DEGENERATION OF THE DENDRITIC ARBOR AS AN INDEX OF NEUROTOXICITY IN IDENTIFIED CATECHOLAMINE NEURONS IN RAT-BRAIN SLICES

Although catecholamine neurons are vulnerable targets for neurotoxins and degenerative disease, few in vitro studies have investigated the m echanisms of neurodegeneration in these cells. We therefore developed a brain slice preparation for this purpose. Rats were killed by cervic al dislocation and 400-mu m-thick horizontal slices containing midbrai n catecholamine neurons were incubated for 2 h in the presence or abse nce of kainic acid (KA, 50 mu M). After fixation, the slices were recu t by a technique that provided thin (40 mu m) sections in the same pla ne as the parent slice. Catecholamine neurons in these coplanar sectio ns were labeled by immunostaining for tyrosine hydroxylase (TH) couple d with diaminobenzidine. The topographical organization of the horizon tal plane of the brain was retained in the coplanar sections, enabling precise identification of catecholamine neurons in the thin sections, by reference to an atlas in the horizontal plane. In this study we ex amined neurons in the substantia nigra (SN). A key feature of the immu nostaining was that it revealed both the cell body and also the extens ive dendritic projections of SN neurons in the horizontal plane. After treatment with KA, cell bodies remained intact but the dendrites were truncated or fragmented. The loss of dendrites is a sensitive and rea dily quantifiable indicator of damage. KA caused significant reduction s in the proportion of SN neurons with intact dendrites and in the tot al length of the dendrites, measured using a computer program. The sen sitive index of damage and the facility to clearly distinguish catecho lamine groups that are topographically close yet functionally distinct are the principal features of the experimental approach that we have developed. The preparation offers major advantages for investigating t he selective vulnerability or resistance of particular types of catech olamine neurons to damage. (C) 1998 Academic Press.