Ultrasonic vocalization in rats self-administering heroin and cocaine in different settings: evidence of substance-specific interactions between drug and setting. - Avvisati, Riccardo; Contu, Laura; Stendardo, Emiliana; Michetti, Caterina; Montanari, Christian; Scattoni, Maria; Badiani, Aldo (Psychopharmacology, 2016)