Modification of neurotransmitter receptor sensitivity in cat visual cortex during the critical period

We have examined the characteristics of various receptors in cat visual cortex during postnatal development. These included β-adrenergic, GABA, benzodiazepine and acetylcholine receptors. For each population of receptor the number (B_max) and affinity (K_d) were examined as a function of postnatal age (3 days-adult). For all receptors examined, the B_max increased during development from low early values to a peak within the critical period. The K_d also changed during development for most receptors. The simultaneous alterations in B_max and K_d necessitate defining a term which takes both of these receptor properties into consideration. This term, called receptor sensitivity (R_s), provides a more comprehensive measure of receptor function than either B_max or K_d alone. Using this measure, we find that receptor sensitivity is low near birth for the 4 receptor populations studied, rises to a peak within the first two months of life, and then declines to near-neonatal levels for 3 of the 4 receptor populations.