By use of selective breeding, Croatian scientists have gradually developed two sublines of rats with high or low activity of platelet serotonin (5HT) transporter (5HTt) (Wistar-Zagreb 5HT rats). These rat sublines demonstrated clear neurochemical and behavioural alterations indicating also differences in their brain 5HT neurotransmission. These results were also confirmed by the two leading Spanish neuroscientific laboratories in Barcelona and Seville, and the model was internationally indexed as 'Wistar-Zagreb 5HT rat'.

The model was a result of 20 years-serotonin research conducted by scientists at the Laboratory of Neurochemistry and Molecular Neurobiology. Research was almost entirely conducted at the Ruđer Bošković Institute and recently our scientists have started cooperation with the Croatian Institute for Brain Research at the Medical Faculty in Zagreb in the field of finer characterizations of the brain alliterations in Zagreb serotonin rat.