The ontogenetic development of serotonin (5-HT1) receptors in various cortical regions of the rat brain.

The distribution of serotonin (5-HT1) receptors in various cortical regions of the rat brain has been examined during ontogenesis by quantitative autoradiography. An increase in binding site density between the first postnatal day and adult age was observed and could be approximated by a sigmoid shaped (logistic) growth curve. A marked heterochrony in the increase of binding site density is found in the 13 analyzed cortical regions. Binding sites develop earlier in neocortex than in allocortical areas. Fifty percent of the binding site density of adult age is reached in the motor cortex at the 9th postnatal day, followed by the primary somatosensory cortex one day later, by the medial prefrontal cortex on the 12th day, by the fascia dentata on the 14th day and by the CA 1-region on the 20th day. A detailed analysis of the frontal, medial prefrontal and hippocampal regions also shows a heterochrony within these regions. Adult values of binding site densities are also reached at different ages in the various cortical regions. The highest receptor densities were observed in the dorsal subiculum, the lowest in the primary somatosensory cortex.