Immunohistochemical study of two phosphoinositide-linked metabotropic glutamate receptors (mGluR1 alpha and mGluR5) in the cat visual cortex before, during, and after the peak of the critical period for eye-specific connections.

The distribution of two phosphoinositide-linked metabotropic glutamate receptors (mGluR1 alpha and mGluR5) was studied immunohistochemically in area 17 before, during and after the peak of use-dependent modification of eye-specific connections. In the adult, mGluR1 alpha immunoreactivity is high in all layers except layer IV, where mGluR5 immunoreactivity is concentrated. This difference in distribution indicates different functions for these two receptor subtypes. The laminar pattern of mGluR1 alpha immunoreactivity is similar in all three ages, but the overall labeling intensity decreases after the peak (6 weeks of age) of the critical period. The laminar pattern of mGluR5 immunoreactivity changes with age. It is expressed in most layers at 2 days of age and is found mainly in layer IV in the adult. This laminar distribution and developmental pattern match the distribution and the development of the geniculocortical terminals. The change in mGluR1 alpha labeling intensity and mGluR5 laminar distribution over time is consistent with both of these mGluRs being involved in sensory-dependent plasticity for eye-specific connections in the visual cortex.