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- The CB1 receptor is a protein in the brain that is targeted by the active ingredients in cannabis (marijuana). Brain systems that react to cannabis may be involved in the causes and symptoms of schizophrenia and schizoaffective disorder. For instance, research studies have shown that the number of CB1 receptors may be different in people with schizophrenia, and there may be differences in the receptors themselves. Researchers are interested in using positron emission tomography (PET) to study CB1 receptors in people with and without schizophrenia, using a chemical tracer that attaches specifically to CB1 receptors.
- To determine whether the CB1 receptor brain protein is different in people with and without schizophrenia.
- Individuals between 18 and 55 years of age who either have been diagnosed with schizophrenia/schizoaffective disorder or are healthy volunteers.
- Participants in the study must have previously enrolled in the National Institute of Mental Health protocol A Neurobiological Investigation of Patients with Schizophrenia Spectrum Disorders and Their Siblings (95-M-0150).
- Participants will provide blood samples to test for the gene that contains information on the specific type of CB1 receptor each participant has.
- Participants will have a PET scan and/or a magnetic resonance imaging (MRI) scan.
- The PET scan will last approximately 2 hours. Participants will receive an injection of a small amount of chemical tracer to improve the quality of the images taken during the scan.
- The MRI scan will last approximately 1 hour.
Schizophrenia is a debilitating mental disorder with a complex and multifactorial etiology. The exact pathophysiological mechanisms have remained elusive, but a large body of evidence points toward abnormalities in a number of brain neurotransmitter systems: dopamine, glutamate, and gamma-amino butyric acid (GABA). Pharmacological studies have shown that acute exposure to cannabis is able to induce psychotic symptoms in healthy individuals and exacerbate symptoms in patients with an established psychotic illness. In addition, epidemiological studies have established that cannabis use in early adolescence is associated with an increased risk of developing schizophrenia later in life. Together, this evidence suggests that the neural systems targeted by cannabis may be involved in the pathophysiology of schizophrenia.
The brain endocannabinoid (EC) system is a recently discovered brain neurotransmission system, which involves endogenous cannabinoid agents (ECs) that act upon specific receptors (CB1 and CB2). CB1 receptor is abundant in the human brain and acts as an inhibitory modulator of classical neurotransmitters. ECs and CB1 receptors appear to be involved in the pathophysiology of schizophrenia. EC levels are elevated in the cerebrospinal fluid of patients with schizophrenia, and post-mortem studies have shown increased density of radioligand binding to brain CB1 receptors. To what extent CB1 receptors are involved in the pathophysiology of schizophrenia in the living human brain is currently unknown. The lack of suitable methods to reliably quantify CB1 receptors in the living human brain have to date hindered the progress in this field.
In this protocol, we outline studies aiming at elucidating the role of CB1 receptors in schizophrenia by using positron emission tomography (PET) and the recently developed radiotracer for CB1 receptors, [18F]FMPEP-d(2). The aim of this project is to explore CB1 receptor abnormalities in human patients with schizophrenia. The primary hypothesis is that CB1 receptor density is increased in patients with schizophrenia in comparison with healthy subjects. Insight into the role of CB1 receptor function in schizophrenia may help guide future development of pharmacotherapies.
Time Perspective: Prospective
National Institutes of Health Clinical Center, 9000 Rockville Pike
National Institutes of Health Clinical Center (CC)
Published on BioPortfolio: 2014-08-27T03:16:08-0400
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