Use of positron emission tomography to study drugs of abuse

Positron Emission Tomography (P.E.T.) has been used in man to study the mode of action of illicit drugs, mainly cocaine, alcohol and marihuana on brain metabolism and circulation. Acute cocaine administration decreases brain metabolic activity in cortical and subcortical regions. After chronic cocaine administration, a significant and persistent decrease in cerebral blood flow is observed. An increased metabolic activity is recorded in orbito-frontal cortex and basal ganglia during early cocaine withdrawal. Alcohol intoxication is associated with a decrease in whole metabolic activity of the brain, mostly in the frontal and parietal lobes. I.V. administration of THC (2 mg) was associated with a significant increase in cerebellar metabolic activity (glucose utilization). Chronic marihuana smokers also presented increased metabolic activity in the frontal lobe. However the increase cerebellar metabolism produced by THC administration was smaller in the chronic cannabis user than in the non smoking control. Deregulated cerebellar activity could translate in disruptions in functions associated with the cerebellum such as motor coordination, proprioception and learning.