Mitotic index, influx and mean transit time in the hamster cheek pouch epithelium, a partially synchronized cell system. Presentation of a mathematical model based on a non-stationary probability density function for the transit time in a compartment

Mitotic activity was followed in the epithelium of the hamster cheek pouch for about 12 hr in two experiments under different conditions of noise and light intensity. A mathematical model based on a non-stationary probability density function for the transit time through mitosis was developed, making an analysis of this partially synchronized cell system possible. The most important result of the two experiments is the indication of a non-stationary mean transit time for cells in mitosis. In the first experiment (70 dB, 103 lux), which produced high mitotic indices (maximum 2.0%), the influx changed from 0. to 0.9%/hr (mean of 7-hourly determinations: 0.4%/hr), and the mean transit time from 1.9 to 5.5 hr. In the second experiment (70 dB, 265 lux), which had a lower level of MI (maximum 1.3%), the influx changed from 0 to 1.8%/hr (mean of 13-hourly determinations: 0.4%/hr), and the mean transit time from 0.3 to 3.3 hr. It was difficult to say precisely whether the variation in influx or in mean transit time was the main factor in the increase and decrease of MI. The data could not be simulated with a stationary mean transit time. It is suggested that changes in MI due to different external circumstances are mainly the result of variation in the mean transit time.     

Comparison of gene flow estimates between species of darters in different streams

Allozyme variation was assessed at two localities for 38 loci in Etheostoma blennioides and 43 loci in E. flabellare . Percent polymorphism (P) ranged from 18·4 to 31·6 and average heterozygosity (H) ranged from 0·026 to 0·079. Estimates of gene flow indicated panmictic populations of E. blennioides and sub-divided populations of E. flabellare , with significantly more substructuring of E. flabellare from one population. Population structuring of E. flabellare and no structuring of E. blennioides is consistent with predictions based on life history data. Significantly different gene flow estimates for E. flabellare between streams imply that each stream environment induced different population structures. Reduced heterozygosity for both species and significantly less population structuring in one population are consistent with drought-induced extinction and recolonization that probably occurs in the smaller stream.     

Thyroid hormone metabolism in hypermetabolic patients with haematological disorders

Turnover tracer studies of T4 and T3 using the single injection, noncompartmental approach were performed in 6 hypermetabolic patients with haematological disorders (HHD) (basal metabolic rate (BMR): median 141%, range 122-166%), in 10 controls with stable, nonthyroidal illness (NTIC), and in 14 healthy controls (HC). The main finding was an increase of approximately 30% of the production rate (PR) of both T4 and T3 in patients with HHD. Median PR of T4 was 134 nmol/day x 70 kg in HHD, compared to 78 nmol/day x 70 kg in NTIC (P less than 0.05) and 98 nmol/day X 70 kg in HC (p less than 0.1), whereas median PR of T3 was 40.3 nmol/day x 70 kg in HHD, compared to 25.6 nmol/day x 70 kg in NTIC (P less than 0.01) and 31.1 nmol/day x 70 kg in HC (P less than 0.1). An increase of similar magnitude was found for the apparent distribution volume and the pool size of both T4 and T3. In contrast, the mean transit times of the hormones were similar in the 3 groups. Patients with HHD had normal levels of basal serum TSH as well as of the TSH response to TRH. Only PR of T3 correlated to the BMR (R = 1.00, P less than 0.02). The data are compatible with an increased consumption of thyroid hormones by malignant haematologic cells, and the increase of BMR seems to be dependent on the production of T3.     

Effects of cadmium exposure on feeding of freshwater planktonic crustaceans

1. Effects of cadmium exposure (0.010-0.100 ppm) on food consumption and assimilation rates of crustacean zooplankton from 2 lakes were studied in laboratory using radioisotope (14C) technique. 2. The inhibiting effects were significant 48 hr after Cd-exposure, but not after 20 hr exposure. 3. Daphnia spp. were the most affected cladocerans; copepods, especially the cyclopoids, appeared less sensitive. 4. The decrease in assimilation rates was much more marked than in the consumption rates. 5. The 14C-technique offers quick and sensitive means of studying the effects of heavy metal toxicity.     

Comparative analysis of avian hearts provides little evidence for variation among species with acquired endothermy

Mammals and birds acquired high performance hearts and endothermy during their independent evolution from amniotes with many sauropsid features. A literature review shows that the variation in atrial morphology is greater in mammals than in ectothermic sauropsids. We therefore hypothesized that the transition from ectothermy to endothermy was associated with greater variation in cardiac structure. We tested the hypothesis in 14 orders of birds by assessing the variation in 15 cardiac structures by macroscopic inspection and histology, with an emphasis on the atria as they have multiple features that lend themselves to quantification. We found bird hearts to have multiple features in common with ectothermic sauropsids (synapomorphies), such as the presence of three sinus horns. Convergent features were shared with crocodylians and mammals, such as the cranial offset of the left atrioventricular junction. Other convergent features, like the compact organization of the atrial walls, were shared with mammals only. Pacemaker myocardium, identified by Isl1 expression, was anatomically node-like (Mallard), thickened (Chicken), or indistinct (Lesser redpoll, Jackdaw). Some features were distinctly avian, (autapomorphies) including the presence of a left atrial antechamber and the ventral merger of the left and right atrial auricles, which was found in some species of parrots and passerines. Most features, however, exhibited little variation. For instance, there were always three systemic veins and two pulmonary veins, whereas among mammals there are 2–3 and 1–7, respectively. Our findings suggest that the transition to high cardiac performance does not necessarily lead to a greater variation in cardiac structure.     

Approaches to reduce the retroaction of long-term monitoring of bioelectric events in ergonomic field studies (author's transl)

When monitoring bioelectric signals the surface electrodes can cause a retroaction on the subject thereby introducing an error of measurement. There are two types of retroaction: physical and psycho-physiological. A physical retroaction due to the hydration process of the skin occurs if 'wet' electrodes are used for the recording of the skin conductance level (SCL) causing a continuous drift of the SCL and a decrease in sensitivity to SCL changes. Therefore a dry electrode was developed with improved performance: It exhibits less sensitivity to motion, is not subject to polarization, and features better SCL long-term stability. When recording the electrocardiogram or the electromyogram a psychophysiological retroaction occurs due to the annoyance caused by the skin-irritating abrading techniques in order to decrease the skin impedance and reduce the motion artifact. In an attempt to abandon the skin preparation whenever permissible without sacrificing the measurement accuracy a performance estimation procedure was developed. Basing on the information on the signal frequency content, the electrode contact area, the required accuracy of measurement and the amplifier input impedance a decision on the necessity of skin preparation is made. Moreover, the results of a study are reported investigating the reduction of motion artifacts by means of electrode design and appropriate electrode jelly formulation.