Evidence for serotonergic involvement in saccharin preference in a two-choice test in rehydrating rats.

Adult male rats were adapted to a 20-h water-deprivation schedule and trained to drink a 0.1% sodium saccharin and water in a two-choice test (30 min). Several direct acting serotonergic receptor agonists (putatively agonists at the 5-HT2C receptor), MK212, mCPP, and TFMPP, respectively, blocked the saccharin taste preference normally exhibited in this test. Water intake was unaffected. Taken with earlier evidence that these drugs reduce salt taste preference in rehydrating rats, it appears that they may inhibit taste preferences more generally, and that this effect may be closely related to their well-documented anorectic effect. At 3.0 mg/kg, d-fenfluramine almost completely blocked the saccharin taste preference, although l-fenfluramine (0.3 and 1.0 mg/kg) exhibited only hyperdipsic effects. 5-HT creatinine sulphate (0.3-3.0 mg/kg) also produced hyperdipsic effects, but showed no sign of blocking sweet taste preference. As a positive control, it was also shown that the opioid receptor antagonist, naloxone, reduced saccharin taste preference.