Micturitional disturbance in subacute myelo-optico-neuropathy (SMON)

BACKGROUND: Micturitional disturbance is known to occur in subacute myelo-optico-neuropathy (SMON). However, its pathophysiology is uncertain and few data are available concerning urodynamic findings. We described our results of micturitional histories and urodynamic studies in patients with SMON. METHODS: A history of urinary symptoms was obtained from six patients with SMON (two men, four women; age, 49-72 years, mean 60 years; duration of illness, 14-25 years, mean 19 years). All patients underwent urodynamic studies including measurement of post-micturition residuals, urethral pressure profilometry, cystometry and simultaneous sphincter electromyography. RESULTS: All patients had micturitional symptoms including voiding symptoms in four, filling symptoms in four and urge urinary incontinence in a patient. Urodynamic studies revealed an increased maximum urethral closure pressure in two of four patients studied, decreased bladder volume at first sensation in two, detrusor hyperreflexia in three, absent bulbocavernosus reflex in a patient, and none had detrusor-sphincter dyssynergia or post-micturition residuals. Repeated urodynamic study (10 years after initial study) in a patient with detrusor hyperreflexia showed the same findings. CONCLUSION: Our results indicate that supranuclear pelvic nerve dysfunction to be mainly responsible for the micturitional disturbance in patients with SMON.     

Neuropathology of longstanding subacute myelo-optico-neuropathy (SMON): an autopsy case of SMON with duration of 28 years]

The present case, 78-years-old female, had been troubled with SMON during 28 years, and was suddenly died from cerebral hemorrhage. The neuropathology characteristic for SMON could not be revealed in the spinal cord on routine histological preparations. There were decreasing number of immunopositive granules in the nucleus gracilis of medulla oblongata for synaptophysin, and in the marginal zone of the lumbar dorsal horn for substance P. These findings showed the presence of tractus gracilis degeneration and the disappearance of nociceptive fibers from the dorsal roots, respectively. To elucidate the histopathological changes of the spinal cord in long standing cases with SMON, the 11 cases reported were reviewed. The mean duration from the onset to death was 22.8 years(16 to 33 years). The mean age was 76.3 years old(54 to 92), and the 10 cases were female. All cases showed sensory impairment of the lower extremities, while deep tendon reflex exaggerated was seen in 7 cases. There were nine cases involving dorsal funiculi degeneration of the spinal cord, in contrast the lateral funiculi alternation were noticed in only two cases. It was considered that the corticospinal tract alteration becomes undiscernible during the long course, although the dorsal funiculi degeneration remained.     

Sural nerve conduction velocity in peripheral neuropathies and subacute myelo-optico-neuropathies (SMON)

Sensory conduction velocity in the sural nerve (S-SCV) was measured in 10 cases of motor neuropathy, 35 cases of neuropathy with sensory symptoms and in 16 cases of subacute myelo-optico-neuropathy (SMON).In 2 cases of Friedreich's ataxis and 1 case of Charcot-Marie-Tooth disease, evoked sensory action potentials could not be recorded or S-SCV was reduced though sensation was normal; this finding suggests latent or subclinical involvement of the sensory nerves in these cases. In the other 7 cases of motor neuropathy, S-SCV was normal.In the cases of polyneuropathy with sensory symptoms, S-SCV was abnormal in 5 of 11 cases with subjective sensory complaints and in 6 of 10 cases with mild impairment of superficial sensation. No nerve potential could be evoked in 2 cases with severe impairment of superficial sensation, in 7 of 8 cases with mild impairment of deep sensation, and in 4 cases with severe impairment of deep sensation. These data suggest that S-SCV may be useful in confirming the extent of sensory nerve involvement in mildly-affected cases.In the case of SMON, though the S-SCVs could generally be correlated with the severity of the sensory symptoms, the degree of decrease in S-SCV was far less than in the cases of sensory neuropathy with similar symptoms. This discrepancy suggests that myelopathy in addition to peripheral neuropathy plays an important part in causing the sensory symptoms of SMON.     

Modulation of cortical and pyramidal tract induced motor responses by electrical stimulation of the basal ganglia.

Two general mechanisms based on anatomical studies are possible for modulation of motor activity by the caudate nucleus and globus pallidus. These mechanisms are: (1) modulation of the output of cortical neurons that exert motor influences; and (2) modulation of subcortical neurons that exert motor influences. Differentiation between these two mechanisms was accomplished in the present study by two experimental approaches, both of which employed the conditioning-test paradigm. The first approach was an investigation of caudate nucleus or globus pallidus modulation (conditioning stimulus) of flexor responses of the anterior tibialis muscle elicited by electrical stimulation of the sensorimotor cortex (test stimulus) or pyramidal tract (test stimulus). These investigations were carried out in the intact and in decorticate cats. The second approach was an analysis of modulation or cortically induced pyramidal tract responses (direct and indirect, D-I potentials) by conditioning shock trains delivered to various loci within the caudate nucleus or globus pallidus. Both approaches were designed to determine whixh inhibitory and facilitatory motor influences of the basal ganglia occurred at a cortical or subcortical level. Simultaneous stimulation of a locus within the caudate nucleus and the sensorimotor cortex evoked either an enhancement, reduction or no alteration of the cortically induced increase in flexor responses (measured by Ia afferent activity, EMG, myogram). In contrast, no inhibitory influences occurred from caudate nucleus stimulation upon pyramidal tract induced flexor responses in either the intact or decorticate preparation. Inhibitory loci were distributed toward the rostral portion of the caudate nucleus, whereas facilitatory loci were distributed throughout; this distribution was statistically significant (chi2; P less than 0.01). Only enhancement or no influence upon cortical induced or pyramidal tract induced responses were obtained by conditioning stimuli to the globus pallidus. In the unanesthetized but immobilized cat, trains of shocks delivered to the caudate nucleus enhanced, reduced or had no influence upon the cortically evoked direct (D) and indirect (I) potentials recorded in the bulbar pyramidal tract. The distribution of facilitatory and inhibitory loci was organized in a similar fashion as in theanesthetized preparation. From these observations, a model was proposed in which the output of the caudate nucleus exerts both facilitatory or inhibitory modulation of the tonically active globus pallidus cells. The latter in turn predominantly or exclusively facilitate output of pyramidal tract neurons as well as the output of subcortical structures; both effects facilitate motor responses at the spinal level.     

Transient cortical pathways in the pyramidal tract of the neonatal ferret

Anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was used to study transient axons from the visual cortex in the pyramidal tract. Injections at birth restricted to the visual cortex labeled axons in the vicinity of the pontine nuclei. Two to eight days after birth, axons from the occipital cortex were found posterior to the pontine nucleus, their caudalmost stable target. Transient corticospinal axons from the presumptive primary visual cortex did not grow caudal to the pyramidal decussation. Innervation of more distal targets preceded innervation of proximal targets. Innervation of the pontine nucleus is initiated around 68 hours after birth, when the transient extension in the medullary pyramidal tract has attained its maximum caudal extent. Innervation of the superior colliculus begins 9 days after birth. Retrograde tracers were used to follow the developmental changes in the cortical distribution of the parent neurons giving rise to axons in the pyramidal tract. In the adult, labeled neurons following injection of retrograde tracer in the pyramidal tract occupied less than a third of the neocortex and were centred on the anterior part of the coronal and spleniocruciate gyri. In the immature brain, labeled neurons covered more than two-thirds of the neocortex. Areal density measurements in the neonate showed that peak labeling was centred in the anterior coronal and spleniocruciate gyri, where corticospinal cells in the adult are located. There was a marked rostral-caudal gradient so that labeled neurons were very scarce towards the occipital pole. These results, showing transient neocortical axons in the pyramidal tract in a carnivore, suggest that this may be a common feature of mammalian development. The finding that the adult pattern of corticospinal projections does not emerge from a uniform distribution is discussed with respect to the areal specification of cortical connectivity. © 1993 Wiley-Liss, Inc.     

The sensitivity of transcranial cortical magnetic stimulation in detecting pyramidal tract lesions in clinically definite multiple sclerosis

We determined central motor conduction time (CMCT) (motor cortex to root C-8 and motor cortex to root S-1) as well as the amplitude of the compound muscle action potentials in the hypothenar and the abductor hallucis muscles on both sides in 44 patients with definite MS. We compared the values with standards obtained from 86 healthy controls and correlated them with the degree of clinical deficit of the limbs examined. Thirty-nine patients (88.6%) showed a prolonged CMCT. By comparison, only 74.4% of patients had abnormal visual evoked potentials.     

Task-dependent compensation after pyramidal tract and dorsolateral spinal lesions in rats

The purpose of this research was to investigate whether pathways in the dorsal part of the lateral spinal funiculus (DLF) can compensate for loss of corticospinal input (CST) to the spinal cord. The CST is known to control skilled limb movements in rats. The DLF contains several different pathways, including the rubrospinal tract (RST) which is also thought to influence limb movements. After lesions of either the corticospinal or the rubrospinal system, it is unclear how much of the remaining forelimb function is due to the presence of the alternate pathway. To begin to address this issue, the present study investigates the compensatory role of pathways in the DLF, including the rubrospinal tract, after bilateral lesions of the pyramidal tract (PT). We initially performed bilateral PT lesions in rats, which effectively removed the CST input to the spinal cord. We tested these rats during overground locomotion, skilled locomotion and skilled forelimb usage. After a 6 week recovery period, we then performed bilateral DLF lesions and compared the behavioural abilities of these rats to those of animals which underwent simultaneous PT and DLF lesions. If DLF pathways do compensate for PT lesions, then animals with PT lesions would rely more on DLF pathways than animals without PT lesions. Thus we hypothesized that animals with DLF lesions which were performed 6 weeks after PT lesions would exhibit more deficits on several behavioural tasks compared to animals which received PT and DLF lesions simultaneously. Our hypothesis was supported only for skilled pellet retrieval. Hence some DLF pathways, including the RST, were able to compensate for loss of CST input during skilled reaching but not during overground or skilled locomotion in PT-lesioned rats. These differential responses suggest that behavioural tasks vary in their reliance on specific pathways after injury, and, furthermore, that compensation for loss of specific connections can arise from numerous sources.     

Electrical and magnetic spinal and cortical stimulation in man

With the technique of transcranial and spinal electrical and magnetic stimulation it is possible to study the function of motor pathways in normal subjects. This technique is also a valuable tool in the investigation of motor pathways in patients with motor disturbances.     

Study of central motor pathways using cortical magnetic stimulation and spinal electrical stimulation: results in 20 normal subjects

Evoked motor potentials can be elicited by magnetic cortical or electric spinal stimulations. The central conduction time (CCT) corresponds to the difference in latencies between the total conduction time (from cortex to muscle) and the peripheral conduction time (from spinal cord to muscle). CCT is the sum of the conduction time in the cortico-spinal fibers, of the spinal synaptic delay, and of the conduction time in the proximal part of the motor roots. CCT values (mean + standard deviation) were determined in 20 healthy subjects ranging from 21 to 56 years of age (mean 31.2). Results of magnetic cortical stimulation were compared to the results of electrical stimulation of the cortex. CCTs after magnetic cortical stimulation were longer than CCTs after electric cortical stimulation. This could be explained by the fact that electrical stimulation elicits a direct response in the cortico-spinal tract whereas magnetic cortical stimulation has indirect effects on the pyramidal cells of the motor cortex through excitatory interneurons. Compared with electrical stimulation, the magnetic stimulation has the great advantage of being painless and allows a safe evaluation of the central motor pathways in man.     

The non-crossing of the pyramidal tract in procavia capensis (storr) and other instances of absence of the pyramidal crossing

In Procavia capensis the pyramidal tract descends uncrossed in the ventral funiculus of the cord, in which it can be followed throughout, the thoracic and lumbar segments. Termination of it fibers is almost entirely crossed similar to mammals with a substantial pyramidal corssing. Other instances of absence of a substantial pyramidal crossing are reported and it is concluded that the pyramidal crossing does not depend only on the termination of the pyramidal fibers in the medulla and the cord, and that the fibers can reach their contralateral endings without such a crossing.     

Synaptic responses of cortical pyramidal neurons to light stimulation in the isolated turtle visual system

The resistance of the turtle brain to hypoxic injury permits a unique in vitro preparation in which the organization and function of visual cortex can be explored. Intracellular recordings from cortical pyramidal neurons revealed biphasic responses to flashes of light, consisting of an early phase (50-100 msec) of concurrent inhibitory and excitatory activation, followed by a longer, inhibitory phase (250-600 msec) composed of summated Cl- -dependent postsynaptic potentials mediated by GABA. This response sequence results from the coactivation of pyramidal and GABAergic non-pyramidal cells, followed by feed-forward and possibly feed-back pyramidal cell inhibition, and is partly dependent on differences in the membrane properties of pyramidal and non-pyramidal neurons.