Operant responding for oral ethanol in the alcohol-preferring P and alcohol-nonpreferring NP lines of rats.

Rats of the P (n = 4) and NP (n = 5) lines were housed in operant chambers with food available ad lib, but all liquid was obtained by responding on either of two levers according to a FR5 schedule. Presses on one lever produced water from an automated dipper, while the other lever gave access to a dipper containing ethanol in concentrations ranging from 2 to 30% (v/v). P rats worked to obtain the ethanol at all concentrations offered and preferred the ethanol over water. The highest ethanol intake averaged 7.7 +/- 0.5 g/kg body weight/day at the 15% concentration and at least 5.8 +/- 0.9 g/kg/day for the 20-30% range. The NP rats responded more for the 2 and 5% concentrations of ethanol than for water, but responded predominantly for water when the ethanol concentrations were 10% and higher. In a second experiment, NP rats drank water rather than 10% ethanol by free-choice, even though the ethanol was mixed with a preferred flavor and the water with a nonpreferred flavor. The findings indicate that ethanol is rewarding to P rats in concentrations up to 30% (v/v) but is not rewarding to NP rats when the concentration is 10% and above.