The Development of Circadian Rhythms in Human Infants

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crucial in physiological development and maturation. However it should be noted that the study did not include extremely premature infants. It included only nine infants born between 31 and 34 weeks gestation. The HPA axis of extremely premature infants would be expected to be significantly immature and not likely to mature at a similar postnatal age to term infants. The visual data were based on working definitions of the appearance of a diurnal pattern of secretion for the secretion of the hormones melatonin and cortisol, sleep and peripheral gene expression. Detailed statistical analysis to determine the exact timing of the maturation of each aspect of physiology studied was not feasible due to the sample size, and the inherent difficulties comparing different types of outputs. For example it is problematic to attempt to link hormone secretion directly to gene expression; whilst comparing age of maturation of cortisol secretion with melatonin secretion by determining timing of maximal diurnal rhythmicity (as there are both humoral outputs) is more straightforward. Although there are limitations as to what can be inferred from the data, there is a possible suggestion that the physiological maturation of the different, but interrelated systems, occurs over a period of weeks, rather than simultaneously. The box and whisker plots show there is wide variability within each physiological system measured for the age at which „maturation‟ took place but does not clearly give any indication of the precision of the estimate of the mean for each week of maturation. This study does, however, contribute strongly towards the argument for larger studies, to more accurately answer the question whether there is actually a 226
systematic, ordered developmental process that is universal and upon which environment and external factors have no effect. Alternatively might the ordering of the maturation of the different systems change if an alternative system of reference was used to define maturity, for example using sleep as a term of reference rather than core body temperature? Further work is needed to confirm the emergence of these rhythms and elicit their relationship to each other. 227
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The Development of Circadian Rhythm
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Table of Contents LIST OF FIGURES .
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7.1 Analysis of infant sleep measur
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List of Figures Figure 1.1 - Diagra
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List of Tables Table 3.1 - Descript
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1 Introduction Happiness is not a m
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Each of these independently is impo
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There is general agreement, that al
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Summary 1. Development encompasses
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Figure 1.1 - Diagram illustrating c
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A phase shift is used to describe a
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1.4 Ontogeny in Human Infants Well
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1.5.2 Circadian Rhythms in Temperat
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1.5.4 Factors affecting Temperature
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1.6 Melatonin (Reviewed in Cardinal
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mechanism by which this occurs is n
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It is at this time that infant slee
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1.7 Cortisol Cortisol is a hormone,
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1.7.3 Circadian pattern of Cortisol
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In a separate study, Weerth et al u
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Summary 1. Cortisol is crucial to a
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NREM sleep has 4 stages. It occupie
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1.8.1 Functions of Sleep The functi
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1.8.3 Ontogeny of Sleep in Infants
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Sleep can clearly be used as marker
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For the purpose of this study, the
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Summary 1. Sleep is defined by lack
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Overall the SCN generates signals (
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Figure 1.2 - The mammalian circadia
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1.9.3 Molecular Components of the C
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Figure 1.3 - Mechanisms from SCN to
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1.9.7 Melatonin and Clock Melatonin
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The links between the central clock
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Chapter 2 Methods
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There were strict inclusion and exc
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This personal contact on the postna
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2.1.3 Home monitoring visits The fi
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2.1.4 Further monitoring informatio
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Core body temperature was taken sim
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2.3 Collection of urine samples Pai
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were read against air at 429 nm aft
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allowed the display and comprehensi
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2.8.1 RNA preparation and cDNA synt
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In total three methods were trialle
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2.11 Statistical methods For compar
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test that each infant‟s height an
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Power calculation Sample size: Fift
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3 Results 3.1 Recruited subjects an
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predominantly affluent areas of the
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Birth history and past medical hist
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3.1.3 Socioeconomic demographics of
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her best friend losing her battle w
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Sleep environment of infants All mo
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Summary 1. This study had higher ra
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4 Results 4.1 Core body temperature
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Degrees Celsius 36.70 36.60 36.50 3
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11-13 weeks There is no significant
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Core body temperature (degrees Cels
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Number of infants 10 8 6 4 2 0 7 8
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Mean minimum rectal temperature in
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Mean minimum rectal temperature in
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Figure 4.7 shows the changes in the
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Chapter 5 Result
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4 or 6 hourly samples. Circadian rh
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Figure 5.1 - Distribution of mean n
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5.1.2 Emergence of diurnal rhythm f
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Figure 5.3 - Histogram showing dist
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Figure 5.4 - Changes in night time
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Night-day difference in melatonin s
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Summary 1. There is an increase in
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6 Results DESCRIPTION OF THE URINAR
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6.1.2 Emergence of diurnal rhythm f
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Figure 6.3 - Histogram showing dist
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Cortisol values were corrected to a
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6.1.4 Relationship between night an
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Chapter 7 Results
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Mean Length of Sleep/ Wake Bouts Th
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Sleep parameters were recorded as m
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7.3 Development of infant sleep rel
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Figure 7.2 - Changes in infant slee
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Figure 7.4 - Changes in percentage
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Figure 7.5 - Changes in infant frag
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Figure 7.7 - Changes in number of m
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Figure 7.9 - Changes in the percent
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Sleep efficiency (%) 100.0 90.0 80.
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Chapter 8 Results
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Considering only those weeks of mea
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8.2 Description of peripheral gene
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18:30 hours 0.9927; 01:00 ours 1.01
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The weeks after temperature maturat
Page 185 and 186: Further peripheral gene graphical r
Page 187 and 188: Raw data points are represented by
Page 189 and 190: H3f3b/Gap H3f3b/Gap H3f3b/Gap H3f3b
Page 191 and 192: 8.3 Detailed gene expression analys
Page 193 and 194: Summary 1. H3f3b was selected as ge
Page 195 and 196: 9 Results FACTORS AFFECTING SLEEP A
Page 197 and 198: Care and infant related factors �
Page 199 and 200: Table 9.3 - Effect of family occupa
Page 201 and 202: * Class 7 used as reference group
Page 203 and 204: Table 9.6 - Effect of measured infa
Page 205 and 206: Summary: 1. A mature physiological
Page 207 and 208: 10 Results 10.1 Circadian rhythms -
Page 209 and 210: value of above 0.5 for R squared wa
Page 211 and 212: Table 10.1 - Temporal relationship
Page 213 and 214: Chapter 11 Discussion
Page 215 and 216: � What if any are the factors whi
Page 217 and 218: 11.1 Physiological development - ag
Page 219 and 220: There are other proven factors whic
Page 221 and 222: drawbacks of the spread of data - a
Page 223 and 224: presented in table 6.1 do not have
Page 225 and 226: separate methods were applied to th
Page 227 and 228: significant. Sleep latency was cons
Page 229 and 230: The function of sleep in developmen
Page 231 and 232: Melatonin secretion was higher on n
Page 233 and 234: In this study sleeping in the same
Page 235: Timing of sleep maturation was diff
Page 239 and 240: individual gene plots that provide
Page 241 and 242: temperature recording devices adapt
Page 243 and 244: Both melatonin and cortisol rhythms
Page 245 and 246: Extension of this period of monitor
Page 247 and 248: Second, we demonstrated the gene of
Page 249 and 250: Cortisol and melatonin Slope based
Page 251 and 252: Summary and Future work This study
Page 253 and 254: � Maximise technique for measurin
Page 255 and 256: “There is a science of infant car
Page 257 and 258: References
Page 259 and 260: Bajanowski, T., Vege, Å., Byard, R
Page 261 and 262: Chamley, C.A., Carson P, Randall D,
Page 263 and 264: Frank, M.G., Heller, H.C., 2003. Th
Page 265 and 266: intrahypothalamic administration of
Page 267 and 268: Mirmiran, M. & Ariagno, R.L., 2000.
Page 269 and 270: Rawson, D., Petersen, S.A., Wailoo,
Page 271 and 272: Stokkan, K.A., Yamazaki, S., Tei, H
Page 273 and 274: Winter, J.S.D., 1985. The adrenal c
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