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Dopamin igra ulogu neurotransmitera i neuromodulatora u živčanom sustavu ne samo kralježnjaka već i nekih beskralježnjaka. Zbog svoje jednostavne strukture i svestrane uloge kao poveznice različitih dijelova mozga predmet je mnogih istraživanja na području biologije, biokemije, psihologije i drugih znanosti. Dopaminergički sustav guštera, iako slabije istražen, pokazuje svojstva specifična vrstama guštera, ali i svojstva zajednička svim kralježnjacima. Najbitnija razlika koja dijeli sauropside (gmazove i ptice) od ostalih kralježnjaka je nedostatak gena za dopamin transporter, koji služi u brzoj reapsorpciji dopamina i održavanju njegove stalne koncentracije, te posljedično sinteza noradrenalin transportera (koji preuzima njegovu ulogu) u dopaminergičkim stanicama. Kod sisavaca, vodozemaca i riba oba transportera se sintetiziraju odvojeno, isključivo u svojim jezgrama. Građa dopaminergičkog sustava guštera slična je onoj kod bolje istraženih kralježnjaka (miševa i primata), no sama uloga metaboličkih puteva dopamina se razlikuje ponekad i od vrste do vrste. Uloga dopaminergičkog sustava u agresivnom i seksualnom ponašanju guštera ustanovljena je malim brojem istraživanja koja pokazuju inhibitornu ulogu prekursora sinteze dopamina u agresivnom ponašanju jedinki zelene anole te ekscitornu ulogu agonista D1 receptora na predseksualno ponašanje (naskakivanje) dvije vrste roda Aspidoscelis (prije Cnemidophorus). Dostupna literatura o dopaminergičkom sustavu guštera poprilično je oskudna te će buduća istraživanja zasigurno pružiti bolji uvid u detalje funkcije dopamina u organizmu. Dopamine has the role of a neurotransmitter and neuromodulator in the nervous system of not only vertebrates but also some invertebrates. Thanks to its simple structure and versatile role as a connector of different parts of the brain it is a topic of study in many sciences including biology, biochemistry and psychology. The dopaminergic system in lizards, although not very well researched, shows characteristics specific to lizard species, but also those similar to other vertebrates. The biggest difference that separates sauropsids (reptiles and birds) from other vertebrates is the lack of a dopamine transporter gene, which has a role in the fast reuptake of dopamine and controlling its concentration, and consequently synthesis of the noradrenaline transporter (which takes on its role) in the dopaminergic cells. In mammals, amphibians and fish the transporters are both synthesized separately in their respective nuclei. The dopaminergic system in lizards consists of dopaminergic nuclei and paths connecting them which are similar to those in other better studied vertebrates (mice and primates), but the functions of dopamine metabolical pathways can differ from species to species. The role of the dopaminergic system on aggressive and sexual behaviour has been investigated in a small number of studies that show the inhibitory role of dopamine synthesis precursor on aggressive behaviour of green anole lizards, and the excitatory role of a D1 receptor agonist on sexual behaviour of lizards in the genus Aspidoscelis (former Cnemidophorus). Available literature on the dopaminergic system of lizards is quite scarce and future studies will definitely give us a better insight of all the functions dopamine has in a lizard. |
