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D R Humphrey

Publications and source records attributed to D R Humphrey.

At least 19 recordsLinked to original sources
PubMed1992

Glycan components in the glycoinositol phospholipid anchor of human erythrocyte acetylcholinesterase. Novel fragments produced by trifluoroacetic acid.

Inositol glycans were prepared from reductively radiomethylated human erythrocyte acetylcholinesterase by sequential treatment with Proteinase K, methanolic KOH, and phosphatidylinositol-specific phospholipase C. Four glycans denoted alpha-delta were resolved by anion exchange high performance liquid chromatography (HPLC). Each glycan was subjected to hydrolysis in 4 M trifluoroacetic acid, and their hexose and hexose phosphate compositions were determined by anion exchange HPLC. The predominant glycan alpha showed a relative stoichiometry of 2 mannoses, 1 mannose 6-phosphate, 1 radiomethylated glucosamine, 1 radiomethylated ethanolamine, and 1 inositol. In contrast, the stoichiometry of glycan beta was 1 mannose, 2 mannose 6-phosphates, 1 radiomethylated glucosamine, 2 radiomethylated ethanolamines, and 1 inositol. Glycans alpha and beta were analyzed by electrospray ionization-mass spectrometry, and respective parent ions of m/z 1266 and 1417 were observed. The fragmentation pattern produced by collision-induced dissociation mass spectrometry of these parent ions was consistent with a common linear core glycan sequence prior to radiomethylation of ethanolamine-phosphate-mannose - mannose - mannose - glucosamine - inositol. Glycan alpha contained a single additional radiomethylated phosphoethanolamine branching from the mannose adjacent to glucosamine, whereas glycan beta contained two additional radiomethylated phosphoethanolamines, one branching from each of the mannoses nearest to glucosamine. Trifluoroacetic acid hydrolysis did not cleave within the N,N-dimethylglucosamine-inositol-phosphate moiety in these glycans, and this component was resolved by anion exchange HPLC and structurally confirmed by mass spectrometry. Dephosphorylation of this component by treatment with 50% HF produced N,N-dimethylglucosamine-inositol, and this conjugate was shown to have a characteristic elution time on cation exchange chromatography in an amino acid analyzer. Both of these fragments involving an intact radiomethylated glucosamine-inositol bond are proposed as new diagnostic indicators in the search for minor glycoinositol phospholipids in cells and tissues.

Acetylcholinesterase↗
PubMed1992

Ambenonium is a rapidly reversible noncovalent inhibitor of acetylcholinesterase, with one of the highest known affinities.

Steady state patterns of inhibition of purified human erythrocyte acetylcholinesterase by three inhibitors were analyzed. Edrophonium acted essentially as a competitive inhibitor, whereas tacrine and ambenonium gave mixed competitive and uncompetitive inhibition with acetylthiocholine as substrate. Inhibition constants for the competitive components were 470 microM for edrophonium, 65 microM for tacrine, and 0.12 nM for ambenonium. The extremely high affinity of ambenonium permitted analysis of the rates of approach to steady state inhibition. These rates were characterized by a single exponential time course with rate constants, kexp, that showed a linear dependence when plotted against ambenonium concentration, at fixed substrate concentration. The intercepts of these plots were independent of the substrate concentration and indicated an ambenonium dissociation rate constant of 0.013 +/- 0.002 sec-1. The slope of the plot at the lowest substrate concentration approximated the ambenonium bimolecular or association rate constant and gave a value of 5.2 +/- 0.6 x 10(7) M-1 sec-1. Three models were examined to account for the nearly linear dependence of the slopes of these plots on the substrate concentration. These models indicated that ambenonium and acetylthiocholine competed for a peripheral anionic site in the acetyl-enzyme intermediate formed during substrate hydrolysis. The apparent equilibrium dissociation constant of acetylthiocholine for this peripheral site (1.2-1.4 mM) was significantly different from that calculated from substrate inhibition data (20.1 +/- 2.8 mM). We propose that acetylthiocholine can interact with the acetyl-enzyme both at the peripheral site and at the active site but that only the latter interaction inhibits substrate hydrolysis.

Acetylcholinesterase↗
PubMed1987

The compensatory role of the parvocellular division of the red nucleus in operantly conditioned rats.

To assess the role of the parvocellular division of the red nucleus in motor control, rats were operantly conditioned to walk on a rotating bar and their red nuclei were lesioned with the fiber sparing agent, quinolinic acid. Since both parvocellular and magnocellular divisions of the red nucleus overlap in the rat, they both became involved in this lesion. To differentiate between them, two paradigms were used. (1) Prior to the lesion, the magnocellular division was dysfunctioned by transecting its spinal output, namely, the rubrospinal tract, in the dorso-lateral funiculus (DLF) of the spinal cord. After compensation for this transection had occurred in a few days, the red nucleus was lesioned with quinolinic acid. Rats again compensated rapidly, suggesting that the remaining red nuclear outflow systems, such as the rubro-olivary tract, play no detectable role in the control of on-going movements. (2) In the second paradigm, the red nucleus was lesioned without a preceding DLF transection. This lesion involved both the rubro-bulbar and rubro-spinal projections. Rats did not compensate, or did so very slowly. For compensation to occur, therefore, rubro-bulbar projections need to be intact. This suggests that such projections, that include the rubro-olivary tract, play a role in the compensation for DLF transections.

Animals↗
PubMed1986

Intracortical stimulation in pyramidotomized monkeys.

In order to examine, separately, the organizations of pyramidal and extrapyramidal projections from the primary motor cortex, efforts were made to map the forelimb area of two rhesus monkeys with microstimulation before and after unilateral pyramidotomy. However, microstimulation was not effective in evoking motor responses following complete pyramidal tract section. Movements were evoked using a modified intracortical electrode with a large exposed tip and using stimulation parameters similar to those used for surface stimulation. The results from this modified intracortical stimulation generally agree with those from surface stimulation studies in that: (1) the extrapyramidal topography is similar to the normal motor cortex topography and (2) while peripheral responses can be evoked from the cortex following pyramidotomy, greater spatial and temporal summation are necessary to evoke these responses. In addition, the modified intracortical technique revealed a more widespread post-pyramidotomy digit representation than observed previously with surface stimulation. Results from an incomplete pyramidal tract lesion suggest that recovery of motor function may include plastic changes in surviving corticospinal axons.

Animals↗
PubMed1986

Representation of movements and muscles within the primate precentral motor cortex: historical and current perspectives.

A major problem with the study of the control of movement and posture is to determine how specific brain areas contribute to the selection of those particular muscle patterns that underlie a coordinated movement. With this problem in mind, a selective review is presented of mapping studies of the primate motor cortex, whose results bear on the question of how the spatial organization of cortical efferent cells might contribute to the production of organized muscle synergies. More recent findings are also summarized, which appear to resolve previous controversies on the question of whether movements or muscles are the primary units of motor cortex organization. These same findings suggest also a form of spatial organization within the primate precentral gyrus that would allow spatially simple afferent inputs to evoke the muscle synergies that are necessary for a variety of simple movements of the arm and hand.

Animals↗
PubMed1984

Sizes, laminar and topographic origins of cortical projections to the major divisions of the red nucleus in the monkey.

The retrograde transport of horseradish peroxidase was used to study the topographic and laminar origins of the cortical projections to the parvocellular and the magnocellular divisions of the red nucleus in Macaca mulatta and Macaca fascicularis. Approximately 90% of the corticorubral projection is directed to the parvocellular division of the nucleus. Corticoparvocellular (CRp) neurons are pyramidally shaped, are smaller in size than corticospinal neurons, and are more numerous. They are found principally in sublamina Va of cytoarchitectonic areas 4 and 6, and in moderate quantities in sublamina Vb of posterior area 8 and area 5. In areas 4 and 6, the cells are grouped in clusters of three to 15 neurons each and are arranged in cellular bands of varying rostrocaudal thickness which course mediolaterally. With respect to functionally defined zones, CRp neurons are found throughout the supplementary motor area and the precentral motor cortex. In addition, they are found in parts of areas 5, 6, and 24 that project to these cortical motor areas, and that are thought to have "premotor" or movement-programming functions. The corticomagnocellular (CRm) projection arises principally from cells in sublamina Vb of the precentral arm and leg areas (area 4), and from adjacent parts of posterior area 6, CRm cells are pyramidally shaped, and their size distribution is bimodal, with peaks that correspond, respectively, to the modal diameters of CRp and of corticospinal neurons. These results and those of previous studies suggest that CRm neurons are involved principally in the control of hand and foot movements, with little effect on more proximal musculature. The massive CRp projection, however, is clearly part of a large cerebrocerebellar communication system, with motor and/or movement programming functions that have yet to be clearly defined.

Animals↗
PubMed1984

A sequential pulse generator for producing true biphasic stimuli.

The ability to generate biphasic pulses during electrical stimulation of nervous tissue has important advantages over monophasic or capacitively coupled stimulation. A comparatively simple circuit is described which, when used with standard electrophysiological laboratory equipment, can economically implement biphasic stimulation. The resultant system is quite flexible, yet easy to operate.

Electric Stimulation↗
PubMed1982

Separate cell systems in the motor cortex of the monkey for the control of joint movement and of joint stiffness.

A series of new observations is described from experiments with alert monkeys, who have been trained to control the position of the wrist in the presence of perturbing forces. The results suggest that the wrist control area of the precentral motor cortex contains separate neuronal populations for the control of 2 major forms of motor output. The first activates particular groups of synergists independently, or the members of a set of antagonist muscles reciprocally; this form of activation provides, under natural conditions, for smooth movement of the joint from one position to another. The second population of cells evokes co-activation of antagonist muscles, at one or more joints in the arm. This population provides for the cortical control of the postural supporting reactions which must occur in the arm when one or more of its joints are moved. In addition, it appears to provide for a separate control of joint stiffness, thus allowing for a control of joint position in the presence of very rapid or unpredictable external force perturbations. A possible role for this system as a means of joint position control during the early phases of motor learning is also discussed.

Animals↗
PubMed1980

A simple computerized system for plotting the locations of cells of specified sizes in a histological section.

A computerized plotting system is described which generates an outline of a histological section on an oscilloscope screen, and displays within its boundaries the positions of labeled neurons whose coordinates are sent to the computer electronically. Measured cell diameters can also be entered, allowing the computer to generate displays of the distributions of cells within specified size ranges. All data are saved by the computer, and any portion of a distribution may be examined oscilloscopically at several levels of magnification; moreover, three-dimensional displays may be generated wit appropriate programs.

Animals↗
PubMed1978

Properties of the pyramidal tract neuron system within the precentral wrist and hand area of primate motor cortex.

1. To obtain basic anatomical data that will be useful in interpreting the results of studies of primate pyramidal tract neurons (PTNs), extracellular, single-unit recording techniques were used to determine a number of the properties of the PTN population within the electrically defined, precentral wrist zone of the monkey's motor cortex. 2. Recordings were obtained from a total of 1,375 antidromically identified PT and corticospinal tract (CST) cells. A mathematical model was then used to correct the statistics of the sample for variations in the probability of unit detection, which arise from variations in neuronal size and extracellular field dimensions. 3. Both the experimentally observed and theoretically corrected results suggest that the PT projection from this cortical zone is derived principally from slowly conducting, and presumably small to medium-sized cells (an estimated 85% of the resident PTN population). 4. Both the fast and slow cell subpopulations were found to be concentrated within cortical layer V, where they tend to congregate in small, mixed clusters of 2 to 5 neurons. Estimates of the total packing density of PTNs within layer V of this cortical zone suggest that they account for only 10-20% of the neurons within this major efferent layer. 5. 70% of the slow and 82% of the fast PT neurons within this cortical area were found to send their axons into the contralateral, lateral corticospinal tract. Thus, in futur functional studies of PTNs in this cortical area, it can be assumed that three of every four neurons will in fact influence segmental cells of one category or another directly. 6. Extensive data are also presented on the incidence of axon collateral branching from PT and CST cells to the red nucleus, the medial medullary reticular formation and the cuneate nucleus. 7. Some general implications of these findings for the design of future functional studies of anatomically identified motor cortex cell systems are then discussed.

Action Potentials↗
PubMed1970

Predicting measures of motor performance from multiple cortical spike trains.

Recordings have been obtained simultaneously from several, individually selected neurons in the motor cortex of unanesthetized monkey as the animal performed simple arm movements. With the use of comparatively simple quantitative procedures, the activity of small sets of cells was found to be adequate for rather accurate real-time prediction of the time course of various response measurements. In addition, the results suggest that hypotheses concerning the response variables "controlled" by cortical motor systems may well depend upon whether or not the temporal relations between simultaneously active neurons are taken into account.

Animals↗