CNS Assessment Using Functional Neuro-PET Imaging

Obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a common heterogeneous psychiatric disorder manifesting with obsessions and compulsions. Obsessions are intrusive, recurrent, and persistent unwanted thoughts. Compulsions are repetitive behaviors or mental acts that an individual feels driven to perform in response to the obsessions. The heterogeneity of OCD includes themes of obsessions, types of rituals, presence or absence of tics, etiology, genetics, and response to pharmacotherapy. Complications of OCD include interpersonal difficulties, unemployment, substance abuse, criminal justice issues, and physical injuries. Areas of the brain involved in the pathophysiology include the orbitofrontal cortex, anterior cingulate gyrus, and basal ganglia. Overall, OCD may be due to a malfunction in the cortico-striato-thalamo-cortical circuit in the brain. Neurotransmitters implicated in OCD include serotonin, dopamine, and glutamate. Numerous drugs such as atypical antipsychotics and dopaminergic agents can cause or exacerbate OCD symptoms. The etiology includes genetics and neurological insults. Treatment of OCD includes psychotherapy, pharmacotherapy, electroconvulsive therapy, transcranial magnetic simulation, and in extreme cases surgery. Exposure and response prevention is the most effective form of psychotherapy. Selective serotonin reuptake inhibitors (SSRIs) are the preferred pharmacotherapy. Higher doses than listed in the package insert and a longer trial are often needed for SSRIs than compared to other psychiatric disorders. Alternatives to SSRIs include clomipramine and serotonin/norepinephrine reuptake inhibitors. Treatment of resistant cases includes augmentation with atypical antipsychotics, pindolol, buspirone, and glutamate-blocking agents.

Neuroimaging in Drug Discovery and Development: Paradigms for Accelerating New Drug Availability

The process of discovering and developing new drugs is complicated. Neuroimaging methods can facilitate this process. An analysis of the conceptual bases and practical limitations of different neuroimaging modalities reveals that each technique can best address different kinds of questions. Radioligand studies are well suited to preclinical and Phase II questions when a compound is known or suspected to affect well-understood mechanisms; they are also useful in Phase IV to characterize effective agents. Cerebral blood flow studies can be extremely useful in evaluating the effects of a drug on psychological tasks (mostly in Phase IV). Glucose metabolism studies can answer the simplest questions about whether a compound affects the brain, where, and how much. Such studies are most useful in confirming central effects (preclinical and early clinical phases), in determining effective dose ranges (Phase II), and in comparing different drugs (Phase IV).