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Biomedical subjects

L R Cohen

Publications and source records attributed to L R Cohen.

32 records · Page 2Linked to original sources
PubMed1994

Privatizing public research.

With the end of the cold war, national defense has given way to international competitiveness as the theme for federal support of research. As it now stands, the idea will probably not work well.

Financing, Government↗
PubMed1989

Self-selection of protein during pregnancy and lactation in rats.

Protein self-selection was investigated in female rats throughout pregnancy and lactation. In the first experiment, impregnated rats were presented with either a choice between low and high protein (casein) diets, or standard lab chow and their protein intake was compared to that of non-impregnated controls. Impregnated females showed an increase in both absolute and relative protein intake at the end of pregnancy and during the second week of lactation when compared to both their own baseline intake and that of non-impregnated rats. In the second experiment, lactating rats and non-lactating controls were presented with a choice between low and high protein (casein) diets, a high protein (soybean meal) and a high carbohydrate diet, or lab chow. Lactating rats consumed more protein than non-lactating rats regardless of diet condition, but percentage protein intake was found to differ across diet choice conditions. Differences in diet fraction choice are discussed in terms of protein: carbohydrate ratios, and how different sources of protein might be utilized differently within the body.

Animals↗
PubMed1988

Diastolic abnormalities in young asymptomatic diabetic patients assessed by pulsed Doppler echocardiography.

Indexes of left ventricular diastolic filling were measured by pulsed Doppler echocardiography in 21 insulin-dependent diabetic patients and 21 control subjects without clinical evidence of heart disease. No patient had chest pain or electrocardiographic changes during exercise testing. The mean age of patients was 32 years. All patients had a normal ejection fraction. Six (29%) of the 21 diabetic patients had evidence of diastolic dysfunction as assessed by the presence of at least two abnormal variables of mitral inflow velocity. The ratio of peak early to peak late (atrial) filling velocity was significantly decreased in diabetic compared with control subjects (1.24 +/- 0.21 versus 1.66 +/- 0.30, p. less than 0.001). Atrial filling velocity was significantly increased in diabetic patients (74.3 +/- 16.7 versus 60.3 +/- 12.2 cm/s, p less than 0.004), whereas early filling velocity was reduced by a nearly significant degree (88.8 +/- 12.6 versus 98.5 +/- 18.8 cm/s, p less than 0.057). The atrial contribution to stroke volume as assessed by area under the late diastolic filling envelope compared to total diastolic area was also significantly increased in diabetic compared with control subjects (35 versus 27%, p less than 0.001). Left ventricular diastolic filling abnormalities in diabetic patients did not correlate with duration of diabetes, retinopathy, nephropathy or peripheral neuropathy. These data suggest that approximately one-third of such patients have subclinical myocardial dysfunction unrelated to accelerated atherosclerosis. Doppler echocardiography may offer a reliable noninvasive means to assess diastolic function and to follow up diabetic patients serially for any deterioration in cardiac status before the appearance of clinical symptoms.

Adult↗
PubMed1987

Effects of food restriction during concurrent lactation and pregnancy in the rat.

The ability of rat dams to cope with food restriction as well as a concurrent lactation and pregnancy was examined by varying the duration, time of onset and severity of the food restriction schedule. Groups of females impregnated in the postpartum estrus and nursing 8 pups were either allowed to feed ad lib, given 60% of an ad lib ration from days 1-7, 1-14, 8-14 or 15-21 postpartum or 40% of an ad lib ration from days 1-7. Food restriction regimens that extended through the estimated time of implantation for females nursing 8 pups (days 1-14 and 8-14) resulted in a prolongation of pregnancy. Food restriction in the first week postpartum did not result in a prolongation of pregnancy and did not affect the number of females carrying the pregnancy to term. Dams food restricted in the third week postpartum had pregnancies of the same length as ad lib females but a smaller proportion of this group gave birth to a second litter.

Animals↗
PubMed1981

The test-retest reliability of the McCarthy Screening Test.

Examined the test-retest reliability of the MST. Ss were 971 5- and 6-year-olds, who were tested early in the school year. Those "at risk" on the first test were retested 4 to 10 weeks later (N = 276). Obtained reliability coefficients for the six subtests ranged from .30 to .83. A comparison of the results with the statistics reported in the test manual was made, and it was concluded that the MST is not stable enough to be used alone to identify children with potential learning problems.

Child↗
PubMed1977

Conditional discrimination performance by pigeons on a response-independent procedure.

Pigeons were trained on a differential autoshaping procedure in which both components of two-stimulus sequences predicted delivery or nondelivery of food. All birds acquired the conditional discrimination. When the subjects were exposed to an extinction procedure, the stimuli maintained conditional control as long as the birds continued to peck the key. When a delay interval was imposed between the two components of a stimulus sequence using a titration procedure, the stimuli maintained conditional control up to delay values of 7 to 10 sec. These data are consistent with the view that the controlling stimuli in conditional discrimination situations are compounds of stimulus elements.

Journal Article↗
PubMed1976

Differential sample response schedules in the acquisition of conditional discriminations by pigeons.

Pigeons were trained on four matching-to-sample tasks with various schedule requirements in effect on the sample key. Differential sample-schedule requirements (a differential-reinforcement-of-low-rates of 3 sec in the presence of one sample and a fixed-ratio 16 in the presence of the other) produced rapid rates of acquisition that did not differ across tasks. Nondifferential sample-schedule requirements (fixed-ratio 1, fixed-ratio 16 or a differential-reinforcement-of-low-rates of 3 sec in the presence of both samples) produced slower rates of acquisition, which depended on the difficulty of the discriminations between samples and between comparisons. Patterns of stimulus and position preferences were influenced both by the comparison stimuli in each task and by the sample-schedule requirements. Detailed analyses of acquisition revealed frequent instances of complete differential sample control of comparison responding at intermediate levels of overall "accuracy".

Journal Article↗
PubMed1969

Generalization during acquisition, extinction, and transfer of matching with an adjustable comparison.

Three groups of pigeons were given conditional discrimination training in which the number of standard stimuli was varied across groups. In the presence of each standard, a pigeon adjusted the comparison stimulus on a second key until the two keys matched. A report of this match (response on the first key) was reinforced. Transfer of the matching performance was investigated by adding new standards to the ones already available. All pigeons were exposed to two extinction sessions after 155 sessions of training. Rapidity of acquisition was inversely related to the number of standards presented. Generalization gradients derived from the several comparison stimuli showed that all pigeons reached a high level of accuracy in the presence of at least one standard, and some pigeons did so in the presence of as many as four of the six standards. There was no evidence of a systematic effect of extinction upon overall accuracy, or the individual generalization gradients. When a new standard was added, a given pigeon's performance (in terms of responding to the comparisons) was similar to performance in the presence of one of the old standards. However, the pigeons did not show evidence of confusion among the comparisons.

Journal Article↗