The effects of early rearing environment on the hormonal induction of maternal behavior in virgin rats

The present study investigated the effects of isolation rearing, through the artificial rearing paradigm (AR), on the hormonal induction of maternal behavior (MB) in female Sprague-Dawley rats. Between postnatal days (PND) 4 and 18, rat pups were raised either with their mothers (MR) or artificially, without their mothers (AR). As well, some of the AR pups were provided with additional maternal-like licking stimulation (AR-MAX) while the others were not given any additional stimulation (AR-MIN). At PND 60-100, AR (n = 28) and MR (n = 25) animals were ovariectomized (OVX). One week after the surgery, rats were either treated with a 2-week estrogen (E2) and progesterone (P) hormonal regimen or not treated with the hormone replacement. Maternal behavior testing with foster pups commenced 24 h following the removal of P treatment. Results demonstrated that MR animals showed increased pup licking and hover-crouching in comparison to AR animals and that hormonally primed groups became maternal more quickly than non-primed groups, regardless of the rearing history. There was also a significant interaction between the rearing condition (MR vs. AR) and hormonal treatment on the quality of maternal behavior exhibited. The highest level of licking and crouching was shown by the hormone-treated MR group. Mechanisms for these effects are discussed.     

The effects of early rearing environment on the hormonal induction of maternal behavior in virgin rats

The present study investigated the effects of isolation rearing, through the artificial rearing paradigm (AR), on the hormonal induction of maternal behavior (MB) in female Sprague–Dawley rats. Between postnatal days (PND) 4 and 18, rat pups were raised either with their mothers (MR) or artificially, without their mothers (AR). As well, some of the AR pups were provided with additional maternal-like licking stimulation (AR-MAX) while the others were not given any additional stimulation (AR-MIN). At PND 60–100, AR (n = 28) and MR (n = 25) animals were ovariectomized (OVX). One week after the surgery, rats were either treated with a 2-week estrogen (E2) and progesterone (P) hormonal regimen (Bridges, R.S., 1984. A quantitative analysis of the roles of dosage, sequence, and duration of estradiol and progesterone exposure in the regulation of maternal behavior in the rat. Endocrinology 114, 930–940) or not treated with the hormone replacement. Maternal behavior testing with foster pups commenced 24 h following the removal of P treatment. Results demonstrated that MR animals showed increased pup licking and hover-crouching in comparison to AR animals and that hormonally primed groups became maternal more quickly than non-primed groups, regardless of the rearing history. There was also a significant interaction between the rearing condition (MR vs. AR) and hormonal treatment on the quality of maternal behavior exhibited. The highest level of licking and crouching was shown by the hormone-treated MR group. Mechanisms for these effects are discussed.     

Effect of low extracellular calcium and ryanodine on muscle contraction of the mouse during postnatal development.

We have examined the effects of low Ca2+ solutions, Co2+, and ryanodine on the isometric tension and contraction speed of isolated, developing mouse EDL muscles. Twitch responses of young muscles (7-14 days postnatal) were more sensitive to lowered [Ca2+]o than those of more fully developed muscles (22-35 days postnatal). Responses of EDL muscles from a middle-aged group (15-21 days postnatal) were intermediate between the two other groups. Overall, the time course of contraction in a single twitch was accelerated by low [Ca2+]o. Ca(2+)-free solution induced a 7.95 and 9.25 mV depolarization in young and "old" muscle fibres, respectively. The presence of cobalt ions (5 mM) in the Krebs solution had a similar effect as Ca(2+)-free Krebs in terms of reduction of the isometric twitch and tetanic tensions of EDL muscles from the various age groups. In contrast, the shortening of the contraction time seen with Ca(2+)-free solution did not take place following exposure to Co(2+)-containing solutions. Finally, young (7-14 days postnatal) muscles were less sensitive to the inhibitory action of ryanodine on the twitch compared with more fully developed muscles (22-35 days postnatal). Taken together, our results indicate that from birth to maturity, there is a gradual change in the spectrum of calcium utilization for the contractile process.     

Maturational differences between vascular and bladder smooth muscle during ovine development

Maturation rates of vascular and visceral smooth muscle (SM) during ovine development were compared by quantifying contractile protein, myosin heavy chain (MHC) isoform contents, and contractile properties of aortas and bladders from female fetal (n = 19) and postnatal (n = 21) sheep. Actin, myosin, and protein contents rose progressively throughout development in both tissues (P 相似文献   

Denervation alters myosin heavy chain expression and contractility of developing rat diaphragm muscle.

We hypothesized that unilateral denervation (DNV) of the rat diaphragm muscle (Dia(m)) in neonates at postnatal day 7 (D-7) alters normal transitions of myosin heavy chain (MHC) isoform expression and thereby affects postnatal changes in maximum specific force (P(o)) and maximum unloaded shortening velocity (V(o)). The relative expression of different MHC isoforms was analyzed electrophoretically. With DNV at D-7, expression of MHC(neo) in the Dia(m) persisted, and emergence of MHC(2X) and MHC(2B) was delayed. By D-21 and D-28, relative expression of MHC(2A) and MHC(2B) was reduced in DNV compared with control (CTL) animals. Expression of MHC(neo) also reappeared in adult Dia(m) by 2-3 wk after DNV, and relative expression of MHC(2B) was reduced. At each age, P(o) was reduced and V(o) was slowed by DNV, compared with CTL. In CTL Dia(m), postnatal changes in P(o) and V(o) were associated with an increase in fast MHC isoform expression. In DNV Dia(m), no such association existed. We conclude that, in the Dia(m), DNV induces alterations in both MHC isoform expression and contractile properties, which are not necessarily causally linked.     

Impact of beta-myosin heavy chain isoform expression on cross-bridge cycling kinetics

Myosin heavy chain (MHC) isoforms alpha and beta have intrinsically different ATP hydrolysis activities (ATPase) and therefore cross-bridge cycling rates in solution. There is considerable evidence of altered MHC expression in rodent cardiac disease models; however, the effect of incremental beta-MHC expression over a wide range on the rate of high-strain, isometric cross-bridge cycling is yet to be ascertained. We treated male rats with 6-propyl-2-thiouracil (PTU; 0.8 g/l in drinking water) for short intervals (6, 11, 16, and 21 days) to generate cardiac MHC patterns in transition from predominantly alpha-MHC to predominantly beta-MHC. Steady-state calcium-dependent tension development and tension-dependent ATP consumption (tension cost; proportional to cross-bridge cycling) were measured in chemically permeabilized (skinned) right ventricular muscles at 20 degrees C. To assess dynamic cross-bridge cycling kinetics, the rate of force redevelopment (ktr) was determined after rapid release-restretch of fully activated muscles. MHC isoform content in each experimental muscle was measured by SDS-PAGE and densitometry. alpha-MHC content decreased significantly and progressively with length of PTU treatment [68 +/- 5%, 58 +/- 4%, 37 +/- 4%, and 27 +/- 6% for 6, 11, 16, and 21 days, respectively; P < 0.001 (ANOVA)]. Tension cost decreased, linearly, with decreased alpha-MHC content [6.7 +/- 0.4, 5.6 +/- 0.5, 4.0 +/- 0.4, and 3.9 +/- 0.3 ATPase/tension for 6, 11, 16, and 21 days, respectively; P < 0.001 (ANOVA)]. Likewise, ktr was significantly and progressively depressed with length of PTU treatment [11.1 +/- 0.6, 9.1 +/- 0.5, 8.2 +/- 0.7, and 6.2 +/- 0.3 s(-1) for 6, 11, 16, and 21 days, respectively; P < 0.05 (ANOVA)] Thus cross-bridge cycling, under high strain, for alpha-MHC is three times higher than for beta-MHC. Furthermore, under isometric conditions, alpha-MHC and beta-MHC cross bridges hydrolyze ATP independently of one another.     

Comparison of twitch potentiation in the gastrocnemius of young and elderly men

The capacity for twitch potentiation in the gastrocnemius muscle was determined following maximal voluntary contractions (MVC) in 11 elderly (means +/- SD; 66.9 +/- 5.3 years) and 12 young (25.7 +/- 3.8 years) men. Potentiation was observed by applying selective stimulation to the muscle belly, 2 s after a 5 s MVC. With this procedure, both groups showed significant (P less than 0.05) increases in twitch tension in the gastrocnemius (ratios of potentiated twitch to baseline were means = 1.68 +/- 0.40 for young vs means = 1.40 +/- 0.20 for the elderly, P less than 0.001). Time to peak tension of the twitch decreased from means = 101.5 +/- 17.9 ms to means = 88.0 +/- 15.8 ms in the young men following potentiation; the respective values for the older men were 136.7 +/- 17.9 ms and 133.1 +/- 28.6 ms. These changes resulted in a greater rate of tension development in the potentiated state. The elderly gastrocnemius thus showed qualitatively similar changes in the isometric twitch following potentiation, but reduced and prolonged responses in comparison to young adults. Slowed muscle contraction and reduced capacity for potentiation may be physiological correlates of the reported morphological changes in aged skeletal muscle.     

Early postnatal development of electrophysiological and histological properties of sensory sural nerves in male rats that were maternally deprived and artificially reared: Role of tactile stimulation

Early adverse experiences disrupt brain development and behavior, but little is known about how such experiences impact on the development of the peripheral nervous system. Recently, we found alterations in the electrophysiological and histological characteristics of the sensory sural (SU) nerve in maternally deprived, artificially reared (AR) adult male rats, as compared with maternally reared (MR) control rats. In the present study, our aim was to characterize the ontogeny of these alterations. Thus, male pups of four postnatal days (PND) were (1) AR group, (2) AR and received daily tactile stimulation to the body and anogenital region (AR‐Tactile group); or (3) reared by their mother (MR group). At PND 7, 14, or 21, electrophysiological properties and histological characteristics of the SU nerves were assessed. At PND 7, the electrophysiological properties and most histological parameters of the SU nerve did not differ among MR, AR, and AR‐Tactile groups. By contrast, at PND 14 and/or 21, the SU nerve of AR rats showed a lower CAP amplitude and area, and a significant reduction in myelin area and myelin thickness, which were accompanied by a reduction in axon area (day 21 only) compared to the nerves of MR rats. Tactile stimulation (AR‐Tactile group) partially prevented most of these alterations. These results suggest that sensory cues from the mother and/or littermates during the first 7–14 PND are relevant for the proper development and function of the adult SU nerve. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 351–362, 2018     

Prenatal stress in rat causes long-term spatial memory deficit and hippocampus MRI abnormality: differential effects of postweaning enriched environment

Prenatal stress (PS) can cause long-term hippocampus alternations in structure and plasticity in adult offspring. Enriched environment (EE) has an effect in rescuing a variety of neurological disorders. Pregnant dams were left undisturbed (prenatal control, PC) or restrained 6h per day from days 14 to 21 (prenatal stress, PS). Control and prenatal stressed offspring rats were subjected to a standard rearing environment (SE) or an EE on postnatal days 22-120 (PC/SE PC/EE, PS/SE, and PS/EE; n=5, each group). At ～4 months of age, all rats underwent Morris water maze test and brain MRI examination. Hippocampi were then dissected for biochemical analyses, including, Western blot for NMDA receptor (NR) subunits and synaptophysin and RT-PCR forβ1 integrin and tissue-plasminogen activator (t-PA). MRI showed all 5 rats in the PS/SE group and 5 in the PS/EE group exhibited increased signals in bilateral hippocampus and increased T2 time in the PS/SE group. Exposure to EE treatment on postnatal days 22-120 counteracted the deficit in spatial memory and increased NR1 protein expression, but it did not affect the rate of high signals and increased T2 time, decreased NR2, synaptophysin, β1 integrin and t-PA mRNA expressions in PS adult offspring. The results of this study indicate PS in rats causes long-term spatial memory deficits and gross hippocampus pathology. Postnatal EE treatment has differential benefits in terms of spatial learning, signaling molecules, and gross hippocampus pathology.     

Postnatal development of adrenergic responsiveness in the rabbit heart

It is uncertain how changes in the beta-adrenoceptor population influence the contractility of developing heart. To resolve this we have examined postnatal developmental changes in the adrenergic responsiveness of the rabbit heart. The inotropic effect of isoproterenol on isolated left ventricular papillary muscles from rabbits aged 3, 21, and 90 days was compared with the relative number of beta-adrenoceptors at each age measured using [3H]dihydroalprenolol ([3H]DHA) as the specific ligand. The maximum tension developed in response to isoproterenol increases from 37 +/- 7 to 175 +/- 33% above control twitch tension between 3 and 21 days of age; this is followed by a decrease to 68 +/- 12% in the young adult. During this period of development, there is a decline in EC50 towards increased sensitivity. These differences are partially accounted for by an increase in the numbers of specific [3H]DHA binding sites from 17.3 +/- 2.3 to 56.6 +/- 9.9 fmol/mg wet tissue weight from 3 to 21 days, and a subsequent decrease to 32 +/- 4.5 fmol/mg tissue in the young adult. The proportionally larger increase in contractility compared with the number of beta-adrenoceptor binding sites during the first 3 weeks of life is discussed in terms of the developmental changes in the efficacy of coupling between receptor occupancy and contraction.     

Progressive resistance training reduces myosin heavy chain coexpression in single muscle fibers from older men.

The purpose of this study was to examine myosin heavy chain (MHC) and myosin light chain (MLC) isoforms following 12 wk of progressive resistance training (PRT). A needle biopsy was taken from the vastus lateralis to determine fiber-type expression [ATPase (pH 4.54) and MHC/MLC] in seven healthy men (age = 74.0 +/- 1.8 yr). Subjects were also tested for 1-repetition maximum (1-RM), pre- and posttraining. The progressive knee extensor protocol consisted of three sets at 80% of 1-RM 3 days/wk for 12 wk. Freeze-dried, single muscle fibers were dissected for MHC and MLC analysis and then subjected to SDS-PAGE and silver staining, pre- and posttraining. MHC expression increased in the I (10.4%; P < 0.05) and decreased in I/IIa (9.0%; P < 0.05), I/IIa/x (0.9%; P < 0.05), and IIa/x (8.9%; P < 0.05) isoforms, with no change in the IIa and IIx isoforms, pre- vs. posttraining (total fibers = 3,059). The MLC(3f)-to-MLC(2) ratio did not change with the PRT in either the MHC I or MHC IIa isoforms (total fibers = 902), pre- to posttraining. ATPase fiber distribution did not significantly differ following training (I: 50. 4 +/- 6.7 vs. 51.9 +/- 7.9, IIa: 36.8 +/- 5.3 vs. 41.1 +/- 7.0, IIb: 12.8 +/- 5.6 vs. 7.0 +/- 4.0%; pre- vs. posttraining, respectively). 1-RM increased (51.9%; P < 0.05) from pre- to posttraining. The PRT provide a stimulus for alterations in MHC isoforms, which demonstrated a decrease in all hybrid isoforms and an increase in MHC I expression (not found in the ATPase results), unlike the MLC ratio (3:2), which was not altered with training.     

Skeletal muscle adaptations to microgravity exposure in the mouse.

To investigate the effects of microgravity on murine skeletal muscle fiber size, muscle contractile protein, and enzymatic activity, female C57BL/6J mice, aged 64 days, were divided into animal enclosure module (AEM) ground control and spaceflight (SF) treatment groups. SF animals were flown on the space shuttle Endeavour (STS-108/UF-1) and subjected to approximately 11 days and 19 h of microgravity. Immunohistochemical analysis of muscle fiber cross-sectional area revealed that, in each of the muscles analyzed, mean muscle fiber cross-sectional area was significantly reduced (P < 0.0001) for all fiber types for SF vs. AEM control. In the soleus, immunohistochemical analysis of myosin heavy chain (MHC) isoform expression revealed a significant increase in the percentage of muscle fibers expressing MHC IIx and MHC IIb (P < 0.05). For the gastrocnemius and plantaris, no significant changes in MHC isoform expression were observed. For the muscles analyzed, no alterations in MHC I or MHC IIa protein expression were observed. Enzymatic analysis of the gastrocnemius revealed a significant decrease in citrate synthase activity in SF vs. AEM control.     

Time-resolved X-ray diffraction studies of frog skeletal muscle isometrically twitched by two successive stimuli using synchrotron radiation

In order to clarify the delay between muscular structural changes and mechanical responses, the intensity changes of the equatorial and myosin layer-line reflections were studied by a time-resolved X-ray diffraction technique using synchrotron radiation. The muscle was stimulated at 12-13 degrees C by two successive stimuli at an interval (80-100 ms) during which the second twitch started while tension was still being exerted by the muscle. At the first twitch, the intensity changes of the 1.0 and 1.1 equatorial reflections reached 65 and 200% of the resting values, and further changes to 55 and 220% were seen at the second twitch, respectively. Although the second twitch decreased not only the time to peak tension but also that to the maximum intensity changes of the equatorial reflections (in both cases, about 15 ms), the delay (about 20 ms) between the intensity changes and the development of tension at the first twitch were still observed at the second twitch. On the other hand, the intensities of the 42.9 nm off-meridional and the 21.5 nm meridional myosin reflections decreased at the first twitch to the levels found when a muscle was isometrically tetanized, and no further decrease in their intensities was observed at the second twitch. These results indicate that a certain period of time is necessary for myosin heads to contribute to tension development after their arrival in the vicinity of the thin filaments during contraction.     

反复电刺激大鼠上矢状窦后的抑郁行为学表现

目的 观察反复电刺激清醒状态下大鼠上矢状窦后的行为学表现.方法 24只雄性SD大鼠随机分为对照组和实验组,实验组连续给予21d电刺激(电流1～2 mA、频率20 Hz、正弦波,脉冲宽度250 μs,持续15分钟/次,1次/天),通过观察大鼠体重变化、液体消耗实验及旷场实验来评价大鼠是否抑郁.结果 电刺激21d后,实验组较对照组大鼠体重增长减慢(P＜0.05),其差别有统计学意义;实验组旷场实验得分、液体消耗实验中糖水消耗量和蔗糖偏嗜度均明显下降,与对照组相比有统计学差异(P＜0.05);而纯水消耗量显著升高(P＜0.05).结论 21d反复电刺激清醒状态下大鼠上矢状窦,大鼠有抑郁的行为学表现.     

Adaptive responses to creatine loading and exercise in fast-twitch rat skeletal muscle

We investigated the effects of chronic creatine loading and voluntary running (Run) on muscle fiber types, proteins that regulate intracellular Ca2+, and the metabolic profile in rat plantaris muscle to ascertain the bases for our previous observations that creatine loading results in a higher proportion of myosin heavy chain (MHC) IIb, without corresponding changes in contractile properties. Forty Sprague-Dawley rats were assigned to one of four groups: creatine-fed sedentary, creatine-fed run-trained, control-fed sedentary, and control-fed run-trained animals. Proportion and cross-sectional area increased 10% and 15% in type IIb fibers and the proportion of type IIa fibers decreased 11% in the creatine-fed run-trained compared with the control-fed run-trained group (P < 0.03). No differences were observed in fast Ca2+-ATPase isoform SERCA1 content (P > 0.49). Creatine feeding alone induced a 41% increase (P < 0.03) in slow Ca2+-ATPase (SERCA2) content, which was further elevated by 33% with running (P < 0.02). Run training alone reduced parvalbumin content by 50% (P < 0.05). By comparison, parvalbumin content was dramatically decreased by 75% (P < 0.01) by creatine feeding alone but was not further reduced by run training. These adaptive changes indicate that elevating the capacity for high-energy phosphate shuttling, through creatine loading, alleviates the need for intracellular Ca2+ buffering by parvalbumin and increases the efficiency of Ca2+ uptake by SERCAs. Citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities were elevated by run training (P < 0.003) but not by run training + creatine feeding. This indicates that creatine loading during run training supports a faster muscle phenotype that is adequately supported by the existing glycolytic potential, without changes in the capacity for terminal substrate oxidation.     

Maternal Separation Induced Alterations of Neurogenesis in the Rat Rostral Migratory Stream

1. The aim of our study was to investigate the possibility that maternal separation, an experimental model for studies of early environmental influences, has an effect on postnatal neurogenesis in neurogenic pathway—the rostral migratory stream (RMS). 2. Rat pups were subjected to maternal separation daily for 3 h, starting from the first postnatal day (P1) till P14 or P21. In the first two groups, brains were analyzed at the age of P14 and P21, respectively. In the third group, after 3 weeks of maternal separation, 1 week of normal rearing was allowed, and the brains were analyzed at P28. The controls matched the age of maternally separated animals. Dividing cells were labeled by bromodeoxyuridine; dying cells were visualized by Fluoro-Jade C and nitric oxide (NO) producing cells by NADPH-diaphorase histochemistry. 3. Quantitative analysis of proliferating cells in the RMS showed that maternal separation decreased the number of dividing cells in all experimental groups. This decrease was most prominent in the caudal part of the RMS. The amount of dying cells was increased at the end of 3 weeks of maternal separation as well as 1 week later. The number of differentiated nitrergic cells in the RMS was increased at the end of 2 or 3 weeks of maternal separation, respectively. Besides quantitative changes, maternally separated animals showed an accelerated maturation of nitrergic cells. 4. Our results indicate that an exposure of rats to adverse environmental factors in early postnatal periods may induce acute site-specific changes in the RMS neurogenesis.     

Mechanical properties of denervated amphibian muscle

Denervated amphibian muscle does not show the prolongation of action potential found in mammalian denervated muscle. It was, therefore, predicted that denervated amphibian muscle would not show prolongation of the mechanical twitch. The sartorius muscles in one leg of toads--Xenopus borealis--were denervated for 140-268 days. Isometric twitch time to peak, time to half relaxation and twitch/tetanus ratio were not changed following denervation, confirming our prediction. Twitch tension decreased to 68% and tetanic tension decreased to 75% of control values. The maximum velocity of unloaded shortening (muscle length/s) was also unchanged.     

Burn injury to trunk of rat causes denervation-like responses in the gastrocnemius muscle

Thermal injury results in dystropic changes in skeletal muscle and abnormal pharmacological responses to neuromuscular relaxants, each of which suggests a denervation-like phenomenon. In the rat thermal injury model we examined whether, as in denervation states, increases in nicotinic acetylcholine receptors (AChR) and hyposensitivity to d-tubocurarine (dTc) are found. While anesthetized, thermal injury was imposed to trunk only. At 10, 14, and 21 days after injury the effective doses of dTc for left gastrocnemius tension suppression to 95% of control tension (ED95) were 0.213 +/- 0.039, 0.305 +/- 0.070, and 0.214 +/- 0.032 mg/kg, respectively. These values were significantly higher (P less than 0.05) than control values (0.155 +/- 0.006 mg/kg). The AChR concentrations in the left gastrocnemius, quantitated by 125I-alpha-bungarotoxin binding, increased at 10, 14, and 21 days to 182 +/- 20% (P less than 0.001), 166 +/- 22% (P less than 0.03), and 164 +/- 18% (P less than 0.001) of control, respectively. AChR concentrations in the right gastrocnemius also increased subsequent to thermal injury. Changes in effective dose of dTc for 50 and 95% twitch suppression in the left gastrocnemius correlated significantly with changes in AChR concentrations for the same muscle (r = 0.73 and 0.81, P less than 0.001, respectively). This study confirms the hypothesis that the systemic effects of thermal injury include an increase in AChR at sites distant from thermal injury, which may account for the skeletal muscle dysfunction and aberrant responses to neuromuscular relaxants.