Microbiomes in Birds: A Review of Links to Health and Reproduction.

Microbiomes have emerged as a key component essential for maintaining the health of an organism. Additionally, the roles of microbiomes are multifaceted, some unique to specific body areas and organs while others, particularly the gut microbiome, having broader effects on the entire organism. Comparative literature is emerging that compares microbiomes across mammals and birds. Domestic poultry have been the most extensively studied relative to their role in production agriculture. These data have provided a great deal of information about the effects of diet and nutritional requirements relative to the gut microbiome, productivity, and resilience to diseases. Conversely, limited such research has been conducted on wild birds, despite them inhabiting a broad array of ecological niches and environments, providing a rich diversity in their adaptations to different habitats. Migratory birds and raptors are of particular interest. Migratory birds encounter a range of ecosystems and provide a link between allopatric populations. Raptors occupy high positions in the food chain, with potential exposure to biomagnification of environmental contaminants and pathogens. This review overviews our current understanding of the structure and function of avian microbiomes as related to avian health and reproduction in domestic and wild birds, highlighting knowledge gaps in need of further investigation for more effective conservation of rapidly declining avian populations.

Role of angiotensin type 2 receptor in improving lipid metabolism and preventing adiposity.

Recent studies on mice with null mutation of the angiotensin type 2 receptor (AT2R) gene have implicated the involvement of AT2R in regulating adipocyte size and obesity, a major risk factor for metabolic syndrome. However, the outcome from these studies remains inconclusive. Therefore, current study was designed to test whether pharmacological activation of AT2R regulates adiposity and lipid metabolism. Male mice (5-weeks old) were pre-treated with vehicle or AT2R agonist (C21, 0.3 mg/kg, i.p., daily, for 4 days) and fed normal diet (ND). Then these animals were subdivided into ND and high-fat diet (HFD) regimen and concomitantly treated with vehicle or C21 through day 14. Vehicle-treated HFD-fed mice demonstrated an increase in epididymal white adipose tissue (eWAT) weight and adipocyte size, which were associated with increased eWAT expression of the lipogenic regulators, fatty acid binding protein and fatty acid synthase, decreased expression of adipose triglyceride lipase and increased expression of hormone-sensitive lipase. Interestingly, C21 pre-treatment altered HFD-induced changes in lipogenic and lipolytic regulators. C21 pre-treatment prevented decrease in expression of uncoupler protein-1 in brown adipose in HFD-fed mice, which was associated with increased core temperature. In addition, C21 pre-treatment ameliorated plasma-free fatty acids, triglycerides, insulin and tumor necrosis factor-α in HFD-fed mice. Ex-vivo study in isolated primary epididymal adipocytes revealed that C21 inhibits long chain fatty acid transporter, via a nitric oxide synthase/guanylate cyclase/protein kinase G-dependent pathway. Collectively, we propose pharmacological activation of AT2R regulates fatty acid metabolism and thermogenesis and prevents HFD-induced adiposity in mice.

Knockout of the Histone Demethylase Kdm3b Decreases Spermatogenesis and Impairs Male Sexual Behaviors.

Kdm3b is a JmjC domain-containing histone H3 (H3) demethylase and its physiological functions are largely unknown. In this study, we found that Kdm3b protein is highly expressed in multiple cell types in the mouse testes, including Leydig cells, Sertoli cells, spermatogonia and spermatocytes at different differentiation stages. We also observed Kdm3b protein in the epithelial cells of the caput epididymis, prostate and seminal vesicle. Breeding tests revealed that the number of pups produced by the breeding pairs with Kdm3b knockout (Kdm3bKO) males and wild type (WT) females was reduced 68% because of the decreased number of litters when compared with the breeding pairs with WT males and females. Further analysis demonstrated that Kdm3bKO male mice produced 44% fewer number of mature sperm in their cauda epididymides, displaying significantly reduced sperm motility. No significant differences in the circulating concentration of testosterone and the expression levels of androgen receptor and its representative target genes in the testis were observed. However, the circulating levels of 17ß-estradiol, a modulator of sperm maturation and male sexual behaviors, was markedly reduced in Kdm3bKO male mice. Strikingly, abrogation of Kdm3b in male mice significantly increased the latencies to mount, intromit and ejaculate and decreased the number of mounts and intromissions, largely due to their loss of interest in female odors. These findings indicate that Kdm3b is required for normal spermatogenesis and sexual behaviors in male mice.

Research resource: loss of the steroid receptor coactivators confers neurobehavioral consequences.

Steroid receptor coactivators (SRCs) are important transcriptional modulators that regulate nuclear receptor and transcription factor activity to adjust transcriptional output to cellular demands. Highlighting their pleiotropic effects, dysfunction of the SRCs has been found in numerous pathologies including cancer, inflammation, and metabolic disorders. The SRC family is expressed strongly in the brain including the hippocampus, cortex, and hypothalamus. Studies focusing on the effect of SRC loss using congenic SRC knockout mice (SRC(-/-)) are limited in number, yet strongly indicate that the SRCs play important roles in regulating reproductive behavior, development, and motor coordination. To better understand the unique functions of the SRCs, we performed a neurobehavioral test battery focusing on anxiety and exploratory behaviors, motor coordination, sensorimotor gating, and nociception in both male and female null mice and compared them with their wild-type (WT) littermates. Results from the test battery reveal a role for SRC1 in motor coordination. Additionally, we found that SRC1 regulates anxiety responses in SRC1(-/-) male and female mice, and nociception sensitivity in SRC1(-/-) male but not female mice. By comparison, SRC2 regulates anxiety response with SRC2(-/-) females showing decreased anxiety in novel environments, as well as increased exploratory behavior in the open field compared with WT littermates. Additionally, SRC2(-/-) males were shown to have deficits in sensorimotor gating. Loss of SRC3 also shows sex differences in anxiety and exploratory behaviors. In particular, SRC3(-/-) female mice have increased anxiety and reduced exploratory activity and impairments in prepulse inhibition, whereas SRC3(-/-) male mice show no significant behavioral differences. In both genders, ablation of SRC3 decreases nocifensive behaviors. Collectively, these resource data suggest that loss of the SRCs results in behavioral phenotypes, underscoring the importance of understanding both the general and gender-based activity of SRCs in the brain.

Distribution and estrogen regulation of membrane progesterone receptor-ß in the female rat brain.

Although several studies have reported the localization of membrane progesterone (P(4)) receptors (mPR) in various tissues, few have attempted to describe the distribution and regulation of these receptors in the brain. In the present study, we investigated expression of two mPR subtypes, mPRα and mPRß, within regions of the brain, known to express estradiol (E(2))-dependent [preoptic area (POA) and hypothalamus] and independent (cortex) classical progestin receptors. Saturation binding and Scatchard analyses on plasma membranes prepared from rat cortex, hypothalamus, and POA demonstrated high-affinity, specific P(4)-binding sites characteristic of mPR. Using quantitative RT-PCR, we found that mPRß mRNA was expressed at higher levels than mPRα, indicating that mPRß may be the primary mPR subtype in the rat brain. We also mapped the distribution of mPRß protein using immunohistochemistry. The mPRß-immunoreactive neurons were highly expressed in select nuclei of the hypothalamus (paraventricular nucleus, ventromedial hypothalamus, and arcuate nucleus), forebrain (medial septum and horizontal diagonal band), and midbrain (oculomotor and red nuclei) and throughout many areas of the cortex and thalamus. Treatment of ovariectomized female rats with E(2) benzoate increased mPRß immunoreactivity within the medial septum but not the medial POA, horizontal diagonal band, or oculomotor nucleus. Together, these findings demonstrate a wide distribution of mPRß in the rodent brain that may contribute to functions affecting behavioral, endocrine, motor, and sensory systems. Furthermore, E(2) regulation of mPRß indicates a mechanism through which estrogens can regulate P(4) function within discrete brain regions to potentially impact behavior.

Impaired male sexual behavior in activin receptor type II knockout mice.

Integration of multiple hormonal and neuronal signaling pathways in the medial preoptic area (mPOA) is required for elicitation of male sexual behavior in most vertebrates. Perturbation of nitric oxide synthase (NOS) activity in the mPOA causes significant defects in male sexual behavior. Although activins and their signaling components are highly expressed throughout the brain, including the mPOA, their functional significance in the central nervous system (CNS) is unknown. Here, we demonstrate a neurophysiologic role for activin signaling in male reproductive behavior. Adult activin receptor type II null (Acvr2-/-) male mice display multiple reproductive behavioral deficits, including delayed initiation of copulation, reduced mount, and intromission frequencies, and increased mount, intromission, and ejaculation latencies. These behavioral defects in the adult mice are independent of gonadotropin-releasing hormone (GnRH) homeostasis or mating-induced changes in luteinizing hormone (LH) and testosterone levels. The impairment in behavior can be correlated to the nitric oxide content in the CNS because Acvr2-/- males have decreased NOS activity in the mPOA but not the rest of the hypothalamus or cortex. Olfactory acuity tests confirmed that Acvr2-/- mice have no defects in general odor or pheromone recognition. In addition, motor functions are not impaired and the mutants demonstrate normal neuromuscular coordination and balance. Furthermore, the penile histology in mutant mice appears normal, with no significant differences in the expression of penile differentiation marker genes compared with controls, suggesting the observed behavioral phenotypes are not due to structural defects in the penis. Our studies identify a previously unrecognized role of activin signaling in male sexual behavior and suggest that activins and/or related family members are upstream regulators of NOS activity within the mPOA of the forebrain.