Neurotensin gene expression and behavioral responses following administration of psychostimulants and antipsychotic drugs in dopamine D(3) receptor deficient mice.

Exposure to psychostimulants and antipsychotics increases neurotensin (NT) gene expression in the striatum and nucleus accumbens. To investigate the contribution of D(3) receptors to these effects we used mice with targeted disruption of the D(3) receptor gene. Basal NT mRNA expression was similar in D(3) receptor mutant mice and wild-type animals. Acute administration of haloperidol increased NT gene expression in the striatum in D(3)+/+, D(3)+/- and D(3)-/- mice. Similarly, acute cocaine and amphetamine induced NT mRNA expression in the nucleus accumbens shell and olfactory tubercle to a comparable extent in D(3) mutants and wild-type mice. Daily injection of cocaine for seven days increased NT mRNA in a restricted population of neurons in the dorsomedial caudal striatum of D(3)+/+ mice, but not in D(3)-/- and D(3)+/- animals. No differences were observed between D(3) receptor mutant mice and wild-type littermates in the locomotor activity and stereotyped behaviors induced by repeated cocaine administration. These findings demonstrate that dopamine D(3) receptors are not necessary for the acute NT mRNA response to drugs of abuse and antipsychotics but appear to play a role in the regulation of NT gene induction in striatal neurons after repeated cocaine. In addition, our results indicate that the acute locomotor response to cocaine and development of psychostimulant-induced behavioral sensitization do not require functional D(3) receptors.

Tissue distribution and cellular localization of the levocabastine-sensitive neurotensin receptor mRNA in adult rat brain.

The aim of this study was to determine the regional and cellular distribution of the neurotensin type 2 receptor (NT-2R) mRNA in the rat brain. Using a radioactive in situ hybridization approach, the distribution of NT-2R transcripts was quantified from autoradiograms, and the cellular localization was examined in liquid emulsions. In rat brain, NT-2R mRNAs, are more widespread than the neurotensin type 1 receptor mRNA. NT-2R transcripts are diffusely distributed throughout the brain, with higher quantities found in the pia mater, the ventricles, the subfornical organ, the subiculum, the substantia nigra, the ventral tegmental area, the superior colliculus, the periaqueductal gray matter, the Purkinje cells and certain hypothalamic and brainstem nuclei. At the cellular level, silver grains appear to be concentrated on glia, neurons and ependymal cells, such as cell bodies of the glia-rich corpus callosum, Purkinje neurons in the cerebellum and ependymal cells lining the ventricles. In contrast, the thalamus and the amygdala contain low amounts of NT-2R mRNA. We discuss the anatomical location of NT-2R mRNA in relation to possible roles for this new receptor subtype.

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 compared with the distribution of the levocabastine-insensitive NT1 receptor. NT2 receptor mRNA was absent at birth from all brain structures except the ependymal cell layer lining the ventricles. The development of NT2 receptor mRNA followed three ontogenetic patterns. The first pattern, involving the majority of the cerebral gray matter, was characterized by a continuous increase from postnatal day 5 (P5) to P30. The second one, involving regions rich in myelinated fibers such as the corpus callosum and lacunosum moleculare layer of the hippocampus, exhibited a pronounced increase between P5 and P10, peaked at P15 and was followed by a plateau or a slight decrease. The third pattern was observed in the ependymal cell layer lining the olfactory and lateral ventricles, where the high labeling already present at birth continued to increase during development. These different developmental patterns could reflect the variety of cells expressing NT2 receptor mRNA, including neurons, protoplasmic astrocytes in gray matter, fibrous astrocytes present in myelinated fibers tracts, and ependymal cells. In contrast, NT1 receptor mRNA, which seems to be associated only with neurons, was highly and transiently expressed during the perinatal period in the cerebral cortex, hippocampus 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 differential localization and ontogenetic profiles of NT1 and NT2 receptor mRNAs suggest different involvement of these two receptors in brain functions and development.

Regulation of the neurotensin NT(1) receptor in the developing rat brain following chronic treatment with the antagonist SR 48692.

The aim of the present study was to investigate the role of neurotensin in the regulation of NT(1) receptors during postnatal development in the rat brain. Characterization of the ontogeny of neurotensin concentration and [(125)I]neurotensin binding to NT(1) receptors in the brain at different embryonic and postnatal stages showed that neurotensin was highly expressed at birth, reaching peak levels at postnatal day 5 (P5) and decreasing thereafter. The transient rise in neurotensin levels preceded the maximal expression of NT(1) receptors, observed at P10, suggesting that neurotensin may influence the developmental profile of NT(1) receptors. Using primary cultures of cerebral cortex neurons from fetal rats, we showed that exposure to the neurotensin agonist JMV 449 (1 nM) decreased (-43%) the amount of NT(1) receptor mRNA measured by reverse transcription-PCR, an effect that was abolished by the nonpeptide NT(1) receptor antagonist SR 48692 (1 microM). However, daily injection of SR 48692 to rat pups from birth for 5, 9, or 15 days did not modify [(125)I]neurotensin binding in brain membrane homogenates. Moreover, postnatal blockade of neurotensin transmission did not alter the density and distribution of NT(1) receptors assessed by quantitative autoradiography nor NT(1) receptor mRNA expression measured by in situ hybridization in the cerebral cortex, caudate-putamen, and midbrain. These results suggest that although NT(1) receptor expression can be regulated in vitro by the agonist at an early developmental stage, neurotensin is not a major factor in the establishment of the ontogenetic pattern of NT receptors in the rat brain.