The development of stereospecific sigma opiate/phencyclidine (PCP)-binding sites in fetal and neonatal rat brain was examined. Displaceable PCP binding was detected from day 13 of gestation. Bmax values increased to adult levels just prior to birth. Apparent KD values did not change. Stereospecific binding became detectable after day 19, concomitant with a rapid increase in Bmax. Despite the early appearance of binding, pharmacologically relevant stereospecific sigma opiate/PCP-binding sites do not become evident until shortly prior to parturition.
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