Age-related changes in serotonin content and its release reaction of rat platelets

The serotonin content of platelets, serum and plasma from rats of various ages was examined. In male rats, platelet serotonin content, which was about 0.65 nmol/10(8) platelets at young age (6-7 months), increased slightly at middle age (12-14 months) but decreased markedly at old age (25-26 months). Significant difference (P less than 0.05) was observed between young and old rats, and between middle-aged and old rats. In female rats, on the other hand, no age-related change in the platelet serotonin content was found. In both sexes, the serotonin content of rat sera changed with age in the same pattern as that of the platelets. No plasma serotonin was detected in rats of either sex and at any ages examined. Serotonin release from rat platelets was also studied using collagen and thrombin as stimulants. In males, the responsiveness of platelets to these two stimulants showed almost the same age-dependent changes. It was lower in middle-aged rats than in young rats but increased greatly in old rats. Significant difference (P less than 0.05) was observed between middle-aged and old rats. In females, collagen and thrombin had the opposite effect on the sensitivity of the platelets as age increased. The amount of serotonin released in response to collagen was low until middle age but increased markedly at old age, while the content of serotonin released by thrombin remained high until middle age and decreased greatly at old age. These results imply that age-related changes in the serotonin release reaction in rat platelets differed according to the stimulants used.     

大鼠海马结构内有髓神经纤维老年性改变的体视学研究

目的 探讨雌性Long-Evans大鼠海马结构及其内有髓神经纤维的老年性改变。 方法 运用透射电子显微镜和体视学方法分别对5只青年(6月龄)、5只中老年(18月龄)和6只老年(28月龄)雌性Long-Evans大鼠海马结构及其内有髓神经纤维进行定量研究。 结果 青年组、中老年组和老年组大鼠的海马结构总体积,海马结构内有髓神经纤维的体积分数和总体积,有髓神经纤维的长度密度和有髓神经纤维平均直径均未见显著性改变。中老年组大鼠海马结构内有髓神经纤维总长度与青年组相比增加了63.6%,老年组有髓神经纤维总长度与中老年组相比下降了47.5%,老年组有髓神经纤维总长度与青年组比较下降了13.8%。 结论 本研究结果进一步支持正常老年大脑的有髓神经纤维存在广泛性老年改变。     

Effect of traditional Chinese herbal medicines on the pharmacokinetics of western drugs in Sprague-Dawley rats of different ages (II): Aminophylline-huan shao tan and aminophylline-pu chung yi chi tang.

The effect of Chinese herbal medicines (Huan Shao Tan and Pu Chung Yi Chi Tang) and western drugs (sodium phenobarbital and cimetidine) on the serum concentration and pharmacokinetic parameters of theophylline and cytochrome P-450 of Sprague-Dawley (SD) rats of three different ages were examined. The older rats without pretreatment with Chinese herbal medicines and western drugs exhibited higher serum theophylline concentration and lower pharmacokinetic parameters of theophylline than middle-aged and younger rats (P < 0.05), but there was no difference in cytochrome P-450 activity among the three different ages of rats. All rats when pretreated with sodium phenobarbital showed lower serum theophylline concentration and higher pharmacokinetics parameters of theophylline. Also, the activity of cytochrome P-450 was higher (P < 0.05). When cimetidine was pre-administered in SD rats of three age groups, all rats exhibited lower serum theophylline concentration and higher pharmacokinetics parameters (P < 0.05), but the activity of cytochrome P-450 remained unchanged (P > 0.05). The results were opposite to other studies, probably because the dose and dosing intervals were different. No single effect occurred on the younger and middle-aged rats after pretreatment with Huan Shao Tan and Pu Chung Yi Chi Tang: their serum theophylline concentration, pharmacokinetics parameters and cytochrome P-450 activity were the same as the control group. However, the older rats after pretreatment with Huan Shao Tan or Pu Chung Yi Chi Tang showed lower serum theophylline concentration and higher pharmacokinetics parameters than the younger and middle-aged rats pretreated with similar Chinese herbal medicines. This indicates that Huan Shao Tan and Pu Chung Yi Chi Tang may perhaps improve the elimination of theophylline in older rats. This might be attributed to the increase in hepatic blood flow or in liver volume, since the activity of cytochrome P-450 was not affected by the administration of Chinese herbal medicines.     

Sex-differences in age-related cognitive decline in C57BL/6J mice associated with increased brain microtubule-associated protein 2 and synaptophysin immunoreactivity

Understanding cognitive aging is becoming more important as the elderly population grows. Here, the effects of age and sex on learning and memory performance were compared in female and male young (3-4 months old) middle-aged (10-12 months old) and old (18-20 months old) wild-type C57BL/6J mice. Old males and females performed worse than young or middle-aged mice in novel location, but not novel object recognition tasks. Old mice, of both sexes, also showed impaired spatial water maze performance during training compared with young or middle-aged mice, however only old females failed to show robust spatial bias during probe trials. While there was no age-difference in passive avoidance performance for males, females showed an age-related decline. There was no difference in cognitive performance between young and middle-age mice of either sex on any task. Cognitive performance was associated with alterations in immunoreactivity of microtubule-associated protein 2-positive dendrites and synaptophysin-positive pre-synaptic terminals in hippocampal CA1, CA3, and dentate, entorhinal cortex, and central nucleus of amygdala. Overall, microtubule-associated protein 2 immunoreactivity was increased in old females compared with both young and middle-age females with no significant difference in males. In contrast, synaptophysin immunoreactivity increased from young to middle-age in females, and from middle-age to old in males; females had higher levels of synaptophysin immunoreactivity than males in middle-age only. Elevated levels of microtubule-associated protein 2 and synaptophysin may constitute a compensatory response to age-related functional decline in mice.     

Decreased expression of ErbB4 and tyrosine hydroxylase mRNA and protein in the ventral midbrain of aged rats

Decreased availability or efficacy of neurotrophic factors may underlie an increased susceptibility of mesencephalic dopaminergic cells to age-related degeneration. Neuregulins (NRGs) are pleotrophic growth factors for many cell types, including mesencephalic dopamine cells in culture and in vivo. The functional NRG receptor ErbB4 is expressed by virtually all midbrain dopamine neurons. To determine if levels of the NRG receptor are maintained during aging in the dopaminergic ventral mesencephalon, expression of ErbB4 mRNA and protein was examined in young (3 months), middle-aged (18 months), and old (24–25 months) Brown Norway/Fischer 344 F1 rats. ErbB4 mRNA levels in the substantia nigra pars compacta (SNpc), but not the adjacent ventral tegmental area (VTA) or subtantia nigra pars lateralis (SNl), were significantly reduced in the middle-aged and old animals when compared to young rats. Protein expression of ErbB4 in the ventral midbrain was significantly decreased in the old rats when compared to the young rats. Expression of tyrosine hydroxylase (TH) mRNA levels was significantly reduced in the old rats when compared to young animals in the SNpc, but not in the VTA or SNI. TH protein levels in the ventral midbrain were also decreased in the old animals when compared to the young animals. These data demonstrate a progressive decline of ErbB4 expression, coinciding with a loss of the dopamine-synthesizing enzyme TH, in the ventral midbrain of aged rats, particularly in the SNpc. These findings may implicate a role for diminished NRG/ErbB4 trophic support in dopamine-related neurodegenerative disorders of aging such as Parkinson's disease.     

Establishment and survival of the strobilar stage ofTaenia crassiceps in hamsters,gerbils, and mice,with reference to different helminth isolates

Following the oral administration of metacestodes of two isolates ofTaenia crassiceps, the enteral establishment and survival of the strobilar stage were examined in golden hamsters (Mesocricetus auratus), Mongolian gerbils (Meriones unguiculatus) and laboratory mice. The origin of the isolates wasMicrotus montebelli caught in Japan in 1985 orClethrionomys rutilus captured on St. Lawrence Island, Bering Sea, in 1988 (abbreviated as JPN and SLI isolates), respectively. The enteral establishment of the SLI isolate was distinctly higher than that of the JPN isolate in golden hamsters and mice, whereas the difference was marginal in Mongolian gerbils. All initially-established parasites survived to become gravid adults in prednisolone-treated golden hamsters and Mongolian gerbils; the average recovery of cestodes of the SLI and JPN isolates were 55.8%–76.7% vs 11.7%–35.0% in the former and 28.0%–52.7% vs 25.8%–32.2% in the latter. The distinctly higher level of enteral establishment of the SLI isolate in golden hamsters makes available a model for quantitative studies on parasite-host relationships in experimental taeniasis.This study was supported by grants 01790490, 02044083 and 03044016 from the Ministry of Education, Science and Culture, Japan     

Age-dependent alterations in the physicochemical properties of rat liver microsomes

Aging results in a significant decline in liver drug metabolism which is largely attributable to changes in the microsomal mixed function oxidase system. For example, the mixed function oxidase system in the livers of senescent rats is characterized by: (1) a reduced cytochrome P-450 content; (2) a decline in the specific activity of NADPH-cytochrome c (P-450) reductase; and (3) a slower rate of ethylmorphine N-demethylation in comparison to young adult animals. Since several factors intrinsic to the microsomes may influence the efficacy of the mixed function oxidase system, e.g. the phospholipid and cholesterol contents, the saturation index of the fatty acids and the fluidity of the membranes, we conducted a physicochemical analysis of liver microsomes isolated from young adult (3-4 months), mature (12-16 months) and senescent (25-27 months) male Fischer rats. Although the microsomal cholesterol content did not change appreciably between maturity and senescence, there was a marked decline in the total phospholipid content. This resulted in a significant increase in the cholesterol/phospholipid ratio, 0.49 to 0.65 between 16 and 27 months of age. The age-related changes in the total phospholipid content were largely reflected in each of the major fractions, i.e. phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine + phosphatidylserine. Small increases in the relative percentages of highly unsaturated fatty acid species were offset by similar decreases in the more frequent and more saturated species as a function of increased age. As a result, the net change in the fatty acid saturation index was probably minimal. However, the increase in the cholesterol/phospholipid ratio most likely contributes to the significant decline in the order parameter of microsomes isolated from old rats which, in turn, may impair the functional capacity of the hepatic mixed function oxidase system.     

Age-related changes in paternal responses of gerbils parallel changes in their testosterone concentrations.

Results of previous studies in our laboratory have shown that testosterone (T) inhibits parental response in adult male Mongolian gerbils. Here, we examined developmental changes in parental responses of male gerbils before, during, and after a naturally occurring surge in T that peaks on Day 75 postpartum. On the hypothesis that T inhibits parental response in male gerbils, we predicted that (a) 75-day-old male gerbils would be less responsive to neonates than would either younger or older male gerbils, and (b) young male gerbils whose T titers were rising as the litters that they were helping to rear matured would show a decrease over days in parental effort relative to older male gerbils whose T titers were falling as the litters that they were helping to rear matured. Both predictions were confirmed, providing evidence consistent with the view that naturally occurring, developmental changes in circulating concentrations of T play a role in age-related changes in the level of parental response of male Mongolian gerbils.     

Age-dependent changes in rat liver microsomal membrane structure and functions under benzene treatment

The influence of benzene on 3 and 24 months old rat liver microsomes was studied. Some structural and functional changes occur under benzene treatment in the cytochrome P-450 system which are more pronounced in 3 months old rat microsomes than in the 24 months ones. Glucose-6-phosphatase and glucose dehydrogenase activities indicate that 3 months old rat microsomal vesicles are more stable against benzene injury than those, of 24 months old ones. In vitro benzene hydroxylation activation by NADPH addition decreased disruptive xenobiotic's effect on 3 but not on 24 months old rat liver microsomal vesicles. This fact suggests that the rate of benzene hydroxylation is important for its membrane damaging action effect. Thus, age-related differences in xenobiotic action on liver microsomes could be related to the decrease of benzene metabolism rate with senescence.     

Effects of a novel melatonin analog on circadian rhythms of body temperature and activity in young, middle-aged, and old rats

Circadian rhythms of body temperature and activity were recorded in young, middle-aged, and old rats. A new melatonin analog, S20242, was administered daily around the onset of darkness for a 2-week period. Compared to the young animals, there was a significant age-related reduction in the amplitude and stability of body temperature and activity in both the middle-aged and old rats. In these two groups there was an improvement of the circadian rhythm of body temperature as a result of daily application of the melatonin analog.     

Ultrastructural changes and immunohistochemical localization of advanced glycation end products in the heart of streptozotocin-treated Mongolian gerbils

This study was designed to clarify the developing mechanism of cardiomyopathy and vasculopathy in streptozotocin-treated Mongolian gerbils. Twenty male Mongolian gerbils (MG; 10-12 weeks old) were used, and 150 mg/kg of streptozotocin (STZ) was injected into the left femoral vein. Six control male MG were injected intravenously with normal saline. The animals showed severe hyperglycemia (up to 330 - 96.4 mg/dl) by 1 week after streptozotocin administration. At 1 week after STZ treatment, cardiomyocytes revealed no significant change, but unclear striated structures were demonstrated in cardiomyocytes at 4 weeks. After 1 year, anisocytosis was observed, and in the perinuclear region granular components were stained positively with periodic acid-Schiff reagent. Ultrastructurally, at 4 weeks and 1 year after STZ treatment, cardiomyocytes were irregular in size, and oval amorphous and lysosomal electron-dense bodies were observed in perinuclear and cytoplasmic regions. In coronary arteries, endothelial and medial cells revealed increased vesicles and intercellular collagen fibrils. Capillaries showed slight swelling of endothelial cells associated with the lamellar thickening of basement membrane and collagen fibrils in the perivascular regions. Immunohistochemically, advanced glycation end products (AGE) were observed in the cytoplasm of vascular and heart cells, and ultrastructurally the reaction products were demonstrated in the endoplasmic reticulum and lysosomes of cardiomyocytes and vascular cells in the STZ-treated Mongolian gerbils. AGE may play an important role not only in angiopathy but also in cardiomyopathy of STZ-treated Mongolian gerbils after STZ treatment.     

Neural correlates of age-related declines in frequency selectivity in the auditory midbrain

Reduced frequency selectivity is associated with an age-related decline in speech recognition in background noise and reverberant environments. To elucidate neural correlates of age-related alteration in frequency selectivity, the present study examined frequency response areas (FRAs) of multi-unit clusters in the inferior colliculus of young, middle-aged, and old CBA/CaJ mice. The FRAs in middle-aged and old mice were found to be broader and more asymmetric in shape. In addition to a decrease of closed/complex FRAs in both middle age and old groups, there was a transient decrease in V-shaped FRAs and a concomitant increase in multipeak FRAs in middle age. Intensity coding was also affected by age, as observed in an increase of monotonic responses in middle-aged and old mice. While a decline in low-level activity began in middle age, reduced driven rates at suprathreshold levels occurred later in old age. Collectively, these results support the view that aging alters frequency selectivity by widening excitatory FRAs and that these changes begin to appear in middle age.     

Age-related changes in potassium-evoked overflow of dopamine in the striatum of the rhesus monkey

Rapid (5Hz) chronoamperometric recordings using Nafion-coated carbon fiber electrodes (30–90 microns o.d.) combined with pressure-ejection of potassium from micropipettes were used to investigate potassium-evoked overflow of dopamine (DA) in the striatum of young (5 to 10 years old) and middle-aged (19 to 23 years old) anesthetized rhesus monkeys. The potassium-evoked DA-like signals from the 19- to 23-year-old animals were significantly lower in amplitude than those recorded in the young animals. In addition, the temporal dynamics of DA signals in the caudate nucleus of middle-aged animals were faster, while the time courses of the signals recorded in the putamen of middle-aged monkeys were significantly longer as compared to the signals recorded from young animals. Moreover, home cage activity levels of the middle-aged animals were significantly lower. Taken together, these data support age-related changes in the output of DA from DA fibers in the striatum of middle-aged monkeys.     

Evoked responses of the dentate gyrus during seizures in developing gerbils with inherited epilepsy

When they are 1-2 mo old, domesticated Mongolian gerbils begin having initially mild seizures which become more severe with age. To evaluate the development of this increasing seizure severity, we obtained field potential responses of the dentate gyrus to paired-pulse stimulation of the perforant path during seizures. In 18 gerbils that were 1.5-8.0 mo old, 73 seizures were analyzed. We measured population spike amplitude, the slope of the field excitatory postsynaptic potential (fEPSP), and the population spike amplitude ratio (2nd/1st) to evaluate excitatory and inhibitory synaptic processes. In gerbils <2 mo old, exposure to a novel environment was followed by an increase in population spike amplitude and then by seizure onset, but population spike amplitude ratio and fEPSP slope remained at baseline levels, and multiple population spikes were never evoked. As previously reported for chronically epileptic gerbils, these findings provide little evidence of a disinhibitory seizure-initiating mechanism in the dentate gyrus when young gerbils begin having seizures. In young gerbils evoked responses changed little during the behaviorally mild seizures. In contrast, most seizures in older gerbils included generalized convulsions, postictal depression, and evoked responses that changed dramatically. In older gerbils, shortly after seizure onset the dentate gyrus became hyperexcitable. Population spike amplitude and fEPSP slope peaked, and multiple population spikes were evoked, suggesting that mechanisms for seizure amplification and spread are more developed in older gerbils. Next, dentate gyrus excitability decreased precipitously, and population spike amplitude and fEPSP slope diminished. This period of hypoexcitability began before the end of the seizure, suggesting it may contribute to seizure termination. After the convulsive phase of the seizure, older gerbils remained motionless during a period of postictal depression, and population spike amplitude remained suppressed until the abrupt switch to normal exploratory activity. These findings suggest that the mechanisms of postictal depression may suppress granule cell excitability. The population spike amplitude ratio peaked after the convulsive phase and then gradually returned to the baseline level an average of 12 min after seizure onset, suggesting that granule cell inhibition recovers within minutes after a spontaneous seizure. Although it is unclear whether the seizure-related changes in evoked responses are a cause or an effect of increased seizure severity in older gerbils, their analysis provides clues about developmental changes in the mechanisms of seizure spread and termination.     

Changes in the levels and the rate of synthesis of transfer RNA in tissues of mice of different ages

Levels of transfer RNA (tRNA) were determined in liver, kidney, skeletal muscle, heart, and brain of young (35-day), adult (12-month) and old (24-month) female C57BL/6J mice. Kidney and liver showed little change in tRNA levels between young and adult mice, but the levels decreased in old mice. Skeletal muscle tRNA decreased steadily from young to old mice. Heart tRNA increased during maturation to adult organisms and then decreased in old individuals. Brain levels of tRNA increased steadily.No age-related change in the rate of transport of orotic acid into cells was observed. However, all tissues exhibited a decrease in uridine pools between adult and old mice. Most importantly, all tissues of aging mice showed a decrease in the rate of tRNA synthesis.     

Age-related decrease in proopiomelanocortin gene expression in the arcuate nucleus of the male rat brain.

The decline in reproductive function with aging is due in part to decreased gonadotropin-releasing hormone (GnRH) secretion. beta-Endorphin (beta E), an endogenous opioid peptide derived from proopiomelanocortin (POMC), is thought to exert a tonic inhibitory effect upon hypothalamic GnRH secretion. We tested the hypothesis that the age-related decrease in GnRH secretion in male rats is due to increased beta E synthesis, by comparing POMC mRNA levels in the arcuate nucleus (ARC) of intact young, middle-aged and old male rats. In an initial study (Study 1), sixteen 20-microns coronal sections each from the ARC of 3- (n = 5) and 23-month-old (n = 4) male Fischer 344 rats were anatomically matched and analyzed. In a second study (Study 2), four anatomically matched sections of caudal arcuate nucleus from 3- (n = 4), 11- (n = 7) and 23-month-old (n = 5) male rats were compared. POMC mRNA levels were quantitated by in situ hybridization histochemistry, using a 35S-labeled oligodeoxynucleotide probe complementary to a portion of rat POMC cDNA and computerized image analysis. The number of grains per cell and cells per section were used as indices of cellular POMC mRNA content and the number of neurons expressing the POMC gene, respectively. Cellular POMC mRNA content was significantly lower in old compared to young animals (Study 1: 54 +/- 3 vs. 74 +/- 2 grains/cell, p less than 0.01; Study 2: 59 +/- 2 vs. 71 +/- 2 grains/cell, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of heme metabolism during senescence: activity of several heme-containing enzymes and heme oxygenase in the liver and kidney of aging rats

The activities of several heme-containing enzymes plus succinate dehydrogenase, the content of mitochondrial cytochromes, the amount of microsomal cytochrome P-450, and the activity of heme oxygenase, the major enzyme of heme degradation, have been compared in young, mature and senescent rats. Measurements were made in liver, a tissue previously reported to have an age-related decrease in δ-aminolevulinic acid synthetase, and in kidney, a tissue previously reported to have no age-related change in this enzyme, the rate-limiting enzyme of heme biosynthesis (Paterniti, Lin and Beattie, Arch. Biochem. Biophys., 191 (1978) 792–797). The activity of cytochrome oxidase in liver mitochondria did not decrease with age while this activity in kidney mitochondria was highest in animals one year old and decreased in the two-year-olds. By contrast, succinate dehydrogenase of both kidney and liver mitochondria decreased markedly in the aging rats. No age-related change in the content of cytochromes b, c or aa₃ was observed in liver mitochondria; however, a marked age-related decrease in cytochrome aa₃ was observed in kidney mitochondria. Similarly no change in cytochrome P-450 levels was observed in either tissue obtained from aging animals. In the liver, catalase activity increased while in the kidney it decreased in senescent as compared to mature animals. Heme degradation does not decrease with age as the activity of heme oxygenase increased in both liver and kidney of two-year-old rats as compared to one-year-olds. These results suggest that the lower activity of δ-aminolevulinic acid synthetase observed in the aging rat may not be correlated with a decrease in the activity of heme-containing proteins and that the regulation of the heme pool used for the synthesis of various intracellular hemo-proteins may be complex.     

Differential effects of nucleus basalis lesions in young adult and aging rats

To characterize age-related changes in frontal cortical plasticity, we assessed maze learning and frontal cortical pharmacology in young adult, middle-aged, and aged rats. Rats received either ibotenic acid or sham lesions of the nucleus basalis magnocellularis (NBM) and were then trained on a radial maze task. After training, we assessed [3H]desmethylimipramine (DMI), [3H]muscimol, [3H]AMPA, and [3H]QNB binding using quantitative autoradiography. Both middle-aged and aged rats were impaired on the radial maze task. DMI binding was increased in both middle-aged and aged rats, while QNB binding was decreased in aged rats. While lesions impaired maze performance at all ages, middle-aged and aged rats showed more profound lesion-induced deficits. Lesions increased GABA, and AMPA receptor binding in young adult rats only. These lesion-induced changes may reflect a compensatory response that is lost with advancing age.