The SWI/SNF chromatin remodeling complex: a critical regulator of metabolism.

The close relationship between chromatin and metabolism has been well-studied in recent years. Many metabolites have been found to be cofactors used to modify chromatin, and these modifications can in turn affect gene transcription. One chromatin-associated factor responsible for regulating transcription is the SWI/SNF complex, an ATP-dependent chromatin remodeler conserved throughout eukaryotes. SWI/SNF was originally described in yeast as regulating genes involved in carbon source metabolism and mating type switching, and its mammalian counterpart has been extensively studied for its role in diseases such as cancer. The yeast SWI/SNF complex is closely associated with activation of stress response genes, many of which have metabolic functions. It is now recognized that this is a conserved function of the complex, and recent work has shown that mammalian SWI/SNF is also a key regulator of metabolic transcription. Emerging evidence suggests that loss of SWI/SNF introduces vulnerabilities to cells due to this metabolic influence, and that this may present opportunities for treatment of SWI/SNF-deficient cancers.

The Swi-Snf chromatin remodeling complex mediates gene repression through metabolic control.

In eukaryotes, ATP-dependent chromatin remodelers regulate gene expression in response to nutritional and metabolic stimuli. However, altered transcription of metabolic genes may have significant indirect consequences which are currently poorly understood. In this study, we use genetic and molecular approaches to uncover a role for the remodeler Swi-Snf as a critical regulator of metabolism. We find that snfΔ mutants display a cysteine-deficient phenotype, despite growth in nutrient-rich media. This correlates with widespread perturbations in sulfur metabolic gene transcription, including global redistribution of the sulfur-sensing transcription factor Met4. Our findings show how a chromatin remodeler can have a significant impact on a whole metabolic pathway by directly regulating an important gene subset and demonstrate an emerging role for chromatin remodeling complexes as decisive factors in metabolic control.

Systematic analysis of tup1 and cyc8 mutants reveals distinct roles for TUP1 and CYC8 and offers new insight into the regulation of gene transcription by the yeast Tup1-Cyc8 complex.

The Tup1-Cyc8 complex in Saccharomyces cerevisiae was one of the first global co-repressors of gene transcription discovered. However, despite years of study, a full understanding of the contribution of Tup1p and Cyc8p to complex function is lacking. We examined TUP1 and CYC8 single and double deletion mutants and show that CYC8 represses more genes than TUP1, and that there are genes subject to (i) unique repression by TUP1 or CYC8, (ii) redundant repression by TUP1 and CYC8, and (iii) there are genes at which de-repression in a cyc8 mutant is dependent upon TUP1, and vice-versa. We also reveal that Tup1p and Cyc8p can make distinct contributions to commonly repressed genes most likely via specific interactions with different histone deacetylases. Furthermore, we show that Tup1p and Cyc8p can be found independently of each other to negatively regulate gene transcription and can persist at active genes to negatively regulate on-going transcription. Together, these data suggest that Tup1p and Cyc8p can associate with active and inactive genes to mediate distinct negative and positive regulatory roles when functioning within, and possibly out with the complex.

Macrophages, Metabolites, and Nucleosomes: Chromatin at the Intersection between Aging and Inflammation.

Inflammation is the body's means of defense against harmful stimuli, with the ultimate aim being to restore homeostasis. Controlled acute inflammation transiently activates an immune response and can be beneficial as protection against infection or injury. However, dysregulated inflammatory responses, including chronic inflammation, disrupt the immune system's ability to maintain homeostatic balance, leading to increased susceptibility to infection, continuous tissue damage, and dysfunction. Aging is a risk factor for chronic inflammation; their coincidence is termed "inflammaging". Metabolic disorders including obesity, neurodegenerative diseases, and atherosclerosis are often encountered in old age. Therefore, it is important to understand the mechanistic relationship between aging, chronic inflammation, and metabolism. It has been established that the expression of inflammatory mediators is transcriptionally and translationally regulated. In addition, the post-translational modification of the mediators plays a crucial role in the response to inflammatory signaling. Chromatin regulation responds to metabolic status and controls homeostasis. However, chromatin structure is also changed by aging. In this review, we discuss the functional contributions of chromatin regulation to inflammaging.

Military Sexual Trauma and Risky Behaviors: A Systematic Review.

INTRODUCTION: Military sexual trauma (MST) is a serious and pervasive problem among military men and women. Recent findings have linked MST with various negative outcomes including risky, self-destructive, and health-compromising behaviors. OBJECTIVE: The current review summarizes the existing literature on the association between MST and risky behaviors among military men and women who have served in the U.S. Armed Forces. METHOD: We systematically searched five electronic databases (PubMed, EMBASE, PSYCINFO, PILOTS, and CINAHL Plus) using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. RESULTS: Of the initial 2,021 articles, 47 met the inclusion criteria. Reviewed studies revealed three patterns of findings: (1) largely studied and consistent (i.e., suicidal behaviors, disordered eating), (2) mixed and in need of future research (i.e., alcohol and drug use, smoking), and (3) underexamined (i.e., sexual behaviors, illegal/aggressive behaviors) or completely neglected (e.g., problematic technology use, gambling). DISCUSSION: The current systematic review advances literature by providing strong support for an association between MST and a wide range of risky behaviors. Moreover, it highlights important areas for future research.

A role for histone acetylation in regulating transcription elongation.

Recently, we reported that a major function of histone acetylation at the yeast FLO1 gene was to regulate transcription elongation. Here, we discuss possible mechanisms by which histone acetylation might regulate RNA polymerase II processivity, and comment on the contribution to transcription of chromatin remodelling at gene coding regions and promoters.

Sas3 and Ada2(Gcn5)-dependent histone H3 acetylation is required for transcription elongation at the de-repressed FLO1 gene.

The Saccharomyces cerevisiae FLO1 gene encodes a cell wall protein that imparts cell-cell adhesion. FLO1 transcription is regulated via the antagonistic activities of the Tup1-Cyc8 co-repressor and Swi-Snf co-activator complexes. Tup1-Cyc8 represses transcription through the organization of strongly positioned, hypoacetylated nucleosomes across gene promoters. Swi-Snf catalyzes remodeling of these nucleosomes in a mechanism involving histone acetylation that is poorly understood. Here, we show that FLO1 de-repression is accompanied by Swi-Snf recruitment, promoter histone eviction and Sas3 and Ada2(Gcn5)-dependent histone H3K14 acetylation. In the absence of H3K14 acetylation, Swi-Snf recruitment and histone eviction proceed, but transcription is reduced, suggesting these processes, while essential, are not sufficient for de-repression. Further analysis in the absence of H3K14 acetylation reveals RNAP II recruitment at the FLO1 promoter still occurs, but RNAP II is absent from the gene-coding region, demonstrating Sas3 and Ada2-dependent histone H3 acetylation is required for transcription elongation. Analysis of the transcription kinetics at other genes reveals shared mechanisms coupled to a distinct role for histone H3 acetylation, essential at FLO1, downstream of initiation. We propose histone H3 acetylation in the coding region provides rate-limiting control during the transition from initiation to elongation which dictates whether the gene is permissive for transcription.

Dietary LC-PUFA in iron-deficient anaemic pregnant and lactating guinea pigs induce minor defects in the offsprings' auditory brainstem responses.

OBJECTIVES: We previously demonstrated that a mild pre-natal/early post-natal iron-deficient anaemic (IDA) diet devoid of long-chain polyunsaturated fatty acids (LC-PUFA) affected development, neurophysiology, and cerebral lipid biochemistry of the guinea pigs' progeny. Impacts of dietary LC-PUFA on altered cerebral development resulting from pre-natal IDA are unknown. To address this health issue, impacts of mild gestational IDA in the presence of dietary LC-PUFA on the offsprings' neural maturation were studied in guinea pigs using auditory brainstem responses (ABRs) and assessments of brain fatty acids (FAs). METHODS: Female guinea pigs (n = 10/group) were fed an iron sufficient (IS) or IDA diet (146 and 12.7 mg iron/kg, respectively) with physiological amounts of LC-PUFA, during the gestation and lactation periods. From post-natal day (PNd) 9 onwards, the IS + PUFA diet was given to both groups of weaned offspring. Cerebral tissue and offsprings' ABR were collected on PNd24. RESULTS: There was no difference in peripheral and brainstem transmission times (BTTs) between IS + PUFA and IDA + PUFA siblings (n = 10/group); the neural synchrony was also similar in both groups. Despite the absence of differences in auditory thresholds, IDA + PUFA siblings demonstrated a sensorineural hearing loss in the extreme range of frequencies (32, 4, and 2 kHz), as well as modified brain FA profiles compared to the IS + PUFA siblings. DISCUSSION: The present study reveals that siblings born from dams exposed to a moderate IDA diet including balanced physiological LC-PUFA levels during pregnancy and lactation demonstrate minor impairments of ABR compared to the control siblings, particularly on the auditory acuity, but not on neural synchrony, auditory nerve velocity and BTT.

Leibniz's Observations on Hydrology: An Unpublished Letter on the Great Lombardy Flood of 1705.

Although the historical reputation of Gottfried Wilhelm Leibniz (1646-1716) largely rests on his philosophical and mathematical work, it is widely known that he made important contributions to many of the emerging but still inchoate branches of natural science of his day. Among the many scientific papers Leibniz published during his lifetime are ones on the nascent science we now know as hydrology. While Leibniz's other scientific work has become of increasing interest to scholars in recent years, his thinking about hydrology has been neglected, despite being relatively broad in extent, including as it does papers on the 'raising of vapours' and the formation of ice, as well as the separation of salt and fresh water. That list can now be extended still further following the discovery of a previously unpublished letter of Leibniz's on the causes of the devastating Lombardy flood of October and November 1705. This letter, which will be the focus of our paper, reveals the depth of Leibniz's understanding of key hydrological processes. In it, he considers various mechanisms for the flood, such as heavy rains on high ground, underwater earthquakes, and a mountain collapse. Over the course of the paper we examine each of these mechanisms in depth, and show that Leibniz was in the vanguard of hydrological thinking. We also show that the letter contains one of the first scholarly attempts to apply aspects of the still-forming notion of the hydrological cycle to account for a flood event.

Telomeric ORFs (TLOs) in Candida spp. Encode mediator subunits that regulate distinct virulence traits.

The TLO genes are a family of telomere-associated ORFs in the fungal pathogens Candida albicans and C. dubliniensis that encode a subunit of the Mediator complex with homology to Med2. The more virulent pathogen C. albicans has 15 copies of the gene whereas the less pathogenic species C. dubliniensis has only two (CdTLO1 and CdTLO2). In this study we used C. dubliniensis as a model to investigate the role of TLO genes in regulating virulence and also to determine whether TLO paralogs have evolved to regulate distinct functions. A C. dubliniensis tlo1Δ/tlo2Δ mutant is unable to form true hyphae, has longer doubling times in galactose broth, is more susceptible to oxidative stress and forms increased levels of biofilm. Transcript profiling of the tlo1Δ/tlo2Δ mutant revealed increased expression of starvation responses in rich medium and retarded expression of hypha-induced transcripts in serum. ChIP studies indicated that Tlo1 binds to many ORFs including genes that exhibit high and low expression levels under the conditions analyzed. The altered expression of these genes in the tlo1Δ/tlo2Δ null mutant indicates roles for Tlo proteins in transcriptional activation and repression. Complementation of the tlo1Δ/tlo2Δ mutant with TLO1, but not TLO2, restored wild-type filamentous growth, whereas only TLO2 fully suppressed biofilm growth. Complementation with TLO1 also had a greater effect on doubling times in galactose broth. The different abilities of TLO1 and TLO2 to restore wild-type functions was supported by transcript profiling studies that showed that only TLO1 restored expression of hypha-specific genes (UME6, SOD5) and galactose utilisation genes (GAL1 and GAL10), whereas TLO2 restored repression of starvation-induced gene transcription. Thus, Tlo/Med2 paralogs encoding Mediator subunits regulate different virulence properties in Candida spp. and their expansion may account for the increased adaptability of C. albicans relative to other Candida species.

Flow in bedrock canyons.

Bedrock erosion in rivers sets the pace of landscape evolution, influences the evolution of orogens and determines the size, shape and relief of mountains. A variety of models link fluid flow and sediment transport processes to bedrock incision in canyons. The model components that represent sediment transport processes are increasingly well developed. In contrast, the model components being used to represent fluid flow are largely untested because there are no observations of the flow structure in bedrock canyons. Here we present a 524-kilometre, continuous centreline, acoustic Doppler current profiler survey of the Fraser Canyon in western Canada, which includes 42 individual bedrock canyons. Our observations of three-dimensional flow structure reveal that, as water enters the canyons, a high-velocity core follows the bed surface, causing a velocity inversion (high velocities near the bed and low velocities at the surface). The plunging water then upwells along the canyon walls, resulting in counter-rotating, along-stream coherent flow structures that diverge near the bed. The resulting flow structure promotes deep scour in the bedrock channel floor and undercutting of the canyon walls. This provides a mechanism for channel widening and ensures that the base of the walls is swept clear of the debris that is often deposited there, keeping the walls nearly vertical. These observations reveal that the flow structure in bedrock canyons is more complex than assumed in the models presently used. Fluid flow models that capture the essence of the three-dimensional flow field, using simple phenomenological rules that are computationally tractable, are required to capture the dynamic coupling between flow, bedrock erosion and solid-Earth dynamics.

The yeast Cyc8-Tup1 complex cooperates with Hda1p and Rpd3p histone deacetylases to robustly repress transcription of the subtelomeric FLO1 gene.

We demonstrate that the yeast flocculation gene, FLO1, is representative of a distinct subset of subtelomeric genes that are robustly repressed by the Cyc8-Tup1 complex. We have examined Cyc8-Tup1 localisation, histone acetylation and long-range chromatin remodelling within the extensive FLO1 upstream region. We show that Cyc8-Tup1 is localised in a DNase I hypersensitive site within an ordered array of strongly positioned nucleosomes around -700 base pairs upstream of the transcription start site. In cyc8 deletion mutant strains, Tup1p localisation is absent, with concomitant histone hyperacetylation of adjacent regions at the FLO1 promoter. This is accompanied by extensive histone depletion across the upstream region and gene activation. The yeast histone deacetylases, Hda1p and Rpd3p, occupy the repressed FLO1 promoter region in a Cyc8-Tup1 dependent manner and coordinate histone deacetylation, nucleosome stabilisation and gene repression. Moreover, we show that the ATP-dependent chromatin remodelling complex Swi-Snf occupies the site vacated by Cyc8-Tup1 in a cyc8 mutant. These data suggest that distinctly bound Cyc8-Tup1 cooperates with Hda1p and Rpd3p to establish or maintain an extensive array of strongly positioned, deacetylated nucleosomes over the FLO1 promoter and upstream region which inhibit histone acetylation, block Swi-Snf binding and prevent transcription.

Mild iron deficiency anaemia during pregnancy and lactation in guinea pigs alters amplitudes and auditory nerve velocity, but not brainstem transmission times in the offspring's auditory brainstem response.

OBJECTIVES: It is well known that postnatal/early childhood iron deficiency (ID) anaemia (IDA) adversely affects infants' cognitive development and neurophysiology. However, the effects of IDA during gestation and lactation on the offspring are largely unknown. To address this health issue, the impact of mild IDA during gestation and lactation on the offsprings' neural maturation was studied in the guinea pig, using auditory brainstem responses (ABRs) latencies and amplitudes. METHODS: Female guinea pigs (n = 10/group) were fed an iron sufficient (ISD) or deficient diet (IDD) (144 and 11.7 mg iron/kg) during the gestation and lactation periods. From postnatal day (PNd) 9 onward, the ISD was given to both groups of weaned offspring. The offsprings' ABRs were collected on PNd24 using a broad range of stimulus intensities in response to 2, 4, 8, 16, and 32 kHz tone pips. RESULTS: Although the IDA siblings (n = 8) did not differ in brainstem transmission times (BTTs) compared to the IS siblings (n = 8), they showed significant delayed peak I latency at 100 and 80 dB, respectively. Additionally, significantly higher ABR wave amplitudes were observed in the IDA female offspring between 35 and 50 dB (4 kHz), a phenomenon suggestive of a neural hyperactivity (hyperacusis). DISCUSSION: In support to our previous findings, the present results indicate that a mild IDA during gestation and lactation can have detrimental effects on early development of the offsprings' hearing and nervous systems, particularly on neural synchrony and auditory nerve conduction velocity, but not on BTT.

'Ecstasy' enhances noise-induced hearing loss.

'Ecstasy' or 3,4-methylenedioxy-N-methamphetamine (MDMA) is an amphetamine abused for its euphoric, empathogenic, hallucinatory, and stimulant effects. It is also used to treat certain psychiatric disorders. Common settings for Ecstasy use are nightclubs and "rave" parties where participants consume MDMA and dance to loud music. One concern with the club setting is that exposure to loud sounds can cause permanent sensorineural hearing loss. Another concern is that consumption of MDMA may enhance such hearing loss. Whereas this latter possibility has not been investigated, this study tested the hypothesis that MDMA enhances noise-induced hearing loss (NIHL) by exposing rats to either MDMA, noise trauma, both MDMA and noise, or neither treatment. MDMA was given in a binge pattern of 5 mg/kg per intraperitoneal injections every 2 h for a total of four injections to animals in the two MDMA-treated groups (MDMA-only and Noise + MDMA). Saline injections were given to the animals in the two non-MDMA groups (Control and Noise-only). Following the final injection, noise trauma was induced by a 10 kHz tone at 120 dB SPL for 1 h to animals in the two noise trauma-treated groups (Noise-only and Noise + MDMA). Hearing loss was assessed by the auditory brainstem response (ABR) and cochlear histology. Results showed that MDMA enhanced NIHL compared to Noise-only and that MDMA alone caused no hearing loss. This implies that "clubbers" and "rave-goers" are exacerbating the amount of NIHL when they consume MDMA and listen to loud sounds. In contrast to earlier reports, the present study found that MDMA by itself caused no changes in the click-evoked ABR's wave latencies or amplitudes.

The effects of aggressive vs. conservative phototherapy on the brainstem auditory evoked responses of extremely-low-birth-weight infants.

INTRODUCTION: This study was a two-center, stratified, parallel-group randomized trial comparing the effects of aggressive vs. conservative phototherapy on brainstem auditory evoked response (BAER) latencies in infants with extremely low birth weight (ELBW, ≤ 1,000 g). RESULTS: BAER latencies of 751-1,000 g birth-weight infants were shorter by 0.37 ms (95% confidence interval (CI) = 0.02, 0.73) for wave V, 0.39 ms (0.08, 0.70) for wave III, and 0.33 ms (0.01, 0.65) for wave I after aggressive phototherapy at one center. Interwave intervals did not differ significantly. Similar nonsignificant trends were recorded for 501-750 g birth-weight infants. At the other participating center, no significant differences were recorded, cautioning against overgeneralizing these results. DISCUSSION: The effects of bilirubin on the auditory pathway in ELBW infants depend on a complex interaction of bilirubin exposure, newborn characteristics, and clinical management. METHODS: Aggressive phototherapy was initiated sooner and continued at lower bilirubin levels than conservative phototherapy. A total of 174 ELBW infants were enrolled in the study; 111 infants were successfully tested at 35 weeks postmenstrual age (PMA); 57 died; and 6 were not successfully tested.

Auditory brainstem response (ABR) abnormalities across the life span of rats prenatally exposed to alcohol.

BACKGROUND: Fetal alcohol syndrome (FAS) is a leading cause of neurodevelopmental impairments (NDIs) in developed countries. Sensory deficits can play a major role in NDI, yet few studies have investigated the effects of prenatal alcohol exposure on sensory function. In addition, there is a paucity of information on the lifelong effects of prenatal alcohol exposure. Thus, we sought to investigate the effects of prenatal alcohol exposure on auditory function across the life span in an animal model. Based on prior findings with prenatal alcohol exposure and other forms of adverse prenatal environments, we hypothesized that animals prenatally exposed to alcohol would show an age-dependent pattern of (i) hearing and neurological abnormalities as postweanling pups, (ii) a substantial dissipation of such abnormalities in young adulthood, and (iii) a resurgence of such abnormalities in middle-aged adulthood. METHODS: Pregnant rats were randomly assigned to an untreated control (CON), a pair-fed control (PFC), or an alcohol-treated (ALC) group. The ALC dams were gavaged with 6 mg/kg alcohol daily from gestation day (GD) 6 to 21. The PFC dams were gavaged daily from GD6 to GD21 with an isocaloric and isovolumetric water-based solution of maltose-dextrins and pair-fed to the ALC dams. The CON dams were the untreated group to which the ALC and CON groups were compared. Hearing and neurological functions in the offspring were assessed with the auditory brainstem response (ABR) at the postnatal ages of 22, 220, and 520 days. RESULTS: In accord with our hypothesis, ABR abnormalities were first observed in the postweanling pups, largely dissipated in young adulthood, and then resurged in middle-aged adulthood. This age-related pattern suggests that the ALC pups had a developmental delay that dissipated in young adulthood and an enhanced age-related deterioration that occurred in middle-aged adulthood. Such a pattern is consistent with the fetal programming hypothesis of adult-onset diseases (the Barker hypothesis). CONCLUSIONS: Our findings have important clinical implications for the assessment and management of (i) childhood hearing disorders and their comorbidities (i.e., speech-and-language, learning, and attention deficit disorders) and (ii) enhanced age-related hearing and neurological degeneration in middle-aged adulthood that can result from prenatal alcohol exposure. We recommend hearing evaluation be a part of any long-term follow-up for FAS patients and patients exposed to any adverse prenatal environment.

Mild maternal iron deficiency anemia during pregnancy and lactation in guinea pigs causes abnormal auditory function in the offspring.

Iron deficiency (ID) anemia (IDA) adversely affects different aspects of the nervous system such as myelinogenesis, neurotransmitters synthesis, brain myelin composition, and brain fatty acid and eicosanoid metabolism. Infant neurophysiological outcome in response to maternal IDA is underexplored, especially mild to moderate maternal IDA. Furthermore, most human research has focused on childhood ID rather than prenatal or neonatal ID. Thus, our study evaluated the consequences of mild maternal IDA during pregnancy and lactation on the offsprings' auditory function using the auditory brainstem response (ABR). This technique provides objective measures of auditory acuity, neural transmission times along the peripheral and brainstem portions of the auditory pathway, and postnatal brain maturation. Female guinea pigs (n = 10/group) were fed an iron sufficient diet (ISD) or an iron deficient diet (IDD) (144 and 11.7 mg iron/kg) during their acclimation, gestation, and lactation periods. From postnatal d (PNd) 9 onward, the ISD was given to all weaned offspring. ABR were collected from the offspring on PNd24 using a broad range of stimulus intensities in response to 2, 4, 8, 16, and 32 kHz tone pips. IDA siblings (n = 4), [corrected] compared with the IS siblings (n = 5), had significantly elevated ABR thresholds (hearing loss) in response to all tone pips. These physiological disturbances were primarily due to a sensorineural hearing loss, as revealed by the ABR's latency-intensity curves. These results indicate that mild maternal IDA during gestation and lactation altered the hearing and nervous system development of the young offspring.

The effect of environmental storage conditions on bone marrow fat determination in three species.

Diagnostic laboratories are frequently required to assess the antemortem nutritional condition of deceased animals. The percentage of fat in the bone marrow is used to diagnose starvation because this fat depot is typically the last in the body to be depleted. Diagnosticians rely on measurement of bone marrow adipose content using fat solvent-extraction methods; however, the effects of tissue storage conditions before processing have not been fully assessed. The current study focuses on evaluating the effects of 3 storage conditions (refrigeration [4 °C], freezing [-20 °C], and ambient temperature [9.9-34.4 °C]) on the percentage of fat in the bone marrow from 3 species. Equine, bovine, and canine humeri and femurs were removed within 24 hr of death from adult animals in adequate body condition and then stored as described for a minimum of 30-60 days. Bone marrow was harvested from these tissues at the time of necropsy and after 30-60 days. Percentage of fat was measured using an automated solvent extractor. Mean percentage of fat in the bone marrow in initial equine, bovine, and canine samples was 81.75%, 86.33%, and 59.96%, respectively. The results indicate that bovine and equine percentage of fat in bone marrow does not change after 30-60 days, regardless of the storage condition, whereas the fat content from canine tissues varies when stored at ambient temperatures. Results suggest that postmortem interval and environmental conditions of samples must be considered in the postmortem evaluation of bone marrow fat concentration in at least some species.

Repeated courses of antenatal corticosteroids: are there effects on the infant's auditory brainstem responses?

Our objective was to assess the effects of repeated antenatal corticosteroid treatments on the neonatal auditory brainstem response (ABR), a sensitive measure of neonatal brain maturity and auditory function. To achieve this, we performed and blindly evaluated neonatal ABRs on a subset of infants delivering within a multicenter randomized placebo-controlled clinical trial comparing single versus repeated courses of antenatal corticosteroid treatments for women at 23-31 weeks gestation who remained at increased risk for preterm birth. The women were randomly assigned to either the single or the repeated antenatal corticosteroid treatment group. Women in the repeated antenatal corticosteroid group received weekly antenatal corticosteroid treatments until 34 weeks gestation or until they reached a study-determined limited number of courses, whereas women in the single antenatal corticosteroid group received an initial course of corticosteroid followed by weekly placebo injections. We performed ABR testing on their infants prior to discharge. The latencies of waves I, III and V and the peak-to-trough amplitudes of waves I and V were compared between those in the single (n=27) and repeated antenatal corticosteroid treatment (n=24) groups. The majority of repeated antenatal corticosteroid infants (20 of 24) were exposed to ≥ 4 antenatal corticosteroid treatments. Even though gestational age was similar between our subset of single and repeated antenatal corticosteroid treatment groups, infant birth weight and length and head circumference were significantly smaller in the repeated antenatal corticosteroid group (p <0.05). Despite these differences in birth sizes, there were no significant group differences in the ABR wave latencies or amplitudes. We concluded that our repeated antenatal corticosteroid treatments, in comparison to a single treatment, did not significantly benefit or harm the neonatal ABR despite significant effects on birth size.