Data claim that rats avoid consumption of the otherwise palatable saccharin cue when paired using a medication of abuse in least partly because the worth from the flavor cue pales in expectation from the option of the highly rewarding medication. of consumption from the flavor cue in Lewis and Fischer rats when the morphine US was implemented subcutaneously instead of ip. Test 2 examined the result of pressure on the suppression of intake from the saccharin cue when matched with spiradoline a selective κ-opioid receptor agonist. The outcomes concur that Fischer rats are even more attentive to the suppressive ramifications of morphine than Lewis rats and that Fischer rats also show greater avoidance of the saccharin cue when combined with spiradoline despite the fact that spiradoline is definitely devoid of reinforcing properties. Taken together the data suggest that the facilitated morphine-induced suppression observed in Fischer rats compared with Lewis rats may reflect an increased level of sensitivity to the aversive κ-mediated properties of opiates. (2009) showing a similar level of avoidance of a saccharin cue for Lewis and Fischer rats when combined with the kappa-agonist U50 488 In their studies however BMS-806 (BMS 378806) rats are restricted to 20 min access to fluid daily and this regimen has been associated with less drug-induced suppression of CS intake (Glowa (7 140 = 3.71 p < .01 (Number 1). Newman-Keuls post hoc checks exposed that while both Fischer and Lewis rats avoided the saccharin cue after one pairing Fischer rats in the saccharin-morphine group consumed significantly less saccharin than Lewis rats on tests 2-8 ps < .05. These data are consistent with Lancellotti (2001) but still amazing as Lewis rats more readily acquire morphine self-administration (Martin (35 602 = 2.31 p<.001. Newman-Keuls post hoc analysis indicated that while Fischer rats significantly reduced saccharin intake on tests 2 and 5 when it expected even the lowest dose of spiradoline (0.25 mg/kg) Lewis rats only started to suppress intake with the 0.5 mg/kg dose. In addition Fischer rats consumed less saccharin than BMS-806 (BMS 378806) Lewis rats on tests 2-8 when tested with both the 0.5 and 1.0 mg/kg dose of spiradoline p<.05. These data display that Fischer rats are more responsive to the suppressive effects of κ-receptor activation as mediated by spiradoline. Number 2 Mean (± SEM) intake (ml/5min) of saccharin as it expected a sc injection of saline (open circles) or spiradoline (closed circles) in Fischer rats. Asterisks show significance compared with settings p<.05. Number 3 Mean (± SEM) intake (ml/5min) of saccharin as it expected a sc injection of saline (open squares) or spiradoline (closed squares) in Lewis rats. Asterisks show significance compared with settings p<.05. General Conversation MHAM Both the incentive comparison BMS-806 (BMS 378806) hypothesis and the conditioned aversive state (e.g. withdrawal) hypothesis predict that Lewis rats would demonstrate higher avoidance of a drug-paired taste cue than Fischer rats. As mentioned Lewis rats typically are more responsive than Fischer rats to BMS-806 (BMS 378806) the cataleptic (Cadoni & Di Chiara 2007 locomotor revitalizing (Cadoni & Di Chiara 2007 and rewarding properties of cocaine and morphine as measured by conditioned place preference (Guitart et al. 1992 Kosten et al. 1994 but see Roma Davis & Riley 2007 acquisition of drug self-administration (Ambrosio et al. 1995 Haile & Kosten 2001 Kosten et al. 1997 Martin et al. 1999 Ranaldi Bauco McCormick Cools & Smart 2001 and progressive proportion responding (Martin et al. 2003 Martin et al. 1999 but see Kosten Zhang & Haile 2007 Relating Lewis rats also display greater avoidance of the saccharin cue when matched with cocaine than Fischer rats (Glowa et al. 1994 Grigson & Freet 2000 but see Kosten et al. BMS-806 (BMS 378806) 1994 This prediction nevertheless was not verified for morphine. Hence the outcomes of Test 1 aswell as previously released data (Lancellotti et al. 2001 demonstrate that morphine-induced suppression of CS intake is normally markedly better in Fischer than Lewis rats. The same holds true for heroin (Davis et al. 2009 which is normally quickly deacetylated to morphine (Nakamura Thornton & Noguchi 1975 in the mind. This seeming conundrum may be explained if differential sensitivity to.