Transrectal ultrasound. An aid to diagnosing prostate cancer.
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Humans↗
Biomedical subjects
J K Stevens
Publications and source records attributed to J K Stevens.
Irregular geometries in normal unmyelinated axons: a 3D serial EM analysis.
Axons have generally been represented as straight cylinders. It is not at all uncommon for anatomists to take single cross-sections of an axonal bundle, and from the axonal diameter compute expected conduction velocities. This assumes that each cross-section represents a slice through a perfect cylinder. We have examined the three-dimensional geometry of 98 central and peripheral unmyelinated axons, using computer-assisted serial electron microscopy. These reconstructions reveal that virtually all unmyelinated axons have highly irregular axial shapes consisting of periodic varicosities. The varicosities were, without exception, filled with membranous organelles frequently including mitochondria, and have obligatory volumes similar to that described in other neurites. The mitochondria make contact with microtubules, while the other membraneous organelles were frequently found free floating in the cytoplasm. We conclude that unmyelinated axons are fundamentally varicose structures created by the presence of organelles, and that an axon's calibre is dynamic in both space and time. These irregular axonal geometries raise serious doubts about standard two dimensional morphometric analysis and suggest that electrical properties may be more heterogeneous than expected from single section data. These results also suggest that the total number of microtubules contained in an axon, rather than its single section diameter, may prove to be a more accurate predictor of properties such as conduction velocity. Finally, these results offer an explanation for a number of pathological changes that have been described in unmyelinated axons.
Animals↗
Development of a preformulation lipophilicity screen utilizing a C-18-derivatized polystyrene-divinylbenzene high-performance liquid chromatographic (HPLC) column.
Alkane/water partition coefficients have been predicted from the retention times of solutes using a C-18-derivatized polystyrene-divinylbenzene HPLC column (Act-I). Several classes of compounds, with molecular weights from 78 to 379 and partition coefficients ranging over several orders of magnitude, were included in the present study. A high correlation coefficient (0.953) was obtained from log-log plots of alkane/water partition coefficients versus capacity factor. A poor correlation was observed for octanol/water partition coefficient, presumably due to the hydrogen-bonding capability of octanol. The alkane/water correlation suggests that the system is devoid of significant specific solute-stationary phase interactions which are known to impart anomalous retention behavior to traditional reverse phase columns. Deviations of calculated alkane/water partition coefficients (and Hansch II alkane coefficients) from observed values could not be explained in terms of solute (or substituent) polarizability, dipole moment, sigma para, or pKHB values, further suggesting that specific interactions between the stationary phase and the solute are not significant. A molecular weight dependence that was independent of lipophilicity was observed. Thermodynamic and extra-thermodynamic parameters of retention were obtained in order to investigate retention mechanisms for the Act-I column. The molecular weight dependence does not appear to be due to size exclusion or entropic expulsion of the solute from the stationary phase. Hansch II substituent coefficients calculated from retention times were found to be similar for benzene and steroid derivatives. Thus, the Act-I column may be utilized as a rapid lipophilicity screen for drug candidates of similar molecular weight.
Alkanes↗
An unusual type of hangman's fracture.
An unusual fracture of the axis was best displayed using three-dimensional reconstruction. The fracture was noted to differ significantly from the usual "hangman's fracture" as it involved the body of C2 with subluxation of the anterior part of C2 forward on C3 and without "decompression" of the spinal canal at the C2 level. Better understanding made feasible by three-dimensional reconstruction had important treatment implications in this case.
Adult↗
Dendritic spines of CA 1 pyramidal cells in the rat hippocampus: serial electron microscopy with reference to their biophysical characteristics.
Serial electron microscopy and 3-D reconstructions of dendritic spines from hippocampal area CA 1 dendrites were obtained to evaluate 2 questions about relationships between spine geometry and synaptic efficacy. First, under what biophysical conditions are the spine necks likely to reduce the magnitude of charge transferred from the synapses on the spine heads to the recipient dendrite? Simulation software provided by Charles Wilson (1984) was used to determine that if synaptic conductance is 1 nS or less, only 1% of the hippocampal spine necks are sufficiently thin and long to reduce charge transfer by more than 10%. If synaptic conductance approaches 5 nS, however, 33% of the hippocampal spine necks are sufficiently thin and long to reduce charge transfer by more than 10%. Second, is spine geometry associated with other anatomical indicators of synaptic efficacy, including the area of the postsynaptic density and the number of vesicles in the presynaptic axon? Reconstructed spines were graphically edited into head and neck compartments, and their dimensions were measured, the areas of the postsynaptic densities (PSD) were measured, and all of the vesicles in the presynaptic axonal varicosities were counted. The dimensions of the spine head were well correlated with the area of PSD and the number of vesicles in the presynaptic axonal varicosity. Spine neck diameter and length were not correlated with PSD area, head volume, or the number of vesicles. These results suggest that the dimensions of the spine head, but not the spine neck, reflect differences in synaptic efficacy. We suggest that the constricted necks of hippocampal dendritic spines might reduce diffusion of activated molecules to neighboring synapses, thereby attributing specificity to activated or potentiated synapses.
Animals↗
Dendritic spines of rat cerebellar Purkinje cells: serial electron microscopy with reference to their biophysical characteristics.
We have used serial electron microscopy and 3-dimensional reconstructions of dendritic spines from Purkinje spiny branchlets of normal adult rats to evaluate 2 questions about the relationship of spine geometry to synaptic efficacy. First, do relationships between spine geometry and other anatomical indicators of synaptic activity suggest that spine size and shape might be associated with synaptic efficacy? Reconstructed spines were graphically edited into head and neck compartments; the area of the postsynaptic density (PSD) was measured; the volume of spine smooth endoplasmic reticulum (SER) was computed; and all of the vesicles in the axonal varicosities were counted. Spine head volume and the volume of SER contained in the head are well correlated with the area of the PSD and the number of vesicles in the presynaptic axonal varicosity. Spine neck diameter does not fluctuate with PSD area, head volume, or the vesicle number. These results suggest that the dimensions of the spine head, but not of the spine neck, are likely to reflect differences in synaptic efficacy. Second, does the geometry of cerebellar spine necks reduce the transfer of synaptic charge to the recipient dendrite from the theoretical maximum that could be transferred if the synapse were on a dendritic shaft? Comparison of volume to surface area showed that the spine heads are approximately spherical and the necks are approximately cylindrical. Application of results from a biophysical model that assumed these geometrical shapes for spines (Wilson, 1984) showed that the cerebellar spine necks are unlikely to reduce transfer of synaptic charge by more than 5-20% even if their SER were to completely block passage of current through the portion of the neck that it occupies. We suggest that the constricted spine neck diameter might serve to isolate metabolic events in the vicinity of activated synapses by reducing diffusion to neighboring synapses, without significantly influencing the transfer of synaptic charge to the postsynaptic dendrite.
Animals↗
Dynamics of behaviour during neuronal morphogenesis in culture.
We report a developmental sequence in the type and frequency of behaviours of neurons differentiating in vitro. We characterised these changes with extensive analysis of time-lapse sequences from both the continuing cell line pheochromocytoma PC12 and primary mixed cell culture of cat and mouse central nervous system. PC12 cells activated by nerve growth factor (NGF) differentiate in a uniform and synchronous manner. This allowed the first quantification of changes in different neuron behaviours during morphogenesis. Shortly after NGF activation, PC12 cells are highly labile in morphology and exhibit a large variety of morphological behaviours. During the first week of differentiation, the frequency of these behaviours declines, and gross morphology becomes more stable. The frequency of neurite initiation after 1 week in NGF is one-seventh what it was after 2 days in NGF. Over the same period, neurite retraction declines to one-third, and somal migration ceases altogether. Growth-cone activity does not decline during development. These behaviour changes correlate with published data on the differentiation of the neurite cytoskeleton. A qualitatively similar ontogeny was noted in the differentiation of CNS neurons in mixed cell culture. Major differences occur in the relative timing of changes in behaviours. Mature, stable morphology is not detected in these cultures until 7 weeks in vitro.
Adrenal Gland Neoplasms↗
Changes in the organization of the neuritic cytoskeleton during nerve growth factor-activated differentiation of PC12 cells: a serial electron microscopic study of the development and control of neurite shape.
After exposure to nerve growth factor, PC12 cells differentiate within a period of only a few days into cholinergic sympathetic neurons. Using computer-assisted three-dimensional serial electron microscopic reconstruction, we describe the progressive cytoskeletal and structural changes of PC12 neurites at different stages in their differentiation. Developmental changes in these neurites can be characterized by two major transitions. First, microtubules (MTs), which define the longitudinal axis of the neurite, increase in number leading to a more cylindrical and uniform neurite shape. Second, there are major changes in the relative numbers of other organelle types, which reflect the functional specialization of the neurite. These changes do not in themselves seriously affect shape change of the neurite during development, however the presence of these organelles and their associated obligatory volumes (volumes surrounding organelle) account for well over 50% of the neurite's volume at all stages of development. The MT-MT distances and obligatory volumes associated with the organelles remain constant throughout development. Thus, we can conclude that many of the observed changes seen in developing PC12 neurites are due simply to the production of a greater number of MTs in the cell, and that many of the other important parameters that can be measured and contribute to neurite shape remain constant during development.
Animals↗
Experimental modification of PC12 neurite shape with the microtubule-depolymerizing drug Nocodazole: a serial electron microscopic study of neurite shape control.
The microtubule-depolymerizing drug Nocodazole has been used to experimentally manipulate the form of PC12 neurites. Both time-lapse photography and serial electron microscopy demonstrate that microtubule depolymerization leads to varicosity formation due to a clustering of membranous organelles in young neurites (nerve growth factor activated within 7 d). Neurites that have been nerve growth factor activated 7 or more d before Nocodazole application are resistant to microtubule depolymerization. These data and data from previous papers has been combined in an attempt to predict quantitatively the volume and the shape of a neurite. The relationship is described mathematically by Vn = 4.52 Vo + 0.0054 MTl, where Vn is local neurite volume, Vo is organelle volume, and MTl is MT length (the constant, 0.0054 is micron2), and 4.52 is the obligatory volume constant derived from serial electron microscopic studies. The equation predicts the total volume of neurites despite alterations of morphology due to Nocodazole and despite changes in morphology during development.
Animals↗
Microcircuitry of beta ganglion cells in cat retina.
We reconstructed from electron micrographs of 189 serial ultrathin sections a major portion of the dendritic tree of an on-beta ganglion cell through its sixth order of branching. One hundred three contacts from three cone bipolar cells were identified. Forty-seven contacts were from a single CBb1 cone bipolar. These were distributed widely over the dendritic tree but were frequently found on the slender "basal tuft" dendrites. Twenty-two additional contacts from a second CBb1 cell were found but not studied in detail. Thirty-four contacts were from a single CBb2 cone bipolar; these also were distributed widely but were primarily on the branches of the main dendritic arborization. A major portion of the dendritic tree of an off-beta cell was also reconstructed through its seventh order of branching. Thirty-five contacts from two cone bipolar cells were identified. Twenty-three contacts were from a single CBa1 cone bipolar and 12 widely distributed over the off-beta cell dendritic tree. We propose that the photopic receptive field center of a beta cell corresponds to the envelope of the receptive fields of the bipolar cells that connect it to the cones. The center response of a beta cell may be generated by a "push-pull" mechanism. For the on-beta cell there would be excitation at light on from CBb1 and disinhibition from CBb2 and the reverse at light off. For the off-beta cell there would be inhibition at light on from CBa2 and withdrawal of excitation from CBa1. Should the bipolars have antagonistic surrounds (so far reported only for CBb1), the beta cell surrounds as well as their centers might be generated by this push-pull mechanism.
Animals↗
Reconstructive three-dimensional electron microscopy. A routine biologic tool.
Twenty years ago a laboratory could devote an entire year or more to the collection and analysis of a single set of serial electron micrographs. In contrast, simple technical improvements have now made it possible to take embedded material and have in hand complete computer reconstructions of cells' organelles, microtubules, etc., in less than a week. With a few additional minor improvements, this time could be reduced to only two or three days. Experience in our laboratory suggests that almost without exception these reconstructions provide new insights into both the structure and function of cells. We illustrate this point by presenting a new, unpublished anatomic feature of mammalian nuclei, the "nuclear tube." This example is typical of many other unpublished incidental findings we have made over the last five years using serial electron microscopy as a routine tool, and we believe it represents only the tip of a largely unexplored world of three-dimensional cytoarchitecture.
Animals↗
Streptococci as indicators in water supplies.
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Bacteriological Techniques↗
Paralysis of the awake human: visual perceptions.
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Adult↗
Spatiotemporal organization of cat lateral geniculate receptive fields.
Spatial and temporal properties of LGN receptive fields were studied by flashing a small bar of light across the field in 28 discrete steps. The flashes at each of the spatial positions were used to produce 28 PST histograms. These histograms were in turn displayed as a plane, with space on the chi axis, time on the psi axis, and probability of firing on the zota axis. These response planes demonstrate that the terms on, off, center, and surround do not adequately describe when the simplest LGN receptive field. We, therefore, introduce a new terminology describing the four major spatiotemporal components of LGN fields. The primary excitatory (PE) domain corresponds to the strongest excitatory response, the secondary excitatory (SE) domain corresponds to the second-strongest excitatory domain, the primary inhibitory (PI) domain corresponds to the strongest inhibitory domain and, finally, the secondary inhibitory (SI) domain corresponds to the second-strongest inhibitory domain. Based on the arrangement of these four domains, it is possible to divide LGN fields into four major categories: 1) homogeneous-on, on-center receptive fields which have a spatially homogeneous distribution of domains; 2) homogeneous-off, off-center receptive fields which have a spatially homogeneous distribution of domains; 3) heterogeneous-on, on-center receptive fields which have a spatially heterogeneous distribution of domains; and 4) heterogeneous-off, off-center receptive fields which have a spatially heterogeneous distribution of domains; 3) heterogeneous-on, on-center receptive fields which have a spatially heterogeneous distribution of domains; and 4) heterogeneous-off, off-center receptive fields which have a spatially heterogeneous distribution of domains. Using grating, it can be demonstrated that our heterogeneous/homogeneous fields correspond to X/Y fields, respectively. These data lead us to suggest that retinal PE domains generage LGN PE and SI domains, while retinal SE domains generate LGN SE and SI domains.
Animals↗
Interactions between cat lateral geniculate neurons.
Action potentials of 31 pairs of cat LGN neurons were recorded on single electrodes. Cross-correlograms, response planes, and a new function, the logical response plane, were calculated. The cross-correlograms between these pairs revealed four interactive classes: 1) a class with a flat cross-correlogram, 2) a class with a peak in the center of the cross-correlogram seen both during spontaneous activity and during driven activity, 3) a class with an inhibitory dip in the center of the cross-correlogram seen only when the cell pairs were driven by a stimulus and predicted by the shift predictor, 4) finally, a class with an inhibitory dip in the center of the cross-correlogram seen both during driven activity and spontaneous activity and not predicted by the shift predictor. Response plane pairs calculated for the unit pairs with flat cross-correlograms showed no predictable relationship. The pairs with a dip in the center of the cross-correlograms always had response planes that were antagonistic (i.e., approximate negative images of each other). When one cell was excited, the second cell was inhibited, and vice versa. More detailed analysis, using the logical response plane, demonstrated that the majority of the antagonistic response planes had either excitatory or inhibitory overlap. That is, the cells were simultaneously excited and/or inhibited at specific spatiotemporal loci on the response plane. These data are consistent with a feed-forward inhibitory circuit in LGN. Furthermore, the data suggest that retinal centers (PE domains) produce LGN excitatory centers (PE domains) and inhibitory centers (PI domains). In turn, retinal excitatory surrounds (SE domains) produce LGN excitatory surrounds (SE domains) and inhibitory surrounds (SI domains).
Action Potentials↗
Cytoskeletal organization following cannabinoid treatment in undifferentiated and differentiated PC12 cells.
Confocal microscopy in association with three-dimensional reconstruction was used to examine the changes in the microtubules and microfilaments following cannabinoid treatment of PC12 cells. Microtubules and microfilaments were disrupted in a dose-dependent manner following treatment with 10-30 microM delta 9-tetrahydrocannabinol (THC). A disruption of microtubules and microfilaments was observed following treatment with 30 microM cannabidiol and cannabinol. The amount of microtubules and microfilaments was reduced in a dose-dependent manner following treatment with 10 and 20 microM THC. Cannabidiol and cannabinol reduced the amount of microtubules and microfilaments; however, the reduction was less than that observed with THC treatment. Following the addition of nerve growth factor, differentiated PC12 cells were generally more sensitive to cannabinoid treatments than undifferentiated cells. The possible mechanisms that may account for the changes in microtubules and microfilaments following cannabinoid treatment are discussed.
Actin Cytoskeleton↗