Chronic administration of alcohol in the developing rat: expression of functional tolerance and alcohol olfactory...

Three experiments were designed to evaluate the acquisition and expression of tolerance to ethanol in preweanling rats. Administrations were begun on Postnatal Day 13 (PD13) and continued, on alternating days, through PD23. Following either three or five administrations of a 2.5 g/kg dose of ethanol, animals expressed tolerance to the motor-impairing consequences of acute ethanol, as measured through attenuated latencies to perform a righting reflex. However, no tolerance was evident when it was assessed through the hypothermic response to ethanol delivery (Experiment 1). The results of subsequent experiments suggested that this tolerance was not due to lower levels of ethanol in the blood and brain of the chronically exposed subjects (Experiment 2) nor to the development of behavioral tolerance, such as learning to perform the motor task in the presence of intoxication (Experiment 3). Additional tests determined that tolerance level did not alter the infant rats' ability to learn about the orosensory cues associated with ethanol delivery. Specifically, tests confirmed previous studies that an aversion to ethanol odor was formed as a result of the chronic administration procedure, presumably due to the animals associating the orosensory properties of eliminated ethanol during intoxication with the aversive consequences of this state. These results provide evidence that tolerance can develop in the preweanling rat, and that at least one measure (righting reflex) can be used to assess its development early in life.