Brain In Part Research Articles

Hematin anhydride (β-hematin): An analogue to malaria pigment hemozoin possesses nonlinearity

Hematin anhydride (β-hematin), the synthetic analogue of the malaria pigment, “hemozoin”, is a heme dimer produced by reciprocal covalent bonds among carboxylic acid groups on the protoporphyrin-IX ring and the iron atom present in the two adjacent heme molecules. Hemozoin is a disposal product formed from the digestion of hemoglobin present in the red blood cells infected with hematophagous malaria parasites. Besides, as the parasites invade red blood cells, hemozoin crystals are eventually released into the bloodstream, where they accumulate over time in tissues. Severe malaria infection leads to significant dysfunction in vital organs such as the liver, spleen, and brain in part due to the autoimmune response to the excessive accumulation of hemozoin in these tissues. Also, the amount of these crystals in the vasculature correlates with disease progression. Thus, hemozoin is a unique indicator of infection used as a malaria biomarker and hence, used as a target for the development of antimalarial drugs. Hence, exploring various properties of hemozoin is extremely useful in the direction of diagnosis and cure. The present study focuses on finding one of the unknown properties of β-hematin in physiological conditions by using the Z-scan technique, which is simple, sensitive, and economical. It is observed that hemozoin possesses one of the unique material properties, i.e., nonlinearity with a detection limit of ∼ 15 µM. The self-defocusing action causes β-hematin to exhibit negative refractive nonlinearity. The observed data is analyzed with a thermal lensing model. We strongly believe that our simple and reliable approach to probing the nonlinearity of β-hematin will provide fresh opportunities for malaria diagnostics & cure in the near future.

Infection in the Developing Brain: The Role of Unique Systemic Immune Vulnerabilities.

Central nervous system (CNS) infections remain a major burden of pediatric disease associated with significant long-term morbidity due to injury to the developing brain. Children are susceptible to various etiologies of CNS infection partly because of vulnerabilities in their peripheral immune system. Young children are known to have reduced numbers and functionality of innate and adaptive immune cells, poorer production of immune mediators, impaired responses to inflammatory stimuli and depressed antibody activity in comparison to adults. This has implications not only for their response to pathogen invasion, but also for the development of appropriate vaccines and vaccination strategies. Further, pediatric immune characteristics evolve across the span of childhood into adolescence as their broader physiological and hormonal landscape develop. In addition to intrinsic vulnerabilities, children are subject to external factors that impact their susceptibility to infections, including maternal immunity and exposure, and nutrition. In this review we summarize the current evidence for immune characteristics across childhood that render children at risk for CNS infection and introduce the link with the CNS through the modulatory role that the brain has on the immune response. This manuscript lays the foundation from which we explore the specifics of infection and inflammation within the CNS and the consequences to the maturing brain in part two of this review series.

Alcohol metabolism contributes to brain histone acetylation.

Emerging evidence suggests that epigenetic regulation is dependent on metabolic state, implicating specific metabolic factors in neural functions that drive behavior1. In neurons, histone acetylation relies on the metabolite acetyl-CoA that is produced from acetate by chromatin-bound acetyl-CoA synthetase 2 (ACSS2)2. Notably, a major source of acetate is via breakdown of alcohol in the liver, leading to rapidly increasing blood acetate3. Neuronal histone acetylation may thus be under the influence of alcohol-derived acetate4, with potential effects on alcohol-induced brain gene expression and behavior5. Here, using in vivo stable isotope labeling in mouse, we show that alcohol metabolism contributes to rapid histone acetylation in the brain in part by direct deposition of alcohol-derived acetyl groups onto histones in an ACSS2-dependent manner. A similar induction was observed with heavy labeled acetate injection in vivo. In a pregnant mouse, exposure to labeled alcohol resulted in incorporation of labeled acetyl groups into gestating fetal brains. In isolated primary hippocampal neurons ex vivo, extracellular acetate induced learning and memory-related transcriptional programs that were sensitive to ACSS2 inhibition. Notably, we showed that alcohol-related associative learning requires ACSS2 in vivo. These findings support a direct link between alcohol metabolism and gene regulation through ACSS2-dependent histone acetylation in the brain.

Influence of diabetes on plasma pharmacokinetics and brain bioavailability of grape polyphenols and their phase II metabolites in the Zucker diabetic fatty rat.

The effect of diabetes on the pharmacokinetics, bioavailability and brain distribution of grape polyphenols and select metabolites was studied in the Zucker diabetic fatty (ZDF) rat model. (ZDF) rats and their lean controls (LN) were dosed with a Standardized Grape Polyphenol (SGP) Mixture consisting of grape seed extract, Concord grape juice and resveratrol (RES) by oral gavage for 10 days. An 8-h pharmacokinetic study was performed. After 24h, a second dose of SGP was administered and 1h later animals were sacrificed and brain tissue was harvested. Plasma, urine, and brain tissue were analyzed for grape polyphenols. ZDF rats exhibited significantly diminished Cmax for all catechin, epicatechin, quercetin and resveratrol conjugated metabolites. Bioavailability was significantly lower in ZDF rats for methylated flavan-3-ol, RES, and quercetin metabolites. Significantly lower levels of metabolites of RES, quercetin, and flavan-3-ols were found in brains of ZDF rats. There was no significant difference between ZDF and LN in anthocyanins in plasma and no anthocyanins were detectable in brain extracts. ZDF rats showed significantly higher urinary excretion for all polyphenols. Diabetes may alter the overall bioavailability of some polyphenols in plasma and brain in part due to higher urinary clearance.

Temperature-Dependent Variation in Self-Reported Contagious Yawning

The thermoregulatory theory posits that yawns function to cool the brain in part due to counter-current heat exchange with the deep inhalation of ambient air. In support of this theory, previous cross-cultural research on humans has shown that self-reported contagious yawning frequency varies between seasons with distinct ambient temperature ranges. However, it remains possible that differences in yawning across seasons are a result of physiological circadian changes across the year rather than variation in ambient temperature. In an attempt to address this question, here we discuss the results of a study investigating the variation in the frequency of self-reported contagious yawning within a restricted range of a single season in one geographic location. A total of 142 pedestrians were recruited outdoors during an 18-day period over the summer in an equatorial monsoon climate in southern Florida, USA. Consistent with the thermoregulatory theory of yawning, results showed that self-reported contagious yawning frequency varied predictably across temperature gradients. This was true after statistically controlling for relative humidity, time of day, time spent outside, testing day, age of participant, and amount of sleep the night before. These findings provide further evidence suggesting a brain cooling function to yawning.

A thermal window for yawning in humans: Yawning as a brain cooling mechanism

The thermoregulatory theory of yawning posits that yawns function to cool the brain in part due to counter-current heat exchange with the deep inhalation of ambient air. Consequently, yawning should be constrained to an optimal thermal zone or range of temperature, i.e., a thermal window, in which we should expect a lower frequency at extreme temperatures. Previous research shows that yawn frequency diminishes as ambient temperatures rise and approach body temperature, but a lower bound to the thermal window has not been demonstrated. To test this, a total of 120 pedestrians were sampled for susceptibly to self-reported yawn contagion during distinct temperature ranges and seasons (winter: 1.4°C, n=60; summer: 19.4°C, n=60). As predicted, the proportion of pedestrians reporting yawning was significantly lower during winter than in summer (18.3% vs. 41.7%), with temperature being the only significant predictor of these differences across seasons. The underlying mechanism for yawning in humans, both spontaneous and contagious, appears to be involved in brain thermoregulation.

Magnetoreception in an Avian Brain in Part Mediated by Inner Ear Lagena

Many animals use the Earth's geomagnetic field for orientation and navigation, but the neural mechanisms underlying that ability remain enigmatic. Support for at least two avian magnetoreceptors exists, including magnetically activated photochemicals in the retina and ferrimagnetic particles in the beak. The possibility of a third magnetoreceptor in the inner ear lagena organs has been suggested. The brain must process magnetic receptor information to derive constructs representing directional heading and geosurface location. Here, we used the c-Fos transcription factor, a marker for activated neurons, to discover where in the brain computations related to a specific set of magnetic field stimulations occur. We found that neural activations in discrete brain loci known to be involved in orientation, spatial memory, and navigation may constitute a major magnetoreception pathway in birds. We also found, through ablation studies, that much of the observed pathway appears to receive magnetic information from the pigeon lagena receptor organs.

Chronic fetal hypoxia produces selective brain injury associated with altered nitric oxide synthases

The purpose of this study was to investigate the impact of chronic hypoxia on the nitric oxide synthase isoenzymes in specific brain structures. Time-mated pregnant guinea pigs were exposed to 10.5% molecular oxygen for 14 days (animals with chronic fetal hypoxia; HPX) or room air (control animals; NMX); L-N6-(1-iminoethyl)-lysine (L-NIL; an inducible nitric oxide synthase inhibitor, 1 mg/kg/d) was administered to HPX group for 14 days (L-NIL + HPX). Fetal brains were harvested at term. Multilabeled immunofluorescence was used to generate a brain injury map. Laser capture microdissection and quantitative polymerase chain reaction were applied; cell injury markers, apoptosis activation, neuron loss, total nitric oxide, and the levels of individual nitric oxide synthase isoenzymes were quantified. Chronic hypoxia causes selective fetal brain injury rather than global. Injury is associated with differentially affected nitric oxide synthases in both neurons and glial cells, with inducible macrophage-type nitric oxide synthase up-regulated at all injury sites. L-NIL attenuated the injury, despite continued hypoxia. These studies demonstrate that chronic hypoxia selectively injures the fetal brain in part by the differential regulation of nitric oxide synthase isoenzymes in an anatomic- and cell-specific manner.

Pericyte-specific expression of PDGF beta receptor in mouse models with normal and deficient PDGF beta receptor signaling

BackgroundPericytes are integral members of the neurovascular unit. Using mouse models lacking endothelial-secreted platelet derived growth factor-B (PDGF-B) or platelet derived growth factor receptor beta (PDGFRβ) on pericytes, it has been demonstrated that PDGF-B/PDGFRβ interactions mediate pericyte recruitment to the vessel wall in the embryonic brain regulating the development of the cerebral microcirculation and the blood-brain barrier (BBB). Relatively little is known, however, about the roles of PDGF-B/PDGFRβ interactions and pericytes in the adult brain in part due to a lack of adequate and/or properly characterized experimental models. To address whether genetic disruption of PDGFRβ signaling would result in a pericyte-specific insult in adult mice, we studied the pattern and cellular distribution of PDGFRβ expression in the brain in adult control mice and F7 mice that express two hypomorphic Pdgfrβ alleles containing seven point mutations in the cytoplasmic domain of PDGFRβ that impair downstream PDGFRβ receptor signaling.ResultsUsing dual fluorescent in situ hybridization, immunofluorescent staining for different cell types in the neurovascular unit, and a fluorescent in situ proximity ligation assay to visualize molecular PDGF-B/PDGFRβ interactions on brain tissue sections, we show for the first time that PDGFRβ is exclusively expressed in pericytes, and not in neurons, astrocytes or endothelial cells, in the adult brain of control 129S1/SvlmJ mice. PDGFRβ co-localized only with well-established pericyte markers such as Chondroitin Sulfate Proteoglycan NG2 and the xLacZ4 transgenic reporter. We next confirm pericyte-specific PDGFRβ expression in the brains of F7 mutants and show that these mice are viable in spite of substantial 40-60% reductions in regional pericyte coverage of brain capillaries.ConclusionsOur data show that PDGFRβ is exclusively expressed in pericytes in the adult 129S1/Sv1mJ and F7 mouse brain. Moreover, our findings suggest that genetic disruption of PDGFRβ signaling results in a pericyte-specific insult in adult F7 mutants and will not exert a primary effect on neurons because PDGFRβ is not expressed in neurons of the adult 129S1/SvlmJ and F7 mouse brain. Therefore, mouse models with normal and deficient PDGFRβ signaling on a 129S1/SvlmJ background may effectively be used to deduce the specific roles of pericytes in maintaining the cerebral microcirculation and BBB integrity in the adult and aging brain as well as during neurodegenerative and brain vascular disorders.

It's all in a day's work: Regulation of DNA excision repair by the circadian clock

In biology, the old adage that “timing is everything” works just as well the other way around, as “everything is timed.” Or, as the last several decades of circadian rhythms research suggest, it certainly seems that way. Biologists have long observed that many aspects of mammalian physiology and behavior are regulated throughout the 24-h day. These processes include regulation of blood pressure and heart rate, metabolic processes such as hormonal rhythms and cholesterol and heme biosynthesis, and sleeping and dependent behaviors such as locomotor activity and feeding (1). In this issue of PNAS, Kang et al. (,2) add to this list by demonstrating that nucleotide excision repair activity oscillates in the brain in part through transcriptional regulation of xeroderma pigmentosum A (XPA).

The Role of the Vagal Nerve in Peripheral PYY3–36-Induced Feeding Reduction in Rats

Peptide YY (PYY), an anorectic peptide, is secreted postprandially from the distal gastrointestinal tract. PYY(3-36), the major form of circulating PYY, binds to the hypothalamic neuropeptide Y Y2 receptor (Y2-R) with a high-affinity, reducing food intake in rodents and humans. Additional gastrointestinal hormones involved in feeding, including cholecystokinin, glucagon-like peptide 1, and ghrelin, transmit satiety or hunger signals to the brain via the vagal afferent nerve and/or the blood stream. Here we determined the role of the afferent vagus nerve in PYY function. Abdominal vagotomy abolished the anorectic effect of PYY(3-36) in rats. Peripheral administration of PYY(3-36) induced Fos expression in the arcuate nucleus of sham-operated rats but not vagotomized rats. We showed that Y2-R is synthesized in the rat nodose ganglion and transported to the vagal afferent terminals. PYY(3-36) stimulated firing of the gastric vagal afferent nerve when administered iv. Considering that Y2-R is present in the vagal afferent fibers, PYY(3-36) could directly alter the firing rate of the vagal afferent nerve via Y2-R. We also investigated the effect of ascending fibers from the nucleus of the solitary tract on the transmission of PYY(3-36)-mediated satiety signals. In rats, bilateral midbrain transections rostral to the nucleus of the solitary tract also abolished PYY(3-36)-induced reductions in feeding. This study indicates that peripheral PYY(3-36) may transmit satiety signals to the brain in part via the vagal afferent pathway.

Hypoxia-induced ischemic tolerance in neonatal rat brain involves enhanced ERK1/2 signaling.

Hypoxic preconditioning (HP) 24 h before hypoxic-ischemic (HI) injury confers significant neuroprotection in neonatal rat brain. Recent studies have shown that the mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-kinase (PI3K) intracellular signaling pathways play a role in the induction of tolerance to ischemic injury in heart and brain. To study the role of MAPK (ERK1/2, JNK, p38MAPK) and PI3K/Akt/GSK3beta signaling pathways in hypoxia-induced ischemic tolerance, we examined the brains of newborn rats at different time points after exposure to sublethal hypoxia (8% O(2) for 3 h). Immunoblot analysis showed that HP had no effect on the levels of phosphorylated Akt, GSK3beta, JNK and p38MAPK. In contrast, significantly increased levels of phosphorylated ERK1/2 were observed 0.5 h after HP. Double immunofluorescence staining showed that hypoxia-induced ERK1/2 phosphorylation was found mainly in microvessels throughout the brain and in astrocytes in white matter tracts. Inhibition of hypoxia-induced ERK1/2 pathway with intracerebral administration of U0126 significantly attenuated the neuroprotection afforded by HP against HI injury. These findings suggest that activation of ERK1/2 signaling may contribute to hypoxia-induced tolerance in neonatal rat brain in part by preserving vascular and white matter integrity after HI.

Hyperthermia prevents metabolic and cerebral flow responses to hypoxia in the fetal sheep.

Fetal brain temperature has been found to decrease during hypoxia, strongly suggesting a reduction in cerebral O2 consumption and increases in cerebral blood flow. These responses may protect the brain in part against hypoxic injury. This study was undertaken to examine whether these compensatory mechanisms are lost during fetal hyperthermia. Intermittent fetal hypoxemia was induced by administering low-O2 gas mixtures to nine near-term ewes. Fetal brain and body core temperature responses were measured with and without fetal hyperthermia induced by circulating warm water through a plastic coil looped about the fetus in utero. In normothermic fetuses, fetal brain temperature relative to core decreased during a 30-minute period of hypoxia and then returned to normal during recovery. This response may be explained by a combination of cerebral hypometabolism and increased cerebral blood flow. However, in hyperthermic fetuses (intrauterine warming for 1 hour, raising body core and brain temperatures 0.66 +/- 0.06 and 0.61 +/- 0.10 C, respectively) a subsequent period of hypoxia no longer induced a reduction in brain temperature relative to body core. When temperature of the fetal sheep is elevated, as may occur with maternal fever, prolonged exercise, and elevated environmental temperatures, the fetal brain is less well protected against hypoxic injury.