Differential expression of mGluR2 in the developing cerebral cortex of the mouse.

Glutamatergic synaptic transmission is an essential component of neural circuits in the central nervous system. Glutamate exerts its effects by binding to various types of glutamate receptors, which are found distributed on neurons throughout the central nervous system. These receptors are broadly classified into two main groups, ionotropic glutamate receptors (iGluRs) and metabotropic glutamate receptors (mGluRs). Unlike iGluRs, the mGluRs are G-protein coupled receptors that exert their effects on postsynaptic membrane conductance indirectly through the downstream modification of ion channels. A subtype of mGluRs, the Group II mGluRs, are particularly interesting since their activation by glutamate results in a hyperpolarizing response. Thus, glutamate can act potentially as an inhibitory neurotransmitter, by binding to postsynaptic Group II mGluRs. Given the potential importance of these receptors in synaptic processing, the development of the central nervous system, and neurological disorders, we sought to characterize the expression of mGluR2 in the developing neocortex of the mouse. Therefore, we examined the distribution of mGluR2 in the developing cerebral cortex. We found a general caudal to rostral gradient in the expression of these receptors, with ventral cortical regions labeled caudally and dorsal regions labeled rostrally. Limbic regions highly expressed mGluR2 throughout the brain, as did sensory and motor cortical areas. Finally, other non-cortical structures, such as the thalamic reticular nucleus, amygdala, and mammillary bodies were found to have significant expression of the receptor. These results suggest that mGluR2 may play important roles in mediating glutamatergic inhibition in these structures and also could have a role in shaping the development of mature neural networks in the forebrain.