The aim of this investigation was to determine whether i) affective touch has a role in mediating beneficial social influences on resilience to depression and ii) whether affective touch acts through specific skin CT afferents to enhance central serotonin function. To develop and validate the Touch Experiences and Attitudes Questionnaire (TEAQ), 117 items about experiences and attitudes to touch were completed online by 618 participants. Principal components analysis reduced this to 57 items and 6 factors. Three factors concerned touch experienced; in social situations (CST), in intimate relationships (CIT) and during childhood (ChT) and 3 factors concerned attitude to touch; in intimate relationships (AIT), with unfamiliar people (AUT) and in Skin Care (ASkC). The shortened TEAQ was completed by a second sample of 704 participants. Confirmatory factor analysis found the 6 factor structure to be a good fit of the data, suggesting the TEAQ to be valid and reliable. Participants completed some demographic questions and some questionnaires to determine their current psychiatric symptoms, social circumstances, recent life events, childhood adversity and personality alongside the TEAQ. Currently depressed participants had lower touch scores for all factors compared to healthy controls. Remitted depressed participants had significantly lower touch scores on all factors except CST, ASkC and AIT compared to healthy controls. A multiple regression analysis found neuroticism, satisfaction with social support, recent life events, CIT and childhood adversity (CHA) to be predictive of depression, whereas extraversion, number of social supports, ChT and CST, did not significantly predict depression score. Logistic regression analysis found ChT, CHA and neuroticism to predict vulnerability to depression, but not AIT or AUT. It was concluded that CIT was the most important aspect of affective touch for promoting resilience to depression. The CNS effects of pleasant and unpleasant touch were investigated using fMRI in healthy female volunteers. It has been hypothesised that a novel class of CT afferent fibres in hairy skin encodes affective touch. Therefore, CNS responses to pleasant stroking of the forearm with stroking of the fingers were compared. No differential CNS effects of forearm stroking over finger stroking were seen. Indeed, more brain regions were activated by pleasant brush stroking of the fingers which lack CT afferents. Pleasant brush responses in left inferior frontal gyrus were attenuated by tryptophan depletion. However, the midbrain raphe was activated by unpleasant brush stroking and de-activated by pleasant and this effect was abolished by tryptophan depletion. This study found little evidence that CT afferents in hairy skin have a specific role in affective touch and serotonin cells of the raphe appear engaged by unpleasant stimuli rather than pleasant. In conclusion, the results of the questionnaire study indicated touch (hugs, kisses, stroking) in intimate relationships may promote resilience to depression whereas touch with other social contacts does not, suggesting type of affective touch to be important. It is suggested that future studies of the role of current social support and of early adversity in depression should include assessments of the correlated dimension of affective touch. The fMRI study found little evidence for a specific peripheral touch receptor encoding pleasant affective touch. The median raphe nucleus was inhibited by pleasant touch and this is in keeping with the idea that that aversive stimuli activate serotonin projections to the forebrain but not that this is strengthened by affective touch. Further investigation is required to identify CNS mechanisms of affective touch.

Tryptophan depletion is a non-pharmacological and non-invasive method extensively used to investigate the role of serotonin (5-hydroxytryptamine in humans and animals. The method is based on reducing the availability of the essential amino acid tryptophan, the dietary serotonin precursor. As a precursor of serotonin, L-Tryptophan has a key role in the regulation of many physiological processes and, inter alia, in the pathology and pathophysiology of neuropsychiatric disorders and diseases. Despite the fact, that the method of tryptophan depletion has been applied in many experimental studies, the exact mechanism, by which tryptophan depletion inducted neurophysiological effects, remain unclear. Also, the protentional use of this method together with other drug coadministration has not been explored in detail yet. In this thesis, the most possible mechanisms of tryptophan depletion are discussed. Biochemical and behavioural effects of low dose of dizocilpine (0.1 mg/kg and 0.15 mg/kg) in animal model of tryptophan depletion are investigated as well. And finally, effects of administration of allopregnanolone and tacrine in model of tryptophan depletion with coadministration of MK-801 are studied. The results show that acute tryptophan depletion with prior starvation, not chronic depletion, caused...

The brain has the capacity to modify itself structurally and functionally, to adapt to novel circumstances. Adaptive changes in neural circuitry that become intransigent, such as continued hypervigilance after resolution of a threat situation, become maladaptive and may facilitate development of psychiatric disorders such as Major Depressive Disorder (MDD). Although MDD pathogenesis is unclear, hypothalamic-pituitary-adrenal axis dysregulation may facilitate the neuroplastic changes observed in MDD. Whether these neuroplastic changes facilitate the development of MDD or develop due to MDD remains unclear. The characterization of neuroplastic changes in MDD has resulted in sometimes contradictory findings. There are gaps in understanding the timing of neuroplastic changes in MDD, and how and when they are affected by antidepressant treatment. Characterization of neuroplasticity in MDD may uncover different phenotypes and aid in the discovery of a predictive biomarker of antidepressant treatment response. This dissertation presents the results of a series of neuroimaging studies. Chapter 1 provides an introduction to neuroplasticity and MDD. In Chapter 2 results of a study examining hippocampal memory function in treatment naïve patients with MDD are presented. Chapter 3 exhibits findings from a study examining effects of an acute tryptophan depletion paradigm in midlife women receiving estrogen-based treatment on an emotional conflict task. Chapter 4 discusses results from an examination of unmedicated patients with MDD and healthy control participants on an emotional conflict task. Chapter 5 presents longitudinal data of the sample from Chapter 4, and the effect of 8 weeks of treatment with antidepressant escitalopram on performance on an emotional conflict task. In Chapter 6 a case study is presented of a patient with long-standing overt ventriculomegaly, whose chief complaint was of mood and cognitive impairments. Chapter 7 summarizes the findings and contributions of this body of research and discusses clinical implications and future directions. / Dissertation / Doctor of Philosophy (PhD) / The characterization of brain changes in Major Depressive Disorder (MDD) has resulted in contradictory findings, and gaps in understanding how the brain changes in response to antidepressant treatment. This dissertation aims to characterize brain changes in MDD through a series of neuroimaging studies. Chapter 1 provides an introduction to MDD and brain changes in MDD. Chapter 2 presents an examination of memory in treatment naïve patients with MDD. Chapter 3 presents a study of acute tryptophan depletion in midlife women receiving estrogen-based treatment on an emotional conflict task. Chapter 4 examines unmedicated patients with MDD and healthy control participants on an emotional conflict task. Chapter 5 examines the effects of antidepressant treatment on performance on an emotional conflict task. Chapter 6 presents a case study of a patient with ventriculomegaly with mood and cognitive impairments. Chapter 7 summarizes the contributions of this research and discusses implications and future directions.

Zielbereiche der vorliegenden Arbeit stellten sowohl die Analysen zur Auswirkung eines Schlafentzuges (SE) unter Tryptophan-Depletion (TD) auf die hormonellen Parameter Prolaktin (PRL), Cortisol, Thyreotropin (TSH), Trijodthyronin (T3) und Thyroxin (T4) als auch die daraus resultierenden Rückschlüsse im Hinblick auf eine Verzahnung dieser Parameter nicht nur mit der depressiven Symptomatik sondern auch mit den SE-Wirkmechanismen dar. Zur Untersuchung dieser bislang im Rahmen der biologischen Depressionsforschung unberücksichtigten Kombination gelangten 22 SE-Responder, die sich einem doppelblind aktiv placebokontrollierten (SHAM) Parallelgruppendesign unterzogen. Die eigenen Beobachtungen einer blanden Response nach SE unter TD im Vergleich zur SHAM-Version des PRL und TSH einerseits sowie des Cortisols andererseits im Sinne eines abgeschwächten Plasmakonzentrationsanstiegs bzw. -abfalls sprechen zugunsten der Hypothese, daß der SE über serotonerge Wirkmechanismen zumindest teilreguliert werden dürfte. Die Konzentrationsunterschiede zwischen den Untersuchungsgruppen, die am SE-Nachmittag für PRL, Cortisol und TSH signifikant ausfallen, trotz gleichzeitig deutlicher Besserung der depressiven Symptomatik aller Patienten, legen zudem die Folgerung nahe, daß die divergierende hormonelle Antwort auf eine TD als Trigger einer klinischen Differenzierbarkeit der Depressionstiefe insuffizient zu sein scheint. / The present double-blind and placebo-controlled study was designed to analyse the impact of sleep-deprivation under tryptophane-depletion in depressed patients on hormones, e.g. prolactine, cortisol, TSH, T3, and T4. Current data support the hypothesis that sleep-deprivation might act as an antidepressant by serotonergic pathways. Thus, alterations of these relevant humoral parameters could expected by decreased serotonergic activity after tryptophane-depletion. We investigated 22 depressed patients who responded to one night of sleep-deprivation. Tryptophane-depletion led to a blunted increase of prolactine and TSH, whereas cortisol plasma-level revealed a blunted decrease. No difference between tryptophane-depletion and placebo could be spot concerning neither T3 nor T4. Our results support the idea that serotonergic pathways might be involved in the interactions following sleep-deprivation, but cannot explain the complex alterations of the aforementioned hormones alone.

Background The serotonin (5-HT) hypothesis of anorexia nervosa (AN) posits that individuals predisposed toward or recovered from AN (recAN) have a central nervous hyperserotonergic state and therefore restrict food intake as a means to reduce 5-HT availability (via diminished tryptophan-derived precursor supply) and alleviate associated negative mood states. Importantly, the 5-HT system has also been generally implicated in reward processing, which has also been shown to be altered in AN. Methods In this double-blind crossover study, 22 individuals recAN and 25 healthy control participants (HC) underwent functional magnetic resonance imaging (fMRI) while performing an established instrumental reward learning paradigm during acute tryptophan depletion (ATD; a dietary intervention that lowers central nervous 5-HT availability) as well as a sham depletion. Results On a behavioral level, the main effects of reward and ATD were evident, but no group differences were found. fMRI analyses revealed a group × ATD × reward level interaction in the ventral anterior insula during reward anticipation as well as in the medial orbitofrontal cortex during reward consumption. Discussion The precise pattern of results is suggestive of a ‘normalization’ of reward-related neural responses during ATD in recAN compared to HC. Our results lend further evidence to the 5-HT hypothesis of AN. Decreasing central nervous 5-HT synthesis and availability during ATD and possibly also by dieting may be a means to normalize 5-HT availability and associated brain processes.