Differences in transneuronal transport of horseradish peroxidase conjugated wheat germ agglutinin in the visual system: marmoset monkey and guinea pig compared.

Conjugates of the lectin wheat germ agglutinin with horseradish peroxidase have been described as effective transneuronal tracers in different neuronal systems of various mammalian species. Here, the failure is described to detect any sign of transneuronal transport of the tracer in the visual system of adult marmoset monkeys (Callithrix jacchus), in spite of heavy anterograde labeling in the primary visual centers after intravitreous injections. In contrast, in the brains of guinea pigs processed by identical technical parameters, transneuronal anterograde labeling was readily recognized in the contralateral striate cortex, thalamic reticular nucleus, and parabigeminal nucleus. Furthermore, transneuronal retrograde labeling of cell bodies was evident in the thalamic reticular and paragibeminal nuclei, and in the striate cortico-geniculate and cortico-collicular cells. The transneuronal labeling of the cell bodies in the guinea pig striate cortex, which has not been demonstrated before, is taken as a measure for the sensitivity of the histological procedures applied. The failure to demonstrate transneuronal labeling in the marmoset monkey, thus, appears to indicate an interspecies difference in the mechanisms of transneuronal transfer of the tracer used. Positive results in other mammalian species such as other rodents, cat, and Old World monkeys, as obtained in this and other laboratories, further support this view.