Browsing Doctoral Degrees (Psychiatry) by Author "Carey, Paul D. (Paul Dermot)"
Now showing 1 - 1 of 1
Results Per Page
- ItemObsessive-compulsive disorder : serotonergic and dopaminergic system involvement in symptom generation and treatment response(Stellenbosch : Stellenbosch University, 2008-03) Carey, Paul D. (Paul Dermot); Stein, Dan; Audenaert, Kurt; Stellenbosch University. Faculty of Health Sciences. Dept. of Psychiatry.ENGLISH ABSTRACT: Investigations into the neurobiology of obsessive-compulsive disorder (OCD) have provided useful insights into this prevalent and disabling disorder in recent decades. Encouraging advances have also been made in the pharmacological treatment of OCD. This has improved the quality of life for many who typically endure chronic unremitting symptoms. Despite the widespread use of first-line agents selective for the serotonergic system in OCD, relatively little is known about the neurobiology of treatment response, the specific components of the serotonin system involved in symptom modulation, and the overlapping and distinct brain regions impacted by alternative treatment options. Despite the advance that selective serotonin re-uptake inhibitors have been, a significant proportion of patients still fail to respond adequately to these agents, and alternative pharmacological interventions are required. The use of dopamine antagonists, a strategy which until recently has had only limited supporting data, presents one such alternative. Little however, is known about which subsets of patients are most likely to respond to these agents. In this thesis, I will present a series of six studies that use pharmacological treatments and single photon emission computed tomography (SPECT) to make contributions to three primary areas in OCD namely; neurobiology, treatment and the intersection of the two. First, I address OCD neurobiology by examining the impact of OCD on resting brain function. I then examine the effects of pharmacological challenge of the serotonin 1B receptor using sumatriptan on regional cerebral blood flow (rCBF) and clinical symptomatology. Second, I examine the intersection of neurobiology and treatment as I explore the changes in rCBF in response to treatment with inositol, a precursor of the phosphoinositol second messenger system. I then examine the distinct and overlapping effects on rCBF of treatment for 12 weeks with the selective serotonin re-uptake inhibitor (SSRI) citalopram across anxiety disorders. Third, I address treatment of OCD by examining the efficacy of controlled augmentation of serotonin re-uptake inhibitors with quetiapine, a dopamine antagonist, in treatment refractory OCD. I then combine this data with a second similar dataset to derive a predictive model for treatment outcome with quetiapine augmentation of SRIs. I demonstrate that rCBF in OCD differs significantly from normal controls, is correlated with severity in frontal brain regions, and remains an important line of investigation for OCD pathophysiology that has yet to fully delineated. Pharmacological challenge of the 5HT1B autoreceptor with the selective agonist sumatriptan results in heterogeneous behavioural and regional brain perfusion changes in OCD. Attenuation of pre-frontal perfusion following 5HT1B agonist administration is in line with the effects of SRIs. This work suggests that direct or indirect effects of SRIs on the 5HT1B receptor may be involved in mediating a clinical response in OCD. In the section exploring the intersection of neurobiology and treatment, I show that changes in rCBF partially parallel treatment response to SSRIs across a range of anxiety disorders. These data suggest that a degree of overlap exists in the neurobiology of treatment response or indeed core neurobiology across different anxiety disorders. I then show that effective treatment with inositol in OCD results in rCBF changes that are partially in line with the effects of SRIs on brain perfusion. These data support suggestions that second messengers may form part of the common pathway of action for effective anti-obsessional compounds. In the study in which we augmented SRIs with quetiapine, no advantage over placebo was found. This data has, however, recently been combined with similar data in meta-analyses and demonstrated a benefit over placebo. Finally, we found that patients who have failed fewer SRI trials, have more severe illness, and clinical dimensions with a putative dopaminergic underpinning, may derive preferential benefit from serotonin/dopamine antagonist augmentation of SRIs. Through this series of clinical treatment and functional brain imaging studies in OCD, I have contributed to the neurobiological understanding of OCD, and its treatment in refractory populations. In addition I have explored the intersection of these two domains using novel as well as conventional treatment across other anxiety disorders. Treatment and pharmacological challenges used, either directly or indirectly impacted the monoamine systems serotonin and dopamine and advanced our understanding of their involvement in symptom generation. Future work should focus on the functional intersection of brain function, treatment response, and functional genetic polymorphisms within the monoamine systems of the brain.