Glutamatergic neurons are present in most, if not all, neuronal circuits and play important roles in the normal function of the nervous system. Dysfucntional glutamatergic signaling is implicated in several diseases, including schizophrenia, pain and depression. In order to study the role of glutamatergic signaling in specific neuronal circuits, and how these specific neuronal circuits play a role in behaviour, we analyze mouse behaviour and brain function after specific inactivation of glutamatergic signaling. Our focus is mainly on neuronal circuits that contain both a glutamatergic and a dopaminergic component, and we interested in the interplay between these cell types and how it controls certain functions. For example, both glutamatergic and dopaminergic signaling are strongly implicated in schizophrenia and glutamatergic signaling has recently been implicated as a modulator of the rewarding effects of dopamine. I will describe some of our efforts aimed at understanding the role of glutamatergic signaling in specific neuronal circuits.