Dual projections of single neurons are visualized simultaneously: use of enzymatically inactive [3H]HRP

The results of neuroanatomical experiments in cats are reported in which double-labeling of single neurons in the thalamus and in spinal ganglia has been made possible by the retrograde axoplasmic transport of two exogenous tracers: i.e. horseradish peroxidase (HRP) and tritiated HRP which has had its enzymatic activity virtually eliminated ([3H]apo-HRP). By this approach evidence is also contributed that other projections (e.g. cuneocerebellar and cuneothalamic) may arise from separate populations of neurons within the same nuclear region. (Auth.)