Percutaneous injuries among dental students.
Explore the source record for details and available documents.
Accidents, Occupational↗
Biomedical subjects
C J Wilson
Publications and source records attributed to C J Wilson.
Dynamic modification of dendritic cable properties and synaptic transmission by voltage-gated potassium channels.
Computer simulations of a dendrite possessing voltage-sensitive potassium conductances were used to determine the effects of these conductances on synaptic transmission and on the propagation of synaptic signals within the dendritic tree. Potassium conductances had two principal effects on voltage transients generated by current injections or synaptic conductances. Locally (near the source of the transient), voltage-gated potassium channels produced a potassium shunt current that reduced the amplitude of voltage transient increased and so acted to prevent large synaptic transients from reaching levels that would saturate due to a reduction in driving force. In the presence of rapidly activating potassium currents, excitatory synapses produced larger synaptic currents that were more linearly related to synaptic conductance, but these produced smaller voltage transients. The maximum amplitudes of the voltage transients were limited by the voltage sensitivity of the K+ conductance and the rate at which it could activate. Sufficiently rapid synaptic currents could outrun the K+ conductance and thus achieve high local peak amplitudes. These effects of K+ conductances were unrelated to whether they were located on dendrites or not, being related only to their proximity to the source of synaptic current. The second class of effects of K+ conductances depended on their alteration of the electronic structure of the postsynaptic cell and so were observed only when they were located on postsynaptic dendrites. Voltage-gated K+ conductances produced voltage-dependent electronic expansion of depolarized dendrites, which had the effect of isolating synaptic inputs on depolarized dendrites from events on the rest of the neuron. Thus, synapses on the same dendrite interacted destructively to a degree much greater than that expected from the classical driving force nonlinearity. Synapses located proximally to a depolarized dendritic region were less effected than those located distally, and the range of the nonlinear interaction between synapses was dependent on the kinetics of activation and deactivation of the conductance. When present in conjunction with rapidly activating dendritic sodium conductance, the potassium conductance sharpened the requirement for spatial and temporal coincidence to produce synaptic boosting by inward currents, and suppressed out-of-synchrony synaptic inputs.
Computer Simulation↗
Striatal interneurones: chemical, physiological and morphological characterization.
The neostriatum is the largest component of the basal ganglia, and the main recipient of afferents to the basal ganglia from the cerebral cortex and thalamus. Studies of the cellular organization of the neostriatum have focused upon the spiny projection neurones, which represent the vast majority of neurones, but the identity and functions of interneurones in this structure have remained enigmatic despite decades of study. Recently, the discovery of cytochemical markers that are specific for each of the major classes of striatal interneurones, and the combination of this with intracellular recording and staining, has revealed the identities of interneurones and some of their functional characteristics in a way that could not have been imagined by the classical morphologists. These methods also suggest some possible modes of action of interneurones in the neostriatal circuitry.
Animals↗
Potassium currents responsible for inward and outward rectification in rat neostriatal spiny projection neurons.
Many of the nonlinear membrane properties displayed by neostriatal spiny projection neurons are conferred by their voltage-gated potassium (K+) currents, including an inwardly rectifying current (IKir), fast (IAt), and slowly (IAs)-inactivating A-currents, and a slow, noninactivating current. The relative contribution of these K+ currents to the pronounced inward and outward rectification of the current-voltage (I-V) relationship of spiny neurons was investigated in a neostriatal slice preparation. Manipulation of the equilibrium potential for K+ (EK) showed that the voltage dependence of activation of inward rectification was identical to that of IKir. In addition, application of barium (100 microM), which is known to reduce IKir in a time- and voltage-dependent manner, had equivalent effects on inward rectification. Subsequent application of cesium (3 mM) or tetraethylammonium (TEA, 25 mM) blocked inward rectification in a solely voltage-dependent fashion consistent with the action of these blockers on IKir. Administration of 4-aminopyridine (4-AP, 100 microM) at concentrations that selectively depress IAs, reduced outward rectification of spiny neurons at subthreshold membrane potentials. Higher concentrations of 4-AP (2 mM), which block both IAs and IAt, revealed an early transient overshoot in voltage deflections at potentials near spike threshold, but rectification persisted at the end of the responses. The transient overshoot and the residual rectification were eliminated by TEA (25 mM), a blocker of the slow, noninactivating K+ current. Collectively, these results indicate that all three depolarization-activated K+ currents contribute to outward rectification at different times and membrane potentials defined by their voltage dependence of activation and kinetics of inactivation. The spontaneous activity of neostriatal spiny neurons recorded in intact animals is characterized by sustained and limited shifts in membrane potential from relatively hyperpolarized potentials to depolarized potentials near spike threshold. The present data suggest that the hyperpolarized state is determined principally by IKir and the limits on the depolarized state are defined by IAf, IAs, and the noninactivating current. These outward K+ currents also are hypothesized to govern the spike discharge characteristics once the depolarized state has been reached.
4-Aminopyridine↗
Understanding the neostriatal microcircuitry: high-voltage electron microscopy.
High voltage electron microscopy (HVEM) and HVEM tomography of selectively stained cell processes in the neostriatum have offered an alternative to serial thin section reconstruction for accurate 3-D visualization and measurement of axons, dendrites, and dendritic spines. Tissue preparation is simple and rapid, allowing examination of large numbers of specimens required for quantitation of neuronal morphology. The resolution of the images exceeds that available from any light microscopic technique and is appropriate for measurement of the finest axons and dendritic spine necks. HVEM tomography allows the direct measurement of dendritic surface area, required for computational modeling of synaptic integration.
Humans↗
Spontaneous firing patterns and axonal projections of single corticostriatal neurons in the rat medial agranular cortex.
1. Spontaneous fluctuations of membrane potential, patterns of spontaneous firing, dendritic branching patterns, and intracortical and striatal axonal arborizations were compared for two types of corticostriatal neurons in the medial agranular cortex of urethan-anesthetized rats: 1) pyramidal tract (PT) cells identified by antidromic activation from the medullary pyramid and 2) crossed corticostriatal (CST) neurons identified by antidromic activation from the contralateral neostriatum. The ipsilateral corticostriatal projections of intracellularly stained PT neurons as well as contralateral corticostriatal neurons were confirmed after labeling by intracellular injection of biocytin. 2. All well-stained PT neurons had intracortical and intrastriatal collaterals. The more common type (6 of 8) was a large, deep layer V neuron that had an extensive intracortical axon arborization but a limited axon arborization in the neostriatum. The less common type of PT neuron (2 of 8) was a medium-sized, superficial layer V neuron that had a limited intracortical axon arborization but a larger and more dense intrastriatal axonal arborization. Both subclasses of PT neurons had anatomic and physiological properties associated with slow PT cells in cats and monkeys and conduction velocities < 10 m/s. All of the PT cells but one were regular spiking cells. The exception cell fired intrinsic bursts. 3. Intracellularly stained CST neurons were located in the superficial half of layer V and the deep part of layer III. Their layer I apical dendrites were few and sparsely branched. Their axons gave rise to an extensive arbor of local axon collaterals that distributed in the region of the parent neuron, frequently extending throughout the more superficial layers, including layer I. Axon collaterals were also traced to the corpus callosum, as expected from their contralateral projections, and they contributed axon collaterals to the ipsilateral neostriatum. In the neostriatum, these axons formed extended arborizations sparsely occupying a large volume of striatal tissue. All CST neurons were regular spiking cells. 4. Both types of cells displayed spontaneous membrane fluctuations consisting of a polarized state (-60 to -90 mV) that was interrupted by 0.1- to 3.0-s periods of depolarization (-55 to -45 mV) accompanied by action potentials. The membrane potential was relatively constant in each state, and transitions between the depolarized and hyperpolarized states were sometimes periodic with a frequency of 0.3-1.5 Hz. A much faster (30-45 Hz) subthreshold oscillation of the membrane potential was observed only in the depolarized state and triggered action potentials that locked to the depolarizing peaks of this rhythm.(ABSTRACT TRUNCATED AT 400 WORDS)
Action Potentials↗
Contribution of a slowly inactivating potassium current to the transition to firing of neostriatal spiny projection neurons.
1. Neostriatal spiny projection neurons display a prominent slowly depolarizing (ramp) potential and long latency to spike discharge in response to intracellular current pulses. The contribution of a slowly inactivating A-current (IAs) to this delayed excitation was investigated in a neostriatal slice preparation using current pulse protocols incorporating information based on the known voltage dependence, kinetics, and pharmacological properties of IAs. 2. Depolarizing intracellular current pulses evoked a slowly developing ramp potential that could last for seconds without reaching steady state and continued until either the pulse was terminated or spike threshold was reached. The slope of the ramp potential was dependent on the level of depolarization achieved by the membrane, and the apparent activation threshold for this ramp depolarization was approximately -65 mV. 3. Application of low concentrations of 4-aminopyridine (4-AP, 30-100 microM) or dendrotoxin (DTX, 30 nM), which are known to selectively block IAs, reduced both the slope of the ramp potential and the latency to first spike discharge. As has been described previously, blockade of inward Na+ and Ca2+ currents with tetrodotoxin (TTX, 1 microM) and cadmium (400 microM) also reduced the slope of the ramp depolarization. 4. A conditioning-test pulse protocol was used to examine the voltage dependence of inactivation of the ramp potential and long first spike latency. In the absence of a conditioning pulse, the test pulse evoked a slowly rising ramp potential and a spike with a long latency to discharge. A conditioning depolarization to approximately -60 mV decreased the slope of the ramp potential and the latency to first spike discharge evoked by the test pulse. A conditioning hyperpolarization to potentials below -100 mV, increased first spike latency. Application of a low concentration of 4-AP (100 microM) abolished the influence of prior membrane potential on the slope of the ramp depolarization and the latency to first spike discharge. 5. The kinetics of recovery from inactivation of the 4-AP-sensitive current were studied in the presence of TTX and cadmium by depolarizing cells to approximately -50 mV and then stepping to approximately -90 mV for increasing periods of time (0.5-5.0 s) before delivering a test pulse. The amplitude of the test pulse response decreased as a function of the hyperpolarizing step duration. When the test pulse response amplitudes were plotted against the hyperpolarizing step duration, the points reflected an exponential decay with an average time constant of 2.05 +/- 1.38 (SD) s.(ABSTRACT TRUNCATED AT 400 WORDS)
4-Aminopyridine↗
Surround inhibition among projection neurons is weak or nonexistent in the rat neostriatum.
1. Antidromic activation of striatal spiny projection neurons by substantia nigra stimulation in vivo did not evoke inhibitory postsynaptic potentials (IPSPs) in the antidromically activated neurons, or in neighboring spiny neurons. 2. More generalized activation of projection cells by stimulation of the efferent pathway in slices did not evoke IPSPs in spiny neurons. Inhibitory mechanisms were operative in these slices, as indicated by the presence of an IPSP component in the orthodromic response to local stimulation. 3. Dual intracellular recordings, obtained from cells located within 50-200 microns of each other in striatal slices also failed to demonstrate any inhibition among striatal spiny cells. Spikes triggered in one spiny neuron by current injection failed to produce any postsynaptic potential in nearby spiny cells at resting or depolarized membrane potentials. Excitatory postsynaptic potentials (EPSPs) evoked by electrical stimulation of the cortex were not affected by spiking of neighboring cells. 4. It is impossible to rule out the presence of inhibition among striatal spiny neurons in all circumstances. However, the absence of demonstrable IPSPs in these experiments argue against the common view that mutual inhibition among spiny neurons is a central organizing principle of striatal function.
Animals↗
Arresting G-protein coupled receptor activity.
Explore the source record for details and available documents.
Journal Article↗
Escherichia coli leader peptidase: production of an active form lacking a requirement for detergent and development of peptide substrates.
The report by Zimmermann et al. (J. Biol. Chem. 257, 1982, 6529-6536) that the active site of Escherichia coli leader peptidase (LPase) is located in the periplasm led us to explore the possibility that soluble, active short forms of LPase could be produced. Detergent-free delta 2-75 mutant protein (LPase-sf) lacking the two N-terminal transmembrane spanning and the cytoplasmic domains was produced in high yield. The mass of the protein determined by electrospray ionization mass spectrometry was 27,952 amu. The increase of 42 amu over that predicted by the expected amino acid sequence indicates that the N-terminus of LPase-sf is acetylated. This is consistent with the inability to obtain an N-terminal sequence. LPase-sf lacks the site of autolysis present in LPase, thus circumventing problems associated with enzyme autocatalytic instability. LPase-sf and wild type LPase displayed comparable activity versus two peptide substrates. The peptides, based upon the cleavage sites of procoat and the precursor of maltose binding protein, were processed at the expected sites. In addition, the activity of both LPase's was not inhibited by classical inhibitors of the four classes of proteases. LPase-sf displayed similar activity in the presence and absence of detergent. Wild type LPase displayed specificity for alanine in the P1 subsite of the peptide WSASALX*KI and did not hydrolyze peptides with glycine, valine, or serine in that position. The availability of a detergent-free active form of LPase should facilitate mechanistic and structural studies.
Amino Acid Sequence↗
The generation of natural firing patterns in neostriatal neurons.
Explore the source record for details and available documents.
Animals↗
Dopamine receptor subtypes colocalize in rat striatonigral neurons.
Dopaminergic neurons of the substantia nigra provide one of the major neuromodulatory inputs to the neostriatum. Recent in situ hybridization experiments have suggested that postsynaptic dopamine receptors are segregated in striatonigral and striatopallidal neurons. We have tested this hypothesis in acutely isolated, retrogradely labeled striatonigral neurons by examining the neuromodulatory effects of selective dopaminergic agonists on Na currents and by probing single-cell antisense RNA populations with dopamine receptor cDNAs. In most of the neurons examined (20/31), the application of the D1 dopamine receptor agonist SKF 38393 reduced evoked whole-cell Na+ current. The D2 agonists quinpirole and bromocriptine had mixed effects; in most neurons (23/42), whole-cell Na+ currents were reduced, but in others (8/42), currents were increased. In cell-attached patch recordings, bath application of SKF 38393 decreased currents as in whole-cell recordings, whereas quinpirole consistently (6/10) enhanced currents--suggesting that D2-like receptors could act through membrane delimited and non-delimited pathways. Changes in evoked current were produced by modulation of peak conductance and modest shifts in the voltage dependence of steady-state inactivation. Antisense RNA probes of dopamine receptor cDNA Southern blots consistently (5/5) revealed the presence of D1, D2, and D3 receptor mRNA in single striatonigral neurons. These findings argue that, contrary to a strict receptor segregation hypothesis, many striatonigral neurons colocalize functional D1, D2, and D3 receptors.
2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
Grafted neostriatal neurons express a late-developing transient potassium current.
Previous anatomical and physiological studies of neostriatal grafts have suggested that transplanted neurons do not develop beyond an early postnatal stage. We have tested whether this hypothesis can be generalized by characterizing the developmentally regulated Ca-independent potassium currents in graft neurons. These currents were studied using a combination of the whole-cell voltage-clamp technique with acutely-dissociated neurons and intracellular recording in slices. In all of the graft neurons examined with voltage-clamp techniques (n = 13), evidence was found for a slowly-inactivating potassium current that is seen only beyond the third or fourth postnatal week in normal rats. A current resembling the delayed rectifier was also seen in all sample neurons. The rapidly inactivating A-current which dominates recordings from nearly all immature neurons was seen in only about half (54%, 7/13) of the graft neurons; in a sample of normal adult striatal neurons, the A-current was detected in a similar percentage of neurons (41%, 25/62). Recordings of graft neurons in slices corroborated the voltage-clamp findings in revealing a slowly inactivating outward current that acts in the subthreshold potential range. These findings suggest that graft neurons express the normal complement of depolarization-activated potassium channel proteins seen in adult neurons.
Animals↗
Morphology of intracellularly stained spiny neurons in rat striatal grafts.
Two to six months after implantation of fetal striatal primordia into the kainic acid-lesioned neostriatum of adult rats, spiny neurons in the grafts were stained intracellularly with biocytin. To determine whether the spiny neurons in the grafts differentiate morphologically as in the host neostriatum, the intracellularly stained spiny neurons in the grafts were studied with light and electron microscopy and compared with that of spiny neurons in the host neostriatum. The spiny neurons in the grafts had ovoid or polygonal cell bodies with dendrites radiating in all directions. The somata were smooth and the dendrites, except for their most proximal portions, were rich in spines. All these features resembled the appearance of spiny neurons in the intact neostriatum. However, quantitative studies showed that the somata of spiny neurons in the grafts were larger than those in the host neostriatum (projected cross-sectional areas of 230 +/- 64.6 microns 2 in the grafts and 158 +/- 28.9 microns 2 in the host) and the spine density of graft neurons was lower than that of host neurons. Cells near the border of the grafts had dendrites extending both into the graft and into the host neostriatum. In these cells, the dendrites in the grafts had fewer spines than the dendrites in the host tissue. The axons of spiny neurons in the grafts had very large and dense intrastriatal collateral arborizations, which occupied a much larger volume than that of the dendritic domain of the parent cells. The local axonal arborizations of each of these cells filled almost the entire graft. In some cells, axonal branches were traced outside the grafts and were seen to enter the internal capsule fascicles. Unlike spiny neurons in the normal adult neostriatum, the spiny cells of the graft could have nuclear indentations. With this exception, the ultrastructural features of spiny neurons in the grafts were very similar to those in the hosts. Many unlabeled boutons made synapses on identified spiny neurons in the grafts. Terminals with small round vesicles made synaptic contacts on dendritic shafts and dendritic spines, while terminals with flattened or pleomorphic vesicles contacted somata, dendrites, and dendritic spines. Labeled axon collaterals of graft neurons made symmetrical synapses on somata, dendrites and spines in the grafts and in the host neostriatum. In the grafts, more than 60% of the axon terminals contacted dendritic shafts. The proportion of axosomatic and axospinous synapses varied substantially from cell to cell.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Measurement of neuronal surface area using high-voltage electron microscope tomography.
High-voltage electron microscopy (HVEM) and axial tomography were used to reconstruct the three-dimensional structure of dendrites of intracellularly stained neostriatal spiny neurons. Neurons were stained using iontophoretic injection of horseradish peroxidase from an intracellular micropipet. Thick sections were cut on a vibratome, reacted with diaminobenzidine, and embedded in plastic. High-voltage electron microscopy was used to obtain high-resolution images of neuronal processes in 2- to 3-micron plastic sections cut from those blocks. Series of high-voltage electron micrographs were taken at 2 degrees increments of specimen tilt over a range of at least +/- 60 degrees, and three-dimensional reconstructions were generated from the series using an R-weighted backprojection method. An interactive procedure was used to draw the dendritic profiles from slices through the reconstructed volume and to measure volumes and surface areas of the dendrites. Values obtained in this manner matched previous findings using reconstruction from serial thin sections. The HVEM-tomography method offers an alternative to the serial-thin-section method for the quantitative analysis of neuronal shape.
Animals↗
The relationship between attitude to disabled siblings and ratings of behavioural competency.
The impact of maturation factors and functioning level on the relationship between disabled and non-disabled siblings was examined. Two groups of adults, distinguished by level of functioning of their mentally retarded sibling, completed a Schaefer Sibling Behavior Inventory (SBI) and participated in a semi-structured interview. The latter explored a number of dimensions of the relationship including degree of warmth, contact and involvement. Judgements about involvement and comfort as remembered from the past and judgements about the present were obtained to derive hypotheses about possible changes with time. Data from the SBI indicated that significantly more competent siblings tended to be involved in relationships with a higher degree of reciprocity. In contrast, measures of attitude derived from interview data did not appear to relate to the functioning level of the sibling in any systematic manner. The results suggest that level of discomfort with peers may decrease significantly over the years with neither level of functioning nor gender being important variables. The extent to which non-disabled individuals expressed a preparedness to participate in the life of their disabled sibling may relate to the life-stage of the two. Males in particular anticipated increased future involvement. Although higher-functioning siblings were described as more active in the relationship, this did not appear to influence perceived positiveness of regard. The implications of these results are discussed briefly.
Activities of Daily Living↗
Restoration of thalamostriatal projections in rat neostriatal grafts: an electron microscopic analysis.
The thalamostriatal projections to rat neostriatal grafts were studied by using the Phaseolus vulgaris-leucoagglutinin (PHA-L) axonal tracing technique. Two to 6 months after implantation of striatal primordia into adult neostriata, PHA-L was injected into two different portions of the intralaminar nuclear complex of the thalamus. In the host neostriatum, labeled fibers from the parafascicular nucleus (PF) arborized in a large region in the neostriatum, but avoided small patchlike areas. Most of the fibers from PF had irregular curved trajectories with short side branches that formed boutons. Labeled fibers from the centromedial and paracentral nuclei (CeM-PC) projected to a similarly large area within the neostriatum but did not show any nonuniformity. CeM-PC axons had relatively straight trajectories and formed boutons en passant. Both sets of thalamostriatal projection fibers were found in the grafts. Some of the labeled fibers in the grafts formed dense, focal arborizations. Compared to the host neostriatum, the distribution of postsynaptic elements in the grafts was altered dramatically. In the host neostriatum, 89% of the terminals from PF terminated onto dendritic shafts; 93% of the CeM-PC terminals contacted dendritic spines. However, only 47% of the PF terminals in the grafts contacted dendritic shafts; 53% of them terminated on dendritic spines. In grafts, 81% of the terminals from CeM-PC region contacted dendritic spines; 19% of them made synapses on dendritic shafts. The shift of postsynaptic elements in the grafts suggests a loss of pathway specificity in the induction of dendritic spines on neostriatal neurons in grafts.
Animals↗
Perioperative management of coronary artery bypass surgery in a patient with factor IX deficiency.
Explore the source record for details and available documents.
Aged↗