Thermosensitive and osmoreceptive afferent fibers in the hepatic branch of the vagus nerve.

The hepatic vagus nerve contains various thermosensitive afferent fibers which are widely varied in their sensitivity. Their Q10 values lie between 4 and 16. The discharge rate is positively correlated with increase of liver temperature (warm fiber type). The result supports the existence of a thermosensitive structure in the liver which may possibly contribute to maintain thermal homeostasis. Neural responses to the osmotic changes in the perfusion solution have been analyzed. It was found that two different types of osmosensitive afferent fibers exist in the hepatic vagus; one is characterized by increasing the frequency of spike discharges in response to higher osmotic pressure, while the other shows the same response to lowered levels. Behavioral changes caused by hepatic vagotomy were observed. These results provide evidence for the existence of an osmoreceptor mechanism. The role of these hepatic afferent nerves in homeostasis are briefly discussed.