Neural control and neurosensory functions of the liver

In addition to the important roles of the mammalian liver in the control of homeostasis, such as the clearance, detoxification, inactivation and storage of fuels, it is subjected to various neural stimuli and appears to act as a sensory organ. The liver is in the ideal position to be involved in the control of metabolism and many changes are signalled to the central nervous system (CNS) by both neural and humoral pathways. Despite a considerable amount of research it is still difficult to draw firm conclusions from the available evidence in view of the often controversial reports in the literature. The neural mechanisms, especially the sensory functions of the liver, have proved to be particularly difficult to interpret for the following reasons: ( I ) lack of clear knowledge of the location and routes of hepatic nerves in different species; (2) difficulty in employing conventional histological and electrophysiological techniques; (3) different experimental approaches resulting in discrepant results; (4) uncertainty of relating effects of neural activation directly to the liver and the possibility that other splanchnic organs are involved, especially the adrenal medulla and pancreas. Combinations of physiological, histological and behavioural approaches need to be made to advance our understanding of the integration of the liver into the whole complex of neural and humoral systems involved in the control of metabolism.