Showing papers by "University of Virginia published in 1986"

Protein sequencing by tandem mass spectrometry

Abstract: Methodology for determining amino acid sequences of proteins by tandem mass spectrometry is described. The approach involves enzymatic and/or chemical degradation of the protein to a collection of peptides which are then fractionated by high-performance liquid chromatography. Each fraction, containing as many as 10-15 peptides, is then analyzed directly, without further purification, by a combination of liquid secondary-ion/collision-activated dissociation mass spectrometry on a multianalyzer instrument. Interpretation of collision-activated dissociation mass spectra is described, and results are presented from a study of soluble peptides produced by treatment of apolipoprotein B with cyanogen bromide and trypsin.

Optimal Trade and Industrial Policy Under Oligopoly

Abstract: We analyze the welfare effects of trade and industrial policy under oligopoly, and characterize optimal intervention under a variety of assumptions about market structure and conduct. When all output is exported, optimal policy with a single home firm depends on the difference between foreign firms' actual responses to the home firm's actions and the responses that the home firm conjectures. A subsidy often is indicated for Cournot behavior, but a tax generally is optimal if firms engage in Bertrand competition. If conjectures are "consistent," free trade is optimal. With domestic consumption, intervention can raise national welfare by reducing the deviation of price from marginal cost.

Cluster analysis: a simple, versatile, and robust algorithm for endocrine pulse detection

Abstract: Endocrine signaling provides one critical means of physiological communication within an organism. Many endocrine signals exhibit an episodic or pulsatile configuration. In an effort to provide a versatile and statistically based algorithm for investigating the regulation of endocrine pulse signals, we have formulated a computerized algorithm in which a pulse is defined as a statistically significant increase in a "cluster" of hormone values followed by a statistically significant decrease in a second cluster of values. The increase or decrease is judged in relation to the actual experimental error expressed by the replicates in the presumptive nadir and peak data clusters. The program permits the operator to specify the cluster sizes of test peaks and pre- and postpeak nadirs. This method is largely insensitive to unstable base-line hormone concentrations and is not adversely affected by varying pulse amplitudes, widths, or configurations within the endocrine series. In addition, the simple statistical basis for this algorithm renders it minimally dependent on explicit or a priori assumptions about rates of hormone secretion or disappearance. The program has been validated for false-positive errors against a wide range of intraseries coefficients of variation (4-52%). We have illustrated its performance for profiles of luteinizing hormone, follicle-stimulating hormone, growth hormone, prolactin, adrenocorticotropic hormone, and cortisol and compared these episodic patterns with those of stable serum constituents (total serum protein and calcium), which do not exhibit pulsatile fluctuation.

An experimental evaluation of the assumption of independence in multiversion programming

Abstract: N-version programming has been proposed as a method of incorporating fault tolerance into software. Multiple versions of a program (i.e. `N') are prepared and executed in parallel. Their outputs are collected and examined by a voter, and, if they are not identical, it is assumed that the majority is correct. This method depends for its reliability improvement on the assumption that programs that have been developed independently will fail independently. An experiment is described in which the fundamental axiom is tested. In all, 27 versions of a program were prepared independently from the same specification at two universities and then subjected to one million tests. The results of the tests revealed that the programs were individually extremely reliable but that the number of tests in which more than one program failed was substantially more than expected. The results of these tests are presented along with an analysis of some of the faults that were found in the programs. Background information on the programmers used is also summarized.

Rigorous coupled-wave analysis of metallic surface-relief gratings

Abstract: A rigorous coupled-wave analysis for metallic surface-relief gratings is presented. This approach allows an arbitrary complex permittivity to be used for the material and thus avoids the infinite conductivity (perfect-conductor) approximation. Both TE and TM polarizations and arbitrary angles of incidence are treated. Diffraction characteristics for rectangular-groove gold gratings with equal groove and ridge widths are presented for free-space wavelengths of 0.5, 1.0 and 10.0 μm for all diffracted orders as a function of period, groove depth, polarization, and angle of incidence. Results include the following: (1) TM-polarization diffraction characteristics vary more rapidly than do those for TE polarization, (2) 95% first-order diffraction efficiency occurs for TM polarization at 10.0 μm, (3) 50% absorption of incident power occurs at 0.5 μm, and (5) the perfect-conductor approximation is not valid for TM polarization at any of the wavelengths and is not valid for TE polarization at 0.5 μm.

Diltiazem and reinfarction in patients with non-Q-wave myocardial infarction. Results of a double-blind, randomized, multicenter trial.

Abstract: We performed a multicenter, double-blind, randomized study to evaluate the effect of diltiazem on reinfarction after a non-Q-wave myocardial infarction. Nine centers enrolled 576 patients: 287 received diltiazem (90 mg every six hours) and 289 received placebo. Treatment was initiated 24 to 72 hours after the onset of infarction and continued for up to 14 days. The primary end point, reinfarction, was defined as an abnormal reelevation of MB creatine kinase in plasma within 14 days. Reinfarction occurred in 27 patients in the placebo group (9.3 percent) and in 15 in the diltiazem group (5.2 percent)--a 51.2 percent reduction in cumulative life-table incidence (P = 0.0297; 90 percent confidence interval, 7 to 67 percent). Diltiazem reduced the frequency of refractory postinfarction angina (a secondary end point) by 49.7 percent (P = 0.0345; 90 percent confidence interval, 6 to 73 percent). Mortality was similar in the two groups (3.1 and 3.8 percent, respectively, in the placebo and diltiazem groups), but adverse drug reactions (most of which were mild) were more common in the diltiazem group. Nevertheless, the drug was well tolerated, despite concurrent treatment with beta-blockers in 61 percent of the patients. We conclude that diltiazem was effective in preventing early reinfarction and severe angina after non-Q-wave infarction and that it was also safe and generally well tolerated.

Electoral Laws and Their Political Consequences

Abstract: electoral laws and their political consequences agathon electoral laws and their political consequences agathon series on representation bernard grofman on amazon com free shipping on qualifying offers the aim of this book is to provide an overview of recent research on electoral laws and their political consequences by scholars who have helped shape the field after several decades of virtual neglect except for douglas rae s seminal work, holdings electoral laws and their political consequences electoral laws and their political consequences edited by bernard grofman and arend lijphart jf 1001 e388 1986 electoral participation a comparative analysis edited by richard rose, electoral laws and their political consequences electoral laws and their political consequences grofman bernard and arend lijphart eds electoral laws and their political consequences new york agathon press 1986 feel free to contribute with a summary under comments, electoral laws and their political consequences google books electoral laws and their political consequences electoral laws and their political consequences bernard grofman arend lijphart limited preview 2003 bibliographic information title electoral laws and their political consequences volume 1 of representation series representation vol 1, electoral laws and their political consequences bernard the university of chicago press books division chicago distribution center, electoral laws and their political consequences google books his edited and co edited books include choosing an electoral system praeger 1984 electoral laws and their political consequences agathon press 1986 and parliamentary versus presidential government oxford university press 1992 he has also published numerous articles in leading journals on comparative politics and democratic theory, electoral laws and their political consequences electoral laws and their political consequences author unknown subject electoral laws and their political consequences keywords unknown electoral laws and their political consequences created date 8 2

Cholinergic and GABAergic afferents to the olfactory bulb in the rat with special emphasis on the projection neurons in the nucleus of the horizontal limb of the diagonal band.

Abstract: We have examined the location of cholinergic and GABAergic neurons that project to the rat main olfactory bulb by combining choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) immunohistochemistry with retrograde fluorescent tracing. Since many of the projection neurons are located in subcortical basal forebrain structures, where the delineation of individual regions is difficult, particular care was taken to localize projection neurons with respect to such landmarks as the ventral pallidum (identified on the basis of GAD immunoreactivity), the diagonal band, and medial forebrain bundle. In addition, sections with fluorescent tracers or immunofluorescence were counterstained for Nissl substance in order to correlate tracer or immunopositive neurons with the cytoarchitecture of the basal forebrain. The majority of the cholinergic bulbopetal neurons are located in the medial half of the nucleus of the horizontal limb of the diagonal band (HDB), whereas only a few are located in its lateral half. A substantial number of cholinergic bulbopetal cells are also found in the sublenticular substantia innominata. A small number of cholinergic bulbopetal neurons, finally, are located in the ventrolateral portion of the nucleus of the vertical limb of the diagonal band. At the level of the crossing of the anterior commissure, approximately 17% of the bulbopetal neurons in the HDB are ChAT-positive. The noncholinergic bulbopetal cells are located mainly in the lateral half of the HDB. GAD-containing bulbopetal neurons are primarily located in the caudal part of the HDB, especially in its lateral part. About 30% of the bulbopetal projection neurons in the HDB are GAD-positive. A few GAD-positive bulbopetal cells, furthermore, are located in the ventral pallidum, anterior amygdaloid area, deep olfactory cortex, nucleus of the lateral olfactory tract, lateral hypothalamic area, and tuberomamillary nucleus. The topography of bulbopetal neurons was compared to other projection neurons in the HDB. After multiple injections of fluorescent tracer in the neocortex, retrogradely labeled neurons were concentrated in the most medial part of the HDB, while neurons projecting to the olfactory and entorhinal cortices were located in the ventral part of the HDB. These results show that the cells of the HDB can be divided into subpopulations based upon projection target as well as transmitter content. Furthermore, these subpopulations correspond, at least to a considerable extent, to areas that can be defined on cyto- and fibroarchitectural grounds.

Effect of gamma rays at the dihydrofolate reductase locus: deletions and inversions

Abstract: A series 11 gamma-ray-induced mutants at the dihydrofolate reductase (dhfr) locus in Chinese hamster ovary cells has been examined for the types of DNA sequence change brought about by this form of ionizing radiation. All 11 mutants were found to have suffered major structural changes affecting the dhfr gene. In eight of the mutants, all or part of the dhfr gene has been deleted. The extent of these deletions was examined in seven of these mutants and, for comparison, in two deletion mutants that were induced by UV irradiation. For this purpose, probes from an overlapping set of cosmids that span 210 kb of DNA in this region were used. Three of seven gamma-ray-induced mutants and one UV-induced mutant were shown to have deleted the entire 210-kb region. In the remaining mutants, endpoints ranging from within the dhfr gene to 100 kb downstream were observed. No upstream endpoints were detected, so that an upper limit on the size of these large deletions could not be assigned. Three of the 11 gamma-ray-induced mutants contained an interruption in the dhfr gene without any detectable loss of sequence. Restriction analysis of these interrupted mutants showed that at least 8-14 kb of "foreign" DNA sequence became joined to the gene at the point of disruption. Cytogenetic analysis of these mutants showed that in two cases an inversion of the banding pattern on chromosome Z-2 had taken place. The inverted dhfr mutants contain very low amounts of dhfr RNA sequences, and the 5' end of an inversion mutant gene exhibits the same pattern of DNA methylation and DNase I-hypersensitivity as the wild-type gene. Our results suggest that ionizing radiation causes primarily, if not exclusively, large deletions and inversions in mammalian cells.

Flow Control among Microvessels Coordinated by Intercellular Conduction

Abstract: Optimal distribution of blood flow requires coordination of vasodilation among resistance vessels. During hyperemia, blood vessels dilate upstream from the initiating stimulus. Spreading vasodilation independent of flow changes has not been previously demonstrated. In the present study, iontophoresis of acetylcholine adjacent to single hamster cheek pouch arterioles in situ (diameter, 20 to 37 micrometers) induced a rapid bidirectional dilation that was not attenuated when blood flow was eliminated with vascular occlusion. This finding indicates that a vasodilatory stimulus is conducted along the arteriole and demonstrates the existence of a mechanism of intercellular communication that is capable of coordinating diameter changes among resistance vessels.

Latent variable growth within behavior genetic models.

Abstract: The purpose of this paper is to introduce one kind of latent-variable structural-equation model for multivariate longitudinal data which includes behavioral genetic components. A generic structural-equation model termedRAM (McArdle, J. J. and McDonald, R. P. (1984).Br. J. Math. Stat. Psychol.,37:239–251.) is used to define the univariate twin design, including both covariances and means. This model is extended to multivariate form using a latent-variable growth-curve model recently presented by W. Meredith and J. Tisak [(1984). “Tuckerizing” curves. Psychometric Society Annual Meetings]. The model presented herein further permits hypothesis testing of various biometric models of the sources of these individual differences in latent growth. Aspects of this model are illustrated using the LISREL algorithm [Joreskog, K. G. and Sorbom, D. (1979).Advances in Factor Analysis and Structural Equation Models, Abt Books, Cambridge, Mass.] and longitudinal twin data on early childhood abilities [Wilson, R. S. (1983).Child Dev. 54:298–316].

GABAergic input to cholinergic forebrain neurons: an ultrastructural study using retrograde tracing of HRP and double immunolabeling.

Abstract: Amygdalopetal cholinergic neurons in the ventral pallidum were identified by combining choline acetyltransferase (CUT) immunohistochemistry with retrograde tracing of horseradish peroxidase (HRP) following injections of the tracer in the basolateral amygdaloid nucleus. Although ChAT-positive terminals were identified in the ventral pallidum, they were never seen in contact with either immunonegative or ChAT-positive amygdalopetal neurons. In material, in which immunostaining against glutamic acid decarboxylase (GAD), the synthesizing enzyme for GABA was combined with retrograde tracing of HRP from the basolateral amygdaloid nucleus, GADpositive terminals were seen to contact immunonegative amygdalopetal neurons. In addition, when sections of the rostral forebrain were processed, first to preserve and identify the transported HRP, and then were sequentially tested for both ChAT and GAD immunohistochemistry with the immunoperoxidase reaction for both tissue antigens, GAD-immunopositive terminals were seen to make synaptic contacts with cholinergic amygdalopetal neurons. These results suggest that amygdalopetal, presumably cholinergic, neurons receive GAD-positive terminals. In separate experiments using immunoperoxidase for ChAT and ferritin-avidin for GAD labeling, we confirmed the presence of GAD-containing terminals on cholinergic neurons. In addition, cholinergic terminals were seen in synaptic contact with GADpositive cell bodies. These morphological studies suggest that direct GABAergic-cholinergic and cholinergic-GABAergic interactions take place in the rostral forebrain.

Increases in cerebral interstitial fluid adenosine concentration during hypoxia, local potassium infusion, and ischemia.

Abstract: This study used the brain dialysis technique to test the hypothesis that the adenosine concentration of cerebral interstitial fluid increases during situations in which cerebral oxygen supply is inadequate for oxygen demand Sealed 300-micron hollow dialysis fibers were implanted in the caudate nucleus of pentobarbital-anesthetized rats and perfused at 2 microliter/min with artificial cerebrospinal fluid In vitro tests indicated the recovery of adenosine, inosine, and hypoxanthine from the external medium to be approximately 20% at 2 microliter/min and close to 100% at 01 microliter/min Three in vivo interventions were tested: hypoxia/hypotension (PaO2 = 419 mm Hg; MABP = 428 mm Hg; n = 9), local potassium infusion (n = 4), and cerebral anoxia/ischemia (n = 10) These interventions produced 10-, 4-, and 30-fold increases in perfusate adenosine concentration, respectively, as well as increases in perfusate concentrations of inosine and hypoxanthine A separate group of rats (n = 9) perfused at 01 microliter/min yielded estimates of cerebral interstitial fluid adenosine, inosine, and hypoxanthine concentrations of 126, 330, and 719 microM, respectively These results are consistent with the adenosine hypothesis for the regulation of CBF

On-the-Job Experience and Skill at Detecting Deception1

Abstract: The role of on-the-job experience in fostering skill at detecting deception was examined. A deception-detection test was administered to three samples of more than 100 subjects each: a group of undergraduates with no special experiences at detecting deceit; a group of new recruits to a federal law enforcement training program, who had some limited on-the-job experience at detecting deceit; and a group of advanced federal law enforcement officers, with years of experience working at jobs in which the detection of deception is very important. Although the officer samples were more confident about their judgments of deceptiveness than were the students, they were no more accurate than the students. None of the three groups showed a significant improvement in deception-detection success from the first half to the second half of the test; however, the advanced officers felt increasingly confident about their performance as they progressed through the test. Correlational analyses of the relationship between accuracy and confidence provided further evidence that experience does not improve people's awareness oi the accuracy or inaccuracy of their judgments. The findings from this research are compared to the results of research on other kinds of professional decision-makers (e.g., clinical psychologists), and several theoretical perspectives on the role of experience in decision making are discussed.

Serum insulin-like growth factors I and II concentrations and growth hormone and insulin responses to arginine infusion in children with protein-energy malnutrition before and after nutritional rehabilitation.

Abstract: Serum insulin, growth hormone (GH), insulin-like growth factors (IGFs) I and II, cortisol, and albumin concentrations were measured in 15 children with kwashiorkor, 15 with marasmic-kwashiorkor, and 21 with marasmus, before and in the survivors, after nutritional rehabilitation, as well as in 10 underweight and eight normal Egyptian children. We also evaluated arginine-induced insulin and GH secretion. IGF-I concentrations were reduced in the three severely malnourished groups (0.07 ± 0.03, 0.05 ± 0.03, and 0.09 ± 0.09 U/ml, respectively) but returned to normal after refeeding. IGF-II concentrations were low in the kwashiorkor (175 ± 79 ng/ml), marasmic-kwashiorkor (111 ± 57 ng/ml), and marasmic children (128 ± 70.9 ng/ml) and returned to normal after nutritional rehabilitation. Basal GH levels were high in the three severely malnourished groups (21.9, 28.8, and 16.6 ng/ml, respectively) and returned to normal after refeeding (8.1, 6.5, and 6.0 ng/ml, respectively). GH responses to arginine were depressed in the three malnourished groups and improved significantly in marasmic-kwashiorkor and marasmic children after nutritional rehabilitation. Insulin responses to arginine were impaired in kwashiorkor, and marasmic-kwashiorkor children and improved significantly after refeeding. IGF-I levels correlated significantly with percent of expected weight (r=0.52, p<0.001), percent of expected height (r=0.42, p<0.001), and weight/ (height)2 index (r=0.34, p<0.01). IGF-I levels correlated positively with insulin levels (r=0.421, p<0.001) and negatively with cortisol concentrations (r=—0.400, p<0.001). It is suggested that effective lipolysis mediated by high GH and possibly low IGF levels, is an important adaptive mechanism to assure fuel (fatty acids) supply for metabolism of brain and peripheral tissues during nutritional deprivation.

Changes in the numerical density of synaptic contacts with long-term potentiation in the hippocampal dentate gyrus

Abstract: Long-term potentiation (LTP) in the rat dentate gyrus is a multifaceted phenomenon, including synaptic potentiation; simultaneous synaptic depression at neighboring, unconditioned synapses; and a change in the amount of cell firing produced by a specified amount of synaptic current (see Levy and Desmond: In G. Buzsaki and C. Vanderwolf (eds): Electrical Activity of The archicortex. Budapest: Akademiai Kiado, pp. 359–373, ′85b). This study presents long-term anatomical modifications that seem related to excitatory synaptic modification. These anatomical alterations appear early and persist for at least 60 minutes following conditioning stimulation. Each animal received test pulse stimulation delivered alternately to the angular bundles before and after brief, unilateral high-frequency conditioning stimulation that is typical of many LTP paradigms. Anataomical preparation followed standard procedures. Double-blind scoring procedures quantified the number of asymmetric synapses in the dentate molecular layer. These counts were converted to the number of synapses per unit volume using stereological corrections that combined geometrically derived theory and modest serial sectioning. Multivariate analysis of variance evaluated the statistical significance of changes in synapse density. Across all three groups of animals, conditioning stimulation does not significantly change the density of synaptic contacts across the entire molecular layer. There is a trend for a decreased density of synaptic contacts in the middle molecular layer, the region activated by the conditioning stimulation. Here the density of concave spine profiles increases significantly in all three groups of animals with conditioning stimulation. This increase accompanies significant decreases in the density of nonconcave, simple and ellipsoid, spine profiles. No significant changes in the density of shaft synapses occur with LTP-inducing conditioning stimulation. These data suggest that the concave spine profiles are a correlate of LTP-inducing stimulation and may be the potentiated synapses. We hypothesize that with synaptic potentiation there occurs an interconversion of spine synapses such that some nonconcave spine profiles become concave spine profiles. Such an interconversion apparently begins shortly after the conditioning stimulation and persists for at least 60 minutes.

The prevalence and clinical significance of residual myocardial ischemia 2 weeks after uncomplicated non-Q wave infarction: a prospective natural history study.

Abstract: Despite having smaller infarct size and better left ventricular function, patients with non-Q wave myocardial infarction (NQMI) appear to have an unexpectedly high long-term mortality that is ultimately comparable to that of patients with Q-wave myocardial infarction (QMI). Patients with NQMI may lose their initial prognostic advantage because there is more viable tissue in the perfusion zone of the infarct-related vessel, rendering myocardium more prone to reinfarction. We tested this hypothesis in a prospective study of 241 consecutive patients 65 years of age or younger with acute uncomplicated myocardial infarction confirmed by creatine kinase levels (MB fraction). All patients received customary care and none underwent thrombolytic therapy or emergency angioplasty. Predischarge coronary angiography, radionuclide ventriculography, 24 hr Holter monitoring, and quantitative thallium-201 (201T1) scintigraphy during treadmill exercise were performed 10 +/- 3 days after infarction. Infarcts were designated as QMI (n = 154) or NQMI (n = 87) by accepted criteria applied to serial electrocardiograms obtained on days 1, 2, 3, and 10. The baseline Norris coronary prognostic index, angiographic jeopardy scores, and prevalence of Lown grade ventricular arrhythmias were similar between groups despite evidence for less necrosis with NQMI vs QMI, reflected by lower peak creatine kinase levels (520 vs 1334 IU/liter; p = .0001, 4 hr sampling), higher resting left ventricular ejection fraction (53% vs 46%; p = .0001), fewer akinetic or dyskinetic segments (1.2 vs 2.4; p = .0001), and fewer persistent 201Tl defects in the infarct zone (0.9 vs 1.9; p = .0001). Patients with NQMI also had more patent infarct-related vessels (54% vs 25%; p less than .0001) and a shorter time from onset of infarction to peak creatine kinase level (16.9 vs 22.5 hr; p = .0001). Importantly, the prevalence and extent of quantitatively determined 201Tl redistribution within the infarct zone on exercise scintigraphy was greater in patients with NQMI vs those with QMI (60% vs 36%, p = .007; and 0.98 vs 0.53 myocardial segments, p = .0003); when the two groups were stratified on the basis of the infarct-related vessel, subset analysis revealed the same findings. During 30 months median follow-up, cardiac mortality was low, 8.4% in the QMI group and 9.2% in the NQMI group (p = NS).(ABSTRACT TRUNCATED AT 400 WORDS)

Differential localization of MAP-2 and tau in mammalian neurons in situ.

Abstract: Microtubules are one of the major constituents of the neuronal cytoskeleton. Although it is generally accepted that these linear polymers play an important role in regulating cell morphology and intracellular transport processes, the mechanisms that dictate their assembly, their interactions with each other, as well as their interactions with other cytoplasmic structures are poorly understood. In addition to their dimeric tubulin subunits, microtubules contain numerous accessory proteins known collectively as microtubule-associated proteins (MAPs).' It is thought that the MAPs control the dimer-polymer equilibrium' and mediate the interaction of microtubules with other cytoskeletal elements and cytoplasmic organelle^.^^ Therefore, it is likely that the MAP composition of microtubules will affect not only microtubule stability but also the structure and stability of the surrounding cytoplasmic elements with which these microtubules interact. Most of what is currently understood regarding microtubule stability stems from studies performed on microtubules isolated by repetitive cycles of in vitro assembly' from soluble adult brain extracts. Initial homogenization of adult whole brain results in the simultaneous mixing of many regions, cell types (neurons and glia), and cell compartments (dendrites and axons) that in turn, results, upon purification by assembly-disassembly procedures, in a composite microtubule polymer containing as many as 21 tubulin isoforms' and numerous MAPS.'~'' In vitro analyses of brain microtubule assembly have definitively demonstrated that two MAPs, MAP-2 (MI > 300,000)\" and tau (MI 55-62,000)L2 stimulate assembly stoichiometrically and can displace each other from binding sites on microtubules (Kim et al., this volume). Results such as these lead one to speculate whether or not these two proteins are present on the same microtubule in situ and raise the possibility that they may be differentially compartmentalized in brain tissue. In this regard, MAP-2 is known to be a predominantly dendritic protein,\"-\" whereas the distribution of tau in brain tissue has not been previously reported. Because different neuronal cell compartments perform different tasks, an understanding of microtubule function requires the precise localization of MAP-2 and tau to specific cell compartments and subclasses of microtubules. To this end, the present monograph outlines our initial immunohistochemical and biochemical localization experiments using monoclonal antibodies to MAP-2 and tau in both adult and developing brain.

Changes in the postsynaptic density with long-term potentiation in the dentate gyrus.

Abstract: The present study documents alterations in the size of the postsynaptic density (PSD) of synapses formed by entorhinal afferents with granule cell dendritic spines with long-term potentiation (LTP). These changes appear early and persist for at least 60 minutes after LTP-inducing conditioning stimulation. Each animal received test and conditioning stimulation typical of LTP paradigms. Electron microscopic preparation of the dentate gyri from each animal followed conventional procedures. PSD trace lengths of identified asymmetric synaptic profiles were measured. The total PSD length for four categories of synaptic profiles was determined for each third of the molecular layer. PSD surface area per unit volume of tissue (Sv) was then computed from these data. Statical analysis of the Sv data used multivariate analysis of variance. PSD surface area per synapse was also estimated. Total PSD surface area per unit volume does not change significantly throughout the entire molecular layer with LTP-inducing conditioning stimulation. However, in the activated portion of the molecular layer, total PSD surface area per unit volume tends to increase with conditioning stimulation. In the middle third of the molecular layer, total PSD surface area per unit volume associated with the concave spine profiles increases significantly while there is a statistically significant decrease in total PSD Sv associated with the nonconcave spine profiles. The PSD surface area per synapse also increases markedly. Since it seems that there is an interconversion of spine synapses from nonconcave to concave with LTP (Desmond and Levy: J. Comp. Neurol. In press, ′86a), these data suggest that potentiated synapses have larger responses because, in part, they have larger neurotransmitter receptive regions.

Neurovascular anatomy and elbow arthroscopy: Inherent risks

Abstract: Five cadaver elbows were examined arthroscopically. Detailed dissections of superficial cutaneous nerves and of deeper neurovascular structures were carried out either before or after arthroscopic examination. Normal neurovascular anatomy and variants were defined in relation to standard portal placement. The danger of neurovascular injury is emphasized due to inappropriate portals, direction of entry, or elbow position. A safe, reliable, and reproducible technique is defined.

Academic Achievement of Children with Epilepsy

Abstract: The academic achievement scores of 122 children with epilepsy were examined in relation to demographic and clinical seizure variables. As a group, these children were making less academic progress than expected for their age and IQ level. Academic deficiencies were greatest in arithmetic, followed by spelling, reading, comprehension, and word recognition. Results of the multiple regression analyses indicated a modest combined predictive significance of the demographic and clinical seizure variables for academic performance. In addition, the magnitude of these relationships varied by academic area. Among the individual variables examined the strongest correlates of academic performance were age of the child, age of seizure onset, lifetime total seizure frequency, and presence of multiple seizures (absence and tonic-clonic). These results are discussed in relation to developing an understanding of the factors which underlie academic vulnerability in children with epilepsy.

Differential dissolution of a Pleistocene reef in the ground-water mixing zone of coastal Yucatan, Mexico

Abstract: A geochemical explanation is provided for the extensive dissolution observed along the carbonate coast of the Yucatan Peninsula, Mexico. Mixing of fresh ground water with subterranean Caribbean seawater generates a highly reactive geochemical zone that enhances aragonite and calcite dissolution and permits neomorphism of aragonite. Mixing-zone dissolution caused by ground-water discharge is a major geomorphic process in developing caves, coves, and crescent-shaped beaches along the Yucatan coast. Such dissolution has probably been a significant control on permeability and porosity distribution in carbonate rocks in the geologic record.