Positron emission tomography as a tool for studying alcohol abuse

Positron emission tomography (PET) is an imaging technology that measures the concentration, distribution, and pharmacokinetics of radiotracers-molecules that are labeled with short-lived positron-emitting variants of chemical elements naturally found in the body. These radioisotopes can be attached to compounds involved in normal brain function and then injected into the blood stream. The signals emitted by these radiotracers then are measured using specific detectors. PET is a highly sensitive method; it measures radioisotope concentrations in the nanomolar to picomolar range (10-9 to 10-12 M) . Therefore, the technique can be used to label compounds that are of pharmacological and physiological relevance. These radiotracers then can be used to probe neurochemical and metabolic processes at the relevant physiological concentrations without perturbing the system that is measured. To exert their effects on the brain, alcohol and other drugs (AODs) act on signaling molecules (i.e., neurotransmitters) in the brain as well as on the molecules on the surface of neurons (i.e., receptors) with which the neurotransmitters interact. Specific compounds that selectively bind to such receptors, to the molecules that transport neurotransmitters back into cells, and to the enzymes that are involved in the synthesis or metabolism of neurotransmitters can be labeled for use as PET radiotracers. As a result, PET can be used to assess the metabolic and neurochemical actions of AODs and to evaluate the consequences of chronic AOD use. Since its inception, PET has been used extensively to study the effects of AODs in human and nonhuman primates; however, the recent development of microPET technology has expanded its applications to research in rodents. In addition, increasing numbers of studies are using PET methodology to assess the involvement of genetic variations in individual genes (i.e., polymorphisms) in brain function and neurochemistry. The studies discussed are divided into those that assess the effects of alcohol on brain function (i.e., brain metabolism and cerebral blood flow) and those that assess the effects of alcohol on brain function (i.e., brain metabolism and cerebral blood flow) and those that assess its effects on neurochemistry.