Aged Control Rats Research Articles

Synaptic vesicle redistribution during hippocampal frequency potentiation and depression in young and aged rats

Technical complexities associated with studies of defined synapses in the mammalian CNS have made it difficult to determine whether CNS synaptic vesicles respond to repetitive monosynaptic activation in the same ways as do PNS vesicles. Moreover, even in the PNS, the specific ultrastructural correlates of short-term synaptic potentiation are not well characterized. In the present studies, therefore, the Schaffer collateral-commissural fiber projection to field CA1 of the hippocampus was used as a model brain system in which to assess quantitative relations between dynamic vesicle patterns and frequency potentiation and depression. Anesthetized rats were perfused with aldehyde fixative during stimulation trains and concomitant microelectrode recording in order to study temporal correlations between physiology and synaptic structure. In addition, young and aged animals were compared to determine whether there are ultrastructural correlates of a previously described age-related impairment of hippocampal frequency potentiation. After 1 min of 10 Hz synaptic stimulation (stim), frequency potentiation of the population spike was correlated with increases in local vesicles (LV; within 150 nm of the active zone) and in vesicles directly apposed (AV) to the active zone membrane of CA 1 synapses. In addition, the ratio LVD: DVD of local-to-distant vesicle (DV; beyond 150 nm) densities was increased under all stimulation conditions. After 10 min of 10 Hz stim, or 1 min of 40 Hz stim, some vesicle depletion (approximately 25%) was present, as was some spike depression or decline from peak potentiation. However, LV depletion was not well correlated with degree of spike depression. Mean dendritic spine area was also increased in association with potentiation (at 1 min of 10 Hz stim) in young rats. Membrane infoldings similar to the cisternae described in other systems were seen with repetitive stimulation, providing evidence of vesicle recycling in these CNS terminals. In comparison to young control animals, terminals in non-stimulated aged group control rats exhibited a higher LVD:DVD ratio and a reduced DVD. In addition, the stimulation-induced increase in AV at 1 min of 10 Hz stim was not present in aged rat synapses. However, no age-related differences in vesicle-density measures were found at any stimulation point.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of irradiation on cortical bone and their time-related changes. A biomechanical and histomorphological study.

The effects of high-dose irradiation on the biomechanical and morphological properties of cortical bone and their time-related changes were studied in male Sprague-Dawley rats. A single fraction of 3500 rads was applied to the middle part of the right thigh. Age and sex-matched control rats that did not receive radiation were used for comparison. Two weeks after irradiation, the animals had lost weight and disappearance of bone cells, shrunken osteocytes, and significantly decreased bone-turnover activities were noted. The bone marrow showed reduced hematopoietic elements and sinusoids with increased fat. No change in the torsional strength and geometric properties of bone was noted at this time. Six to ten weeks after irradiation, histopathological abnormalities of the bone persisted, and there was an accelerated resorption process. However, significant increases in the strength and cortical area of bone appeared only in the non-irradiated, contralateral femur. On the irradiated side, decreased cortical area and increased porosity of bone were found at fourteen to eighteen weeks when compared with the control rats. Other histomorphological properties, such as bone porosity, osteocyte count, and periosteal new-bone formation, appeared to recover eighteen weeks after irradiation, as they became similar to the values for the age-matched normal control rats.

Effect of chronic alcohol consumption on rat brain microsome lipid composition, membrane fluidity and Na+K+-ATPase activity

The present study reports differences in phospholipid classes, fatty acids of individual phospholipids, and changes in membrane fluidity and Na +K +-ATPase activity in brain microsomes of rats maintained on an alcohol diet for 35 days compared to sex, age and weight-matched control rats maintained on a calorically-equivalent, non-alcohol diet. Although no difference in Na +K +-ATPase activity was found in microsomes from alcohol vs control rats when measured in the absence of added alcohol, the presence of low concentrations of ethanol (<100mM) stimulated, while high concentrations (>100mM) inhibited enzyme activity. The stimulation was differentially expressed in that the microsomal enzyme from alcohol rats was stimulated to a lesser extent than the enzyme from control rats. However, the inhibiting effect of high concentrations of alcohol was similar in microsomes from both alcohol and control rats. Also in membranes from alcohol rats, there was a lower quantity of phosphatidylethanolamine (PE) and higher quantities of phosphatidylserine (PS) and phosphatidylinositol (PI) compared to membranes from control rats. The major change in fatty acid composition was a reduction in the level of polyunsaturated fatty acids, which was particularly evident in PI and PS. The linoleic acid: arachidonic acid ratio ( 18:2 20:4 ) and the saturation: unsaturation ratio were also increased in PI and PS in membranes from alcohol animals. However, the ratio of n-6/n-3 fatty acids remained the same or was reduced in membranes from alcoholic animals. Although no difference in the inherent “fluidity” of membranes from alcohol vs control rats could be demonstrated by electron paramagnetic resonance, molecular tolerance to ethanol was demonstrated in the membranes from alcohol rats by the resistance to the disordering effects of added ethanol.

Glycoproteins and proteins in an axolemma-enriched fraction and myelin from developing rats: effect of maternal ethanol consumption.

The present study examined proteins and glycoproteins from an axolemma-enriched fraction from the developing offspring of female rats that were pair-fed control or 6.6% (50 g/liter) ethanol liquid diets on a chronic basis prior to parturition. In addition, this study examined the synthesis of the major CNS myelin-associated glycoprotein (MAG) as an index of myelin maturation. The results of the latter study demonstrated normal MAG maturation in ethanol-treated rats. However, a significant decrease in the proportion of radioactivity associated with MAG was found in the developing offspring of ethanol-treated rats. The major axolemmal proteins from 32-day rats included those with molecular weights of 105 K, 81 K, 62 K, 55 K, 52 K, 36 K, and 33 K. Major peaks of radioactivity were associated with fucosylated axolemmal glycoproteins with apparent molecular weights of 150 K, 130 K, 85 K, 76 K, and 64 K. Several development-related changes in the protein composition of axolemma-enriched fractions were observed in control animals. Between 22 and 32 days of age control rats exhibited a significant (P less than .05) decrease in the proportion of axolemmal proteins that had apparent molecular weights of 150 K, 105 K, and 62 K. A development-related decrease in the 105 K axolemma-associated protein did not occur during the 22-32 day age period in the offspring of ethanol-treated animals. At 22 days the proportion of this 105 K protein in affected offspring was significantly (P less than .05) less than that in age-matched control rats and comparable to that in 32-day control rats. The relative distribution of radioactivity among fucosylated axolemmal glycoproteins also changed significantly between 22 and 32 days of age. These changes include a decrease in the proportion of radioactivity associated with the 110 K, 55 K, and 52 K fucosylated glycoproteins and an increase in the proportion of radioactivity associated with the 85 K and 67 K glycoproteins. Several small, but significant (P less than .05) alterations were found associated with glycoproteins in an axolemma-enriched fraction from 22- and 32-day ethanol-treated rats.

Increased Susceptibility of Livers of Aged F344/NCr Rats to the Effects of Phenobarbital on the Incidence, Morphology, and Histochemistry of Hepatocellular Foci and Neoplasms&lt;xref ref-type="fn" rid="FN2"&gt;2&lt;/xref&gt;&lt;xref ref-type="fn" rid="FN3"&gt;3&lt;/xref&gt;

Aged (875 days old) and young 42 days old) male F344/NCr rats were given sodium phenobarbital (PB) in drinking water for periods up to 233 days. Groups of aged rats were killed at 30 or 60 days or allowed to live their normal life-span, and the cause of death was determined. Young rats killed after 30, 60, and 150 days of PB exposure. Hepatocellular foci were classified into basophilic, eosinophilic, or vacuolated types according to morphologic appearance of the hepatocyte cytoplasm and were characterized by histochemical methods for the presence of gamma-glutamyl transpeptidase (GGT). The most common contributing causes of death for rats in both groups were large granular lymphocyte (LGL) leukemia and pituitary tumors. PB decreased the incidence of LGL leukemia but increased the incidence and multiplicity of hepatocellular GGT-positive foci, eosinophilic foci, and eosinophilic hepatocellular adenomas. GGT-positive eosinophilic foci increased in diameter and volume, but not in number, after appearing early in the experiment. Hepatocellular basophilic foci and neoplasms in aged control rats were usually GGT-negative and did not appear to respond to dietary PB. GGT-positive foci were seen in aged control rat livers and were composed of vacuolated amphophilic hepatocytes that differed morphologically from hepatocytes in naturally occurring liver tumors. Young rats given PB had few GGT-positive foci by 150 days on test. Aged rat livers were thus more sensitive to the effects of PB than were livers of young rats.

Lysosomal enzyme changes in young and aged control and entorhinal-lesioned rats

In the hippocampus of young and aged rats, lysosomal acid phosphate and β-glucuronidase were localized by enzyme histochemistry to the pyramidal and granule cells and to the mossy fiber zone (acid phosphatase only). Following a unilateral entorhinal lesion, enhancement in enzyme staining was observed within GFA (glial fibrillary acidic) protein-positive astrocytes and in cells resembling microglia and oligodendroglia in the ipsilateral dentate outer molecular layer and the hippocampal stratum lacunosum-moleculare. In young animals, these changes, first detected on day 2 post-lesion, were maximum on days 4 and 10 post-lesion and declined subsequently. The aged animals exhibited a delayed time-course of enzyme changes with minimal increases on days 2 and 4 post-lesion and greater increases on days 10 and 30 and gradual diminution thereafter. The delayed lysosomal response in the aged animal paralleled a reduction in the induction of glial cells following the lesion. Our findings suggest that the previously reported impairment in the clearing of degeneration debris in the aged animal is mediated by reduced glial induction and delayed glial lysosomal activation.

A Simple Method for Determining Epithelial Cell Turnover in Small Intestine

Epithelial cell migration in animal gut classically is measured by autoradiography after systemic administration of tritiated thymidine. A migration rate is calculated from observations of the leading edge of villus epithelial cells containing labeled nuclei at varying time periods after tritiated thymidine injection. This method is very accurate, but laborious, time consuming, and costly. A new, simplified method for measuring epithelial cell measurement of [3H] deoxyribonucleic acid specific activity in frozen sections of intestine cryostat-cut from villus tip to crypt base. The leading edge of [3H]deoxyribonucleic acid can be detected reproducibly (coefficient of variation 11.25%). Autoradiographic and chemical methods for determining the leading edge of labeled cells compared favorable (r=0.848). Epithelial cell migration rates in barrier-reared Fisher 344 aging (27 mo) and young control (4-5 mo) rats were compared and no differences were detected in duodenum, jejunum, or ileum. Labeled epithelial cells reached the villus tip sooner in the ileum than in duodenum or jejunum. However, crypt-villus column heights were greater in duodenum and jejunum and the calculated epithelial cell migration rate was faster in upper intestine than in the ileum. Although ileal epithelial cells are shed from the villus sooner than cells in the upper intestine, the rate of cell migration in ileum is slower.

Ultrastructural axonal pathology in experimentally diabetic and aging control rats

Electron microscopic examination of tibial nerves from streptozotocin-diabetic, alloxan-diabetic and age-matched control rats was undertaken at two weeks and two, four, eight, and twelve months following the induction of diabetes. Many myelinated axons of both diabetic and control rats contained glycogen-like granules, axon-Schwann cell networks and fingerlike intrusions of myelin. These axonal changes were observed more frequently with advancing age and duration of diabetes, suggesting that they are related to aging or repeated injury. A larger proportion of diabetic axons than control axons were affected at early time periods, but by eight and twelve months the control axons were as frequently (or more frequently) involved as diabetic axons. Thus, experimental diabetes may confer upon peripheral myelinated axons an increased susceptability to aging or repeated injury. Specific morphologic abnormalities in peripheral myelinated axons associated uniquely with streptozotocin or alloxan diabetes in the rat were not noted.

Glycogen accumulation in tibial nerves of experimentally diabetic and aging control rats

Tibial nerves of streptozotocin-diabetic, alloxan-diabetic, and age-matched control rats were examined at 2 weeks and 2, 4, 8, and 12 months following the induction of diabetes. Glycogen-like granules accumulated within perineurial and Schwann cells of only the diabetic animals. This accumulation may reflect a metabolic abnormality in these cells which could account for the reduced conduction velocities seen in the peripheral nerves of these same diabetic rats (Moore et al. 1980a). Glycogen-like granules were also present and increased with age in myelinated axons of both diabetic and control rats. Quantitative data suggest that axonal accumulation of glycogen-like granules is related to aging or injury related phenomena to which diabetic axons may be more susceptible.

Fluorescence histochemical evidence for decreased noradrenaline synthesis in sympathetic neurones of aged rats

Measurements of formaldehyde-induced fluorescence of noradrenaline (NA) in sympathetic neuronal perikarya of aged (24-month) and younger (4-month) control rats revealed little or no NA fluorescence in many sympathetic neurones of aged rats: neuronal fluorescence in younger rats was substantially greater. Monoamine oxidase inhibition increased NA fluorescence in all rats, but the increase was greater in the 4-month controls. Reserpine administration caused an almost complete disappearance of NA fluorescence after 12 h. However, normal NA levels were restored in the 4-month controls after 48 h but not for 7 days in the aged rats.

Control of proximal tubule fluid reabsorption in experimental glomerulonephritis.

We have recently shown that in the early autologous phase of nephrotoxic serum nephritis (NSN) single nephron glomerular filtration rate is unchanged from values in normal hydropenic control rats, but that single nephron filtration fraction and efferent arteriolar oncotic pressure (piE) are reduced because of a marked reduction in the glomerular capillary ultrafiltration coefficient. The present study was undertaken to examine the influence of this decline in piE as well as the other known determinants of peritubular capillary fluid exchange on absolute proximal fluid reabsorption (APR) in NSN. The findings indicate that APR and proximal fractional reabsorption are reduced significantly in NSN, relative to values in a separate group of age and weight-matched normal hydropenic control rats studied concurrently. In addition to the measured decline in piE, efferent arteriolar plasma flow (Qe) and peritubular capillary hydraulic pressure (Pc) were found to increase significantly, while interstitial oncotic pressure, estimated from hilar lymph, was not significantly different from values in control rats. Using a mathematical model of peritubular capillary fluid uptake we found that, assuming that the capillary permeability-surface area product and interstitial hydraulic pressure are unchanged in NSN, the observed changes in piE and Pc are sufficient to offset the effect of the increase in QE, yielding a calculated reduction in APR of approximately 4 nl/min, in excellent agreement with the observed mean decline of 4.1 nl/min. These findings suggest that control of APR in NSN is mediated by the same factors that regulate APR under normal physiological conditions, namely, the imbalance of forces governing peritubular capillary uptake of isotonic reabsorbate.