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Biomedical subjects

D Fraser

Publications and source records attributed to D Fraser.

At least 163 records · Page 9Linked to original sources
PubMed1987

Olfaction and the "data" memory system in rats.

A set of studies was conducted to characterize the memory system involved in successive olfactory discrimination learning in rats. Two odors emanated from different arms of a radial maze; one of the arms contained a water reward. After training on four or five pairs of odors (20 trials per day), rats learned to discriminate the members of a new pair in 5-10 trials. Experiments in which either member of the pair was compared with a novel cue indicated that the rats learn both positive and negative odors, rather than simply ignoring the negative cue. The memories for the odors were apparently persistent, and no evidence for retroactive interference from subsequent training was obtained. Training on 30 pairs did not result in any slowing of subsequent learning, which suggest that the capacity of the memory system for odors is substantial. In a second group of experiments, we tested whether rats distinguish between odors by identifying unshared subcomponents or instead treat odors in a gestalt (i.e., unitary) fashion. Animals trained on three component odors with two in common did not recognize the elements that were unshared when these were presented by themselves. Even when one of the two shared components was combined with the differentiating component into a cue (i.e., two thirds of the original three-component odor), the new cue was treated as a novel odor. However, inclusion of a previously learned simple odor in a complex odor did affect the learning of that odor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Low dietary calcium reduces 25-hydroxycholecalciferol in plasma of rats.

We investigated whether dietary factors that are known to increase 1,25-(OH)2-cholecalciferol production can deplete plasma 25-OH-cholecalciferol. Plasma concentration of 25-OH-cholecalciferol, its metabolism in vivo and activities of renal mitochondrial 25-OH-cholecalciferol 1-hydroxylase (1-OHase) and 25-OH-cholecalciferol 24-hydroxylase (24-OHase) were measured in rats fed various amounts of calcium (Ca) and phosphorus (P). All diets contained 5 micrograms (200 IU) cholecalciferol per 100 g. For rats fed the "normal" diet (0.7% Ca and 1.2% P) the mean plasma 25-OH-cholecalciferol level was 11.0 +/- 0.8 nmol/L, and the mean 1-OHase activity was 30 +/- 5 fmol/(mg X min). All rats fed the low Ca (0.014%) diet had 1-OHase activities above 200 fmol/(mg X min) and undetectable plasma 25-OH-cholecalciferol levels (less than 2.5 nmol/L). The chi-square test interrelating plasma 25-OH-cholecalciferol and dietary Ca showed statistical significance (P less than 0.001). The high activity of 1-OHase that resulted from dietary Ca restriction increased utilization of 25-OH-cholecalciferol to the point of causing depletion of this metabolite in the circulation.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1987

Hepatitis B infections in a chronic hemodialysis unit in a country where hepatitis B is endemic: a prospective study.

Hepatitis B markers were determined in patients with chronic renal failure and in staff members prior to entry into the hemodialysis unit of a hospital in southern Israel, an area in which hepatitis B is endemic. Patients and staff who were negative for hepatitis B markers were followed for a mean of 26.7 and 29.2 months, respectively, between November 1975 and May 1984. New infections occurred in 25.9% of the patients and 17.3% of the staff; the difference was not statistically significant. Hepatitis B markers were found in 26% of the staff and 41% of the patients (p less than 0.05) prior to their entry into the hemodialysis unit. Furthermore, in the patients, a relatively high rate of carriers was detected (7% compared with 2% in the general population), while no carriers were detected among the staff members. Within the staff group, nurses were at particularly high risk for new infections, accounting for seven of the nine (78%) events recorded. The high risk for the nursing staff is probably due to greater exposure to blood among nurses compared with other staff members.

Carrier State↗
PubMed1987

Ulcerative colitis in the Jewish population of southern Israel 1961-1985: epidemiological and clinical study.

The incidence of ulcerative colitis in the Jewish population of Southern Israel has increased in the period 1961-85 and is presently 5.8/10(5)/year. The mean annual incidence was significantly higher in European and American born (10.8/10(5)/year) than in Asian and African or Israeli born Jews. The disease was significantly more prevalent in women, who developed the illness at a younger age and had a milder course. The age adjusted prevalence rate in each population group was greater than the rates detected by earlier studies in other areas of the country (p less than 0.05). The prevalence rate in the total population now approximates the moderate to high prevalence rates of ulcerative colitis found in many other localities. The particularly high rates of ulcerative colitis in the European and American born population in Israel, in Jews residing in Western countries, and in certain non-Jewish populations in Great Britain and Northern Europe may imply the presence of a common aetiological mechanism.

Adolescent↗
PubMed1987

The effects of estrogens and progestogens on the endometrium. Modern approach to treatment.

The major hazard of postmenopausal cyclic estrogen therapy is endometrial hyperstimulation. The incidence of hyperplasia is dose dependent; the incidence of carcinoma is both dose and duration dependent. The risk of carcinoma is small. Invasive procedures such as endometrial biopsy to detect those patients with hyperplasia and carcinoma are unlikely to be cost-effective and have other disadvantages. With cyclic estrogens, biopsies should be performed at regular intervals irrespective of the bleeding pattern. The possible alterations to cyclic treatments to reduce the risk of endometrial hyperstimulation have been reviewed; only progestogen addition has been shown to be effective. Maximal effects are obtained when progestogens are added for 12 to 13 days each calendar month. To reduce the risk of side effects, the minimum dose of progestogen should be prescribed, and with the nor-testosterone derivatives, a small dose of norethindrone, approximately 1 mg daily, is as effective as 5 mg daily. The smaller doses cause minimal lipid changes. Interpatient variation in response to the 17-hydroxyprogesterone derivatives can occur, and at high doses, adverse lipid effects have been reported. With sequential estrogen/progestogen therapies, the endometrial histology appears to correlate with the bleeding pattern, thereby, perhaps, obviating the need for biopsy. The development of regimens to induce endometrial atrophy and amenorrhea is suboptimal, and further research is required.

Drug Administration Schedule↗
PubMed1987

Incidence of idiopathic ulcerative colitis in Jewish population subgroups in the Beer Sheva region of Israel.

The epidemiology and clinical features of idiopathic ulcerative colitis in different Jewish population groups in the Beer Sheva district of Israel were studied retrospectively over the period 1961-85. The average annual age-adjusted incidence rate increased (p less than 0.05) in all population groups during this period. The incidence rate in the total population in 1981-85 was 5.8 per 10(5) population per yr. In European and American born subjects the incidence rate was twice as high as in Asian and African born and Israeli born subjects. The mean age of onset of ulcerative colitis was significantly lower in Israeli born persons (26.8 yr) than in the other population groups; when the total population was stratified by age, this difference was shown to be caused by the relative youthfulness of the Israeli born subpopulation. Despite these striking epidemiological differences, clinical features were similar in the three population groups.

Adolescent↗
PubMed1986

Studies on retrograde and anterograde amnesia of olfactory memory after denervation of the hippocampus by entorhinal cortex lesions.

The effect of hippocampal denervation on olfactory memory in rats was tested after interrupting the lateral olfactory tract projections at the level of the entorhinal cortex. When lesioned animals were trained to learn new odors, they showed no evidence of retention 3 h after acquisition. These results confirm earlier data on rapid forgetting in rats after hippocampal deafferentation and are in parallel to the anterograde amnesia typically found in humans with hippocampal damage. On the other hand, preoperatively learned information was minimally impaired after hippocampal deafferentation even if it was acquired within less than 1 h before the lesion. This finding differs from reports on humans as well as monkeys with hippocampal damage where memories formed during a critical time span of months or even years before the lesion are found to be impaired. This may suggest that the consolidation process in humans and rodents has different time scales or that the roles of the human and the rat hippocampal structure in memory formation are somewhat different.

Amnesia↗
PubMed1985

Familial hypocalciuric hypercalcemia. Mild expression of the gene in heterozygotes and severe expression in homozygotes.

Autosomal dominant familial hypocalciuric hypercalcemia was found in a kindred with neonatal severe primary hyperparathyroidism, previously judged to be an autosomal recessive trait. Mild hypercalcemia was documented in eight members representing three generations. Mild hypercalcemia was documented at an age as early as one week. In seven adults presumed to be heterozygotes, urinary calcium levels were in the same range as for familial hypocalciuric hypercalcemia. An additional adult member (who previously underwent parathyroidectomy for neonatal severe primary hyperparathyroidism) showed an abnormality in renal clearance of calcium and sodium characteristic of combined familial hypocalciuric hypercalcemia and surgical hypoparathyroidism. Parathyroidectomy in three hypercalcemic members did not cause normocalcemia. Unlike other kindreds with familial hypocalciuric hypercalcemia in whom hypercalcemia is consistent over time and moderate in heterozygotes, this kindred was characterized by heterozygotes showing hypercalcemia that was intermittent and mild. The consanguineous parents of the two previously described severely affected neonates were judged to be heterozygotes for familial hypocalciuric hypercalcemia. In conclusion, (1) a gene presenting as familial hypocalciuric hypercalcemia can be expressed as hypercalcemia that is intermittent and very mild in heterozygotes; (2) such a gene can cause neonatal severe primary hyperparathyroidism in homozygotes.

Adolescent↗
PubMed1984

Isolation of lactoferrin and its concentration in sows' colostrum and milk during a 21-day lactation.

Levels of lactoferrin, an Fe-binding protein with bacteriostatic properties, were determined in the colostrum and milk of Yorkshire sows during a 21-d lactation. Lactoferrin levels averaged 1,100 to 1,300 micrograms/ml near the time of farrowing, then declined sharply during the first week of lactation. Concentration of lactoferrin showed considerable variation among sows, but not among teat positions (anterior to posterior). A method for isolating high purity swine lactoferrin is described.

Animals↗