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:Third, PLCb1 is accumulated at the perisynaptic site of excitatory synapses, and thereby exhibits extensive overlap with mGluR1, mGluR5 and M1 receptors (Fukaya et al., 2008).
Category: