The estradiol induction of the microsomal low-affinity glucocorticoid binding sites (LAGS) in the male rat liver is independent of the endocrine status

The low-affinity glucocorticoid binding sites (LAGS) are entities present in the microsomal fraction of the rat liver, capable of binding several glucocorticoids and progesterone with low affinity. The present work focuses on the demonstration that estradiol exerts a powerful stimulatory effect on the LAGS concentration. For this purpose, we studied the effect of this hormone in immature, hypothyroid, and hypophysectomized rats, three experimental models which present a very low level of LAGS. In all of them, estradiol showed ability to significantly increase the level of LAGS. The positive results obtained in hypophysectomized rats point to a direct action of estradiol on the liver. In immature rats, the estradiol induction of the LAGS was shown to be especially slow, 3–4 days after estradiol administration being necessary to obtain a significant rise in the level of LAGS. Moreover, the dose of estradiol necessary to obtain the LAGS induction in these rats (0.5 mg/100 g body weight) was clearly supraphysiological. From these data we concluded that: (A) estradiol is a powerful stimulator of the LAGS concentration, its effect probably being exerted directly on the liver; and (B) to elicit its effect, estradiol does not need the participation of other hormones known to be implicated in the endocrine regulation of the LAGS.     

Chronic push-pull brain perfusion in unrestrained rhesus macaques

A system was developed to permit perfusion of local brain regions and simultaneous peripheral blood sampling in free-moving caged monkeys. The system comprises a calvarial headpiece that contains multiple push-pull cannulas (PPC), a flexible stainless steel tether, a four-channel fluid swivel, and a surgical procedure for simultaneous multisite brain cannulation. Rhesus macaques were fitted surgically with an indwelling jugular catheter and PPC directed into the third ventricle, median eminence, and preoptic area. These animals were tethered for periods of 14-70 h during which brain perfusates and peripheral blood samples were collected at 10- to 30-min intervals through the tether-swivel assembly. Levels and pulsatile patterns of gonadotropin-releasing hormone in 10-min perfusate samples and luteinizing hormone and cortisol in sequential plasma samples were quantified by specific radioimmunoassays. The normal endocrine profiles in these animals suggest that this system provides a valuable method to study patterns of neurosecretions in an unrestrained simian.     

Length–weight relationships for 24 fish species in a coastal lagoon of the Mexican South Pacific

Length–weight relationships were estimated for 24 species belonging to 16 families of fishes, representing a total of 15 312 measured fish, from the Carretas-Pereyra lagoon, Chiapas, Mexico. Significant length–weight relationships were found for all species. For 13 species, length–weight relationships are published for the first time.     

Selection against toxic aggregation-prone protein sequences in bacteria

Despite genetic variation has the potential to arise new protein functions, spontaneous mutations usually destabilize the native fold. Misfolded proteins tend to form cytotoxic intracellular aggregates, decreasing cell fitness and leading to degenerative disorders in humans. Therefore, it is thought that selection against protein misfolding and aggregation constrains the evolution of protein sequences. However, obtaining experimental data to validate this hypothesis has been traditionally difficult. Here we exploit bacteria as a model organism to address this question. Using variants of the Alzheimer's related Aβ42 peptide designed to exhibit different in vivo aggregation propensities we show here that, in cell competition experiments, the most aggregation-prone variants are always purged out from the growing population. Flow cytometry analysis of cellular metabolism and viability demonstrates that this purifying effect responds to a clear correlation between physiological burden and intrinsic aggregation propensity. Interestingly, the fitness cost of aggregation appears to be associated with aggregation rates rather than with overall protein solubility. Accordingly, we show that, by reducing in vivo aggregation rates, the model osmolyte proline is able to buffer the metabolic impact of protein aggregation. Overall, our data provide experimental support for the role of toxic protein aggregation on the cell fitness landscape and the evolution of natural protein sequences.     

Ingestion and absorption of particles derived from different macrophyta in the cockle Cerastoderma edule: effects of food ration

We analyzed the capacity of the common cockle Cerastoderma edule to utilize detrital food particles obtained from three different macrophytes: the vascular plant Juncus maritimus and two green macroalgae (Ulva lactuca and Enteromorpha sp.). We measured feeding and digestive parameters at three concentrations of detritus (0.5, 1.0 and 3.0 mm³ l^?1), so that functional relationships between ingestive and digestive processes could be assessed. Increasing concentrations of detritus (food) resulted in a reduction in filtering activity (clearance rate l h^?1), but an increase in ingestion rate. Consequently, gut content also increased with increasing food concentration, irrespective of food type. In contrast, the trend followed by absorption efficiency with increasing ingestion rate was determined by food type, being significantly reduced (from 0.63 to 0.11) with Juncus but remaining almost constant with the green macroalgae (0.58 ± 0.07 with Ulva) or only minimally reduced (from 0.66 to 0.48 with Enteromorpha). This differential response had clear consequences for energy uptake: absorption rate increased with increasing particulate organic matter with Enteromorpha but decreased with Juncus. We discuss the possible role of digestive parameters such as digestibility, gut content and gut-residence time in the differential utilization of detrital matter from different vegetal origins by cockles.