The role of capsaicin-sensitive muscle afferents in fatigue-induced modulation of the monosynaptic reflex in the rat.
1. The role of group III and IV afferent fibres of the lateral gastrocnemious muscle (LG) in modulating the homonymous monosynaptic reflex was investigated during muscle fatigue in spinalized rats. 2. Muscle fatigue was induced by a series of increasing tetanic electrical stimuli (85 Hz, 600 ms) delivered to the LG muscle nerve. Series consisted of increasing train numbers from 1 to 60. 3. Potentials from the spinal cord LG motor pool and from the ventral root were recorded in response to proprioceptive afferent stimulation and analysed before and during tetanic muscle activations. Both the pre- and postsynaptic waves showed an initial enhancement and, after a '12-train' series, an increasing inhibition. 4. The enhancement of the responses to muscle fatiguing stimulation disappeared after L3-L6 dorsal root section, while a partial reflex inhibition was still present. Conversely, after section of the corresponding ventral root, there was only a reduction in the inhibitory effect. 5. The monosynaptic reflex was also studied in animals in which a large number of group III and IV muscle afferents were eliminated by injecting capsaicin (10 mM) into the LG muscle. As a result of capsaicin treatment, the fatigue-induced inhibition of the pre- and postsynaptic waves disappeared, while the response enhancement remained. 6. We concluded that the monosynaptic reflex inhibition, but not the enhancement, was mediated by those group III and IV muscle afferents that are sensitive to the toxic action of capsaicin. The afferents that are responsible for the response enhancement enter the spinal cord through the dorsal root, while those responsible for the inhibition enter the spinal cord through both the ventral and dorsal roots. (+info)
Spontaneous network activity transiently depresses synaptic transmission in the embryonic chick spinal cord.
We examined the effects of spontaneous or evoked episodes of rhythmic activity on synaptic transmission in several spinal pathways of embryonic day 9-12 chick embryos. We compared the amplitude of synaptic potentials evoked by stimulation of the ventrolateral funiculus (VLF), the dorsal or ventral roots, before and after episodes of activity. With the exception of the short-latency responses evoked by dorsal root stimulation, the potentials were briefly potentiated and then reduced for several minutes after an episode of rhythmic activity. Their amplitude progressively recovered in the interval between successive episodes. The lack of post-episode depression in the short-latency component of the dorsal root evoked responses is probably attributable to the absence of firing in cut muscle afferents during an episode of activity. The post-episode depression of VLF-evoked potentials was mimicked by prolonged stimulation of the VLF, subthreshold for an episode of activity. By contrast, antidromically induced motoneuron firing and the accompanying calcium entry did not depress VLF-evoked potentials recorded from the stimulated ventral root. In addition, post-episode depression of VLF-evoked synaptic currents was observed in voltage-clamped spinal neurons. Collectively, these findings suggest that somatic postsynaptic activity and calcium entry are not required for the depression. We propose instead that the mechanism may involve a form of long-lasting activity-induced synaptic depression, possibly a combination of transmitter depletion and ligand-induced changes in the postsynaptic current accompanying transmitter release. This activity-dependent depression appears to be an important mechanism underlying the occurrence of spontaneous activity in developing spinal networks. (+info)
Early specification of sensory neuron fate revealed by expression and function of neurogenins in the chick embryo.
The generation of sensory and autonomic neurons from the neural crest requires the functions of two classes of basic helix-loop-helix (bHLH) transcription factors, the Neurogenins (NGNs) and MASH-1, respectively (Fode, C., Gradwohl, G., Morin, X., Dierich, A., LeMeur, M., Goridis, C. and Guillemot, F. (1998) Neuron 20, 483-494; Guillemot, F., Lo, L.-C., Johnson, J. E., Auerbach, A., Anderson, D. J. and Joyner, A. L. (1993) Cell 75, 463-476; Ma, Q., Chen, Z. F., Barrantes, I. B., de la Pompa, J. L. and Anderson, D. J. (1998 Neuron 20, 469-482). We have cloned two chick NGNs and found that they are expressed in a subset of neural crest cells early in their migration. Ectopic expression of the NGNs in vivo biases migrating neural crest cells to localize in the sensory ganglia, and induces the expression of sensory neuron-appropriate markers in non-sensory crest derivatives. Surprisingly, the NGNs can also induce the expression of multiple pan-neuronal and sensory-specific markers in the dermomyotome, a mesodermal derivative. Taken together, these data suggest that a subset of neural crest cells may already be specified for a sensory neuron fate early in migration, as a consequence of NGN expression. (+info)
The lumbosacral dorsal rami of the cat.
The lumbosacral dorsal rami of the cat were studied by gross dissection. The L1-6 dorsal rami form three discrete branches - lateral, intermediate and medial. The lateral branches supply the iliocostalis lumborum and become cutaneous over the back. The intermediate branches ramify in the longissimus lumborum, and are separated from the lateral branches by the lumbar intermuscular septum. The medial branches supply the multifidus and have a constant branch - the nerve to intertransversarii mediales. The L7 dorsal ramus forms only medial and intermediate branches. The S1 and S2 dorsal rami form three branches, the middle of which form the ascending sacral trunk and accessory ascending sacral trunk. The ascending sacral trunk is derived from S1 and S2, the accessory ascending sacral trunk from S2. Both nerves are the exclusive nerve supply of lumbococcygeus. (+info)
Extradural inflammation associated with annular tears: demonstration with gadolinium-enhanced lumbar spine MRI.
Annular tears are manifest on MRI as the high-intensity zone (HIZ) or as annular enhancement. Patients with annular tears may experience low back pain with radiation into the lower limb in the absence of nerve root compression. Inflammation of nerve roots from leak of degenerative nuclear material through full-thickness annular tears is a proposed mechanism for such leg pain. The aim of this study is to illustrate the appearance of extradural enhancement adjacent to annular tears in patients being investigated for low back pain with radiation into the lower limb(s). Sagittal T1- and T2-weighted spin echo and axial T1-weighted spin echo sequences were obtained in eight patients being investigated for low back and leg pain. In all patients, the T1-weighted sequences were repeated following intravenous gadopentetate dimeglumine (Gd-DTPA). Annular tears were identified at 12 sites in eight patients. Extradural inflammation appeared as a region of intermediate signal intensity replacing the fat between the posterior disc margin and the theca, which enhanced following Gd-DTPA. The inflammatory change was always associated with an annular tear, and in four cases directly involved the nerve root. Enhancement of the nerve root was seen in two cases. The findings may be relevant in the diagnosis of chemical radiculopathy secondary to inflammation at the site of an annular leak from a degenerating disc. (+info)
Ten- to 15-year outcome of surgery for lumbar disc herniation: radiographic instability and clinical findings.
The most appropriate treatment for radiculopathy associated with disc pathology is still controversial. Since 1934, surgical treatment has consisted of hemilaminectomy and removal of the herniated material. Many authors believe that these procedures may cause degenerative spondylosis and vertebral instability. Several surgical methods have been proposed, but the long-term effects are still being debated. In addition there appear to be few well-designed outcome studies on the management of this disease. In the present study, 150 patients were selected for surgery with strict criteria and all treated with the standard technique. The series was evaluated by subjective analyses (Roland questionnaire; 120 patients), objective examinations (68 patients - 56.6%) and radiographic studies including dynamic views (analyzed by the Taillard and Boxall methods) to establish the presence of vertebral instability (50 patients - 41.6%). The subjective and objective analyses showed a high rate of good results. Radiographic studies showed vertebral instability in 30 cases, but only 9 were symptomatic. Recurrences were not observed and only a few patients suffered from leg pain. The standard procedure for lumbar disc herniation showed good results at 10- and 15-year follow-up. (+info)
Spondyloptosis and multiple-level spondylolysis.
An unusual case of a combination of multiple bilateral spondylolyses (L2, 3 and 4), spondylolisthesis at L3/4, spondyloptosis at L4/5 and sacralization of L5 in a teenage female is described. The patient had severely increasing lower back pain radiating to the left lower limb. Radiography identified the abnormalities and myelography revealed complete obstruction and compression of the thecal sac at the L4/5 level. The case was treated surgically by posterior decompression, corpectomy and fusion in a three-stage operation. The follow-up was extended to 2 years with no complications. No similar case has previously been reported. (+info)
Optical mapping of neural network activity in chick spinal cord at an intermediate stage of embryonic development.
We have applied multiple-site optical recording of transmembrane potential changes to recording of neuronal pathway/network activity from embryonic chick spinal cord slice preparations. Spinal cord preparations were dissected from 8-day-old chick embryos at Hamburger-Hamilton stage 33, and transverse slice preparations were prepared with the 13th cervical spinal nerve or with the 2nd or 5th lumbosacral spinal nerve intact. The slice preparations were stained with a voltage-sensitive merocyanine-rhodanine dye (NK2761). Transmembrane voltage-related optical (dye-absorbance) changes evoked by spinal nerve stimulation with positive square-current pulses using a suction electrode were recorded simultaneously from many loci in the preparation, using a 128- or 1,020-element photodiode array. Optical responses were detected from dorsal and ventral regions corresponding to the posterior (dorsal) and anterior (ventral) gray horns. The optical signals were composed of two components, fast spike-like and slow signals. In the dorsal region, the fast spike-like signal was identified as the presynaptic action potential in the sensory nerve and the slow signal as the postsynaptic potential. In the ventral region, the fast spike-like signal reflects the antidromic action potential in motoneurons, and the slow signal is related to the postsynaptic potential evoked in the motoneuron. In preparations in which the ventral root was cut microsurgically, the antidromic action potential-related optical signals were eliminated. The areas of the maximal amplitude of the evoked signals in the dorsal and ventral regions were located near the dorsal root entry zone and the ventral root outlet zone, respectively. Quasiconcentric contour-line maps were obtained in the dorsal and ventral regions, suggesting the functional arrangement of the dorsal and ventral synaptic connections. Synaptic fatigue induced by repetitive stimuli in the ventral synapses was more rapid than in the dorsal synapses. The distribution patterns of the signals were essentially similar among C13, LS2, and LS5 preparations, suggesting that there is no difference in the spatiotemporal pattern of the neural responses along the rostrocaudal axis of the spinal cord at this developmental stage. In the ventral root-cut preparations, comparing the delay times between the ventral slow optical signals, we have been able to demonstrate that neural network-related synaptic connections are generated functionally in the embryonic spinal cord at Hamburger-Hamilton stage 33. (+info)