增龄及去卵巢对C57BL/6J小鼠护骨素表达的影响

目的观察增龄和去卵巢状态下小鼠血清护骨素(OPG)水平和骨组织中OPG表达的变化。方法4组C57BL/6J小鼠,每组15只：成年雄鼠组(6月龄),老年雄鼠组(20月龄)；假手术雌鼠组和去卵巢雌鼠组鼠在9月龄时分别行假手术和卵巢切除术,手术6个月后处死小鼠。双能X线检测小鼠骨量变化,实时RT-PCR观察OPG mRNA表达水平,ELISA测定血清中OPG的蛋白水平。结果老年组小鼠和去卵巢组小鼠骨密度明显下降。老年组雄性小鼠血清中OPG水平和成年组[(729±180)ng/Lvs (565±131)ng/L]比较明显上升(P＜0.01)。和假手术组比较(644±140)ng/L,去卵巢组小鼠OPG水平(908±338)ng/L也升高(P＜0.05)。老年组雄鼠骨中OPG mRNA的表达拷贝数为成年组的43.75%(P＜0.05)。与假手术比较,去卵巢组雌鼠骨中OPG mRNA的表达拷贝数下降了75%(P＜0.01)。结论增龄以及去卵巢状态下．小鼠血清中OPG以及骨中OPG mRNA表达水平均有明显变化。     

Age-related differences in behavior across the life span of the C57BL/6J mouse

C57BL/6J mice, representing four divergent age groups (ranging from 3 months to 31 months) were each tested on a number of behavioral procedures, selected to sample a wide spectrum of behaviors. This evaluation demonstrated that, as with other mammalian species, not all behaviors in the mouse are affected by old age. Most severely impaired was retention of a single-trial passive avoidance task, most probably reflecting a deficit in memory ability. On tests of motor function, the most demanding tasks revealed the greatest debilitating effects of age, paralleling the effects of task difficulty previously reported in numerous learning studies. Finally, a deficit in the ability to modify preexisting habits in a T-maze learning situation was observed, corroborating reports of increased perseveration in aged humans and nonhuman primates. The similarity of these results across the life span of the C57 mouse with those previously reported for other aged mammalian species demonstrates that certain common types of behaviors seem to be impaired selectively by increased age across mammalian species and raises the possibility that common neurological etiologies may exist for these behavioral deficits.     

The development of mammotroph adenomas in pituitaries of aging female C57BL/6J mice

The development of pituitary adenomas in female C57BL/6J mice was studied over the lifespan. Mammotrophs and somatotrophs, identified by immunocytochemical staining, appeared normal in 3-4 month old animals, with the exception of an occasional hypertrophic mammotroph and, in one gland, a nest of such cells. At 15 months, hypertrophic mammotrophs, somatotrophs and unstained cells occurred singly or in areas of hyperplasia; a mammotrophic adenoma was present in one gland. At 22 months, pituitaries contained mammotroph adenomas or adenomalike mammotroph clusters within hypertrophic, hyperplastic areas as seen in 15 month old glands. Pituitaries from all 28-30 month old mice contained mammotroph adenomas; nests of hypertrophic cells were present in 5 of 8 glands studied. These results suggest that mammotrophic adenomas may arise from hypertrophic mammotrophs, which are often found in nests with other hypertrophic pituitary cell types. However, this study does not exclude the possibility that mammotroph adenomas and hypertrophic mammotrophs occur independently.     

Age-related changes in hypothalamic-pituitary-adrenal axis activity of male C57BL/6J mice

As there is little known about age-related changes in the hypothalamic-pituitary-adrenal (HPA) axis of mice, we determined the daily patterns of corticosterone secretion every 2 h, together with adrenocorticotropic hormone (ACTH) release and central HPA axis markers in the morning and evening of 3-, 9- and 16-month-old male C57BL/6J mice. We observed that: (i) corticosterone secretion showed a distinct age-related circadian pattern. During the light period this was expressed by relative hypercorticism in 9-month-old mice and relative hypocorticism in 16-month-old mice. ACTH was elevated at 16 months of age; (ii) mineralocorticoid (MR) and glucocorticoid receptor (GR) mRNA expression in the hippocampus was significantly decreased in 9-month-old mice, whereas in 16-month-old mice, expression was similar to young animals. Circadian variation was modest in all age groups; (iii) the parvocellular hypothalamic paraventricular nucleus (PVN) expressed very high vasopressin mRNA, which was subject to circadian variation in 3- and 9-month-old mice. Furthermore, significant levels of MR mRNA were expressed in the PVN. In conclusion, basal HPA axis activity and expression of its central regulatory markers are age-dependent in mice. This suggests that the capacity to adjust to environmental demands is either a function of age, or depends on different dynamics of the HPA axis.     

Physiological and behavioral correlates of lifespan in aged C57BL/6J mice

Physiological and behavioral measurements were made in a cohort of 29-month-old male C57BL/6J mice to determine whether any correlated significantly with lifespan. Significant linear relationships with lifespan were found among the physiological measures, including hematocrit and hemoglobin levels and collagen denaturation rate; however, body weight failed to be a significant predictor of survival. Among the behavioral variables studied, significant quadratic relationships with lifespan were found for exploratory activity and passive avoidance learning, while performance on a rotorod and a tightwire showed no significant relationships with lifespan. Through the use of multiple regression techniques, about one-third of the variance in lifespan could be explained by a combination of physiological variables, and about two-fifths could be explained by a combination of behavioral variables.     

Metabolomic profiling of dietary-induced insulin resistance in the high fat-fed C57BL/6J mouse

The predictive ability of metabolic profiling to detect obesity-induced perturbations in metabolism has not been clearly established. Complex aetiologies interacting with environmental factors highlight the need to understand how specific manipulations alter metabolite profiles in this state. The aim of this study was to determine if targeted metabolomic profiling could be employed as a reliable tool to detect dietary-induced insulin resistance in a small subset of experimental animals (n = 10/treatment). Following weaning, male C57BL/6J littermates were randomly divided into two dietary groups: chow and high fat. Following 12 weeks of dietary manipulation, mice were fasted for 5 h prior to serum collection. The resultant high fat-fed animals were obese and insulin resistant as shown by a euglycaemic-hyperinsulinaemic clamp. Sera were analysed by proton nuclear magnetic resonance spectroscopy, and 46 known compounds were identified and quantified. Multivariate analysis by orthogonal partial least squares discriminant analysis, a projection method for class separation, was then used to establish models of each treatment. Models were able to predict class separation between diets with 90% accuracy. Variable importance plots revealed the most important metabolites in this discrimination to include lysine, glycine, citrate, leucine, suberate and acetate. These metabolites are involved in energy metabolism and may be representative of the perturbations taking place with insulin resistance. Results show metabolomics to reliably describe the metabolic effects of insulin resistance in a small subset of samples and are an initial step in establishing metabolomics as a tool to understand the biochemical signature of insulin resistance.     

Comparative survival of C57BL/6J mice on two commonly used mouse diets

Survival of C57BL/6J male mice was found to improve when fed Old Guilford (OG) mouse food as compared to Purina (P) mouse diet. The median life span increased 3.9%, the longest-lived decile increased 17.3% and the maximum life span by 18.5%. This occurred in spite of the fact that the peak weight attained by mice on the OG diet was 14.7% higher than the maximum weight on the P diet. Mean survival times were 852 days on the P diet and 901 days for the OG diet. The increase in the maximum life span was greater than that for the mean or median, with 933 days for the P diet and 1106 days for OG. The two different commercially available diets were found to differ in their trace element content. The P diet was higher than the OG diet by 908% for aluminum, 1% for boron, 22.3% for cadmium, 231% for calcium, 29.2% for copper and 100% for iron. In addition to these differences in trace element content, other factors may have been involved in determining life span such as differences in food consumption or in the caloric content of the two diets.     

Schedule-induced ethanol self-administration in DBA/2J and C57BL/6J mice

BACKGROUND: The purpose of these experiments was to provide an initial investigation into ethanol self-administration elicited in the schedule-induced polydipsia (SIP) paradigm. METHODS: Mature male mice were food deprived to between 80 and 85% of their baseline weight and received 20 daily 1 hr SIP test sessions in which a food pellet (20 mg) was delivered on a fixed-time 60 sec schedule. In different groups, the acquisition of drinking 5% (v/v) ethanol solution (experiment 1) or water (experiment 2) was recorded along with other behaviors that occurred in the test chambers. RESULTS: Results indicated that C57BL/6J mice drank significantly more ethanol than DBA/2J mice and that C57 mice achieved blood alcohol concentrations as high as 300 mg/dl. Blood alcohol concentrations were consistently correlated with g/kg ethanol intake. The groups did not differ in consumption of water. SIP test sessions using higher concentrations of ethanol (10-20% v/v, experiment 1) or sucrose solutions (0.1-2% w/v, experiment 2) then were performed. Group differences in ethanol consumption were maintained at all ethanol concentrations. Although DBAs drank more of a low concentration of sucrose (0.1%), when expressed as g/kg, sucrose intake was equivalent in the two strains at all concentrations. Analysis of the time course of drinking clearly showed that this behavior was adjunctive in nature. CONCLUSION: These results demonstrate the effectiveness of this procedure in inducing ethanol self-administration and its utility for investigating the genetic bases of vulnerability toward excessive ethanol consumption.     

Intravenous Ethanol Self-administration in C57BL/6J and DBA/2J Mice

Two strains of mice, C57BL/6J (B6) and DBA/2J (D2) were allowed to self-administer intravenous (iv) ethanol. These two strains were selected because they differ greatly in their preference for drinking ethanol solutions: 86 mice are preferrers, whereas D2 mice are avoiders of ethanol. Of interest was whether these strains would also differ in self-administration of iv ethanol when taste factors presumably do not influence consumption. Mice were trained with either 60, 75, or 90 mg/kg per infusion. Mice from both strains acquired nosepoking for all of these doses on an FR-3 schedule of reinforcement during 2-hr daily sessions. Additionally, mice in both strains acquired an equal preference for nosepoking on the side resulting in ethanol infusions, compared with the side that had no scheduled consequence, although B6 mice took somewhat more ethanol early in training than did D2 mice. Mice in both strains achieved equal levels of responding at the conclusion of training, when response rates had stabilized. A subset of animals were then tested at doses of ethanol ranging from 25 to 125 mg/kg per infusion. Although their responding tended to decrease over time regardless of changes in the unit dose of ethanol, these mice showed lower response rates for higher doses of ethanol, and less responding for saline than for ethanol. Together, these findings imply that iv ethanol has reinforcing properties in both these strains, despite the strain difference in preference for oral ethanol. Self-administration of iv ethanol in mice may prove a valuable addition to existing animal models for the study of ethanol reward.     

From the Cover: Age-related hearing loss in C57BL/6J mice is mediated by Bak-dependent mitochondrial apoptosis

Age-related hearing loss (AHL), known as presbycusis, is a universal feature of mammalian aging and is the most common sensory disorder in the elderly population. The molecular mechanisms underlying AHL are unknown, and currently there is no treatment for the disorder. Here we report that C57BL/6J mice with a deletion of the mitochondrial pro-apoptotic gene Bak exhibit reduced age-related apoptotic cell death of spiral ganglion neurons and hair cells in the cochlea, and prevention of AHL. Oxidative stress induces Bak expression in primary cochlear cells, and Bak deficiency prevents apoptotic cell death. Furthermore, a mitochondrially targeted catalase transgene suppresses Bak expression in the cochlea, reduces cochlear cell death, and prevents AHL. Oral supplementation with the mitochondrial antioxidants α-lipoic acid and coenzyme Q₁₀ also suppresses Bak expression in the cochlea, reduces cochlear cell death, and prevents AHL. Thus, induction of a Bak-dependent mitochondrial apoptosis program in response to oxidative stress is a key mechanism of AHL in C57BL/6J mice.     

A congenic line of the C57BL/6J mouse strain that is proficient in melatonin synthesis

The C57BL/6J (B6) is the most common inbred mouse strain used in biomedical research in the United States. Yet, this strain is notoriously known for being deficient in the biosynthesis of melatonin, an important effector of circadian clocks in the brain and in the retina. Melatonin deficiency in this strain results from nonfunctional alleles of the genes coding 2 key enzymes of the melatonin synthesis pathway: arylalkylamine‐N‐acetyltransferase (Aanat) and N‐acetylserotonin‐O‐methyltransferase (Asmt). By introducing functional alleles of the Aanat and Asmt genes from the melatonin‐proficient CBA/CaJ (CBA) mouse strain to B6, we have generated a B6 congenic line that has acquired the capacity of rhythmic melatonin synthesis. In addition, the melatonin‐dependent rhythm of dopamine release in the retina is restored in the B6 congenic line. Finally, we have partially characterized the Aanat and Asmt genes of the CBA strain and have identified multiple differences between CBA and B6 alleles, including single nucleotide polymorphism and deletion/insertion of DNA segments of various sizes. As an improved model organism with functional components of the melatonin synthesis pathway and melatonin‐dependent circadian regulations, the new line will be useful to researchers studying melatonin physiological functions in a variety of fields including, but not limited to, circadian biology and neuroscience. In particular, the congenic line will be useful to speed up introduction of melatonin production capacity into genetically modified mouse lines of interest such as knockout lines, many of which are on B6 or mixed B6 backgrounds. The melatonin‐proficient B6 congenic line will be widely distributed.     

Effects of hydrogen sulfide synthesis inhibitors on posthypoxic ventilatory behavior in the C57BL/6J mouse

Background: H(2)S synthesis inhibitors (HSSI) have been shown to impact respiratory control. For instance, the HSSI hydroxylamine (HA) decreases the respiratory discharge rate from isolated medullary sections, and HA in addition to other HSSIs propargylglycine and amino-oxyacetic acid (AOAA) have been found to reduce hypoxic responsiveness. Objectives: The aim of this study was to determine if administration of HSSIs could improve respiratory stability in an intact organism prone to recurrent central apneas. Methods: Saline and HSSI compounds were administered to C57BL/6J mice (n = 24), a strain predisposed to recurrent central apneas, prior to measurement of hypoxic and posthypoxic ventilatory behavior. Results: Administration of HA and AOAA resulted in a significantly smaller percentage of animals expressing one or more apneas during reoxygenation compared to saline control, and animals given AOAA demonstrated a smaller coefficient of variation for frequency during reoxygenation, a marker suggesting greater respiratory stability. This occurred despite varying effects of the three HSSI compounds on hypoxic ventilatory response. Conclusions: Instability and pause expression are improved by targeting H(2)S synthesis, an effect not predicted by effects on hypoxic responsiveness.     

Experimental scoliosis in melatonin-deficient C57BL/6J mice without pinealectomy

The etiology of idiopathic scoliosis is unknown. Scoliosis with many characteristics closely resembling those seen in idiopathic scoliosis has been produced in young chickens and bipedal rats after pinealectomy. In this study, we induced experimental scoliosis in C57BL/6J mice without pinealectomy and melatonin treatment suppressed the development of scoliosis. A total of 100 mice were divided into four groups: 20 quadrupedal mice served as controls; 30 mice underwent resection of two forelegs and tail at 3 wk of age (bipedal mice); the remaining 20 quadrupedal and 30 bipedal mice received intraperitoneal melatonin (8 mg/kg BW) at 19:00 hr daily. Before killing, blood samples were collected in the middle of dark cycle and melatonin levels were measured by radioimmunoassay. Spine X-ray and helical 3D-CT were examined after killing at 5 months of age. The bipedal mice without a tail were able to walk with standing posture, whereas the quadrupedal mice did not walk with standing posture. In C57BL/6J mice, the serum melatonin was reduced to nearly zero; however, the normal level was restored in both bipedal and quadrupedal mice after the injection of melatonin. Scoliosis with rib humps developed in 29 of 30 bipedal and in five quadrupedal mice. None of mice with melatonin treatment developed scoliosis. The results suggest that melatonin deficiency in bipedal mice appears to play crucial role for development of scoliosis. Also the restoration of melatonin levels prevents the development of scoliosis.     

Soleus and EDL muscle contractility across the lifespan of female C57BL/6 mice

All previous aging research on the contractility of rodent skeletal muscle has been conducted on male rodents. Because males and females age differently, we undertook this study to determine if and when age-related decrements in skeletal muscle contractility occur in female mice. Soleus and extensor digitorum longus (EDL) muscles from female C57BL/6 mice aged 4, 8, 16, 24 and 28 mo were assessed in vitro for contractility and subsequently contractile protein content. EDL muscle was resistant to age-related changes in force generation but displayed characteristics of becoming more slow-twitch like. Maximal isometric tetanic force (P_o) generated by soleus muscle declined with age. Soleus muscle size and contractile protein contents were not affected by age and thus could not explain the age-related force decrements. Soleus muscle specific P_o declined with age being 26% lower in muscles of 16–28 mo-old mice indicating that a deterioration in soleus muscle quality of female mice occurred beginning around the age of ovarian failure. Thus this study provides essential, comprehensive baseline data for future studies on age-related muscle dysfunction in the female mouse.     

Bipedal ambulation induces experimental scoliosis in C57BL/6J mice with reduced plasma and pineal melatonin levels

In addition to the induction of scoliosis in chickens by pinealectomy (PINX), we previously demonstrated that removal of the pineal gland also produces scoliosis in bipedal rats, which can be inhibited by melatonin treatment. Using C57BL/6J mice with genetically low circulating melatonin levels, the main objective of the present study was to investigate whether bipedal ambulation in C57BL/6J mice has the same effects on spinal deformity as those seen in pinealectomized bipedal rats. The present study consisted of two phases. The aim of the first experiment was to determine whether the C57BL/6J mouse strain actually exhibits depressed plasma concentrations and/or pineal contents of melatonin during both the light and the dark phase of the light:dark cycle. The aims of the second experiment were to evaluate; (i) whether bipedal ambulation alone in the C57BL/6J mouse induces scoliosis, and (ii) whether PINX with bipedal ambulation in another mouse strain, i.e. C3H/HeJ, which normally exhibits diurnal fluctuations in melatonin synthesis and secretion, has effects similar to those of bipedal ambulation alone in C57BL/6J mice. C3H/HeJ mice, serving as controls, showed significant increases in both plasma concentrations and pineal contents of melatonin during the dark phase when compared with the light phase. In contrast, there were no differences in either circulating levels or pineal contents of melatonin between the light and dark phases in C57BL/6J mice. Moreover, plasma melatonin levels were below the detection limit of the assay in both phases and pineal melatonin was < 10% of that in C3H/HeJ mice. Bipedal ambulation for 40 wk in C57BL/6J mice induced scoliosis at a rate of 64.3%, and two of nine scoliotic mice showed two sites of spinal deformity. This type of ambulation in C3H/HeJ mice resulted in scoliosis at a lower rate (25%), and affected animals had only a single scoliotic site. However, PINX combined with bipedal ambulation in C3H/HeJ mice produced scoliosis at a rate (70%) similar to that seen in C57BL/6J mice, and some double deformations were induced. These results confirm our previous observations in rats, and also support our hypothesis that melatonin as well as the bipedal ambulation appear to play a critical pathogenic role in scoliosis in experimental mammals.