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Biomedical subjects

C J Woolf

Publications and source records attributed to C J Woolf.

At least 127 records · Page 7Linked to original sources
PubMed1990

Characterization of the cutaneous input to the ventral horn in vitro using the isolated spinal cord-hind limb preparation.

Intracellular recordings were made from 21 ventral horn neurones including 7 flexor motoneurones in a 10-12-day-old rat isolated spinal cord-hind limb preparation. The cutaneous input to these neurones was assessed using natural mechanical stimulation within the cutaneous mechanoreceptive field or electrical stimulation of the sural nerve. The receptive fields of 10 ventral horn neurones including 3 flexor motoneurones were characterized: 60% of cells responded to both low (touch) and high (pinch) threshold mechanical stimulation of the skin while the remaining 40% responded only to noxious mechanical stimuli. The postsynaptic response consisted of either purely subthreshold polysynaptic EPSPS (n = 8) or graded sub- and suprathreshold EPSPS (n = 2). The duration of the EPSP was typically prolonged by as much as a factor of ten compared to duration of the mechanical stimulation. In another 11 neurones (4 flexor motoneurones) the pattern of the postsynaptic response was related to the intensity of sural nerve stimulation. A low intensity single shock produced a short latency (30 ms), short duration EPSP (less than 500 ms) while higher intensities elicited a longer duration (greater than 1 s), more complex EPSP. In 36% of cells tested the EPSP remained subthreshold for cell firing even at the highest stimulus intensity.

Animals↗
PubMed1990

The growth-associated protein GAP-43 appears in dorsal root ganglion cells and in the dorsal horn of the rat spinal cord following peripheral nerve injury.

When adult dorsal root ganglion cells are dissociated and maintained in vitro, both the small dark and the large light neurons show increases in the growth-associated protein GAP-43, a membrane phosphoprotein associated with neuronal development and plasticity. Immunoreactivity for GAP-43 appears in the cytoplasm of the cell bodies as early as 3.5 h post axotomy and is present in neurites and growth cones as soon as they develop. At early stages of culture (4 h to eight days) satellite/Schwann cells are also immunoreactive for GAP-43. Neurons in isolated whole dorsal root ganglion maintained in vitro become GAP-43-immunoreactive between 2 and 3 h after axotomy. It takes three days however, after cutting or crushing the sciatic nerve in adult rats in vivo, for GAP-43 immunoreactivity to appear in the axotomized dorsal root ganglion cells. GAP-43 immunoreactivity can be detected in the central terminals of primary afferent neurons in the superficial laminae of the dorsal horn of the lumbar enlargement four days after sciatic cut or crush. The intensity of the GAP-43 staining reaches a peak at 21 days and becomes undetectable nine weeks following crush injury and 36 weeks following sciatic nerve cut. The pattern of GAP-43 staining is identical to the distribution of sciatic small-calibre afferent terminals. Little or no staining is present in the deep dorsal horn, but GAP-43 does appear in the ipsilateral gracile nucleus 22 days after sciatic injury. In investigating the mechanism of GAP-43 regulation, blockade of axon transport in the sciatic nerve with vinblastine (10(-5) M-10(-4) M) or capsaicin (1.5%) was found to produce a pattern of GAP-43 immunoreactivity in the dorsal horn identical to that found with crush, while electrical stimulation of the sciatic nerve had no effect. Axotomy of primary sensory neurons or the interruption of axon transport in the periphery therefore acts to trigger GAP-43 production in the cell body. The GAP-43 is transported to both the peripheral and the central terminals of the afferents. In the CNS the elevated GAP-43 levels may contribute to an inappropriate synaptic reorganization of afferent terminals that could play a role in the sensory disorders that follow nerve injury.

Animals↗
PubMed1990

Activity-Dependent Changes in Rat Ventral Horn Neurons in vitro; Summation of Prolonged Afferent Evoked Postsynaptic Depolarizations Produce a d-2-Amino-5-Phosphonovaleric Acid Sensitive Windup.

The synaptic responses of lumbar ventral horn neurons including identified flexor motoneurons, to graded stimulation of peripheral nerves have been recorded in vitro in the young rat spinal cord-hindlimb preparation. Single shock stimulation of low threshold myelinated afferents evoked short latency (< 20 ms) short duration (< 1.0 s, 391 +/- 42 ms n=43 SEM) compositive mono- and polysynaptic potentials. Recruitment of both thinly myelinated (A delta) and unmyelinated (C) afferent fibres elicited a prolonged postsynaptic depolarization (> 1 s) in all cells. In the majority of cells (67.4%), this depolarization exceeded 4.0 s in duration (8.01 +/- 0.4 s, n=26, maximum 14 s). In the remainder, shorter responses were evoked (< 3.0 s, mean=1.74 +/- 0.4 s, n=18). In those cells where the postsynaptic response to a single A delta or C fibre strength stimulus exceeded 4 s, low frequency (0.5 - 1.0 Hz) repetitive stimulation resulted in a temporal summation of the postsynaptic depolarizations, which generated a cumulatively increasing depolarization. This incrementing depolarization was sufficient in 33% of the cells to produce a progressive increase in spike discharge (windup). On cessation of the train of stimuli the depolarization decayed slowly (65 +/- 27 s). The N-methyl d-aspartic acid (NMDA) receptor antagonist d-2-amino-5-phosphonovaleric acid (d-APV) reduced the duration and amplitude of the prolonged postsynaptic depolarizations elicited by a single shock stimulation of small diameter afferents by 57% and 50% respectively. A smaller effect was produced on the low threshold afferent evoked early excitatory postsynaptic potentials (EPSP) (3% decrease in amplitude and 24% decrease in duration). In the presence of d-APV the cumulatively incrementing depolarization produced by repetitive stimulation was substantially reduced and windup failed to occur. Activity-dependent amplifications of primary afferent evoked responses in spinal neurons therefore involves a temporal summation of d-APV sensitive prolonged postsynaptic depolarizations.

Journal Article↗
PubMed1990

Dynamic alterations in the cutaneous mechanoreceptive fields of dorsal horn neurons in the rat spinal cord.

The effect of the application to the skin of the chemical irritant mustard oil on the size and responsiveness of the cutaneous mechanoreceptive fields of 32 lumbar dorsal horn neurons has been examined in the adult decerebrate, spinal rat. Mustard oil placed on a small region of skin outside the mechanoreceptive firing zone produced a brief (185 +/- 35 sec, SEM) discharge of action potentials in 17 neurons and, in 23 cells, a prolonged increase of the response to a standard low- or high-intensity mechanical stimulus applied to the firing zone of the receptive field. This increase was shown, in 6 intracellularly recorded cells, to be due to a significantly increased depolarization in response to the stimuli. An expansion of the mechanoreceptive firing zones that peaked at 26 +/- 3.7 min was seen in 21 cells. While 6 of 8 nociceptive-specific neurons and 11 of 18 multireceptive neurons showed such an expansion, it did not occur in the 6 cells with low-threshold-only receptive fields. The expansion of the firing zones in 4 intracellularly recorded cells was found to be due to an increased amplitude of the EPSPs evoked by stimuli applied to what had initially been low probability firing fringes (Woolf and King, 1989) outside the firing zones, so that subthreshold responses became suprathreshold after application of the mustard oil. In 4 of 8 nociceptive-specific cells, the mechanical threshold in the firing zone became reduced to innocuous levels after application of the mustard oil. The demonstration of the capacity of a relatively brief afferent barrage of chemosensitive nociceptors to produce an increase in the spatial extent of the cutaneous receptive fields of dorsal horn neurons, amplify their responsiveness, and reduce their thresholds has implications both for the pathogenesis of postinjury pain hypersensitivity phenomena and for receptive field plasticity in the somatosensory system.

Action Potentials↗
PubMed1989

Morphology and somatotopic organization of the central terminals of hindlimb hair follicle afferents in the rat lumbar spinal cord.

The morphology of the central collateral arborizations of 24 A-beta hair follicle afferents (HFAs) innervating different regions of the skin of the hindlimb were studied by the intra-axonal injection of horseradish peroxidase (HRP) in adult rats. A total of 236 collaterals were recovered. These fell into three classes--complex, simple, and blind-ending--based on numbers of boutons and terminal branch patterns. The morphology of the HFA central arbors innervating the lateral and medial leg and dorsum of the foot was flame-shaped. Afferents with receptive fields on the glabrous-hairy skin border consistently had extra terminal branches running ventromedially into laminae IV/V. Differences in the width of terminal arbors were found. HFA terminals innervating the lateral leg formed narrower sheets than those innervating the dorsum of the foot and toes. The somatotopic organization of the collaterals and terminal arborizations of individual afferents were analyzed both by considering all the collaterals along an axon's rostrocaudal extent and by only examining arbors with boutons (the complex and simple arbors). Thirty-seven percent of blind-ending and 18% of simple collaterals were found to overlap in the rostrocaudal direction with the complex arborizations of afferents whose receptive fields were in a different cutaneous nerve territory. There was no overlap between complex arborizations of afferents from different nerve territories. However, the complex arbors of afferents with receptive fields within a particular nerve territory showed considerable terminal overlap even if they had nonadjacent peripheral receptive fields. The topographical organization of the central terminals of HFAs, forms a coarse somatotopic map of overlapping terminals whereby a particular region of dorsal horn has a maximal, but not exclusive, input from a particular area of skin.

Action Potentials↗
PubMed1989

Differences in the chemical expression of rat primary afferent neurons which innervate skin, muscle or joint.

The fluorescent dye Fast Blue was injected in anaesthetized rats into either skin, muscle or knee joint of the hindlimb. Following retrograde transport of the dye to lumbar dorsal root ganglia, the cell bodies of primary afferent neurons innervating these different target tissues were identified in ganglion sections by fluorescence microscopy. The sections were processed to demonstrate activity of the enzyme thiamine monophosphatase, or immunoreactivity to calcitonin gene-related peptide, substance P, or somatostatin, in Fast Blue labelled neurons. In all cases immunoreactivity to the antineurofilament antibody RT97 was used to classify dorsal root ganglion cells as being either small dark (RT97 negative, unmyelinated axons) or large light (RT97 positive, myelinated axons). The proportion of small dark cells labelled from each target decreased in the order: skin, muscle, joint. Thiamine monophosphatase and somatostatin were present only in small dark cells, while calcitonin gene-related peptide and substance P were found in both small dark and large light cells. In large light cells of all three targets, more contained calcitonin gene-related peptide than substance P. Among small dark cells, thiamine monophosphatase and somatostatin were found predominantly in skin afferents, while calcitonin gene-related peptide and substance P were more common in muscle and joint afferents. The chemical expression of primary afferents is therefore characteristic of the peripheral target they innervate. This could reflect either a maintained influence of the target on the afferents, or the factors which operate only during development.

Animals↗
PubMed1989

Subthreshold components of the cutaneous mechanoreceptive fields of dorsal horn neurons in the rat lumbar spinal cord.

1. Intracellular recordings have been made from 76 neurons in the dorsal horn of the fourth and fifth lumbar segments of the spinal cord in decerebrate-spinal rats. The locations of the neurons were identified after horseradish peroxidase (HRP) ionophoresis (n = 18) or calculated from depth readings (n = 58). Sixty-nine of the neurons were found or estimated to lie within the deep dorsal horn (laminae III-V), with the remaining 7 in laminae I and II. 2. Background excitatory activity was present in all the neurons in the absence of peripheral mechanical stimuli. In 22 neurons, this consisted only of subthreshold excitatory postsynaptic potentials (EPSPs), but in 54, a proportion of the EPSPs reached threshold, producing a spontaneous spike discharge (frequency 0.2-50 Hz) that had a rhythmic component in six cells. Spontaneous hyperpolarizations occurred but were uncommon (n = 10). 3. All the neurons had excitatory cutaneous mechanoreceptive fields on the ipsilateral hindlimb. The receptive fields, defined in terms of action-potential discharge, could be subdivided into two areas: a high-probability "firing zone," where skin stimulation elicited an action-potential discharge above the mean + 1 SD of the background activity; and a low-probability firing fringe, where the stimulus elicited a distinct subthreshold depolarization, but the action-potential response fell within the variability of the background discharge. 4. Mechanical stimulation in the middle of the firing zone in all cells generated both supra- and subthreshold excitatory responses, with the former predominating. As the stimuli were applied progressively farther away from the center of the firing zone, the subthreshold component became relatively more prominent. 5. Fifty percent of the 15 neurons that were recorded from for sufficient time (greater than 30 min) to enable the presence, extent, and characteristics of subthreshold responses to be examined in detail were found to have a low-probability firing fringe to their receptive fields. The response to stimulation within this fringe typically consisted of high-frequency, low-amplitude PSPs riding on a sustained depolarization, with an action-potential discharge that could not readily be distinguished from the spontaneous activity. The size of the fringe ranged from a small area adjacent to the firing zone to almost the entire hindlimb. 6. The firing zones of 20 neurons were low-threshold only and in 5 cells were high-threshold only. The majority of neurons were multireceptive, responding both to low- and high-intensity stimuli (n = 51).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

Sensory innervation of the hairs of the rat hindlimb: a light microscopic analysis.

The sensory innervation of the hair follicles of the furry skin of the rat hindlimb has been investigated by using the Winkelmann silver technique to stain peripheral axons and their terminals. This technique was found to stain only large- and medium-sized dorsal root ganglion cells and all laminae of the dorsal horn except lamina II, and therefore it is likely that, while A beta and A delta afferent fibres in the skin are stained, C fibres are not. Small vellus hairs were the commonest type of hair on the hindlimb particularly above the ankle. Many were not innervated. Those that were had lanceolate terminals arranged as palisades parallel to the hair shaft with circumferential presumptive Ruffini piloneural complexes and free nerve endings external to this. Circumferential innervation patterns without palisades were not uncommon but palisades without circumferential fibres were rare. Guard hairs which varied considerably in size were the next commonest hair type. Considerably more of these were innervated, by three-to-15 afferents forming both palisades of ten-to-30 lanceolate terminals and circumferential terminals. Both the innervated vellus and guard hairs had an associated vertical fibre projecting toward the epidermis. Tylotrichs, the largest hairs on the hindlimb, were rare (1-2%) and were only found above the ankle, but all were densely innervated by many axons. A prominent single nerve contributed to an annular complex by forming a bilaminar arrangement of lanceolate and circumferential terminals within the outer connective tissue sheath. Each tylotrich had an associated Merkel cell-neurite complex (haarscheiben). Differences in the distribution, innervation density, and phase in the growth cycle of the different hair types were found for skin from different regions of the hindlimb, which, together with the extent of the polyneuronal innervation of most follicles, has important implications for the processing by the somatosensory system of the afferent input generated by brushing hairs.

Afferent Pathways↗
PubMed1988

An intracellular analysis of amino acid induced excitations of deep dorsal horn neurones in the rat spinal cord slice.

The rat spinal cord slice preparation has been used to investigate the sensitivity of deep dorsal horn neurones to the excitatory amino acids N-methyl-D-aspartate (NMDA), quisqualate and L-glutamate. Intracellular recordings were made from 44 neurones in laminae III-VI of 14- to 16-day rats. Superfusion of quisqualate (30 microM) excited all neurones, NMDA (50 microM) excited 72% and L-glutamate (0.5-1 mM) 63% of the neurones. Depolarizations were retained after tetrodotoxin but with a reduced amplitude. The NMDA antagonist D-aminophosphonovalerate (D-APV, 10 microM) reduced NMDA and L-glutamate depolarizations by 66% and by 40%, respectively, while the quisqualate responses were enhanced by 27%. Dorsal root stimulation elicited two main patterns of activity; short-latency single/double spikes followed by subthreshold excitatory postsynaptic potentials (EPSPs) or a burst of spikes rising from a long duration composite EPSP. D-APV reduced the long-latency components of the first type and reduced the amplitude and duration of the composite EPSP of the second. These results support a specialized role for NMDA receptors in synaptic transmission in the dorsal horn.

2-Amino-5-phosphonovalerate↗
PubMed1988

The responses recorded in vitro of deep dorsal horn neurons to direct and orthodromic stimulation in the young rat spinal cord.

The electrophysiological properties of 87 neurons in the deep dorsal horn (laminae III-VI) of the rat spinal cord have been investigated in vitro. Two preparations have been used; the transverse spinal cord slice preparation from the third or fourth lumbar segments of 14-16-day-old rats (71 cells) and a hemisected lumbar spinal cord preparation from 10-12-day-old rats (16 cells). The input impedances (range 11-128 M omega), membrane potentials (-67 +/- 8 mV S.D.), action potential amplitude (77 +/- 11.8 mV) duration (1.4 +/- 0.5 ms) and afterpotentials, were effectively identical in the neurons recorded from the two preparations. Neurons in both preparations when activated with long-duration (1-2 s) outward current pulses showed a single steady-state firing range with little adaptation of firing frequency or action potential amplitude. This pattern of responses was unaffected by changing the membrane potential. Orthodromic synaptic activity could be elicited in the neurons by stimulating either the small dorsal root remnants in the slice or the dorsal roots in the hemisected spinal cord. The responses evoked by single stimuli of increasing intensity varied in different neurons in both preparations. The commonest response (32/62) consisted of a short-latency, short-duration composite excitatory postsynaptic potential which generated one or two spikes with no further spiking activity at longer latency when the stimulus intensity was increased beyond threshold. In 20 neurons, graded stimulation produced a graded response with recruitment, at high intensities, of a discharge of action potentials lasting several hundred milliseconds. A small number of cells (4) responded to the single stimulus with a train of action potentials lasting several seconds. Stimulating adjacent dorsal roots in the hemisected cord preparation could evoke quite different responses from the neurons. The heterogeneity of the types of orthodromic responses obtained in both preparations, in spite of the almost uniform intrinsic membrane properties, is likely to reflect differences in the strength, location and type of afferent and interneuronal input to different dorsal horn cells.

Action Potentials↗
PubMed1987

The postnatal development of the ventral root reflex in the rat; a comparative in vivo and in vitro study.

The ventral root reflex (VRR) and its postnatal development has been studied in vivo and in an isolated spinal cord preparation from birth up to 14 days. At postnatal days 0, 7 and 14 the VRR typically consists of an early highly synchronized peak (VRR1) and a later lower amplitude peak (VRR2). In some cases, especially at day 14 in vivo, there is a longer latency asynchronous wave (VRR3). As the age of the animal increases the latencies of the first two components VRR1 and VRR2 progressively decrease mainly due to the decrease in the central delay occurring over this period. Consideration of the central delays for VRR1 and VRR2 recorded in vivo and in vitro indicates that these waves are unlikely to be elicited by C-fibre activation and a long latency C-evoked reflex discharge equivalent to that of the adult could not be reliably recorded. Up to day 7 the appearance of the VRR was similar in both preparations but diverged in the second week of life.

Aging↗
PubMed1987

Central terminations of cutaneous mechanoreceptive afferents in the rat lumbar spinal cord.

The morphology in the dorsal horn of the lumbar spinal cord of the collateral branches and terminal arborizations of three different types of low-threshold mechanoreceptor innervating the skin of the rat hindlimb has been studied by the intracellular injection of horseradish peroxidase into physiologically characterized afferent fibres. The central terminals of five rapidly adapting glabrous skin mechanoreceptors (RA), six hair follicle afferents (HFA), and four slowly adapting type I afferent fibres (SA I; two from glabrous and two from hairy skin) were recovered for detailed analysis. The number of collaterals per axon varied from eight to 12, and the length of axon stained from 3.5 to 4.7 mm. In each afferent, while the majority (52-67%) of the terminal arborizations displayed extensive branching with large numbers of en passant and terminal synaptic boutons, the arborizations at the caudal and rostral extremes of the terminal field tended to be much simpler and less profuse, with few and in some cases no boutons. This did not appear to be the consequence of inadequate filling. The general pattern of the terminal arborizations was one of mediolaterally compressed, rostrocaudally oriented sheets. In the case of the RA afferents there was no overlap between the adjacent terminal arborizations; a few of the arborizations of the SA I afferents overlapped; most, but not all, of the HFA terminal arborizations overlapped. The terminal arborizations of the HFAs had a distinctive morphology identical to the flame-shaped arbors described in earlier Golgi studies and included synaptic boutons extending from inner lamina II to lamina IV. The morphologies of the RA and SA terminal arborizations were similar to each other, but the former tended to be concentrated in lamina IV with branches in III and V, whereas the latter tended to V with few branches more superficial than lamina IV. There were also differences in the intercollateral spacing between these two types of afferent fibre. While there are similarities between the morphology of the central terminals of cutaneous low-threshold mechanoreceptors in the rat and those previously described in the cat (for example, the longitudinally continuous arrangement of the mediolaterally restricted flame-shaped HFA arborizations and the discontinuous RA arborizations arising from a dorsally located axon), there are also some major differences: the large number of HFA arbors extending to lamina IIi and to lamina IV rather than being restricted to lamina III, the deeper location of the RA arbors (in laminae IV and V rather than lamina III),(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Excitatory amino acids increase glycogen phosphorylase activity in the rat spinal cord.

Glycogen phosphorylase is present in nervous tissue in an active and inactive form. Using a histochemical technique, an investigation into which putative neurotransmitters have the capacity to modify the activity of the enzyme, has been performed on the rat spinal cord. Intrathecal injections of L-glutamate and L-aspartate elevate glycogen phosphorylase activity in the dorsal horn, while substance P has no effect and only high doses of adenosine triphosphate (ATP) increase the enzyme activity. In addition the N-methyl-D-aspartate receptor antagonist, 5-amino-phosphonovaleric acid was found to block the elevation of glycogen phosphorylase activity in the dorsal horn produced by the peripheral activation of chemo-sensitive primary afferents. Excitatory amino-acid neurotransmitters can therefore, acting via second messengers and protein kinases, modify glycogen metabolism in the spinal cord.

Animals↗
PubMed1987

Physiology and morphology of multireceptive neurons with C-afferent fiber inputs in the deep dorsal horn of the rat lumbar spinal cord.

Intracellular recording techniques have been used to study neurons that respond to low- and to high-intensity mechanical stimulation of the skin of the hindpaw (wide dynamic range or multireceptive cells) in the deep dorsal horn of the fourth lumbar segment of the spinal cord, in decerebrate-spinal rats. Electrical stimulation of the A-fibers in the sciatic nerve produced a short-latency response in all 32 neurons studied. A long-latency prolonged excitation was produced in 28 of the 32 neurons when the unmyelinated afferents in the sciatic nerve were activated. This paper describes the physiological properties of 12 multireceptive cells with A- and C-fiber inputs, whose cell body location was established by horseradish peroxidase ionophoresis and the morphology of six neurons in this group whose cell bodies lay within lamina V. Single stimuli to the sciatic nerve at an intensity high enough to activate unmyelinated afferent fibers (C-fiber strength) produced two patterns of response in the neurons. In five neurons a number of long-latency postsynaptic potentials (PSPs) clearly separated from the short-latency A-fiber evoked PSPs were produced, resulting in an early discharge, a silent period, and a late discharge. The second pattern, found in seven neurons, was a long-lasting depolarization, only generated by C-strength stimuli, which continued from the early A-fiber evoked PSPs, peaked at 100-200 ms, and lasted for 300-500 ms, producing in six cases a continuous burst of action potentials with a maximal frequency at the expected latency of the C-afferent fiber input but with no clear A- and C-fiber evoked banding of the action potentials. This postsynaptic depolarization was large enough to inactivate action potentials in one cell. Repeated stimuli to the sciatic nerve (1 Hz for 10 s) at C-fiber strength produced five different types of response in the neurons. In three neurons a progressive increase in the size and duration of the C-fiber PSPs occurred, resulting in an increase in the number of action potentials (windup), whereas in two, the repeated stimulation resulted in a progressive moderate depolarization of the neurons and an increase in the total number of action potentials evoked at both early and late latencies. Large depolarizations, sufficient to partially inactivate action potentials, developed during the repeated stimulation in two cells, effectively reducing the number of spikes evoked per stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Prolonged C-fibre mediated facilitation of the flexion reflex in the rat is not due to changes in afferent terminal or motoneurone excitability.

A standard suprathreshold mechanical stimulus applied to the hindpaw of decerebrate-spinal rats produces a discharge in hamstring flexor alpha-motoneurones which is stable for hours, provided no tissue injury is produced. Tissue injury results, however, in a decrease of threshold and an increase in the responsiveness of the reflex. This reflex hypersensitivity can be mimicked by brief (20 s) low frequency (1 Hz) conditioning stimuli to muscle or cutaneous nerves, if C-fibres are recruited. The prolonged post-conditioning facilitation of the flexion reflex by C-afferent volleys is now shown to be independent of changes in the excitability of the test afferent terminals in the dorsal horn and of the motoneurones. The hypersensitivity is therefore due to changes in the interneurones that link cutaneous nociceptive afferents with flexor motoneurones.

Animals↗
PubMed1986

Somatotopic organization of cutaneous afferent terminals and dorsal horn neuronal receptive fields in the superficial and deep laminae of the rat lumbar spinal cord.

The somatotopic organization of A- and C-afferent fibre terminals in the dorsal horn of the rat lumbar spinal cord was compared with the spatial location of second-order dorsal horn neuronal mechanoreceptive fields. The central terminal fields of the sural, saphenous, and tibial nerve were mapped by labelling the nerves with horseradish peroxidase (HRP). A previous study used the transganglionic transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) to produce a somatotopic map of high-threshold C-fibre terminal fields in lamina II (Swett and Woolf: J. Comp. Neurol. 231:66-77, '85). In the present study the terminal fields of low-threshold A beta afferents that terminate in laminae III and IV were mapped by using unconjugated HRP at prolonged survival times (72 hours). Unfixed tissue was used to increase the sensitivity of the tetramethylbenzidine reaction, thus allowing these afferent terminals to be clearly seen. The general spatial arrangement of the terminal fields in laminae III/IV closely resembled that found in lamina II in the mediolateral and rostrocaudal planes but because of a dorsoventral obliquity of the afferent terminals, the superficial and deeper fields are not in strict vertical register. The input to laminae II-IV of the dorsal horn may therefore be viewed as two horizontally arranged sheets of afferent terminals both accurately representing the skin surface, the more superficial sheet representing the high-threshold C-afferents and the deeper sheet, low-threshold A-beta afferents. The spatial organization of high-threshold A-delta afferents in laminae I and V appears to be quite different, with a transverse rather than a longitudinal orientation. To study dorsal horn cell receptive field organization two single units with mechanoreceptive fields were recorded extracellularly in each of 87 vertical tracks in the lumbar spinal cord, one unit in the superficial dorsal horn and the second in the deep dorsal horn. In general the somatotopic organization of the receptive fields of both sets of units followed that of the afferent terminal fields but there were cells with receptive fields that were anomalous relative to the recording site. No evidence of any vertical relation or columnar arrangement in receptive field size, threshold, or location on the body surface was found when comparing the two units in a pair. Furthermore, no laminar functional specialization was found, the majority of neurones having both low- and high-threshold inputs.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗