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 antiapoptotic effects of endothelin in olfactory mucosa primary culture
We had previously found that ET-1 could limit serum deprivationinduced apoptosis in OM primary culture, and gap junction uncoupling has been described to be neuroprotective in the central nervous system (Lin et al., 2003).
Category: