Pain sensitivity and saccharin intake in alcohol-preferring and -nonpreferring rat strains.

The experiments were designed to study the association between consumption of palatable 0.1% (w/v) saccharin solution, voluntary drinking of 10% (v/v) ethanol solution, and pain sensitivity measured with the hot plate test. Rat lines that were genetically selected for high alcohol consumption (P and AA rats), alcohol-preferring Fawn Hooded (FH) rats and their F2[FH x FRL] hybrids, and the Maudsley Nonreactive strain (MNRA) had a high propensity to consume saccharin that resulted in a significant (almost twofold; p < 0.05) increase in their daily fluid intake when saccharin was available. These strains also had lower pain thresholds in the hot plate test than did their parallel strains [NP, ANA, Maudsley Reactive (MR)]. Most alcohol-nonpreferring strains [NP, ANA, and Flinders Resistant Line (FRL)] had preference ratios for saccharin about as high as those of the alcohol-preferring rats but, unlike the high alcohol drinkers, they did not increase their total fluid intake when saccharin was available. The mean saccharin intakes of the lines were strongly correlated with their alcohol drinking during the first 5 days, whereas their latencies on the hot plate were inversely related to their change in alcohol drinking with experience. The results are consistent with an endogenous opioid mechanism being involved in alcohol drinking.