Changes in the renal corpuscles during early postnatal ontogeny of the rat (stereologic analysis)

Kidneys of 60 white rats at the age of 1-45 days of postnatal life have been investigated. Increase in size of the renal corpuscles during the developmental process is accompanied with certain changes in the form and variability of volumes in the structures studied. During early postnatal period, against the background of linear increase in the size of the renal corpuscles, the parameters of variability in volumes, form and in the total number of the renal corpuscles in the organ change non-linear. Stabilization moment of the total number (11-14 days) on the 8th-10th day outgoes that for the parameters of the form and variability of the renal corpuscle volumes.     

Muscle electrolyte measurements during and after hypokinesia in determining muscle electrolyte depletion during hypokinesia in the rat

Hypokinesia (diminished movement) induces muscle mineral depletion. However, the mechanism of muscle mineral depletion during hypokinesia (HK) remains unknown. Measuring electrolyte retention and electrolyte values in muscle, plasma, and urine during and after HK, the aim of this study was to discover if HK could depress mineral retention and lead to muscle mineral depletion. Studies were done on 204 13-wk-old male Wistar rats (370–390 g) during 10 d pre-HK period, 98 d HK period, and 15 d post-HK period. Rats were equally divided into two groups: vivarium control rats (VCR) and hypokinetic rats (HKR). All hypokinetic rats were kept for 98 d in small individual cages, which restricted their movements in all directions without hindering food and water intakes. All control rats were housed for 98 d in individual cages under vivarium control conditions. Both groups of rats were pair-fed. During the HK period skeletal muscle sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), and water content and electrolyte retention decreased significantly (p < 0.05), while urinary and plasma electrolyte levels increased significantly (p < 0.05) in HKR compared with their pre-HK values and their respective VCR. During the initial days of the post-HK period, mineral retention increased significantly (p < 0.05), plasma and urinary electrolyte level decreased significantly (p < 0.05), while muscle electrolyte and water content remained significantly (p < 0.05) depressed in HKR compared with VCR. Muscle mineral and water content, electrolyte retention, plasma, and urinary electrolyte values did not change in VCR compared with their pre-HK values. It was concluded that during HK decreased muscle mineral content may suggest muscle mineral depletion, while increased urinary electrolyte loss and muscle mineral depletion may demonstrate reduced mineral retention. Reduced electrolyte excretion and depressed muscle mineral content during post-HK may indicate skeletal muscle mineral depletion during HK. Dissociation between electrolyte retention and muscle mineral depletion may demonstrate the presence of decreased electrolyte retention as the mechanism of muscle electrolyte depletion during prolonged HK.     

Norepinephrine of the rat myocardium during repeated ischemia

Character of tissue changes as well as their reversibility could vary depending on the duration of myocardial ischemia. Long (over 30 min) ischemia leads to a massive release of myocardial interstitial norepinephrine. We tried to investigate changes in the myocardial sympathetic system produced by a relatively long episode of ischemia-repeperfusion. Myocardial norepinephrine has been collected by means of microdialysis probe during repeated occlusions of the left descending coronary artery. It was shown that long episode of occulusion-reperfusion resulted in suppression of massive norepinephrine release in response to second (test) occlusion. The features of norepinephrine release during successive occlusions make it possible to associate this process with the reversibility of the ischemic tissue damages.     

The influence of hypokinesia on free calcium cation content in myocytes of rat skeletal muscles and myocardium

The influence of hypokinesia on the content of free Ca²⁺ and the level of NAD(P)H in myocytes of rat skeletal muscles and myocardium, and microviscosity of myocyte membranes was investigated. It has been found that hypokinesia increased the free Ca²⁺ content and NAD(P)H level in myocytes of skeletal muscles and myocardium. Alterations of structural-functional properties of membrane that appeared as an increase of membrane fluidity in the regions of lipid bilayer and protein-lipid contact were observed only in skeletal muscles. It was supposed that an increase of calcium cation level in myocytes stimulated the activity of enzymes involved in the apoptosis process that results in the decrease of muscle tissue mass.     

Structure of the thyroid gland in the rat during hypokinesia and after its elimination

The aim of the investigation is to objectively ascertain and study stages of the processes taking into account the zonal structure of the thyroid gland, that is along the whole distance from the center up to the surface of the lobe. Hypokinesia lasts from 1 to 56 days; rehabilitation begins after 28 days of hypokinesia and lasts 28 days. Morphometric analysis of 8 parameters demonstrating the state of the gland are used. In control animals the structural changes from the center towards the surface of the gland lobe occur gradually, the degree of the changes is different and diversily directed [increasing volumetric part (Vv) of the follicular epithelium, decreasing Vv of the colloid, stable Vv of the vascular component]. When both hypokinesia and rehabilitation develop, all signs change wavily. Natural borders of the waves are defined--5, 16, 28 and 51 days for hypokinesia and 13 and 23 days for readaptation. Different structural components of the gland respond variously to the factors mentioned. Changes of every sign in different zones are also not equal and they can be diversily directed. In the course of rehabilitation for 1 month, there is no return to the normal state.     

EPR study of nitric oxide production in rat tissues under hypokinesia

EPR spectroscopy was used to study the intensity of nitric oxide (NO) production upon modeling 60-day progressive hypokinesia (restriction of motor activity) in rats and estimating the content of (DETC)₂-Fe²⁺-NO complexes in heart and liver tissues. In 30 days of hypokinesia, there was a 2–3-fold increase in tissue NO. Administration of a nonspecific inhibitor of NO synthases, L-NAME, to hypokinetic rats prior to measurement decreased their NO level even below the untreated control. Our results show that the intensified NO production in hypokinesia is mainly due to NO synthases, rather than to the nitrite reductase pathway.     

Delay of rat hepatocyte polyploidization in liver growth inhibition during hypokinesia]

Young rats, weighing 55-59g, after being for 10 days in conditions of limited mobility, show a retardation of body growth as well as that of liver growth. The decrease in the rate of organ growth is accompanied by a reduction of the cell proliferation and by a delay in polyploidization of hepatocytes in the liver of experimental rats.     

Titin isoform changes in rat myocardium during development

Developmental changes in the alternative splicing patterns of titin were observed in rat cardiac muscle. Titin from 16-day fetal hearts consisted of a single 3710 kDa band on SDS agarose gels, and it disappeared by 10 days after birth. The major adult N2B isoform (2990 kDa) first appeared in 18-day fetal hearts and its proportion in the ventricle increased to approximately 85% from 20 days of age and older. Changes in three other intermediate-sized N2BA isoform bands also occurred during this same time period. The cDNA sequences of fetal cardiac, adult ventricle, and adult soleus were different in the PEVK and alternatively spliced middle Ig domain. Extensive heterogeneity in splice patterns was found in the N2BA PEVK region. The extra length of the fetal titin isoforms appeared to be due to both a greater number of middle Ig domains expressed plus the inclusion of more PEVK exons. Passive tension measurements on myocyte-sized fragments indicated a significantly lower tension in neonate versus adult ventricles at sarcomere lengths greater than 2.1 microm, consistent with the protein and cDNA sequence results. The time course of the titin isoform switching was similar to that occurring with myosin and troponin I during development.     

Characteristics of the human masseter muscle during hypokinesia

Bioptates of the m. masseter from 20 male persons at the age of 21-30 years have been studied 3, 6, 12 and 24 days after immobilization of the mandible in connection with its fracture. Succinate dehydrogenase (SDG) activity and cross section area of muscle fibers have been determined. Relative volume (Vv) of submicroscopic structures of myons have been found stereologically. In the muscle tissue reactive-destructive changes are revealed; they depend on hypokinesia duration: decreasing SDG activity, cross section area of the fibers and contents of pinocytic vesicles in the endothelial cells of the capillaries. Vv of mitochondria and tubular formations in the sarcoplasmic reticulum change. Certain stageness of structural rearrangements in the muscles are noted, they are considered as a result of the influence of the restricted function and some disturbances occurring between the blood vessels and the muscle fibers.     

Determination of buffering capacity of rat myocardium during ischemia

To determine the buffering capacity of ischemic rat myocardium, lactate production was altered by glycogen depletion prior to total global ischemia. Lactate production was monitored by 1H-NMR spectroscopy in perfused rat hearts and determined by enzymatic assay of freeze-clamped tissue extracts. Intracellular pH was measured by 31P-NMR spectroscopy. The relationship between total lactate produced and pH varied considerably, depending on the final pH reached. At pH greater than 6.4 this relationship is linear with a total buffering capacity (delta lactate/delta pH) of 25 mumol H+/g wet weight per pH unit. At lower pH values (pH less than 6.4), the total buffering capacity increases progressively. Since ischemia is invariably accompanied by ATP and phosphocreatine (PCr) hydrolysis, the proton production/consumption during high-energy phosphate hydrolysis must be considered when evaluating the intrinsic buffering capacity of the myocardium against proton loads produced by lactate production from glucose and glycogen. Schemes are presented which allow an estimation of the contribution of ATP and PCr hydrolysis and the buffering by the CO2/HCO3- system during ischemia. At pH greater than 6.4, the majority (about 60%) of buffering is due to hydrolysis of adenosine triphosphate, phosphocreatine in the heart, and neutralization of sodium bicarbonate in the perfusate. At pH less than 6.4 an increasing proportion of cardiac buffering is from intrinsic cardiac buffers, most likely from intracellular proteins. After correction for these contributions to the observed total cardiac buffering capacity, the intrinsic buffering capacity of the myocardium can be accounted for by a high capacity (170 mumol/g wet weight) but low pKa (5.2) buffering system.     

Mechanism of self-regulation and the inotropic reaction of the rat myocardium during aging

The experiments on rat papillary muscles revealed that in ageing rats myocardium has a decreased distension ability. The curves of shortening value/length and force/velocity for the myocardium of old animals are shifted downwards. The alterations in isotonic contraction parameters had a distinct age differentiation, while the age did not affect the inotropic effects of increased frequency, paired stimulation and external calcium. It is suggested that changes in biomechanical properties of ageing myocardium are associated with alterations in calcium transport in sarcoplasmic reticulum.     

Chromatin organization in the rat hypothalamus during early development.

The organization of chromatin in neuronal and glial nuclei isolated from different brain regions of rats during development was studied by digestion of nuclei with micrococcal nuclease. A short chromatin repeat length (approx. 176 base-pairs compared with that of glial nuclei from foetal cerebral cortex (approx. 200 base-pairs) was present in hypothalamic neurons throughout the ages studied, which was similar to the repeat length of cortical neurons from 7- and 25-day-old animals (approx. 174 base-pairs). Whereas in cortical neurons the chromatin repeat length shortened from approx. 200 base-pairs in the foetus to approx. 174 base-pairs in the first postnatal week, the short chromatin repeat length of hypothalamic neurons was already present 2 days before birth, indicating that hypothalamic neurons differentiate earlier than cortical neurons during brain development.     

Dynamics of oxidation stress markers during long-term antiorthostatic hypokinesia: A retrospective study

Nine volunteers aged 27 to 42 participated in an experiment with 370-day antiorthostatic hypokinesia at–5°C, and their blood serum samples were tested for the concentrations of lipid peroxidation (LPO) derivatives, including diene conjugates (DCs), malonic dialdehyde (MDA), and Schiff bases (SBs), and indices of the antioxidant defense system, including the tocopherol (TP) concentration and total antioxidant activity (AOA). The subjects were divided into two groups, which differed in physical training regimen and prophylaxis measures. Initial LPO steps were inhibited in both of the groups by 54–73% from day 50, while the level of SBs, which are final LPO products, decreased by 50–61% by day 230 and remained much the same up to the end of the experiment. The MDA and SB concentrations decreased by a factor of 1.6–2.3 during recovery. Total AOA decreased as an aftereffect during recovery to a level far lower than physiologically normal. Based on the significant inhibition of free-radical LPO throughout the experiment, long-term adaptation to simulated hypogravity was accompanied by a pronounced decrease in biological oxidation and caused severe stress. Substantial long-term readaptation stress developed during recovery after 370-day antiorthostatic hypokinesia, as was evident from the facts that the LPO activity was almost halved, TP concentration significantly increased, and the functional reserves of water-soluble antioxidants were exhausted. Lack of LPO activation was assumed to reflect adequate compensation in the subjects.     

A cinefluorographic study of mandibular movement during feeding in the rat (Rattus norvegicus)

The anatomy of the masticatory apparatus, and particularly of the mandibular joints, has led to the view that mandibular movement in the Rodentia is predominantly propalinal, or forwards and backwards in direction. As part of an investigation into the mechanism of function of the mandibular joints in these animals, the feeding behaviour of "August" strain and "Wistar" rats was examined by cinephotography and cinefluorography. The rats were trained to feed on barium sulphate impregnated biscuit and animal cake and to drink radio-opaque liquids. Cinefluorographic recordings of ingestion, mastication, deglutition and of drinking were taken in both the lateral and dorso-ventral projections.
Analysis of the recordings has shown a fundamental separation of ingestive and masticatory activity in the rat, which can be attributed to the morphology of the jaws and particularly to the disparity in the lengths of the mandibular and maxillary diastemas. To bring the incisor teeth into occlusion for ingestion, the mandible is brought forward through the rest position and the condyle into articulation with the anterior part of the fossa. In mastication the condyle is moved backwards to bring the molar teeth into occlusion and the condyle into articulation with the posterior articular facet on the fossa. Once the mandible has been moved into the appropriate position for either ingestion or mastication and deglutition, the movements involved in the separation or chewing of the food are cyclical with combined horizontal and transverse movements as well as the fundamental vertical movement acting to open and close the mouth. The basic movement of ingestion carries the mandibular incisors upwards and forwards across the lingual surfaces of the maxillary incisors, so separating the bite. The grinding stroke of mastication is a horizontal movement carrying the mandibular molars anteriorly across the maxillary.     

Preferential uptake of intravenously administered hyaluronidase (Hyalosidase) by damaged rat myocardium

The induction of myocardial infarction in rats by ligation of the left - anterior coronary artery was confirmed by measurement of increased plasma levels of creatine kinase, aspartate aminotransferase and lactate dehydrogenase. Using this model system it has been established t h a t intravenous administration of 12SI-labelled hyaluronidase to rats resulted in a preferential uptake of the enzyme by damaged myocardium as compared to normal heart tissue.     

The use of stereologic image analysis in medicine (peripheral nerves)

The use of image plane scanning for the purpose of quantification of data is becoming increasingly important in medicine and biology. Such equipment allows complex geometric-statistical relationships to be investigated by reduction to a counting process in which picture elements are counted (using a photocell), stored, and evaluated. Various absolute values of interest can then be computed using certain mathematical relationships. These methods, using automatically controlled sampling, are fast, and, since they are able to detect small variations in light intensity, very accurate. Furthermore, even in the presence of highly complex patterns, an accurate surface area measurement can be made. Peripheral nerve cells, for example, lend themselves well to such methods, since the strong contrast between individual structural elements provides excellent conditions for automatic measurement.