LOCALIZATION OF CHOLECYSTOKININ BINDING-SITES IN THE ADULT AND DEVELOPING BRAZILIAN OPOSSUM BRAIN

Cholecystokinin (CCK) is now recognized as one of the most abundant pe ptides in the mammalian central nervous system. We have previously use d immunohistochemistry to localize CCK in the adult and developing Bra zilian opossum brain. However, little is known about the distribution of CCK binding sites in the developing mammalian brain. Therefore, to further our knowledge of the sites of action for CCK during developmen t, we initiated a series of studies to localize CCK binding sites in t he adult and developing Brazilian opossum. This species was chosen bec ause pups are born in a fetus-like state. Receptor autoradiography was performed on coronally sectioned brains of 1 to 60 day postnatal (PN) animals and adults with I-125-Bolton Hunter-CCK-8 as the radioligand. Binding is evident in the 1PN opossum brainstem and is observed in th e developing forebrain by 5PN. Region-specific binding increases durin g development, and binding in the 35PN brain resembles the adult patte rn. Binding is evident prior to the detection of CCK-like immunoreacti vity in many areas. The facial motor nucleus is identifiable and exhib its high levels of binding in Brazilian opossum pups of 10 to 35 days of age. However, binding is undetectable in the facial motor nucleus o f 45 and 60PN pups. In general, the binding patterns for CCK in the ad ult opossum resemble those of other mammals and likely mediate similar physiological functions. However, some cholecystokininergic pathways appear to be unique to neonatal mammals. (C) 1993 Wiley-Liss, Inc.