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:The use of GDNF and GFRa1 to trigger RET downstream pathways is in accordance with other previously published reports [36,48] and also relies on the fact that GDNF is the strongest activator of RET signaling in enteric glial cells upon a number of physiological and pathological events[55].
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