptive fields were classified as OFF-, ON–OFF-, or ON-centers, and their axonal conduction velocities measured by antidromic activation. The rate of encountering single units dropped drastically at 4–8 days postsection when only a few OFF-center units could be recorded, recovering to normal between 42 and 63 days. Receptive-field centers were normal in size, except for the few OFF-centers at 4–8 days which were abnormally large. Maintained discharge rates of all types were depressed up to 42 days, but ON–OFF-center units were more spontaneously active than normal around 42 days. Light-evoked responses in OFF-center units were subnormal at 4–8 days, becoming supernormal at 16 days and normal thereafter. ON–OFF- and ON-center units started to regain responsiveness at 16 days, and became supernormal at 42 days, before returning to normal. Conduction velocities of all fiber groups dropped to a minimum at 8 days, the fastest being affected most. There was a gradual recovery to normal conduction velocity by 63 days. The conduction latencies of OFF- and ON–OFF-center units recovered to normal by 42 days, and ON-center units by 63 days. Recovery of ganglion cell responsiveness correlates with functional recovery in the retinotectal system: OFF-center units recover light-evoked responses at about the time OFF activity first reappears in the tectum. ON- and ON–OFF-center units recover later, exhibiting supernormal spiking activity around the time that ON responses reappear in the tectum.

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.

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

1975 ◽  
Vol 38 (1) ◽  
pp. 132-145 ◽  
Author(s):  
R. D. Foreman ◽  
A. E. Applebaum ◽  
J. E. Beall ◽  
D. L. Trevino ◽  
W. D. Willis
Keyword(s):  
Electrical Stimulation ◽  
Mechanical Stimulation ◽  
Nerve Fibers ◽  
Mechanical Stimuli ◽  
Spinothalamic Tract ◽  
Antidromic Activation ◽  
Lumbosacral Spinal Cord ◽  
Afferent Fibers ◽  
To Receive ◽  
Stimulation Of

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.

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