Ontogeny of dopamine D1 receptors in rat striatum

In recent years direct analysis of dopamine D1 receptors has been made possible by the development of ligands with high affinity and specificity for these receptors. The authors examined the development of dopamine D1 receptors in postnatal rat striatum using standard membrane binding techniques. Rat pups 0 to 35 days of age were decapitated and striata dissected. Membranes were prepared by homogenization and centrifugation. The ligand used was 3H-piflutixol (1.5 nM). Dopamine D2 and serotonin S2 receptors were blocked by 50 nM spiperone. Blanks were generated by 1 μM cis-flupenthixol. Assays were carried out at 370C for 15 min and terminated by vacuum filtration (GF/B). Receptor number increased 9-fold from birth to 26 days of age, when adult levels were reached. Equilibrium was reached within 4 min. half-time of dissociation was approx. 1.5 min. Pharmacologically the receptors were identified as D1 type by the IC50's of numerous compounds: cis-flupenthixol (30nM), SCH 23390 (25 nM), fluphenazine (200 nM), chlorpromazine (300 nM), haloperidol (4 μM). Sulpiride, domperidone, atropine and naloxone had IC50's greater than 10 μM. Initial saturation studies indicate a Km of 0.6 nM with increasing Bmax with increasing age