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Biomedical subjects

J A Berg

Publications and source records attributed to J A Berg.

17 recordsLinked to original sources
PubMed2004

Visuotopic mapping through a multichannel stimulating implant in primate V1.

We report on our efforts to establish an animal model for the development and testing of a cortical visual prostheses. One-hundred-fifty-two electrodes were implanted in the primary visual cortex of a rhesus monkey. The electrodes were made from iridium with an activated iridium oxide film, which has a large charge capacity for a given surface area, and insulated with parylene-C. One-hundred-fourteen electrodes were functional after implantation. The activity of small (2-3) neuronal clusters was first recorded to map the visually responsive region corresponding to each electrode. The animal was then trained in a memory (delayed) saccade task, first with a visual target, then to a target defined by direct cortical stimulation with coordinates specified by the stimulating electrode's mapped receptive field. The SD of saccade endpoints was approximately 2.5 larger for electrically stimulated versus visual saccades; nevertheless, when trial-to-trial scatter was averaged out, the correlation between saccade end points and receptive field locations was highly significant and approached unity after several months of training. Five electrodes were left unused until the monkey was fully trained; when these were introduced, the receptive field-saccade correlations were high on the first day of use (R = 0.85, P = 0.03 for angle, R = 0.98, P < 0.001 for eccentricity), indicating that the monkey had not learned to perform the task empirically by memorizing reward zones. The results of this experiment suggest the potential for rigorous behavioral testing of cortical visual prostheses in the macaque.

Animals↗
PubMed1999

Symptom experience of Filipino American midlife women.

OBJECTIVE: The purpose of this study was to describe the perimenopausal symptom experience of Filipino American midlife women with particular emphasis upon estrogen-related menopause symptoms (day sweats, hot flashes, night sweats, and vaginal dryness). DESIGN: A cross-sectional, descriptive survey was used to generate symptom experience data for 165 Filipina Americans between the ages of 35 and 56 who self-identified as Filipina American and were English-language proficient. The community-based sample completed questionnaires composed of sample characteristic questions and a 51-item menstrual symptom checklist with menopause-related symptoms embedded in it. RESULTS: Sample characteristics and symptom experience were compared among age groups of 35 to 39 (n = 39), 40 to 44 (n = 40), 45 to 49 (n = 37), and 50 to 56 (n = 49) and by perimenopausal phase, defined as premenopausal (n = 85), transitional (n = 33), and menopausal/postmenopausal (n = 47). The most reported individual symptoms were "felt energetic" (86.1%) and "well-being" (83.6%). Estrogen-related menopause symptoms were reported as "vaginal dryness" (39.4%), "hot flashes" (37.6%), "day sweats" (27.9%), and "night sweats" (24.2%) by the total sample. Distress associated with estrogen-related menopause symptoms was reported by 17% (n = 28) of all women. Subjects' chi 2 tests indicated that 50-to-56-year-old women were more likely to report fatigue/sleep symptoms, physical symptoms, and estrogen-related menopause symptoms than all other age groups. When compared by perimenopausal phase, transitional women were more likely to report moderate or extreme severity for day sweats. Premenopausal women were more likely to report minimal or mild severity and women in the perimenopausal transition were more likely to report moderate or extreme severity on estrogen-related menopause symptoms. CONCLUSIONS: Filipino American midlife women appear to consider the perimenopausal transition in a positive light and experience little distress associated with estrogen-related menopause symptoms experienced. Findings from this study suggest that Filipina Americans view perimenopausal symptoms as part of a normal life stage that does not warrant concern.

Adaptation, Physiological↗
PubMed1999

Symptom responses of midlife Filipina Americans.

OBJECTIVE: The purpose of this study was to describe the perimenopausal symptom responses of Filipino American midlife women. DESIGN: This cross-sectional, descriptive survey collected symptom response information on Filipino American midlife women aged 35 to 56 years (n = 165) who self-identified as Filipina American and were proficient in the English language. Women were recruited from community churches and social groups. A survey questionnaire comprised of health history questions and a symptom checklist with symptom response questions were completed by the participants. RESULTS: The symptom responses of women were compared by age groups of 35 to 39 (n = 39), 40 to 44 (n = 40), 45 to 49 (n = 37), and 50 to 56 (n = 49) and by perimenopausal phases of premenopausal (n = 85), transitional (n = 33), and menopausal/postmenopausal (n = 47). Indications from chi 2 tests showed that women in the 35-to-39- and 50-to-56-year groups were more likely to take acetaminophen (Tylenol) or aspirin for symptoms, and women in the 45-to-49- and 50-to-56-year groups were more likely to be on hormone replacement therapy. Surprisingly, women in the 50-to-56-year group were less likely to use talking with friends as a symptom management strategy. CONCLUSIONS: Nonpharmacologic symptom management strategies exceeded the use of medications (hormones, over-the-counter) by Filipina Americans. This may be a strong indicator of their positive attitude toward this phase in their life and sends a message to clinicians about the choices that these women make for symptom management. Culturally relevant care would include alternatives to hormone replacement therapy in education materials about the perimenopausal transition for midlife Filipinas.

Adaptation, Physiological↗
PubMed1997

One-step immunoaffinity purification of recombinant human retinoic acid receptor gamma.

Retinoic acid receptors (RAR) are members of the steroid/thyroid hormone receptor superfamily and serve as ligand-activated transcription factors. In order to facilitate studies of receptor protein, we have generated a monoclonal antibody to the human RAR gamma, and have developed a procedure to purify the full-length receptor expressed in insect cells. The monoclonal antibody (A10) was developed using as antigen a carboxy-terminal fragment of the human RAR gamma expressed as a bacterial fusion protein. The A10 monoclonal antibody binds to both native and denatured forms of the human RAR gamma. This antibody was immobilized on a resin and used to purify full-length, baculovirus-expressed human RAR gamma to near homogeneity. The immunoaffinity-purified receptor is > 90-95% pure as revealed by silver-stained gels. The identity of the single protein band as RAR gamma was verified by immunoblotting using a polyclonal antibody to an epitope distinct from that recognized by the A10 antibody. The pure human RAR gamma is functional with respect to both ligand and DNA binding. Scatchard analysis of 3H-labeled all-trans retinoic acid binding to purified human RAR gamma revealed a single, high-affinity binding site with a Kd of approximately 2 nM. Binding of the pure RAR gamma to a DR5-type retinoic acid response element was also studied. Response element binding by RAR gamma required the presence of the retinoid X receptor, but did not require the presence of additional proteins. Human RAR gamma protein purified in this fashion will be useful in future structural and functional studies.

Animals↗
PubMed1992

A study in normal human volunteers to compare the rate and extent of levothyroxine absorption from Synthroid and Levoxine.

Numerous branded and generic formulations of levothyroxine (LT4) sodium tablets are currently available. Results from previous studies attempting to examine the comparative bioavailability of these formulations are difficult to interpret because of subject heterogeneity, single time-point blood sampling, varying degrees of hypothyroidism, and other factors. This study was devised to compare the rate and extent of absorption of LT4 from different LT4 sodium tablet formulations, in a simple model using a single-dose two-way single-blind, randomized cross-over design in 30 normal, healthy, nonpregnant, female subjects. This design controlled for many factors that limited previous LT4 bioavailability studies. Subjects were given a single 600 micrograms dose of LT4 as either Synthroid (Boots Pharmaceuticals, Inc., Lincolnshire, IL) tablets (formulation A) or Levoxine tablets (Daniels Pharmaceuticals, St. Petersburg, FL; formulation B). Measurements of baseline-corrected total T4 serum concentrations determined at multiple time points demonstrated statistically significant differences between the two formulations at the 1.00, 3.00, 5.00, and 18.00 hour sampling times. Statistically significant differences for area under the curve (AUC) (0 to 48 hours) (formulation A, 159.9 +/- 9.4 micrograms-hour/dL; formulation B, 193.4 +/- 10.1 micrograms-hour/dL) and maximum peak plasma concentration (Cmax) (formulation A, 5.91 +/- .34; formulation B, 7.12 +/- .32) also were demonstrated. Furthermore, the ratio of the baseline-corrected total T4 concentrations (B/A x 100) were 120.9% for AUC and 120.5% for Cmax. These data demonstrate that the administration of Synthroid and Levoxine result in a significantly different rate and extent of absorption of LT4, and therefore these two formulations cannot be considered bioequivalent.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Na:K pump abundance and function in MDCK cells: effect of low ambient potassium.

Side-specific expression and activity of Na:K pump was studied in Madin-Darby canine kidney (MDCK) cells, a tissue culture model of distal renal tubular epithelium, exposed to low ambient potassium. Confluent monolayers grown on teflon filters in dual chambers were treated with a low K+ medium from 45 min to 72 h. After both acute (45 min) and longer-term (24-72 h) exposure to low K+ (0.7 mM), cation cycling rate of existing pump units increased substantially, while there was no significant change in total cell Na-K-ATPase activity or in basolateral surface pump density. Although a small quantity of Na:K pumps (less than 10%) was consistently present apically, it also did not increase after exposure to low K+, or when the monolayers were provided K+ only from the apical side. In MDCK monolayers low K+ enhances the rate of K+ uptake by the existing pump units but does not increase the total number of pumps or their deployment on either cell surface.

Animals↗
PubMed1988

Renal metabolism of atrial natriuretic peptide in the rat.

The purpose of this study was to identify the nephron and cell sites involved in the renal metabolism of alpha-rat atrial natriuretic peptide (alpha-rANP) and to examine the degradation products of the peptide. In micro-dissected nephrons 125I-labeled ANP degradation rate was highest in proximal convoluted (PCT) and straight tubules and lowest in glomeruli and papillary collecting tubules, indicating that the sites of ANP degradation and of the receptors that mediate its biological activity in the nephron do not coincide. Among subcellular fractions of cortical homogenates, the luminal membranes were the most active in metabolizing ANP. In contrast, ANP degradation by isolated basolateral membranes was negligible, and the basolateral uptake route in intact tubules did not contribute significantly to its catabolism. Cortical homogenates, luminal membranes, and isolated PCT degraded ANP without evidence of saturation up to pharmacological concentrations (10(-6) M) of the peptide. A major intermediate metabolite was rapidly formed by luminal membranes and was identified with use of a sequence and compositional analysis. This metabolite had the same amino acid sequence as ANP with a cleavage at position Cys7-Phe8, and the disulfide bridge was preserved. These results demonstrate a rapid degradation of ANP by kidney tissue and suggest that the luminal membrane of the proximal tubule is a major nephron site of ANP catabolism.

Animals↗
PubMedDate not supplied

Gaining access to underresearched populations in women's health research.

Culture is an important variable in women's health research, and sample selection must include plans to recruit participants who represent the overall cultural makeup of the population. However, gaining access to underresearched groups is a major challenge and requires specific planning. Salient access techniques utilized by epidemiological researchers include (a) obtaining the support and endorsement of community leaders, (b) advertising the research in community publications, and (c) utilizing age, gender, and culturally matched research assistants. Although these elements were included in the planning of a study of the perimenopausal transition of Filipino American midlife women, the more powerful attractors for this particular cultural group were their pride in participating in a study that was associated with a major university and their intense community service orientation. Since each cultural group has unique issues and concerns, researchers must familiarize themselves with the values of their target group and emphasize these in recruitment approaches.

Attitude to Health↗
PubMedDate not supplied

Information sources, menopause beliefs, and health complaints of midlife Filipinas.

Although the perimenopausal transition is a universal experience for women who live long enough, its cross-cultural variations have been explored only recently. In this study, we investigated some of the expectations and health beliefs of 165 midlife Filipina Americans using focus groups and a short-answer questionnaire. Participants reported on (a) how they learned about menopause, (b) who they talked to about menopause symptoms or issues, (c) how Filipino women and men feel about menopause, and (d) the most common health complaints of midlife Filipinas. Findings revealed that midlife Filipina Americans primarily obtain their information from and talk about menopause with female relatives and friends. They usually viewed menopause as a normal life phase, yet knew less about how Filipino men feel about menopause. Health complaints of midlife Filipinas were mainly estrogen-related menopause symptoms and negative affect symptoms.

Adult↗
PubMedDate not supplied

The perimenopausal transition of Filipino American midlife women: biopsychosociocultural dimensions.

OBJECTIVES: To describe the biologic, psychological, social, and cultural (biopsychosociocultural) dimensions of the perimenopausal transition of Filipino American midlife women. METHODS: A community-based sample of 165 women (a) self-identified as Filipino American, (b) ages 35 to 56 years, and (c) English language proficient was recruited from churches and social groups. RESULTS: Women in the study were born in the Philippines (93.3%), had lived in the United States an average of 18.4 +/- 8.7 years, were married or partnered (74.6%), had completed college (62.8%) or a graduate degree (15.9%), worked (full-time, 77.9%; part-time, 12.9%), had household incomes greater than $50,000 (>58%). Menopause ages were calculated from reports of last menstrual periods (natural, 48.9 +/- 4.9 years; surgical, 42.2 +/- 5.7 years). Neither the age at menarche nor the number of pregnancies and children born was significantly related to age at menopause. Calcium from food sources was generally low, and the Center for Epidemiological Studies Depression Scale (CES-D) revealed a 24.8% depression rate. The low prevalence of physical health problems confirms previous research that foreign-born individuals have better health than those born in the United States. CONCLUSIONS: The profile of this understudied group identified calcium intake, osteoporosis morbidity, and prevalence of depression as key areas for future study.

Adult↗
PubMedDate not supplied

Dimensions of sexuality in the perimenopausal transition: a model for practice.

A biopsychosocial-cultural model of the sexuality of women during the perimenopausal transition includes dimensions related to physiology, psychosocial issues, and culture. It is an amalgam of biomedical and psychosocial models, yet has the added focus on culture. This holistic approach to sexual health is recommended by researchers and clinicians engaged in the study of midlife women. Clinicians can use this model to guide assessment and interventions, examining all of the dimensions of sexuality during the perimenopausal transition.

Attitude to Health↗