Thesis (Ph.D. (Pastoral))--North-West University, Potchefstroom Campus, 2006.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 94-103).

An increasing amount of people have their work hours displaced to the night and there are indications that shift work and other irregular working schedules are associated with an increased risk of developing the metabolic syndrome and other pathological conditions. It is therefore important to address the consequences of eating at irregular hours, especially nighttime. Papers I-III refer to a study in which 7 males were given a high-carbohydrate diet (HC) or a high-fat diet (HF), using a cross-over design. Subjects were kept awake for 24 h and food was provided as 6 equally spaced isocaloric meals. Higher energy expenditure and non-esterified fatty acids (NEFA) concentration, as well as lower glucose and triacylglycerol (TAG) concentrations were observed with the HF-diet, compared to the HC-diet. With the HF-diet, fat oxidation, heat release, heart rate, glucose, NEFA and TAG concentrations differed depending on time of day. The highest postprandial TAG concentrations were seen after the 04.00 meal with both diets. Insulin and leptin responses to meal intake differed with respect to diet and time of day. Time of day affected glucagon, thyroid stimulating hormone, free thyroxin, total triiodothyronine (tT3), cortisol, chromogranin A and pancreatic polypeptide (PP) concentrations. PP’s postprandial increase was greater during 08.00 – 16.00 compared to 20.00 – 08.00. Furthermore, the subjects felt less irritated when eating the HF-diet but hunger was not related to macronutrient composition. Hunger and thirst decreased throughout the 24 h period despite constant activity and energy intake; and were correlated with several endocrine and metabolic variables. In paper IV 7 males were studied twice during 24-h either given 6 isocaloric meals throughout the 24-h period, or 4 isocaloric meals from 08.00 to 20.00, followed by a nocturnal fast. Energy expenditure, glucose, TAG, insulin and glucagon concentrations were lower; and NEFA concentrations were higher during the nocturnal fast compared to nocturnal eating; although no 24 h differences between the protocols were apparent. The subjects were more passive during the fasting period compared to when food was given. Stepwise regression showed that correlations between metabolic variables and hormones differed between daytime and nighttime. The decreased evening/nocturnal responses of cortisol and PP to meal intake suggest that nocturnal eating might have health implications and that the body reacts unfavorably to nocturnal eating. Smaller meals around the clock, however, showed marginally better effects on postprandial TAG concentrations and mental energy compared to larger meals during daytime. Further studies (long term) are needed before dietary guidelines can be given to shift workers, especially regarding the impact of nocturnal eating on gastrointestinal response and cortisol.

This paper presents verbal working memory test results towards establishing the effects of menstrual cycle on working memory of women. The study comprised of a subject-set of twenty healthy young women with a regular 28 – 32 day menstrual cycles. Subjects were tested twice, once during their menstrual phase and second during their ovulation phase (on approximately day 12). Working memory tests were performed in a random sequence i.e. for some subjects during the menstrual phase (low estrogen level) working memory test occurred before their ovulation phase (high estrogen level) memory test and vice versa for other subjects. Study revealed that the test scores in the ovulatory phase were significantly higher than those in the menstrual phase. These findings suggest that higher levels of estrogen may improve working memory. Moreover, effects of estrogen on mood were also considered during both phases of menstruation. The fluctuation in estrogen levels seems to have an effect on women’s mood during menstrual and ovulation phases.

Several lines of evidence implicate oxidative stress in the pathophysiology of bipolar disorder (BPD). The mood stabilizers lithium and valproate have been shown to protect against oxidative stress-induced cell death. This study examined whether an increase in cellular reductive potential due to glutathione (GSH) synthesis up-regulation underlies this neuroprotective effect. Using primary rat cortical neurons as a model, this study demonstrated that unlike lithium and valproate, carbamazepine and lamotrigine do not exert neuroprotective effects against H2O2-induced cell death. Moreover, the level of GSH and the GSH:GSSG ratio in neurons and in rat brain remained unchanged following chronic treatment with either lithium or valproate. Similarly, this study did not find a significant effect of treatment on the expression of genes encoding γ-glutamylcysteine ligase sub-units, Gclc and Gclm, in both neurons and the rat brain. These findings suggest that other molecular targets of lithium and valproate likely mediate the observed neuroprotective effects.

Several lines of evidence implicate oxidative stress in the pathophysiology of bipolar disorder (BPD). The mood stabilizers lithium and valproate have been shown to protect against oxidative stress-induced cell death. This study examined whether an increase in cellular reductive potential due to glutathione (GSH) synthesis up-regulation underlies this neuroprotective effect. Using primary rat cortical neurons as a model, this study demonstrated that unlike lithium and valproate, carbamazepine and lamotrigine do not exert neuroprotective effects against H2O2-induced cell death. Moreover, the level of GSH and the GSH:GSSG ratio in neurons and in rat brain remained unchanged following chronic treatment with either lithium or valproate. Similarly, this study did not find a significant effect of treatment on the expression of genes encoding γ-glutamylcysteine ligase sub-units, Gclc and Gclm, in both neurons and the rat brain. These findings suggest that other molecular targets of lithium and valproate likely mediate the observed neuroprotective effects.

Mood and cognition, along with numerous other physiological processes, are under circadian regulation. The synthesis and secretion rhythm of the pineal hormone melatonin is under the direct regulation of the central circadian pacemaker and the secretion rhythm of melatonin can be used to assess circadian alterations. In this thesis, it was demonstrated that low levels of endogenous nocturnal melatonin was associated with subsyndromal depression and alterations in sleep architecture. Studies in individuals with endogenous circadian rhythm disorder, with and without comorbid depressive symptoms, revealed that individuals with depressive symptoms had a greater phase delay in melatonin profiles as compared to individuals without depressive symptoms. Furthermore, in the same study, exogenous melatonin administered to induce phase advances significantly improved depression scores and sleep initiation. In addition to endogenous circadian disruption, circadian rhythms can also be disrupted by repeated atypical alterations in environmental time cues. In mammals, light is the strongest environmental cue that can modulate circadian rhythms. Recent studies suggest that circadian response to photic stimuli is preferentially sensitive to short wavelengths in the range of 450-480 nm. Using an animal model it was demonstrated that filtering a 10 nm bandwidth between 470-480 nm from polychromatic white light prevents nocturnal light exposure induced disruptions in melatonin and corticosterone secretion as well as central and peripheral clock gene expression. These findings were further investigated in humans and revealed that filtering short wavelengths below 480 nm attenuates 12 h nocturnal light exposure induced suppression of melatonin secretion, increased cortisol secretion and disrupted peripheral clock gene expression. Furthermore, attenuation of these changes was associated with improvements in mood, alertness and vigilance at a time close to the endogenous circadian wake drive. However, filtering short wavelengths below 460 nm or reducing the optical transmission by up to 30% below 480 nm did not attenuate the disruptive effects of nocturnal light exposure on physiological and behavioural variables. Overall, the results presented in this thesis support the role of circadian dysfunction in neuropsychometric impairment and presents evidence supporting spectral modulation as a promising approach to attenuate light-mediated chronodisruption.

Epigenetics continues to be redefined and new discoveries are likely to revolutionise the field still further. This thesis explores different aspects of how epigenetic regulation of gene expression contributes to human disease. Paper I explores the function of the IKKα kinase in regulating gene expression through the nuclear retinoic acid receptor (RAR). We define a set of genes requiring IKKα for their expression and found recruitment of IKKα to the RAR dependent on structural motifs in its protein sequence. This interplay between the NFκB pathway and nuclear receptor regulated transcription is important to consider when designing therapeutic strategies. Papers II and III focus on the plasma cell malignancy multiple myeloma (MM) and define a gene regulatory circuit defining an underexpressed gene profile in MM dependent on the Polycomb proteins. We provide proof-of-principle that the use of small chemical inhibitors may be operational in reactivating genes silenced by H3K27me3 and that this leads to decreased tumour load and increased survival in the 5T33 in vivo model of MM. We explored the genome-wide distribution of H3K27me3 and H3K4me3, and defined their association with gene expression in freshly-isolated malignant plasma cells from MM patients. Importantly, H3K27me3-marked genes in MM associated with more aggressive stages of the disease and less favourable survival. We present evidence that gene targeting by H3K27me3 is likely to not only involve a small population of tumour cells, but rather represent a common MM profile and further provide a rationale for evaluating epigenetic therapeutics in MM. Paper IV shows that pro-inflammatory gene expression in monocytes of psychiatric patients can be induced in vitro by sodium pump inhibitors, as the steroid hormone ouabain. We suggest that the ouabain-induced gene expression is regulated by an intricate network involving microRNAs, Polycomb and the H3K27me3 demethylase JMJD3. Our data indicates that epigenetic regulators play a role in transmitting cues between intrinsic and/extrinsic stimuli and gene expression in psychiatric illness. This thesis provides novel insights on how seemingly unrelated pathways may converge on transcriptional regulation and evidence that epigenetic modifiers contribute to the pathogenesis of human complex diseases such as multiple myeloma and mood disorders.

Females are disproportionately affected by stress- related mood disorders. Child abuse is the single greatest environmental risk factor for mood disorders. An animal model of child abuse, juvenile social subjugation (JSS), was used to determine whether males and females differentially process stress, specifically in the bed nucleus of the stria terminalis (BST). Rats (n=36) were randomly assigned to one of three conditions: JSS, Benign Control (BC) or Handled Control (HC). Following this procedure, brains were processed for Fos, which indicates neural activity. It was hypothesized that the JSS condition would evoke more neural activation than other conditions and would do so more in females. Across both sexes, we hypothesized there would be significantly more activation in the posterior BST than in the anterior BST. Based on earlier research, we hypothesized there would be and a sex difference in total neuron number, favoring males, in the posterior BST.

The focus of this thesis is to explore the impact of positive affective state and mood salience on intertemporal decision making. We found that positive affect significantly influence intertemporal preference. We also found that when current mood becomes salient to the decision maker, the direction of preference changes. Specifically, we hypothesized and found that individuals with positive mood are more likely to choose the later larger (long term) rewards than the individuals with a neutral mood. We discuss three factors that could explain choice behaviour in such situations. These factors are the willingness to maintain positive mood, temporal orientation and risk perception, and increase in the level of dopamine in brain. Moreover, our results indicate that when current positive mood is salient, individuals become more concerned about their affective state, and are more likely to engage in affect regulation, and as a result, more likely to prefer the sooner smaller (immediate) rewards. These findings suggest that experiencing positive affect would increase patience and self-control. However, this is the case when the level of mood salience is not high. When individuals’ attention is directed to their emotional states, they tend to choose sooner smaller rewards that could assist them in keeping their good mood and avoiding negative feelings.