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:In the present study, we clarified the precise localization of L-PGDS in several cell types of rat brain using postembedding immunoelectron microscopy, and confirmed the results reported in other studies (Urade et al. 1987, 1993; Bl dorn et al. 1996; Yamashima et al. 1997; Beuckmann et al. 2000).
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