[125I]alpha-bungarotoxin binding marks primary sensory area developing rat neocortex.

The postnatal ontogeny of [125I]alpha-bungarotoxin (alpha-Btx) binding distribution in rat neocortex was described and quantified using autoradiography of in vitro labeled brain sections. During the first two weeks, distinctive transitory radial and laminar patterns emerged. Dense columnar bands of alpha-Btx binding extended through the depth of primary sensory cortex, including somatosensory, visual and auditory areas. An association of alpha-Btx binding with thalamic input zones was further demonstrated within developing somatosensory cortex, where discrete radial bands appeared over the whisker barrels around the time that ingrowing thalamocortical fibers segregate as they selectively innervate the barrels. The early laminar distribution of alpha-Btx binding also resembled that of developing thalamocortical afferents. From P12 to P20, alpha-Btx radial distinctions faded and the laminar pattern changed further to achieve the adult distribution. The spatiotemporal ontogeny of alpha-Btx binding suggests a role for alpha-Btx binding sites in the development of cortical connectivity.