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:In line with the previously mentioned regulatory role of glutamate on the HPA axis VGluT1 and even more VGluT2 were found in the hypothalamus, suggesting a direct glutamatergic innervation of the PVN (Herman et al. 2004) (Fig.
Category: