Neuroendocrine response patterns in dominant and subordinate mice.

The sequence and type of neuroendocrine and behavioral patterns resulting from the development of a social hierarchy in colonies of mice were studied. It was found that dominant males were more active and responded to social interaction with predominantly a sympathetic adrenal-medullary pattern. Subordinate males were less active and predominantly responded with a pituitary adrenal-cortical pattern. The neuroendocrine patterns were reversed when the social position of the animal was reversed. Also the subordinate males demonstrated greater plasma corticosterone responsiveness to ACTH administration and immobilization stress as compared to dominant males.     

A single thiourea group is not enough to get stable thiourea lipoplexes

The preparation of a new family of lipothiourea is reported using an automatic synthetic workstation. In these compounds the headgroups were made from single thiourea derivatives. The physicochemical properties and the transfection efficiency of several members of the family were studied. It was found that in the presence of DMPC small lipoplexes could be prepared. In opposite to the previously described di- and tri-lipothioureas most of these liposomes are unstable overtime. In addition, even the stable ones show no transfecting efficiency. All these data demonstrate that at least two thiourea groups are necessary to produce stable lipoplexes, to condense DNA and to give efficient transfection.     

Canopy structure and nitrogen distribution in dominant and subordinate plants in a dense stand of Amaranthus dubius L. with a size hierarchy of individuals

The objective was to investigate how nitrogen allocation patterns in plants are affected by their vertical position in the vegetation (i.e. being either dominant or subordinate). A garden experiment was carried out with Amaranthus dubius L., grown from seed, in dense stands in which a size hierarchy of nearly equally aged individuals had developed. A small number of dominant plants had most of their leaf area in the highest layers of the canopy while a larger number of subordinate plants grew in the shade of their dominant neighbours. Canopy structure, vertical patterns of leaf nitrogen distribution and leaf photosynthetic characteristics were determined in both dominant and subordinate plants. The light distribution in the stands was also measured. Average N contents per unit leaf area (total canopy nitrogen divided by the total leaf area) were higher in the dominant than in the subordinate plants and this was explained by the higher average MPA (leaf dry mass per unit area) of the dominant plants. However, when expressed on a weight basis, average N contents (LNC_av; total canopy N divided by the total dry weight of leaves) were higher in the subordinate plants. It is possible that these higher LNC_av values reflect an imbalance between carbon and nitrogen assimilation with N uptake exceeding its metabolic requirement. Leaf N content per unit area decreased more strongly with decreasing relative photon flux density in the dominant than in the subordinate plants showing that this distribution pattern can be different for plants which occupy different positions in the light gradient in the canopy. The amount of N which is reallocated from the oldest to the younger, more illuminated leaves higher up in the vegetation may depend on the sink strength of the younger leaves for nitrogen. In the subordinate plants, constrained photosynthetic activity caused by shading might have reduced the sink intensity of these leaves.     

青春期雌性根田鼠初次择偶行为与雄性优势等级

在实验室条件下，研究了性刚成熟的雌性根田鼠对一对互为同胎同胞的以体重划分为优势和从势的雄性个体的择偶行为，目的在于检验雄性社会等级是否影响其配偶选择。结果发现：(1)根田鼠存在显著的偏雄性二型，而雄性动物优势度与体重大小成正比；(2)在Y字型迷宫中，初次发情雌鼠对优势雄鼠的访问时间、社会探究频次和友好频次等显著大于从属雄鼠；(3)在随后24h的一雌二雄共居中，优势雄优先交配；从属雄的干扰不能中断优势雄鼠的交配。这些结果说明，体重差异可以作为划分雄性优势的指标，社会等级可以作为择偶行为的一个依据。优势雄鼠与处于从属地位的同胞相比，能获得优先交配机会。同胎同胞虽具有遗传相似性，但雄性竞争的结果表现在体重和社会等级上具有显著差异，表明配偶选择在发挥着作用。根田鼠是一雄多雌制，而且具有较大的偏雄性二型，提示社会等级、雌性选择和婚配制度有密切关联[动物学报49(3)：303—309，2003]。     

Intraovarian relationships among dominant and subordinate follicles and the corpus luteum in heifers

Previous studies demonstrated that waves of follicular activity develop approximately every 9 d in cattle during the estrous cycle and early pregnancy. A dominant follicle develops from each wave and the remaining follicles (subordinates) begin to regress after a few days. In this study, intraovarian luteal and follicular interrelationships were examined during the follicular waves of the estrous cycle and pregnancy using data obtained by ultrasonography. During the estrous cycle, no intraovarian relationships were found between the ovary containing the corpus luteum and the ovary containing the dominant follicle (n = 165), or between the location of the corpus luteum and the characteristics of the dominant follicle. During pregnancy, however, the frequency distribution for the number of follicular waves with the dominant follicle and corpus luteum on the same or opposite ovaries differed (P<0.05) among Waves 1 to 10. The two structures (dominant follicle and corpus luteum) were more often in opposite ovaries during Waves 3 to 10 (combined frequency, 75%) than during Waves 1 and 2. During pregnancy, dominant follicles of consecutive waves differed (P<0.05) among Waves 1 to 8 in the frequency with which they appeared in the same versus the opposite ovary. The difference seemed primarily due to an increased frequency of consecutive follicles on the same ovary for Waves 4 to 8 (combined frequency, 80%). During both the estrous cycle and pregnancy, there was no significant intraovarian effect of the dominant follicle on the day of detection of the next dominant follicle, on the growth rate of the largest subordinate follicle, or on the length of the interval from wave origin to cessation of growth of the largest subordinate; these results indicate that previously postulated suppressive effects between follicles are exerted through systemic channels.     

Stimulation of the largest subordinate follicle by intrafollicular treatment with insulin-like growth factor 1 is associated with inhibition of the dominant follicle in heifers

The effect of intrafollicular treatment of the second-largest follicle (F2) with insulin-like growth factor (IGF) 1 on the largest follicle (F1) and F2 was studied in heifers. Treatment of F2 was done when F1 reached ≥8.2 mm (expected beginning of follicle deviation; Day 0 or Hour 0). In each of two experiments, three groups (n = 6 or 7 heifers/group) were used: controls, F2 treated with vehicle and F2 treated with IGF1. The IGF1 treatment consisted of 200 μg of recombinant human IGF1 (pharmacological dose) in 20 μL of vehicle. In Experiment 1, the hypothesis that treatment of F2 with IGF1 has a stimulatory effect on F2 was supported by a greater (P < 0.05) incidence of F2 dominance (≥10 mm) in the IGF1 group (71%) than in the other two groups (8%), and a greater (P < 0.02) growth rate of F2 on Days 0-2. Unexpectedly, treatment of F2 with IGF1 had an inhibitory effect on F1, as indicated by a reduced (P < 0.03) growth rate of F1 during Days 0-1 and Days 0-4 and a lesser (P < 0.05) maximum diameter of F1 in the IGF1 group. In Experiment 2, the hypothesis of an inhibitory effect on F1 when F2 was treated with IGF1 was supported by a lesser (P < 0.04) increase in diameter of F1 and a lesser (P < 0.04) percentage of follicle wall with power-Doppler signals of blood flow between Hours 0 and 14 in the IGF1 group. Circulating concentrations of FSH and LH were not altered significantly in either experiment. In conclusion, treatment of F2 with IGF1 at the expected beginning of deviation had a stimulatory effect on F2, but an inhibitory effect on F1.     

Lipopolysaccharide administration in the dominant mouse destabilizes social hierarchy

Sickness behavior is a set of behavioral changes that are part of an adaptive strategy to overcome infection. Mice that interact with conspecifics displaying sickness behavior also show relevant behavioral changes. In this work we sought to determine the role of sickness behavior display by a dominant mouse as a promoter of hierarchy instability. We treated the dominant mouse within a dyad with lipopolysaccharide (LPS) (400 μg/kg, i.p.) for three consecutive days and assessed social dominance behavior. Since elder animals display increased inflammatory responses and the behaviors toward conspecifics are influenced by kinship we also assessed whether kinship and age, might influence sickness related hierarchy instability. Our results show that administration of LPS in the dominant mouse promotes social instability within a dyad, and indicates that this instability could be influenced by kinship and age.     

Arbuscular mycorrhizal fungi reduce the differences in competitiveness between dominant and subordinate plant species

In grassland communities, plants can be classified as dominants or subordinates according to their relative abundances, but the factors controlling such distributions remain unclear. Here, we test whether the presence of the arbuscular mycorrhizal (AM) fungus Glomus intraradices affects the competitiveness of two dominant (Taraxacum officinale and Agrostis capillaris) and two subordinate species (Prunella vulgaris and Achillea millefolium). Plants were grown in pots in the presence or absence of the fungus, in monoculture and in mixtures of both species groups with two and four species. In the absence of G. intraradices, dominants were clearly more competitive than subordinates. In inoculated pots, the fungus acted towards the parasitic end of the mutualism–parasitism continuum and had an overall negative effect on the growth of the plant species. However, the negative effects of the AM fungus were more pronounced on dominant species reducing the differences in competitiveness between dominant and subordinate species. The effects of G. intraradices varied with species composition highlighting the importance of plant community to mediate the effects of AM fungi. Dominant species were negatively affected from the AM fungus in mixtures, while subordinates grew identically with and without the fungus. Therefore, our findings predict that the plant dominance hierarchy may flatten out when dominant species are more reduced than subordinate species in an unfavourable AM fungal relationship (parasitism).     

Agonistic encounters and brain activation in dominant and subordinate male greater long-tailed hamsters

During an agonistic encounter test, dominant male greater long-tailed hamsters (Tscheskia triton) initiated attacks sooner and displayed higher levels of aggression and flank marking behavior than their subordinate counterparts. Accordingly, subordinate males exhibited more defensive behavior than dominant ones. Specific patterns of neuronal activation, measured by Fos-immunoreactive staining (Fos-ir), were found in the hamster brain following agonistic interactions. Increased Fos-ir was observed in the bed nucleus of the stria terminalis (BST), ventromedial hypothalamus (VMH), and medial (MeA) and anterior cortical (ACo) nuclei of the amygdala (AMYG) in both dominant and subordinate males. In contrast, dominant males had significantly higher Fos-ir densities in the medial preoptic area (MPOA) than subordinate males, whereas subordinate males expressed higher densities of Fos-ir in the anterior hypothalamus (AH) and central nucleus of the amygdala (CeA). Additionally, Fos-ir levels in the MPOA were significantly correlated with aggression and Fos-ir levels in the AH and CeA were correlated with defensive behavior. Together, our data indicate distinct patterns of neuronal activation associated with agonistic encounters in a behavior-specific manner in male greater long-tailed hamsters.     

Brain levels of arginine-vasotocin and isotocin in dominant and subordinate males of a cichlid fish

The nonapeptides arginine-vasotocin (AVT) and isotocin (IT), which are the teleost homologues of arginine-vasopressin and oxytocin in mammals, have well established peripheral effects on osmoregulation and stress response, and central effects on social behavior. However, all studies that have looked so far into the relationship between these nonapeptides and social behavior have used indirect measures of AVT/IT activity (i.e. immunohistochemistry of AVT/IT immunoreactive neurons, or AVT/IT or their receptors mRNA expression with in situ hybridization or qPCR) and therefore direct measures of peptide levels in relation to social behavior are still lacking. Here we use a recently developed high-performance liquid chromatography analysis with fluorescence detection (HPLC-FL) method to quantify the levels of both AVT and IT in macro-dissected brain areas [i.e. olfactory bulbs, telencephalon, diencephalon, optic tectum, cerebellum, and hindbrain (= rhombencephalon minus cerebellum)] and pituitary of dominant and subordinate male cichlid fish (Oreochromis mossambicus). The pituitary shows higher levels of both peptides than any of the brain macroareas, and the olfactory bulbs have the highest AVT among all brain areas. Except for IT in the telencephalon there is a lack of correlations between central levels and pituitary peptide levels, suggesting an independent control of hypophysial and CNS nonapeptide secretion. There were also no correlations between AVT and IT levels either for each brain region or for the pituitary gland, suggesting a decoupled activity of the AVT and IT systems at the CNS level. Subordinate AVT pituitary levels are significantly higher than those of dominants, and dominant hindbrain IT levels are significantly higher than those of subordinates, suggesting a potential involvement of AVT in social stress in subordinate fish and of IT in the regulation of dominant behavior at the level of the hindbrain. Since in this species dominant males use urine to communicate social status and since AVT is known to have an antidiuretic effect, we have also investigated the effect of social status on urine storage. As predicted, dominant males stored significantly more urine than subordinates. Given these results we suggest that AVT/IT play a key role in orchestrating social phenotypes, acting both as central neuromodulators that promote behavioral plasticity and as peripheral hormones that promote integrated physiological changes.     

Kinase pathways in dominant and subordinate ovarian follicles during the first wave of follicular development in sheep

The mechanism by which one or more dominant ovarian follicles continue development while other subordinate follicles regress is not known. The mitogen activated protein kinases (MAPKs) are a group of kinases that are activated by hormonal factors and form a cascade of processes that regulate cell growth, division and differentiation. The aim of the present experiment was to characterise the presence of the MAPKs, Erk 1/Erk 2 and Akt in healthy dominant follicles and regressing subordinate follicles. Following in vivo monitoring of ovarian follicle development, three ewes were ovariectomised and the follicular fluid and follicle wall (theca and granulosa cells) saved from the dominant and largest subordinate follicle. The dissected diameter and follicular fluid oestradiol concentration of the dominant follicle was larger (P<0.01) than the largest subordinate follicle (6.5+/-0.0mm and 41.3+/-4.9ng/ml versus 4.7+/-0.3mm and 0.6+/-0.4ng/ml). Western blot analyses showed that there was more Akt (202.7+/-6.4 versus 59.6+/-32.7 units; P<0.05) and Erk 1/Erk 2 (104.5+/-10.6 versus 0.3+/-0.2 units; P<0.01) present in follicle wall samples from the dominant compared to the largest subordinate follicles. Phosphorylated forms of Akt and Erk 1/Erk 2 were detected in samples from dominant but not subordinate follicles. We suggest that signal transduction pathways involving Akt and Erk 1/Erk 2 may play an important role in determining the outcome of ovarian follicle growth and development in sheep.     

The pathological dominant and the stable pathological state]

The pathological dominant is considered at a model of alcohol motivation which is in competitive relations with drinking motivation. The steady pathological state is considered at a model of seizure readiness in rats with audiogenic epileptiform seizures. The alcohol motivation might be ceased by the activation of competitive systems (thirst motivation), but the level of seizure readiness might be lowered intrasystemically, for example, by the habituation mechanisms.     

The ability of subordinate follicles of the second follicular wave to become dominant is lost by day 15 of the estrous cycle in cattle

Generally, unilateral ovariectomy before a critical period in the latter part of the estrous cycle induces a transitory increase in plasma FSH, which causes subordinate follicles to develop and maintain ovulation rates characteristic of the species. A limiting period for subordinate follicles to assume dominance and from which ovulation occurs has not been shown for cattle. Growth and/or regression of subordinate follicles were characterized following removal of the dominant follicle at different days of the luteal phase of the estrous cycle in cattle in this study. In the mid-luteal phase (Day 13 or 15), the ovary with the dominant follicle of the second wave was ablated via unilateral ovariectomy; the corpus luteum also was removed. In the late luteal phase (Day 17 or 19), the dominant follicle was ablated with an ultrasonically guided 20 gauge needle. When the dominant follicle was removed on Day 13, the largest subordinate follicle of the second wave of follicular development became dominant and ovulation occurred from this follicle in 4 of 4 animals. However, when the dominant follicle was removed on Day 15, 17 or 19, a new wave of follicular development was induced in 14 of 15 animals. Moreover, the recovered subordinate follicle of the second wave of follicular development had similar growth characteristics to naturally occurring dominant follicles. In conclusion, the subordinate follicle in the second follicular wave in cattle retained the ability to become dominant, but this ability was lost by Day 15 of the estrous cycle. However, cattle then were able to maintain ovulation by developing a new wave of follicular growth.     

The role of resource dispersion in promoting the co‐occurrence of dominant and subordinate ant species

Dominant competitors govern resource use in many communities, leading to predictions of local exclusion and lower species diversity where dominant species are abundant. However, subordinate and dominant species frequently co‐occur. One mechanism that could facilitate resource sharing and co‐occurrence of dominant and subordinate competitors is fine‐scale resource dispersion. Here, we distributed 6 g of a food resource into 1, 2, 8, 32 or 64 units in small 0.40 m² areas centred on nests of the dominant ant Monomorium sydneyense. We tested three hypotheses. First, we hypothesized that the species richness and abundance of foraging ants would increase with increasing resource dispersion. Accordingly, species richness doubled and total ant abundance was two orders of magnitude higher in high resource dispersion treatments. Secondly, we hypothesized that increasing resource dispersion would reduce competitive interactions such as resource turnover events and lower the probability of food resources being occupied. Substantial support for this hypothesis was observed. Finally, we tested the hypothesis that the foraging time of each species would be proportional to the relative abundance of each species solely in high resource dispersion treatments. Expected and observed foraging times were statistically similar for only the dominant ant M. sydneyense. The subdominant Pheidole rugosula increased its foraging time much more than was expected, while two subordinate ants showed no relationship between observed and expected times. Thus, while increasing resource dispersion significantly increased overall species richness, this increase in co‐occurrence did not correlate with a significant increase in foraging time for the two subordinate species. Rather, changes in resource dispersion appeared to benefit only the subdominant species. Inter‐site variation appeared more important for other subordinate species indetermining co‐occurrence and foraging time. Multiple mechanisms facilitate co‐occurrence and resource sharing in this community, and probably in most other communities.     

Suppression of dominant and subordinate ovarian follicles by a proteinaceous fraction of follicular fluid in heifers

Nulliparous Holstein heifers were examined ultrasonically once daily during an interovulatory interval (ovulation = Day 0). Follicles with a diameter >/=4 mm were sequentially identified. Heifers were randomized into four groups (n = 4 heifers per group): untreated control heifers and those treated on Days 0 to 3, Days 3 to 6, or Days 6 to 11. Heifers designated for treatment were given an intravenous injection, twice daily, of a proteinaceous fraction of follicular fluid (PFFF; 16 ml) prepared by extracting bovine follicular fluid with activated charcoal. Mean cessation of growth of the dominant follicle of Wave 1 was later (P<0.005) in control heifers (Day 5.5) than in heifers treated on Days 0 to 3 (Day 1.5) or Days 3 to 6 (Day 3.5). Mean onset of regression of the dominant follicle of Wave 1 was later (P<0.005) in control heifers (Day 12.0) than in heifers treated on Days 0 to 3 (Day 5.0) or Days 3 to 6 (Day 7.5). Mean cessation of growth of the largest subordinate follicle of Wave 1 was later (P<0.05) in control heifers (Day 3.0) than in heifers treated on Days 0 to 3 (Day 1.2). Mean onset of regression of the largest subordinate follicle of Wave 1 was later (P<0.05) in control heifers (Day 7.0) than in heifers treated on Days 0 to 3 (Day 4.8). In heifers treated on Days 6 to 11, cessation of growth and onset of regression of the dominant follicle (means, Days 5.2 and 12.0, respectively) were not significantly different from those of the controls. The hypothesis that PFFF treatment on Days 0 to 3 would cause suppression of all follicles of Wave 1 was supported. The hypothesis that PFFF treatment on Days 3 to 6 would not alter growth of the dominant follicle of Wave 1 was not supported. The mean day of detection of the dominant follicle of Wave 2 was different (P<0.005) in control heifers (Day 8.5) than in heifers treated on Day 0 to 3 (Day 5.5) or Days 6 to 11 (Day 14.2). The mean length of the interovulatory interval was shorter (P<0.05) in control heifers (20.5 d) than in heifers treated on Days 6 to 11 (23.2 d). The hypothesis that PFFF treatment on Days 6 to 11 would delay the emergence of Wave 2 was supported. The proportion of heifers with 2-wave interovulatory intervals was 3 4 for control heifers and 0 4 , 1 4 , and 4 4 for heifers treated on Days 0 to 3, Days 3 to 6, and Days 6 to 11, respectively (3 4 vs 0 4 , P<0.05); the remaining heifers had 3-wave interovulatory intervals. On average, in PFFF-treated heifers, follicles stopped growing 1 d after treatment was started, and Wave 2 was detected 3 d after treatment was stopped.     

Intestinal polyposis in mice with a dominant stable mutation of the beta-catenin gene.

Ectopic expression of certain Wnt genes in mouse mammary tissue is tumorigenic, and mutations that stabilize beta-catenin are found in various human cancers including colorectal cancer. To determine the role of stabilized beta-catenin in intestinal tumorigenesis in mice, we constructed by embryonic stem (ES) cell-mediated homologous recombination, a mutant beta-catenin allele whose exon 3 was sandwiched by loxP sequences. When the germline heterozygotes were crossed with mice expressing Cre recombinase in the intestines, the serines and threonine encoded by exon 3 and to be phosphorylated by glycogen synthase kinase 3beta (GSK3beta) were deleted in the offspring intestines, which caused adenomatous intestinal polyps resembling those in Apc(Delta716) knockout mice. Some nascent microadenomas were also found in the colon. These results present experimental genetic evidence that activation of the Wnt signaling pathway can cause intestinal and colonic tumors.