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).

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.

Intraaxonal injection of neurobiotin reveals the long-ranging projections of A beta-hair follicle afferent fibers to the cat dorsal horn

1996 ◽  
Vol 76 (1) ◽  
pp. 242-254 ◽  
Author(s):  
P. Wilson ◽  
P. D. Kitchener ◽  
P. J. Snow
Keyword(s):  
Spinal Cord ◽  
Horseradish Peroxidase ◽  
Hair Follicle ◽  
Dorsal Horn ◽  
Receptive Fields ◽  
Dorsal Horn Neurons ◽  
Somatotopic Organization ◽  
Afferent Fibers ◽  
Synaptic Boutons

1. The morphology and somatotopic organization of the spinal arborizations of identified A beta-hair follicle afferent fibers (HFAs) with receptive fields (RFs) on the digits have been investigated in the cat by the use of intraaxonal injection of the tracer n-(2 aminoethyl) biotinamide. 2. In three cats, the long-ranging projections of six HFAs were examined by selectively injecting afferents with RFs on digit 2, 4, or 5, directly over the digit 3 representation, and examining their collateral morphology in transverse sections of the spinal cord. The rostral and caudal boundaries of the digit 3 representation were determined by mapping the RFs of identified spinocervical tract (SCT) neurons. 3. In two more cats, three HFAs were injected at random rostrocaudal positions and their morphology was examined in parasagittal sections. In one animal (2 HFAs), the somatotopy of the digit representation was again determined by mapping the RFs of SCT neurons. In the remaining cat (1 HFA), the somatotopy of the dorsal horn was mapped from the RFs of unidentified dorsal horn neurons. 4. Hair follicle afferents emitted many more collaterals, over much greater rostrocaudal distances, than indicated by previous horseradish peroxidase studies, and all collaterals gave rise to synaptic boutons. 5. HFAs that have RFs confined to a small part of a digit give rise to bouton-bearing axonal branches throughout the entire rostrocaudal extent of the hindpaw representation.

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.

Dorsal Root Rhizotomy and Avulsion in the Cat: A Comparison of Long Term Effects on Dorsal Horn Neuronal Activity

Neurosurgery ◽  
1984 ◽  
Vol 15 (6) ◽  
pp. 921-927
Author(s):  
Janice Ovelmen-Levitt ◽  
Betty Johnson ◽  
Purvis Bedenbaugh ◽  
Blaine S. Nashold
Keyword(s):  
Spinal Cord ◽  
Neuronal Activity ◽  
Dorsal Root ◽  
Receptive Fields ◽  
Substantia Gelatinosa ◽  
Inhibitory Influence ◽  
Long Term Effects ◽  
Avulsion Injury ◽  
Dorsal Horns

Abstract We performed an extracellular microelectrode analysis of the neuronal activity of cells located in deeper laminae of dorsal horns that had been deafferented by ipsilateral lumbar dorsal root rhizotomy or avulsion. Special attention was given to those cells that were recorded in preparations that were more than 6 weeks chronic. We compared the results to those obtained in nondenervated controls and in experiments in which the spinal cord was acutely transected at a midthoracic level, but had intact dorsal roots. There was an increase in ipsilateral flank and contralateral input in the chronically deafferented as compared to nondenervated controls. Differences were observed between long term rhizotomized and avulsed dorsal horns. Receptive fields extended on to flank and thoracic dermatomes after rhizotomy, often requiring only light cutaneous stimuli. Receptive fields were more restricted with avulsion injury, generally requiring moderate to strong, superficial or deep pinch. Histological analysis revealed consistent differential damage to the medial portion of Lissauer's tract with avulsion injury and subsequently more gliosis in the substantia gelatinosa. The loss of this propriospinal pathway may explain the lack of receptive field expansion on to the thoracic dermatomes and the stronger natural stimuli that were required. A higher percentage of cells with bilateral and inhibitory receptive fields was found in experiments in which the spinal cord was transected at a midthoracic level than in the controls. Ipsilateral excitatory receptive fields were also expanded as compared with control observations, but were not found on the flank. It is concluded that descending fibers have an inhibitory influence on both excitatory and inhibitory receptive fields, both ipsilaterally and contralaterally, which can be released by acute spinal cord transection. These alterations or release from inhibition may form a substrate for observations made after dorsal root denervations.

GABA-Receptor–Independent Dorsal Root Afferents Depolarization in the Neonatal Rat Spinal Cord

1998 ◽  
Vol 79 (5) ◽  
pp. 2581-2592 ◽  
Author(s):  
E. Kremer ◽  
A. Lev-Tov
Keyword(s):  
Spinal Cord ◽  
Dorsal Root ◽  
Gaba Receptor ◽  
Neonatal Rat ◽  
Extracellular Potassium ◽  
Rat Spinal Cord ◽  
Extracellular Potassium Concentration ◽  
Dorsal Roots ◽  
Intact Brain ◽  
Dorsal Root Afferents

Kremer, E. and A. Lev-Tov. GABA-receptor–independent dorsal root afferents depolarization in the neonatal rat spinal cord. J. Neurophysiol. 79: 2581–2592, 1998. Dorsal root afferent depolarization and antidromic firing were studied in isolated spinal cords of neonatal rats. Spontaneous firing accompanied by occasional bursts could be recorded from most dorsal roots in the majority of the cords. The afferent bursts were enhanced after elevation of the extracellular potassium concentration ([K+]e) by 1–2 mM. More substantial afferent bursts were produced when the cords were isolated with intact brain stems. Rhythmic afferent bursts could be recorded from dorsal roots in some of the cords during motor rhythm induced by bath-applied serotonin and N-methyl-d-aspartate (NMDA). Bilaterally synchronous afferent bursts were produced in pairs of dorsal roots after replacing the NaCl in the perfusate with sodium-2-hydroxyethansulfonate or after application of the γ-aminobutyric acid-A (GABAA) receptor antagonist bicuculline with or without serotonin (5-HT) and NMDA. Antidromic afferent bursts also could be elicited under these conditions by stimulation of adjacent dorsal roots, ventrolateral funiculus axons, or ventral white commissural (VWC) fibers. The antidromic bursts were superimposed on prolonged dorsal root potentials (DRPs) and accompanied by a prolonged increase in intraspinal afferent excitability. Surgical manipulations of the cord revealed that afferent firing in the presence of bicuculline persisted in the hemicords after hemisection and still was observed after removal of their ventral horns. Cutting the VWC throughout its length did not perturb the bilateral synchronicity of the discharge. These findings suggest that the activity of dorsal horn neurons is sufficient to produce the discharge and that the bilateral synchronicity can be maintained by cross connectivity that is relayed from side to side dorsal to the VWC. Antagonists of GABAB, 5-HT2/5-HT1C, or glutamate metabotropic group II and III receptors could not abolish afferent depolarization in the presence of bicuculline. Depolarization comparable in amplitude to DRPs, could be produced in tetrodotoxin-treated cords by elevation of [K+]e to the levels reported to develop in the neonatal rat spinal cord in response to dorsal root stimulation. A mechanism involving potassium transients produced by neuronal activity therefore is suggested to be the major cause of the GABA-independent afferent depolarization reported in our study. Possible implications of potassium transients in the developing and the adult mammalian spinal cord are discussed.

Developmental Changes in the Fidelity and Short-Term Plasticity of GABAergic Synapses in the Neonatal Rat Dorsal Horn

2008 ◽  
Vol 99 (6) ◽  
pp. 3144-3150 ◽  
Author(s):  
Rachel A. Ingram ◽  
Maria Fitzgerald ◽  
Mark L. Baccei
Keyword(s):  
Spinal Cord ◽  
Dorsal Horn ◽  
Receptive Fields ◽  
Neuronal Firing ◽  
Neonatal Rat ◽  
Superficial Dorsal Horn ◽  
Short Term ◽  
Dorsal Horn Neurons ◽  
Gabaergic Synapses

The lower thresholds and increased excitability of dorsal horn neurons in the neonatal rat suggest that inhibitory processing is less efficient in the immature spinal cord. This is unlikely to be explained by an absence of functional GABAergic inhibition because antagonism of γ-aminobutyric acid (GABA) type A receptors augments neuronal firing in vivo from the first days of life. However, it is possible that more subtle deficits in GABAergic signaling exist in the neonate, such as decreased reliability of transmission or greater depression during repetitive stimulation, both of which could influence the relative excitability of the immature spinal cord. To address this issue we examined monosynaptic GABAergic inputs onto superficial dorsal horn neurons using whole cell patch-clamp recordings made in spinal cord slices at a range of postnatal ages (P3, P10, and P21). The amplitudes of evoked inhibitory postsynaptic currents (IPSCs) were significantly lower and showed greater variability in younger animals, suggesting a lower fidelity of GABAergic signaling at early postnatal ages. Paired-pulse ratios were similar throughout the postnatal period, whereas trains of stimuli (1, 5, 10, and 20 Hz) revealed frequency-dependent short-term depression (STD) of IPSCs at all ages. Although the magnitude of STD did not differ between ages, the recovery from depression was significantly slower at immature GABAergic synapses. These properties may affect the integration of synaptic inputs within developing superficial dorsal horn neurons and thus contribute to their larger receptive fields and enhanced afterdischarge.

Effect of neonatal denervation of hindlimb digits on the somatotopic organization of lumbar spinocervical tract neurons in the cat

1991 ◽  
Vol 66 (3) ◽  
pp. 762-776 ◽  
Author(s):  
P. Wilson ◽  
P. J. Snow
Keyword(s):  
Dorsal Horn ◽  
Receptive Fields ◽  
Large Degree ◽  
Mirror Image ◽  
Light Touch ◽  
Single Digit ◽  
Somatotopic Organization ◽  
The Right ◽  
Alpha Chloralose ◽  
Neonatal Denervation

1. The effect of transection and ligation of the digital nerves of either one (toe 3) or two (toe 3 and toe 4) hindpaw digits, in the first postnatal week, on the tactile receptive fields (RFs) of spinocervical tract (SCT) neurons was studied in adult, alpha-chloralose-anesthetized cats. Immediately before recording, the digital nerves of the corresponding digit(s) of the opposite, intact hindpaw were transected, and the neonatally lesioned digital nerves were recut proximal to the transection neuroma. 2. In the medial part of the dorsal horn at the L6-L7 level, the digits of the hindlimb are represented in the RFs of SCT cells in a precise axial sequence from the most medial digit (toe 2) rostrally to the most lateral digit (toe 5) caudally. Acute denervation of one or two digits in the adult produced an area in the ipsilateral dorsal horn in which SCT cells lacked any RFs. When acute denervation was restricted to a single digit, the unresponsive region of dorsal horn was approximately 3 mm in length, and when two digits were denervated the unresponsive zone was approximately 6 mm long. Because the representation of the toes of the left hindpaw is a mirror image of that of the right, the rostrocaudal extent and position of the region of unresponsive SCT cells was used to assess the location of the borders of the chronically deprived region on the opposite side of the cord. 3. In all cats examined after neonatal denervation of toe 3, most (89%) of the SCT cells sampled within the chronically deprived toe 3 representation had RFs. These RFs were either on toe 2 (44%) or toe 4 (18%), and a large proportion of cells (38%) had multiple RFs with components on both toe 2 and toe 4. In most cases the cells fired briskly to displacement of hairs or light touch of the skin within these RFs. SCT cells with a RF on toe 2 and/or toe 4 were found throughout the whole 3-mm length of the chronically deprived toe 3 region, but cells with a RF on toe 2 were more commonly found than cells with a RF on toe 4 at axial distances greater than or equal to 1.5 mm from the boundary of the normal representations of the respective digit. 4. After chronic, neonatal denervation of both toe 3 and toe 4, 59% of SCT cells sampled overall had RFs, but there was a large degree of interanimal variation in the proportion of unresponsive neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Five Sources of a Dorsal Root Potential: Their Interactions and Origins in the Superficial Dorsal Horn

1997 ◽  
Vol 78 (2) ◽  
pp. 860-871 ◽  
Author(s):  
Patrick D. Wall ◽  
Malcolm Lidierth
Keyword(s):  
Motor Cortex ◽  
Dorsal Horn ◽  
Dorsal Root ◽  
Repetitive Stimulation ◽  
Superficial Dorsal Horn ◽  
Dorsal Horn Neurons ◽  
Dorsal Roots ◽  
Myelinated Fibers ◽  
Root Potential ◽  
Stimulation Of

Wall, Patrick D. and Malcolm Lidierth. Five sources of a dorsal root potential: their interactions and origins in the superficial dorsal horn. J. Neurophysiol. 78: 860–871, 1997. The dorsal root potential (DRP) was measured on the lumbar dorsal roots of urethan anesthetized rats and evoked by stimulation of five separate inputs. In some experiments, the dorsal cord potential was recorded simultaneously. Stimulation of the L3 dorsal root produced a DRP on the L2 dorsal root containing the six components observed in the cat including the prolonged negative wave (DRP V of Lloyd 1952 ). A single shock to the myelinated fibers in the sural nerve produced a DRP on the L6 dorsal root after the arrival in the cord of the afferent volley. The shape of this DRP was similar to that produced by dorsal root stimulation. Repetitive stimulation of the myelinated fibers in the gastrocnemius nerve also produced a prolonged negative DRP on the L6 dorsal root. When a single stimulus (<5 μA; 200 μs) was applied through a microelectrode to the superficial Lissauer Tract (LT) at the border of the L2 and L3 spinal segments, a characteristic prolonged negative DRP (LT-DRP) began on the L2 dorsal root after some 15 ms. Stimulation of the LT evoked DRPs bilaterally. Recordings on nearby dorsal roots showed this DRP to be unaccompanied by stimulation of afferent fibers in those roots. The LT-DRP was unaffected by neonatal capsaicin treatment that destroyed most unmyelinated fibers. Measurements of myelinated fiber terminal excitability to microstimulation showed that the LT-DRP was accompanied by primary afferent depolarization. Repetitive stimulation through a microelectrode in sensorimotor cortex provoked a prolonged and delayed negative DRP (recorded L2–L4). Stimulation in the cortical arm area and recording on cervical dorsal roots showed that the DRP was evoked more from motor areas than sensory areas of cortex. Interactions were observed between the LT-DRP and that evoked from the sural or gastrocnemius nerves or motor cortex. The LT-DRP was inhibited by preceding stimulation of the other three sources but LT stimulation did not inhibit DRPs evoked from sural or gastrocnemius nerves on the L6 dorsal root or from motor cortex on the L3 root. However, LT stimulation did inhibit the DRP evoked by a subsequent Lissaeur tract stimulus. Recordings were made from superficial dorsal horn neurons. Covergence of input from LT sural, and gastrocnemius nerves and cortex was observed. Spike-triggered averaging was used to examine the relationship between the ongoing discharge of superficial dorsal horn neurons and the spontaneous DRP. The discharge of 81% of LT responsive cells was correlated with the DRP.

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