Introduction: The aim of the project was to investigate the effects of antidepressants on brain networks whilst at rest. My hypothesis was that antidepressants work by reversing persistent activity in the brain’s default mode network (DMN). The DMN is implicated in self-reflection and rumination in MDD. The methodologies and results of studies of resting state networks in MDD and the effects of antidepressants are reviewed in the thesis. Increasing evidence implicates glutamate in the action of antidepressant drugs. Whether there are illness related changes in glutamate function is unresolved, largely because of the lack of techniques for assessing it. Ketamine and other NMDA antagonists have improved MDD symptoms within 24 hours though the effects are short lasting. The molecular neural networks involved in ketamine’s putative antidepressant effects are unclear. The thesis reviews the evidence. Much evidence implicates ACC as a site of action of antidepressant effects but whether this is through its regulation of the DMN or other networks is not known. This thesis compares the effect of ketamine and citalopram on ACC-related systems. Method: The thesis combines two systematic reviews of the effects of MDD and antidepressant drugs on i) resting state networks (53 studies) and ii) glutamate neurotransmission (45 studies of clinical efficacy of ketamine). There are two experimental chapters. The first describes investigation into two rapid acting antidepressant drugs acting via glutamate mechanisms. 54 unmedicated cMDD were scanned across two centres on 3T MRI scanners while being infused with placebo (0.5% saline), 0.5mg/kg ketamine or 100mg AZD6765 over 1 hour. fMRI resting state data between drug treatments was compared for the final 25 minutes of the drug infusion and for a 25 minute resting state scan a day later. The second experimental chapter examines whether these effects were shared by citalopram, a standard antidepressant. 67 unmedicated cMDD, rMDD and HC were administered citalopram 7.5mg i.v. and scanned on a 1.5T MRI scanner. In a second study 63 cMDD and HC were administered i.v. citalopram 7.5mg or placebo (0.5% saline). fMRI resting state data for the final 12 ½ minutes following drug infusion was compared. Independent Component Analysis was performed using the Group ICA for fMRI toolbox. The resting component with the highest spatial correlation to the ACC was used. Brain maps of the intensity of the selected component were constructed for each individual. Group averages were calculated and compared using SPM. Regional analysis was performed using Marseille Boite a Regions d'interet. Results: On day 1 AZD6765 significantly increased mean intensity of ACC resting component in the right insula, right IPL and left cingulate gyrus greater than ketamine or placebo. Ketamine increased mean intensity of ACC resting component greater than placebo in the right lentiform nucleus and left mFG. Significantly decreased mean intensity of ACC resting component in the left insula in the AZD6765 group compared to placebo was noted. On day 2 AZD6765 increased mean intensity of ACC resting component greater than ketamine and placebo in the left and right lentiform nuclei. AZD6765 reduced mean intensity of the ACC resting component in the left and right MFG. The first citalopram study revealed reduced mean intensity of ACC resting component in cMDD compared to rMDD and HC in PCC. rMDD had reduced mean intensity of ACC resting component in the precuneus compared to HC. In the second study, citalopram had no effect in HC but normalised precuneus activity in cMDD producing a significant drug x group interaction. Conclusions: The acute antidepressant effects of citalopram are modulated by changes in the bilateral precuneus. The precuneus is central to connectivity with other regions in MDD. It has a prominent role in the DMN and is linked to rumination. The mechanism of the antidepressant effects of AZD6765 is different from those of ketamine and citalopram. The insula, IPL, MFG, cingulate gyrus and lentiform nuclei are all regions implicated in MDD suggesting antidepressant effects. The rapid antidepressant effects of AZD6765 are possibly due to a resetting of the interface between DMN and salience networks.

MDD is a severe and debilitating disorder that is associated with a growing global economic burden due to reduced workplace productivity along with increased healthcare resource utilization. Furthermore, depression markedly enhances the risk for suicide, mortality that is especially worrisome given that 30% of depressed individuals have an inadequate response to current antidepressants. This inadequacy of antidepressants necessitates the discovery of a better understanding of the pathobiology of MDD. Most current antidepressants work through monoamine neurotransmitters, and their relative efficacy in depression led to the now dated monoamine-deficiency hypothesis. The limited usefulness of antidepressants has led to a reinvigorated search for other pathologies in depression that might yield clues for the development of better drug treatments. In this regard, a strong association has been found between oxidative stress and MDD. Our lab recently found increased DNA oxidation and elevated poly(ADP)ribose polymerase (PARP1) gene expression in the brain from donors that had MDD at the time of death. Besides DNA damage repair, PARP1 mediates several downstream inflammatory effects that may contribute to pathology in MDD. In fact, our lab has demonstrated that PARP-1 inhibition produces antidepressant-like effects in rodents, suggesting that PARP-1 inhibitors hold promise as a novel antidepressant drug. While our lab had previously demonstrated elevated PARP1 gene expression in the frontal cortex in MDD, whether PARP1 protein levels were also increased in depression had not been verified. My thesis research was performed to determine whether PARP1 protein expression was also elevated in the brain in MDD. I studied primarily the hippocampus because it is part of the limbic (mediating emotion) system of the brain and because previous research has shown numerous other pathologies in the hippocampus. My study was carried out simultaneously as others in our lab were measuring PARP1 protein levels in frontal cortex in MDD. This latter work was important since the lab’s previous work had observed elevated PARP1 gene expression in the frontal cortex, rather than in the hippocampus which was not previously studied. Hippocampal and frontal cortical brain sections were cut from frozen blocks of both MDD and psychiatrically normal control brain donors for these studies. PARP1 protein levels were estimated by assisted-imaging software. The findings herein demonstrate that levels of PARP1 immunoreactivity are significantly elevated in the frontal cortex of MDD donors as compared to control donors. However, there was no change in PARP1 immunoreactivity in the hippocampus in MDD.

Several trials have reported rapid antidepressant response from the anesthetic drug ketamine although the mechanism behind this effect is not fully understood. Research has focused mainly on ketamine’s action in the brain, including its effects on chemical balance, connections between brain cells and networks, and cognition. Trials with psychedelic drugs have had similar antidepressant results as ketamine, and the quality of the subjective psychedelic experience seems to mediate antidepressant action. Ketamine causes similar alterations of consciousness, which have been viewed as side effects. This thesis examines whether ketamine works in a similar way as psychedelics, where the ketamine-induced dissociative-like experience has a relationship to antidepressant response. Leading theories of depression and ketamine’s action in the brain are presented, and eight studies examining the relationship between ketamine-induced subjective experience and antidepressant response are reviewed. Three included studies found a relationship between psychedelic- and dissociative-like symptoms and reduction in depression, while five did not. The supposed relationship between psychedelic- and dissociative-like symptoms and antidepressant action has not been adequately explored and needs further examination in clinical trials.

Background: Major depressive disorder is associated with elevated levels of DNA oxidation, DNA damage, and gene expression of DNA repair enzymes including poly (ADP-ribose) polymerase-1 (PARP1). Elevated PARP1 activity is directly linked to neuroinflammation and PARP inhibitors are anti-inflammatory and neuroprotective. We previously showed that PARP inhibitors produce antidepressant-like effects equivalent to fluoxetine in rodent models. Here, we examined whether the PARP inhibitor 3-aminobenzamide (3AB) is effective in a rat model of treatment-resistant depression. Methods: Treatment-resistant depression was modeled with injections of lipopolysaccharide (LPS; 0.1 ug/kg/day) and daily chronic unpredictable stress (CUS) for 28 days. Anhedonia and helplessness were indexed with sucrose preference and forced swim tests, respectively, in 5 groups of rats (n¼6-8 rats/group) including unstressed, CUS, and CUS+LPS rats treated with saline, and CUS+LPS rats treated with either 3AB or fluoxetine. Results: Anhedonia induced by CUS+LPS was significantly attenuated by 3AB (p¼0.01), while fluoxetine failed to do so. Likewise, 3AB was superior to fluoxetine in reducing helplessness, where latency to immobility times were significantly lower in CUS+LPS rats treated with fluoxetine (p¼0.001) compared to unstressed rats, but not significantly different for 3AB-treated CUS+LPS rats. Conclusions: The PARP inhibitor 3AB demonstrated robust and unique antidepressant activity superior to fluoxetine in the TRD rat model. PARP is linked to neuroinflammation through release of microglia-activating factors including poly (ADP-ribose) and HMGB1, and through NF-kB activation, pathways under investigation by our lab. PARP inhibitors are currently used clinically to facilitate cytotoxicity of DNA-damaging anti-cancer treatments. Further research could implicate re-purposing non-cytotoxic PARP inhibitors for treatment-resistant depression.

Treatment of rats with reserpine, an inhibitor of the vesicular monoamine transporter (VMAT), depletes norepinephrine (NE) and regulates NE transporter (NET) expression. The present study examined the molecular mechanisms involved in regulation of the NET by reserpine using cultured cells. Exposure of rat PC12 cells to reserpine for a period as short as 5min decreased [ H]NE uptake capacity, an effect characterized by a robust decrease in the V of the transport of [ H]NE. As expected, reserpine did not displace the binding of [ H]nisoxetine from the NET in membrane homogenates. The potency of reserpine for reducing [ H]NE uptake was dramatically lower in SK-N-SH cells that have reduced storage capacity for catecholamines. Reserpine had no effect on [ H]NE uptake in HEK-293 cells transfected with the rat NET (293-hNET), cells that lack catecholamine storage vesicles. NET regulation by reserpine was independent of trafficking of the NET from the cell surface. Pre-exposure of cells to inhibitors of several intracellular signaling cascades known to regulate the NET, including Ca /Ca -calmodulin dependent kinase and protein kinases A, C and G, did not affect the ability of reserpine to reduce [ H]NE uptake. Treatment of PC12 cells with the catecholamine depleting agent, α-methyl-p-tyrosine, increased [ H]NE uptake and eliminated the inhibitory effects of reserpine on [ H]NE uptake. Reserpine non-competitively inhibits NET activity through a Ca -independent process that requires catecholamine storage vesicles, revealing a novel pharmacological method to modify NET function. Further characterization of the molecular nature of reserpine's action could lead to the development of alternative therapeutic strategies for treating disorders known to be benefitted by treatment with traditional competitive NET inhibitors.

An increasing amount of research suggests Ketamine in subanaesthetic doses to be an effective antidepressant for Major Depressive Disorder (MDD) and Treatment-Resistant Disorder (TRD). After the finding that NMDA-receptor antagonists may hold antidepressant effect, several studies have suggested Ketamine to have great effect in relief of depressive symptoms. A time lag between biological and behavioural effects have been shown in currently available antidepressants and are not guaranteed to be efficient; only 30% of patients reach adequate response. The aim for this thesis is to systematically review available studies on the efficiency of Ketamine's antidepressant effects in patients with TRD. Scopus, Web of Science, and PubMed were the databases searched for relevant research regarding the subject. Six articles were included in the analysis. A compilation of the results presented a moderate to large effect size for Ketamine compared to placebo at 24 hours through day seven. It is of immense weight that prolonged adverse effects and possible abuse are taken into consideration for future research, as well as how to sustain the dramatic acute antidepressant effect of Ketamine.

To assess the long-term effects of antidepressant medication on balance, equilibrium, and postural reflexes, we studied 30 patients, ages 20-76 years, who had a diagnosis of depressive disorder (as defined by DSM-III-R criteria) and had been treated with tricyclic antidepressants (TCAs) or selective serotonin reuptake inhibitors (SSRIs) for ≤1 year. They were assessed by a Balance Master System. The assessment included three tasks: static balance, rhythmic weight shift, and limits of stability. When compared with 30 nonhospitalized healthy controls (of comparable age and the same sex), patients who took TCAs showed impaired balance function in all main indices. The results suggest that the impairment of balance function includes motor coordination, fine-motor control, postural reflexes,maintaining equilibrium, and reaction time. No obvious impairment of balance function was observed in patients who took SSRIs.

Mindfulness-based cognitive therapy (MBCT) is a meditation-based psychotherapeutic intervention suggested to be equally effective as antidepressant medication for preventing depressive relapse. A lot of patients with major depressive disorder (MDD) have preference for psychotherapeutic intervention compared to antidepressant medication, currently being the most common treatment for preventing depressive relapse. The aim of this systematic review was to examine the effectiveness of MBCT compared to antidepressant medication for preventing depressive relapse in individuals with MDD, treatment-resistant depression, or suicidal ideation. After a literature search in the databases Scopus and Web of Science, 16 articles were included in this systematic review. Results were mixed. While two studies demonstrated that MBCT is equally effective as antidepressant medication in preventing depressive relapse, four studies showed evidence of reduced relapse rates after MBCT treatment alone. Further, four studies suggested that MBCT is inferior to antidepressant medication in preventing depressive relapse. Future studies should focus on comparing MBCT alone to specific antidepressant medication in order to further evaluate the effectiveness of MBCT vs antidepressant medication.

Early life stress has been found to be a strong predictor of depression severity, with genetic risk factors such as the serotonin transporter promotor (5-HTTLPR) and brain derived neurotrophic factor (BDNF) polymorphisms moderating depression development. Our investigation aims to extend these findings to examine the impact of depression severity, genetic risk factors, and childhood maltreatment on neuronal connectivity changes using tract based spatial statistics (TBSS) and probabilistic tractography. Fifty-five medication-free patients with major depressive disorder (MDD) [x̅ age: 36.4, M/F: 22/33] and 18 controls [x̅ age: 33.2, M/F: 8/10] underwent diffusion tensor imaging scanning, genotyping and completed the Childhood Trauma Questionairre. Corrected TBSS findings revealed trends toward significantly reduced FA in the right anterior internal capsule [p=0.051], fornix [p=0.085] and right anterior corona radiata [p=0.084] in the MDD group. Probabilistic tractography analysis examined fractional anisotropy (FA) in the cingulum bundle, uncinate fasciculus and superior longitudinal fasciculus. Individuals scoring high in depression severity and who experienced severe childhood physical neglect (PN) and emotional neglect (EN) had higher FA in the uncinate [PN: p=0.003, EN: p=0.029] and superior longitudinal fasciculus [PN: p=0.0748], with BDNF and 5-HTTLPR moderating these associations. BDNF polymorphisms also exhibited a stronger impact on uncinate FA in individuals with high depression severity, with val-BDNF exhibiting higher FA than met carriers [p=0.021]. In conclusion, MDD patients exhibit widespread decreases in FA across many neural regions. Furthermore, the impact that depression severity has on FA is considerably influenced by early life neglect. / Thesis / Master of Science (MSc)

Objective: The project aimed to compare marginal structural models, and propensity score adjusted models with Cox Proportional Hazards models to address confounding by indication due to time-dependent confounders. These methods were applied to data from approximately 120,000 women in the Women’s Health Initiative to evaluate the causal effect of antidepressant medication with respect to diabetes risk. Methods: Four approaches were compared. Three Cox Models were used. The first used baseline covariates. The second used time-varying antidepressant medication use, BMI and presence of elevated depressive symptoms and adjusted for other baseline covariates. The third used time-varying antidepressant medication use, BMI and presence of elevated depressive symptoms and adjusted for other baseline covariates and propensity to taking antidepressants at baseline. Our fourth method used a Marginal Structural Cox Model with Inverse Probability of Treatment Weighting that included time-varying antidepressant medication, BMI and presence of elevated depressive symptoms and adjusted for other baseline covariates. Results: All approaches showed an increase in diabetes risk for those taking antidepressants. Diabetes risk increased with adjustment for time-dependent confounding and results for these three approaches were similar. All models were statistically significant. Ninety-five percent confidence intervals overlapped for all approaches showing they were not different from one another. Conclusions: Our analyses did not find a difference between Cox Proportional Hazards Models and Marginal Structural Cox Models in the WHI cohorts. Estimates of the Inverse Probability of Treatment Weights were very close to 1 which explains why we observed similar results.