“…The role of serotonin in mediating a hunger/feeding behavioural state has been suggested and proved in many invertebrates (Horvitz et al, 1982;Lent and Dickinson, 1988;Sakharov, 1990a;Sakharov, 1990b;Palmer and Kristan, 2011;Donnelly et al, 2013), including molluscs (Alania et al, 2004;Hernádi et al, 2004;Gillette, 2006;Hirayama and Gillette, 2012;Hirayama et al, 2014;Dyakonova, 2014). In this study, we utilized the advantages of the mollusc Lymnaea stagnalis to elucidate how a hunger behavioural state is represented at a single serotonergic cellular level.…”