Serotonin 1B receptors form a transient vibrissa-related pattern in the primary somatosensory cortex of the developing rat.

Serotonin (5-HT)-immunoreactive axons have a patterned distribution in the primary sensory cortices of developing rodents. This distribution becomes apparent shortly after birth and disappears around the end of the second postnatal week. We employed binding of [125I]cyanopindolol in the presence of isoproterenol to determine whether 5-HT1B receptors have a similar transient spatiotemporal distribution. In rats killed on postnatal day (P-) 8, 5-HT1B receptors have a distribution closely matching that of 5-HT-immunoreactivity. The receptors are very dense in lamina IV of both the primary visual and somatosensory cortices and, like 5-HT immunoreactive axons within the somatosensory cortex, form patches matching the distribution of the mystacial vibrissae. In adult animals, the density of these receptors in lamina IV and the supragranular layers of the visual and somatosensory cortices is reduced relative to that in the surrounding cortex. Autoradiograms of the flattened cortices of adult rats yield a 'negative image' of the pattern observed in perinatal animals. Thus, one subclass of 5-HT receptors, the 5-HT1B receptor, has a spatial distribution in cortex which changes in development much like that for serotoninergic axons.