Quantified distribution of serotonin transporter and receptors during the postnatal development of the rat barrel field cortex.

Serotonin membrane transporter and 5-HT1B and 5-HT2A receptors were visualized and measured by autoradiography in the rat barrel field cortex at postnatal days 4, 8, 12, 16 and in adult (> P60). [3H]citalopram binding, reflecting the presence of 5-HT transporter on thalamocortical fibers, produced a clearcut barrel pattern from P4 to P16 (peak at P8), and decreased to a dispersed, low density in the adult. The patterning and temporal profile of 5-HT1B receptor binding ([125I]cyanopindolol) followed a parallel course. The 5-HT2A receptor binding ([125I]DOI) also conformed transiently to a barrel pattern; it increased in density from P8 to P16 and returned to a level as low as at P4 in the adult. These data suggest that 5-HT exerts a dual role in the developing somatosensory cortex: a local regulation of the peripherally-induced activity of thalamocortical axons via 5-HT1B receptors, and a trophic-like influence mediated by 5-HT2A receptors and possibly involving BDNF.