CAMP LEVELS INCREASED BY ACTIVATION OF METABOTROPIC GLUTAMATE RECEPTORS CORRELATE WITH VISUAL PLASTICITY

We have investigated the cAMP level increased by stimulation of metabo tropic glutamate receptors (mGluRs) in cat visual cortex during develo pment. The cAMP level increases activated by the general mGluR agonist (1S,3R)-1-amino-1,3-cyclopentane-dicarboxylic acid (ACPD) were closel y correlated with the critical period for ocular dominance plasticity in both light- and dark-reared animals. Activation of either group I o r group II mGluRs increased the cAMP level. Group II mGluR activation also reduced the forskolin-stimulated cAMP increase. The correlation w as emulated by a mixture of groups I, II, and III mGluR agonists but n ot by agonists applied singly; therefore, the correlation is attributa ble to activation of multiple groups of mGluRs. The cAMP level increas ed by the mixture was greater than the sum of the increases produced b y the agonists applied singly (super-additive effect), suggesting an i nteraction between the G-proteins and/or second messengers controlled by these mGluRs. The basal cAMP level also correlated closely with the critical period until shortly after the peak of the critical period. Therefore, the major factor that contributes to the correlation betwee n the ACPD-stimulated cAMP increase and the peak of the critical perio d is the basal level of cAMP: the activation of multiple mGluRs amplif ies the basal cAMP. We suggest that both basal activity of cAMP produc tion and activation of mGluRs may be important in plasticity in the vi sual cortex.