The bottom-up pathway of this loop includes DAergic projections to the hippocampus and other cortical brain areas (Lisman and Grace 2005). If the novelty detection hypothesis (Lisman and Grace 2005) works then conditioning upstream of the comparator region should not affect novelty detection and hence should maintain the place reinforcing effects of METH. Consistent with this hypothesis, our finding in “Intra-VTA reverse microdialysis application of METH produces positive place reinforcement learning” suggests

that stimulating the VTA produced positive CPP potentially because stimulation did not perturb the novelty comparator region of the hippocampus Inhibitors,research,lifescience,medical and hence the memory of the appetitive properties of METH remained intact. We therefore hypothesized that conditioning the bottom-up pathway of the hippocampus-VTA loop produces positive reinforcement our website learning following conditioning each of the three brain areas of interest Inhibitors,research,lifescience,medical within this loop. To do so, we conditioned another batch of rats in the order of VTA first followed by the VHC, and former finally the NAc (refer Fig. 1B for experimental design). The

following three successive experiments (“METH produced positive Inhibitors,research,lifescience,medical place learning following conditioning the VTA,”“In rats previously trained with intra-VTA-METH CPP, intra-VHC-METH produced positive place reinforcement learning 24 h following conditioning,” and “In rats previously trained with intra-VTA-METH followed by intra-VHC METH, intra-NAc-METH also produced an augmented positive place reinforcement Inhibitors,research,lifescience,medical learning 24 h following conditioning”) assessed the role of each of the three brain areas in METH-induced CPP learning. METH produced positive place learning following conditioning the VTA Based on criteria described in “Behavioral Assay”, the rats satisfied the requirement for baseline place preference (Fig. 3A). The rats in each group underwent intra-VTA CPP followed by testing. There

was a significant interaction between treatments (Base [n = 11], Ringer’s [n = 7], METH [n = 10]) and Test (test 1, test 2, test 3) (F [6, 46] = 8.74, Inhibitors,research,lifescience,medical P < 0.001). In agreement with the above experiments in part I, the first intra-VTA conditioning session with METH, but not with Ringer's, increased the time deviation values (P < 0.001). The place conditioning effects of METH were also significantly greater Drug_discovery than the baseline condition (P < 0.05). Additionally a positive increase in the time deviation from baseline was observed in the METH-paired chambers compared to the Ringer’s-paired chambers (P < 0.001) (Fig. 3B–D). When tested 24 h following conditioning, without intra-VTA treatment, METH-treated rats, but not Ringer’s rats, showed increased time deviation values toward the METH-paired chambers (P < 0.005). The place reinforcing effects of METH was also greater than the baseline condition (P < 0.05) (Fig. 3E).