Effects of artificial sweetners on licking behavior in schedule-induced polydipsia

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Abstract
Male adult rats (5) were trained for 2 h-sessions/day on a fixed interval (FI) 1.5 min schedule of food reinforcement under a situation in which water was freely provided. The schedule-induced polydipsia was produced in these conditions after 10-15 sessions. After the stabilization of FI-responses (lever-pressings) and post-pellet licking bursts in a polydipsic state, effects of sucrose and 3 artificial sweetners (saccharin Na, aspartame and Na cyclamate) were investigated by exchanging water for those solutions. Effects of NaCl solutions were also studied. When 0.3-4% sucrose solutions were given, the lickings were enhanced in proportion to the concentraions, while no marked change of the FI-responses was observed. At 16% sucrose solution, the lickings were markedly enhanced in the first 20 min, then strongly inhibited, and simultaneously the FI-responses were decreased throughout the session. When 0.03-0.4% saccharin solutions were presented, the lickings and the total intake of fluid were significantly increased regardless of the concentrations. Saccharin solution (1.6%) was rejected, thus the licking counts lowered. The FI-responses were not affected by any concentration of saccharin. After the presentations of 0.1-0.8% aspartame and 0.03-0.2% cyclamate solutions, neither the licking counts nor the FI-responses changed significantly, but 0.4% cyclamate was rejected. No marked change was observed either in the licking counts or the FI-responses after the provision of hypotonic saline solutions (below 0.8%), but 1.6% solution was rejected. The sense of taste to artificial sweetners was clearly different between rat and man.

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