Archivio di scienze biologiche最新文献

Some cytological and histochemical characteristics of skin, the kidney and interrenal tissue were studied in Xenopus laevis adult specimens (1) kept in their natural aquatic environment; (2) gradually exposed to dry conditions under which they were kept one week; and (3) returned from the dry environment to water for 24 hr or a week. In the skin, the most relevant changes are those exhibited by epidermal "flask" cells. These cells are generally rather lean, tall and PAS-positive in "dry" animals and in those 24 hr after replacement in water, whereas in animals placed back in water for a week "flask" cells are often large and faintly stainable. In "dry" animals, the skin mucous glands look more emptied of secretion granules than in control animals kept in water or in "dry" specimens returned to water. Difference in the epidermis thickness or in its histochemically evidenced alkaline phosphatase activity were not observed between different groups. In the kidney a clearcut difference between animal groups was found in the glycogen content of the proximal convoluted tubules of the nephron. Glycogen level is very low in "dry" animals. These variations are tentatively ascribed to different degrees of electrolyte resorption. In the interrenal cells, the sudanophil material is scanty in "dry" animals, while it is much more abundant in those returned to water for 24 hr. Similar, though less pronounced, effects had been obtained in previous experiments of ours, in which some of the animals were kept out of water on moist moss, that is under less severe conditions of water deficiency than in the present experiments.

Were studied in healthy human subjects under conditions of hydro-saline retention the intrarenal mechanism underlying the hydronatriuretic effect of Dopamine (DA) and the changes in DA renal effects induced by Sulpiride (S). DA was infused i.v. in a subpressor dose (0,1 microgram/kg . min) during induced hypotonic polyuria. In each experiment four clearance periods of 15 min were performed; DA was administered during the second and third clearance periods. The glomerular filtration rate and renal effective plasma flow were estimated as endogenous creatinine and PAH clearances, respectively. Tubular sodium and potassium reabsorptions were also determined. 1) In the state of hydro-saline retention, renal arteriolar (mainly preglomerular) vasodilation was produced by DA. Moreover, both sodium isosmotic reabsorption as a percentage of sodium filtered load and sodium anisosmotic reabsorption as a percentage of sodium distal load were inhibited. These tubular inhibitions were found to be correlated with the haemodynamic effects of DA. 2) Sulpiride treatment (4,4 mg/kg . day given orally for two days prior to the experiment and 100 mg i.m. 40 min before DA infusion) caused (a) an increase in the hydro-natriuretic response to hydration during control clearance and (b) a decrease in DA haemodynamic effects. An interpretation is proposed accounting for these DA effects as well as for dependence of DA renal effects on the extracellular fluid volume.

Noradrenaline has been applied by microelectrophoresis to a small portion of the atrial pacemaker area in the rabbit's heart in order to study the local effects of this chemical transmitter separately from the ones deriving from other parts of the pacemaker area. In a first group of cells, whose action potential and location assimilate them to true pacemaker cells, noradrenaline caused a reduction in cycle length and an increase in the steepness of slow diastolic depolarization. In a second group of cells similar to latent pacemaker cells, noradrenaline caused no change in cycle length, the outstanding effect being an increase in the steepness of the slow diastolic depolarization which afterwards changed into a subthreshold oscillation. A third type of cells showed intermediate characteristics between the two previous groups. These results suggest that: a) the chronotropic effect of noradrenaline on the heart atrial pacemaker seems to be due to changes in the steepness of slow diastolic depolarization which can assume, in some instances, the shape of subthreshold oscillations; the effects on the other parameters in our preparation seem to be either less constant or less significant; b) the different effects which are obtained on various kinds of cells seem to be the result of a different degree of sensitivity to noradrenaline and to the more or less premature activation of mechanisms antagonizing the action of noradrenaline. The results are discussed on the basis of a model of spontaneous atrial pacemaking which has been recently proposed.

The histofunctional picture of the hypophysis, thyroid and testis was studied in Xenopus laevis specimens 1) kept in their natural aquatic environment; 2) gradually exposed to dehydration conditions under which they were kept one week; and 3) returned from the dry environment to water for 24 hr or 7 days. Of particular interest are the changes displayed in the hypophysis by type II acidophils, i.e. presumably prolactin producing cells. In the pituitary of "dry" animals and of those 24 hr after their replacement in water these cells appear numerous, large-sized and heavily stained whereas they are small and slightly stainable in the pituitary of control animals or of "dry" ones 7 days after their replacement in water. On the basis of these results it is surmised that prolactin is continuously synthesized and released into the circulation in Xenopus specimens kept or replaced in water, thereby contributing to the animals adaptation to the aquatic environment, whereas in those kept under waterless condition prolactin synthesis is not discontinued, but its release into the bloodstream declines or is abolished. In the testis of the animals kept in dry conditions or 24 hr after replacement in water, the germ cells do not seem to have undergone substantial changes, while the sudanophilic material, which can be detected in interstitial tissues in the animals kept in water, is lacking. In all groups the thyroid histofunctional pattern suggests an intense activity, particularly in control animals or in "dry" specimens 7 days after replacement into water.

The brain of the guinea pig in stereotaxic coordinates is proposed as a tool for neurophysiologists who are interested in the guinea pig as an experimental animal. The frontal sections of guinea pig brain in stereotaxic coordinates extend from anterior (A) 17.0 to posterior (P) 5.0. The frontal sections of the brain are reproduced as drawings in which brain contours as well as nuclear and fibre structures are outlined. The procedure used for setting the stereotaxic coordinates and zero planes is reported and the limitation of the use of the tables is discussed.

The influence of norepinephrine and/or acetylcholine on K uptake of the guinea pig sinus node was investigated. Both "high" (10(-6) M) and "low" (10(-9) M) mediator concentrations were employed. The following results were obtained: 1) high concentration of norepinephrine increased K uptake; 2) high concentration of acetylcholine had a similar effect; 3) simultaneous exposure to both mediators did not lead to summation of the effects; 4) low concentration of norepinephrine depressed K uptake; 5) high concentration of acetylcholine overcame the inhibitory effect of the small concentration of norepinephrine; 6) 2-deoxy-D-glucose did not abolish the stimulating effect of acetylcholine on potassium uptake; and 7) strophanthidin abolished the stimulatory effect of norepinephrine, but not that of acetylcholine. The following conclusions are drawn: 1) both neuromediators in suitable concentrations increase K uptake in the sinus node; 2) the mechanism of such an increase is different, norepinephrine increasing the active and acetylcholine increasing the passive potassium transport; 3) a low concentration of norepinephrine depresses K uptake; and 4) when the two mediators are administered together, acetylcholine suppresses the action of norepinephrine on K transport.

Histones were prepared and purified from chick embryo, chick and chicken liver nuclei. The comparative analysis of these histone preparations, fractionated by polyacrylamide gel electrophoresis, indicates that histone fractions of chick embryo, chick and chicken livers are respectively identical and they comigrate with calf thymus histones.

In order to evaluate the effect on embryonic development of a solvent commonly used in pharmacological investigations, glycerol formal was administered to pregnant rats from days 6 through 15 of gestation at the daily doses of 0.25, 0.50 and 1.0 ml/Kg i.m. Glycerol formal did not induce systemic toxicity in the mothers, but showed an embryotoxic and teratogenic activity on the products of conception.

Responses were evoked in the lateral geniculate body (L.G.B.) of "encéphale isolé" cats by single-shock stimulation of either the geniculate body or the optic tract of the other side. Responses to optic tract stimulation were modified following excitability changes in the contralateral L.G.B. due to topical application of strychnine and KCl. Laminar stimulation and recording in different layers (A, A1, and B) suggested the existence of a certain homotopic organization of L.G.B. interconnections. The activity evoked in the L.G.B. was found to be abolished by electrocoagulation of the posterior commissure and intermediate gray matter. These results point to the presence of a transthalamic pathway which might mediate L.G.B. activity to the contralateral visual cortex.