Sub-population of cultured hippocampal astrocytes expresses neuropeptide Y Y1 receptors

The expression and pharmacological characterization of neuropeptide Y (NPY) receptors of the Y 1 subtype on cultured hippocampal neurons was reported using radioreceptor assays and immunohistochemical approaches (St-Pierre et al., 1998). The present study aimed to establish the presence of NPY Y 1 receptors on cultured hippocampal astrocytes using similar strategies. Immunocytochemical experiments were carried out using three antisera directed against distinct domains (amino acids sequence 185-203, 198-213 and 355-382) of the Y 1 receptor. Double-labeling experiments and confocal microscopy with these Y 1 receptor antisera demonstrated their recognition of the same sub-population (20%) of GFAP-positive astrocytes in culture. The immunostaining seen with all three Y 1 receptor antisera took the form of large irregular clusters distributed throughout cell bodies and processes. Further experiments using radioactive ligands confirmed the presence of NPY receptors on cultured hippocampal astrocytes. Emulsion receptor autoradiography using a newly developed ligand, [ 125 I]GR231118 in the presence of PYY, hPP or BIBP3226 (1 μM), pharmacologically established the Y 1 nature of these receptors. Specific [ 125 I]GR231118 binding was competed by PYY and the selective Y 1 antagonist BIBP3226 but not by hPP (a Y 4 /Y 5 agonist). Similar autoradiographic labeling patterns were obtained using [ 125 I][Leu 31 .Pro 34 ]PYY (a Y 1 /Y 4 /Y 5 agonist) whereas [ 125 I]PYY 3-36 (a Y 2 /Y 5 agonist) failed to generate any specific signal. Hence, rat cultured hippocampal astrocytes express a typical Y 1 receptor without evidence for the presence of Y 2 , Y 4 or Y 5 subtypes. These data suggest a preferential regulation by NPY, acting via the Y 1 receptors, of astrocytic function.