Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…kisspeptin was identified as a ligand for the orphan G-protein coupled receptor 54 (GPR54), which was first described in the rat brain and subsequently in human (then named AXOR12 and hOT7T175) (Lee et al., 1999; Muir et al., 2001; Ohtaki et al., 2001), now termed KISS1R (Gottsch et al., 2009).
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