Postnatal changes in serotonin₁ receptors following prenatal alterations in serotonin levels: further evidence for functional fetal serotonin₁ receptors

Recent work by ourselves and others has indicated that serotonin (5-HT) acts as a regulator of neuronal growth in fetal tissue, probably through an action on the high affinity 5-HT receptors known to be present. In order for our hypothesis to be correct, these receptors must be shown to be functional in fetal tissue. Furthermore, since 5-HT has a dual role in neuronal development, these receptors must be functional both in the region of the serotonergic cell body (brainstem) and in projection areas (forebrain). We have tested the functional status of fetal 5-HT receptors by testing their ability to adapt to changes in the level of 5-HT. Pregnant rats were treated with saline, p-chlorophenylalanine (a 5-HT depletor) or 5-methoxytryptamine (a 5-HT agonist) and the characteristics of the high affinity 5-HT receptors in the rat pups determined using a binding assay with [³H]5-HT. Our results show that both forebrain and brain stem receptors respond to alterations in transmitter level in a manner similar to adult brain. Thus, fetal 5-HT receptors are functional and capable of playing a role in neuronal development.