Behavioral effects of spinal cord transection in the developing rat

Albino rats, 0, 9, 12, 15, 18, 21 or greater than 90 days of age, were given a mid-thoracic spinal cord transection. Evaluation of responses of the hindlimbs to a variety of behavioral tasks was begun on the day of surgery and at intervals throughout the postoperative survival period (up to 300 days). Two investigators, independently and without knowledge of the animals' ages or survival times, rated the response data. Histological study showed all transections to be complete. Large differences in behavior are observed when animals trasected at the neonatal stage (0-4 days of age) are compared with animals transected at the weanling stage (21-26 days of age)37. Results of the present investigation indicate a critical period near 15 days of age; animals lesioned prior to this age (0, 9, 12 days of age) show response development and recovery similar to the neonatally lesioned animal, whereas those animals lesioned at a later age (18, 21, greater than 90 days of age) show little recovery and are behaviorally similar to the weanling transected animal. In animals lesioned prior to the fifteenth postnatal day, postural responses appear depressed for a brief period but recover rapidly while most responses of animals in the older groups are depressed for longer periods and never attain the degree of recovery characteristic of the neonatally transected animal. Finally, like the neonatally transected animal, rats lesioned on the ninth and twelfth postnatal day develop certain responses at appropriate times relative to normal response development. If, however, these responses are mature and supraspinal control is present at the time of lesioning, they appear to be permanently depressed and fail to recover.     

Topographical organization of group II afferent input in the rat spinal cord

Recent data suggest that patients with Alzheimer's disease (AD) are able to show perceptual priming and, to some extent, conceptual priming for material which has preexisting representations in memory, and that normal elderly subjects are able to automatically activate pre-existing representations in both perceptual and conceptual priming tasks. An important question concerns the capacity of showing priming for materials without pre-existing representations in memory in normal and pathological aging. In order to address this issue, 20 patients with mild AD, 20 elderly controls and 20 young controls subjects were assessed with a paradigm of priming for new verbal associations. Neither the patients nor the normal elderly subjects demonstrated priming effects for new associations, while young subjects showed significant priming effects. These results suggest that the absence of priming for new verbal associations is attributable more to an effect of aging than to a specific effect of Alzheimer's disease.     

Effect of spinal cord transection on N-methyl-D-aspartate receptors in the cord

Spinal cord injury can lead to an exaggeration of transmission through spinal pathways, resulting in muscle spasticity, chronic pain, and abnormal control of blood pressure and bladder function. These conditions are mediated, in part, by N-methyl-D-aspartate (NMDA) receptors on spinal neurons, but the effects of cord injury on the expression or function of these receptors is unknown. Therefore, antibodies to the NMDA-R1 receptor subunit and binding of [3H]MK-801 were used to assess NMDA receptors in the spinal cord. Receptor density in rats with intact spinal cords was compared to that in rats 1 and 2 weeks after spinal cord transection (SCT) at the mid-thoracic level. At 1 and 2 weeks after SCT, [3H]MK-801 binding was reduced in most laminae in cord segments caudal to the injury, whereas no decrease in amount of R1 subunit immunoreactivity was observed. No significant changes in [3H]MK-801 binding and NMDA-R1 immunoreactivity could be seen rostral to the transection. Since [3H]MK-801 binding requires an open ion channel, the discrepancy between [3H]MK-801 binding and immunocytochemistry may indicate a loss of functional receptors without a consistent change in their total number. Therefore, the exaggerated reflexes that are well established in rats 2 weeks after cord injury must be mediated by a mechanism that withstands attenuation of NMDA receptor function.     

Effect of sciatic nerve transection or TTX application on enzyme activity in rat spinal cord

BACKGROUND/PURPOSE: Treatment of several congenital anomalies is frequently hindered by lack of enough tissue for surgical reconstruction in the neonatal period. The purposes of this study were (1) introduction of a novel concept in perinatal surgery, involving minimally invasive harvest of fetal tissue, which is then processed through tissue engineering techniques in vitro while pregnancy is allowed to continue, so that, at delivery, the newborn can benefit from having autologous, expanded tissue promptly available for surgical implantation at birth; (2) analysis of the progress of an engineered fetal skin graft with time, after implantation in the neonate; and (3) study of the effects of current tissue engineering techniques on fetal keratinocytes and fetal dermal fibroblasts. METHODS: Ten 90- to 95-day-gestation fetal lambs underwent surgical creation of two large paramedian excisional skin defects on the posterior body wall. Subsequently, fetal skin specimens no larger than 1.5 x 1.5 cm were videofetoscopically harvested. Fetal keratinocytes and dermal fibroblasts were then separately cultivated and expanded in vitro for 45 to 50 days, resulting in a total of approximately 250 to 300 million cells. Seven to 10 days before fetal delivery, all cells were seeded in two layers on a 16 to 20-cm2, 3-mm thick biodegradable polyglycolic acid polymer matrix. One to 4 days after delivery, the autologous engineered skin was implanted over one of two previously created skin defects. The second skin defect region received an absorbable polymer scaffold without cells as a control. If necessary, the original skin wounds were further amplified before implantation. Each animal provided at least one time-point for histological analysis of both types of repair through excisional biopsies performed at weekly intervals, up to 8 weeks postimplantation. Normal skin specimens were also used as controls. RESULTS: Fetal and neonatal survival rates were 100%. Based on previous postnatal skin engineering studies, fetal dermal fibroblasts multiplied significantly faster in vitro (approximately fivefold) than expected. Fetal keratinocytes multiplied at expected postnatal rates. The engineered grafts induced faster epithelization of the wound (partial at 1 week and complete between 2 and 3 weeks postoperatively) than did the acellular ones (partial at 3 weeks and complete between 3 and 4 weeks postoperatively). Analysis of skin architecture showed a higher level of epidermal organization and less dermal scarring in the wounds that received the engineered, cell-implanted polymer scaffold. CONCLUSIONS: (1) Videofetoscopically assisted fetal tissue engineering is a viable method for obtaining expanded autologous tissue for prompt surgical reconstruction at birth. (2) Fetal skin can be expanded and engineered in vitro at faster rates than expected postnatally, with current tissue engineering techniques. (3) Engineered autologous fetal skin induces a faster and more organized healing of neonatal skin defects than that observed with second intention. This concept may prove useful for the treatment of certain human neonatal conditions such as giant neoplasias, ectopia cordis, and other body wall defects.     

Regeneration of lesioned corticospinal tract fibers in the adult rat spinal cord under experimental conditions

The absence of fiber regrowth in the injured spinal cord and brain is influenced by several different factors and mechanisms. Among these are factors which inhibit neurite growth which are found on the surface of oligodendrocytes and central myelin. Their neutralization by a specific antibody allowed regeneration of transected corticospinal tract fibers in the adult rat spinal cord. Using a recently introduced novel neuroanatomical tracer, biotin-dextran-amine, we demonstrate the extensive regenerative sprouting of lesioned corticospinal fibers in the lesioned adult spinal cord. In the presence of the antibody against the myelin-associated neurite growth inhibitors, some of these fibers grew over remaining tissue bridges into the caudal spinal cord. They branched extensively in the lumbar spinal cord segments. These branches were decorated with synapse-like boutons. This neuroanatomical configuration probably contributes importantly to the functional recovery observed earlier in these antibody-treated animals.     

Selective cortical and segmental control of primary afferent depolarization of single muscle afferents in the cat spinal cord

This study was primarily aimed at investigating the selectivity of the cortico-spinal actions exerted on the pathways mediating primary afferent depolarization (PAD) of muscle spindle and tendon organ afferents ending within the intermediate nucleus at the L6-L7 segmental level. To this end we analyzed, in the anesthetized cat, the effects produced by electrical stimulation of sensory nerves and of the cerebral cortex on (a) the intraspinal threshold of pairs of single group I afferent fibers belonging to the same or to different hindlimb muscles and (b) the intraspinal threshold of two collaterals of the same muscle afferent fiber. Afferent fibers were classified in three categories, according to the effects produced by stimulation of segmental nerves and of the cerebral cortex. Twenty-five of 40 fibers (62.5%) were depolarized by stimulation of group I posterior biceps and semitendinosus (PBSt) or tibialis (Tib) fibers, but not by stimulation of the cerebral cortex or of cutaneous and joint nerves, which instead inhibited the PBSt- or Tib-induced PAD (type A PAD pattern, usually seen in Ia fibers). The remaining 15 fibers (37.5%) were all depolarized by stimulation of the PBSt or Tib nerves and the cerebral cortex. Stimulation of cutaneous and joint nerves produced PAD in 10 of those 15 fibers (type B PAD pattern) and inhibited the PBSt- or Tib-induced PAD in the 5 remaining fibers (type C PAD pattern). Fibers with a type B or C PAD pattern are likely to be Ib. Not all sites in the cerebral cortex inhibited with the same effectiveness the segmentally induced PAD of group I fibers with a type A PAD pattern. With the weakest stimulation of the cortical surface, the most effective sites that inhibited the PAD of individual fibers were surrounded by less effective sites, scattered all along the motor cortex (area 4gamma and 6) and sensory cortex (areas 3, 2 and 1), far beyond the area of projection of group I fibers from the hindlimb. With higher strengths of cortical stimulation, the magnitude of the inhibition was also increased, and previously ineffective or weakly effective sites became more effective. Maps obtained when using the weakest cortical stimuli have indicated that the most effective regions that produced PAD of group I fibers with a type B or type C PAD pattern were also scattered throughout the sensory-motor cortex, in the same general area as those that inhibited the PAD of group I afferents with a type A PAD pattern. In eight fibers with a type A PAD pattern it was possible to examine the intraspinal threshold of two collaterals of the same single afferent fiber ending within the intermediate nucleus at the L7 segmental level. In six fibers, stimulation of the PBSt nerve with trains of pulses between 1.5 and 1.86 times threshold (xT) produced a larger PAD in one collateral than in the other. In seven fibers, stimulation of the sensory-motor cortex and of cutaneous nerves produced a larger inhibition of the PBSt-induced PAD in one collateral than in the other. The ratio of the cortically induced inhibition of the PAD elicited in the two collaterals could be modified by changing the strength of cortical and of PBSt stimulation. In three fibers it was possible to inhibit almost completely the background PAD elicited in one collateral while having little or no effect on the PAD in the other collateral. Changes in the intraspinal threshold of pairs of collaterals following electrical stimulation of segmental nerves and of the somato-sensory cortex were examined in three fibers with a type B and two fibers with a type C PAD pattern. In four fibers the PAD elicited by stimulation of cutaneous (4-20xT) and muscle nerves (1.54-3.7xT), or by stimulation of the sensory-motor cortex, was of different magnitude in the two collaterals. In two experiments it was possible to find cortical sites in which weak surface stimulation produced PAD in one collateral only. (ABSTRACT TRUNCATED)     

Restitution of functional neural connections in chick embryos assessed in vitro after spinal cord transection in Ovo

Functional neural reconnection is not common after spinal cord transection in the CNS of adult higher vertebrates but has been demonstrated in embryonic avian and neonatal mammalian CNS. Chick brainstem spinal cord preparations from nontransected controls and embryos transected at the cervical level on embryonic days (E) 8, 9, or 10 in ovo were assessed in vitro between E12 and E20 for their ability to produce and maintain episodic motor activity (EMA) using electrophysiological, voltage sensitive dye and anatomical tract-tracing techniques. After 3 to 4 days recovery, cycle-by-cycle coupling of EMA between segments separated by a transection was absent or inconsistent, although otherwise normal bouts of locally stimulated and spontaneous EMA were routinely observed restricted to segments of a cord separated by a transection site. After 5-7 days recovery in ovo the cross-transection coordination during bouts of EMA approached that of nontransected controls. The delay between the initiation of EMA in cervical segments to its initiation in lumbosacral segments caudal to a transection was an indicator of reconnection strength. The delay shortened from 0.5 to a few seconds after 3 days of recovery to around 150 ms (i.e., normal) after 5 days of recovery. We conclude that the reconnection of spinal central pattern generators for EMA across the transection was served mainly by axons which established connections with local circuits after extending 1-3 segments through a transection. Propriospinal axons that originated within 1-3 segments rostral to the transection then served to serially initiate EMA in distal caudal segments.     

Graded histological and locomotor outcomes after spinal cord contusion using the NYU weight-drop device versus transection

Injury reproducibility is an important characteristic of experimental models of spinal cord injuries (SCI) because it limits the variability in locomotor and anatomical outcome measures. Recently, a more sensitive locomotor rating scale, the Basso, Beattie, and Bresnahan scale (BBB), was developed but had not been tested on rats with severe SCI complete transection. Rats had a 10-g rod dropped from heights of 6.25, 12.5, 25, and 50 mm onto the exposed cord at Tl 0 using the NYU device. A subset of rats with 25 and 50 mm SCI had subsequent spinal cord transection (SCI + TX) and were compared to rats with transection only (TX) in order to ascertain the dependence of recovery on descending systems. After 7-9 weeks of locomotor testing, the percentage of white matter measured from myelin-stained cross sections through the lesion center was significantly different between all the groups with the exception of 12.5 vs 25 mm and 25 vs 50 mm groups. Locomotor recovery was greatest for the 6.25-mm group and least for the 50-mm group and was correlated positively to the amount of tissue sparing at the lesion center (p < 0.0001). BBB scale sensitivity was sufficient to discriminate significant locomotor differences between the most severe SCI (50 mm) and complete TX (p < 0.01). Transection following SCI resulted in a drop in locomotor scores and rats were unable to step or support weight with their hindlimbs (p < 0.01), suggesting that locomotor recovery depends on spared descending systems. The SCI + TX group had a significantly greater frequency of HL movements during open field testing than the TX group (p < 0.005). There was also a trend for the SCI + TX group to have higher locomotor scores than the TX group (p > 0.05). Thus, spared descending systems appear to modify segmental systems which produce greater behavioral improvements than isolated cord systems.     

Central projections of primary afferent fibers from the rat trigeminal nerve labeled with isolectin B4-HRP

The central projections of unmyelinated primary afferent fibers from the rat trigeminal nerve were investigated using retrograde and transganglionic transport of isolectin B4-horseradish peroxidase (B4-HRP). After the injection of a small amount of the tracer into various areas of the facial dermis and oral mucosa, small neuronal somata were retrogradely labeled in the trigeminal ganglion. Clearly delineated transganglionic labeling was observed exclusively in lamina II of the medullary and upper cervical dorsal horn. Its distribution showed a somatotopic organization. Fibers from the oral mucosa terminated in the region 0-1.7 mm caudal to the obex, whereas those from the facial skin terminated in the region from 1.3 mm caudal to the obex through the second cervical segment. In each of these two terminal regions, the rostral areas in the periphery were represented more rostrally than the caudal areas, and the dorsal areas in the periphery were represented more ventrolaterally than the ventral areas.     

Reconstruction of trajectory of primary afferent collaterals in the dorsal horn of the cat spinal cord, using Golgi-stained serial sections

Using Golgi-stained serial sections obtained at the sacro-caudal levels of the cat spinal cord, it was possible to reconstruct the trajectory of primary afferents. They were classified into two groups: reliable primary afferents directly traced from the dorsal root and probable primary afferents traced from the dorsal funiculus or Lissauer's tract. The diameters of the reliable primary afferents vary from 0.88-1.88 mum. According to their courses, reliable primary afferents as well as probable primary afferents were classified into three groups: the first is distributed to both medial and lateral halves of the dorsal horn, the second to the medial half, and the third to the lateral half. Commissural fibers were also observed among the probable primary afferents. The rostro-caudal and medio-lateral extents of reliable primary afferents are found to be between 250 and 950 mum and 270 and 700 mum respectively, while those of the probable primary afferents were between 125 and 670 mum and 270 and 1,640 mum respectively. These primary afferent fibers are connected with at least two or more laminae of the dorsal horn gray matter.     

Lidocaine toxicity in primary afferent neurons from the rat

Evidence from both clinical studies and animal models suggests that the local anesthetic, lidocaine, is neurotoxic. However, the mechanism of lidocaine-induced toxicity is unknown. To test the hypothesis that toxicity results from a direct action of lidocaine on sensory neurons we performed in vitro histological, electrophysiological and fluorometrical experiments on isolated dorsal root ganglion (DRG) neurons from the adult rat. We observed lidocaine-induced neuronal death after a 4-min exposure of DRG neurons to lidocaine concentrations as low as 30 mM. Consistent with an excitotoxic mechanism of neurotoxicity, lidocaine depolarized DRG neurons at concentrations that induced cell death (EC50 = 14 mM). This depolarization occurred even though voltage-gated sodium currents and action potentials were blocked effectively at much lower concentrations. (EC50 values for lidocaine-induced block of tetrodotoxin-sensitive and -resistant voltage-gated sodium currents were 41 and 101 microM, respectively.) At concentrations similar to those that induced neurotoxicity and depolarization, lidocaine also induced an increase in the concentration of intracellular Ca++ ions ([Ca++]i; EC50 = 21 mM) via Ca++ influx through the plasma membrane as well as release of Ca++ from intracellular stores. Finally, lidocaine-induced neurotoxicity was attenuated significantly when lidocaine was applied in the presence of nominally Ca(++)-free bath solution to DRG neurons preloaded with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). Our results indicate: 1) that lidocaine is neurotoxic to sensory neurons; 2) that toxicity results from a direct action on sensory neurons; and 3) that a lidocaine-induced increase in intracellular Ca++ is a mechanism of lidocaine-induced neuronal toxicity.     

Blood-spinal cord barrier function and morphometry after single doses of x-rays in rat spinal cord

PURPOSE: The effects of irradiation on blood-spinal cord barrier (BSCB) function and ultrastructure were evaluated using a rat spinal cord model. METHODS AND MATERIALS: Rats received a single dose of 25 Gy to the cervical spinal cord (C2-T2). At various times following irradiation and before the onset of paralysis, BSCB function was assessed using horseradish peroxidase (HRP) as a vascular tracer, and barrier-related structural changes in the capillaries were evaluated using morphometric techniques. RESULTS: Focal extravasation of HRP was seen at 93 days after irradiation, and extensive extravasation was apparent by 114 days in white matter, but not in gray matter. At 93 days, pathologic changes apparent by light microscopy were very minor in the white matter of the irradiated segment. By 107 days, myelin beading, Wallerian degeneration, edema, and histiocytes were apparent in white matter, and these features became increasingly prominent over the following weeks. No noteworthy changes were seen in gray matter at these times. Electron microscopic examination showed that, during the first 93 days following irradiation, more than half of the endothelial cells in white matter had disappeared (p < 0.05). In terms of the putative vascular pores, no abnormalities in endothelial junctions (the presumed small pore) were found, but there was an increase in the density of endothelial vesicles (a putative form of the large pore) in irradiated white matter (p < 0.001), but not in gray matter. Pericytes, thought to act as a second line of defence in the blood-brain barrier, increased in size but not in number in the irradiated white matter of the spinal cord. CONCLUSION: We suggest that radiation damage to endothelial cells, which form the BSCB prior to the onset of neurological deficit, may play an important role in the pathogenesis of white matter necrosis.     

Long-term depression of C-fibre-evoked spinal field potentials by stimulation of primary afferent A delta-fibres in the adult rat

Long-term potentiation (LTP) of spinal C-fibre-evoked field potentials can be induced by brief electrical stimulation of afferent C-fibres, by natural noxious stimulation of skin or by acute nerve injury. Here, we report that in urethane anaesthetized, adult rats prolonged high frequency burst stimulation of the sciatic nerve at Adelta-fibre strength produced long-term depression (LTD) of C-fibre-evoked field potentials, and also depressed the increased amplitudes of C-fibre-evoked field potentials recorded after LTP had been established (depotentiation). Electrical stimulation of Abeta-fibres failed to induce LTD or depotentiation. In spinalized rats, prolonged Adelta-fibre conditioning stimulation induced LTP rather than LTD of C-fibre-evoked field potentials. Thus, tonic descending inhibition may determine the direction of plastic changes in C-fibre-mediated synaptic transmission. Spinal application of the N-methyl-D-aspartic acid receptor antagonist D-APV blocked induction of LTD in intact rats and LTP in spinalized rats. The presently described LTD and the depotentiation of established LTP of C-fibre-evoked field potentials in spinal dorsal horn may underlie some forms of prolonged analgesia induced by peripheral nerve stimulation procedures.     

Adult opossums (Didelphis virginiana) demonstrate near normal locomotion after spinal cord transection as neonates

When the thoracic spinal cord of the North American opossum (Didelphis virginiana) is transected on postnatal day (PD) 5, the site of injury becomes bridged by histologically recognizable spinal cord and axons which form major long tracts grow through the lesion. In the present study we asked whether opossums lesioned on PD5 have normal use of the hindlimbs as adults and, if so, whether that use is dependent upon axons which grow through the lesion site. The thoracic spinal cord was transected on PD5 and 6 months later, hindlimb function was evaluated using the Basso, Beattie, and Bresnahan (BBB) locomotor scale. All animals supported their weight with the hindlimbs and used their hindlimbs normally during overground locomotion. In some cases, the spinal cord was retransected at the original lesion site or just caudal to it 6 months after the original transection and paralysis of the hindlimbs ensued. Surprisingly, however, these animals gradually recovered some ability to support their weight and to step with the hindlimbs. Similar recovery was not seen in animals transected only as adults. In order to verify that descending axons which grew through the lesion during development were still present in the adult animal, opossums subjected to transection of the thoracic cord on PD5 were reoperated and Fast blue was injected several segments caudal to the lesion. In all cases, neurons were labeled rostral to the lesion in each of the spinal and supraspinal nuclei labeled by comparable injections in unlesioned, age-matched controls. The results of orthograde tracing studies indicated that axons which grew through the lesion innervated areas that were appropriate for them.     

Peripheral and central contributions to the persistent expression of spinal cord fos-like immunoreactivity produced by sciatic nerve transection in the rat

In the absence of reliable baseline data for normal neuron density in the intestine, the diagnosis of hypo- and hyperganglionosis is purely subjective. This study has established the normal neuron density by neuron counts in paraffin sections taken both transversely (transverse sections, TS) and longitudinally (longitudinally sections, LS) in relation to the long axis of normal postmortem jejunum, ileum, and colon from 21 children (aged 4 weeks to 10 years). Intestine from two adults (aged 16 and 42 years) and colon alone from a further six adults (aged 16 to 83 years) were also studied. The mean density values in childhood were for jejunum 3.6/mm (TS), 3.7/mm (LS); for ileum 4.3/mm (TS, LS); and for colon 7/mm (LS), 7.7/mm (TS). The proximal margins of surgically resected colons from six patients with Hirschsprung's disease and one patient with suspected isolated hypoganglionosis were also analyzed and the neuron densities compared with the established postmortem data. Neuron density values outside two standard deviations from the postmortem mean were shown to correlate with continuing pseudo-obstructive symptoms in these patients.     

Endomorphin-2 is an endogenous opioid in primary sensory afferent fibers

Evidence is presented that the recently discovered endogenous mu-selective agonist, endomorphin-2, is localized in primary sensory afferents. Endomorphin-2-like immunoreactivity was found to be colocalized in a subset of substance P- and mu opiate receptor-containing fibers in the superficial laminae of the spinal cord and spinal trigeminal nucleus. Disruption of primary sensory afferents by mechanical (deafferentation by dorsal rhizotomy) or chemical (exposure to the primary afferent neurotoxin, capsaicin) methods virtually abolished endomorphin-2-like immunoreactivity in the dorsal horn. These results indicate that endomorphin-2 is present in primary afferent fibers where it can serve as the endogenous ligand for pre- and postsynaptic mu receptors and as a major modulator of pain perception.     

Glutamate receptor-mediated hyperexcitability after ethanol exposure in isolated neonatal rat spinal cord

The influence of maternal opioid receptor blockade (50 mg/kg naltrexone, NTX) or saline (controls) throughout pregnancy on nociception and brain opioid receptor characteristics of rat offspring were examined; all animals were crossfostered to untreated mothers at birth. At 21 and 30 days, NTX-exposed pups weighed 8.2-24.3% more than controls, but both NTX and control groups were of similar body weights at 48, 60, and 80 days. Rats in the NTX and control groups displayed comparable baseline reactions to the hotplate. Morphine challenge tests and nociceptive measures revealed that NTX-subjected offspring examined at 21, 30, 48, and 60 days did not react to dosages that invoked 42-132% decreases from baseline levels in controls. Animals exposed prenatally to NTX were analgesic when injected with the opioid butorphanol or the nonopioid xylazine. The binding affinity (Kd) and capacity (Bmax) of delta and kappa opioid receptors were similar in NTX and control groups at 21 and 80 days. However, the Bmax, but not the Kd, of mu opioid receptors was subnormal in NTX offspring by about 20% in contrast to control rats at 21 and 80 days. The results imply that the interactions of some endogenous opioids with opioid receptors during development are determinants of certain aspects of pain sensitivity as well as the density of particular opioid receptors in the postnatal period.     

ATP P2x receptors and sensory synaptic transmission between primary afferent fibers and spinal dorsal horn neurons in rats

ATP P2x receptors and sensory synaptic transmission between primary afferent fibers and spinal dorsal horn neurons in rats. J. Neurophysiol. 80: 3356-3360, 1998. Glutamate is a major fast transmitter between primary afferent fibers and dorsal horn neurons in the spinal cord. Recent evidence indicates that ATP acts as another fast transmitter at the rat cervical spinal cord and is proposed to serve as a transmitter for nociception and pain. Sensory synaptic transmission between dorsal root afferent fibers and neurons in the superficial dorsal horn of the lumbar spinal cord were examined by whole cell patch-clamp recording techniques. Experiments were designed to test if ATP could serve as a transmitter at the lumbar spinal cord. Monosynaptic excitatory postsynaptic currents (EPSCs) were completely abolished after the blockade of both glutamatergic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate and N-methyl--aspartate receptors. No residual current was detected, indicating that glutamate but not ATP is a fast transmitter at the dorsal horn of the lumbar spinal cord. Pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), a selective P2x receptor antagonist, produced an inhibitory modulatory effect on fast EPSCs and altered responses to paired-pulse stimulation, suggesting the involvement of a presynaptic mechanism. Intrathecal administration of PPADS did not produce any antinociceptive effect in two different types of behavioral nociceptive tests. The present results suggest that ATP P2x2 receptors modulate excitatory synaptic transmission in the superficial dorsal horn of the lumbar spinal cord by a presynaptic mechanism, and such a mechanism does not play an important role in behavioral responses to noxious heating. The involvement of other P2x subtype receptors, which is are less sensitive to PPADS, in acute nociceptive modulation and persistent pain remains to be investigated.