Furosemide-induced food avoidance: evidence for a conditioned response

Furosemide (Furo) is a potent natriuretic drug that is often used experimentally to investigate the brain mechanisms underlying salt appetite. Within this experimental paradigm, however, Furo also has anorectic activity that has received only modest attention. In Experiment 1 we varied two things-administering a 10-mg dose of Furo in a single or a divided dose and preinjection exposure to a Na-free diet. In the 24 h after Furo, all four groups of rats reduced ingestion of Na-free diet. Both the division of the Furo dose and the preexposure to Na-free diet reduced the amount of food consumed even more than a single dose or continuous access to normal chow did. The fact that preexposure to Na-free diet increased the post-Furo anorexia implied an associative component to the phenomenon. Experiments 2 and 3 investigated the ability of Furo (2 and 10 mg) to serve as an unconditioned stimulus in taste aversion learning using 0.2 M sucrose as the conditioned stimulus. A saline (Sal) injection group served as control in both experiments. The results show that animals avoided sucrose when its ingestion was immediately followed by 10 mg Furo but not with 2 mg Furo or Sal. An aversion to sucrose did not develop when 10 mg Furo was administered the day prior to sucrose access. Thus, the suppressive effects of high-dose Furo on food intake might be due to a conditioned response.