Aversion learning in 5-day-old rats: Taste–toxicosis and texture–shock associations.

Abstract

Rats (5 day old) that received a single pairing of a novel saccharin flavor with Li treatment learned to suppress ingestion of saccharin on subsequent occasions. This flavor aversion learning was inversely related to the interval between the novel flavor experience and drug administration, with significant aversions being learned with intervals of 0 and 30 min but not with intervals of 60 and 90 min. The conditioning was observed when hypertonic Li served as the unconditioned stimulus but did not occur with isotonic Li or hypertonic saline injections. Flavor aversion learning in infant rats is a result of the joint action of 2 factors, pure drug effects and the somatic pain and irritation produced by the tonicity of the injected agent. The taste aversion learning was specific to the drug-paired flavor and evidence was presented suggesting that 5 day old rats display a natural hesitancy to consume novel edibles (neophobia). Rats 5 day old selectively associate flavor stimuli with the gastrointestinal consequences of Li injection but not with cutaneous shock and they selectively associate tactile stimuli with shock but not with the gastrointestinal consequences of Li. Implications of the mechanisms involved in flavor aversion learning in infant rats are discussed as they relate to adaptation and food selection in adult animals.