Functional changes at periphery and cortex following dorsal root lesions in adult monkeys

Chronic peripheral nerve injuries produce neural changes at different levels of the somatosensory pathway, but these responses remain poorly defined. We selectively removed cutaneous input from the index finger and thumb in young adult macaque monkeys by lesioning dorsal rootlets to examine both immediate and long-term systemic responses to this deficit. Corresponding digit representations within somatosensory cortex (SI) were initially silenced, but two to seven months later again responded to cutaneous stimulation of the 'deafferented' digits. We remapped cutaneous receptive fields (RFs) within adjacent intact dorsal rootlets two to four months after lesioning. RF distributions had greatly expanded, so that rootlets previously innervating adjacent hand regions now responded to stimulation of the index finger and/or thumb. Thus our results demonstrate peripherally mediated central reorganization.

Survival and regeneration of motoneurons in adult rats by reimplantation of ventral root following spinal root avulsion

The present study examines whether reimplantation of the ventral root could prevent motoneuron death after root avulsion. In the control animals about 65% or 39% of motoneurons survived at 3 or 6 weeks post-injury respectively. More than 60% of them expressed nitric oxide synthase (NOS). In contrast, in animals with ventral root reimplantation, nearly 90% or 80% of motoneurons survived at 3 or 6 weeks post-injury respectively. Expression of NOS due to root avulsion was significantly inhibited in these experimental animals. More interestingly, about 80% of the surviving motoneurons were found to regenerate their axons into the reimplanted ventral root, and all of these regenerating motoneurons were NOS negative. Results of the present study show that reimplantation of avulsed ventral root can greatly enhance motoneuron survival and the surviving motoneurons can regrow their axons into the original ventral root.

Enzymatic incorporation of bioactive peptides into fibrin matrices enhances neurite extension

Fibrin plays an important role in wound healing and regeneration, and enjoys widespread use in surgery and tissue engineering. The enzymatic activity of Factor XIIIa was employed to covalently incorporate exogenous bioactive peptides within fibrin during coagulation. Fibrin gels were formed with incorporated peptides from laminin and N-cadherin alone and in combination at concentrations up to 8.2 mol peptide per mole of fibrinogen. Neurite extension in vitro was enhanced when gels were augmented with exogenous peptide, with the maximal improvement reaching 75%. When this particular fibrin derivative was evaluated in rats in the repair of the severed dorsal root within polymeric tubes, the number of regenerated axons was enhanced by 85% relative to animals treated with tubes filled with unmodified fibrin. These results demonstrate that it is possible to enhance the biological activity of fibrin by enzymatically incorporating exogenous oligopeptide domains of morphoregulatory proteins.

Robust changes of afferent-induced excitation in the rat spinal dorsal horn after conditioning high-frequency stimulation

We investigated the neuronal plasticity in the spinal dorsal horn and its relationship with spinal inhibitory networks using an optical-imaging method that detects neuronal excitation. High-intensity single-pulse stimulation of the dorsal root activating both A and C fibers evoked an optical response in the lamina II (the substantia gelatinosa) of the dorsal horn in transverse slices of 12- to 25-day-old rat spinal cords stained with a voltage-sensitive dye, RH-482. The optical response, reflecting the net neuronal excitation along the slice-depth, was depressed by 28% for more than 1 h after a high-frequency conditioning stimulation of A fibers in the dorsal root (3 tetani of 100 Hz for 1 s with an interval of 10 s). The depression was not induced in a perfusion solution containing an NMDA antagonist, DL-2-amino-5-phosphonovaleric acid (AP5; 30 microM). In a solution containing the inhibitory amino acid antagonists bicuculline (1 microM) and strychnine (3 microM), and also in a low Cl(-) solution, the excitation evoked by the single-pulse stimulation was enhanced after the high-frequency stimulation by 31 and 18%, respectively. The enhanced response after conditioning was depotentiated by a low-frequency stimulation of A fibers (0.2-1 Hz for 10 min). Furthermore, once the low-frequency stimulation was applied, the high-frequency conditioning could not potentiate the excitation. Inhibitory transmissions thus regulate the mode of synaptic plasticity in the lamina II most likely at afferent terminals. The high-frequency conditioning elicits a long-term depression (LTD) of synaptic efficacy under a greater activity of inhibitory amino acids, but it results in a long-term potentiation (LTP) when inhibition is reduced. The low-frequency preconditioning inhibits the potentiation induction and maintenance by the high-frequency conditioning. These mechanisms might underlie robust changes of nociception, such as hypersensitivity after injury or inflammation and pain relief after electrical or cutaneous stimulation.

Pseudorabies virus tracing of neural pathways between the uterine cervix and CNS: effects of survival time, estrogen treatment, rhizotomy, and pelvic nerve transection

The transneuronal tracer, pseudorabies virus (PRV), was used to identify pathways from the uterine cervix which may be involved in induction of analgesia and abbreviation of estrus by vaginocervical stimulation. In Experiment I, PRV immunoreactivity (PRV-IR) in brain and spinal cord was examined 3-5 days after injection into the cervix of ovariectomized (OVX) female rats given estrogen (E) or control treatments. No differences in viral labeling were observed between OVX and OVX+E females at any time. PRV-infected cells were observed to increase as a function of time and at progressively higher CNS levels. PRV-IR neurons were first observed on day 3 post-infection at L6 in the SPN. Increased labeling was observed at day 4 in the SPN and the DGC at L6 and S1 spinal segments. Dorsal horn neurons showed PRV-IR by 4.5 days. Five days post-infection, labeling was seen in the IML and lamina X in T12-L1 segments, and in medullary raphe, A5, nPGi, nGi, DMV, lateral reticular, Barrington's nuclei, and in the midbrain PAG. In Experiment II, the effects of bilateral L6 dorsal root rhizotomy (RH) combined with unilateral (UPx) or bilateral (BPx) pelvic nerve transection on PRV infectivity were examined 5 days after infection. Despite reductions in substance P labeling in the dorsal horn following RH, PRV-IR neurons persisted in this area. In RH+UPx females, labeling persisted bilaterally in the SPN and DGC at L6. RH+BPx almost completely eliminated the PRV labeling in L6 and S1. Horizontal sections showed distinct patterns of infectivity within the IML of thoracolumbar and SPN of lumbosacral segments consistent with infection in the hypogastric and pelvic nerves, respectively. Our data indicate that retrograde transport of PRV occurs via the hypogastric and pelvic nerves after injection of the virus into the uterine cervix. Furthermore, significant intraspinal processing is likely to occur between thoracolumbar and lumbosacral levels in the modulation of reproductive tract function.

Distinct localization and target specificity of galanin-immunoreactive sympathetic preganglionic neurons of a teleost, the filefish Stephanolepis cirrhifer

Immunoreactivity for galanin was examined in the sympathetic preganglionic neurons in the spinal cord, adrenal glands, sympathetic ganglia, and some sensory ganglia of the filefish Stephanolepis cirrhifer. Galanin-immunoreactive neurons were found only in the rostral part, but not in the caudal part of the central autonomic nucleus (a column of sympathetic preganglionic neurons of teleosts). Many galanin-immunoreactive nerve terminals were found in contact with neurons in the celiac ganglia and the cranial sympathetic ganglia on both sides of the body. Most neurons encircled by galanin-immunoreactive nerve fibers were negative for tyrosine hydroxylase. Galanin-immunoreactive nerve fibers were very sparse in the spinal sympathetic paravertebral ganglia. No galanin-immunoreactive nerve fibers were found in the adrenal glands. No sensory neurons of the trigeminal, vagal, or spinal dorsal root ganglia were positive for galanin-immunoreactivity. These results suggest that galanin-immunoreactive sympathetic preganglionic neurons have distinct segmental localization and might project specifically to a population of non-adrenergic sympathetic postganglionic neurons in the celiac and cranial sympathetic ganglia.

Developmental and lesion-induced changes in the distribution of the glucose transporter Glut-1 in the central and peripheral nervous system

The active transport of D-glucose from the vascular to the neural compartment requires the presence of a carrier molecule at the blood-brain and the blood-nerve barrier. The glucose transporter 1 (Glut-1) seems to be the main carrier in blood-tissue barriers of endothelial and perineurial type. The distribution of Glut-1 was assessed in the normal central and peripheral nervous system of young and adult animals and compared with changes after nerve injury. Immuno-histochemistry, in situ hybridization, and perfusions with Evans Blue were carried out. Glut- I was not expressed in the perineurium of peripheral nerves at birth, but appeared in the perineurium of peripheral nerves, spinal roots, in the capsule of dorsal-root ganglia, and in the pia mater of adult animals. The perineurium of peripheral nerves subjected to Wallerian degeneration presented a faint Glut-1 immunoreaction, which was restored after regeneration. Glut-1 was expressed in capillaries of the gray substance of the spinal cord. Perineurial-derived lamellar cells of Pacinian corpuscles exhibited a strong Glut-1-like immunoreactivity in response to denervation and during development. Merkel cells and Meissner corpuscles were found to be Glut-1 negative. Glut-1 seems to reflect the quality of an adult, mature perineurial and blood-nerve barrier.

Electrophysiological evidence for afferent nerve fibers in human ventral roots

This study was designed to test the hypothesis that ventral roots in humans contain afferent nerve fibers. We made direct electrophysiological recordings of compound nerve action potentials in dorsal and ventral roots in children undergoing selective dorsal rhizotomy for spastic cerebral palsy. We stimulated the saphenous or sural nerves, which are pure sensory nerves, with electrical stimuli while systematically recording from ventral and dorsal roots from L3 to S2. In addition to the dorsal root nerve action potentials which we expected, we found smaller compound nerve action potentials, which were clearly afferent, in the ventral roots. This confirms the limited amount of experimental evidence that ventral roots do contain some afferent nerve fibers. The functional significance of these observations is not yet clear.

Glial cell proliferation in the spinal cord after dorsal rhizotomy or sciatic nerve transection in the adult rat

Proliferation of glial cells is one of the hallmarks of CNS responses to neural injury. These responses are likely to play important roles in neuronal survival and functional recovery after central or peripheral injury. The boundary between the peripheral nervous system (PNS) and CNS in the dorsal roots, the dorsal root transitional zone (DRTZ), marks a distinct barrier for growth by injured dorsal root axons. Regeneration occurs successfully in the PNS environment, but ceases at the PNS-CNS junction. In order to understand the role of different glial cells in this process, we analysed the proliferation pattern of glial cells in central (CNS) and peripheral (PNS) parts of the dorsal root and the segmental white and grey spinal cord matter after dorsal rhizotomy or sciatic nerve transection in adult rats 1-7 days after injury. Monoclonal antibody MIB-5 or antibodies to bromodeoxyuridine were used to identify proliferating cells. Polyclonal antibodies to laminin were used to distinguish the PNS and CNS compartments of the dorsal root. Dorsal root lesion induced glial cell proliferation in the CNS as well as PNS beginning at 1 day, with peaks from 2 to 4 days postoperatively. After sciatic nerve injury, cell proliferation occurred only in the CNS, was minimal at 1 day, and peaked from 2 to 4 days postoperatively. Double immunostaining with specific glial cell markers showed that after dorsal root transection 60% of the proliferating cells throughout the postoperative period examined were microglia, 30% astrocytes and 10% unidentified in the CNS, while in the PNS 40% were Schwann cells, 40% macrophages and 20% unidentified. After sciatic nerve injury virtually all proliferating cells were microglia. These findings indicate that non-neuronal cells in the CNS and PNS are extremely sensitive to the initial changes which occur in the degenerating dorsal root axons, and that extensive axonal degeneration is a prerequisite for astroglial and Schwann cell, but not microglial cell, proliferation.

Silent NMDA receptor-mediated synapses are developmentally regulated in the dorsal horn of the rat spinal cord

In vitro whole cell patch-clamp recording techniques were utilized to study silent pure-N-methyl-D-aspartate (NMDA) receptor-mediated synaptic responses in lamina II (substantia gelatinosa, SG) and lamina III of the spinal dorsal horn. To clarify whether these synapses are present in the adult and contribute to neuropathic pain, transverse lumbar spinal cord slices were prepared from neonatal, naive adult and adult sciatic nerve transected rats. In neonatal rats, pure-NMDA receptor-mediated excitatory postsynaptic currents (EPSCs) were elicited in SG neurons either by focal intraspinal stimulation (n = 15 of 20 neurons) or focal stimulation of the dorsal root (n = 2 of 7 neurons). In contrast, in slices from naive adult rats, no silent pure-NMDA EPSCs were recorded in SG neurons following focal intraspinal stimulation (n = 27), and only one pure-NMDA EPSC was observed in lamina III (n = 23). Furthermore, in rats with chronic sciatic nerve transection, pure-NMDA EPSCs were elicited by focal intraspinal stimulation in only 2 of 45 SG neurons. Although a large increase in Abeta fiber evoked mixed alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and NMDA receptor-mediated synapses was detected after sciatic nerve injury, Abeta fiber-mediated pure-NMDA EPSCs were not evoked in SG neurons by dorsal root stimulation. Pure-NMDA receptor-mediated EPSCs are therefore a transient, developmentally regulated phenomenon, and, although they may have a role in synaptic refinement in the immature dorsal horn, they are unlikely to be involved in receptive field plasticity in the adult.

Location of the spinal nucleus of the accessory nerve in the human spinal cord

The segmental extent and topography of the spinal nucleus of the accessory nerve (SNAN) was investigated in the adult human spinal cord. Transverse sections of segments between the lower medulla and C6 were stained with cresyl violet and the motor cell columns identified according to the numerical locations defined by Elliott (1942). The segmental extent and topography of the cervical part of column 2 resembled that previously described for the SNAN of primates.

Effects of intracolonic opioid receptor agonists on polymodal pelvic nerve afferent fibers in the rat

We studied the effects of intracolonic administration of opioid receptor agonists (ORAs) on responses of pelvic nerve afferent fibers to colorectal distension (CRD) and heat. Single-fiber recordings were made from the decentralized S1 dorsal rootlet in the rat. An approximately 7-cm length of descending colon was isolated in situ to permit intracolonic perfusion with Krebs solution, which, when the outflow was clamped, was used to distend the colon. Responses to noxious CRD (40 mmHg, 30 s) were tested after intracolonic instillation of mu-, delta- or kappa-ORAs. Intracolonic administration of the kappa-ORAs EMD 61,753 (n = 5/12) and U62,066 (n = 8/11), but not either the mu-ORA fentanyl or the delta-ORA SNC-80, concentration-dependently inhibited responses of afferent fibers. For fibers unaffected by intracolonic administration of EMD 61,753 or U62,066, intra-arterial administration of kappa-ORAs was effective. Forty-one of 54 mechanosensitive fibers also responded to intracolonic instillation of heated Krebs solution (50 degrees C). Intra-arterial injection of fentanyl or SNC-80 did not attenuate responses to heat. Either intracolonic or intra-arterial administration of EMD 61,753 or U62, 066, however, inhibited afferent fiber responses to heat. These results document that mechanical and thermal sensitivity of polymodal pelvic nerve afferent fibers innervating the rat colon can be inhibited peripherally by intracolonic instillation of kappa-ORAs.

Neuropilin-2 regulates the development of selective cranial and sensory nerves and hippocampal mossy fiber projections

Neuropilin-1 and neuropilin-2 bind differentially to different class 3 semaphorins and are thought to provide the ligand-binding moieties in receptor complexes mediating repulsive responses to these semaphorins. Here, we have studied the function of neuropilin-2 through analysis of a neuropilin-2 mutant mouse, which is viable and fertile. Repulsive responses of sympathetic and hippocampal neurons to Sema3F but not to Sema3A are abolished in the mutant. Marked defects are observed in the development of several cranial nerves, in the initial central projections of spinal sensory axons, and in the anterior commissure, habenulo-interpeduncular tract, and the projections of hippocampal mossyfiber axons in the infrapyramidal bundle. Our results show that neuropilin-2 is an essential component of the Sema3F receptor and identify key roles for neuropilin-2 in axon guidance in the PNS and CNS.

Spontaneous activity of rat dorsal horn cells in spinal segments of sciatic projection following transection of sciatic nerve or of corresponding dorsal roots

Natural forms of stimulation were used to compare the spontaneous and evoked activity of dorsal horn neurons in three groups of rats: controls with no surgical lesion, rats with transection of the sciatic nerve and rats with transection of the dorsal roots at the same segmental level. In control rats, cells encountered in the dorsal horn were classified according to their peripheral field as tactile specific, convergent tactile and nociceptive, nociceptive, or movement driven. In 20 control animals, only 20% of the 140 cells with a peripheral field were spontaneously active. After sciatic nerve transection made on the side of recording a few days previously (18 rats), all of the 141 cells studied showed spontaneous activity, only 69 of them having a peripheral field. After dorsal root transections a few days previously (nine rats), 25 spontaneously active cells were found in the dorsal horn ipsilateral to the section, none with a peripheral field. Spontaneous activities of cells without a peripheral field were separated into three types as a function of bursting pattern, which were similar following both types of transection. The spontaneous activity shown by dorsal horn cells without peripheral fields following dorsal root transection precludes attribution of spontaneous spiking in such cells to abnormal input from the periphery, and shows that abnormal activity can develop in deafferented dorsal horn cells themselves. A possible role played by this spontaneous activity in deafferentation pain is considered.

Coding of locomotor phase in populations of neurons in rostral and caudal segments of the neonatal rat lumbar spinal cord

Several experiments have demonstrated that rostral segments of the vertebrate lumbar spinal cord produce a rhythmic motor output more readily and of better quality than caudal segments. Here we examine how this rostrocaudal gradient of rhythmogenic capability is reflected in the spike activity of neurons in the rostral (L(2)) and caudal (L(5)) lumbar spinal cord of the neonatal rat. The spike activity of interneurons in the ventromedial cord, a region necessary for the production of locomotion, was recorded intracellularly with patch electrodes and extracellularly with tetrodes during pharmacologically induced locomotion. Both L(2) and L(5) neurons tended to be active in phase with their homologous ventral root. L(5) neurons, however, had a wider distribution of their preferred phases of activity throughout the locomotor cycle than L(2) neurons. The strength of modulation of the activity of individual L(2) neurons was also larger than that of L(5) neurons. These differences resulted in a stronger rhythmic signal from the L(2) neuronal population than from the L(5) population. These results demonstrate that the rhythmogenic capability of each spinal segment was reflected in the activity of interneurons located in the same segment. In addition to paralleling the rostrocaudal gradient of rhythmogenic capability, these results further suggest a colocalization of motoneurons and their associated interneurons involved in the production of locomotion.

Influence of age on regeneration in the peripheral nervous system

Studies on the influence of age on regeneration in the peripheral nervous system are reviewed. Observations in the human are limited, but clinical experience indicates that the efficiency of regeneration is less in later life. The results of experimental studies in animals, although sometimes variable, indicate a decline with age. This may be correlated with reduced axonal transport. At motor nerve terminals, the capacity to produce ultraterminal sprouting secondary to partial denervation is reduced, but not the capacity to eliminate terminal sprouts or reinnervation. Frequency and accuracy of reoccupation of the sites of motor nerve terminals are impaired. Nerve transection is more likely to result in loss of the parent neurons following nerve transection in young than in older animals. Chromatolysis is more intense and does not return to normal as rapidly in old animals, and the degree of retrograde axonal atrophy is less. This suggests a diminished dependence on peripheral growth factor support.

Long-term effects of a single dose of brain-derived neurotrophic factor on motoneuron survival following spinal root avulsion in the adult rat

The long-term effect of a single dose of Brain-derived neurotrophic factor (BDNF) treatment on adult motoneuron survival and on expression of nitric oxide synthase (NOS) following nerve injury (avulsion) was investigated and compared with that of continuous BDNF treatment. By 6 weeks post-injury, more than 80% of motoneurons survived in animals treated with either a single dose or continuous treatment of BDNF, while only 30% of motoneurons survived in control animals (avulsion only). There were no significant differences in motoneuron survival between animals receiving a single dose and those with continuous treatment of BDNF. Additionally, the expression of NOS in avulsed motoneurons was almost completely inhibited in all BDNF treatment groups regardless of the mode of administration (single vs. continuous). These data indicate that treatment with a single dose of BDNF at the time of injury can inhibit NOS expression and provide the first evidence that in this situation BDNF has a long-term rescue effect on adult motoneuron survival after root avulsion.

Ethanol reduces neuronal excitability and excitatory synaptic transmission in the developing rat spinal cord

Effects of acute ethanol (EtOH) exposure on motoneuron excitability and properties of synaptic transmission were examined in spinal cords of postnatal rats. Whole-cell patch clamp recordings and intracellular recordings with high-resistance electrodes were carried out in motoneurons of 1- to 4-day-old postnatal rats. To determine the effects of extracellular EtOH on action potential waveform, properties of current-evoked soma action potentials and motoneuron ability to generate repetitive action potential firing were examined. During a brief EtOH (70 mM) exposure, larger depolarizing current was required for action potential generation, the duration of the after hyperpolarizing potential increased, and fewer action potentials were produced during a prolonged intracellular current injection. These effects were reversed within 20 min of EtOH removal from the extracellular solution. To determine whether the reduced probability of action potential generation was associated with changes in synaptic transmission, properties of evoked synaptic potentials and spontaneous synaptic currents were investigated. In the presence of EtOH, the amplitude of dorsal root-evoked synaptic potentials was reduced, the frequency of spontaneous excitatory postsynaptic currents decreased, while the frequency of inhibitory postsynaptic currents increased. Our data suggested that acute EtOH exposure suppressed motoneuron electrical activity by decreasing motoneuron excitability and shifting the balance between excitatory and inhibitory synaptic transmission toward inhibition.

Hypothalamic orexin A-immunoreactive neurons project to the rat dorsal medulla

Retrograde tract tracing combined with immunohistochemical techniques were used to identify the origin of orexin A-immunoreactive (OrA-ir) fibers in the rat medulla. One to 5 days following injection of the fluorescent dye Fluorogold into the dorsal medulla, labeled neurons were found in the lateral half of the lateral hypothalamus, paraventricular, perifornical, dorsomedial, dorsal and posterior hypothalamic nuclei. Labeling the same sections with OrA antisera revealed a concentration of OrA-ir neurons in the perifornical and dorsomedial regions of the tuberal hypothalamus. A maximum of 10% of Fluorogold-labeled hypothalamic neurons were OrA-ir and 15% of OrA-ir hypothalamic neurons contained Fluorogold. Our results demonstrate that a fraction of OrA-ir neurons in the tuberal hypothalamus project to areas of the medulla that are involved in autonomic functions.

Antidromic discharges of dorsal root afferents in the neonatal rat

Presynaptic inhibition of primary afferents can be evoked from at least three sources in the adult animal: 1) by stimulation of several supraspinal structures; 2) by spinal reflex action from sensory inputs; or 3) by the activity of spinal locomotor networks. The depolarisation in the intraspinal afferent terminals which is due, at least partly, to the activation of GABA(A) receptors may be large enough to reach firing threshold and evoke action potentials that are antidromically conducted into peripheral nerves. Little is known about the development of presynaptic inhibition and its supraspinal control during ontogeny. This article, reviewing recent experiments performed on the in vitro brainstem/spinal cord preparation of the neonatal rat, demonstrates that a similar organisation is present, to some extent, in the new-born rat. A spontaneous activity consisting of antidromic discharges can be recorded from lumbar dorsal roots. The discharges are generated by the underlying afferent terminal depolarizations reaching firing threshold. The number of antidromic action potentials increases significantly in saline solution with chloride concentration reduced to 50% of control. Bath application of the GABA(A) receptor antagonist, bicuculline (5-10 microM) blocks the antidromic discharges almost completely. Dorsal root discharges are therefore triggered by chloride-dependent GABA(A) receptor-mediated mechanisms; 1) activation of descending pathways by stimulation delivered to the ventral funiculus (VF) of the spinal cord at the C1 level; 2) activation of sensory inputs by stimulation of a neighbouring dorsal root; or 3) pharmacological activation of the central pattern generators for locomotion evokes antidromic discharges in dorsal roots. VF stimulation also inhibited the response to dorsal root stimulation. The time course of this inhibition overlapped with that of the dorsal root discharge suggesting that part of the inhibition of the monosynaptic reflex may be exerted at a presynaptic level. The existence of GABA(A) receptor-independent mechanisms and the roles of the antidromic discharges in the neonatal rat are discussed.

Oscillatory interaction between dorsal root excitability and dorsal root potentials in the spinal cord of the turtle

The response to dorsal root stimulation, at one to two times threshold, was investigated in the isolated cervical enlargement of the turtle spinal cord. At frequencies near 10 Hz the synaptic response in motoneurons and the cord dorsum potential, after an initial lag time, oscillated in amplitude with a period of more than 1 s. The mono- and polysynaptyic postsynaptic response in motoneurons, the pre- and postsynaptic component of the cord dorsum potential and the dorsal root potential oscillated in synchrony. These oscillations were only observed with stimulus frequencies in the range 9-11 Hz. The oscillating response could only be evoked from stimulus sites to which dorsal root potentials were conducted from the spinal cord (2-3 mm). At more distant stimulus sites cyclic variations in amplitude of the cord dorsum potential and the synaptic response in motoneurons were not observed. During an oscillating spinal response to a stimulus train in one dorsal root filament, the response evoked by a stimulus in another short filament (2-3 mm) from the same root varied in amplitude with the induced oscillation. The spinal response to a stimulus in a longer filament (i.e. more than 3 mm) did not oscillate. It is argued that the oscillating responses described rely on interactions between distributed elements rather than on unit oscillators. We also show that primary afferent transmission is unaffected by the substantial variations in dorsal root potentials during oscillations.

Age-related changes in the response to thermal noxious heat and reduction of C-fibers by neonatal treatment with capsaicin

Developmental changes of the response to nociceptive heat were examined in mice treated with capsaicin (50 mg/kg) on postnatal days 2-15. Tests of hot-plate (55 degrees C) and irradiation by infrared (IR test) were carried out after 10 days of capsaicin administration up to 120 days at intervals of 10 or 20 days. The time until forepaw (hot-plate) and hindpaw (IR test) withdrawal was assessed as the response latencies to suprathreshold and thermal threshold, respectively. Moreover, the numbers of unmyelinated C-fibers and myelinated fibers in the L4 dorsal roots of the animals treated on postnatal days 2 and 5 were counted on electron micrograph montages. Despite the marked reduction of C-fibers (60% mean decrease) in the 4 dorsal roots of the animals treated on postnatal day 2, thresholds were normal compared with those of controls. However, the animals treated with capsaicin on postnatal day 5 showed an apparent delay of thermal threshold latency only in the IR test, although the mean reduction of C-fibers was very likely the same as that of the animals pretreated on day 2. The reduction of C-fibers in mice treated on postnatal days 10 and 15 was lower than the animals treated on days 2 or 5, but their threshold latencies were significantly increased (hypoalgesia). A possible implication of these findings is discussed on the basis of the development of inhibitory systems in the intraspinal and supraspinal dorsal horn and sprouting from the surviving primary afferent neurons in the superficial dorsal horn.

Vasoactive intestinal polypeptide in sacral primary sensory pathways in the cat

Unmyelinated sensory axons in the sacral spinal cord may play a role in bladder reflexes under certain pathological conditions. Previous data suggested vasoactive intestinal polypeptide (VIP) might be contained exclusively in sensory C-fibers, some of which innervate the bladder. This study was undertaken to describe the morphology of these VIP fibers in the sacral cord of the cat. VIP immunoreactivity was confined to unmyelinated axons observed at several levels of the sensory pathway including the dorsal root ganglia, dorsal roots, Lissauer's tract, and the lateral collateral pathway. A combination of light and electron microscopic observations showed VIP-immunoreactive fibers with labeled varicosities and synaptic terminals in laminae I, IIo, V, VII, and X. VIP-immunolabeled varicosities had a mean diameter of 1.6 microm (range = 0.11-7.4 microm, S.D. = 1.01, n = 311) with a small percentage (8%) being relatively large (3-7.4 microm). VIP varicosities contained a mixture of small clear vesicles (CLV) and large dense core vesicles (LDV). Although most varicosities contained a moderate number of LDVs (14.86 LDVs/microm2), some varicosities contained a large number of LDVs, whereas others contained very few. Varicosities that possessed synaptic specializations were classed as terminals and were divided into three morphological classes. Two of these resembled Gray's Type I terminal, whereas a third was similar to the Gray's Type II terminal. There was no consistent relationship between vesicle content of the terminal and the type of synaptic contact it possessed. This study shows that in the sacral spinal cord of the cat, VIP terminals originate only from C-fibers, terminate primarily in laminae I and V, and exhibit a variety of morphologies consistent with heterogeneous origins and functions of the lower urinary tract.

Rostrocaudal progression in the development of periodic spontaneous activity in fetal rat spinal motor circuits in vitro

Rostrocaudal progression in the development of periodic spontaneous activity in fetal rat spinal motor circuits in vitro. Developmental changes in the periodic spontaneous bursts in cervical and lumbar ventral roots (VRs) were investigated using isolated spinal cord preparations obtained from rat fetuses at embryonic days (E) 13.5-18. 5. Spontaneous bursts were observed in the cervical VR at E13.5-17.5, and in the lumbar VR at E14.5-17.5. Bursts occurrence in the cervical and lumbar VRs was correlated in a 1:1 fashion at E14.5-16. 5. The bursts in the cervical VR preceded those in the lumbar VR at E14.5, but the latter came to precede the former by E16.5. The interval between spontaneous bursts in the lumbar VR was greatly prolonged after spinal cord transection at the midthoracic level at E14.5, whereas that in the cervical VR became significantly longer at E14.5-16.5. These results suggest that the dominant neuronal circuit initiating the spontaneous bursts shifts from cervical to lumbar region during this period. Bath application of a glutamate receptor antagonist, kynurenate (4 mM), had little effect on the spontaneous bursts in either cervical or lumbar VRs at E14.5-15.5. At E16.5, kynurenate abolished the spontaneous bursts in the cervical VR. Concomitant application of kynurenate and strychnine (5 microM), a glycine receptor antagonist, abolished all spontaneous bursts, suggesting that the major transmitter mediating the spontaneous bursts changes from glycine to glutamate in the cervical region by E16.5, but not in the lumbar region during this period.

Denervation and reinnervation in congenital brachial palsy

Motor unit number estimation (MUNE) was shown to be useful in assessing the neurophysiological status of 18 subjects with congenital brachial palsy. This was especially so since conventional M-wave measurements may give misleading impressions as to the extent of motor axon regeneration. In most subjects the involvement of sensory nerve fibers indicated that the traumatic lesions included postganglionic segments of the fibers, with or without preganglionic damage. In a minority the lesions were purely preganglionic. Digital sensory nerve involvement was more in a mediolateral direction, consistent with greater damage to the uppermost elements in the brachial plexus. In 5 individuals, MUNE and sensory testing showed that there had been trauma to the supposedly unaffected arm. Discrepancies between sensory and motor results suggested that reinnervation of the biceps brachii muscle was greater than that of the intrinsic muscles of the hand. In one subject examined serially, reinnervation of the hand muscles was detected by 10 months and continued in the hypothenar muscles for the next 6 years.