Ingestional aversion learning in preweanling rats.

Ingestional aversions were conditioned in 12- and 15-day-old rats by infusing a .5% solution of saccharin into the oral cavity and following this oral infusion by the injection of lithium chloride. At both ages, subjects for which the saccharin exposure was followed by lithium injection within 2-3 min drank less when the saccharin solution was again presented by oral infusion 12 hr later; such suppressions of intake were not observed in subjects that previously received the saccharin and lithium in an unpaired fashion (Experiments 1 and 3). Ingestional aversions were also learned by 12-day-olds when a 30-min interval was introduced between saccharin exposure and lithium toxicosis but not when toxicosis was delayed by 120 min (Experiment 2). In contrast, 15-day-olds learned aversions with both the 30- and 120-min-delay intervals (Experiment 3). Despite the absence of long-delay learning in 12 day olds, ingestional aversions conditioned at 12 days of age were retained for 2 wk (Experiment 4). These results provide further evidence of the associative abilities of neonatal rats and illustrate a developmental aspect of long-delay learning.