Axonal uptake and retrograde transport of exogenous proteins in the hypoglossal nerve

Abstract

Exogenous proteins (albumin labelled with Evans blue (EBA) and horseradish peroxidase) were injected into the tongue of various laboratory animals (rats, rabbits, mice and guinea pigs). At various time intervals thereafter the hypoglossal nuclei were examined with regard to the cytological localization of the tracers. In the hypoglossal neurones red fluorescent cytoplasmic were seen 10 h after injection of EBA into adult rats and rabbits indicating the presence of protein tracer. Peroxidase also accumulated in these neurones of suckling and adult mice and rats. The neuronal uptake of the protein tracers was blocked by crush injuries to the hypoglossal nerve and by arrest of blood circulation. Our results show that the hypoglossal neurones have the capacity to accumulate exogenous proteins after peripheral injection. This process must be a consequence of a fast retrograde axonal transport. As shown in previous studies, a similar transport also occurs in the peripheral motor neurones of the spinal cord in suckling mice. This phenomenon therefore exists in different species, ages and kinds of nerve.