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:…each of the three PIcoupled receptors on dopamine cells (mACh, mGluR, 1) is that the outward current induced by transient application of agonist was desensitized during the superfusion of a low concentration of agonist (Fiorillo and Williams, 1998; Paladini et al., 2001; Morikawa et al., 2003).
Category: