ROLE OF METABOTROPIC GLUTAMATE RECEPTORS IN THE CATS VISUAL-CORTEX DURING DEVELOPMENT

We have studied the effect of metabotropic glutamate receptors on the second messenger cAMP, and how it varies with age in light- and dark-r eared cats; the overall level of the metabotropic glutamate receptors mGluR1, 213, and 5 during development; the laminar distribution of the se receptors; and how the physiological effect of the metabotropic glu tamate receptor agonist ACPD varies with layer. The increase in cAMP p roduced by ACPD correlates well with the critical period for ocular do minance plasticity in both light- and dark-reared animals. Basal level s of cAMP also correlate well, but overall levels of mGluRs do not. Th us, the second messenger is likely to be the critical factor in plasti city, rather than the mGluRs. Both group I mGluRs (1 and 5) and group II mGluRs (2 and 3) contribute to the increase in cAMP. However, mGluR 5 is affected by rearing in the dark, while mGluR1 is not. Moreover, t he laminar distribution of mGluRs 213 and 5 changes with age, while mG luR1 does not. The laminar distribution is correlated with the functio nal effect of ACPD, which varies with layer. In upper layers, ACPD has a depressive effect on both visual response and spontaneous activity, while in lower layers it has a depressive effect on visual response a nd a facilitatory effect on spontaneous activity. These variations in functional effect with layer need to be taken into account before the role of metabotropic glutamate receptors in development will be fully understood.