Neurotensin receptor expression in the rat forebrain and midbrain: A combined analysis by in situ hybridization and receptor autoradiography

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Abstract
The aim of the present study was to examine the distribution of the levocabastine‐insensitive high‐affinity neurotensin binding sites in the rat forebrain and midbrain in relation to the distribution of the cloned neurotensin receptor mRNA by using a combination of both high‐resolution in vitro receptor autoradiography and in situ hybridization approaches. Groups of cells rich in neurotensin receptor mRNA were observed in the basal forebrain nuclei, the ventral tegmental area, the substantia nigra and in the interfascicular and caudal linear nuclei and the retrorubral field. Cells expressing lower levels of neurotensin receptor mRNA were found in several subdivisions of the cortex; the dentate gyrus; the septofimbrial, suprachias‐matic, medial habenular, and mammillary nuclei; the dorsal part of the lateral septum; the zona incerta; and the dorsomedial and perifornical hypothalamic areas. Most of the brain areas containing neurotensin receptor mRNA demonstrated a selective association of neurotensin binding sites with neuronal cell bodies. In contrast, in several telencephalic and diencephalic structures, the presence of neurotensin binding sites was not correlated with that of neurotensin receptor mRNA, suggesting that neurotensin receptors were mainly located on axon terminals. This study provides a better understanding of the anatomical organization of neurotensin receptor expressing systems in the rat brain and gives further insight into the pre‐vs. postsynaptic location of neurotensin receptors in various brain regions. Moreover, it indicates that all neurons expressing the cloned neurotensin receptor harbour neurotensin binding sites on their perikaryal membrane.