Developmental and sensory-dependent changes of group II metabotropic glutamate receptors

Metabotropic glutamate receptors (mGluRs) are potential participants of sensory-dependent modification of neural connections. Here, we examined the involvement of cAMP-linked mGluRs (mGluR2/3) in sensory-dependent plasticity by studying the correlation of mGluR2/3 changes with the critical period of ocular dominance plasticity, a form of sensory-dependent plasticity, and exploring the effects of dark rearing on mGluR2/3 in the primary visual cortex of cats. Immunohistochemistry showed that the laminar distribution of mGluR2/3 changed with the critical period and was sensitive to dark rearing. The mGluR2/3 immunostaining became most intense in layer IV at the beginning of the critical period and was reduced in layer IV but became intense in layers I-III at the peak of the period, then was concentrated primarily in layers I-upper III at the end of the critical period. Dark rearing delayed these pattern changes for weeks and elevated the normally declining mGluR2/3 quantity shortly after the peak of the critical period. The effects of dark rearing and the correlation of early mGluR2/3 laminar changes with geniculocortical afferent segregation indicate that mGluR2/3 circuitry in the visual cortex is influenced by visual inputs. Our data suggest that mGluR2/3 together with another sensory-influenced mGluR, mGluR5, may participate in the sensory-dependent modification of neural connections in the visual cortex.