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:…stimulation. nlp-3p::gfp is expressed in the ADF, NSMR and HSN serotonergic neurons, as well as many sensory neurons, suggesting that peptides encoded by nlp-3 are released as cotransmitters with 5-HT from the serotonergic neurons and glutamate from the sensory neurons (Nathoo et al., 2001).
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