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B Chau

Publications and source records attributed to B Chau.

8 recordsLinked to original sources
PubMed2005

Only low levels of exogenous N-acetyltransferase can be achieved in transgenic mice.

Therapeutic and environmental aromatic amines and hydrazines are substrates for the arylamine N-acetyltransferases (NAT). In all, 10 transgenic lines containing either the human NAT1 or NAT2 transgene were developed using multiple promoters. The presence of the transgene was confirmed by determining copy number, mRNA and enzyme activity. Despite some lines having high copy numbers of the transgene, only modest or no increases in enzymatic activity could be found in a variety of tissues. The NAT1 transgene could not be bred to homozygosity. The cytomegalovirus (CMV)-promoted NAT1 transgene increased endogenous Nat1 mRNA levels in liver and had little effect on endogenous Nat2 mRNA levels. The presence of the CMV-promoted NAT2 transgene appeared to suppress endogenous hepatic Nat2 mRNA, but did not alter Nat1 mRNA levels. The failure to achieve high expression of any of the transgenes suggests that overexpression of NAT genes may have harmful effects during development.

Animals↗
PubMed2002

Effects of maternal tobacco smoking, sleeping position, and sleep state on arousal in healthy term infants.

OBJECTIVES: To investigate whether a history of maternal tobacco smoking affected the maturation of arousal responses and whether sleeping position and infant age alters these relations. DESIGN: Healthy term infants (13 born to mothers who did not smoke and 11 to mothers who smoked during pregnancy) were studied using daytime polysomnography on three occasions: (a) two to three weeks after birth, (b) two to three months after birth, and (c) five to six months after birth. Multiple measurements of arousal threshold in response to air jet stimulation were made in both active sleep (AS) and quiet sleep (QS) when infants slept both prone and supine. RESULTS: Maternal smoking significantly elevated arousal threshold in QS when infants slept supine at 2-3 months of age (p<0.05). Infants of smoking mothers also had fewer spontaneous arousals from QS at 2-3 months in both prone (p<0.05) and supine (p<0.001) sleeping positions. In infants of non-smoking mothers, arousal thresholds were elevated in the prone position in AS at 2-3 months (p<0.01) and QS at 2-3 weeks (p<0.05) and 2-3 months (p<0.001). CONCLUSIONS: Maternal tobacco smoking significantly impairs both stimulus induced and spontaneous arousal from QS when infants sleep in the supine position, at the age when the incidence of sudden infant death syndrome is highest.

Arousal↗
PubMed2001

Apnoea of prematurity and arousal from sleep.

The incidence of sudden infant death syndrome (SIDS) has been found to be consistently higher in preterm and low birth weight infants than in infants born at term and this increase is inversely related to gestational age. The incidence and severity of apnoea of prematurity, are also inversely related to gestational age. The aim of this study was to investigate whether a neonatal history of apnoea/bradycardia affected the maturation of arousal responses. Twenty-five premature infants were studied. A perinatal risk score was determined for each infant and infants were divided into those with a neonatal history of apnoea/bradycardia (n=16) and those without (n=9). All infants were studied using daytime polysomnography on three occasions: (a) a preterm study around 36 weeks gestation, (b) within 3 weeks of term, and (c) 2-3 months post-term. Multiple measurements of arousal threshold (cm H2O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep (AS) and quiet sleep (QS). Arousal thresholds were elevated in apnoeic infants compared to control infants in both AS (P<0.05) and QS (P<0.001) at the term study and in QS at 2-3 months post-term (P<0.01). In addition, arousal thresholds were positively correlated with perinatal risk score in both sleep states, in all studies, with the exception of AS at 2-3 months when all infants were readily arouseable. We conclude that a history of prematurity with neonatal apnoea has a persisting effect on decreasing arousabilty from sleep and these infants may be at increased risk for SIDS.

Apnea↗
PubMed2001

The prone sleeping position impairs arousability in term infants.

OBJECTIVE: To investigate whether the prone sleeping position impaired arousal from sleep in healthy infants and whether this impairment was related to cardiorespiratory variables, temperature, or age. STUDY DESIGN: Healthy term infants (n = 24) were studied with daytime polysomnography on 3 occasions: 2 to 3 weeks after birth, 2 to 3 months after birth, and 5 to 6 months after birth. Multiple measurements of arousal threshold (cm H(2)O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep and quiet sleep when infants slept both prone and supine. RESULTS: Arousal thresholds were significantly higher in both active sleep and quiet sleep when infants slept prone at 2 to 3 weeks and 2 to 3 months, but not at 5 to 6 months. These increases were independent of any sleep position-related change in either rectal or abdominal skin temperature, respiratory rate, oxygen saturation, or heart rate. CONCLUSIONS: The prone position significantly impairs arousal from both active sleep and quiet sleep in healthy term infants. This impairment in arousability occurred with no clinically significant changes in cardiorespiratory variables or body temperature. Decreased arousability from sleep in the prone position provides an important insight into its role as a risk factor for sudden infant death syndrome.

Arousal↗
PubMed2000

Effects of prematurity on arousal from sleep in the newborn infant.

The incidence of sudden infant death syndrome has been found to be consistently higher in preterm and low birth weight infants than in infants born at term. Failure to arouse from sleep is one possible mechanism for sudden infant death syndrome. This study compared the arousal responses to nasal air-jet stimulation in a longitudinal study between groups of healthy preterm and term infants. Preterm infants (n = 9) were born at 31-35 wk gestation with normal birth weights for gestational age and studied on three occasions: a preterm study at 36 wk, at 2-3 wk post-term, and at 2-3 mo post-term. Term infants (n = 22) were born at 37-42 wk and were studied at 2-3 wk and 2-3 mo post-term. Arousal thresholds were determined in both active sleep (AS) and quiet sleep (QS). In preterm infants, there was no state-related difference in arousal thresholds at either the 36 wk or 2-3 wk study; however, at 2-3 mo, arousal threshold was significantly greater in QS than AS (p < 0.05). In contrast, in term infants, arousal thresholds were significantly elevated in QS compared with AS at both 2-3 wk and 2-3 mo (p < 0.001). Arousal thresholds in AS were not different between the two groups of infants, with both groups of infants remaining readily arousable. However, in QS at 2-3 mo, arousal thresholds were significantly lower in the preterm infants (p < 0.05). This study has demonstrated that arousability is altered by gestational and postnatal age. The lower arousability that characterizes QS in term infants regardless of age is not evident in preterm infants until 2-3 mo post-term age.

Adult↗
PubMed1998

Immunization has no effect on arousal from sleep in the newborn infant.

OBJECTIVE: To investigate arousal from sleep in infants before and after triple antigen immunization (DTP). METHODOLOGY: Arousal thresholds were determined in both active sleep (AS) and quiet sleep (QS) the day before and the day following the first DTP immunisation in 14 infants. Arousal was induced using a pulsatile puff of air delivered alternately to the nostrils of the infant. RESULTS: Arousal threshold was significantly higher in QS compared to AS in both studies (P < 0.001). Mean arousal threshold in the pre immunization study was not different from that in the post immunization study in either sleep state. Core temperature and heart rate measured at the time of stimulus delivery were both significantly elevated in the post immunisation study (P < 0.001). Sleep duration and number of awakenings from sleep were unaffected by immunization. CONCLUSION: The first triple antigen immunisation has no effect on arousal from sleep in either AS or QS in this group of infants.

Arousal↗
PubMed1980

Concentration-dependent morphologic effects of cytochalasin B in the aqueous outflow system.

Cytochalasin B at concentrations of 1, 5, 10, 15, 20, or 40 microgram/ml was continuously exchange-perfused into the eyes of nine living Macaca mulatta monkeys while intraocular pressure (IOP) was maintained at 25 mm Hg for 30 min. Pressures were then slowly reduced to 4 mm Hg to permit blood to reflux into Schlemm's canal as a tracer, and the eyes were fixed while maintained at 4 mm Hg IOP. Tissues were examined in all eyes by light and transmission electron microscopy. At concentrations of 1, 5, and 10 microgram/ml cytochalasin B, the integrity of the endothelial lining of the trabecular wall of Schlemm's canal was maintained. At 15 microgram/ml cytochalasin B, 6% of the length of the endothelial lining was disrupted; at 20 microgram/ml, 54%; and at 40 microgram/ml, 83%. There was a washout of extracellular material at the site of breaks and also a reflux of blood from Schlemm's canal into the trabecular meshwork in the same regions.

Animals↗