Audiogenic immobility reaction and open-field behavior in AA and ANA rat lines

Individual predispositions in emotional reactivity have been suggested as factors involved in the development of alcoholism. To approach this problem, we assessed emotional reactivity in alcohol-naive animals from the alcohol-preferring (AA) and alcohol-avoiding (ANA) rat lines of Alko Ltd. AA rats are known to have higher brain levels of 5-hydroxytryptamine (5-HT) than ANA rats. Emotional reactivity was therefore assessed by an audiogenic immobility reaction (freezing), which is specifically sensitive to and shortened by depletion of 5-HT. The results showed that AA rats of both sexes displayed increased immobility reactions compared to the corresponding sex of the ANA rats. During the period of adaptation to the test cage ANA rats of both sexes showed increased locomotor activity compared to the corresponding sex of the AA rats. Levels of plasma corticosterone did not differ between the rat lines, either during resting or stressful conditions. The present results suggest that a passive, inhibited style of defensive behavior is associated with a high alcohol consumption.