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 beta-adrenergic, GABA, benzodiazepine and acetylcholine receptors. For each population of receptor the number (Bmax) and affinity (Kd) were examined as a function of postnatal age (3 days-adult). For all receptors examined, the Bmax increased during development from low early values to a peak within the critical period. The Kd also changed during development for most receptors. The simultaneous alterations in Bmax and Kd necessitate defining a term which takes both of these receptor properties into consideration. This term, called receptor sensitivity (RS), provides a more comprehensive measure of receptor function than either Bmax or Kd 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.