Opioid receptors undergo axonal flow.

Previous studies have indicated the presence of opiate receptors on axons of the rat vagus nerve and on other small diameter fibers. In examinations of the effect of ligation on the distribution of receptors in the vagus nerve by in vitro labeling light microscopic autoradiography, a large buildup of receptors was found proximal to the ligature. This result indicates an axonal flow of receptors.