Striatal dopamine responses to intranasal cocaine self-administration in humans

The reward circuit: linking primate anatomy and human imaging

Although cells in many brain regions respond to reward, the cortical-basal ganglia circuit is at the heart of the reward system. The key structures in this network are the anterior cingulate cortex, the orbital prefrontal cortex, the ventral striatum, the ventral pallidum, and the midbrain dopamine neurons. In addition, other structures, including the dorsal prefrontal cortex, amygdala, hippocampus, thalamus, and lateral habenular nucleus, and specific brainstem structures such as the pedunculopontine nucleus, and the raphe nucleus, are key components in regulating the reward circuit. Connectivity between these areas forms a complex neural network that mediates different aspects of reward processing. Advances in neuroimaging techniques allow better spatial and temporal resolution. These studies now demonstrate that human functional and structural imaging results map increasingly close to primate anatomy.

Imaging neurotransmitter release by drugs of abuse

Previous studies have shown that imaging with positron emission tomography (PET) and single photon emission computed tomography (SPECT) radiotracers that are specific for brain dopamine receptors can be used to indirectly image the change in the levels of neurotransmitters within the brain. Most of the studies in addiction have focused on dopamine, since the dopamine neurons that project to the striatum have been shown to play a critical role in mediating addictive behavior. These imaging studies have shown that increased extracellular dopamine produced by psychostimulants can be measured with PET and SPECT. However, there are some technical issues associated with imaging changes in dopamine, and these are reviewed in this chapter. Among these are the loss of sensitivity, the time course of dopamine pulse relative to PET and SPECT imaging, and the question of affinity state of the receptor. In addition, animal studies have shown that most drugs of abuse increase extracellular dopamine in the striatum, yet not all produce a change in neurotransmitter that can be measured. As a result, imaging with a psychostimulant has become the preferred method for imaging presynaptic dopamine transmission, and this method has been used in studies of addiction. The results of these studies suggest that cocaine and alcohol addiction are associated with a loss of dopamine transmission, and a number of studies show that this loss correlates with severity of disease.