αMSH (Tocris, UK), HS014 (Tocris, UK), D-trp8-γMSH (γMSH; Tocris, UK,), AGRP (83–132)-amide (Phoenix Pharmaceuticals, USA), and α-flupenthixol dihydrochloride (Sigma Aldrich, USA) were dissolved in sterile saline. 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, Tocris, UK), DL-2-Aminophosphonopentanoic acid (APV, Tocris, UK), and bicuculline (Tocris, UK) were prepared as a stock solution.
For i.c.v. infusions, rats were briefly restrained and 2 μl of drug solution was injected over 10 s into the ventricular cavity. Intra-VTA infusions were performed through an injector (9 mm, 33GA, Plastics One, USA) inserted into the guide cannula. Bilateral infusions (300 nl over 30 s) were made using a syringe pump with the injectors left in place for another 30 s to allow for diffusion. α-Flupenthixol dihydrochloride was injected intraperitoneally (i.p.) 30 min before intra-VTA infusions. All animals received all drug doses/combinations, according to a Latin-square design. Behavioral testing commenced 5 min after drug infusions and a minimum 1 day drug-free period was maintained between infusions during which the animals were trained but not tested.
For i.c.v. infusions, rats were briefly restrained and 2 μl of drug solution was injected over 10 s into the ventricular cavity. Intra-VTA infusions were performed through an injector (9 mm, 33GA, Plastics One, USA) inserted into the guide cannula. Bilateral infusions (300 nl over 30 s) were made using a syringe pump with the injectors left in place for another 30 s to allow for diffusion. α-Flupenthixol dihydrochloride was injected intraperitoneally (i.p.) 30 min before intra-VTA infusions. All animals received all drug doses/combinations, according to a Latin-square design. Behavioral testing commenced 5 min after drug infusions and a minimum 1 day drug-free period was maintained between infusions during which the animals were trained but not tested.