Water intake during chronic preoptic infusions of osmotically active or inert solutions.

To further elucidate the role of the lateral preoptic area (LPO) as an osmoreceptive region, rats received chronic infusions (2 weeks) of low volumes (0.5 microliters/h) solutions of hypertonic sodium chloride (NaCl; 0.16 M), hypertonic potassium chloride (KCl; 0.16 M), hypertonic (0.32 M) or hypotonic (0.16 M) mannitol, isotonic saline, or water delivered bilaterally via subcutaneous osmotic minipumps attached to intracranial cannulae. All cannulae terminated within the anterior hypothalamus-preoptic region. Hypertonic NaCl and KCl increased water intake over preinfusion levels in the majority of animals tested. However, the effects were variable, including some sizable increases as well as decreases. Hypertonic mannitol decreased daily water intake in 15 of 25 rats and produced essentially no change in the average intake of the group. Isotonic NaCl produced smaller increases and decreases, while water produced larger changes in individual rats, but neither solution had a significant effect on the average intake of the group. None of the infusates significantly altered food intake.