Retrograde degeneration of neurite membrane structural integrity of nerve growth cones following in vitro exposure to mercury.

Inhalation of mercury vapor (Hg0) inhibits binding of GTP to rat brain tubulin, thereby inhibiting tubulin polymerization into microtubules. A similar molecular lesion has also been observed in 80% of brains from patients with Alzheimer disease (AD) compared to age-matched controls. However the precise site and mode of action of Hg ions remain illusive. Therefore, the present study examined whether Hg ions could affect membrane dynamics of neurite growth cone morphology and behavior. Since tubulin is a highly conserved cytoskeletal protein in both vertebrates and invertebrates, we hypothesized that growth cones from animal species could be highly susceptible to Hg ions. To test this possibility, the identified, large Pedal A (PeA) neurons from the central ring ganglia of the snail Lymnoea stagnalis were cultured for 48 h in 2 ml brain conditioned medium (CM). Following neurite outgrowth, metal chloride solution (2 microl) of Hg, Al, Pb, Cd, or Mn (10(-7) M) was pressure applied directly onto individual growth cones. Time-lapse images with inverted microscopy were acquired prior to, during, and after the metal ion exposure. We demonstrate that Hg ions markedly disrupted membrane structure and linear growth rates of imaged neurites in 77% of all nerve growth cones. When growth cones were stained with antibodies specific for both tubulin and actin, it was the tubulin/microtubule structure that disintegrated following Hg exposure. Moreover, some denuded neurites were also observed to form neurofibrillary aggregates. In contrast, growth cone exposure to other metal ions did not effect growth cone morphology, nor was their motility rate compromised. To determine the growth suppressive effects of Hg ions on neuronal sprouting, cells were cultured either in the presence or absence of Hg ions. We found that in the presence of Hg ions, neuronal somata failed to sprout, whereas other metalic ions did not effect growth patterns of cultured PeA cells. We conclude that this visual evidence and previous biochemical data strongly implicate Hg as a potential etiological factor in neurodegeneration.

Development and evaluation of a Research Project Program for medical students at the University of Calgary Faculty of Medicine.

This essay outlines the development and evaluation of the Research Project Program (RPP) ten years after its introduction into the medical curriculum at the University of Calgary. The RPP consists of two mandatory for-credit courses. Students have the option of conducting either two smaller independent research projects or one larger project over the two years. At the end of the second-year course the students complete an evaluation of the RPP in which they are asked to assess and comment upon various aspects of the program. The authors compared data available from years one (the class of 1990) and ten (the class of 2000) and found significant differences between the two classes' approaches to the RPP. Most of the class of 2000 (89%) carried out two-year independent in-depth research projects spanning a wide range of topics. Half of these projects involved individual collection and analyses of data using experimental methods; this represented a 2.25-fold increase over the first year of the program. In the class of 2000, 44% of students presented their results at a newly implemented research symposium; an additional 22% of students presented their results at local, national, or international meetings. Further, 59% of the class of 2000 had either submitted or were planning to submit their research for peer-reviewed publication. In contrast, none of the students of the class of 1990 formally presented their research, and only 11% planned to submit their research findings for publication. The RPP has evolved in the ten years since its implementation, but the authors believe the program continues to foster independent learning and analytic and problem-solving skills.

Cuing effect of "all of the above" on the reliability and validity of multiple-choice test items.

It is generally acknowledged that alternatives such as none of the above and all of the above should be used sparingly in multiple-choice (MC) items. But the effect that all of the above has on the reliability and validity of an MC item is unclear. This study compared the results of a single-response (SRa) item format that included all of the above as the correct response to a multiple-response (MR) item format that required examinees to select all of the available alternatives for a correct response. A crossover design was used to compare the effect of formats on student performance while item content, scoring method, and student ability levels remained constant. Results indicated that the SRa format greatly distorted examinee performance by elevating their scores because examinees who recognized two or more alternatives as being correct were cued to select all of the above. In addition, the SRa format significantly reduced the reliability and concurrent validity of examinee scores. In summary, the MR format was found to be superior. Based upon new empirical evidence, this study recommends that whenever an educator wishes to evaluate student understanding of an issue that has multiple facts, the SRa format should be avoided and the MR format should be used instead.

Mercury from maternal "silver" tooth fillings in sheep and human breast milk. A source of neonatal exposure.

Neonatal uptake of mercury (Hg) from milk was examined in a pregnant sheep model, where radioactive mercury (Hg203)/silver tooth fillings (amalgam) were newly placed. A crossover experimental design was used in which lactating ewes nursed foster lambs. In a parallel study, the relationship between dental history and breast milk concentration of Hg was also examined in 33 lactating women. Results from the animal studies showed that, during pregnancy, a primary fetal site of amalgam Hg concentration is the liver, and, after delivery, the neonatal lamb kidney receives additional amalgam Hg from mother's milk. In lactating women with aged amalgam fillings, increased Hg excretion in breast milk and urine correlated with the number of fillings or Hg vapor concentration levels in mouth air. It was concluded that Hg originating from maternal amalgam tooth fillings transfers across the placenta to the fetus, across the mammary gland into milk ingested by the newborn, and ultimately into neonatal body tissues. Comparisons are made to the U. S. minimal risk level recently established for adult Hg exposure. These findings suggest that placement and removal of "silver" tooth fillings in pregnant and lactating humans will subject the fetus and neonate to unnecessary risk of Hg exposure.

Mercury vapor inhalation inhibits binding of GTP to tubulin in rat brain: similarity to a molecular lesion in Alzheimer diseased brain.

Hg2+ interacts with brain tubulin and disassembles microtubules that maintain neurite structure. Since it is well known that Hg vapor (Hg0) is continuously released from "silver" amalgam tooth fillings and is absorbed into brain, rats were exposed to Hg0 4h/day for 0, 2, 7, 14 and 28 d at 250 or 300 micrograms Hg/m3 air, concentrations present in mouth air of some humans with many amalgam fillings. Average rat brain Hg concentrations increased significantly (11-47 fold) with duration of Hg0 exposure. By 14 d Hg0 exposure, photoaffinity labelling on the beta-subunit of the tubulin dimer with [alpha 32P] 8N3 GTP in brain homogenates was decreased 41-74%, upon analysis of SDS-PAGE autoradiograms. The identical neurochemical lesion of similar or greater magnitude is evident in Alzheimer brain homogenates from approximately 80% of patients, when compared to human age-matched neurological controls. Total tubulin protein levels remained relatively unchanged between Hg0 exposed rat brains and controls, and between Alzheimer brains and controls. Since the rate of tubulin polymerization is dependent upon binding of GTP to tubulin dimers, we conclude that chronic inhalation of low-level Hg0 can inhibit polymerization of brain tubulin essential for formation of microtubules.

Metallothionein induction in fetal rat brain and neonatal primary astrocyte cultures by in utero exposure to elemental mercury vapor (Hg0).

Brain metallothionein (MT) protein and mRNA levels were determined in the fetal rat following in utero (gestational days 7-21) exposure to elemental mercury vapor (Hg0; 300 microg Hg/m3; 4 h/day). Total RNA was probed on Northern blots with [alpha-32P]dCTP-labeled synthetic cDNA probes specific for rat MT isoform mRNAs. The probes for MT-I and MT-II mRNA hybridized to a single band of approximately 550 and 450 nucleotides, respectively. Expression of whole brain MT-I mRNA in full-term fetal rats (day 21) was significantly increased (P < 0.03) by in utero exposure to Hg0 compared to nonexposed controls. This corresponded to a 14-fold increase (P < 0.001) in fetal brain Hg concentration after in utero Hg0 exposure. In addition, astrocytes from both control and in utero Hg0-exposed fetuses were isolated, and neonatal primary astrocyte cultures were established and maintained in vitro for up to 3 weeks without additional experimental intervention. Astrocyte monolayers derived from in utero Hg0-exposed fetuses consistently expressed increased abundance of MT-I mRNA transcripts after 1, 2, and 3 weeks in culture (P < 0.03, P < 0.01, and P < 0.03, respectively) compared with controls. The abundance of astrocyte MT-II mRNA was unchanged at 1 and 2 weeks in culture, but was significantly increased at 3 weeks in cultures derived from brains of Hg0-exposed fetuses (P < 0.04). Consistent with the increase in MT mRNA, an increase in astrocytic levels of MT proteins was noted by Western blot analysis and MT-immunoreactivity. These studies suggest that in utero exposure to Hg0 induces brain MT gene expression, and that MT mRNAs and their respective proteins are useful quantitative biochemical markers of intrauterine exposure to Hg0, a potentially cytotoxic challenge to astrocytes in the developing brain. It is concluded that induction of MT by fetal/neonatal astrocytes represents an attempt by these glial cells to protect against Hg cytotoxicity in maintaining cerebral homeostasis.

Relationship between Myers-Briggs Type Indicator and Gregorc Style Delineator.

The relationship between the Myers-briggs Type Indicator and Gregorc Style Delineator, and achievement was examined by administering these instruments to 259 first-year nursing students enrolled in an introductory human anatomy and physiology course. A principal component factor analysis using a varimax rotation of the scores from the two psychometric instruments, achievement examinations and an over-all grade point average indicated that each learning style from the Gregorc Style Delineator corresponds to certain traits on the Myers-Briggs Type Indicator. An individual who had a preference for the learning style of Concrete Sequential tended to have the traits of sensing and judging on the Myers-Briggs Type Indicator, while an individual who used the learning style of Concrete Random tended to have the traits of intuition and perceiving on the Myers-Briggs Type Indicator. One who had a preference for the learning style of Abstract Sequential tended to use the trait of thinking while another who used the learning style of Abstract Random tended to have the trait of feeling. The factor analysis also indicates no relationship of any scores of the traits on the Myers-Briggs Type Indicator or learning styles of the Gregorc Style Delineator with the examination scores achieved in the human anatomy and physiology course or to the students' over-all grade point average. However, factor analysis indicates that the Myers-Briggs Type Indicator traits of Judging vs Perceiving collapsed into the Sensing vs Intuition scale, and that the Gregorc Style Delineator consists of two bipolar scales that are different from those proposed by Gregorc.

Relationship between Myers-Briggs psychological traits and use of course objectives in anatomy and physiology.

The results from the Myers-Briggs Type Indicator (MBTI), which identified preferred psychological traits for 131 nursing students, were compared to their usage levels of course objectives in an undergraduate course in anatomy and physiology. The three usage levels (user, occasional user, and nonuser) were also compared to exam scores in the course, overall grade point averages (GPA) in first-year nursing, and the various psychological traits measured by the MBTI. A multivariate analysis of variance (MANOVA) indicated that users of objectives achieved significantly higher exam scores and maintained a higher GPA than occasional and nonusers. The MANOVA also indicated that users of course objectives preferred a sensing judging modality, whereas nonusers preferred an intuiting perceiving style to guide their studying and learning.

Gregorc learning styles and achievement in anatomy and physiology.

Results from the Gregorc Style Delineator (GSD), administered to 260 undergraduate nursing students, were compared with achievement scores in a human anatomy and physiology course. Factor analysis and VARIMAX rotation demonstrate that there is no relationship between any of the four learning styles allegedly identified by the GSD and achievement in anatomy and physiology. Factor analysis also shows that the GSD measures only a single bipolar scale of sequential vs. random ability rather than two bipolar scales comprising four learning styles, as suggested by Gregorc. These findings question the validity of the GSD and recommend discontinuing its use as an indicator of learning styles.

Myers-Briggs psychological type and achievement in anatomy and physiology.

Results from the Myers-Briggs Type Indicator (MBTI) for 259 nursing students were compared with their achievement on examinations in an undergraduate course in anatomy and physiology. Factor analysis demonstrated that no relationship existed between any of the eight individual personality traits purported to be measured by MBTI (i.e., E, Extrovert; I, Introvert; S, Sensing; N, Intuition; T, Thinking; F, Feeling; J, Judging; P, Perceiving) and examination scores in this course. The analysis also showed that the bipolar scales S vs. N and J vs. P collapsed into a single bipolar scale (S/J vs. N/P). This means that the MBTI is only capable of measuring three bipolar scales of personality traits instead of four scales as currently claimed. Contrary to other findings, results from an analysis of variance revealed no meaningful relationship between course achievement and psychological types.

Mercury exposure from "silver" tooth fillings: emerging evidence questions a traditional dental paradigm.

For more than 160 years dentistry has used silver amalgam, which contains approximately 50% Hg metal, as the preferred tooth filling material. During the past decade medical research has demonstrated that this Hg is continuously released as vapor into mouth air; then it is inhaled, absorbed into body tissues, oxidized to ionic Hg, and finally covalently bound to cell proteins. Animal and human experiments demonstrate that the uptake, tissue distribution, and excretion of amalgam Hg is significant, and that dental amalgam is the major contributing source to Hg body burden in humans. Current research on the pathophysiological effects of amalgam Hg has focused upon the immune system, renal system, oral and intestinal bacteria, reproductive system, and the central nervous system. Research evidence does not support the notion of amalgam safety.

The dental amalgam mercury controversy--inorganic mercury and the CNS; genetic linkage of mercury and antibiotic resistances in intestinal bacteria.

Mercury (Hg) vapor exposure from dental amalgam has been demonstrated to exceed the sum of all other exposure sources. Therefore the effects of inorganic Hg exposure upon cell function in the brain and in the intestinal bacteria have recently been examined. In rats we demonstrate that ADP-ribosylation of tubulin and actin brain proteins is markedly inhibited, and that ionic Hg can thus alter a neurochemical reaction involved with maintaining neuron membrane structure. In monkeys we show that Hg, specifically from amalgam, will enrich the intestinal flora with Hg-resistant bacterial species which in turn also become resistant to antibiotics.

ADP-ribosylation of brain neuronal proteins is altered by in vitro and in vivo exposure to inorganic mercury.

ADP-ribosylation is an essential process in the metabolism of brain neuronal proteins, including the regulation of assembly and disassembly of biological polymers. Here, we examine the effect of HgCl2 exposure on the ADP-ribosylation of tubulin and actin, both cytoskeletal proteins also found in neurons, and B-50/43-kDa growth-associated protein (B-50/GAP-43), a neuronal tissue-specific phosphoprotein. In rats we demonstrate, with both in vitro and in vivo experiments, that HgCl2 markedly inhibits the ADP-ribosylation of tubulin and actin. This is direct quantitative evidence that HgCl2, a toxic xenobiotic, alters specific neurochemical reactions involved in maintaining brain neuron structure.

Measurement of total mercury in biological specimens by cold vapor atomic fluorescence spectrometry.

An ultrasensitive method for determining total mercury concentrations in biological specimens is a prerequisite for monitoring exposure to chronic low-dose levels of Hg vapor such as those from dental silver amalgam fillings. The clinical consequences of such doses are currently in question. We describe an adaptation of a two-stage gold amalgamation preconcentration step combined with cold vapor atomic fluorescence spectrometric detection for Hg. At Hg concentrations of 40 and 350 nmol/L, the within-day assay CVs were 5% and 3%, respectively; between-day assay CVs were 8% and 5%, respectively. Accuracy, as demonstrated by analytical recovery, ranged from 98% to 105%. The detection limit for the assay is 50 pmol/L, which is suitable for measuring total Hg concentrations in specimens of human urine, blood, and breast milk, and in monkey kidney cortex and feces, obtained from subjects with and without amalgam fillings.

Mercury released from dental "silver" fillings provokes an increase in mercury- and antibiotic-resistant bacteria in oral and intestinal floras of primates.

In a survey of 640 human subjects, a subgroup of 356 persons without recent exposure to antibiotics demonstrated that those with a high prevalence of Hg resistance in their intestinal floras were significantly more likely to also have resistance to two or more antibiotics. This observation led us to consider the possibility that mercury released from amalgam ("silver") dental restorations might be a selective agent for both mercury- and antibiotic-resistant bacteria in the oral and intestinal floras of primates. Resistances to mercury and to several antibiotics were examined in the oral and intestinal floras of six adult monkeys prior to the installation of amalgam fillings, during the time they were in place, and after replacement of the amalgam fillings with glass ionomer fillings (in four of the monkeys). The monkeys were fed an antibiotic-free diet, and fecal mercury concentrations were monitored. There was a statistically significant increase in the incidence of mercury-resistant bacteria during the 5 weeks following installation of the amalgam fillings and during the 5 weeks immediately following their replacement with glass ionomer fillings. These peaks in incidence of mercury-resistant bacteria correlated with peaks of Hg elimination (as high as 1 mM in the feces) immediately following amalgam placement and immediately after replacement of the amalgam fillings. Representative mercury-resistant isolates of three selected bacterial families (oral streptococci, members of the family Enterobacteriaceae, and enterococci) were also resistant to one or more antibiotics, including ampicillin, tetracycline, streptomycin, kanamycin, and chloramphenicol. While such mercury- and antibiotic-resistant isolates among the staphylococci, the enterococci, and members of the family Enterobacteriaceae have been described, this is the first report of mercury resistance in the oral streptococci. Many of the enterobacterial strains were able to transfer mercury and antibiotic resistances together to laboratory bacterial recipients, suggesting that the loci for these resistances are genetically linked. Our findings indicate that mercury released from amalgam fillings can cause an enrichment of mercury resistance plasmids in the normal bacterial floras of primates. Many of these plasmids also carry antibiotic resistance, implicating the exposure to mercury from dental amalgams in an increased incidence of multiple antibiotic resistance plasmids in the normal floras of nonmedicated subjects.

Mercury from dental "silver" tooth fillings impairs sheep kidney function.

In humans Hg vapor is released from "silver" amalgam fillings that contain 50% Hg by weight. Previous studies show that when 12 such fillings are placed in sheep teeth, the kidneys will concentrate amalgam Hg at levels ranging from 5 to 10 micrograms Hg/g renal tissue 4-20 wk after placement. In the present study 12 occlusal fillings were placed in each of six adult female sheep under general anesthesia, using standard dental procedures. Glass ionomer occlusal fillings (12) were inserted in two control sheep. At several days before dental surgery, and at 30 and 60 days after placement of fillings, renal function was evaluated by plasma clearance of inulin and by plasma and urine electrolytes, urea, and proteins. An average plasma inulin clearance rate of 69.5 +/- 7.2 ml/min before amalgam placement was reduced to 32.3 +/- 8.1 ml/min by 30 days and remained low at 27.9 +/- 8.7 ml/min after 60 days. Inulin clearance did not change in controls. After amalgam placement urine concentration of albumin decreased from 93.0 +/- 20.5 to 30.1 +/- 15.3 mg/l and urine Na+ concentration increased steadily from 24.8 +/- 7.7 to 82.2 +/- 20.3 mmol/l at 60 days. Concentrations of K+, urea, gamma-glutamyl transpeptidase, alkaline phosphatase, and total protein did not change significantly from 0 to 60 days in urine. Plasma levels of Na+, K+, urea, and albumin remained unchanged from 0 to 60 days after amalgam. Renal histology remained normal in amalgam-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)