Development of delta-opioid receptors in rat brain characterised by [3H]-[D-Pen2,D-Pen5] enkephalin binding.

The development of rat brain delta-opioid receptors has been studied in the postnatal period using the highly selective delta-site ligand [3H]-[D-Pen2, D-Pen5] enkephalin (DPDPE) in binding studies. Between day 10 and day 25 there was a three-fold increase in the number of binding sites (expressed per mg protein) and the KD was constant throughout the postnatal period. Specific binding could not be detected earlier than day 10.