Gustatory determinants of suckling in albino rats 5-20 days of age

Taste reactivity in suckling rat pups was assessed. Five-day-old rats in Experiment I were equipped with tongue cannulae seated 2 mm rostral, 0-3 mm caudal, or 4-6 mm caudal to the intermolar eminence. Either water, 1.4 X 10(-3) QHC1, .50M NH4Cl, or .43M NaCl was delivered in one of three fashions during suckling: (1) continuous: fluid was continuously available from a reservoir connected to the cannula, and could be obtained by exerting suction; (2) discrete: same procedure as above, save that fluid was available for only 30 sec every 3 min of the 30-min test; (3) pulsatile: here, .05 ml fluid was delivered by infusion pump 8-10 sec every 3 min, provided the pups were attached to a nipple. Based on intake, time and behavioral measures, we conclude behavioral reactivity exists especially to NH4Cl and NaCl. As to quinine, Day 5 pups were responsive only when QHCl was delivered in the continuous mode. In Experiment II, rats 10, 15, and 20 days of age received the above solutions by infusions with the cannulae located in one of the three positions. Quinine reactivity developed sequentially in an anterior to posterior direction. NH4Cl disrupted behavior in 5-, 10-, and especially 20-day-old rats. Remarkably, Day 15 rats were not behaviorally reactive to NH4Cl. Sodium chloride, especially in the anterior and middle positions, was treated as an aversive solution during suckling throughout development. Based on existing electrophysiological data, the last finding was unexpected.