Dorsal Root Fibers Research Articles

Membrane potential oscillations of neonatal rat spinal motoneurons evoked by electrical stimulation of dorsal root fibres.

Intracellular recording from lumbar motoneurons of the neonatal rat isolated spinal cord bathed in standard saline solution was used to study membrane potential oscillations which accompanied the decay phase of excitatory postsynaptic potentials (EPSP) induced by single electrical pulses to an adjacent dorsal root. About 60% of motoneurons displayed rhythmic oscillations of 10 +/- 2 mV maximal amplitude and 7 +/- 0.5 Hz frequency. Ability to generate oscillations could not be correlated to the cell membrane properties or to the age of the preparation (5-13 days). The oscillation frequency was independent of membrane potential (-100 to -45 mV) or of the intensity of dorsal root stimuli. The oscillation amplitude was linearly related to the cell potential within the same voltage level. Fast Fourier transform analysis showed that the power spectrum of oscillations peaked at approximately 8 Hz. Electrically evoked activities and spontaneous events displayed similar cut-off frequencies. When the cell membrane potential was steadily depolarized, a hyperpolarizing pulse applied during the decay phase of the EPSP promptly revealed the presence of oscillatory behaviour. Pharmacological block of neurokinin-1 or N-methyl-D-aspartate receptors depressed the decay phase of the EPSP and the associated oscillatory responses. It is suggested that rhythmic oscillations were probably due to summated synaptic potentials generated at the premotoneuron level and are perhaps of functional relevance to motoneuron behaviour.

Effects of electrode geometry and combination on nerve fibre selectivity in spinal cord stimulation.

The differential effects of the geometry of a rostrocaudal array of electrode contacts on dorsal column fibre and dorsal root fibre activation in spinal cord stimulation are analysed theoretically. 3-D models of the mid-cervical and mid-thoracic vertebral areas are used for the computation of stimulation induced field potentials, whereas a cable model of myelinated nerve fibre is used for the calculation of the excitation thresholds of large dorsal column and dorsal root fibres. The size and spacing of 2-D rectangular electrode contacts are varied while mono-, bi- and tripolar stimulation are applied. The model predicts that the highest preferential stimulation of dorsal root fibres is obtained in monopolar stimulation with a large cathode, whereas dorsal column fibre preference is highest in tripolar stimulation with small contacts and small contact spacings. Fibre type preference is most sensitive to variations of rostrocaudal contact size and least sensitive to variations of lateral contact size. Dorsal root fibre preference is increased and sensitivity to lead geometry is reduced as the distance from contacts to spinal cord is increased.

Multiple protracted cauda equina constrictions cause deep derangement in the lumbosacral spinal cord circuitry in the dog

Neuropathological changes of the neuronal pools and spinal cord circuitry in the lumbosacral segments were studied in a canine model of multiple protracted cauda equina constrictions. Anterograde degeneration of all sacrococcygeal and L7 dorsal root fibers was detected in S1–S3 and lower lumbar segments. A narrow degenerated gracile fascicle was found in all thoracic and cervical segments terminating in the gracile nucleus. Transneuronal degeneration of middle-sized and large neurons, located in S1–S3 and sporadically in L7 segments, was noted. Identical transneuronal degeneration was seen in a group of small neurons located in the ventralmost part of lamina VII in S1–S3 segments. Simultaneously, a terminal degeneration was detected in the lateral cervical nucleus and in the ventral posterior lateral nucleus of the ventrobasal thalamic complex. Concomitantly, a fully developed retrograde degeneration affecting motoneurons in the ventrolateral portion of the anterior horn in S1–S3 segments appeared.

Functional changes in dorsal root ganglion cells after chronic nerve constriction in the rat

1. We studied the effects of a chronic nerve constriction on the evoked responses in dorsal root fibers in the rat to norepinephrine and to thermal stimuli applied either to the dorsal root ganglion (DRG) or the site of nerve injury. We recorded a total of 59 C fibers, 15 A delta-fibers, and 46 A beta-fibers from the L5 dorsal root of the rats 11-52 days after a loose ligation of the ipsilateral sciatic nerve. Most fibers were identified by the presence of spontaneous activity (SA) that originated partially at and/or proximal to the injury site. In addition, we recorded 20 C fibers, 1 A delta-fiber, and 28 A beta-fibers from the dorsal roots of normal, uninjured neurons. 2. In nerve-injured rats, the SA of some C fibers was generally increased by cooling and decreased by heating either site. In contrast, the SA of most A beta-fibers was increased by heating either the injury site or the DRG. Cooling the DRG decreased SA in A beta-fibers, whereas cooling the injury site typically had no effect. Excitatory responses were not evoked in any fiber group when the same thermal stimuli were applied to the nerve or DRG tested in normal, uninjured rats. 3. Norepinephrine (< 0.5 mM) applied either to the injury site or the DRG increased the SA of most C fibers and A delta-fibers but only a minority of A beta-fibers in previously injured nerves. The threshold concentration for excitation of the DRG somata of C fibers was 0.01 mM. No effects were found for fibers in uninjured nerves. 4. The effect of norepinephrine was blocked by a pretreatment with yohimbine, an alpha 2-blocker, but not with prazosin, an alpha 1-blocker. 5. Stimulation of the sympathetic trunk (L2-L3) excited most C fibers and a minority of A beta-fibers. In contrast, the SA of a minority of C fibers and A beta-fibers was depressed during sympathetic stimulation. 6. After a chronic nerve constriction the DRG becomes a source of abnormal activity modulated by sympathetically released norepinephrine acting on alpha 2 receptors in DRG somata. This neuropathic activity may contribute to cutaneous pain and hyperalgesia.

Plasticity of complex terminals in lamina II in partially deafferented spinal cord: The cat spared root preparation

Projections to the dorsal horn change in adult mammals in response to complete or partial deafferentation. The number of synaptic terminals remains constant after complete lumbosacral deafferentation, indicating replacement of lost dorsal root terminals by newly formed terminals from spared intrinsic systems. The density of a spared central projection of a dorsal root is increased in dorsal horn after partial deafferentation, consistent with sprouting by the axons in the spared root. In this study, we have used electron microscopy to study morphological changes in a specific class of terminals in the dorsal horn induced by partial deafferentation. Complex terminals (CTs) in the dorsal horn originate exclusively from dorsal roots and are readily distinguished morphologically. The CTs and the postsynaptic densities (PSDs) associated with CTs were measured in lamina II at L5 and L6 in cats subjected to unilateral spared root (L6) dorsal rhizotomies and compared to CTs in the control side. Acutely following partial deafferentation, the number of CT profiles decreased. At more chronic survivals, the number of CT profiles were restored to normal levels, and both the number and the length of PSDs were increased. The changes in CTs and PSDs suggest sprouting and synaptogenesis by the spared dorsal root fibers that produce changes in the postsynaptic neuron. Spared root deafferentation thus elicits compensatory changes in presynaptic terminals of the spared root and also in their postsynaptic target neurons.

Neuropeptide Y and galanin binding sites in rat and monkey lumbar dorsal root ganglia and spinal cord and effect of peripheral axotomy.

Using monoiodinated peptide YY (PYY) and galanin as radioligands, and neuropeptide Y (NPY) fragments, the distribution of NPY binding sites and its subtypes Y1 and Y2, and of galanin binding sites, was investigated in rat and monkey lumbar (L) 4 and L5 dorsal root ganglia (DRG) and spinal cord before and after a unilateral sciatic nerve cut, ligation or crush. Receptor autoradiography revealed that [125I]PYY bound to some DRG neurons and a few nerve fibres in normal rat DRG, and most of these neurons were small. NPY binding sites were observed in laminae I-IV and X of the rat dorsal horn and in the lateral spinal nucleus, with the highest density in laminae I-II. [125I]PYY binding was most strongly attenuated by NPY13-36, a Y2 agonist, and partially inhibited by [Leu31,Pro34]NPY, a Y1 agonist, in both rat DRG and the dorsal horn of the spinal cord. These findings suggest that Y2 receptors are the main NPY receptors in rat DRG and dorsal horn, but also that Y1 receptors exist. After sciatic nerve cut, PYY binding markedly increased in nerve fibres and neurons in DRG, especially in large neuron profiles, and in laminae III-IV of the dorsal horn, as well as in nerve fibres in dorsal roots and the sciatic nerve. Incubation with NPY13-36 completely abolished PYY binding, which was also reduced by [Leu31,Pro34] NPY. However, the increase in PYY binding seen in laminae I-IV of the ipsilateral dorsal horn after axotomy was not observed after coincubation with [Leu31,Pro34] NPY. NPY binding sites were seen in a few neurons in monkey DRG and in laminae I-II, X and IX of the monkey spinal cord. The intensity of PYY binding in laminae I-II of the dorsal horn was decreased after axotomy. Galanin receptor binding sites were not observed in rat DRG, but were observed in the superficial dorsal horn of the spinal cord, mainly in laminae I-II. Axotomy had no effect on galanin binding in rat DRG and dorsal horn. However, galanin receptor binding was observed in many neurons in monkey L4 and L5 DRG and in laminae I-IV and X of monkey L4 and L5 spinal cord, with the highest intensity in laminae I-II. No marked effect of axotomy was observed on the distribution and intensity of galanin binding in monkey DRG or spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)

Inflammation and hyperalgesia in rats neonatally treated with capsaicin: effects on two classes of nociceptive neurons in the superficial dorsal horn

To address the mechanisms of hyperalgesia and dorsal horn plasticity following peripheral tissue inflammation, the effects of adjuvant-induced inflammation of the rat hindpaw on behavioral nociception and nociceptive neuronal activity in the superficial dorsal horn were examined in neonatally capsaicin-treated rats 6–8 weeks of age. Capsaicin treatment resulted in an 82% loss of unmyelinated fibers in L5 dorsal roots, a dramatic reduction of substance P-like immunoreactivity in the spinal cord, and a significant decrease in the percentage of dorsal horn nociceptive neurons that reponded to C-fiber stimulation and noxious heating of the skin. The thermal nociceptive threshold was significantly increased in capsaicin-treated rats, but behavioral hyperalgesia to thermal stimuli still developed in response to inflammation. Following inflammation, there was a significant decrease in mechanical threshold and an increase in response duration to mechanical stimuli in both vehicle- and capsaicin-treated rats, suggesting that a state of mechanical hyperalgesia was also induced. The capsaicin treatment appears to have differential effects on nociceptive specific (NS) and wide-dynamic-range (WDR) neurons in inflamed rats. Expansion of the receptive fields of nociceptive neurons, a measure of the effect of inflammation-induced CNS plasticity, was less extensive for NS than for WDR neurons in capsaicin-treated rats. Compared to vehicle-treated rats, a smaller population of NS neurons, but a similar percentage of WDR neurons, had background activity in inflamed capsaicin-treated rats. C-fiber strength electrical stimulation of the sciatic nerve produced expansion of the receptive fields in a greater portion of NS neurons (53%, P < 0.05) in capsaicin- than in vehicle-treated rats (32%). There was no difference in stimulation-induced expansion of the receptive fields for WDR neurons between vehicle- or capsaicin-treated rats. An N- methyl- d-aspartate receptor antagonist, MK-801, attenuated the behavioral hyperalgesia and reduced the receptive field size of dorsal horn neurons in inflamed capsaicin- and vehicle-treated rats. The data suggest that while capsaicin-sensitive primary afferents may be involved in neuronal plasticity induced by peripheral tissue inflammation, changes in the capsaicin-insensitive WDR and NS populations are sufficient to produce thermal and mechanical hyperalgesia after the loss of capsaicin-sensitive primary afferents.

The up-regulation of trkA and trkB in dorsal column astrocytes following dorsal rhizotomy

One week after rat dorsal root fibers were severed, immunoreactivity for the high affinity neurotrophin receptors, trkA and trkB, was up-regulated on glial cells in the spinal cord dorsal column. Immunoreactivity for glial fibrillary acidic protein (GFAP) also increased. In contrast, no changes in immunoreactivity for trkA or trkB, or for GFAP were observed in the brainstem cuneate nucleus, a principal termination site for many of the severed dorsal root fibers.

Conduction abnormalities are restricted to the central nervous system in experimental autoimmune encephalomyelitis induced by inoculation with proteolipid protein but not with myelin basic protein.

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory demyelinating disease of the central nervous system (CNS) and can be induced by inoculation of animals with homogenized CNS tissue or highly purified myelin proteins such as myelin basic protein (MBP) or proteolipid protein (PLP). It is widely studied as a possible animal model of multiple sclerosis. We performed the present neurophysiological study to define the location of nerve conduction abnormalities in EAE induced by immunization with PLP (PLP-EAE) and in EAE induced by immunization with MBP (MBP-EAE) in the Lewis rat. In rats with tail weakness due to acute PLP-EAE, conduction was normal in the spinal nerve roots and peripheral nerves but there was evidence of conduction block in a high proportion of the fibres in the dorsal columns of the lumbosacral spinal cord. In contrast, in acute MBP-EAE, there was conduction block in a high proportion of fibres in the sacral dorsal and ventral roots of the peripheral nervous system (PNS) and in the dorsal columns of the lumbosacral spinal cord. The distribution of nerve conduction abnormalities is consistent with previous histological studies showing that inflammation and primary demyelination are restricted to the CNS in PLP-EAE, but are present in the CNS and in the spinal roots of the PNS in MBP-EAE. The restriction of functional abnormalities to the CNS in PLP-EAE but not in MBP-EAE may have implications for the human inflammatory demyelinating diseases, including multiple sclerosis.

Anatomical Identification of a Postsynaptic Dorsal Column System in a Reptile, &lt;i&gt;Caiman crocodilus&lt;/i&gt;

The presence of a postsynaptic dorsal column system was investigated in reptiles, Caiman crocodilus. Several experiments were undertaken. First, a cytoarchitectonic analysis of the spinal cord was performed to identify its laminar organization. Second, the termination of dorsal root fibers in the dorsal horn of the upper cervical cord, brachial enlargement, and lumbar intumescence was studied utilizing anterograde tracing techniques. Third, placement of retrograde tracers into the dorsal column nucleus identified spinal cord neurons that projected to the dorsal column nucleus. These experiments document that, in addition to direct primary dorsal root input, a second pathway exists whereby nonfacial somatosensory information can reach the dorsal column nucleus in this reptilian group. This neural path arises primarily from neurons in the ipsilateral lamina V and, to a much lesser extent, from lamina IV in the cervical area and, to a far smaller degree, from the thoracic and lumbar dorsal horn. Each of these laminae whose neurons project to the dorsal column nucleus receive direct dorsal root input. This neural circuit in Caiman is similar to a neural pathway described in pigeons and several mammalian groups. These observations suggest that a postsynaptic dorsal column system is phylogenetically ancient and may well be a feature common to all amniotes.

Different effects of 4-aminopyridine on regenerated cutaneous and muscular rat sciatic nerve branches

Developing and regenerated myelinated rat dorsal and ventral root fibers respond differently to the fast potassium channel blocking agent 4-aminopyridine (4-AP). To pursue this issue further, we made unilateral sciatic nerve crushes in adult rats. Sural (SN) and lateral gastrocnemius (LGN) nerve branches were collected 4–6 months later, for physiological and morphological examination. Regenerated and control nerves in Ringers solution showed generally similar compound action potential (CAP) waveforms, but CAPs of regenerated SNs and LGNs in 4-AP were markedly different. While regenerated SNs showed a prominent late CAP negativity with a “rippled” appearance and markedly compromised recovery properties, the CAP and recovery properties of regenerated LGNs were minimally changed. Light and electron microscopic examination of SN and LGN fibers failed to reveal any features obviously related to the observed physiological differences. We conclude, that the effect of 4-AP on regenerated cutaneous afferents differs from its action on regenerated muscular afferents and efferents. This physiological diversity lacks obvious structural correlates.

Spread of the dorsal root reflex in an isolated preparation of hamster spinal cord.

In an isolated preparation of hamster spinal cord maintained at 27 degrees C, stimulation of a single dorsal root has been shown to evoke dorsal root reflexes in ipsilateral roots throughout the lumbar and thoracic cord. The dorsal root reflex was evoked by activity in low threshold dorsal root fibres, and left the cord through dorsal root fibres conducting at 5.9 m/s. The ipsilateral dorsal root reflex travelled equally well in both directions along the cord at a calculated velocity of 0.5 m/s at 27 degrees C. Comparison of the stimuli required to evoke dorsal root reflexes in adjacent and distant ipsilateral dorsal roots suggests that once this system is activated it operates largely in an all-or-none manner. The delay in the generation of the dorsal root reflex within the cord was calculated to be 4.7 +/- 0.2 ms at 27 degrees C, corresponding to approximately 2 ms at body temperature, suggesting that a trisynaptic pathway is involved in the generation of the dorsal root reflex at the segmental level.

Increased spike-frequency adaptation and tea sensitivity in dorsal root fibers after sciatic nerve injury.

Excitability of rat dorsal root axons were studied 3 weeks after injury to the sciatic nerve. Whole nerve recordings were obtained from injured and control nerves in a sucrose gap chamber. Constant current depolarization pulses (30-200 ms) applied approximately 50% above the stimulus strength required for maximal amplitude compound action potentials (CAPs) evoked a burst of action potentials in the dorsal root which displayed spike adaptation. The depolarization-induced burst response of the dorsal roots was greatly reduced after crush or transection of the sciatic nerve. However, application of the potassium channel blocker, tetraethylammonium (TEA), restored the burst discharge in injured dorsal root axons. Brief tetanic stimulation of the dorsal root also induced an afterhyperpolarization (AHP) that was twice as large in the transection group as compared to the control group, and which was blocked by TEA. There were no changes seen in the amplitude of the compound action potential, frequency-following characteristics, refractory properties, or 4-AP sensitivity in the dorsal roots after peripheral nerve injury. These results suggest that there is enhanced spike adaptation that occurs at the same time as an increase in the sensitivity to the potassium channel blocker, TEA, in axon regions proximal to the site of nerve injury and have implications for the pathophysiology of nerve injury.

The Recovery of Postural Reflexes and Locomotion Following Low Thoracic Hemisection in Adult Cats Involves Compensation by Undamaged Primary Afferent Pathways

Spinal hemisection in the adult cat results in motor impairments followed by substantial recovery of function (16, 20, 39, 53). The present study was undertaken to assess the contribution of undamaged ipsilateral segmental and contralateral descending systems to recovery of motor function. Quantitative behavioral methods were used to examine monopedal reflex and bipedal locomotor functions after thoracic hemisection. Different facets of motor behavior recover at different times. The recovery of monopedal postural reflexes precedes the recovery of more complex motor behavior. Since the reflexes tested are initiated by segmental afferent input and show recovery and normal motor patterns during locomotion, as defined by kinematic analysis show recovery, it is likely that dorsal root input compensates for the loss of descending input to one side of the spinal cord. Quantitative immunocytochemical methods for visualizing the central projections of dorsal root fibers (monoclonal antibody RAT-102; 49) and the descending serotoninergic pathway were used to examine the response of these pathways to hemisection. Hemisection results in a permanent decrease in the density of serotoninergic projections and a permanent increase in dorsal root projections in the spinal cord. The increased density of RAT-102 may represent an increase in the projection of dorsal root fibers and provide the increased input necessary to mediate enhanced reflex control. A transient increase in GAP-43 in the dorsal horn ipsilateral to the hemisection suggests that the increased density of RAT-102 immunoreactivity is associated with growth. Taken together, our results suggest that sprouting of primary afferents within the spinal cord is one mechanism underlying the recovery of function after hemisection.

Paresthesia thresholds in spinal cord stimulation: a comparison of theoretical results with clinical data

The potential distributions produced in the spinal cord and surrounding tissues by dorsal epidural stimulation at the midcervical, midthoracic, and low thoracic levels were calculated with the use of a volume conductor model. Stimulus thresholds of myelinated dorsal column fibers and dorsal root fibers were calculated at each level in models in which the thickness of the dorsal cerebrospinal fluid (CSF) layer was varied. Calculated stimulus thresholds were compared with paresthesia thresholds obtained from measurements at the corresponding spinal levels in patients. The influences of the CSF layer thickness, the contact separation in bipolar stimulation and the laterality of the electrodes on the calculated thresholds were in general agreement with the clinical data. >

Development of immunoreactivity for calcitonin gene-related peptide, substance p and glutamate in primary sensory neurons, and for serotonin in the spinal cord of fetal sheep

In study we have described the ontogeny of immunoreactivity for calcitonin gene-related peptide, substance P and glutamate in primary sensory neurons, and for serotonin in the sacral spinal cord, of fetal sheep ( n = 37) from 56 to 140 days of gestation (term = 146 days). A few fine, varicose fibres immunoreactive for calcitonin gene-related peptide were present in Lissauer's tract, the dorsolateral funiculus and in laminae I and V in the dorsal horn of the spinal cord at 56–61 days of gestation. At this age, two groups of intensely staining immunoreactive cells were present in the motoneuron pool in laminae VIII and IX in the ventral horn of the spinal cord. By 77 days, immunoreactive fibres were also present in laminae II and X. With advancing gestational age, an increase in the intensity of staining was observed throughout the cord to term, with the exception of laminae VIII and IX, where a decrease was seen. Intense staining of cells in the motoneuron pool was evident until c. 128 days, after which time staining became very faint. Fine fibres immunoreactive for substance P were present in Lissauer's tract and lamina I of the spinal cord at 56–61 days of gestation. They were also present throughout laminae IV–VI and X as well as throughout the entire ventral horn. Immunoreactive fibres in lamina II were evident by 77 days. The staining increased in density but remained similar in distribution with increasing gestational age to term in the dorsal horn, but decreased markedly in the ventral horn. Cells immunoreactive for substance P were evident from 56 days, particularly on the border of laminae II and III, until late in gestation. Ultrastructural studies showed that axon terminals immunoreactive for calcitonin gene-related peptide and for substance P were present in lamina I by 61 days. Immunoreactivity for glutamate was evident at 83 days in dorsal root fibres and also in lamina I and II, where it was more prominent in cells than in fibres. At all ages examined, the dorsal horn stained more intensely than the ventral horn. Immunoreactivity for glutamate and neuropeptides appeared in the cells and fibres of dorsal root ganglia at 97–100 days. In the skin, immunoreactivity for calcitonin gene-related peptide and substance P was present at 85 days, some time after its appearance in the cord. Fibres immunoreactive for serotonin appeared in lamina I, at the neck of the dorsal horn and in the ventral horn at 83 days of gestation. Few immunoreactive fibres were seen at any stage during gestation in laminae II and III. Staining increased in laminae IV–X during gestation, but there was eventually a slight decrease in the ventral horn prior to term. These studies have shown that neurochemicals thought to be involved in the transmission and modification of somatosenory information in the spinal cord are present in fetal sheep from early in gestation, with neuropeptides appearing before glutamate and serotonin.

Rate of rise of the cumulative depolarization evoked by repetitive stimulation of small-caliber afferents is a predictor of action potential windup in rat spinal neurons in vitro.

1. The summation of depolarizing postsynaptic potentials (PSPs) evoked by stimulation of primary afferent fibers in lumbar dorsal roots was studied in dorsal and ventral horn neurons in the rat hemisected spinal cord in vitro with current-clamp intracellular recording techniques. PSPs evoked by activation of A delta and/or C fibers could summate after repetitive stimulation at low frequencies: this resulted in a progressive, long-lasting change in the neuronal membrane potential (Vm) (cumulative depolarization). Cumulative depolarization was not observed after stimulation at A beta-fiber intensity or at frequencies < 0.2 Hz. 2. Effective PSP summation resulting in a significant cumulative depolarization (> 5 mV) was observed only if the PSPs evoked were longer than 4 s. On the other hand, there was no correlation between the amplitude of cumulative depolarization achieved in a neuron and the absolute duration of the PSP or the neuronal resting membrane properties (Vm and input resistance). 3. With relation to the changes in Vm during the stimulation train, three patterns of response to repetitive stimuli could be detected in both dorsal horn (DH) and ventral horn (VH) neurons: 1) little or no depolarization throughout the train; 2) an initial depolarization, which either remained stationary or decayed to the resting Vm after the first 3-4 s of stimulation; or 3) a progressive cumulative depolarization increasing throughout the train. 4. Depolarizing the cell by DC current injection resulted in a steeper rise in Vm in response to repetitive stimuli in one half of VH neurons and in one out of nine DH neurons tested. 5. Action potential windup, an increase in the number of action potentials elicited by each stimulus as the train progresses, was observed both in DH and in VH cells. C-fiber strength stimulation was the most effective in eliciting windup. Windup was associated with Vm responses to repetitive stimulation belonging to the progressive cumulative depolarization pattern. Indeed, cumulative depolarizations that resulted in windup had significantly steeper slopes for the Vm trajectory than those that did not. In those neurons in which DC depolarization by intracellular current injection increased the slope of the Vm trajectory, DC depolarization could also bring about action potential windup. 6. These results indicate that, although the generation of long-lasting "slow" PSPs by high-threshold primary afferents is necessary for the summation of synaptic activity in the spinal cord at low frequencies, the rate and pattern of the summation does not depend on the absolute duration of the PSPs.(ABSTRACT TRUNCATED AT 400 WORDS)

The characteristics of the formation of temperature information in afferent units

Impulse activity of single afferent fibres of the spinal cord dorsal roots of cats was investigated under local mechanical, heat and cold influence on receptive fields of their skin. These influences did not change the frequency of impulsation, but changed redistribution of interimpulse intervals. It is supposed that formation of polyfunctional properties of single afferent fibres is realized due to their polychannel information.

Transient expression of stage-specific embryonic antigen-1 (CD15) in the developing dorsal rat spinal cord.

The localization of CD15 (synonyms: stage-specific embryonic antigen-1 (SSEA-1), 3(alpha)-fucosyl-N-acetyl-lactosamine or FAL), which is implicated in neuronal differentiation, in the developing dorsal rat spinal cord was studied by immunocytochemistry. A embryonal day 9 (E9), SSEA-1 was detected in the neural ectoderm and, at E11, in cells near the ventricle of the matrix layer. This localization indicated that SSEA-1 is present in proliferating premigratory cells of the rat spinal cord. Between E12 and E16, cells of the alar plate expressed SSEA-1. Expression of the antigen was restricted to neuroblasts that will form the dorsal horn. SSEA-1, therefore, can be used at this stage as a marker for a subdivision of the matrix layer. At E14, the dorsal root entrance zone showed SSEA-1. This indicated that SSEA-1 is associated with ingrowing primary afferents. From E16 on, SSEA-1 was present in the dorsal raphe, which suggested a function for SSEA-1 in the guidance of developing fibres. After E17, the antigen was also found within the dorsal mantle layer. SSEA-1 was first present in Rexed's laminae II, IV and V. Later on in development the antigen was detected only in Rexed's laminae II (substantia gelatinosa). These distribution patterns indicated that SSEA-1 is present on migratory and/or postmigratory cells. In addition, SSEA-1 is associated with small-diameter dorsal root fibres, the C fibres and A(sigma) fibres, that terminate within the substantia gelatinosa. After birth, SSEA-1 was present throughout the dorsal horn, probably as a result of the myelination of the fibres.

Peripheral injury and anterograde transport of wheat germ agglutinin-horse radish peroxidase to the spinal cord

Previous observations have revealed labeling in the extracellular space surrounding boutons and unmyelinated fibers in superficial laminae of the spinal cord after injection of the tracer wheat germ agglutinin conjugated to horseradish peroxidase in dorsal root ganglia. The degree of extracellular labeling appeared related to the extent of the damage to the ganglia at the time of the injection. To determine whether injury might produce extracellular labeling, we investigated the effects of unilateral nerve crush or transection on spinal labeling after bilateral injections of the tracer into sciatic nerves. Confirming previous reports, labeling was confined to small dorsal root ganglion cells and to spinal laminae I and II, suggesting a selective affinity of this tracer for unmyelinated fibers. Labeling of both ganglion neurons and superficial spinal laminae was increased on the injured side, probably as a result of increased efficiency of receptor-mediated endocytosis. Electron microscopical observations revealed that the tracer was largely confined to unmyelinated dorsal root fibers bilaterally; a higher percentage of these fibers were labeled on the injured side. In the dorsal horn, the tracer was predominantly within unmyelinated axons and their terminals on the control side, whereas most of the labeling was extracellular and transneuronal on the injured side. The extracellular labeling surrounded unmyelinated fibers and their terminals in the spinal cord, but was excluded from the synaptic cleft. The demonstration that injury is accompanied by significantly increased release of this tracer from the terminals of unmyelinated fibers into the extracellular space suggests that endogenous substances may be released after peripheral lesions as a central signal of injury.