Norbin Knockout Metabotropic glutamate receptors (mGluRs) are critical neurotransmitter sensors implicated in central neuronal functions like learning and memory and in diseases of the nervous system. Wang et al. (p. 1554 ) searched for proteins that interact with mGluR5a and identified a previously unrecognized component of the receptor signaling complex. The protein Norbin directly interacted with the receptor. Loss of Norbin in mice or cultured cells showed that it is necessary for the accumulation of mGluR5a in the cell membrane, for normal modulation of synaptic plasticity, and for some behavioral responses.