To our knowledge, the data presented here represent the first direct assessment of incentive motivation and consumption of ethanol following the increasingly popular Roux-en-Y gastric bypass procedure in an outbred dietary obese rat strain. Although our rats did not differ in preoperative body weight, significant differences were observed after postoperative week three, and continued throughout the course of our experiments. As can be seen in , RYGB rats had significantly lower body weights than their Sham counterparts throughout the 20 experimental days, indicative of successful surgical results and corroborated by other RYGB studies that consistently show decreased body weight following RYGB surgery 
. Although our rats did display the characteristic changes in body weight, these were not accompanied by significantly increased high fat diet consumption during testing, as our subjects only showed significantly increased diet consumption on one of the 20 test days ().
Perhaps of more interest, we found that RYGB rats displayed significantly increased drug-seeking behavior when compared to their Sham controls. As can be seen from , rats that underwent RYGB made significantly more responses on the active spout to earn an alcohol reward during the majority of the testing sessions for 2, 4, and 8% ethanol. Accordingly, subjects that underwent RYGB also had significantly higher breakpoints (cycles completed) than their Sham controls during the majority of the test sessions, and particularly for 4 and 8% ethanol, as can be seen in . Increased active spout responding and higher breakpoints denote that RYGB subjects were more willing to work for ethanol reward than controls, indicative of increased incentive motivation or “wanting” of the drug. Thus, although the literature suggests that RYGB may reduce the incentive (rewarding) effects elicited by certain foods, the converse may be true with regard to alcohol. Our current data corroborate recent clinical reports that show increased susceptibility to alcohol abuse following gastric bypass surgery 
and are consistent with observation of augmented alcohol preference in dietary obese rats that received RYGB 
Also of interest was that our RYGB subjects showed significantly increased consummatory behavior when compared to Sham controls. As can be seen from , RYGB rats made more licks on the ethanol spout than Sham control subjects. Although this is an operationally defined measure of intake, the results show that particularly once acclimated to the behavioral paradigm, RYGB rats made significantly more lick-responses for 4% and 8% ethanol on the last five test days. It could be suggested that the augmented intakes are due to increased caloric need. However, the rats consume such little ethanol during the 30 minute behavioral sessions due to the high PR requirement, which makes it highly unlikely that caloric need is the decisive factor. Indeed, recent clinical studies found no correlation between increased alcohol use and the degree of weight loss 
. Moreover, distinct to RYGB patients there were no changes in alcohol use reported in patients that underwent a laparoscopic adjustable gastric band 
, which indicates that increased alcohol intake is not a compensation for restricted meal-size. Rather, these observations of increased responding for ethanol reward, and increased consummatory behavior are more likely a result of changes in incentive motivation which is mediated through the DA reward system and modulated by peripheral hormones involved in the gut-brain system.
We next measured the responses of RYGB and Sham rats to work for and consume 4% EtOH following intraperitoneal injection of the GHS-R1A antagonist D-[Lys3]-GHRP-6. Rats working for 4% EtOH on a PR-10 schedule of reinforcement did not reduce intake immediately following either dose of D-[Lys3]-GHRP-6 (), but RYGB rats did reduce the number of licks made on the active spout following 100 nmol D-[Lys3]-GHRP-6 whereas the same dose was ineffective on the Sham rats (). Furthermore, for all behavioral measures RYGB rats showed significant reductions in the days following D-[Lys3]-GHRP-6 injections (). This delayed response could be due to a carry-over effect from the D-[Lys3]-GHRP-6 injections (for the higher dose), and may also indicate that the ghrelin system is involved in long-term (associative and learning) aspects of ethanol-seeking and consumption. Furthermore, these data posit that RYGB rats may be more sensitive to inactivation of the ghrelin system, strongly indicating a change in ghrelin sensitivity following RYGB surgery.
While our observation of increased alcohol reward after RYGB is supported by various human studies, several factors may explain the differential results seen here from those in a prior rodent study 
. One likely factor is the selectively bred rat strain used in the Davis et al. study, which is quite different than the diet induced obese Sprague Dawley rats used in the current investigation, and therefore, differential results could be expected. Another factor could be differences in procedures between these two studies, i.e. no sucrose fading was used in the Davis et al. investigation. Although EtOH preferring rats seem more likely to readily consume ethanol, it is known to be aversive to rats, which is why some form of sucrose fading is used in most EtOH ingestion paradigms involving rodents. Additional differences in the paradigms include the use of a two bottle test as a measure of ethanol intake, while CPP was used as a measure of reward. Thus, strain and procedural differences are likely to underlie the discrepancies between these two studies.
RYGB has gained popularity due to its ability to produce long-lasting changes such as reduced appetite, decreased body weight, improved glucose control, and changes in taste preference 
. Despite its increasing popularity, the precise underlying mechanisms through which RYBG may produce these changes remain to be determined. Reports indicate that a number of gastrointestinal hormones change following surgery, including the orexigenic hormone ghrelin 
. Since recent studies in rodents showed that ghrelin increased their ethanol consumption and ghrelin antagonism blocked alcohol's rewarding effects 
, we investigated how ghrelin influenced EtOH intake in our surgical model.
Ghrelin may influence both food intake and the motivation to obtain palatable foods and rewarding substances through its actions in the ventral tegmental area (VTA) where the cell bodies of the dopamine reward system are located 
. Ghrelin has been shown to stimulate dopamine neurons and to increase dopamine release in terminal areas of the mesolimbic dopamine system, including the nucleus accumbens 
. Indeed in obese subjects a recent PET study reported that ghrelin levels were inversely associated with D2R availability in limbic brain regions including ventral striatum (location of the nucleus accumbens), such that higher levels were associated with lower D2R availability presumably from increased dopamine release and receptor occupancy 
. Because of the multiple factors that modulate the activity of dopamine neurons, it is remarkable that ghrelin exerts such a strong stimulatory influence on alcohol reward as evidenced by the lack of alcohol-induced dopamine increases in ghrelin knock-out mice 
. Our finding that RYGB rats were more sensitive to D-[Lys3]-GHRP-6 in reducing their alcohol intake compared to controls suggests improvement in ghrelin signaling after the surgery. Irrespective of whether such improvements affect peripheral or central ghrelin signaling or both, it may also influence the neuronal and hormonal signals upstream of the reward system. Should this effect (i.e. increased alcohol reward) rely on the dopamine system, then it may be that RYGB can improve the sensitivity of the dopamine system, which is believed to be blunted in obesity 
. In fact, gastric bypass has been shown to increase the expression of dopamine D2 receptors in the ventral striatum and caudate nucleus, although the reports are still mixed 
. As the ventral striatum is believed to be involved in modulating alcohol's rewarding effects, such changes could be especially impactful on alcohol intake and abuse potential 
In summary, we show that RYGB rats increased alcohol reward and consumption of low EtOH concentrations compared to their dietary obese controls, which supports the clinical findings that bariatric surgery is associated with an increased risk for alcohol abuse. We also found that changes in the responsiveness of the ghrelin system may be partly involved in the modulation of alcohol intake following RYGB, although further studies are needed to determine the precise role of ghrelin on these responses.