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Biomedical subjects

H D Cohen

Publications and source records attributed to H D Cohen.

At least 19 recordsLinked to original sources
PubMed1996

Nocturnal melatonin levels in human volunteers exposed to intermittent 60 Hz magnetic fields.

Two double-blind laboratory-based studies were performed to determine whether a suppression of nocturnal melatonin similar to that observed in rodents occurs when humans are exposed to magnetic fields at night. In study 1, 33 men were exposed to sham, 10 mG, or 200 mG intermittent, circularly polarized magnetic fields from 2300 to 0700 h under controlled environmental and exposure test conditions. Overall, exposure had no effect on melatonin levels. Men with preexisting low levels of melatonin, however, showed significantly greater suppression of melatonin when they were exposed to light and also when they were exposed to the 200 mG magnetic-field condition. Study 2 directly tested the hypothesis that low-melatonin subjects show enhanced sensitivity when exposed to light and to 200 mG magnetic fields. After preexposure screening, each of 40 men slept in the exposure facility on two nights. On one night, the men were sham exposed. On the other night, they were exposed to the 200 mG field condition used previously. Again, exposure had no overall effect on melatonin levels. The original finding of enhanced sensitivity in low-melatonin subjects was not replicated in this study. We conclude that the intermittent exposure conditions used in these two studies were not effective in altering nocturnal melatonin release patterns in human volunteers. Further research is underway with regard to exposure parameters, hormonal and immune system measures, and individual differences.

Adolescent↗
PubMed1996

The amino terminus of Cdk2 binds p21.

The cyclin-dependent kinase (Cdk) inhibitor known as p21, which is transcriptionally regulated by p53, can induce G1 arrest when overexpressed and inhibit the kinase activity of a wide variety of cyclin-Cdk complexes. Previous studies have demonstrated that a portion of the conserved region of p21 (amino acids 46-78), which is homologous to similar regions in the related Cdk inhibitors p27 and p57, can bind to Cdk2, and that this region is essential for kinase inhibition. However, the site(s) on Cdk2 that are involved in p21 binding have not been identified. We therefore created mutant Cdk2 molecules with various N-terminal and C-terminal deletions and tested each for their ability to bind to p21 by the yeast two-hybrid and the double-tagging assays. None of the deletion mutants tested bound to p21 by either assay. We next tested whether p21 could bind to Cdk7, a component of the cyclin-activating kinase complex. By both the double-tagging and yeast two-hybrid assays, p21 failed to bind to this protein, consistent with previous reports. However, hybrid molecules consisting of the amino-terminal half of Cdk2 and the carboxy-terminal half of Cdk7 (Cdk2/Cdk7) could bind to p21 by both assays, whereas the Cdk7/Cdk2 hybrids could not. Furthermore, the yeast Cdc28 protein, which is 65% identical with Cdk2, failed to bind to p21 by both the yeast two-hybrid and double-tagging assays. Cdk2/Cdc28 hybrids but not Cdc28/Cdk2 hybrids could bind to p21. These results suggest that the amino-terminal half of Cdk2 is important for p21 binding, consistent with the recently published crystal-lographic data. Our data also suggest that the three-dimensional structure of Cdk2 is likely altered by creating deletion mutants from either the amino- or carboxy-terminal end of the protein. Finally, we have mutated the Cdc28/Cdk2 hybrid protein and isolated several mutants, which are able to bind to p21. This approach may be useful for identifying residues in Cdk2 and Cdc28 that affect their ability to bind to p21 and complement the crystallographic data.

Amino Acid Sequence↗
PubMed1995

Smoking and EEG power spectra: effects of differences in arousal seeking.

Reversal theory, a general theory of motivation, emotion and action, has recently been shown to predict lapses in smoking cessation. Individuals are less likely to lapse if they are in the telic (serious-minded, arousal avoidant, goal-oriented) state than when they are in the paratelic (playful, arousal seeking, spontaneous) state. The literature indicates that people can smoke in such a way as to either increase or decrease central nervous system arousal; smoking in the telic and paratelic states might therefore differentially affect the resting electroencephalograph, as quantified by Fast Fourier Transform analysis. The basic hypothesis was supported. Theta power was decreased when subjects in the telic state smoked, while beta 2 power was increased when subjects in the paratelic state smoked; the latter finding was, however, true only for men. The results have important implications for research on changing health behaviors and for smoking cessation programs.

Adolescent↗
PubMed1995

Periodontal treatment needs and oral hygiene among Ethiopian immigrants.

Periodontal disease studies in developing countries over the past four decades indicate periodontitis to be a major problem, even in populations with relatively low caries rates. The aim of this study was to document levels of periodontal treatment needs, as well as oral hygiene levels for a large sample covering all ages of an Ethiopian Jewish population recently immigrated into Israel. Over 800 subjects from the total of 15,000 Ethiopians who immigrated were examined utilising the PTNS Index and the OHI-S Index. Results indicate that all the examined population was in need of oral hygiene instruction. Almost 80 per cent are in need of scaling and approximately 20 per cent are in need of more complex treatment such as surgery. Significant differences were found according to age. This could be attributed to the high OHI-S scores, ranging from 2.53 at age 0-12 to 4.82 at the 51+ age group, with a mean Debris Index of 2.12 for the total population. It is suggested that this population should be exposed immediately to preventive and treatment programmes to improve oral hygiene and decrease needs for future, costly periodontal treatment.

Adolescent↗
PubMed1994

Dose response study of human exposure to 60 Hz electric and magnetic fields.

This human exposure study examined the relationship between field strength and biological response and tested whether the exposure levels at which the greatest effects occur differ for different endpoints. Three matched groups of 18 men each participated in two 6 h exposure test sessions. All subjects were sham exposed in one session. In the other session, each group of subjects was exposed at a different level of combined electric and magnetic field strength (low group:6 kV/m, 10 microT; medium group:9 kV/m, 20 microT; and high group: 12 kV/m, 30 microT). The study was performed double blind, with exposure order counterbalanced. Significant slowing of heart rate, as well as alternations in the latency and amplitude of event-related brain potential measures derived from the electro encephalogram (EEG), occurred in the group exposed to the 9 kV/m, 20 microT combined field (medium group). Exposure at the other field strength levels had no influence on cardiac measures and differential effects on EEG activity. Significant decrements in reaction time and in performance accuracy on a time estimation task were observed only in the low group. These results provide support for the hypothesis that humans may be more responsive to some combinations or levels of field strength than to others and that such differences in responsivity may depend, in part, on the endpoint of interest.

Action Potentials↗
PubMed1992

ELF exposure facility for human testing.

A laboratory facility specifically designed for controlled human exposure to 60-Hz electric (0 to 16 kV/m) and magnetic (0 to 32 A/m, B = 0 to 40 microT) fields has been constructed. The facility presents uniform fields under controlled temperature and humidity. Special control systems allow collection of physiological data during, as well as before and after, exposure to electric fields at strengths to 16 kV/m under verified double-blind control. Exposure to continuous or intermittent fields is possible in the facility. The capability of obtaining physiological data during actual exposure to constant or intermittent, 60-Hz fields, and of doing so without either the subject or the experimenter being aware of actual field conditions, is a critical factor in valid experimentation.

Electromagnetic Fields↗
PubMed1992

A replication study of human exposure to 60-Hz fields: effects on neurobehavioral measures.

The purpose of this study was to reproduce and extend an earlier investigation of the effects of human exposure to combined, 60-Hz electric and magnetic fields. This paper presents the neurobehavioral results. Thirty men participated in one training session and four testing sessions. Subjects were randomly assigned to two groups. The 18 subjects in Group I were exposed (9 kV/m, 20 microT) and sham exposed in two counterbalanced orders. In Group II, half of 12 subjects were exposed (9 kV/m, 20 microT) every session, and the remaining half were sham exposed every session. The study was doubly blinded. Measures of cardiac interbeat interval, event-related brain potentials, and performance were obtained before, during, and after exposures. As in the earlier study, exposure to the combined field resulted in a statistically significant slowing of heart rate, in changes in late components of event-related brain potentials, and in decreased errors on a choice reaction-time task. In addition, field effects on several other measures approached statistical significance. The physiological measures obtained during exposure indicated that effects were greatest soon after the field was switched on, and again when it was switched off. The data indicate that changes in exposure level may be more important than duration of exposure for producing effects in human beings.

Adult↗
PubMed1991

Effects of methanol vapor on human neurobehavioral measures.

Methanol could become an important motor fuel. The objective of this exploratory study was to provide preliminary information about whether or not acute exposure to methanol at 250 mg/m3 for 75 minutes would have adverse effects on human neurobehavioral functions important in everyday life. This concentration level was selected because it is at the upper limit of the traffic scenario estimates provided by the U.S. Environmental Protection Agency (EPA)2 (86 to 240 mg/m3), but is below the maximum concentrations for eight-hour average exposures currently recommended by the National Institute of Occupational Safety and Health (NIOSH) and the American Conference of Government and Industrial Hygienists (ACGIH) (260 mg/m3). Although traffic scenario exposure estimates suggest that such high levels of exposure last less than 15 minutes, we used a 75-minute exposure to increase the probability of identifying dependent measures that should be studied in more detail in a future confirmatory study. Twelve healthy young men, each serving as his own control, participated in two sham exposures and two methanol exposures under counterbalanced, double-blind control conditions. Because methanol is present in many foods, and because high preexposure levels of methanol or formate might obscure exposure effects, subjects were required to strictly limit their diets for 12 hours before each experimental session. The following endpoints were examined before, during, and after exposure to methanol and sham vapors: blood and urinary methanol; plasma formate; oral temperature; blood pressure; subjective mood, alertness, fatigue, workload, and symptom scales; spectral analysis of the electroencephalogram; visual- and auditory-event-related potentials; contingent negative variation; respiration; cardiac interbeat interval; Symbol Digit substitution task; three-choice reaction time; Stroop color-word test; simple reaction time; visual function; critical flicker fusion frequency; hand steadiness; visual search task; Gamberale reaction time task; visual tracking task; Sternberg memory task; interval production task; and speeded addition task. Two dual tasks were also included in the task batteries. These endpoints were selected from those indicated in the literature to be sensitive to solvents, and from those that are widely used in other neurobehavioral test batteries to identify the effects of environmental pollutants. Because the number of endpoints examined was large and the number of subjects was small, procedures designed to reduce the number of statistical tests performed were used. Mean methanol concentration in the exposure room during methanol exposures was 249 mg/m3 (SD +/- 7 mg/m3). Exposure produced significant increases in blood and urine methanol concentration. As expected, no changes in plasma formate were observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1990

Association of smoking with periodontal treatment needs.

A total of 344 Jerusalem hospital personnel participated in the present survey which examined periodontal needs according to CPITN (a measure of treatment needs) and smoking habits. Females and younger subjects were found to be generally periodontally healthier than their male and older counterparts. The effect of both smoking and the number of cigarettes smoked were shown to have a clearly deleterious effect on periodontal status when assessed using the CPITN. Younger women were found to be most susceptible to this effect.

Adolescent↗
PubMed1988

Exercise testing in the evaluation of human responses to powerline frequency fields.

The present study used exercise testing to examine the effects of 60-Hz electric and magnetic field exposure. Eleven males, 21-29 years, were tested during four experimental sessions (counterbalanced order and double-blind design). These included either 45-min exercise (50% of VO2 max) or no-exercise periods followed by either real field (9-kV/m, 16-A/m) or sham exposure for 2 h in a 60-Hz human exposure facility. Exercise produced a decrease in plasma volume and increases (p less than 0.05) in lactic acid, cortisol, growth hormone and testosterone levels, but these were not different under real and sham field conditions during the 2-h recovery periods. During no-exercise sessions, cardiac interbeat interval was increased (p less than 0.05), i.e., heart rate was slower, when subjects were exposed to real fields. Our results suggest that future studies should focus on evaluation of the effects of 60-Hz fields on the entire process of exercise-induced activation and recovery.

Adult↗
PubMed1986

Effects of variation in physical effort on frontalis EMG activity.

The physiological mechanisms underlying forehead muscle biofeedback for stress reduction are not well understood. A common hypothesis considers the frontales to be "key muscles" uniquely indexing the degree of tension present in the general musculature. We tested this hypothesis under conditions ranging from relaxation to maximum physical effort. The hypothesis was not supported. Changes in forehead muscle activity were limited primarily to reflecting changes in head and neck muscle tension.

Adult↗
PubMed1977

Appetitive and replacement naps: EEG and behavior.

Consistent subjective, behavioral, and electroencephalographic sleep-stage differences were found between afternoon naps of 11 habitual appetitive nappers (who nap lightly for psychological reasons apparently unrelated to reported sleep needs) and 10 replacement nappers (who apparently nap regularly in response to temporary sleep deficits). Both types of naps were compared with naps of 12 confirmed non-nappers.

Adult↗
PubMed1976

Electroencephalographic laterality changes during human sexual orgasm.

Left and right parietal EEGs were recorded while seven subjects experienced sexual climax through self-stimulation. EEG data were quantified by continuous cumulated measurements of the integrated areas of EEG recording during successive 1-sec epochs. In eight out of 12 experiments, this measure revealed a statistically significant change in laterality. Controlled replications with two of the original subjects obviated the possibility that two potential sources of artifact (hand used for masturbation and gross body movements) accounted for the changes. While previous research has focused on vasomotor and myotonic indices of sexual response, this study demonstrates the significance of brain phenomena in sexual orgasm.

Adult↗
PubMed1968

Memory impairment after subcutaneous injection of acetoxycycloheximide.

Subcutaneous injection of 240 micrograms of acetoxycycloheximide in mice rapidly produces marked inhibition of cerebral protein synthesis. Treated mice were trained to escape shock by choosing the lighted limb of a T-maze. When trained five or more minutes after injection, they had a normal capacity to learn. They remembered normally 3 hours after training, but 6 hours after training they had markedly impaired retention. Amnesia persisted thereafter. Injections immediately after training had a less marked but significant amnesic effect. These studies suggest that protein synthesis is not necessary for learning or for memory for 3 hours after training but that it is required for long-term memory. The protein synthesis which appears to be necessary for long-term e3memory occurs during training, or within minutes after training, or both.

Amnesia↗