Aroclor 1254 impairs the hearing ability of Xenopus laevis

In this study we assessed the effects of chronic, dietary exposure of Aroclor 1254 (A1254) on the hearing of Xenopus frogs. We used the auditory brainstem response (ABR) to assay changes in hearing physiology; ABR thresholds, as well as latency-intensity and amplitude-intensity profiles of the initial positive (P1) and negative (N1) peaks were measured. Two groups of animals that received 50 ppm and 100 ppm of A1254 in their diet from 5 days post-fertilization through metamorphosis were compared to a control group that received untreated chow. The results showed significant threshold elevations in the 3–4 kHz range and significantly delayed peak latencies and reduced amplitudes at these frequencies in A1254 treated animals as compared to control animals. These findings indicate that A1254 selectively damages the high-frequency sensorineural hearing system associated with the basilar papilla of frogs. This preferential damage may be related to inherent differences in the vulnerability of the basilar versus amphibian papilla in the frog. The overall results of this study are also consistent with the reported A1254-induced auditory deficits in mammals indicating that the basilar papilla of the Xenopus frog may serve as an effective model for studying the effects of A1254 on the auditory system.     

A comparison of auditory brainstem responses and behavioral estimates of hearing sensitivity in Lemur catta and Nycticebus coucang

Primates depend on acoustic signals and cues to avoid predators, locate food, and share information. Accordingly, the structure and function of acoustic stimuli have long been emphasized in studies of primate behavioral and cognitive ecology. Yet, few studies have addressed how well primates hear such stimuli; indeed, the auditory thresholds of most primate species are unknown. This empirical void is due in part to the logistic and economic challenges attendant on traditional behavioral testing methods. Technological advances have produced a safe and cost‐effective alternative—the auditory brainstem response (ABR) method, which can be utilized in field conditions, on virtually any animal species, and without subject training. Here we used the ABR and four methods of threshold determination to construct audiograms for two strepsirrhine primates: the ring‐tailed lemur (Lemur catta) and slow loris (Nycticebus coucang). Next, to verify the general efficacy of the ABR method, we compared our results to published behaviorally‐derived audiograms. We found that the four ABR threshold detection methods produced similar results, including relatively elevated thresholds but similarly shaped audiograms compared to those derived behaviorally. The ABR and behavioral absolute thresholds were significantly correlated, and the frequencies of best sensitivity and high‐frequency limits were comparable. However, at frequencies ≤2 kHz, ABR thresholds were especially elevated, resulting in decreased agreement with behavioral thresholds and, in Lemur, the ABR 10‐dB range starting points were more than 2 octaves higher than the behavioral points. Finally, a comparison of ABR‐ and behaviorally‐derived audiograms from various animal taxa demonstrates the widespread efficacy of the ABR for estimating frequency of best sensitivity, but otherwise suggests caution; factors such as stimulus properties and threshold definition affect results. We conclude that the ABR method is a promising technique for estimating primate hearing sensitivity, but that additional data are required to explore its efficacy for estimating low‐frequency thresholds. Am. J. Primatol. 72:217–233, 2010. © 2009 Wiley‐Liss, Inc.     

Hormone replacement therapy enhances IGF‐1 signaling in skeletal muscle by diminishing miR‐182 and miR‐223 expressions: a study on postmenopausal monozygotic twin pairs

MiRNAs are fine‐tuning modifiers of skeletal muscle regulation, but knowledge of their hormonal control is lacking. We used a co‐twin case–control study design, that is, monozygotic postmenopausal twin pairs discordant for estrogen‐based hormone replacement therapy (HRT) to explore estrogen‐dependent skeletal muscle regulation via miRNAs. MiRNA profiles were determined from vastus lateralis muscle of nine healthy 54–62‐years‐old monozygotic female twin pairs discordant for HRT (median 7 years). MCF‐7 cells, human myoblast cultures and mouse muscle experiments were used to confirm estrogen's causal role on the expression of specific miRNAs, their target mRNAs and proteins and finally the activation of related signaling pathway. Of the 230 miRNAs expressed at detectable levels in muscle samples, qPCR confirmed significantly lower miR‐182, miR‐223 and miR‐142‐3p expressions in HRT using than in their nonusing co‐twins. Insulin/IGF‐1 signaling emerged one common pathway targeted by these miRNAs. IGF‐1R and FOXO3A mRNA and protein were more abundantly expressed in muscle samples of HRT users than nonusers. In vitro assays confirmed effective targeting of miR‐182 and miR‐223 on IGF‐1R and FOXO3A mRNA as well as a dose‐dependent miR‐182 and miR‐223 down‐regulations concomitantly with up‐regulation of FOXO3A and IGF‐1R expression. Novel finding is the postmenopausal HRT‐reduced miRs‐182, miR‐223 and miR‐142‐3p expression in female skeletal muscle. The observed miRNA‐mediated enhancement of the target genes' IGF‐1R and FOXO3A expression as well as the activation of insulin/IGF‐1 pathway signaling via phosphorylation of AKT and mTOR is an important mechanism for positive estrogen impact on skeletal muscle of postmenopausal women.     

Auditory brain stem responses to monoaural stimulation registered in symmetrical areas of cat's brain cortex

In five anaesthetized cats (Nembutal 35 mg/kg) with 14 chronically implanted recording epidural electrodes the auditory brain stem responses (ABR) to monoaural stimulation (click) in symmetrical areas of the brain cortex were recorded. Each ABR to acoustic stimulus of sufficient intensity is formed by a complex of alternating five positive (P1-P5) and four negative (N1-N4) peaks; two further small peaks often follow on this complex. The amplitude of ABR peaks N3, P4, N4 and P5 to monoaural stimulation in symmetrical areas of cat's cortex was always higher in records from the hemisphere contralateral to the stimulated ear than in records from the ipsilateral one. The amplitude of P3 ABR peak behaved to the contrary--it was higher on ipsilateral hemisphere. On the other hand the amplitude of ABR peaks P1, N1, P2 and N2 to monoaural stimulation in symmetrical areas of the brain cortex showed no degree of lateralization in our experimental animals. The present findings support indirectly the presumption that each peak of the ABR is generated by a particular acoustic brain stem structure.     

Methods for determining auditory evoked brain-stem response thresholds in human newborns

Previous investigators have reported that newborn auditory evoked brain-stem responses (ABRs) are 20–30 dB higher than adult psychophysical thresholds to the same stimuli. These investigators reduced the intensity of the stimulus until they no longer reported an ABR to the stimulus. We adapted 2 widely used psychophysical methods, the up-down-transformed response (UDTR) method and the method of constant stimuli, for ABR threshold determination of human newborns. Response judgments were made blindly. ABR thresholds of healthy normal newborns by both procedures were no more than 10–15 dB higher than adult psychophysical thresholds. The differences between the newborn ABR thresholds we reported and those in the literature were probably explained by different procedures including the method used to estimate adult psychophysical thresholds. The correlations between ABR thresholds and suprathreshold ABR latencies and amplitudes and latency and amplitude/intensity functions were modest at best. In normal newborns suprathreshold ABR measurements are of little value in predicting ABR thresholds.     

Melanin precursors prevent premature age-related and noise-induced hearing loss in albino mice

Strial melanocytes are required for normal development and correct functioning of the cochlea. Hearing deficits have been reported in albino individuals from different species, although melanin appears to be not essential for normal auditory function. We have analyzed the auditory brainstem responses (ABR) of two transgenic mice: YRT2, carrying the entire mouse tyrosinase (Tyr) gene expression-domain and undistinguishable from wild-type pigmented animals; and TyrTH, non-pigmented but ectopically expressing tyrosine hydroxylase (Th) in melanocytes, which generate the precursor metabolite, L-DOPA, but not melanin. We show that young albino mice present a higher prevalence of profound sensorineural deafness and a poorer recovery of auditory thresholds after noise-exposure than transgenic mice. Hearing loss was associated with absence of cochlear melanin or its precursor metabolites and latencies of the central auditory pathway were unaltered. In summary, albino mice show impaired hearing responses during ageing and after noise damage when compared to YRT2 and TyrTH transgenic mice, which do not show the albino-associated ABR alterations. These results demonstrate that melanin precursors, such as L-DOPA, have a protective role in the mammalian cochlea in age-related and noise-induced hearing loss.     

No effects of mobile phone electromagnetic field on auditory brainstem response

The present study investigated the possible effects of the electromagnetic field (EMF) emitted by an ordinary GSM mobile phone (902.4 MHz pulsed at 217 Hz) on brainstem auditory processing. Auditory brainstem responses (ABR) were recorded in 17 healthy young adults, without a mobile phone at baseline, and then with a mobile phone on the ear under EMF‐off and EMF‐on conditions. The amplitudes, latencies, and interwave intervals of the main ABR components (waves I, III, V) were compared among the three conditions. ABR waveforms showed no significant differences due to exposure, suggesting that short‐term exposure to mobile phone EMF did not affect the transmission of sensory stimuli from the cochlea up to the midbrain along the auditory nerve and brainstem auditory pathways. Bioelectromagnetics 31:48–55, 2010. © 2009 Wiley‐Liss, Inc.     

脑干缺血对听觉脑干反应影响的实验研究

目的 :探讨脑干缺血模型ABR变化特点及其在脑缺血早期诊断中的应用价值。方法 :阻断猫基底动脉不同部位血流 ,观察记录阻断血流后不同时间ABR变化特点及其规律。结果 :①夹闭基底动脉上、下段或小脑下前动脉 10min左右 ,ABRP3 ,P4振幅明显减小 (P <0 .0 1,P <0 .0 5 ) ,60min恢复夹前水平 ;②夹闭基底动脉上段 10～60minP5明显减小 (P <0 .0 5 ) ,直到 12 0min尚未恢复至夹前状态。结论 :①猫的ABRP3脑区的血供主要来自小脑下前动脉 ,P1,P2产生部位基本不依赖基底动脉供血 ;②轻度暂短性脑缺血时ABR振幅比潜伏期更敏感 ,振幅减小的程度与脑干缺血的程度密切相关 ;③ABR可用于脑缺血定位诊断及脑功能动态观察的电生理检测。     

Placental insulin‐like growth factor II (IGF‐II) and its relation to litter size in the common marmoset monkey (Callithrix jacchus)

The primate placenta produces a wide variety of hormones throughout gestation that regulate placental function and fetal growth. One such hormone is insulin‐like growth factor‐II (IGF‐II), a peptide implicated in cell division, differentiation, and amino acid transport. IGF‐II concentrations were measured in 23 common marmoset (Callithrix jacchus) term placentas from twin and triplet litters in order to determine whether previously described differences in fetoplacental phenotype such as placental and litter mass and placental surface area were related to differences in endocrine function. IGF‐II was extracted from frozen tissue samples and measured using an enzyme‐linked immunosorbent assay kit designed for human tissue, which was validated for marmoset placenta. IGF‐II concentrations were not related to placental or litter mass, and twin and triplet placentas did not differ in total concentration. However, per individual fetus, triplets were associated with a significant 42% reduction in IGF‐II concentration (P=0.03), and IGF‐II concentration per gram of fetal mass was a third lower in triplet litters. The triplet placenta exhibits a global expansion of the surface area which was contrasted by a per unit area reduction in IGF‐II concentration (r=?0.75, P=0.01), a pattern that explains why twin and triplet placentas overall did not differ in concentration. Per fetus, triplet pregnancies are associated with relatively less maternal mass, placental mass and microscopic surface area suggesting that the intrauterine growth of triplets is supported by systems that increase the efficiency of nutrient transfer. The finding that individual triplet fetuses are also associated with significantly lower IGF‐II concentrations is consistent with the view that the marmoset fetoplacental unit exhibits a flexible pattern of placental allocation and metabolism. Plasticity in placental endocrine and metabolic function is likely to play an important role in the ability of the fetus to sense and accommodate the intrauterine environment and, by extension, the external ecology. Am. J. Primatol. 71:969–975, 2009. © 2009 Wiley‐Liss, Inc.     

Changes in intra-abdominal fat in early postmenopausal women: effects of hormone use

Objective: Intra‐abdominal fat (IAF) accumulates with age, is greater among postmenopausal vs. premenopausal women, and is linked to risk for both type 2 diabetes and cardiovascular disease. Whether hormone replacement therapy (HRT) prevents or attenuates changes in IAF and related risk factors is not clear. The objectives of this observational study were to 1) determine whether HRT attenuated the expected age‐related increase in IAF and 2) identify the independent effects of HRT and fat distribution on changes in disease risk factors. Research Methods and Procedures: Subjects were early postmenopausal white women 45 to 55 years of age. Women either used HRT at the time of enrollment (n = 33) or did not (n = 17). Subjects were evaluated at baseline and 2 years for body composition (DXA), body fat distribution (computed tomography), insulin sensitivity (Si; minimal model), and serum lipids. Results: IAF increased significantly over 2 years, and this increase was not attenuated by HRT. HRT users had less IAF throughout the study. HRT users showed an increase in Si, whereas non‐users showed a decrease. Superficial subcutaneous adipose tissue was significantly and independently related to total cholesterol, whereas IAF was related to high‐density lipoprotein cholesterol, triglycerides, and Si. Discussion: HRT users had less IAF at baseline and throughout the study. Whether HRT altered the relationship between total body fat and IAF or whether differences between groups existed before the study should be addressed through a randomized, interventional study design. HRT had a significant effect on Si; IAF and superficial subcutaneous adipose tissue were significant determinants of disease risk factors.     

Topography of estradiol‐modulated genomic responses in the songbird auditory forebrain

Sex steroids facilitate dramatic changes in behavioral responses to sociosexual signals and are increasingly implicated in the sensory processing of those signals. Our previous work demonstrated that in female white‐throated sparrows, which are seasonal breeders, genomic responses in the auditory forebrain are selective for conspecific song over frequency‐matched tones only when plasma estradiol (E2) reaches breeding levels. Here, we sought to map this E2‐dependent selectivity in the best‐studied area of the auditory forebrain, the caudomedial nidopallium (NCM). Nonbreeding females with low endogenous levels of E2 were treated with E2 or a placebo and exposed to conspecific song, tones, or no sound playback. Immunoreactive protein product of the immediate early gene zenk (egr‐1) was then quantified within seven distinct subregions, or domains, of NCM. We report three main findings: (1) regardless of hormone treatment, the zenk response is significantly higher in dorsal than in ventral NCM, and higher in medial than in lateral NCM; (2) E2‐dependent selectivity of the response is limited to the rostral and medial domains of NCM; in the more caudal domains, song induces more zenk expression than tones regardless of hormone treatment; (3) even when no sound stimuli were presented, E2 treatment significantly increased zenk expression in the rostral, but not the caudal, domains of NCM. Together, the latter two findings suggest that E2‐dependent plasticity in NCM is concentrated in rostral NCM, which is hodologically and neurochemically distinct from caudal NCM. Activity in rostral NCM may therefore be seasonally regulated in this species. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 2010     

A comparative study of hearing ability in fishes: the auditory brainstem response approach

Auditory brainstem response (ABR) techniques, an electrophysiological far-field recording method widely used in clinical evaluation of human hearing, were adapted for fishes to overcome the major limitations of traditional behavioral and electrophysiological methods (e.g., invasive surgery, lengthy training of fishes, etc.) used for fish hearing research. Responses to clicks and tone bursts of different frequencies and amplitudes were recorded with cutaneous electrodes. To evaluate the effectiveness of this method, the auditory sensitivity of a hearing specialist (goldfish, Carassius auratus) and a hearing generalist (oscar, Astronotus ocellatus) was investigated and compared to audiograms obtained through psychophysical methods. The ABRs could be obtained between 100 Hz and 2000 Hz (oscar), and up to 5000 Hz (goldfish). The ABR audiograms are similar to those obtained by behavioral methods in both species. The ABR audiogram of curarized (i.e., Flaxedil-treated) goldfish did not differ significantly from two previously published behavioral curves but was lower than that obtained from uncurarized fish. In the oscar, ABR audiometry resulted in lower thresholds and a larger bandwidth than observed in behavioral tests. Comparison between methods revealed the advantages of this technique: rapid evaluation of hearing in untrained fishes, and no limitations on repeated testing of animals. Accepted: 8 August 1997     

Reductions in serum IGF‐1 during aging impair health span

In lower or simple species, such as worms and flies, disruption of the insulin‐like growth factor (IGF)‐1 and the insulin signaling pathways has been shown to increase lifespan. In rodents, however, growth hormone (GH) regulates IGF‐1 levels in serum and tissues and can modulate lifespan via/or independent of IGF‐1. Rodent models, where the GH/IGF‐1 axis was ablated congenitally, show increased lifespan. However, in contrast to rodents where serum IGF‐1 levels are high throughout life, in humans, serum IGF‐1 peaks during puberty and declines thereafter during aging. Thus, animal models with congenital disruption of the GH/IGF‐1 axis are unable to clearly distinguish between developmental and age‐related effects of GH/IGF‐1 on health. To overcome this caveat, we developed an inducible liver IGF‐1‐deficient (iLID) mouse that allows temporal control of serum IGF‐1. Deletion of liver Igf ‐1 gene at one year of age reduced serum IGF‐1 by 70% and dramatically impaired health span of the iLID mice. Reductions in serum IGF‐1 were coupled with increased GH levels and increased basal STAT5B phosphorylation in livers of iLID mice. These changes were associated with increased liver weight, increased liver inflammation, increased oxidative stress in liver and muscle, and increased incidence of hepatic tumors. Lastly, despite elevations in serum GH, low levels of serum IGF‐1 from 1 year of age compromised skeletal integrity and accelerated bone loss. We conclude that an intact GH/IGF‐1 axis is essential to maintain health span and that elevated GH, even late in life, associates with increased pathology.     

Reduced acoustic startle response and peripheral hearing loss in the 5xFAD mouse model of Alzheimer's disease

Hearing dysfunction has been associated with Alzheimer's disease (AD) in humans, but there is little data on the auditory function of mouse models of AD. Furthermore, characterization of hearing ability in mouse models is needed to ensure that tests of cognition that use auditory stimuli are not confounded by hearing dysfunction. Therefore, we assessed acoustic startle response and pre‐pulse inhibition in the double transgenic 5xFAD mouse model of AD from 3–4 to 16 months of age. The 5xFAD mice showed an age‐related decline in acoustic startle as early as 3–4 months of age. We subsequently tested auditory brainstem response (ABR) thresholds at 4 and 13–14 months of age using tone bursts at frequencies of 2–32 kHz. The 5xFAD mice showed increased ABR thresholds for tone bursts between 8 and 32 kHz at 13–14 months of age. Finally, cochleae were extracted and basilar membranes were dissected to count hair cell loss across the cochlea. The 5xFAD mice showed significantly greater loss of both inner and outer hair cells at the apical and basal ends of the basilar membrane than wild‐type mice at 15–16 months of age. These results indicate that the 5xFAD mouse model of AD shows age‐related decreases in acoustic startle responses, which are at least partially due to age‐related peripheral hearing loss. Therefore, we caution against the use of cognitive tests that rely on audition in 5xFAD mice over 3–4 months of age, without first confirming that performance is not confounded by hearing dysfunction.     

正常和卡那霉素中毒豚鼠听觉脑干诱发反应及频率跟随反应的比较研究

通过测定阈值和频谱分析,比较了正常和卡那霉素中毒后豚鼠听觉脑干反应(ABR)及频率跟随反应(FFR)的特性.正常FFR的非线性随刺激频率的减低而增加,表现为高次谐波的出现.从频谱中基频成分的峰很容易识别FFR阈值.卡那霉素作用后,高频FFR首先受到影响,波幅下降,阈值显著升高.低频FFR受到影响较小.同一动物ABR阈值尚未变化时高频FFR的基频峰值已下降,乃至消失.实验结果表明FFR对耳毒性药物中毒反应由于其包含有频率特性比ABR更灵敏,更便于定量分析.     

Effects of Progesterone,Testosterone, and Estrogen on Sexual Reproduction of the Rotifer Brachionus calyciflorus

It is known that some vertebrate reproductive hormones have effects on rotifer reproduction, but little is known about their effects in combination. This motivated us to examine the effects of waterborne progesterone (P), testosterone (T), and estradiol (E) on reproduction of the rotifer Brachionus calyciflorus, comparing exposures to single hormones and mixtures with a total concentration of 1000 μg/L. Asexual population growth (r) was high in all treatments, ranging from 1.28 to 1.43 d^–1 (P‐E), and from 0.99 to 1.22 d^–1 (P‐T). These results indicate that E, P, or T alone, or in combinations of P‐E and P‐T totaling 1000 µg/L, and the 3‐way combination P‐E‐T at 1200 µg/L do not reduce the asexual reproduction of B. calyciflorus. However, significant effects were detected on sexual reproduction with exposure to these hormone concentrations. Exposure to P‐T and P‐E at 1000 μg/L decreased resting egg production significantly. Analysis of mating indicated that fertilization was 5.3 times higher in the control than in treatments where females were exposed to 500 µg/L each P‐T. A similar result was observed when both females and males were exposed to 500 µg/L each of P‐T. When males alone were treated with 500 µg/L each of P‐T, there was no significant difference in male fertility compared to the control. These results suggest that B. calyciflorus uses oxidized sterols similar to P and T to regulate sexual reproduction and waterborne exposure of females to these compounds interferes with fertilization and resting egg production. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Serum concentrations of insulin‐like growth factor‐i and insulin‐like growth factor binding protein‐2 and ‐3 in eight hoofstock species

The somatotropic axis, which includes growth hormone, insulin‐like growth factor (IGF)‐I, and IGF binding proteins (IGFBP), is involved in the regulation of growth and metabolism. Measures of the somatotropic axis can be predictive of nutritional status and growth rate that can be utilized to identify nutritional status of individual animals. Before the somatotropic axis can be a predictive tool, concentrations of hormones of the somatotropic axis need to be established in healthy individuals. To begin to establish these data, we quantified IGF‐I, IGFBP‐2, and IGFBP‐3 in males and females of eight threatened hoofstock species at various ages. Opportunistic blood samples were collected from Bos javanicus (Java banteng), Tragelaphus eurycerus isaaci (bongo), Gazella dama ruficollis (addra gazelle), Taurotragus derbianus gigas (giant eland), Kobus megaceros (Nile lechwe), Hippotragus equines cottoni (roan antelope), Ceratotherium simum simum (white rhinoceros), and Elephas maximus (Asian elephant). Serum IGF‐I and IGFBPs were determined by radioimmunoassay and ligand blot, respectively. Generally, IGF‐I and IGFBP‐3 were greater in males, and IGFBP‐2 was greater in females. In banteng (P = 0.08) and male Nile lechwe (P<0.05), IGF‐I increased with age, but decreased in rhinoceros (P = 0.07) and female Nile lechwe (P<0.05). In banteng, IGFBP‐3 was greater (P<0.01) in males. In elephants (P<0.05) and antelope (P = 0.08), IGFBP‐2 were greater in females. Determination of concentrations of hormones in the somatotropic axis in healthy animals makes it possible to develop models that can identify the nutritional status of these threatened hoofstock species. Zoo Biol 30:275–284, 2011. © 2010 Wiley‐Liss, Inc.     

Peripheral auditory processing changes seasonally in Gambel’s white-crowned sparrow

Song in oscine birds is a learned behavior that plays important roles in breeding. Pronounced seasonal differences in song behavior and in the morphology and physiology of the neural circuit underlying song production are well documented in many songbird species. Androgenic and estrogenic hormones largely mediate these seasonal changes. Although much work has focused on the hormonal mechanisms underlying seasonal plasticity in songbird vocal production, relatively less work has investigated seasonal and hormonal effects on songbird auditory processing, particularly at a peripheral level. We addressed this issue in Gambel’s white-crowned sparrow (Zonotrichia leucophrys gambelii), a highly seasonal breeder. Photoperiod and hormone levels were manipulated in the laboratory to simulate natural breeding and non-breeding conditions. Peripheral auditory function was assessed by measuring the auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAEs) of males and females in both conditions. Birds exposed to breeding-like conditions demonstrated elevated thresholds and prolonged peak latencies when compared with birds housed under non-breeding-like conditions. There were no changes in DPOAEs, however, which indicates that the seasonal differences in ABRs do not arise from changes in hair cell function. These results suggest that seasons and hormones impact auditory processing as well as vocal production in wild songbirds.     

No Decrease in Free IGF‐I with Increasing Insulin in Obesity‐Related Insulin Resistance

Objective: Different facts suggest that the insulin growth factor (IGF)/ insulin growth factor‐binding protein (IGFBP) system may be regulated by factors other than growth hormone. It has been proposed that, in healthy subjects, free IGF‐I plays a role in glucose metabolism. The role of free IGF‐I in glucose homeostasis in insulin resistance is poorly understood. This study was undertaken to evaluate the effects of acute changes in plasma glucose and insulin levels on free IGF‐I and IGFBP‐1 in obese and non‐obese subjects. Research Methods and Procedures: Nineteen lean and 24 obese subjects were investigated. A frequently sampled intravenous glucose tolerance test was performed. Free IGF‐I and IGFBP‐1 were determined at 0, 19, 22, 50, 100, and 180 minutes. Results: Basal free IGF‐I levels tended to be higher and IGFBP‐1 lower in obese than in lean subjects. IGFBP‐1 levels inversely correlated with basal insulin concentration. To determine the effects of insulin on the availability of free IGF‐I and IGFBP‐1, changes in their plasma concentrations were measured during a frequently sampled intravenous glucose tolerance test. After insulin administration, a significant suppression of free IGF‐I at 22% was observed in lean subjects. In contrast, plasma‐free IGF‐I levels remained essentially unchanged in the obese group. The differences between both groups were statistically significant at 100 minutes (p < 0.01) and 180 minutes (p < 0.05). Serum IGFBP‐1 was suppressed to a similar extent in both groups. Discussion: These data suggest that the concentrations of free IGF‐I and IGFBP‐1 are differentially regulated by obesity. Obesity‐related insulin resistance leads to unsuppressed free IGF‐I levels.     

The spectral structure of vocalizations match hearing sensitivity but imprecisely in Philautus odontotarsus

It is generally thought that for species using vocal communication the spectral properties of the sender’s calls should match the frequency sensitivity of the receiver’s auditory system. Nevertheless, few studies have investigated both sender and receiver characteristics in anuran species. In the present study, auditory brainstem responses (ABRs) were recorded in the serrate legged treefrog, Philautus odontotarsus, in order to determine if male call spectral structure and hearing sensitivity in males and females have co-evolved in this species. The results showed that the spectral structures of male vocalization match both male and female hearing sensitivity, even though the dominant frequencies of male calls (2.5 kHz) are mismatched with the regions of best frequency sensitivity (1.4 and 2.8 kHz). In addition, the results show that, in contrast with most previous ABR studies in non-human animals, but consistent with human studies, there are noticeable sex differences in peripheral auditory sensitivity in Philautus insofar as females exhibit lower auditory thresholds than males across the entire 1.8–18 kHz frequency range. The results also show that the dominant frequency of male calls is negatively correlated with body size, indicating that call characteristics reflect body size in this species which may be used by females during mate choice.