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Biomedical subjects

G W Sypert

Publications and source records attributed to G W Sypert.

At least 37 records · Page 2Linked to original sources
PubMed1986

Regeneration in peripheral nerve grafts to the cat spinal cord.

Peripheral nervous system grafts have long been known to promote CNS axonal elongation in the rodent. To investigate whether these principles also apply to a higher order animal, more suitable for physiologic studies, we performed autogenous sciatic nerve grafts to the adult cat spinal cord. This report is a brief, initial study of these grafts. In an effort to study both descending and ascending fibers as separately as possible, laminectomies were performed at both thoracic (T2-T9) and lumbar (L2-L4) levels. Aspiration lesions were made in the left side of the cord and the sciatic grafts were introduced. Three cats were studied with standard histological techniques, confirming previous reports of glial scar formation, collagen deposition, and cyst formation at the graft-CNS junction. In 7 other animals, at 146-179 days after the initial operation, the axonal origins were traced retrogradely using horseradish peroxidase and the tetramethyl benzidine technique. Reinnervation of the graft was found by intrinsic spinal cord neurons and dorsal root ganglia neurons. The number of reinnervating neurons was found to be greater than previously reported in the rodent. There was, however, no evidence of regeneration from brainstem nuclei when the grafts were placed at spinal levels where this has been seen in the rat. This may support an absolute maximum for regenerative distances vs a relative one. Although the amount of data was limited, it did support previous reports that peripheral axotomy enhances the regenerative response seen in primary sensory neurons.

Animals↗
PubMed1986

Anomolous path taken by branch of medial gastrocnemius nerve.

An anomolous branch of the cat medial gastrocnemius nerve was found to travel with the combined lateral gastrocnemius and soleus nerves in the popliteal fossa before innervating muscle fibers in the medial gastrocnemius. The innervation pattern was confirmed by EMG recording, elicitation of contraction in the medial gastrocnemius by stimulating the branch, isolation of a single motor unit innervating the medial gastrocnemius whose axon traveled in the branch, and glycogen depletion of medial gastrocnemius muscle fibers by stimulating the branch. Awareness of such anatomic variation is important, for example, in interpreting studies of synaptic connections and of mechanical properties during reinnervation of muscle.

Animals↗
PubMed1986

Plasticity of medial gastrocnemius motor units following cordotomy in the cat.

Experiments were performed in adult cats to determine the effects of lumbar cordotomy on synaptic potentials, motoneuron membrane electrical properties, muscle-unit contractile properties, and whole-muscle histochemical properties of a heterogeneous skeletal muscle. Medial gastrocnemius (MG) motor units were examined 1 wk to 7 mo following complete transection of the lumbar spinal cord (cordotomy). Motor units were classified on the basis of their contractile properties as type FF, FI, FR, or S (8, 68). Muscle fibers were classified as type FG, FOG, or SO on the basis of histochemical staining (59). Motoneuron electrical properties (axonal conduction velocity, action-potential amplitude, rheobase, input resistance, afterhyperpolarization), group I EPSPs, and muscle-unit contractile properties (unpotentiated and potentiated twitch, unfused and fused tetanus, fatigability) were measured. Reduced numbers of type FR motor units and increased numbers of types FI + FF motor units were found in electrophysiological experiments 2 wk to 7 mo following cordotomy. Corroborative data were obtained from histochemical studies of the same MG muscles. Electrical properties of the motoneurons of each motor-unit type were normal following cordotomy. The close correspondence between motoneuron electrical properties and muscle-unit contractile properties found in normal MG muscle (68) was preserved following cordotomy. Contractile strength of muscle units of all types was severely reduced following cordotomy; partial recovery occurred 4-7 mo following cordotomy. Cross-sectional area of muscle fibers was reduced at all times investigated (2 wk to 7 mo). In three cats, homonymous group Ia single-fiber-motoneuron EPSPs were studied 1 or 2 mo following cordotomy at spinal level L4-5 or L5. EPSP amplitude and afferent-to-motoneuron projection frequency were normal. In 12 other cats, composite heteronymous group I EPSPs were studied 2 wk to 7 mo following cordotomy at various levels. Amplitude of these EPSPs was increased, dependent upon level of cordotomy and postoperative time. Hypotheses concerning the influence of motoneurons on muscle, and of muscle on motoneurons, are presented as possible mechanisms whereby the close relation between motoneuron electrical and muscle-unit contractile properties is preserved in the face of redistributed motor-unit populations.

Afferent Pathways↗
PubMed1986

Properties of self-reinnervated motor units of medial gastrocnemius of cat. I. Long-term reinnervation.

This work tested whether the membrane electrical properties of cat motoneurons, the contractile properties of their muscle units, and the normal relationships among them would be restored 9 mo after section and resuture of their muscle nerve. Properties of medial gastrocnemius (MG) motor units were examined 9 mo following section and resuture of the MG nerve in adult cats. Motoneuron electrical properties and muscle-unit contractile properties were measured. Motor units were classified on the basis of their contractile properties as type fast twitch, fast fatiguing (FF), fast twitch with intermediate fatigue resistance (FI), fast twitch, fatigue resistant (FR), or slow twitch, fatigue resistant (S) (8, 20). Muscle fibers were classified as type fast glycolytic (FG), fast oxidative glycolytic (FOG), or slow oxidative (SO) on the basis of histochemical staining for myosin adenosine triphosphatase, nicotinamide adenine dinucleotide diaphorase, and alpha-glycerophosphate dehydrogenase (48). Following 9 mo self-reinnervation, the proportions of each motor-unit type were the same as in normal control animals. Motoneuron membrane electrical properties [axonal conduction velocity, afterhyperpolarization (AHP) half-decay time, rheobase, and input resistance] also returned to control levels in those motoneurons that made functional reconnection with the muscle (as determined by ability to elicit measurable tension). The relationships among motoneuron electrical properties were normal in motoneurons making functional reconnection. Approximately 10% of MG motoneurons sampled did not elicit muscle contraction. These cells' membrane electrical properties were different from those that did elicit muscle contraction. Contractile speed and fatigue resistance of reinnervated muscle units had recovered to control levels at 9 mo postoperation. Force generation did not recover fully in type-FF units. The reduced tensions were apparently due to failure of recovery of FG muscle fiber area. Following reinnervation, relationships between motoneuron electrical and muscle-unit contractile properties were similar to controls. This was reflected in a degree of correspondence between motor-unit type and motoneuron type similar to normal units (84 vs. 86%, as defined by Ref. 61). There was a significantly increased proportion of type-SO muscle fibers and a decrease in the fast muscle fibers (especially type FOG) in 9 mo reinnervated MG. Together with the unchanged proportions of motor-unit types, this led to an estimate of average innervation ratios being increased in type-S motor units and decreased in type-FR units.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Properties of self-reinnervated motor units of medial gastrocnemius of cat. II. Axotomized motoneurons and time course of recovery.

This study tested the hypothesis that functional connection to muscle is necessary for expression of normal motoneuron electrical properties. Also examined was the time course of self-reinnervation. Properties of individual medial gastrocnemius (MG) motor units were examined following section and reanastomosis of the MG nerve. Stages examined were 3-5 wk (prior to reinnervation, no-re), 5-6 wk (low-re), 9-10 wk (med-re), and 9 mo (long-re, preceding paper) after nerve section. Motor units were classified on the basis of their mechanical response as type fast twitch, fast fatiguing (FF), fast twitch with intermediate fatigue resistance (FI), fast twitch, fatigue resistant (FR), or slow twitch, fatigue resistant (S) (11, 24). Motoneuron electrical properties were measured. Muscle fibers were classified using histochemical methods as type fast glycolytic (FG), fast oxidative glycolytic (FOG), or slow oxidative (SO) (60). Prior to functional reinnervation, MG motoneurons exhibited increased input resistance, decreased rheobase, decreased rheobase/input resistance, and decreased axonal conduction velocity. There was no change in mean afterhyperpolarization (AHP) half-decay time. Normal relationships between motoneuron electrical properties were lost. These data are consistent with dedifferentiation of motoneuron properties following axotomy (35, 47). At 5-6 wk after reanastomosis, motor-unit tensions were small, and motoneuron membrane electrical properties were unchanged from the no-re stage. There were no differences in motoneuron electrical properties between cells that elicited muscle contraction and those that did not. Motor-unit types were first recognizable at the med-re stage. The proportions of fast and slow motor units were similar to normal MG. Within the fast units, there were fewer type-FF units and more type-FI and type-FR units than normal, reflecting a general increase in fatigue resistance at this stage. Neither motoneuron membrane electrical properties nor muscle contractile properties had reached normal values, although both were changed in that direction from the low-re stage. Normal relationships between muscle properties, between motoneuron properties, and between motoneuron and muscle properties were re-established. The correspondence between motor-unit type and motoneuron type was similar to normal or 9 mo reinnervated MG. Muscle-unit tetanic tensions became larger with time after reinnervation. Most of the increase in muscle tension beyond the med-re stage could be accounted for by increase in muscle fiber area. There was an increased proportion of SO muscle fibers observed in the med-re muscles, as at the long-re stage.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Low back pain disorders: lumbar fusion?

The role of lumbar spine arthrodesis in the treatment of low back pain disorders remains a highly disputed and controversial subject. There are no clear-cut indications for lumbar spine fusion in lumbar degenerative disc disease. In fact, lumbosacral fusion when added to appropriate decompressive surgery has failed on careful statistical analysis to significantly improve the results over decompressive surgery alone. Moreover, in several large series in the literature of lumbosacral fusion in conjunction with discectomy, the results in patients who developed a pseudoarthrosis did as well as matched cases who obtained an excellent arthrodesis. These results should not be surprising since there does not appear to exist a generally accepted operational definition of mechanical (lumbar instability) pain. The author, however, is of the opinion that lumbosacral arthrodesis will prove to have a definite, albeit small, role in the management of the intractable and incapacitating low back pain disorders. This is based on personal clinical experience and the belief that the phenomenon of intractable and incapacitating mechanical low back pain syndromes do exist. Carefully performed prospective clinical studies are requisite to define the mechanical low back pain syndrome and the role of lumbar arthrodesis in the treatment of the low back pain disorders. Given our present limitations, the author suggests that lumbosacral arthrodesis be reserved for patients suffering spondylotic low back pain syndromes who have the following characteristics: intractable and disabling pain; primary complaint of segmental mechanical pain; radiologic evidence consistent with "instability"; minimal or no segmental disease above proposed site of arthrodesis; and minimal or absent psychosocial-economic pain.

Adult↗
PubMed1985

Membrane electrical properties and prediction of motor-unit type of medial gastrocnemius motoneurons in the cat.

Membrane electrical properties [time constant, action potential afterhyperpolarization (AHP), rheobase, input resistance, and axonal conduction velocity] were measured in motoneurons of cat medial gastrocnemius (MG) motor units. Motor units were classified on the basis of their mechanical responses as fast twitch, fast fatiguing (FF); fast twitch with intermediate fatigue resistance (FI); fast twitch, fatigue resistant (FR); or slow twitch, fatigue resistant (S; 11, 22). Motoneuron membrane time constant, estimated from the voltage response at the onset or termination of long (50-100 ms) current pulses and corrected for voltage-response nonlinearities (32), was found to differ significantly among the major motor-unit types, increasing in the order FF less than FR less than S. Afterhyperpolarization magnitude, half-decay time, and duration were all significantly greater for the fast (FF + FI + FR) versus the slow (S) motor units. The AHP half-decay time was correlated with muscle unit twitch time over the entire motoneuron population and within the type S motor-unit population. There was no significant correlation between twitch time and AHP half-decay time among the types FF and FR motor-unit populations. In agreement with previous studies, we found a significant difference in both rheobase and input resistance among the major motor-unit types, with rheobase increasing in the order S less than FR less than FF and input resistance decreasing in that order (S greater than FR greater than FF). The differences in input resistance were present both before and after correcting for voltage-response nonlinearities (32). Also in agreement with previous studies, the mean axonal conduction velocity was significantly faster among the fast (FF + FI + and FR) compared with the slow (S) motor units. These data were used to examine the properties alone to determine motor-unit type, which has traditionally been defined on the basis of the muscle unit's mechanical properties (11, 22). We used a discriminant analysis program to classify 73 mechanically typed motor units for which we had measures of rheobase, input resistance, membrane time constant, and AHP half-decay time. This model was able to properly classify 71 of the 73 motor units of this data set, indicating that the motor units of this data set could be grouped into three categories representing the three major motor-unit types (FF, FR, and S) on the basis of their rheobase, input resistance, membrane time constant, and AHP half-decay time.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1985

Ruptured intracranial aneurysms in cases of sickle cell anemia.

The authors present two cases of ruptured cerebral aneurysms in patients with sickle cell anemia. Only three previous cases with similar presentations have been reported. The various complications of sickle cell anemia and ruptured aneurysms are reviewed. The importance of early aggressive adjunctive medical management, including the use of partial exchange transfusions and surgical intervention, is emphasized.

Adolescent↗
PubMed1984

Synaptic and mechanical coupling between type-identified motor units and individual spindle afferents of medial gastrocnemius muscle of the cat.

Experiments were performed to test the possibility that motor unit-muscle spindle pairs that are coupled especially strongly mechanically will also be coupled especially strongly synaptically ("weighted ensemble input": Ref. 4). Synaptic and mechanical coupling between one or two individual muscle spindle afferents and individual motor units of the medial gastrocnemius (MG) muscle were measured in barbiturate-anesthetized cats. Synaptic coupling was assessed by measuring the amplitude of single-fiber monosynaptic excitatory postsynaptic potentials (EPSPs) generated in motoneurons by individual spindle afferents. Mechanical coupling was assessed by measuring the alteration in discharge rate of these spindle afferents caused by tetanic activation of the same motor units. Afferents were classified as primary or secondary on the basis of conduction velocity and response to muscle stretch and contraction. Motor units were classified as slow twitch (S); fast twitch, fatigue resistant (FR); fast twitch, intermediate fatigue resistance (FI); and fast twitch, fatigue sensitive (FF) on the basis of twitch contraction time and resistance to fatigue. In 85% of 138 motor unit-primary afferent interactions tested, tetanic activation of the single motor unit unloaded (i.e., decreased the discharge rate of) the primary afferent. A very weak though significant correlation was found between tetanic contraction strength and primary afferent unloading. In 66% of 155 motor unit-secondary afferent interactions tested, tetanic activation of the single motor unit unloaded the secondary afferent. Again, afferent unloading was but weakly related to tetanic contraction strength. Single-fiber EPSPs generated by primary or secondary muscle spindle afferents were recorded in type-identified motor units. EPSPs generated by primary afferents were significantly larger in oxidative (S + FR) than in glycolytic (FF) motor units. No such differences were seen for EPSPs generated by secondary afferents. The magnitude of the EPSP generated in a motoneuron by a spindle afferent was compared to the magnitude of the unloading of that afferent by tetanic activation of the corresponding motor unit. Overall, no relationship was found between these measures.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Early management of spinal injuries.

Traumatic spinal injuries are a major health problem. Any accident victim suspected of having a spinal injury must be immobilized immediately to prevent further damage to the spine. Management is directed toward achieving the most favorable environment for spinal cord recovery. This includes maintaining adequate oxygenation and blood flow and restoring the integrity of the spinal canal as rapidly as possible.

First Aid↗
PubMed1983

Presynaptic inhibition, EPSP amplitude, and motor-unit type in triceps surae motoneurons in the cat.

1. Composite group Ia excitatory postsynaptic potentials (EPSPs) produced by heteronymous nerve stimulation were recorded from triceps surae motoneurons of barbiturate-anesthetized cats. Motoneuron rheobase, input resistance, and axonal conduction velocity were measured, and motor units were classified on the basis of the mechanical responses of their muscle units. 2. The amplitude of EPSPs recorded from 33 medial gastrocnemius (MG) motoneurons ranged from 0.6 to 4.3 mV. The mean EPSP amplitude differed among the major MG motor-unit types, increasing in the order fast twitch, fast fatiguing (FF); fast twitch, fatigue resistant (FR); slow twitch, fatigue resistant (S) (FF less than FR less than S). The amplitude of EPSPs recorded from 15 soleus motoneurons ranged from 0.3 to 3.4 mV, with a mean of 1.4 mV. 3. Presynaptic inhibition of EPSPs was produced by trains of conditioning volleys in the posterior biceps-semitendinosus (PBST) nerve. In 33 MG cells PBST conditioning stimulation reduced the amplitude of EPSPs by 11-50%, with a mean inhibition of 27%. The amplitude of EPSPs in 15 soleus motoneurons was decreased by 5-84%, with a mean inhibition of 37%. 4. When the magnitude of presynaptic inhibition was expressed as percent inhibition, there was no relation between presynaptic inhibition and either motor-unit type or the amplitude of the EPSP. However, when presynaptic inhibition was expressed as the absolute amount of inhibition in millivolts, the magnitude of inhibition was highly correlated with EPSP amplitude both across the entire triceps surae population (MG, lateral gastrocnemius, soleus) as well as within each muscle population. This correlation was also significant within the MG FF and FR motor-unit populations. 5. We conclude that EPSP amplitude and not motor-unit type is the major determinant of the magnitude of presynaptic inhibition. However, because of the effect of motor-unit type on EPSP amplitude, the net effect is that presynaptic inhibition increases in the order FF less than FR less than S.

Animals↗
PubMed1983

Aneurysms of the posterior inferior cerebellar artery. A clinical and anatomical analysis.

The clinical and anatomical features of 21 surgically treated saccular aneurysms of the posterior inferior cerebellar artery (PICA) are analyzed. Seventeen of these lesions originated from the PICA-vertebral junction, and four arose from distal PICA branching sites. Twelve lesions arose from the left PICA, nine were right-sided, and all were small (less than 12.5 mm). Most of these aneurysms occurred in females (16 of 21) and presented as classic subarachnoid hemorrhage. The lack of specific focal deficits prevented an accurate pre-angiographic determination of aneurysm location in most instances. Clinically significant vasospasm and aneurysm multiplicity occurred with approximately equal frequency as at other locations. The angiographic and surgical features of these lesions are determined by the course of the vertebral artery and PICA; that is, they occur at branching sites and at curves in the parent vessel, and point in the direction in which flow would have continued if the curve at the aneurysm's origin had not been present. Aneurysms at the PICA-vertebral junction usualthese lesions are determined by the course of the vertebral artery and PICA; that is, they occur at branching sites and at curves in the parent vessel, and point in the direction in which flow would have continued if the curve at the aneurysm's origin had not been present. Aneurysms at the PICA-vertebral junction usualthese lesions are determined by the course of the vertebral artery and PICA; that is, they occur at branching sites and at curves in the parent vessel, and point in the direction in which flow would have continued if the curve at the aneurysm's origin had not been present. Aneurysms at the PICA-vertebral junction usually occur at least 1 cm above the foramen magnum level, arise distal to the PICA origin in the angle between the two vessels, and are best approached by a paramedian incision with the patient in the lateral recumbent position. Isolated clipping of the aneurysm neck is essential in this instance, as trapping may compromise vital perforating arteries of the brain stem. More distal (retromedullary) PICA aneurysms are sometimes associated with another vascular anomaly (two cases in this series), and are best handled through a bilateral suboccipital craniectomy. Clipping of the neck is the preferred treatment, but trapping is usually safe, if necessary.

Adult↗
PubMed1982

Successful treatment of the normal perfusion pressure breakthrough syndrome.

Massive, multifocal bleeding after the technically successful removal of a cerebral arteriovenous malformation (AVM) represents a frightening and usually catastrophic complication. This phenomenon, termed normal perfusion pressure breakthrough by Spetzler et al., is caused by the diversion of blood flow from the AVM into adjacent, maximally dilated, and nonautoregulating small vessels. We recently encountered three cases of cerebral AVM that exhibited breakthrough bleeding immediately after an apparently successful operation. In all cases, the surgeon was unable to control the resultant hemorrhage by standard microsurgical techniques. High dose barbiturate anesthesia, combined with blood pressure reduction to the lower levels of the normal cerebral perfusion curve, was then initiated in each case. Controlled hyperventilation, steroids, and osmotic dehydrating agents were also used to control intracranial pressure elevation. After maintenance of this regimen for several days, the patients were returned to the operating room for hematoma evacuation. At this time, bleeding was controlled easily and breakthrough did not occur. Although this regimen requires intensive anesthetic, pulmonary, and cerebral monitoring, it successfully salvaged all three patients. Two made immediate, remarkable recoveries, and the third patient is slowly improving. This protocol therefore seems promising for the management of the massive, uncontrollable cerebral swelling or bleeding that may occur as a consequence of AVM removal.

Adult↗