Plasticity of 5-hydroxytryptamine1B receptors during postnatal development in the rat visual cortex

The distribution of 5-hydroxytryptamine_1A and 5-hydroxytryptamine_1B receptors in the visual cortex was studied by quantitative autoradiography during postnatal development. Overall, receptor densities increased throughout development, but exhibited regional rearrangements, particularly in the case of 5-hydroxytryptamine_1B receptors. Neonatal treatment with 5,7-dihydroxytryptamine, which causes selective degeneration of serotoninergic neurons, had no effect on the density of 5-hydroxytryptamine_1A receptors in the visual cortex. However, a transient increase in 5-hydroxytryptamine_1B at postnatal days 10–12 was observed after this treatment, suggesting a regulation of postsynaptic receptors. Neonatal enucleation resulted in a marked increase in 5-hydroxytryptamine_1B binding sites in all layers of the visual cortex by P16, whereas it had no effect upon 5-hydroxytryptamine_1A binding sites.These results show that both receptor subtypes do not exhibit striking transient features in the visual cortex during postnatal development, but rather undergo discrete reorganizations. 5-Hydroxytryptamine_1B receptors show changes in density after either neonatal degeneration of serotoninergic neurons or enucleation, indicating that the serotoninergic system involving this receptor subtype can exhibit some postnatal plasticity in the visual cortex.