Localization and characterization of NPY/PYY receptors in rat frontoparietal cortex during development

Neuropeptide Y(NPY) is present in most cerebrocortical areas during fetal a nd postnatal development. In the rat frontal cortex, a dense radial fiber n etwork containing NPY immunoreactivity is observed transiently as early as embryonic day 17 (E17) and disappears at the end of the first postnatal wee k. We have investigated the distribution of NPY receptors in the frontopari etal cortex at 13 stages of development, from E15 fetuses to adults, by in vitro autoradiography, using I-125-pPYY as a radioligand. Quantitative rece ptor density was measured through all cortical layers at each developmental stage. Pharmacological identification of I-125-pPPY binding sites was made by competition experiments using pNPY or [Leu(31), Pro(34)]pNPY and pNPY(1 3-36) as selective competitors for Y1 and Y2 receptors, respectively. NPY r eceptors were first detected in the cerebral cortex at low densities at E19 in a thin layer of tissue corresponding to the inner half of the intermedi ate zone (IZ) and the upper ventricular zone (VZ). The neuroepithelium did not contain binding sites. High densities of sites were observed by E21 onw ard to P10 in the deep cortical layers corresponding to the IZ and layers V -VL A decreasing gradient of receptor density was observed from layer VI to the marginal zone (layer I). The distribution of NPY receptors does not ma tch with the perikarya of transient NPY-immunoreactive neurons located in t he cortical plate but does coincide with their axonal extension. The recept or density decreased abruptly between P10 and P12 in deep layers, whereas a moderate expression of binding sites is detected from P10 to P12 in layers I-III. By P14, the binding level was the lowest observed in the postnatal period. From P21 onward, receptors were observed in superficial layers I-II I, and their density rose by two- to threefold up to adulthood. Competition studies indicated that the NPY receptors located in the deep cortical laye rs of the E21 or P1 rat cortex exhibit Y2 receptor type characteristics. Th e binding sites detected in the superficial layers from P10 to P12 rats als o show Y2 receptors characteristics, unlike the NPY receptors in layers II- III of the adult, which behave like Y1 receptors. These data show that diff erent NPY receptor types are successively expressed in specific layers duri ng late gestation and early postnatal life in the rat frontoparietal cortex . (C) 2002 Wiley-Liss, Inc.