New approaches to imaging based on effects of neurotoxins.

Positron and single-photon emission tomography at present visualize only loss of overall brain substance, with a few exceptions. This has improved diagnostic accuracy in the clinic but further improvements could be made. By using toxins, such as volkensin, brain tissues can be produced that are deficient in various subpopulations of cortical pyramidal neurone. Experimental lesions in rats and quantitative autoradiography were used to investigate the cellular localization of receptors. Lesions were produced by intrastriatal or intracortical injections of volkensin to destroy corticofugal and corticortical pyramidal neurones respectively. Volkensin treatment caused significant loss of pyramidal neurones which was accompanied by reduced binding to certain receptors. Results are discussed in terms of the biology of cortical pyramidal neurones and in vivo imaging in Alzheimer's disease.