Beta-adrenergic binding sites in fetal rat central nervous system and pineal gland: their relation to other receptor...

Regional development of beta-adrenergic binding sites in the rat fetal central nervous system and pineal gland were studied in relation to the ontogeny of different drug and neurotransmitter binding sites. 3H-dihydroalprenolol labels the olfactory bulb very early in fetal life. A comparatively early development of binding sites is also seen for benzodiazepines during late gestation. 3H-serotonin, 3H-muscimol, 3H-GABA and 3H-(N)-methylscopolamine additionally label the olfactory bulb, revealing quite different patterns. Around gestational day 16, beta-adrenergic sites were found in the neocortex, then in choroid plexus and in the pineal gland. Besides beta-adrenergic, only 3H-flunitrazepam binding sites are detectable in the fetal eye, the latter with a more restricted regional distribution. In the fetal pineal, beta-adrenergic, muscarinic cholinergic and serotonergic binding sites appear at different times in gestation. In the neocortex a variety of binding site patterns develop. Two more general types can be distinguished: appearance along with caudorostral maturation of the brain and appearance within distinct brain regions, possibly related to local differentiation processes. The simultaneous onset of various binding sites in distinct areas of the fetal brain might result in higher sensitivity of individual brain areas to drugs.