Differential ontogenetic patterns of levocabastine-sensitive neurotensin NT2 receptors and of NT1 receptors in the rat brain revealed by in situ hybridization

The postnatal ontogeny of the levocabastine-sensitive neurotensin receptor (NT2) mRNA was studied by in situ hybridization in the rat brain and compar ed with the distribution of the levocabastine-insensitive NT1 receptor. NT2 receptor mRNA was absent at birth from all brain structures except the epe ndymal cell layer lining the ventricles. The development of NT2 receptor mR NA followed three ontogenetic patterns. The first pattern, involving the ma jority of the cerebral gray matter, was characterized by a continuous incre ase from postnatal day 5 (P5) to P30. The second one, involving regions ric h in myelinated fibers such as the corpus callosum and lacunosum moleculare layer of the hippocampus, exhibited a pronounced increase between P5 and P 10, peaked at P15 and was followed by a plateau or a slight decrease. The t hird pattern was observed in the ependymal cell layer lining the olfactory and lateral ventricles, where the high labeling already present at birth co ntinued to increase during development. These different developmental patte rns could reflect the variety of cells expressing NT2 receptor mRNA, includ ing neurons, protoplasmic astrocytes in gray matter, fibrous astrocytes pre sent in myelinated fibers tracts, and ependymal cells. In contrast, NT1 rec eptor mRNA, which seems to be associated only with neurons, was highly and transiently expressed during the perinatal period in the cerebral cortex, h ippocampus and striatal neuroepithelium. Other regions, notably the ventral tegmental area and substantia nigra compacta, exhibited a gradual increase in NT1 receptor signal, reaching adult levels by P21. Both the differentia l localization and ontogenetic profiles of NT1 and NT2 receptor mRNAs sugge st different involvement of these two receptors in brain functions and deve lopment. (C) 1999 Elsevier Science B.V. All rights reserved.