Introduction: Ethanol-preferring (P) rats and high-alcohol-drinking (HAD1 and HAD2) rats have been selectively bred to consume greater amounts of ethanol than nonselected rat strains. These three rat lines also show increased levels of responding for ethanol in operant paradigms that assess a combined appetitive/consummatory response.
Methods: The present experiment used a model of reinforced responding that procedurally separates the appetitive, or seeking, response requirement from consummatory responding to compare seeking and intake responding in P and HAD rats. Subjects (n = 7 or 8 per group) were trained to make 25 lever-press responses, which were followed by 20 min of access to a sipper tube spout containing either 10% ethanol (10E) or (in separate groups of subjects) 3% sucrose (3S). After training, a single nonreinforced session was conducted to assess the limit to appetitive responding under extinction conditions. After this single nonreinforced session, three successive across-session breakpoint determinations were made for 10E and 3S by increasing the response requirement over days until subjects failed to complete the requirement. A final extinction session was then conducted.
Results: Appetitive responding during both the nonreinforced and breakpoint sessions indicated that P rats made significantly more responses overall than HAD rats in both the ethanol and sucrose groups. P rats also consumed more sucrose than HAD rats, with no differences in ethanol consumption between the lines (1.0-1.5 g/kg/20 min). Appetitive responding in the HAD rats in the ethanol groups was comparable to that reported previously for nonselected Long-Evans rats.
Conclusions: These findings indicate that appetitive and consummatory processes are distinct and that P rats have an increased tendency to both seek and drink ethanol and sucrose solutions, making this selected line useful when modeling both "craving" and "loss of control" related behaviors involved in excessive alcohol consumption.