Do rat strain differences in ethanol consumption reflect differences in ethanol sensitivity or the preparedness to learn?

Three strains of rats (Wistar, Sprague-Dawley, Long-Evans; n = 10/strain) were trained to drink various concentrations of ethanol (ETOH) in the rats' home cage in daily 30-min drinking sessions using a modified "Samson" sucrose-fading procedure. Wistar and Sprague-Dawley rats were similar in their voluntary intake of a wide range of ETOH concentrations and both of these strains drank considerably more ETOH than the Long-Evans strain. For comparison purposes only, pharmacological pretreatment tests were later conducted with the Sprague-Dawley strain of rats using a maintenance concentration of 20% w/v ETOH. Low-dose ETOH pretreatments increased (125% of control), and high-dose ETOH pretreatments decreased the subsequent voluntary consumption of ETOH. Low-dose nicotine pretreatments increased ETOH consumption to 148% of control intake, and high doses of nicotine decreased ETOH consumption. Both opiate antagonists, naloxone and naltrexone, produced dose-dependent decreases in ETOH consumption. The dopamine antagonist, haloperidol, produced dose- and time-dependent increases in voluntary ETOH consumption. The strain differences in voluntary ETOH consumption described in the present study differ from those previously described by other labs. We suggest that this strain-dependent disparity between laboratories, with respect to ETOH consumption/preference tasks, may reflect genetic differences in the preparedness to condition (learn) voluntary ETOH consumption rather than genetic differences in ETOH's reward/reinforcement attributes.