Quantitative analysis of dorsal horn cell receptive fields following limited deafferentation

1995 ◽  
Vol 74 (5) ◽  
pp. 2065-2076 ◽  
Author(s):  
H. R. Koerber ◽  
P. B. Brown
Keyword(s):  
Dorsal Horn ◽  
Receptive Fields ◽  
Afferent Input ◽  
Width Ratio ◽  
Survival Times ◽  
Long Survival ◽  
Dorsal Horns ◽  
Length Width ◽  
Low Threshold ◽  
And Control

1. To test the hypothesis that subtotal deafferentation of dorsal horn cells can stimulate plastic changes in their receptive fields (RFs), diffuse deafferentation of the cat hindlimb dorsal horn was produced by transection of L7 or L6 and L7 dorsal roots. The following single-unit cutaneous low-threshold mechanoreceptor RF properties were compared between operated and control dorsal horns: 1) distance of RF center from tips of toes, 2) RF length-width ratio; and 3) RF area. 2. In both L7 and L6-L7 rhizotomized animals there was an increased incidence of silent electrode tracks in the most deafferented portion of the hindlimb map (the foot and toe representation). In the rhizotomized L6-L7 animals, there was also an increased incidence of symmetrically placed tracks in deafferented and control dorsal horns, in which cell RFs had no mirror-symmetrical components. In addition, cells in the lateral half of the L6 and L7 dorsal horns exhibited a proximal shift in the location of their RFs. In the rhizotomized L7 animals there was a distal shift of RFs in the L5 segment at long survival times. RFs had lower length-width ratios in L5 and L6 at short survival times and in L6 at long survival times. 3. In intact preparations, dorsal horn cells normally respond to inputs via single or small numbers of low-threshold cutaneous mechanoreceptors. Because these rhizotomies do not remove all inputs from any given area of skin, the deafferentations would produce only patchy loss of input from individual receptors. Therefore observed changes cannot be accounted for entirely by loss of afferent input, suggesting that some reorganization of dorsal horn cell RFs occurred. We conclude that the threshold stimulus for plastic change is less than total deafferentation of dorsal horn cells. At least some of the mechanisms underlying these changes may be active in normal animals in the maintenance of the somatotopic map or in conditioning.

Organization and receptive fields of primate spinothalamic tract neurons

1975 ◽  
Vol 38 (3) ◽  
pp. 572-586 ◽  
Author(s):  
A. E. Applebaum ◽  
J. E. Beall ◽  
R. D. Foreman ◽  
W. D. Willis
Keyword(s):  
Receptive Field ◽  
Receptive Fields ◽  
Ventral Surface ◽  
Field Size ◽  
Width Ratio ◽  
High Threshold ◽  
Spinothalamic Tract ◽  
Dorsal Funiculus ◽  
Length Width ◽  
Low Threshold

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.

Dorsal Horn Spatial Representation of Simple Cutaneous Stimuli

1998 ◽  
Vol 79 (2) ◽  
pp. 983-998 ◽  
Author(s):  
Paul B. Brown ◽  
Ronald Millecchia ◽  
Jeffrey J. Lawson ◽  
Stephanie Stephens ◽  
Paul Harton ◽  
...  
Keyword(s):  
Dorsal Horn ◽  
Spatial Representation ◽  
Single Point ◽  
Receptive Fields ◽  
Width Ratio ◽  
Contour Plots ◽  
Somatotopic Map ◽  
Length Width ◽  
Stimulus Features ◽  
Segmental Representations

Brown, Paul B., Ronald Millecchia, Jeffrey J. Lawson, Stephanie Stephens, Paul Harton, and James C. Culberson. Dorsal horn spatial representation of simple cutaneous stimuli. J. Neurophysiol. 79: 983–998, 1998. A model of lamina III–IV dorsal horn cell receptive fields (RFs) has been developed to visualize the spatial patterns of cells activated by light touch stimuli. Low-threshold mechanoreceptive fields (RFs) of 551 dorsal horn neurons recorded in anesthetized cats were characterized by location of RF center in cylindrical coordinates, area, length/width ratio, and orientation of long axis. Best-fitting ellipses overlapped actual RFs by 90%. Exponentially smoothed mean and variance surfaces were estimated for these five variables, on a grid of 40 points mediolaterally by 20/segment rostrocaudally in dorsal horn segments L4–S1. The variations of model RF location, area, and length/width ratio with map location were all similar to previous observations. When elliptical RFs were simulated at the locations of the original cells, the RFs of real and simulated cells overlapped by 64%. The densities of cell representations of skin points on the hindlimb were represented as pseudocolor contour plots on dorsal view maps, and segmental representations were plotted on the standard views of the leg. Overlap of modeled and real segmental representations was at the 84% level. Simulated and observed RFs had similar relations between area and length/width ratio and location on the hindlimb: r( A) = 0.52; r( L/ W) = 0.56. Although the representation of simple stimuli was orderly, and there was clearly only one somatotopic map of the skin, the representation of a single point often was not a single cluster of active neurons. When two-point stimuli were simulated, there usually was no fractionation of response zones or addition of new zones. Variation of stimulus size (area of skin contacted) produced less variation of representation size (number of cells responding) than movement of stimuli from one location to another. We conclude that stimulus features are preserved poorly in their dorsal horn spatial representation and that discrimination mechanisms that depend on detection of such features in the spatial representation would be unreliable.

Somatotopic organization in cat spinal cord segments with fused dorsal horns: caudal and thoracic levels

1985 ◽  
Vol 54 (5) ◽  
pp. 1167-1177 ◽  
Author(s):  
L. A. Ritz ◽  
J. L. Culberson ◽  
P. B. Brown
Keyword(s):  
Spinal Cord ◽  
Dorsal Horn ◽  
Dorsal Root ◽  
Receptive Fields ◽  
Vertical Orientation ◽  
Dorsal Roots ◽  
Somatotopic Organization ◽  
Dorsal Horns ◽  
Spinal Cord Regions ◽  
Low Threshold

We have explored the somatotopic organization of the two cat spinal cord regions where the dorsal horns are fused (i.e., continuous across the midline): the caudal and thoracic segments. We have mapped the low-threshold component of dorsal horn cell receptive fields (RFs) in these segments and have charted the locations of dorsal root low-threshold mechanoreceptive dermatomes. We also have determined the projections of caudal and thoracic dorsal roots to laminae III and IV by using degeneration techniques. The dorsal skin of the tail or thorax is represented laterally, and ventral skin is represented at the midline, in the fused dorsal horns. Many caudal and thoracic dorsal horn units had RFs that crossed the dorsal or ventral midline of the skin; these units were encountered near the edges or the midline, respectively, of the fused dorsal horns. The tail is fully represented within dorsal root dermatomes S3 to Ca5. Roots more caudal than Ca5 represent progressively smaller skin areas of the distal tail. Adjacent dermatomes overlapped 15-65%. Thoracic dermatomes had a nearly vertical orientation; adjacent dermatomes overlapped by 30-75%. Dorsal roots in caudal and thoracic regions have crossed projections to the medial and lateral (but not middle) portions of the contralateral dorsal horn. These crossed projections are a possible anatomical substrate for RFs that cross the ventral or dorsal midline. The dorsal root projection patterns are consistent with those that would be predicted from the dorsal root dermatomes and dorsal horn cell somatotopy, assuming that the presynaptic terminals' somatotopy is in register with that of dorsal horn cells (the presynaptic somatotopy hypothesis; see Ref. 12).

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)

Structure-function relationships in rat medullary and cervical dorsal horns. II. Medullary dorsal horn cells

1986 ◽  
Vol 55 (6) ◽  
pp. 1187-1201 ◽  
Author(s):  
W. E. Renehan ◽  
M. F. Jacquin ◽  
R. D. Mooney ◽  
R. W. Rhoades
Keyword(s):  
Receptive Field ◽  
Dorsal Horn ◽  
Dynamic Range ◽  
Receptive Fields ◽  
Noxious Stimulation ◽  
Medial Lemniscus ◽  
Guard Hair ◽  
Primary Afferent ◽  
Medullary Dorsal Horn ◽  
Low Threshold

In Nembutal-anesthetized rats, 31 physiologically identified medullary dorsal horn (MDH) cells were labeled with horseradish peroxidase (HRP). Ten responded only to deflection of one or more vibrissae. Six cells were activated by guard hair movement only, six by deflection of guard hairs or vibrissa(e), and seven by pinch of facial skin with serrated forceps. Different classes of low-threshold cells could not be distinguished on the basis of their somadendritic morphologies or laminar distribution. Neurons activated by multiple vibrissae were unique, however, in that one sent its axon into the medial lemniscus, and three projected into the trigeminal spinal tract. None of the guard hair-only or vibrissae-plus-guard hair neurons had such projections. Cells that responded best to noxious stimulation were located mainly in laminae I, II, and deep V, while neurons activated by vibrissa(e) and/or guard hair deflection were located in layers III, IV, and superficial V. Low-threshold neurons generally had fairly thick dendrites with few spines, whereas high-threshold cells tended to have thinner dendrites with numerous spines. Moreover, the dendritic arbors of low-threshold cells were, for the most part, denser than those of the noxious cells. Neurons with mandibular receptive fields were located in the dorsomedial portion of the MDH; cells with ophthalmic fields were found in the ventrolateral MDH, and maxillary cells were interposed. Cells sensitive to deflection of dorsal mystacial vibrissae and/or guard hairs were located ventral to those activated by more ventral hairs. Neurons with rostral receptive fields were found in the rostral MDH, while cells activated by hairs of the caudal mystacial pad, periauricular, and periorbital regions were located in the caudal MDH. Receptive-field types were encountered that have not been reported for trigeminal primary afferent neurons: multiple vibrissae; vibrissae plus guard hairs; and wide dynamic range. The latter two can be explained by the convergence of different primary afferent types onto individual neurons. Our failure to find a significant relationship between dendritic area (in the transverse plane) and the number of vibrissae suggests that primary afferent convergence may not be responsible for the synthesis of the multiple vibrissae receptive field. Excitatory connections between MDH neurons may, therefore, account for multiple vibrissae receptive fields in the MDH.

Reorganization of the receptive fields of spinocervical tract neurons following denervation of a single digit in the cat

1987 ◽  
Vol 57 (3) ◽  
pp. 803-818 ◽  
Author(s):  
P. Wilson ◽  
P. J. Snow
Keyword(s):  
Dorsal Horn ◽  
Receptive Fields ◽  
Light Touch ◽  
Single Digit ◽  
Dorsal Horn Neurons ◽  
Somatotopic Organization ◽  
Low Threshold ◽  
Adult Cat ◽  
Adult Cats ◽  
Central Reorganization

The effect of acute and chronic section of the digital nerves of a single toe on the organization of low-threshold, mechanoreceptive fields of lumbosacral spinocervical tract (SCT) neurons has been studied in adult cats anesthetized with chloralose. The immediate effect of sectioning the digital nerves of a single toe is to produce a patch of dorsal horn in the medial region of the ipsilateral lumbosacral cord in which SCT neurons lack any peripheral receptive field when gentle hair movement or light touch of glabrous skin are used as stimuli. Other SCT neurons in the region may lose only part of their receptive fields. Between 30 and 70 days later most of the affected SCT neurons have established receptive fields. These are mainly on somatotopically inappropriate areas of skin medially and laterally adjacent to the denervated region. A small proportion of SCT neurons form discontinuous receptive fields. The relative somatotopic organization within the affected region remains unchanged. As there is no sign of regeneration of the sectioned nerves the new receptive fields must result from a central reorganization of excitatory inputs to SCT neurons. It is concluded that chronic peripheral nerve section affects the anatomical and physiological mechanisms underlying the formation of light touch receptive fields of dorsal horn neurons in the lumbosacral cord of the adult cat, but that the resulting reorganization of receptive fields is spatially restricted.

Parametric studies of dorsal horn neurons responding to tactile stimulation

1975 ◽  
Vol 38 (1) ◽  
pp. 19-25 ◽  
Author(s):  
P. B. Brown ◽  
J. L. Fuchs ◽  
D. N. Tapper
Keyword(s):  
Dorsal Horn ◽  
Discharge Rate ◽  
Spontaneous Discharge ◽  
Width Ratio ◽  
Size And Shape ◽  
Dorsal Horn Neurons ◽  
Tactile Input ◽  
Somatotopic Map ◽  
Length Width ◽  
Central Delay

Dorsal horn neurons responding to tactile input were recorded in segments L3-S2 of unanesthetized, low-spinal cats. Single units were characterized with regard to receptive field (RF) location, RF size and shape, spontaneous discharge rate, central delay, and convergence of four tactile afferent types. 1. RF size increased from the toes to the calf region. 2. Length-width ratio increased from the toes to the calf and declined from the calf to the hip. 3. The relation between RF size and position on the limb was independent of segmental and laminar location of the neurons. 4. RF size was positively correlated with spontaneous discharge rate. 5. The relation between RF size and shape and RF position can be interpreted in terms of regional variations in the magnitude of the gradient of representation in the dorsal horn somatotopic map. 6. Central delay was negatively correlated with both RF size and rate of ongoing discharge. 7. There were no statistically significant differences among the laminae with respect to central delay, RF size or shape, ongoing discharge, or convergence combinations of the four tactile afferent systems. 8. Data presented were at variance with Wall's laminar cascading model for laminae IV-VI. Our results suggest that the model should be modified, at least to emphasize monosynaptic tactile input to all three of these laminae.

Cat hindlimb tactile dermatomes determined with single-unit recordings

1978 ◽  
Vol 41 (2) ◽  
pp. 260-267 ◽  
Author(s):  
P. B. Brown ◽  
H. R. Koerber
Keyword(s):  
Dorsal Root ◽  
Single Unit ◽  
Field Size ◽  
Width Ratio ◽  
Single Unit Recording ◽  
Unit Recording ◽  
Length Width ◽  
Low Threshold ◽  
Single Unit Recordings ◽  
Different Parts

1. Single-unit recording from dorsal root ganglia was used to determine the dermatomes of L4-S2 segments in the cat. Dermatomes for low-threshold myelinated mechanoreceptor afferents are smaller than those reported in earlier studies of whole-root dermatomes. There are also sufficient discrepancies among earlier studies and with the present data to merit reexamination of hindlimb whole-root dermatomes. 2. Receptive-field size varies directly with distance from toes. Length/width ratio is essentially constant for different parts of the hindlimb. 3. Estimates of innervation density verify the long-standing assumption that innervation density is greater for foot and toes than for proximal hindlimb, at least for low-threshold cutaneous myelinated afferents.

Low-threshold neuronal activity of spinal dorsal horn neurons increases during REM sleep in cats: comparison with effects of anesthesia

1995 ◽  
Vol 74 (2) ◽  
pp. 763-769 ◽  
Author(s):  
K. Kishikawa ◽  
H. Uchida ◽  
Y. Yamamori ◽  
J. G. Collins
Keyword(s):  
Receptive Field ◽  
Dorsal Horn ◽  
Slow Wave ◽  
Rem Sleep ◽  
Spinal Dorsal Horn ◽  
Neuronal Response ◽  
Receptive Fields ◽  
Spinal Dorsal ◽  
Tungsten Microelectrode ◽  
Low Threshold

1. Cats were prepared for chronic recordings from the lumbar enlargement of the spinal dorsal horn. At the beginning of each recording session, a tungsten microelectrode was advanced through the dura in a physiologically intact, awake, drug-free animal, until amplitude discrimination provided a single neuron with a receptive field on the hindquarters. 2. Extracellular recordings of activity of each neuron were made during receptive field stimulation with tactile and thermal nonnoxious and noxious stimuli. 3. Baseline responses obtained in the awake state were compared with responses of the same neurons during slow-wave or rapid-eye-movement (REM) sleep. In a subpopulation of neurons, the effects of anesthesia (propofol, 7.5 mg/kg iv) were observed after the completion of sleep studies. 4. The low-threshold receptive fields of the seven neurons studied during REM sleep were all increased in size when compared with the baseline value. The average increase was 52.6% (range 26.2–96.7%). 5. The low-threshold receptive fields of the seven neurons studied during REM sleep were reduced by propofol anesthesia by an average of 49.1% (range 29–74%). 6. Neuronal response to receptive field brushing was observed in 15 neurons during REM sleep. The effect of propofol on receptive field brushing was observed in 8 of those neurons. In only one of those eight neurons were the effects of REM sleep and anesthesia in the same direction. 7. Changes in neuronal responses were less consistent during slow-wave sleep but still differed from changes induced by propofol.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory Effects Evoked From the Anterior Hypothalamus Are Selective for the Nociceptive Responses of Dorsal Horn Neurons With High- and Low-Threshold Inputs

1997 ◽  
Vol 77 (5) ◽  
pp. 2831-2835 ◽  
Author(s):  
B. J. Workman ◽  
B. M. Lumb
Keyword(s):  
Dorsal Horn ◽  
Receptive Fields ◽  
Radiant Heat ◽  
Anterior Hypothalamus ◽  
Neuronal Activation ◽  
Inhibitory Effects ◽  
Dorsal Horn Neurons ◽  
Arterial Blood ◽  
Nociceptive Responses ◽  
Low Threshold

Workman, B. J. and B. M. Lumb. Inhibitory effects evoked from the anterior hypothalamus are selective for the nociceptive responses of dorsal horn neurons with high- and low-threshold inputs. J. Neurophysiol. 77: 2831–2835, 1997. The aim of the present study was to examine the selectivity of descending control of nociceptive information in the spinal dorsal horn following neuronal activation at “pressor” sites in the anterior hypothalamus. Extracellular single-unit activity was recorded from 11 dorsal horn neurons in the lower lumbar spinal cord of anesthetized rats. Neurons selected for investigation were those that responded to noxious (pinch and radiant heat >46°C) and nonnoxious (prod, stroke, and/or brush) stimulation within their cutaneous receptive fields on the ipsilateral hind paw. These are referred to as Class 2 neurons. Micropipettes were inserted stereotaxically into the anterior hypothalamus at sites where injection of the excitatory amino acidl-homocysteic acid (l-HCA) evoked increases in arterial blood pressure. The effects of microinjection of l-HCA at “pressor” sites in the anterior hypothalamus were then tested on the responses of Class 2 neurons to noxious and nonnoxious stimulation of their excitatory receptive fields. The high-threshold (pinch and/or radiant heat) responses of 7/7 Class 2 neurons tested were inhibited by an average of 66.3 ± 8.8% (mean ± SE) by neuronal activation at hypothalamic pressor sites. The low-threshold (prod) responses of 10/10 Class 2 neurons tested were not inhibited by neuronal activation at hypothalamic pressor sites; in 6 of these cells the response to low-intensity stimulation was increased by between 4 and 20%. Control injections of the inhibitory amino acid γ-aminobutyric acid (GABA) at the same hypothalamic pressor sites had no significant effects on arterial blood pressure or neuronal activity. With regard to sensory processing in the spinal cord, these data suggest that descending inhibitory control that originates from neurons in pressor regions of the anterior hypothalamus is highly selective for nociceptive inputs to Class 2 neurons.

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