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:…κ receptor agonists also increases feeding (Morley & Levine, 1983; Silva et al. 2002) and fasting causes an increase in the expression of pre-prodynorphin mRNA and dynorphin levels in areas of the rat hypothalamus involved in energy homeostasis (Berman et al. 1994, 1997; Herve & Fellmann, 1997).
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