Seasonal recruitment of hippocampal neurons in adult free-ranging black-capped chickadees.

Neurogenesis and neuronal replacement in a population of wild free-ranging animals are described. Our subjects were adult black-capped chickadees (Parus atricapillus). Neuronal birth dates were determined by a single systemic injection of [3H]thymidine, followed by release of the bird and its recapture 6 or more weeks later. Newly formed neurons appeared in the hippocampal complex during all times of year, but with a marked peak in the fall (October). New neurons were also added to the hippocampal complex of captive chickadees, but at levels only half as high as seen in the wild birds. Neurons born at different times of the year lived for a few months and then disappeared. We suggest that the neurons added are part of a process of neuronal replacement and that they are important for the acquisition of new spatial memories, a need that is particularly acute in the fall. Hormonal and experiential factors may determine the rate of neuronal replacement.     

Monte Carlo studies of x-ray scattering in transmission diagnostic radiology

Monte Carlo methods have been used to simulate the scattering of x rays in polystyrene and water phantoms. In particular, the ratio of the scattered to total x-ray fluence (scatter fraction) has been calculated for monoenergetic x-ray beams in the energy region relevant to diagnostic radiology and nuclear medicine (30-660 keV). Simulations have been made for representative values of the pertinent geometrical factors; phantom thickness from 5 to 21 cm, x-ray beam diameters of 10 and 25 cm, and scatterer-to-image-plane separations from 0 to 20 cm. As a function of x-ray energy, the scatter fraction was found to vary slowly between 30 and 100 keV, and to decrease between 100 and 660 keV. The present results were generated with a special transport code which included the effects of special geometries and the response of the x-ray detector. With the inclusion of these effects, the results resolved inconsistencies and showed good agreement with previous measured and calculated data.     

Coronary autoregulation and optimal myocardial oxygen utilization

The complex relationship among myocardial contractility, preload, afterload, and coronary autoregulation was studied using both analytical and numerical methods. To study autoregulation and coronary reserve changes in response to changes in cardiac oxygen consumption and in arterial pressure generation, a new variable was introduced: myocardial resistance to oxygen flow ( ). This variable was defined as the ratio of the coronary driving pressure to left-ventricular oxygen uptake. High values for this variable indicate small consumption relative to the generated aortic pressure. Conditions which produce the highest obtainable value for are considered as optimal. An expression relating to ventricular hemodynamic variables was developed and studied using a mathematical model of the cardiovascular system. The model included a mechanism of local autoregulation based on the assumption that, in steady state, the amount of oxygen consumed equals the amount extracted from coronary blood. Heart rate, peripheral resistance, end-diastolic volume, and myocardial contractility were varied while the coronary circulation was adjusted to meet ventricular oxygen consumption at each state. The model predicts that, for each state of the circulation, there is an optimal level of cardiac contractility for which the coronary reserve is maximized.     

Incretin,insulinotropic and glucose-lowering effects of whey protein pre-load in type 2 diabetes: a randomised clinical trial

Aims/hypothesis

Since protein ingestion is known to stimulate the secretion of glucagon-like peptide-1 (GLP-1), we hypothesised that enhancing GLP-1 secretion to harness its insulinotropic/beta cell-stimulating activity with whey protein pre-load may have beneficial glucose-lowering effects in type 2 diabetes.

Methods

In a randomised, open-label crossover clinical trial, we studied 15 individuals with well-controlled type 2 diabetes who were not taking any medications except for sulfonylurea or metformin. These participants consumed, on two separate days, 50 g whey in 250 ml water or placebo (250 ml water) followed by a standardised high-glycaemic-index breakfast in a hospital setting. Participants were randomised using a coin flip. The primary endpoints of the study were plasma concentrations of glucose, intact GLP-1 and insulin during the 30 min following meal ingestion.

Results

In each group, 15 patients were analysed. The results showed that over the whole 180 min post-meal period, glucose levels were reduced by 28% after whey pre-load with a uniform reduction during both early and late phases. Insulin and C-peptide responses were both significantly higher (by 105% and 43%, respectively) with whey pre-load. Notably, the early insulin response was 96% higher after whey. Similarly, both total GLP-1 (tGLP-1) and intact GLP-1 (iGLP-1) levels were significantly higher (by 141% and 298%, respectively) with whey pre-load. Dipeptidyl peptidase 4 plasma activity did not display any significant difference after breakfast between the groups.

Conclusions/interpretation

In summary, consumption of whey protein shortly before a high-glycaemic-index breakfast increased the early prandial and late insulin secretion, augmented tGLP-1 and iGLP-1 responses and reduced postprandial glycaemia in type 2 diabetic patients. Whey protein may therefore represent a novel approach for enhancing glucose-lowering strategies in type 2 diabetes. Trial registration ClinicalTrials.gov NCT01571622 Funding The Israeli Ministry of Health and Milk Council funded the research.     

Differential sub-cellular compartmentalization of thyrotropin releasing hormone (TRH) and gonadotropin releasing hormone (LRH) in hypothalamic tissue.

Homogenates of male rat hypothalami were fractionated by differential centrifugation. Of the total quantity of TRH and LRH in the homogenate, about 50% was in particles sedimenting at 11,500 X g. and 15-20% was in particles sedimenting between 20,000 and 105,000 X g. No LRH or TRH was recovered in the 105,000 X g supernatant fluid. When the 900 X g supernatant fluid was subjected to continuous sucrose density gradient centrifugation, TRH-containing particles distributed as two peaks located at 0.9 and 1.1 M sucrose. On the other hand, LRH-containing particles distributed as only one peak located at 1.2 M sucrose. The 11,500 X g pellet contained those particles comprising the 1.2 M peak of LRH and the 1.1 M peak of TRH. Acid phosphatase activity was found in the gradient fractions containing TRH and LRH, whereas NADPH-cytochrome c reductase and cytochrome c oxidase activities were separated from the peaks of TRH and LRH. Norepinephrine, dopamine, and TRH distributed identically on the gradient. Hypo-osmotic treatment changed the gradient profile of TRH but not that of LRH. Most of the TRH was found near the top of the gradient, but a small amount of TRH was associated with particles which were lighter than those previously noted. The peak of LRH was reduced but its location on the gradient was unchanged. It is concluded that in hypothalamic homogenates TRH and LRH are localized in synaptosome-like particles which have different physical properties.     

Stimulatory effect of prolactin on human placental progesterone secretion at term in vitro: possible inhibitory effect on oestradiol secretion

Maternal and fetal circulating prolactin (PRL) increases 10-fold compared with the non-pregnant state. We examined the effect of PRL upon placental steroidogenesis. It had a significant (P less than 0.05) time-dependent stimulatory effect upon placental explants/P4 accumulation and secretion into the medium. The maximal stimulatory effect (two-fold) in dose-dependent experiments was found to be 200 ng/ml. The effect of PRL upon oestradiol secretion was mainly inhibitory. This inhibition was most pronounced at 200 ng/ml. In conclusion, placental steroid secretion is modulated by PRL. This effect occurs mainly at concentrations seen in the placenta at term, suggestive of its physiologic role.