“…The rats emit 50-kHz USV during different elements of behavior related to their high arousal states ( Bell, 1974 ; Berz et al, 2021 ) such as: socio-sexual interactions including copulation ( Barfield et al, 1979 ; Bialy et al, 2000 ; Burgdorf et al, 2008 ), fighting ( Sales, 1972 ; Burke et al, 2017 ), playing ( Reinhold et al, 2019 ), and even tickling by the experimenter ( Burgdorf et al, 2005 ; Panksepp, 2005 ). Additionally, pharmacologically induced high levels of general arousal [related to movement activity and sensory sensitization associated with increased level of wakefulness during activation of the gigantocellular reticular nucleus and associated structures ( Pfaff, 2017 )] result in the expression of 50-kHz vocalizations with a strong positive correlation between the number of 50-kHz ultrasounds emitted and the level of activation of the dopaminergic and noradrenergic pathways ( Brudzynski, 2007 , 2015 ; Wright et al, 2012 ; Simola, 2015 ; Hamed et al, 2016 ; Simola and Costa, 2018 ; Kuchniak et al, 2019 ).…”