L1.1 is involved in spinal cord regeneration in adult zebrafish

Adult zebrafish, in contrast to mammals, regrow axons descending from the brainstem after spinal cord transection. L1.1, a homolog of the mammalian recognition molecule L1, is upregulated by brainstem neurons during axon regrowth. However, its functional relevance for regeneration is unclear. Here, we show with a novel morpholino-based approach that reducing L1.1 protein expression leads to impaired locomotor recovery as well as reduced regrowth and synapse formation of axons of supraspinal origin after spinal cord transection. This indicates that L1.1 contributes to successful regrowth of axons from the brainstem and locomotor recovery after spinal cord transection in adult zebrafish.

Continuous Intrathecal Meperidine for Severe Refractory Cancer Pain

The control of severe cancer pain may be problematic despite advances in pain management. Patients with severe intractable pain and/or intractable side effects may require aggressive interventional pain management strategies including the administration of medications by the continuous intrathecal route and/or neurosurgical procedures. Various medications, including opioids, local anesthetics, and alpha-2 agonists may be used intrathecally for the control of cancer pain. Failure of the intrathecal route may require the additional use of neurosurgical procedures such as cordotomy for pain control. We describe a case of severe cancer pain refractory to conventional intrathecal medications and cordotomy that was successfully managed by the addition of meperidine to the intrathecal regimen.

[Spinal cord regeneration in rats after thoracic segmentectomy: restoration of the anatomical integrity of the spinal cord]

Spinal cord (SC) segmentectomy was performed at ThX level in 28 rats. The scar formation in place of surgery and the degree of restoration of anatomical integrity were studied in control rats (group I) and in rats, in which SC defect was replaced by either Spherogel neuromatrix (group II) or Spherogel containing dispersed embryonic nerve cells (group II). While in group I rats by weeks 1-2 SC defect was filled with fibrin masses, in rats of experimental groups II and III the formation of connective tissue scar was found by the same time. By weeks 10-11 these animals demonstrated partial restoration of motion in three joints of the hindlimb. In the scar tissue and in adjacent SC zones numerous regenerating thin myelinated nerve fibers were found. They were clearly demonstrated in the zones of cranial and caudal borders along the whole distance until the appearance of typical tissue of SC. In slides from the animals of control group, thin myelinated nerve fibers were found only in close proximity to SC substance, while in the scar tissue and in the cellular bands of the intermediate zone nerve fibers were scarce.

Comparison of the effects on spinal reflexes of acetylsalicylate and metamizol in spinalized and normal rats

The effects of nonsteroidal antiinflammatory drugs, acetylsalicylate and metamizol, on spinal monosynaptic reflexes were investigated in spinalized and normal rats. Adult rats (n=36) weighing 150-200 g were anesthetized with ketamine and artificially ventilated. Half of rats were spinalized at C1 level. A laminectomy was performed in the lumbosacral region. Following electrical stimulation of the sciatic nerve by single pulses, reflex potentials were recorded from the ipsilateral L5 ventral root. Acetylsalicylate was administered orally (100 mg/kg for both spinalized and normal rats). Metamizol was administered intramuscularly (15 mg/kg for both spinalized and normal rats). These drug administrations significantly decreased the amplitude of reflex response in all groups (p < 0.05). These data verify that observed inhibition by acetylsalicylicate and metamizol may be at the level of spinal cord. Also we suggested that the cyclooxygenase products of arachidonic acid may play an important role in regulating the reflex potential.

Ablative procedures for chronic pain

The advent of neuroaugmentative techniques has reduced the application of neuroablative procedures, especially as regards pain of functional origin. Although intracranial ablative procedures are now rarely performed, spinal ablative procedures, such as anterolateral cordotomies or midline myelotomies, remain important in the management of cancer pain. These procedures produce immediate and satisfactory pain relief with acceptable complication rates. An important future trend will be the application of radiosurgery guided by functional imaging (eg,fMRI, PET) to place such intracranial lesions as cingulotomies or medial thalamotomies.

The surgical treatment of chronic pain: destructive therapies in the spinal cord

Stereotactic pain surgery is accepted as a group of procedures. These are usually highly sophisticated and technically risky procedures. In practice, the most important part of this discipline is not the technical abilities of the surgeon, but selection of the most appropriate patients for the available procedures. We must remember that we are performing all these procedures with the cooperation of patients. The energy that is used for lesioning can be stopped when desired. The target we want to approach can be definitely and anatomically visualized and demonstrated, and the function of the target is evaluated with neurophysiologic impedance techniques and stimulation. Thus, if we are able to understand the language of the central nervous system, these are available, effective, and safe procedures in neurosurgical practice. We must remember that if intractable pain can be controlled by minimally invasive destructive techniques, the patients will not be dependent on implantable systems, drugs,and medical units. This independent lifestyle is a critical goal central to quality of life for patients having intractable pain.

Multiple Spontaneous Rhythmic Activity Patterns Generated by the Embryonic Mouse Spinal Cord Occur Within a Specific Developmental Time Window

Spontaneous rhythmic activity is a ubiquitous phenomenon in developing neural networks and is assumed to play an important role in the elaboration of mature circuitry. Here we describe the day-by-day evolution of spontaneous activity in the embryonic mouse spinal cord and show that, at a specific developmental stage, 2 distinct rhythms coexist. On embryonic days E12.5 and E13.5, we observed a single type of regularly recurring short spike-episodes synchronized across cervical, thoracic, and lumbar levels. By E14.5, in addition to this motor rhythm, another type of spontaneous synchronous activity appeared, characterized by much longer lasting episodes separated by longer time intervals. On E15.5, these long episodes disappeared. Short episodes were less numerous and more irregular except at the cervical level where a rhythm was occasionally observed. By E16.5, this cervical rhythm became more robust, whereas the lumbar level fell almost silent. Surprisingly, at E17.5, spontaneous activity resumed at caudal levels, now characterized by numerous erratic short episodes. A striking ontogenetic feature of spontaneous activity was the occurrence of long episodes only at E14.5. Although concomitant at all levels of the spinal cord, long episodes displayed different patterns along the spinal cord, with tonic firing at the thoracic level and rhythmic discharge with occasional sequences of left/right alternation at the lumbar level. Thus at E14.5, the originally synchronized network has started to segregate into more specialized subnetworks. In conclusion, this work suggests that ongoing spontaneous rhythms do not follow a smooth evolution during maturation, but rather undergo profound changes at very specific stages.

Effect of spinal cord injury on urinary bladder spinal neural pathway: a retrograde transneuronal tracing study with pseudorabies virus

OBJECTIVES

To determinate the effect of acute and chronic spinal cord injury (SCI) resulting from thoracic cord transection on the urinary bladder spinal neural pathway.

METHODS

Seventy-six adult Sprague-Dawley rats were randomly divided into four groups, non-SCI (normal rats undergoing no surgical procedure except pseudorabies virus [PRV] injection), SCI(b) (SCI and PRV injected immediately after SCI), SCI(c) (SCI and PRV injected at 3 weeks after SCI), and SCI(d) (SCI and PRV injected at 3 months after SCI). Transcardiac perfusion fixation was done at appropriate survival periods after PRV injection into the bladder wall tissue. Sections of the dorsal root ganglion, spinal cord, and brain were processed for visualization of the virus by the streptavidin-peroxidase immunohistochemical procedure.

RESULTS

The bladder weight of the non-SCI, SCI(b), SCI(c), SCI(d) rats was 144 +/- 9 mg, 142 +/- 8 mg, 486 +/- 51 mg, and 656 +/- 69 mg, respectively. The time-ordered flow charts of PRV tracing were similar in the non-SCI and SCI rats. The cross-sectional area of the labeled dorsal root ganglion cell profiles increased significantly after SCI (P <0.001): 593 +/- 40 microm2, 588 +/- 39 microm2, 815 +/- 53 microm2, and 902 +/- 57 microm2 in the non-SCI, SCI(b), SCI(c), SCI(d) rats, respectively. The number of labeled cells in the dorsal horn in the L6 and S1 segments 3 days after PRV injection markedly increased in chronic SCI rats, as did the number of labeled motor neurons 4 days after injection.

CONCLUSIONS

Acute and chronic SCI have no effect on the process of virus transneuronal transport below the level of the lesion. Subsequent to chronic SCI, reorganization of the micturition reflex pathways may occur.

The role of the dorsal columns in neuropathic behavior: evidence for plasticity and non-specificity

Despite conflicting clinical and experimental evidence, textbook description of somatic sensations continues to follow a rigid dichotomy based on the concept that pain sensation is transmitted cephalad primarily through anterolateral pathways, while touch is mediated through the dorsal column pathway. This study provides an example of the dynamic rerouting in the transmission of the nociceptive signals following injuries to the peripheral and central processes of sensory neurons. In two rat models for mononeuropathy, the chronic constriction injury model [Bennett, G.J., Xie, Y.K., Pain 33 (1988) 87-107] and the spared nerve injury model [Decosterd, I., Woolf, C.J., Pain 87 (2000) 149-158], we demonstrate that selective dorsal columns lesion produced significant decrease of tactile and cold allodynias and thermal hyperalgesia which were assessed by the Von Frey hair filaments, the acetone drop test and the heat-induced paw withdrawal, respectively. These manifestations, however, can reappear 2 weeks after bilateral dorsal column lesion in rats subjected to spared nerve injury mononeuropathy and appear also in animals sustaining chronic bilateral dorsal column lesion followed by either model of mononeuropathy. Lesion of the dorsal column on the side opposite to the neuropathic leg did not alter the neuropathic manifestations in both animal models. Changes in the sequence of timing of the dorsal column lesion and induction of mononeuropathy, suggest that the effects of the former last for 1 to 2 weeks. The results of this study show that the dorsal columns are involved in neuropathic manifestations and at the same time are not necessary for their full development and persistence. Furthermore, these results shade doubts on the validity of the concept of segregation of pathways involved in the transmission of neuropathic manifestations. Therefore, principles governing acute pain transmission are not necessarily applicable to chronic pain situations. The latter conditions seem to engage other available pathways to reestablish the pain signaling system.

Functional plasticity in the human primary somatosensory cortex following acute lesion of the anterior lateral spinal cord: neurophysiological evidence of short-term cross-modal plasticity

The primary somatosensory cortex (S1) in adult animals and humans is capable of rapid modification after deafferentation. These plastic changes may account for a loss of tonic control by nociceptive inputs over inhibitory mechanisms within structures of the dorsal column-medial lemniscal system. Most studies, however, have been performed under conditions where deafferentation of C and A delta fibres coexists with large-diameter fibres deafferentation. In this study the effect of the acute lesion of one ascending anterior lateral column on neuronal activity within the dorsal column-medial lemniscal system was assessed by recording somatosensory evoked potentials (SEPs) in seven patients who underwent unilateral percutaneous cervical cordotomy (PCC) as treatment for drug-resistant malignant pain.Spinal, brainstem and cortical SEPs were recorded 2h before and 3h after PCC by stimulating the posterior tibial nerve at both ankles. Amplitudes of cortical potentials obtained by stimulation of the leg contralateral to PCC were significantly increased after PCC. No significant changes in spinal or brainstem potentials were observed. PCC did not affect SEP components obtained by stimulation of the leg ipsilateral to PCC. Our results suggest that nociceptive deafferentation may induce a rapid modulation of cortical neuronal activity along the lemniscal pathway, thus providing the first evidence in humans of short-term cortical plasticity across the spinothalamic and lemniscal systems.

Axonally transported peripheral signals regulate alpha-internexin expression in regenerating motoneurons

The class IV neuronal intermediate filament (IF) family proteins includes the neurofilament (NF) triplet proteins NF-L, NF-M, and NF-H and also the more recently characterized alpha-internexin-NF66. It is well established that NF-L, -M, and -H protein and mRNA are downregulated after peripheral nerve injury. We examined alpha-internexin protein expression after three facial nerve lesion paradigms: crush, transection, and resection. Alpha-internexin immunoreactivity was absent in the perikarya of uninjured facial motoneurons but increased dramatically in all three injury paradigms, with maximum immunoreactivity observed at 7 d after injury. Twenty-eight days after nerve crush or transection, there was a dramatic decrease in the number of alpha-internexin-positive cells. In contrast, alpha-internexin remained elevated 28 d after nerve resection, an injury that hinders regeneration and target reinnervation. In situ hybridization studies showed an increase in alpha-internexin mRNA expression in the facial nucleus at 7 and 14 d after injury. Retrograde transport of fluorogold from the whisker pads to the facial nucleus was seen only in motoneurons that lacked alpha-internexin immunoreactivity, supporting the idea that target reinnervation and inhibitory signals from the periphery regulate the expression of alpha-internexin. Blockage of axonal transport through local colchicine application induced strong immunoreactivity in motoneurons. Alpha-internexin expression was also examined after central axotomy of rubrospinal neurons, which constitutively show alpha-internexin immunoreactivity. After rubrospinal tractotomy, alpha-internexin immunoreactivity transiently increased by 7 d after injury but returned to control levels by 14 d. We conclude that alpha-internexin upregulation in injured motoneurons suggests a role for this IF protein in neuronal regeneration.

Association of spinothalamic lamina I neurons and their ascending axons with calbindin-immunoreactivity in monkey and human

The calbindin-immunoreactivity of spinothalamic (STT) lamina I neurons and their ascending axons was examined in two experiments. In the first experiment, lamina I STT neurons in macaque monkeys were double-labeled for calbindin and for retrogradely transported WGA*HRP following large (n=2) or small (n=1) injections that included the posterior thalamus. Most, but not all (78%) of the contralateral retrogradely labeled lamina I STT cells were positive for calbindin. Calbindin-immunoreactivity was not selectively associated with any particular anatomical type of lamina I STT cell; 82% of the fusiform cells, 78% of the pyramidal cells and 67% of the multipolar cells were double-labeled. In the second experiment, oblique transverse sections from upper cervical spinal segments of three macaque monkeys, one squirrel monkey and five humans were stained for calbindin-immunoreactivity. In each case, a distinct bundle of fibers was densely stained in the middle of the lateral funiculus. This matches the location of anterogradely labeled ascending lamina I axons observed in prior work in cats and monkeys, and it matches the location of the classically described 'lateral spinothalamic tract' in humans. This bundle had variable shape across cases, an observation that might have clinical significance. These findings support the view that lamina I STT neurons are involved in spinal cordotomies that reduce pain, temperature and itch sensations.

The roles of pathways in the spinal cord lateral and dorsal funiculi in signaling nociceptive somatic and visceral stimuli in rats

The spinothalamic tract (STT) is a major ascending nociceptive pathway, interruption of which by cordotomy is used for pain relief, whereas the dorsal column (DC) pathway is usually not considered to be involved in pain transmission. However, recent clinical studies showed good relief of visceral pain in cancer patients after a DC lesion. Electrophysiological recordings in animals suggest that the analgesic effect is due to interruption of axons ascending from postsynaptic dorsal column (PSDC) neurons located in the vicinity of the central canal. In this behavioral study, we used a decrease in exploratory activity in rats after a noxious stimulus as an indicator of perceived pain, independent of withdrawal reflexes. Intradermal capsaicin injection almost abolished exploratory activity in naïve animals or in rats after a DC lesion, but did not change it in rats after ipsilateral dorsal rhizotomy or a lesion of the lateral funiculus on the side opposite to the injection. In contrast, a bilateral DC lesion counteracted the decrease in exploratory activity induced by noxious visceral stimuli for at least 180 days after the surgery. Although neurons projecting in both the STT and the PSDC path can be activated by noxious stimuli of cutaneous or visceral origin, our results suggest that the STT plays a crucial role in the perception of acute cutaneous pain and that the DC pathway is important for transmission of visceral pain.

Norepinephrine metabolism in neuron: dissociation between 3,4-dihydroxyphenylglycol and 3,4-dihydroxymandelic acid pathways

AIM

To investigate the pre-synaptic metabolism of norepinephrine (NE), judged by variations in plasma concentration of 3,4-dihydroxyphenylglycol (DHPG) and 3,4-dihydroxymandelic acid (DOMA).

METHODS

Pithed and electrically stimulated (2.5 Hz) rats were given intravenous infusion of exogenous NE (6 nmol . kg-1 . min-1). Plasma NE, DHPG, DOMA, and the activities of mono- amine oxidases (MAO) were measured with the radio-enzymatic assay.

RESULTS

Exogenous NE induces an about 100-fold increase in plasma NE concentration while blood pressure remained within normal limits. A 12-fold increase in plasma DHPG and 1.2-fold increase for DOMA were observed. When NE transportation across the pre-synaptic membrane was inhibited by desipramine (2 mg/kg, iv), a great reduction in plasma DHPG concentration (about 25 % of control) was observed while DOMA remained unchanged. When MAO-A activity was inhibited to 25 % of control by clorgyline (2 mg/kg, iv) and MAO-B to 30 % by deprenyl, the plasma DHPG and DOMA concentrations were reduced to 15 % and 70 % of controls, and to 26 % and 76 % of controls, respectively. When clorgyline and deprenyl were combined, plasma DHPG was vanished (less than 2 % of control) while plasma DOMA remained in the same range (72 % of control).

CONCLUSION

The metabolizing system of NE in pre-synapse, associating with the pre-synaptic reuptake plus oxidative deamination on the external membrane of mitochondria, is predominant for the reduction to DHPG.

Neurosurgical approaches to pain treatment

In a multidisciplinary approach to the management of chronic pain, neurosurgical methods are an indispensable part of the therapeutic armamentarium. With the exception of percutaneous interventions for trigeminal neuralgia and facet joint syndromes, most ablative pain surgery procedures (neurotomy, rhizotomy, sympathectomy, etc.) have been replaced by neuromodulatory approaches such as electrical stimulation of the central nervous system (CNS). However, cordotomy is still a valuable operation for certain forms of cancer related pains (Pancoast's syndrome, breakthrough pain) which are relatively resistant to pharmacotherapy. Another example of ablative surgery is the dorsal root entry zone (DREZ) operation, which is generally the only treatment option for pain due to root avulsion and segmental pain in spinal cord injury. Spinal cord stimulation (SCS) has proven to be most useful for the management of pain following peripheral nerve injury (including complex regional pain syndromes) and rhizopathy. For these conditions which are otherwise often therapy resistant, SCS may produce substantial and long-lasting pain relief in 60-70% of the patients. Considering that such pains are common and the fact that SCS has been shown to be cost-effective, this treatment is no doubt at present underused. Complications and side-effects are very rare. SCS has also been found to be useful for pain in peripheral vascular disorders and angina pectoris. In the latter condition the overall results are favorable in about 80% of patients with a significant reduction of the frequency and severity of angina attacks and the need for nitrates. Stimulation of the motor cortex is a novel and promising treatment of central, post-stroke pain and painful trigeminal neuropathy.

Adaptations in myosin heavy chain profile in chronically unloaded muscles

In this review, myosin heavy chain (MHC) adaptations in response to several models of decreased neuromuscular activity (i.e. electrical activation and loading of a muscle) are evaluated. In each of these "reduced-activity" models it is important to: a) quantify the changes in electrical activation of the muscle as a result of the intervention; b) quantify the forces generated by the muscle; and c) determine whether the neuromuscular junction remains normal. Most of the models, including spaceflight, hindlimb suspension, spinal cord isolation, spinal cord transection, denervation, and limb immobilization in a shortened position, result in increases in the percentage of fast MHCs (or fast MHC mRNA) in normally slow rat muscles. It also can be inferred from histochemical data that increases in fast MHCs occur with TTX application and bed rest. The only "reduced-activity" model to consistently increase slow muscle myosin mRNA, and slow fibers is limb immobilization in a stretched position; however, this model results in at least a temporary increase in tension. It appears that the most common feature of these models that might induce MHC adaptations is the modification in loading rather than a change in the neuromuscular activity.

New pain following cordotomy: clinical features, mechanisms, and clinical importance

OBJECT

The clinical features, possible causes, and contributing factors associated with novel spontaneous pain following unilateral cordotomy were investigated to clarify the mechanism and clinical importance of this pain.

METHODS

Forty-five patients who underwent cordotomy for severe unilateral cancer pain were included in this study. New pain occurred in 33 (73.3%) of 45 patients. Pathological conditions of tissue demonstrated on imaging corresponded to new pain in eight patients, referred pain in five, and neither of these in 15 patients. New pain was centered opposite the site of the original pain in a mirror-image location in 28 patients and rostral to the original pain in five patients. It was temporary in seven patients, weaker than the original pain in 25, and as severe as the original pain in one patient. The incidence of moderate or severe pain was significantly higher in patients with confirmed tissue disease (six of eight patients) than in those without (six of 20 patients). An important contributing factor to the occurrence of new pain was the achievement of analgesia by performing the cordotomy.

CONCLUSIONS

The present results indicate that new pain occurs frequently after unilateral cordotomy. Nonetheless, cordotomy may still be indicated for unilateral uncontrollable pain because new pain, when present, was weaker and more easily controlled than the original pain in nearly all cases. The authors speculate that new pain may represent a type of referred pain from the original painful area or may arise from sensitization of contralateral spinal nociceptive circuits due to metastasis or tumor infiltration, and that new pain is potentiated by the interruption of descending inhibitory pathways.

Inhibition of pudendal reflexes in spinal rats. Reassessing the role of serotonin

The effects of serotonin (5-HT) and thyrotropin-releasing hormone (TRH) on penile reflexes were investigated in intact and spinally transected male rats. Doses of intrathecal 5-HT (0.0, 1.13, 2.26, 11.3, 22.6, and 113.0 nmol), in a range previously shown to inhibit pudendal reflexes in anesthetized spinal preparations, prolonged the latency to the first penile erection in awake intact rats. However, these doses also provoked hyperreactivity and vocalization. Doses of intrathecal TRH (100 and 500 pmol) that effectively inhibited penile erection in intact animals were less effective in spinalized animals. Finally, a combination of subthreshold doses of TRH (100 pmol) and 5-HT (4.0 nmol) at a ratio known to affect other TRH/5-HT-mediated circuits significantly extended erection latency in animals with spinal transections. These data suggest that 5-HT and TRH are both involved in the inhibitory circuits regulating penile erection, either through corelease onto the same population of cells or through independent release onto different populations of neurons.

Posttraumatic therapeutic vaccination with modified myelin self-antigen prevents complete paralysis while avoiding autoimmune disease

Spinal cord injury results in a massive loss of neurons, and thus of function. We recently reported that passive transfer of autoimmune T cells directed against myelin-associated antigens provides acutely damaged spinal cords with effective neuroprotection. The therapeutic time window for the passive transfer of T cells was found to be at least 1 week. Here we show that posttraumatic T cell-based active vaccination is also neuroprotective. Immunization with myelin-associated antigens such as myelin basic protein (MBP) significantly promoted recovery after spinal cord contusion injury in the rat model. To reduce the risk of autoimmune disease while retaining the benefit of the immunization, we vaccinated the rats immediately after severe incomplete spinal cord injury with MBP-derived altered peptide ligands. Immunization with these peptides resulted in significant protection from neuronal loss and thus in a reduced extent of paralysis, assessed by an open-field behavioral test. Retrograde labeling of the rubrospinal tracts and magnetic resonance imaging supported the behavioral results. Further optimization of nonpathogenic myelin-derived peptides can be expected to lead the way to the development of an effective therapeutic vaccination protocol as a strategy for the prevention of total paralysis after incomplete spinal cord injury.

Cordotomy for bilateral cord abductal paralysis

OBJECTIVE

To investigate the clinical effects of cordotomy on bilateral cord abductal paralysis.

METHODS

With unilateral cordotomy, we treated 4 patients with bilateral cord paralysis whose glottis size was about 2.0 mm to 2.5 mm. They were followed up for over one year.

RESULTS

One week after surgery, the tracheotomy tubes of all 4 patients were plugged and no dyspnea occurred during rest and mild action. Their voices were more hoarse than before surgery. After 3 months, the tracheotomy tubes were successfully decannulated, and in the following one year, their respiration was normal and then speech was clear, although their voices were still a little hoarse.

CONCLUSION

We suggest that cordotomy be one option in the treatment of bilateral cord abductal paralysis.

The crossing of the spinothalamic tract

The question whether the spinothalamic and spinoreticular fibres cross the cord transversely or diagonally was investigated in cases of anterolateral cordotomy and in a case of thrombosis of the anterior spinal artery. The pattern of sensory loss following transection of the anterolateral quadrant of the cord consists of a narrow area of decreased nociception and thermanalgesia at the level of the incision; it extends for 1-2 segments cranial and cordal to the incision. This area is immediately cranial to the area of total loss of these modalities. This pattern of sensory loss is explained as follows. The cordotomy incision transects two groups of fibres: those that are already within the anterior and anterolateral funiculi and those that are crossing the cord. The area of total thermanaesthesia and analgesia is due to transection of fibres that are already within this region. The area of partial sensory loss is due to transection of the fibres that are crossing the cord at that level. Owing to the craniocaudal extent of the branches of the dorsal roots, there is an overlap of their collaterals that results in every spinothalamic neurone receiving an input from several dorsal roots. The narrow cordotomy incision thus divides the few fibres crossing at that level, causing diminished noxious and thermal sensibility over a few segments above and below the incision. These facts can be accounted for only on the assumption that these spinothalamic fibres are crossing the cord transversely. This evidence of transverse crossing was found in the cervical, thoracic and lumbar segments. There were three of 63 cordotomies for which this explanation of the partial sensory loss could not be maintained. Although no explanation has been suggested, this is unlikely to be due to the fibres crossing the cord diagonally.

Delayed glial cell death following wallerian degeneration in white matter tracts after spinal cord dorsal column cordotomy in adult rats

The devastating consequences of spinal cord injury (SCI) result primarily from damage to long tracts in the spinal white matter. To elucidate the secondary injury processes occurring after SCI, we investigated the relationship between apoptosis and Wallerian degeneration in spinal white matter tracts. In the rat spinal cord, the corticospinal tract (CST) and the dorsal ascending tract (DAT) are separated from each other in the dorsal column and relay information in opposite directions. A dorsal column cordotomy at the eighth thoracic (T8) level simultaneously induces Wallerian degeneration in the CST caudal to and in the DAT rostral to the injury. Using the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) method, we demonstrate that apoptosis occurred in areas of Wallerian degeneration in both tracts throughout the length of the cord segments studied (from T3 to T12). This delayed cell death, more apparent in the DAT, began at 7 days after injury and peaked at 14 days for the DAT and 28 days for the CST. Although a few TUNEL+ cells, slightly above the noninjury control level, were found in intact areas of both tracts, statistically significant differences in the number of TUNEL+ cells were found between the intact and the lesioned tract segments (CST, F < 0.01; DAT, F < 0.001). Within a particular spinal segment, a mean number of 64 and 939 TUNEL+ cells in the degenerating CST and DAT, respectively, were estimated stereologically at 14 days postinjury. TUNEL+ cells in degenerating tracts outnumber their intact counterparts by 3.8:1 in the CST and 4.1:1 in the DAT, although a statistically significant difference between the two was only found in the DAT at this time point (P < 0.05). Finally, we demonstrated that oligodendrocytes, the myelin-forming cells in the central nervous system, constitute at least a portion of the cells undergoing apoptosis within areas of Wallerian degeneration.

Blunted pressor responsiveness to intravenous quinpirole in conscious, chronic spinal cord-transected rats: peripheral vs. spinal mechanisms

Intravenous quinpirole (1 mg/kg) in conscious rats with chronic spinal cord transection (at T5-T7) induced an initial pressor effect, which was significantly reduced in both magnitude and duration compared with that in sham-operated rats, which was then followed by a long-lasting depressor effect. To distinguish the spinal and/or peripheral origin of this phenomenon, conscious, spinal cord-transected rats were also pretreated with either intravenous (0. 5 mg/kg), intrathecal (40 microg/kg) or combined intravenous and intrathecal domperidone, a dopamine D(2) receptor antagonist that does not cross the blood-brain barrier. Intravenous pretreatment with domperidone enhanced, but did not completely restore, the pressor effect of quinpirole, and had no effect upon the depressor component. However, both the depressor component and the reduction of the pressor effect induced by spinal section were fully abolished by intrathecal or combined intrathecal and intravenous domperidone. Quinpirole-induced changes in mean aortic pressure were also fully abolished by intravenous pretreatment with metoclopramide (5 mg/kg). Neither the pressor nor the bradycardiac response to intravenous phenylephrine differed between sham-operated and spinal rats. These results suggest that the blunted pressor response to quinpirole after spinal cord transection is related to an enhanced spinal dopamine D(2) receptor-mediated depressor effect rather than to hypersensitivity of peripheral dopamine D(2) receptors or vascular hyporesponsiveness to alpha(1)-adrenoceptor stimulation. Thus, in conscious intact rats, the prominent central pressor effect of quinpirole seems to oppose, not only a peripheral sympathoinhibitory depressor effect, as previously thought, but also a spinal depressor effect.