Visualizing receptors for neurotransmitters in the human brain with autoradiography.

Receptors for neurotransmitters and drugs are now well characterized at the molecular level. Thanks to the development of numerous radiolabeled molecules and to the use of autoradiography it is possible to study the characteristics and distribution of these receptors with the anatomical resolution of the microscope. We have used quantitative receptor autoradiography to examine receptors in the human brain and to study receptor alterations in neurodegenerative diseases of the human brain. Alterations in the density and distribution of receptors have been found in diseases such as amyothrophic lateral sclerosis, Huntington's Chorea, Parkinson's disease and Alzheimer's disease. In these diseases different types of receptor alterations have been found. The most characteristic ones are selective receptor losses associated with neuronal losses. Alterations such as receptor hypersensitivity due to degeneration of target areas have also been observed. In some cases no correlations between alterations of the neurotransmitters and receptors have been found. These results indicate that different receptors are associated with specific neuronal systems and could be used as markers for these neuronal populations in different pathological studies. The possibility of visualizing receptors in the living human with non-invasive techniques such as PET could lead to the future use of receptor alterations as a diagnostic tool.