Endogenous estradiol and testosterone levels are associated with cognitive performance in older women and men

Relatively few studies have investigated the relationship between endogenous sex steroid levels and cognition in older people and the reported results have been inconsistent. A number of experimental hormone replacement studies have suggested that estrogen replacement in older women enhances cognition, especially verbal memory. In contrast, little research has been done focusing on men. In the current study the association between endogenous sex steroids (estradiol and testosterone) and cognition was investigated in 38 healthy older women (mean age 68 years) and 30 healthy older men (mean age 69 years). Five cognitive tests measuring verbal memory, spatial memory, verbal fluency, mental rotation, and susceptibility to interference were administered. Results revealed that in women higher estradiol levels as well as testosterone levels were associated with better verbal memory (paired associates and estradiol; r =.38, P < 0.05; paired associates and testosterone; r =.33, P < 0.05;). Moreover estradiol, but not testosterone was associated with less susceptibility to interference (Stroop color word test; r = -0.34, P < 0.05). In men the only significant association was a negative correlation between testosterone and verbal fluency (r = -0.38, P < 0.05). The associations observed in this small study support the notion that estradiol is protecting verbal memory and possibly also frontal lobe mediated functions in older women. In contrast to the positive findings in women endogenous sex steroids do not appear to be closely linked to better cognition in older men.     

Testosterone, endurance, and Darwinian fitness: natural and sexual selection on the physiological bases of alternative male behaviors in side-blotched lizards

The mechanistic bases of natural and sexual selection on physiological and behavioral traits were examined in male morphs of three colors of the side-blotched lizard, Uta stansburiana. Orange-throated males are aggressive and defend large territories with many females. Blue-throated males defend smaller territories with fewer females; however, blue-throated males assiduously mate guard females on their territory. Yellow-throated males do not defend a territory, but patrol a large home range. They obtain secretive copulations from females on the territories of dominant males. Males with bright orange throats had higher levels of plasma testosterone (T), endurance, activity, and home range size and concomitantly gained greater control over female home ranges than blue- or yellow-throated males. Experimentally elevating plasma T in yellow- and blue-throated males increased their endurance, activity, home range size, and control over female territories to levels that were seen in unmanipulated orange-throated males that had naturally high plasma T. However, the enhanced performance of orange-throated males is not without costs. Orange-throated males had low survival compared to the other morphs. Finally, some yellow-throated males transformed to a partial blue morphology late in the season and the endurance of these transforming yellow-throated males increased from early to late in the season. In addition, yellow-throated males that transformed to blue also had significantly higher plasma T late in the season compared to the plasma T earlier in the season. T appears to play an important role in the physiological changes that all three color morphs undergo during the process of maturation. In some yellow males, T plays an additional role in plastic changes in behavior and physiology late in the reproductive season. We discuss natural and sexual selection on physiological and behavioral traits that leads to the evolution of steroid regulation in the context of alternative male strategies.     

应急大鼠肾上腺髓质嗜铬细胞颗粒数目与其钙含量的关系

采用电镜细胞立体形态计量法及电镜Ｘ射线显微定量分析术,对制动应急大鼠的肾上腺髓质细胞内嗜铬颗粒数密度和颗粒内Ｃａ浓度变化进行测量。结果显示,两者在制动过程中均呈进行性下降,但颗粒内钙浓度的下降快于颗粒数目的减少（Ｐ〈０．０１）。该结果支持颗粒内钙释放入胞质,参与胞质内游离钙浓度的升高,进而激发颗粒胞吐的假设,为主宰嗜铬颗粒是一种细胞内钙库并参与细胞分泌提供了实验依据。     

A Single Genetic Determinant that Prevents Sex Reversal in C57BL-YPOS Congenic Mice

Sex determination in the mammalian embryo begins with the activation of a gene on the Y chromosome which triggers a cascade of events that lead to male development. The mechanism by which this gene, designated SRY in humans and Sry in mice (sex determining region of the Y chromosome), is activated remains unknown. Likewise, the downstream target genes for Sry remain unidentified at present. C57BL mice carrying a Y chromosome from Mus musculus musculus or molossinus develop normally as males. In contrast, C57BL/6 mice with the Y chromosome from M. m. domesticus often show sex reversal, i.e., develop as XY females. It has been documented that C57BL mice with the Y chromosome from Poschiavinus (Y^POS), a domesticus subtype, always develop as females or hermaphrodites. This suggests that a C57BL gene either up- or downstream of Sry is ineffective in interacting with Sry, which then compromises the processes that lead to normal male sex development. Nonetheless, by selective breeding, we have been able to generate a sex reversal-resistant C57BL/6-congenic strain of mice in which the XY^POS individuals consistently develop as normal males with bilateral testes. Because the resistance to sex reversal was transferred from strain 129S1/Sv (nonalbino) by simple selection over 13 backcross generations, it is inferred that a single autosomal gene or chromosomal region confers resistance to the sex reversal that would otherwise result. XY^POS normal males generated in these crosses were compared to XY^POS abnormal individuals and to C57BL/6 controls for sexual phenotype, gonadal weight, serum testosterone, and major urinary protein (MUP) level. A clear correlation was found among phenotypic sex, MUP level, and testis weight in the males and in the incompletely masculinized XY^POS mice. The fully masculinized males of the congenic strain resemble C57BL/6 males in the tested parameters. DNA analysis confirmed that these males, in fact, carry the Y^POS Sry gene.     

Phytosterol feeding induces alteration in testosterone metabolism in rat tissues

The objective of the present study was to examine the metabolism of testosterone in rat tissues as influenced by dietary phytosterols. Testosterone metabolism includes reductions to more active metabolites or aromatization to estrogen. Both higher levels of androgens and estrogens are implicated as risk factors in the development of prostate cancer. Tissues studied included liver, testis, and prostate. Feeding 2% phytosterols with 0.2% cholic acid to rats for 22 days resulted in a 33% reduction in serum testosterone compared with controls, which received only 0.2% cholic acid in the diet. 5-α-Reductase was reduced by 41 to 44% and 33% in the liver and prostate, respectively. No effect of phytosterols was observed in the testis. Only aromatase activity of the prostate was reduced by 55% upon feeding phytosterols. It was concluded that dietary phytosterols may reduce the risk of prostate cancer by lowering the activities of the enzymes of testosterone metabolism.     

Testing extraction and storage parameters for a fecal hormone method

Four experiments were conducted to test different aspects of a “field‐friendly” fecal hormone extraction method that utilizes methanol extraction in the field followed by storage on C18 solid‐phase extraction cartridges. Fecal samples were collected from geladas (Theropithecus gelada) housed at the Bronx Zoo, and the experiments were conducted in a laboratory setting to ensure maximum control. The experiments were designed to either simulate the conditions to which fecal samples are subjected during fieldwork or improve on an existing protocol. The experiments tested the relationship between fecal hormone metabolite preservation/recovery and: (1) the amount of time a sample is stored at ambient temperature; (2) the number of freeze/thaw cycles a sample undergoes; (3) the effectiveness of different extraction solutions; and (4) the effectiveness of different cartridge washes. For each experiment, samples were assayed by radioimmunoassay for fecal glucocorticoid (GC) and testosterone (T) metabolites. Results for each of the experiments were as follows. First, storage at ambient temperature did not affect hormone levels until 4 weeks of storage, with significant increases for both GC and T metabolites at 4 weeks. Second, hormone levels significantly decreased in samples after two freeze/thaw cycles for GCs and six freeze/thaws cycles for T. Third, for both GCs and T, hormone extraction using various methanol solutions was significantly higher than using 100% ethanol. Finally, using a 20% methanol solution to wash cartridges significantly increased GC levels but had no effect on T levels. These results suggest that, when utilizing C18 cartridges for fecal steroid storage, researchers should consider several methodological options to optimize hormone preservation and recovery from fecal samples. Am. J. Primatol. 72:934–941, 2010. © 2010 Wiley‐Liss, Inc.     

Hatching late in the season requires flexibility in the timing of song learning

Most songbirds learn their songs from adult tutors, who can be their father or other male conspecifics. However, the variables that control song learning in a natural social context are largely unknown. We investigated whether the time of hatching of male domesticated canaries has an impact on their song development and on the neuroendocrine parameters of the song control system. Average age difference between early- and late-hatched males was 50 days with a maximum of 90 days. Song activity of adult tutor males decreased significantly during the breeding season. While early-hatched males were exposed to tutor songs for on average the first 99 days, late-hatched peers heard adult song only during the first 48 days of life. Remarkably, although hatching late in the season negatively affected body condition, no differences between both groups of males were found in song characteristics either in autumn or in the following spring. Similarly, hatching date had no effect on song nucleus size and circulating testosterone levels. Our data suggest that late-hatched males must have undergone accelerated song development. Furthermore, the limited tutor song exposure did not affect adult song organization and song performance.     

Modulation of synaptic plasticity by brain estrogen in the hippocampus

The hippocampus is a center for learning and memory as well as a target of Alzheimer's disease in aged humans. Synaptic modulation by estrogen is essential to understand the molecular mechanisms of estrogen replacement therapy. Because the local synthesis of estrogen occurs in the hippocampus of both sexes, in addition to the estrogen supply from the gonads, its functions are attracting much attention.     

Seasonal variation in fecal testosterone levels in free-ranging male Japanese macaques

Seasonal variation in fecal testosterone levels in free-ranging male Japanese macaques (Macaca fuscata) was examined with reference to their dominance rank and age class. Six adult (>or=7 years old, three higher-ranking and three lower-ranking) and four adolescent (5-6 years old, two higher-ranking and two lower-ranking) males were selected as target animals. Fecal samples of these males were collected during the first 3-5 days of each month and analyzed by the method developed by Barrett et al. [Primates 43:29-39, 2002 b]. Testosterone levels varied significantly across the 12 months, and were highest in the early and middle parts of the mating season (i.e., October and November). Higher-ranking adult males displayed a peak testosterone level in October, whereas lower-ranking adults had no clear peak in the mating season. Such a difference in testosterone peaks in males could provide higher-ranking males more opportunities to fertilize females at first ovulation in the mating season than lower-ranking males.