Fos induction in rat brain neurons following stimulation of the hepatoportal na-sensitive mechanism. Morita, Hironobu, Yoichi Yamashita, Yasuhiro Nishida, Masaaki Tokuda, Osamu Hatase, and Hiroshi Hosomi. Department of Physiology, Gifu University School of Medicine, Gifu 500, Japan and the Department of Physiology, Kagawa Medical School, Kagawa 761-07, Japan
APStracts 3:0273R, 1996.
The responses of hepatic afferent nerves to intraportal bolus injection of hypertonic solutions were examined in anesthetized rats. Hepatic afferent nerve activity increased in response to an intraportal injection of 0.75 M NaCl or NaHCO3, but did not respond to a similar injection of 1.5 M mannitol, 0.75 M LiCl or 0.15 M NaCl, implying that nerves in the hepatoportal area are sensitive to increases in Na concentrations and that this leads to stimulation of hepatic afferent nerve activity. To study central activation in response to stimulation of the hepatic Na-sensitive mechanism, c-fos induction was monitored. Following electrical stimulation of the hepatic afferent nerves, neurons containing Fos-like immunoreactivity (Fos-LI) were found in the area postrema, nucleus of the solitary tract, paraventricular hypothalamic nucleus and supraoptic nucleus at 90 min after the stimulation. Induction of Fos-LI was also studied following the simultaneous infusion of 0.45 M NaCl into the portal vein and distilled water into the inferior vena cava in conscious rats so as to keep the total amount of solution introduced into the systemic circulation isotonic, thus avoiding changes in mean arterial pressure, plasma osmolality and plasma NaCl concentrations. Fos-LI -containing neurons were found in the same regions as those seen following electrical stimulation. However, few, if any, Fos-LI -containing cells were found if the rats were hepatically-denervated or if they received an intraportal infusion of hypertonic LiCl or mannitol. These data provide evidence for the involvement of the brainstem and forebrain structures in the NaCl regulatory functions induced by stimulation of the hepatoportal Na-sensitive mechanism. However, stimulation of the hepatoportal osmo-sensitive mechanism does not activate these central structures. 

Received 26 July 1995; accepted in final form 20 June 1996.
APS Manuscript Number R463-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996