Surface Of Spinal Cord Research Articles

Topical bicuculline to the rat spinal cord induces highly localized allodynia that is mediated by spinal prostaglandins

The purpose of this study was to investigate the allodynic effect of bicuculline (BIC) given topically to the dorsal surface of the rat spinal cord, and to determine if spinal prostaglandins (PGs) mediate the allodynic state arising from spinal GABAA-receptor blockade. Male Sprague–Dawley rats (325–400 g) were anaesthetized with halothane and maintained with urethane for the continuous monitoring of blood pressure (MAP), heart rate (HR) and cortical electroencephalogram (EEG). A laminectomy was performed to expose the dorsal surface of the spinal cord. Unilateral application of BIC (0.1 μg in 0.1 μl) to the L5 or L6 spinal segment induced a highly localized allodynia (e.g. one or two digits) on the ipsilateral hind paw. Thus, hair deflection (brushing the hair with a cotton-tipped applicator) in the presence, but not absence of BIC, evoked an increase in MAP and HR, abrupt motor responses (MR; e.g. withdrawal of the hind leg, kicking, and/or scratching) on the affected side, and desynchrony of the EEG. BIC-allodynia was dose-dependent, yielding ED50’s (95% CI's) of 45 ng (31–65) for MAP; 68 ng (46–101) for HR and 76 ng (60–97) for MR. Allodynia was sustained for up to 2 h with repeated BIC application without any detectable change in the location or area of peripheral sensitization. Pretreatment with either the EP1- receptor antagonist, SC-51322, the cyclooxygenase (COX)-2 selective inhibitor, NS-398, or the NMDA-receptor antagonist, AP-7, inhibited BIC-allodynia in a dose-dependent manner. The results demonstrate: (a) BIC, applied to the dorsal surface of the spinal cord, induces highly localized allodynia; (b) this effect can be sustained with repeated BIC application; (c) it is evoked by NMDA-dependent afferent input; (d) spinal PGs are synthesized by constitutive COX-2 during BIC-allodynia; and (e) spinal PGs contribute to the abnormal processing of tactile input via spinal EP1-receptors.

Effect of akatinol (memantine) in central spinal pain syndrome.

On the model of central spinal pain syndrome in rats induced by application of penicillin to the dorsal surface of the lumbar spinal cord, akatinol injected intraperitoneally at the peak of syndrome or applied locally simultaneously with penicillin produced a dose-dependent analgesic effect. Intraperitoneal injection of akatinol at the peak of pain syndrome inhibited neuronal activity in spinal dorsal horn: the amplitude of total evoked neuronal response significantly decreased and the duration of action potentials returned to normal. It is concluded that activation of NDMA receptors plays a significant role in the development of central spinal pain syndrome, in particular spontaneous pain attacks, hyperalgesia, and tactile allodynia. Akatinol can be an essential component of the complex pathogenetic therapy of central pains.

Therapeutic Window after Spinal Cord Trauma Is Longer than after Spinal Cord Ischemia

Department of Anesthesiology University of California, San Diego La Jolla, California 92093-0818mmarsala@ucsd.eduIn Reply:—We read carefully the comments of Drs. Albin and White on our recent article. 1As indicated by these authors, induction of spinal cord hypothermia (10°C) after traumatic spinal injury is still effective in providing protection if initiated 4 h after injury. 2,3In contrast, in our study, we observed a significant protection only if spinal hypothermia (27°C) was initiated immediately (5 min) after ischemia. Although the differences between the therapeutic efficacy of spinal hypothermia after spinal trauma and spinal ischemia are not clear, there are several points that need to be addressed.After injurious intervals of spinal ischemia, the development of irreversible neuronal degeneration shows very rapid onset. Using Nauta silver impregnation technique in rat, rabbit, or dog spinal ischemia models, we have found that irreversible neuronal degeneration is clearly developed as soon as 60–120 min after reflow following injurious intervals of ischemia. 4–7These data indicate that the process of irreversible neuronal degeneration is likely initiated during the early period (0–30 min) of reflow. Importantly, based on the data from our study, this process shows high temperature sensitivity. The lack of hypothermic protection after a longer period of normothermic reflow thus likely reflects the fact that the process of irreversible degeneration was already initiated or completed.In our study, intrathecal temperature was measured during and after a period of subcutaneous cooling. It is possible that the magnitude of the decrease in spinal parenchymal temperature does not completely reflect measured intrathecal temperature. However, in our previous methodologic study 8describing this cooling technique, we showed that there is a 2–3°C temperature gradient if measured on dorsal versus ventral spinal cord surface. Based on these data, we believe that spinal temperature is in the range of temperatures measured between dorsal and ventral spinal cord surface. Accordingly, measurement of spinal somatosensory evoked potentials showed a temperature-dependent increase in the N3 (postsynaptic) component during the period of cooling and a return to baseline after rewarming.Based on our previous data describing a very rapid onset of irreversible neuronal degeneration after spinal ischemia, the possibility that the therapeutic window could be enlarged if intrinsic spinal cord temperature were reduced to lower levels is uncertain. However, it is possible that the fraction of neurons undergo prolonged or delayed degeneration and that rescue of these neurons will eventually improve outcome. In this case, it is possible that deeper hypothermia (10–20°C) will be more effective in protecting this neuronal pool than temperatures (27°C) tested in our study. Accordingly, it would be important, using localized epidural or intrathecal cooling techniques 2,3,6,9(which are required to achieve deep spinal hypothermia), to determine the efficacy of such hypothermic treatment.

Effects of omega-agatoxin IVA, a P-type calcium channel antagonist, on the development of spinal neuronal hyperexcitability caused by knee inflammation in rats.

Both N- and P-type high-threshold calcium channels are located presynaptically in the CNS and are involved in the release of transmitters. To investigate the importance of P-type calcium channels in the generation of inflammation-evoked hyperexcitability of spinal cord neurons, electrophysiological recordings were made from wide-dynamic-range neurons with input from the knee joint in the anesthetized rat. The responses of each neuron to innocuous and noxious pressure onto the knee and the ankle were continuously assessed before and during the development of an inflammation in the knee joint induced by the injections of K/C into the joint cavity. The specific antagonist at P-type calcium channels omega-agatoxin was administered into a 30-microl trough on the spinal cord surface above the recorded neuron. In most neurons the application of omega-agatoxin before induction of inflammation slightly enhanced the responses to pressure onto the knee and ankle or left them unchanged. Two different protocols were then followed. In the control group (13 rats) only Tyrode was administered to the spinal cord during and after induction of inflammation. In these neurons the responses to mechanical stimuli applied to both the inflamed knee and to the noninflamed ankle showed a significant increase over 4 h. In the experimental group (12 rats) omega-agatoxin was applied during knee injection and in five 15-min periods up to 180 min after kaolin. This prevented the increase of the neuronal responses to innocuous pressure onto the knee and to innocuous and noxious pressure onto the ankle; only the responses to noxious pressure onto the knee were significantly enhanced during development of inflammation. Thus the development of inflammation-evoked hyperexcitability was attenuated by omega-agatoxin, and this suggests that P-type calcium channels in the spinal cord are involved in the generation of inflammation-evoked hyperexcitability of spinal cord neurons. Finally, when omega-agatoxin was administered to the spinal cord 4 h after the kaolin injection, i.e., when inflammation-evoked hyperexcitability was fully established, the responses to innocuous and noxious pressure onto the knee were reduced by 20-30% on average. The shift in the effect of omega-agatoxin, from slight facilitation or no change of the responses before inflammation to inhibition in the state of hyperexcitability, indicates that P-type calcium channels are important for excitatory synaptic transmission involved in the maintenance of inflammation-evoked hyperexcitability.

Intramedullary cavernous haemangiomas: clinical features, imaging diagnosis, surgical resection and outcome

The diagnosis, surgical treatment and outcome of seven patients with histologically verified intramedullary cavernous haemangiomas are reported. Five males and two females, with progressive myelopathy were observed. The patients were aged between 7 and 61 years. The duration of their symptoms and signs before diagnosis varied from one month to 5 years. Magnetic resonance (MR) imaging was performed in all patients and spinal angiography was performed in five. All the patients underwent microsurgical resection of the cavernous haemangiomas. MR imaging diagnosed cavernous haemangiomas in all seven patients. T1-weighted images with or without contrast enhancement best defined the margins and size of the lesions. They also illustrated the exophytic components and the change in spinal cord surface well, and were important to surgical planning. T2-weighted images may be suboptimal due to their magnetic susceptibility artifacts. In all lesions, total removal was achieved. Postoperative neurological function improved in all patients in long term follow-up. With the advantages of MR examinations and more understanding about the pathological characteristics of intramedullary cavernous haemangiomas, total removal of the mass lesion should be attempted and the outcome is generally good.

Modulation of fibronectin expression in the central nervous system of Lewis rats with experimental autoimmune encephalomyelitis.

Fibronectin (FN), a large family of plasma and extracellular matrix (ECM) glycoproteins, plays an important role in leukocyte migration. In normal central nervous system (CNS), a fine and delicate mesh of FN is virtually restricted to the basal membrane of cerebral blood vessels and to the glial limitans externa. Experimental autoimmune encephalomyelitis (EAE), an inflammatory CNS demyelinating disease, was induced in Lewis rats with a spinal cord homogenate. During the preclinical phase and the onset of the disease, marked immunolabelling was observed on the endothelial luminal surface and basal lamina of spinal cord and brainstem microvasculature. In the paralytic phase, a discrete labelling was evident in blood vessels of spinal cord and brainstem associated or not with an inflammatory infiltrate. Conversely, intense immunolabelling was present in cerebral and cerebellar blood vessels, which were still free from inflammatory cuffs. Shortly after clinical recovery minimal labelling was observed in a few blood vessels. Brainstem and spinal cord returned to normal, but numerous inflammatory foci and demyelination were still evident near the ventricle walls, in the cerebral cortex and in the cerebellum. Intense expression of FN in brain vessels ascending from the spinal cord towards the encephalon preceded the appearance of inflammatory cells but faded away after the establishment of the inflammatory cuff. These results indicate an important role for FN in the pathogenesis of CNS inflammatory demyelinating events occurring during EAF.

Peculiarities of extraspinally recorded field spinal potentials

It is demonstrated that field potentials generated in the lumbosacral spinal cord and usually recorded as a dorsal surface potential spread to the tissues of the back body surface. The component composition of these extraspinally recorded responses somewhat differs from that of the potential recorded from the spinal cord surface. The reasons for such a difference and possible approaches providing higher informative value of non-invasive studies of spinal cord potentials are discussed.

Mu- and delta-opioid receptor mRNAs are expressed in spinally projecting serotonergic and nonserotonergic neurons of the rostral ventromedial medulla.

The rostral ventromedial medulla (RVM) is an important mediator of the supraspinal component of opioid antinociception. Previous studies have suggested that activation of the cloned mu- and delta-opioid receptors (MOR1 and DOR1 respectively) in the RVM produces the antinociception mediated by spinally projecting neurons. In the present study, we investigated the expression of mRNA encoding either MOR1 or DOR1 in the RVM of rats. In addition, we examined quantitatively the expression of MOR1 and DOR1 mRNAs in spinally projecting RVM neurons including serotonergic (5HT) cells by using in situ hybridization, immunocytochemistry, retrograde tract-tracing, and the physical disector. Brainstem neurons were labeled in 14 male Sprague-Dawley rats by applying Fluoro-Gold (FG) topically to the dorsal surface of the lumbosacral spinal cord. Five-micrometer-thick cryostat sections were cut and in situ hybridization was performed by using full-length cRNA probes labeled with 35S-UTP. We found that 43% of RVM projection neurons expressed MOR1 mRNA and 83% of RVM projection neurons expressed DOR1 mRNA. Of 192 retrogradely labeled cells in the RVM, 51 cells (27%) were immunoreactive for 5HT. Of this population, half appeared to be labeled for the mRNA encoding MOR1 and over three-fourths appeared to be labeled for the mRNA encoding DOR1. Thus, we conclude that bulbospinal neurons express MOR1 and DOR1; moreover, MOR1 and DOR1 are expressed by significant proportions of 5HT neurons projecting to or through the dorsal spinal cord.

脊椎脊髄疾患に対する術中超音波検査の有用性

The purpose of this study is to clarify the usefullness of intraoperative spinal sonography (IOSS) for spinal diseases.Our IOSS procedure is as follows; 1) After laminectomy or laminoplaty, water is properly applied over the dura surface, 2) The probe used for IOSS is the 7.5MHz Toshiba probe, 3) Scanning of acurate sagittal and axial images.More information the spinal cord can be obtained using IOSS than MRI imaging in some cases. IOSS provides an excellent visualization of the spinal cord and anterior surface of the spinal canal. This method is therefore quite useful for monitoring the decompression of the spinal cord in cervical myelopathy and OPLL. We can also observe the position and extent of syrinx and evaluate the shunt, as well as observe the size of syrinx which changes with breathing in the case of syringomyelia. IOSS may play a significant role for solving the extending mechanism of syrinx.TOSS has thus been concluded as being extremely useful for reconfirming the decompression of the spinal cord during real-time operations. This method also allows evaluation of dynamic spinal cord motion in various kinds of spinal diseases.

Developmental anomalies of the spinal cord

A review of the literature and a personal collection of human spinal cord anomaly cases revealed a kaleidoscope of malformations and normal variations of this anatomical structure. One of the most frequently found anomalies is dysraphism and, thus, this is clinically one of the most important malformations of the spinal cord. There are different forms of spinal dysraphism combined with brain anomalies. Other forms of spinal malformations should also be discussed in relation to cranial and brain malformations. Certain kinds of neoplasms, such as my‐xopapillary ependymomas and paragangliomas of the medullary conus/filum terminale and sacrococcygeal subcutaneous ependymomas, can be discussed in relation to their embryological aspects. Regarding pathological histogenesis in cases of abnormal course of fibers, fiber tract‐related pathological sulcus formation, neuronal heterotopia etc., many experimental investigations are currently being performed. They include investigations concerned with neural stem cell exploration, target search or crossing of the developing axons and migration of neurons. Senescent changes of survived malformations may also be of interest, such as senile degeneration of the heterotopia. In this review, we propose: (i) a hypothesis on morphogenesis of the ascending course of spinal nerve roots in Chiari anomaly type 2, emphasizing the idea of the ‘craniocervical growth conflict of both neural and mesodermal tissues’(Roth); (ii) at least two possible causes resulting in abnormal longitudinal sulcus formation of the spinal cord surface; (iii) three probable histological types of the filum terminale in the tethered cord; and (iv) a speculation on multipotentiality of the cellular differentiation of ependymal vestiges originating from the embryonal canalization phase.

Treatment strategy of spinal arteriovenous malformations based on a simple classification

We propose a treatment strategy of the spinal arteriovenous malformation (AVM) based on a simple classification. This classification includes three types: dural arteriovenous fistula (AVF), perimedullary AVF and intramedullary AVM. Dural AVF has its shunt at the dura and can be treated with either surgery or embolization with liquid adhesive. Perimedullary AVF has shunt on the spinal cord surface and it can be subcategorized into types 1–3 depending on the size of vascular pedicles. Types 1 and 2 are treated with surgery, type 3 by balloon or coil embolization. Intramedullary AVM has its nidus in the cord and is difficult to treat either by surgery or endovascular technique.

Avulsion injury of cervical nerve roots: enhanced intradural nerve roots at MR imaging.

To study the magnetic resonance (MR) imaging features of intradural nerve roots in avulsion injury of the cervical nerve roots. Presurgical gadolinium-enhanced MR imaging was performed in 27 consecutive patients. The images were evaluated for enhancement of the intradural nerve roots and enhancement of the spinal cord surface at the root entry zone ("root stump" enhancement) by two radiologists, who were blinded to the clinical information. Intradural nerve roots were classified as enhanced, normal, or not visible. Root stumps were classified as enhanced or normal. The results were compared with the results of nerve root continuity studies (exploratory surgery with intraoperative recording of somatosensory evoked potentials or neurologic examination). At the 250 nerve levels (500 nerve roots) studied, 12 enhanced nerve roots and 42 enhanced root stumps were found. Seven enhanced nerve roots and 38 enhanced root stumps were related to preganglionic injury. Results of the kappa test for interobserver concordance on findings of intradural nerve roots and root stumps were 0.55 and 0.93, respectively. Although visualization of nerve roots is a problem, enhanced MR imaging is a noninvasive means of obtaining anatomic information and unique physiologic information on injured intradural nerve roots.

Effects of neurotransplants and BDNF on the survival and regeneration of injured adult spinal motoneurons.

We compared the effects of peripheral nerve grafts, embryonic spinal cord transplants and brain-derived neurotrophic factor (BDNF) on the survival and axon regeneration of adult rat spinal motor neurons undergoing retrograde degeneration after ventral root avulsion. Following implantation into the dorsolateral funiculus of the injured spinal cord segment, neither a peripheral nerve graft nor a combination of peripheral nerve graft with embryonic spinal cord transplant could prevent the retrograde motor neuron degeneration induced by ventral root avulsion. However, intrathecal infusion of BDNF promoted long-term survival of the lesioned motor neurons and induced abundant motor axon regeneration from the avulsion zone along the spinal cord surface towards the BDNF source. A combination of ventral root reconstitution and BDNF treatment might therefore be a promising means for the support of both motor neuron survival and guided motor axon regeneration after ventral root lesions.

Microiontophoretic application of serotonin (5HT)1B/1D agonists inhibits trigeminal cell firing in the cat.

Migraine is a common and debilitating condition. Its treatment has received considerable attention in recent times with the introduction into clinical use of the 5HT1B/1D agonist sumatriptan. It is known from human studies that the intracranial blood vessels and dura mater are important pain-producing structures since mechanical or electrical stimulation of these vessels, such as the superior sagittal sinus, causes pain. We have developed a model of craniovascular pain by stimulating the superior sagittal sinus and monitoring trigeminal neuronal activity using electrophysiological techniques. Cats were anaesthetized with alpha-chloralose (60 mg/kg, intraperitoneally), paralysed (gallamine 6 mg/kg, intravenously) and ventilated. The superior sagittal sinus was accessed and isolated for electrical stimulation by a mid-line circular craniotomy. The region of the dorsal surface of C2 spinal cord was exposed by a laminectomy and an electrode placed for recording evoked activity from sinus stimulation and spontaneous activity of the same cells. The electrode was a custom-made seven barrel glass microelectrode with the central barrel containing a tungsten recording wire. Signals were amplified and monitored on-line using a custom-written sampling program. Cells were recorded that were activated by electrical stimulation of the sinus and were also spontaneously activated. Cells fired with latencies consistent with A delta and C fibres, generally firing three or four times per stimulus (0.3 Hz, 250 microseconds duration, 100 V) delivered to the sinus. Both evoked and spontaneous firing could be inhibited by iontophoresis of ergometrine (9/10 cells), sumatriptan (2/3 cells) and zolmitriptan (9/15 cells) but not by saline (3/10 cells). These data are the first demonstration of inhibition of second order trigeminal neurons by direct local application of 5HT1B/1D agonists. Although intravenous administration of these compounds has demonstrated inhibition of sinus evoked firing in previous studies, it is not possible using the intravenous route to be clear at which anatomical site inhibition is taking place, whereas microiontophoresis offers a clear locus of action. These data demonstrate that the second order trigeminal nucleus synapse in the brainstem and upper cervical cord is the most likely site of action for brain penetrant anti-migraine drugs of the 5HT1B/1D class.

Inhibition of trigeminal neurones after intravenous administration of naratriptan through an action at 5-hydroxy-tryptamine (5-HT(1B/1D)) receptors.

1. The observation that 5-hydroxytryptamine (5-HT) is effective in treating acute attacks of migraine when administered intravenously resulted in a research effort that led to the discovery of the 5-HT(1B/1D) receptor agonist sumatriptan. 2. Clinical experience has shown sumatriptan to be an effective treatment with some limitations, such as relatively poor bioavailability, which naratriptan was developed to address. Increasing bioavailability has been achieved with greater lipophilicity and thus the potential for greater activity in the central nervous system. 3. In this study the increased access to central sites has been exploited in an attempt to characterize the pharmacology of those central receptors with the newer tools available. Trigeminovascular activation was examined in the model of superior sagittal sinus stimulation. 4. Cats were anaesthetized with alpha-chloralose (60 mg kg(-1), intraperitoneal), paralyzed (gallamine 6 mg kg(-1), intravenously) and ventilated. The superior sagittal sinus was accessed and isolated for electrical stimulation (250 micros pulses, 0.3 Hz, 100 V) by a mid-line circular craniotomy. The region of the dorsal surface of C2 spinal cord was exposed by a laminectomy and an electrode placed for recording evoked activity from sinus stimulation. 5. Stimulation of the superior sagittal sinus resulted in activation of cells in the dorsal horn of C2. Cells fired with a probability of 0.69+/-0.1 at a latency of 9.2+/-0.2 ms. Intravenous (i.v.) administration of naratriptan at clinically relevant doses (30 and 100 microg kg(-1)), inhibited neuronal activity in trigeminal neurones of the C2 dorsal horn, reducing probability of firing without affecting latency. 6. The effect of naratriptan could be reversed by administration of the selective 5-HT(1B/1D) receptor antagonist GR127935 (100 microg kg(-1), i.v.). 7. These data establish that naratriptan acts on central trigeminal neurones since sagittal sinus stimulation activates axons within the tentorial nerve and there are no inhibitory effects mediated within the trigeminal ganglion. Furthermore, given that this inhibition could be reversed by the relatively selective 5-HT(1B/1D) receptor antagonist GR127935, it is highly likely that the anti-migraine effects of drugs of this class with central nervous system access are mediated, at least in part, by 5-HT(1B/1D) receptors within the trigeminal nucleus.

Long sensory tracts (cuneate fascicle) in cervical somatosensory evoked potential after median nerve stimulation

Low amplitude high frequency waves (LHW) were investigated in normal and patient cervical somatosensory evoked potentials after median nerve stimulation (CSEP) in parallel to normal and patient conducted somatosensory evoked potentials (SEP) after tibial nerve stimulation. Normal recordings were obtained in five subjects undergoing dorsal root entry zone (DREZ) coagulation for pain relief. Patient recordings were obtained in 11 subjects suffering from either syringomyelia, spinal cord tumour, or both. All recordings were made intraoperatively from the dorsal spinal cord surface using the subpial recording technique. Normal CSEP showed typical triphasic potential starting with an initial P9, followed by N13 and a final positivity, P1. Numerous LHW were superimposed on slow triphasic potential. To improve the visibility of LHW, slow triphasic potential was removed from the original CSEP. Potentials thus obtained contained only high frequency components of CSEP, i.e. LHW. They were compared with conducted SEP after tibial nerve stimulation. Comparison revealed similarities in high frequency, low amplitude and general wave form, LHW thus showing characteristics of conducted potential. Duration was found to be significantly shorter than normal duration in both patient LHW (Student's t-test, P<0.0005) and patient conducted SEP (Student's t-test, P=0.064). A shorter duration was associated with worsening of configuration in patient LHW and patient conducted SEP. These changes of LHW could not be connected with distortion of N13 seen in patient CSEP. A shorter duration and worsening of configuration in patient LHW were most prominent in cases with a loss of vibration and posture senses, but were also observed in cases where only pain and temperature senses were affected. We therefore concluded that cuneate fascicle is the most likely generator of LHW, although the participation of other cervical long sensory tracts, e.g. spinothalamic tract, cannot be ruled out.

Localization of laminin subunits in the central nervous system in Fukuyama congenital muscular dystrophy: an immunohistochemical investigation.

We have undertaken an immunohistochemical study of laminin subunits in the central nervous system (CNS) of fetuses and patients with Fukuyama congenital muscular dystrophy (FCMD) and of controls including five fetuses. Immunoreaction product deposits with antibodies to laminin alpha 1, alpha 2, beta 1 and gamma 1, and beta-dystroglycan were detected on the surface and vessels of the CNS of controls. No staining with anti-alpha-sarcoglycan antibody was detected in the CNS. Neurons and glia did not react with any of the antibodies used. In utero expression of laminin subunits and beta-dystroglycan seemed to be lower in the cerebrum than in the spinal cord. Moreover, immunostaining for laminin alpha 2 and beta 1 tended to be weak on the fetal spinal cord surface. Expression of laminin subunits and dystrophin-associated proteins in the CNS may be modulated during development, as in the skeletal muscle. The distribution of immunoreaction product deposits was basically the same in FCMD and controls, although laminin alpha 2 and beta-dystroglycan expression appeared to be decreased in the CNS of the FCMD cases. Defects of the pial-glial barrier of the fetal brain surface have been considered the main cause of micropolygyria in FCMD, and these observations suggest that the co-localization and secondary loss of these proteins in association with the unknown product(s) of the FCMD gene might be involved in the CNS lesions of this disorder.

Efficacy of combined inspiratory intercostal and expiratory muscle pacing to maintain artificial ventilation.

Many patients with ventilator-dependent quadriplegia have coincident phrenic nerve injury and therefore cannot be offered phrenic nerve pacing. The purpose of this study was to assess the utility of combined inspiratory intercostal and expiratory muscle pacing to provide complete ventilatory support. Studies were performed in 15 anesthetized dogs. An electrode was positioned on the epidural surface of the upper thoracic spinal cord to activate the inspiratory intercostal muscles; a separate electrode was positioned on the epidural surface of the lower thoracic spinal cord to activate the expiratory muscles. In an attempt to replicate the effects of inspiratory intercostal pacing alone in humans, stimulus parameters during upper thoracic spinal cord stimulation were adjusted to provide suboptimal levels of ventilation (end-tidal PCO2 of 55 to 60 mm Hg). Expiratory muscle activation was triggered electrically by the inspiratory signal with a 4.2-s delay resulting in alternate inspiratory and expiratory muscle pacing at a combined rate of 14 breaths/min. Combined pacing was maintained for an arbitrary period of 3 h. Initial intercostal muscle pacing alone resulted in an end-tidal PCO2 of 57.1 +/- 1.1 mm Hg. After the addition of expiratory muscle pacing, end-tidal PCO2 fell to 36.3 +/- 1.2 mm Hg. Tidal volume during both inspiratory and expiratory muscle pacing and end-tidal PCO2 remained stable throughout the study period. Our results suggest that combined alternate inspiratory and expiratory muscle pacing may be a viable alternative method of artificial ventilation in ventilator-dependent quadriplegic patients.

Human dorsal root ganglion neurons from embryonic donors extend axons into the host rat spinal cord along laminin-rich peripheral surroundings of the dorsal root transitional zone.

Following dorsal root crush, the lesioned axons regenerate in the peripheral compartment of the dorsal root, but stop at the boundary between the peripheral and the central nervous system, the dorsal root transitional zone. We have previously shown that fibres from human fetal dorsal root ganglia grafted to adult rat hosts are able to grow into the spinal cord, but were not able to specify the route taken by the ingrowing fibres. In this study we have challenged the dorsal root transitional zone astrocyte boundary with human dorsal root ganglion transplants from 5-8-week-old embryos. By tracing immunolabelled human fibres in serial sections, we found that fibres consistently grow around the dorsal root transitional zone astrocytes in laminin-rich peripheral surroundings, and extend into the host rat spinal cord along blood vessels, either into deep or superficial laminae of the dorsal horn, or into the dorsal funiculus. Human fibres that did not have access to blood vessels grew on the spinal cord surface. These findings indicate, that in spite of a substantial growth capacity by axons from human embryonic dorsal root ganglion cells as well as their tolerance to non-permissive factors in the mature mammalian CNS, these axons are still sensitive to the repellent effects of astrocytes of the mature dorsal root transitional zone. Furthermore, this axonal ingrowth is consistently associated with laminin-expressing structures until the axons reach the host spinal cord.

Reversible Cervical Hemispinalization of the Rat Spinal Cord by a Cooling Device

Differentiation between traumatic and activity dependent plasticity in the CNS has been a challenge to neuroscientists in the past. We describe a cooling device that allows reversible block of the inspiratory drive to phrenic motoneurons without injury to the spinal cord at the C2 level. Thus, this experimental approach can be used to differentiate between the plasticity induced by blockade of synaptic activity in the phrenic nucleus from the trauma-induced plasticity caused by a C2 spinal cord hemisection which would also interrupt descending inspiratory drive. Complete block of axon transmission of the respiratory pathways running unilaterally in the ventral as well as in the lateral funiculus was achieved by approximation of a cold probe to the ventral surface of the spinal cord. The spinal cord surface temperature was lowered to 7°C. The temperature was maintained by a cold recirculated alcohol system. The efficacy of the reversible block was assessed by bilateral continuous EMG activity recording from the hemidiaphragms ipsilateral and contralateral to the cold application. Quantitative analysis of the EMG hemidiaphragmatic signals was performed in two sham-operated control (no cold application) and an experimental (cold application) group of Sprague–Dawley rats. The control groups were employed to confirm that the surgical exposure of the cord and/or the chronic placement of the probe and the administration of IV dopamine given to maintain stable blood pressure did not affect respiration. No significant change occurred in EMG hemidiaphragmatic activity in control animals. The descending pathway from the rVRG to the phrenic nucleus was completely and continuously blocked for 4 h in all four experimental animals as demonstrated by abolition of the EMG hemidiaphragmatic signal ipsilateral to cold block. In all experimental animals hemidiaphragmatic activity returned when the cold block was removed. The recovered EMG activity was significantly higher than preblock values. Interestingly, EMG activity contralateral to the block did not change significantly from control values after the block was removed, but was significantly enhanced during cold block. The present results suggest that cold block provides a means of studying activity-dependent plasticity in the respiratory pathways of the spinal cord.