Infiltration of carbon-labelled monocytes into the dorsal motor nucleus following an intraneural injection of ricinus communis agglutinin-60 into the vagus nerve in rats.

A marked increase in the number of non-neuronal cells occurred in the neuropil of the ipsilateral dorsal motor nucleus (DMN) 6 days after an intraneural injection of Ricinus communis agglutinin-60 into the vagus nerve in the cervical region of rats. Other structural changes in the DMN were the hypertrophy and reduction in number of the neurons. In order to verify the origin of the non-neuronal cells, a single intravenous injection of carbon was administered into these rats 4 days before, simultaneously, or 4 days after, the injection of the RCA-60. Thus, in rats given carbon 4 days before the RCA-60 injection, none of the non-neuronal cells were labelled. A few labelled cells, however, were observed in rats given carbon and RCA-60 simultaneously. Labelled non-neuronal cells were most common in rats given carbon 4 days after the RCA-60 injection. They were located in the neuropil as well as in the walls of blood vessels. Some blood elements in the lumen of blood vessels in the DMN were also labelled by carbon. Histochemical study at the electron microscopical level showed that some of the non-neuronal cells present in the neuropil of DMN were stained positively for non-specific esterase. They were located in the perivascular region and in the neuropil far removed from the blood vessels. Occasional non-specific esterase-positive mononuclear cells were observed seemingly in their passage through the endothelium of blood vessels. It was concluded from this study that a small proportion of non-neuronal cells which appear in the DMN following a RCA-60 injection into the vagus nerve are derived from blood monocytes. The infiltration of these cells, which had been labelled by intravenous carbon injection, is probably elicited by the degenerating neurons destroyed by the retrograde transport of RCA-60.