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:Moreover, there is emerging recognition that putrescine is an alternative precursor source of GABA (53, 67), a major neurotransmitter that has an important reproductive role because of its stimulatory actions on gonadotropin-releasing hormone and luteinizing hormone release in goldfish (46).
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