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:Consistent with previous reports that acute in vitro exposure of brain slices to kynurenine enhances KYNA synthesis (Turski et al., 1989; Gramsbergen et al., 1997; Scharfman et al., 1999), incubation of rat hippocampal slices with 200 M kynurenine led to a continuous de novo synthesis of endogenous‚Äö√Ñ¬∂
Category: