Shinya Yanagita

Gene Expression Changes in the Olfactory Bulb of Mice Induced by Exposure to Diesel Exhaust Are Dependent on Animal Rearing Environment

There is an emerging concern that particulate air pollution increases the risk of cranial nerve disease onset. Small nanoparticles, mainly derived from diesel exhaust particles reach the olfactory bulb by their nasal depositions. It has been reported that diesel exhaust inhalation causes inflammation of the olfactory bulb and other brain regions. However, these toxicological studies have not evaluated animal rearing environment. We hypothesized that rearing environment can change mice phenotypes and thus might alter toxicological study results. In this study, we exposed mice to diesel exhaust inhalation at 90 µg/m3, 8 hours/day, for 28 consecutive days after rearing in a standard cage or environmental enrichment conditions. Microarray analysis found that expression levels of 112 genes were changed by diesel exhaust inhalation. Functional analysis using Gene Ontology revealed that the dysregulated genes were involved in inflammation and immune response. This result was supported by pathway analysis. Quantitative RT-PCR analysis confirmed 10 genes. Interestingly, background gene expression of the olfactory bulb of mice reared in a standard cage environment was changed by diesel exhaust inhalation, whereas there was no significant effect of diesel exhaust exposure on gene expression levels of mice reared with environmental enrichment. The results indicate for the first time that the effect of diesel exhaust exposure on gene expression of the olfactory bulb was influenced by rearing environment. Rearing environment, such as environmental enrichment, may be an important contributive factor to causation in evaluating still undefined toxic environmental substances such as diesel exhaust.

Emotional stress evoked by classical fear conditioning induces yawning behavior in rats.

Yawning is often observed not only in a state of boredom or drowsiness but also in stressful emotional situations, suggesting that yawning is an emotional behavior. However, the neural mechanisms for yawning during stressful emotional situations have not been fully determined, though previous studies have suggested that both parvocellular oxytocin (OT) and corticotropin-releasing factor (CRF) neurons in the hypothalamic paraventricular nucleus (PVN) are responsible for induction of yawning. Thus, using ethological observations and c-Fos immunohistochemistry, we examined whether emotional stress evoked by classical fear conditioning is involved in induction of yawning behavior in freely moving rats. Emotional stress induced yawning behavior that was accompanied by anxiety-related behavior, and caused neuronal activation of the central nucleus of the amygdala (CeA), as well as increases in activity of both OT and CRF neurons in the PVN. These results suggest that emotional stress may induce yawning behavior, in which the neuronal activation of the CeA may have a key role.

Effect of high-fat diet prior to pregnancy on hepatic gene expression and histology in mouse offspring.

Abstract Maternal overnutrition and obesity are associated with fetal development and cause long-term effects in offspring. However, the effects of a high-fat diet specific to the pre-pregnancy period are not determined. The present study aimed to examine the effect of high-fat diet prior to pregnancy on the liver of mouse offspring. Female C57BL/6J mice were fed a normal chow (15.2% fat by energy) [control diet (CTR) and CTR pre-pregnancy (PP) groups] or a high-fat chow (31.2% fat by energy) [high-fat diet (HFD) and HFD-pre-pregnancy (PP) groups] for 3–4 weeks and then mated with male C57BL/6J mice fed normal chow. Some mothers continued on the same diet until pups reached 21 days of age (CTR and HFD), and others were fed the different chows from gestational day 0 (CTR-PP and HFD-PP) to determine the effects of a high-fat diet during the pre-pregnancy period in HFD-PP/CTR and HFD/CTR-PP comparisons. Liver tissues from pups were subjected to gene expression analysis by quantitative reverse transcription-polymerase chain reaction (RT-PCR) and microarray, and histological analysis using Oil Red O staining (Sigma Chemical Co., Ltd., Balcatta, WA, USA). Lipid droplets were increased in hepatocytes of mice in HFD-PP compared to CTR and those in HFD compared to CTR-PP. Expression of stearoyl-coenzyme A desaturase 1 (Scd1), acetyl-coenzyme A carboxylase beta (Acacb), and fatty acid binding protein 5 (Fabp5) was increased by maternal high-fat diet during pre-pregnancy. The results showed that maternal high-fat diet intake prior to pregnancy uniquely affects metabolic phenotype related to health and disease in the liver of the next generation.

Effects of prenatal exposure to diesel exhaust on cell number in the motor cortex of neonatal rat

Neuregulin-1 (NRG-1) belongs to the family of epidermal growth factor (EGF) and is implicated in the regulation of glutamatergic transmission, GABAergic function and myelination. Recent genetic studies also indicate the association of this gene with a schizophrenia risk. Mature NRG1 is produced from its membrane-anchored precursors (type 1–3) through ectodomain shedding by methalloproteinases such as ADAMs. However, the regulation of NRG1 processing and release is poorly understood. We previously reported that the activation of dopamine receptors regulates processing and release of EGF precursors in striatal cultures. Here we examined NRG1 processing and release in cultured cortical and hippocampal neurons. Cultured neurons were challenged with various types of neurotransmitters for 30 min and culture supernatants were subjected to a two site ELISA for pan-NRG1 protein. Among the neurotransmitters examined, glutamate and acetylcholine triggered NRG1 release in a dose dependent manner, whereas dopamine stimulation had no effects. The acetylcholine-triggered release was attenuated by the glutamate receptor antagonists, CNQX and AP-5. These results suggest that glutamate neurotransmission has a regulatory role in NRG1 processing and release. Currently we are analyzing the difference of the NRG1 release/processing among type 1–3 NRG1 variants. Research fund: The Uehara Memorial Foundation.

Prenatal exposure to diesel exhaust particles affected cholinergic systems in senile mice

balance ability was measured by a stabilometer, G6100 (Anima Ltd.) The training prolonged the balance holding time while standing on one foot with both eyes closed or eyes opend, and reduced the locus length per unit area both while standing on one foot with and without eyes closed, shortened the performance time of Kazufusen, but did not show a significant effect on Kana Pick Up Test. The leg muscle strength and body weight ratio were not changed before and after the training. These results indicate the existence of interaction between the cognitive and vestibular function.

Regular voluntary exercise enhances neuronal activation of serotonergic neurons during acute running

In order to assess whether toothless (extracting the upper molar teeth) at an early period after eruption of teeth (early toothless) exerts greater effects on hippocampal aging processes than late toothless, morphological and behavioral studies were done in the SAMP8 mice. Not only early toothless enhanced age-dependent decline in learning ability in a water maze test, but also in more decreased the number of hippocampal neurons than those in the age-matched control condition. However, the effects of late toothless was not significant, when compared with those in the control condition. The data suggest that a long-lasting toothless condition may result in progressing aging processes in the hippocampus.