Characterization and visualization of neurotensin binding to receptor sites in human brain

Regional and Cellular Mapping of Sortilin Immunoreactivity in Adult Human Brain

Sortilin is a member of the vacuolar protein sorting 10 protein (VPS10P) domain receptor family, which carries out signal transduction and protein transport in cells. Sortilin serves as the third, G-protein uncoupled, receptor of neurotensin that can modulate various brain functions. More recent data indicate an involvement of sortilin in mood disorders, dementia and Alzheimer-type neuropathology. However, data regarding the normal pattern of regional and cellular expression of sortilin in the human brain are not available to date. Using postmortem adult human brains free of neuropathology, the current study determined sortilin immunoreactivity (IR) across the entire brain. Sortilin IR was broadly present in the cerebrum and subcortical structures, localizing to neurons in the somatodendritic compartment, but not to glial cells. In the cerebrum, sortilin IR exhibited differential regional and laminar patterns, with pyramidal, multipolar and polymorphic neurons in cortical layers II–VI, hippocampal formation and amygdaloid complex more distinctly labeled relative to GABAergic interneurons. In the striatum and thalamus, numerous small-to-medium sized neurons showed light IR, with a small group of large sized neurons heavily labeled. In the midbrain and brainstem, sortilin IR was distinct in neurons at the relay centers of descending and ascending neuroanatomical pathways. Dopaminergic neurons in the substantia nigra, cholinergic neurons in the basal nuclei of Meynert and noradrenergic neurons in the locus coeruleus co-expressed strong sortilin IR in double immunofluorescence. In comparison, sortilin IR was weak in the olfactory bulb and cerebellar cortex, with the mitral and Purkinje cells barely visualized. A quantitative analysis was carried out in the lateral, basolateral, and basomedial nuclei of the amygdaloid complex, as well as cortical layers II–VI, which established a positive correlation between the somal size and the intensity of sortilin IR among labeled neurons. Together, the present study demonstrates a predominantly neuronal expression of sortilin in the human brain with substantial regional and cell-type variability. The enriched expression of sortilin in pyramidal, dopaminergic, noradrenergic and cholinergic neurons suggests that this protein may be particularly required for signal transduction, protein trafficking and metabolic homeostasis in populations of relatively large-sized projective neurons.

Developmental dynamics of neurotensin binding sites in the human hypothalamus during the first postnatal year

The aim of the present study was to determine a detailed mapping of neurotensin (NT) in the human hypothalamus, during the first postnatal year using an in vitro quantitative autoradiography technique and the selective radioligand monoiodo-Tyr3-NT. Ten human postmortem hypothalami obtained from control neonates and infants (aged from 2 h to 1 year of postnatal age) were used. The biochemical kinetics of the binding in all obtained in this study revealed that the binding affinity constants were of high affinity (in the nanomolar range) and did not differ significantly between all cases investigated. Furthermore, competition experiments show insensitivity to levocabastine and were in favor of the presence of the high affinity site of NT receptor. Autoradiographic distribution showed that NT binding sites were widely distributed throughout the rostrocaudal extent of the hypothalamus. However, the distribution of NT binding sites was not homogenous and regional variations exist. In general, the highest densities were mainly present in the anterior hypothalamic level, particularly in the preoptic area. High NT binding site densities are also present at the mediobasal hypothalamic level, particularly in the paraventricular, parafornical, and dorsomedial nuclei. At the posterior level, low to very low densities could be observed in all the mammillary complex subdivisions, as well as the posterior hypothalamic area. Although this topographical distribution is almost identical during the postnatal period analyzed, age-related variations exist in discrete structures of the hypothalamus. The densities were higher in neonates/less aged infants than older infants in preoptic area (medial and lateral parts). The developmental profile is characterized by a progressive decrease from the neonate period to 1 year of postnatal age with a tendency to reach adult levels. On the other hand, the low levels of NT binding sites observed in posterior hypothalamus did not vary during the first postnatal year. They contrast in that with the very high levels we reported previously in adult. In conclusion, the present study demonstrates the occurrence of high NT binding sites density in various structures in many regions in the human neonate/infant hypothalamus, involved in the control of neuroendocrine and/or neurovegetative functions.

Impact and mechanisms of action of neurotensin on cardiac contractility in the rat left ventricle

Using immunoassay measurements, neurotensin was identified in rat ventricular tissue and in coronary effluent samples. Exogenous neurotensin evoked contractile responses in isolated ventricular preparations, which were equivalent in magnitude to those of norepinephrine and histamine, but greater than those for serotonin and angiotensin II. EC(50) values revealed neurotensin to be as potent as serotonin, but more potent than norepinephrine, histamine and angiotensin II. Structure-activity studies indicated that the contractile effects are attributed to the C-terminal portion of neurotensin. Neurotensin-induced responses were decreased by SR 48692, a specific neurotensin receptor antagonist. Neurotensin elicited an increase in coronary effluent norepinephrine concentrations, and a strong relationship between the magnitude of neurotensin-induced contractile effects and increments in myocardial norepinephrine release were noted. Neurotensin-induced contractile responses were abolished by beta-adrenoceptor antagonists, but not by histamine, serotonin or angiotensin II receptor antagonists. In conclusion, neurotensin increases ventricular contractility through stimulation of myocardial norepinephrine release.

Agonist and antagonist modulation of [35S]-GTP gamma S binding in transfected CHO cells expressing the neurotensin receptor

1. The functional interaction of the cloned rat neurotensin receptor with intracellular G-proteins was investigated by studying the binding of the radiolabelled guanylyl nucleotide analogue [35S]-GTP gamma S induced by neurotensin to membranes prepared from transfected Chinese hamster ovary (CHO) cells. 2. The agonist-induced binding of [35S]-GTP gamma S was only detected in the presence of NaCl in the incubation buffer. However, it was also demonstrated that the binding of [3H]-neurotensin to its receptor was inhibited by NaCl. In the presence of 50 mM NaCl, the binding of the labelled nucleotide was about 2 fold increased by stimulation with saturating concentrations of neurotensin (EC50 value of 2.3 +/- 0.9 nM). 3. The stimulation of [35S]-GTP gamma S binding by neurotensin was mimicked by the stable analogue of neurotensin, JMV-449 (EC50 value of 1.7 +/- 0.4 nM) and the neurotensin related peptide neuromedin N (EC50 value of 21 +/- 6 nM). 4. The NT-induced [35S]-GTP gamma S binding was competitively inhibited by SR48692 (pA2 value of 9.55 +/- 0.28), a non-peptide neurotensin receptor antagonist. SR48692 alone had no effect on the specific binding of [35S]-GTP gamma S. 5. The response to neurotensin was found to be inhibited by the aminosteroid U-73122, a putative inhibitor of phospholipase C-dependent processes, indicating that this drug may act at the G-protein level. 6. Taken together, these results constitute the first characterization of the exchange of guanylyl nucleotides at the G-protein level that is induced by the neuropeptide neurotensin after binding to its receptor.

Neurotensin and neuroendocrine regulation

More than two decades of research indicate that the peptide neurotensin (NT) and its cognate receptors participate to a remarkable extent in the regulation of mammalian neuroendocrine systems, potentially at multiple levels in a given system. NT-synthesizing neurons appear to exert a direct or indirect stimulatory influence on neurosecretory cells that synthesize gonadotropin-releasing hormone, dopamine (DA), somatostatin, and corticotropin-releasing hormone (CRH). In addition, context-specific synthesis of NT occurs in hypothalamic neurosecretory cells located in the arcuate nucleus and parvocellular paraventricular nucleus, including distinct subsets of cells which release DA, CRH, or growth hormone-releasing hormone into the hypophysial portal circulation. At the level of the anterior pituitary, NT stimulates secretion of prolactin and occurs in subsets of gonadotropes and thyrotropes. Moreover, circulating hormones influence NT synthesis in the hypothalamus and anterior pituitary, raising the possibility that NT mediates certain feedback effects of the hormones on neuroendocrine cells. Gonadal steroids alter NT levels in the preoptic area, arcuate nucleus, and anterior pituitary; adrenal steroids alter NT levels in the hypothalamic periventricular nucleus and arcuate nucleus; and thyroid hormones alter NT levels in the hypothalamus and anterior pituitary. Finally, clarification of the specific neuroendocrine roles subserved by NT should be greatly facilitated by the use of newly developed agonists and antagonists of the peptide.

Cellular distribution of neurotensin receptors in rat brain: immunohistochemical study using an antipeptide antibody against the cloned high affinity receptor

Receptors for the neuropeptide, neurotensin, were localized by immunohistochemistry in the rat brain by using an antibody raised against a sequence of the third intracellular loop of the cloned high affinity receptor. Selective receptor immunostaining was observed throughout the brain and brainstem. This immunostaining was totally prevented by preadsorbing the antibody with the immunogenic peptide. The regional distribution of the immunoreactivity conformed for the most part to that of [3H]- or [125I]-neurotensin binding sites previously identified by autoradiography. Thus, the highest levels of immunostaining were observed in the islands of Calleja, diagonal band of Broca, magnocellular preoptic nucleus, pre- and parasubiculum, suprachiasmatic nucleus, anterodorsal nucleus of the thalamus, substantia nigra, ventral tegmental area, pontine nuclei and dorsal motor nucleus of the vagus, all of which had previously been documented to contain high densities of neurotensin binding sites. There were, however, a number of regions reportedly endowed with neurotensin binding sites, including the central amygdaloid nucleus, periaqueductal gray, outer layer of the superior colliculus and dorsal tegmental nucleus, which showed no or divergent patterns of immunostaining, suggesting that they might be expressing a molecularly distinct form of the receptor. At the cellular level, neurotensin receptor immunoreactivity was predominantly associated with perikarya and dendrites in some regions (e.g., in the basal forebrain, ventral midbrain, pons and rostral medulla) and with axons and axon terminals in others (e.g., in the lateral septum, bed nucleus of the stria terminalis, neostriatum, paraventricular nucleus of the thalamus and nucleus of the solitary tract). These data indicate that neurotensin may act both post- and presynaptically in the central nervous system and confirm that some of its effects are exerted on projection neurons. There were also areas, such as the cerebral cortex, nucleus accumbens and para- and periventricular nucleus of the hypothalamus, which contained both immunoreactive perikarya/dendrites and axon terminals, consistent with either a joint association of the receptor with afferent and efferent elements or its presence on interneurons. Taken together, these results also suggest that the neurotensin high affinity receptor protein is associated with a neuronal population that is more extensive than originally surmised from in situ hybridization studies.

Neurotensin receptors in the human amygdaloid complex. Topographical and quantitative autoradiographic study

The distribution of high affinity 125I-neurotensin (NT) binding sites were investigated in the amygdaloid complex of adult humans by means of dry film and emulsion autoradiography. Autoradiograms were analysed quantitatively using [125I] standards and an image analyser system, and data obtained were converted to nCi of ligand bound per mg tissue. High densities of 125I-NT binding sites were found in the following amygdaloid structures the dorsal part of the accessory basal nucleus, the medial part of the cortical nucleus, the lateral subdivision of the central nucleus, the paralaminar nucleus, the amygdalohippocampal transition area and the rostral portions of the anterior amygdaloid area. The ventral part of the accessory basal nucleus, the intercalated cell groups and the remaining parts of the anterior amygdaloid area showed moderate density of NT binding sites, while the medial, basal and lateral amygdaloid nuclei, the lateral part of the cortical nucleus, the medial subdivision of the central nucleus, as well as the corticoamygdaloid transition area exhibited low densities of 125I-NT binding sites. At microscopic level, silver grains appeared more or less evenly distributed over both neuronal perikarya and the surrounding neuropil. In comparison to NT-immunoreactivity, NT receptors showed mismatching distribution throughout most parts of the amygdala, with the exception of the lateral subdivision of the central nucleus, where NT-immunoreactive perikarya and nerve fibers as well as 125I-NT binding sites were found in high density.

Neurotensin receptor interaction with dopaminergic systems in the guinea-pig brain shown by neurotensin receptor antagonists

Neurotensin has been suggested to be involved in neurological and mental disorders associated with altered dopaminergic transmission. The lack of a potent neurotensin receptor antagonist had prevented us from studying the real physiological implication of this peptide in brain function. We thus recently developed such a non-peptide neurotensin receptor antagonist, SR 48692, (2-(1-(7-chloroquinolin-4-yl)-5-(2,6-dimethoxyphenyl)-1H-pyrazole- 3-carbonyl)amino)-adamantane-2-carboxylic acid), which appeared to be potent in various central and peripheral preparations. In the present study, we tested the pharmacological properties of SR 48692 and of two optically synthetic analogs of this compound on neurotensin binding to both adult guinea-pig brain membrane homogenates and coronal brain sections, as well as on neurotensin stimulation of the K(+)-evoked release of [3H]dopamine in guinea-pig striatal slices. Our results demonstrated that (1) high-affinity neurotensin binding sites are present in the guinea-pig brain in regions rich in both dopamine cell bodies and terminals; (2) the binding of neurotensin is inhibited by SR 48692 and its related S(+) active analog, SR 48527, with IC50 values in the nM range and (3) the non-peptide antagonist has no agonist effect but antagonizes neurotensin-induced [3H]dopamine release from guinea-pig striatal nerve terminals.

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

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, suprachiasmatic, 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.

Solubilization and purification of a high affinity neurotensin receptor from newborn human brain

High affinity neurotensin receptors were solubilized in an active form from newborn human brain using the non-denaturing detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid (CHAPS). The solubilized receptor was purified in a single step by affinity chromatography. The binding properties of the purified receptor towards [125I-Tyr3]neurotensin are very similar to those of the membrane bound and of the crude CHAPS-solubilized receptor in terms of affinity and specificity. The purified receptor is a single protein chain of molecular weight 100 kDa as shown by gel filtration and by affinity labelling with [125I-Tyr3]neurotensin in the presence of the cross-linking agent disuccinimidyl suberate.

Investigations about a direct neurotensin-dopamine interaction by nuclear magnetic resonance study, synaptosomal uptake of dopamine, and binding of neurotensin to its receptors

Interactions between dopamine and neurotensin can occur at various levels of the dopaminergic pathways. By using different approaches in vitro, we investigated the proposed hypothesis that neurotensin might bind to dopamine in the synaptic cleft. Nuclear magnetic resonance spectra of neurotensin were not modified by the addition of dopamine, and no nuclear Overhauser effect was detected. Synaptosomal uptake of [3H]dopamine in the presence of neurotensin did not lead to any modifications of the kinetic constants of the uptake. Neurotensin binding was not modified by the addition of dopamine. These results did not confirm the suggestion that neurotensin can form a complex with dopamine.

Ontogenesis and binding properties of high-affinity neurotensin receptors in human brain

The ontogenesis of neurotensin binding sites was studied in human brain of subjects deceased from Sudden Infant Death Syndrome. Monoiodo-Tyr3 neurotensin specifically recognized 2 distinct classes of binding sites in human brain homogenate. The high affinity sites were already present at birth and increased to a maximal level of 240 fmol/mg protein 1 month after birth. Thereafter, the density of these sites decreased to reach a value of 8 fmol/mg protein in 15-month-old brain, a value similar to that found in adult brain. The dissociation constant of the high-affinity sites (about 0.3 nM) did not vary from birth to adulthood. The high-affinity binding sites were sensitive to GTP which decreased their affinity for neurotensin by a factor of 3, indicating that these sites are functional receptors coupled to GTP-binding proteins. By contrast, the low-affinity sites were insensitive to GTP and could be partly blocked by the antihistaminic drug levocabastine. These sites were absent in human brain during the first post-natal year and could be detected only in brain homogenate of 15-month-old infants. The transient increase in high-affinity neurotensin binding sites after birth suggests that neurotensin could act as a regulatory peptide during brain development.

Coactivation of dopamine D1 and D2 receptors increases the affinity of cholecystokinin-8 receptors in membranes from post-mortem human caudate-putamen

The effects of dopamine in vitro were investigated on the binding sites for cholecystokinin-8 (sulphated, CCK-8) and neurotensin in membrane preparations of the caudate-putamen and nucleus accumbens of post-mortem human brains. Dopamine reduced the IC50 value of competition curves with CCK-8 for [125I]CCK-8 binding in membranes from the caudate-putamen, but not the nucleus accumbens, with a maximal decrease of -25 +/- 9% at 300 nM of dopamine. This decrease could be antagonized by 100 nM of SCH 23390 or 100 nM of raclopride. Kinetic analysis of [125I]CCK-8 binding showed a decrease in the first order dissociation rate constant and in the kinetic Kd (-22 +/- 6% and -24 +/- 6%, respectively) at 300 nM of dopamine, without any significant effect on the apparent or actual association rate constant. Competition curves with neurotensin versus [125I]neurotensin were not affected by dopamine (10-1000 nM) in membranes from the caudate-putamen or the nucleus accumbens. These results suggest that dopamine, by synergistic stimulation of both D1 and D2 receptors, selectively increases the affinity of CCK-8 receptors in the human caudate-putamen, by a selective inhibition of ligand dissociation. This increase may reflect a positive feed-back mechanism, further enhancing the modulatory effects of CCK-8 on dopamine neurotransmission.

Purification and characterization of neurotensin receptor from rat brain with special reference to comparison between newborn and adult age rats

Scatchard analysis of saturation curves was performed to compared newborn and adult rat neurotensin receptor using [3H] neurotensin as a tracer. The membrane fraction of newborn rat cerebral cortex has a single population of neurotensin receptor (Kd = 0.13 nM, Bmax = 710 fmol/mg protein), whereas adults have two distinct neurotensin binding sites (high affinity site, Kd1 = 0.13 nM; low affinity site, Kd2 = 20 nM). High affinity neurotensin receptor, solubilized with digitonin, was purified from newborn rat cortex by affinity chromatography. An overall purification of 14,000-fold was achieved. The binding of [3H] neurotensin to the purified receptor is saturable and specific, with a Kd of 0.45 nM. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in the presence of 2-mercaptoethanol revealed purified material of a single major band of Mr = 55,000.

Structure-antinociceptive activity of neurotensin and some novel analogues in the periaqueductal gray region of the brainstem

Neurotensin, an endogenous tridecapeptide, produces a potent, naloxone-insensitive antinociceptive response when it is microinjected into the periaqueductal gray region of the rat brainstem. In the present study, the ED50 for neurotensin in inducing antinociception was 1.5 nmol, two times more potent than morphine. We sought to find whether neurotensin's antinociceptive effects were mediated by the same receptor that mediates its other functions. We found that the structure-activity relationship of neurotensin-induced antinociception was different from that required for the stimulation of intracellular cyclic GMP production in neuroblastoma clone N1E-115 and the binding to N1E-115 cells, human brain tissue, or rat periaqueductal gray. These data suggest there exists a subtype of neurotensin receptors in neural tissue that mediates its antinociceptive actions.

Neurotensin receptor binding levels in basal ganglia are not altered in Huntington's chorea or schizophrenia

Autoradiographic techniques were used to examine the distribution and levels of neurotensin receptor binding sites in the basal ganglia and related regions of the human brain. Monoiodo ([125I]-Tyr3)neurotensin was used as a ligand. High amounts of neurotensin receptor binding sites were found in the substantia nigra pars compacta. Lower but significant quantities of neurotensin receptor binding sites characterized the caudate, putamen, and nucleus accumbens, while very low quantities were seen in both medial and lateral segments of the globus pallidus. In Huntington's chorea, the levels of neurotensin receptor binding sites were found to be comparable to those of control cases. Only slight but not statistically significant decreases in amounts of receptor binding sites were detected in the dorsal part of the head and in the body of caudate nucleus. No alterations in the levels of neurotensin receptor binding sites were observed in the substantia nigra pars compacta and reticulata. These results suggest that a large proportion of neurotensin receptor binding sites in the basal ganglia are located on intrinsic neurons and on extrinsic afferent fibers that do not degenerate in Huntington's disease.

Neurotensin high affinity binding sites and endopeptidase 24.11 are present respectively in the meningothelial and in the fibroblastic components of human meningiomas

The presence of neurotensin receptors and endopeptidase 24.11 (E-24.11) in 16 human meningioma specimens, obtained at surgery, was assessed by measuring the binding of 125I-[tyrosyl3]neurotensin(1-13) (125I-NT) and the inhibitor 3H-N(2RS)-3-hydroxyaminocarbonyl-2-benzyl-1-oxopropyl)glycine (3H-HACBO-Gly), for the receptor and enzyme, respectively. E-24.11 activity was also measured. Autoradiography, on the 16 meningiomas, showed that specific 125I-NT labeling (nonspecific labeling was assessed in the presence of excess NT) was exclusively located in the meningothelial regions. In contrast, specific 3H-HACBO-Gly labeling (nonspecific labeling was assessed in the presence of an excess of the E-24.11 inhibitor thiorphan) was exclusively found in fibroblastic regions. No specific labeling of either ligand was found on collagen or blood vessels. In vitro binding assays were performed on membranes of 10 of the 16 meningiomas. In the 4 meningiomas rich in meningothelial cells, 125I-NT specifically bound to one population of sites with Bmax ranging from 57 to 405 fmol/mg protein and Kd around 0.3 nM. These sites share common properties with the brain NT receptor, since the carboxy terminal acetyl NT(8-13) fragment bound to the same sites but with a higher affinity. The carboxy terminal analogue of NT, neuromedin N, also bound to the same sites with a 10-fold lower affinity and the sites were bradykinin and levocabastine insensitive. In the 4 meningiomas rich in fibroblastic cells, 3H-HACBO-Gly specifically bound to one population of sites with Bmax ranging from 251 to 739 fmol/mg protein and Kd around 2.8 nM.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of 125I-neurotensin binding sites in human forebrain: comparison with the localization of acetylcholinesterase

The distribution of 125I-neurotensin binding sites was compared with that of acetylcholinesterase reactivity in the human basal forebrain by using combined light microscopic radioautography/histochemistry. High 125I-neurotensin binding densities were observed in the bed nucleus of the stria terminalis, islands of Calleja, claustrum, olfactory tubercle, and central nucleus of the amygdala; lower levels were seen in the caudate, putamen, medial septum, diagonal band nucleus, and nucleus basalis of Meynert. Adjacent sections processed for cholinesterase histochemistry demonstrated a regional overlap between the distribution of labeled neurotensin binding sites and that of intense acetylcholinesterase staining in all of the above regions, except in the bed nucleus of the stria terminalis, claustrum, and central amygdaloid nucleus, where dense 125I-neurotensin labeling was detected over areas containing only weak to moderate cholinesterase staining. At higher magnification, 125I-neurotensin-labeled binding sites in the islands of Calleja, supraoptic nucleus of the hypothalamus, medial septum, diagonal band nucleus, and nucleus basalis of Meynert were selectively associated with neuronal perikarya found to be cholinesterase-positive in adjacent sections. Moderate 125I-neurotensin binding was also apparent over the cholinesterase-reactive neuropil of these latter three regions. These data suggest that neurotensin (NT) may directly influence the activity of magnocellular cholinergic neurons in the human basal forebrain, and may be involved in the physiopathology of dementing disorders such as Alzheimer's disease, in which these neurons have been shown to be affected.

Neurotensin reduces the affinity of dopamine D2 receptors in membranes from post mortem human caudate-putamen

The effects of neurotensin in vitro were investigated on the binding characteristics of N-[3H]propylnorapomorphine [( 3H]NPA) binding sites in crude membrane preparations from post mortem human caudate-putamen, obtained within 10 h after death from 3 patients without reported neurological or psychiatric diseases. Neurotensin (0.1-30 nM) was found to increase the KD value of [3H]NPA binding sites with a maximal increase of about 50% (420 +/- 45 pM) at 3 nM of neurotensin, without significantly affecting the Bmax value (123 +/- 20 pmol/g protein). These results indicate the existence of an intramembrane regulation by neurotensin receptors of D2 receptors in the human caudate-putamen.

Transient neurotensin high-affinity binding sites in the human inferior olive during development

High-affinity binding sites for neurotensin 1-13 are found transiently in the human inferior olive during development. An in vitro membrane binding assay demonstrates, in the fetus, a specific binding to a single population of sites (Kd = 561 pM) which are levocabastine-insensitive and possess a Bmax value of 71 fmol/mg protein. No specific binding is present in the adult. Film radioautography shows, in fetuses of 15 weeks, a labelling in the whole inferior olive. At 25 weeks and at 33 weeks, the labelling is concentrated in the ventral lamella of the principal olive and in the caudal accessory olives. At birth and until 1 month of age, the labelling is still detected in the medial part of the ventral lamella of the principal olive. The labelling disappears after 3 months of age, is absent at 4 and 6 months and remains absent in the adults from 55 to 81 years of age. At the light microscopic level, the labelling is located mostly outside olivary neuronal cell bodies suggesting its presence on afferent nerve fibers. This ontogeny and localization of the binding sites in the inferior olive is quite different from that of the neurotensin 1-13 nerve terminals.

Neurotensin receptors in Parkinson's disease and progressive supranuclear palsy: an autoradiographic study in basal ganglia

The technique of receptor autoradiography was used to study the distribution of neurotensin receptors in post mortem brain tissues from patients affected by Parkinson's disease, progressive supranuclear palsy and from age-matched controls. [125I]Neurotensin was used as ligand. Significant receptor decreases were found in the substantia nigra, both pars compacta and reticulata, and in the putamen in Parkinson's disease and progressive supranuclear palsy. In addition, significant decreases of neurotensin receptors were found in the ventral tegmental area, nucleus accumbens and dorsal part of caudate head in patients with Parkinson's disease but not in patients with progressive supranuclear palsy, indicating differential involvement of neurotensin receptors in these two neurological disorders. In addition, both in Parkinson's disease and progressive supranuclear palsy the decrement of striatal neurotensin binding sites was less than expected from the reported decrease of dopamine content in this nucleus, suggesting only partial localization of neurotensin receptors on mesostriatal dopaminergic projections.

Neurotensin elevates cytosolic calcium in small cell lung cancer cells

The ability of neurotensin (NT) to elevate cytosolic Ca2+ in small cell lung cancer (SCLC) cells was investigated using the fluorescent Ca2+ indicator Fura 2-AM. Using SCLC cell line NCI-H345, NT elevated cytosolic Ca2+ levels in a concentration-dependent manner. Using a 10 nM dose, NT and C-terminal fragments such as NT(8-13) but not N-terminal fragments such as NT(1-8) elevated the cytosolic Ca2+ levels. Because EGTA (5 mM) did not affect the NT response, NT may cause release of Ca2+ from intracellular stores. These data indicate that SCLC NT receptors may use Ca2+ as a second messenger.

Characteristics and displaceability of neurotensin binding sites in the rat cerebral cortex and corpus striatum

1. Neurotensin binding to synaptosomes isolated from the rat cerebral cortex and corpus striatum reached saturation after 4 min of incubation. 2. The rates of binding were found to be higher in the corpus striatum than in the cerebral cortex. 3. Concentration study revealed the presence of two different and independent classes of neurotensin binding sites with a negative cooperative interaction within each class of binding sites. 4. At saturation levels, the low affinity binding component was found to have a flat regional difference, while the high affinity binding component showed regional differences in terms of maximal binding capacity, suggesting a higher number of high affinity binding sites in the striatum than in the cortex. 5. In the competition related experiments, dopamine was found to displace around 70% of neurotensin binding sites in the corpus striatum and the cerebral cortex. 5. Substance P displaced around 50% of [3H]neurotensin in the cerebral cortex. Whereas, 50% and 70% displacement were observed in the striatum at high and low affinity binding sites, respectively. 6. These results show the overlap in the binding sites of neurotensin, dopamine and substance P.

Correspondence between high affinity 125I-neurotensin binding sites and dopaminergic neurons in the rat substantia nigra and ventral tegmental area: a combined radioautographic and immunohistochemical light microscopic study

Several lines of anatomical, biochemical, and pharmacological evidence have suggested that specific high affinity neurotensin binding sites are associated with dopamine-containing neurons in the rat ventral tegmentum. In the present study we confirmed and quantified the extent of this association by combining monoiodinated neurotensin radioautography and tyrosine hydroxylase immunohistochemistry on adjacent 5-10 microns-thick midbrain sections. We found that 95-100% tyrosine hydroxylase-immunoreactive neurons detected in all subdivisions of the substantia nigra (pars compacta, pars lateralis, and pars reticulata) exhibited intense 125I-neurotensin labeling in adjacent light microscopic radioautographs. Tyrosine hydroxylase-positive dendrites radiating downward from compacta neurons were also heavily labeled throughout the pars reticulata. In the paranigral subdivision of the ventral tegmental area, silver grains were evenly distributed over neuropil and perikarya and therefore could not be readily attributed to any given tyrosine hydroxylase-positive element. In contrast, within the parabrachial pigmentous subdivision of the ventral tegmental area, 80-90% of the tyrosine hydroxylase-immunoreactive somata and proximal processes were clearly in register with 125I-neurotensin labeled cells. Finally, all tightly packed TH-positive neurons in the interfascicular nucleus showed intense 125I-neurotensin labeling. The vast majority of the neurotensin binding sites observed in the ventral midbrain tegmentum were of the high affinity, physiologically active receptor type since levocabastine, a selective blocker of the low affinity neurotensin binding component, had minimal effect on the binding density in any of the midbrain regions examined. The present results demonstrate an extensive overlap between specific, high affinity neurotensin binding sites and dopamine perikarya and dendrites in the rat ventral tegmentum, and thereby provide a direct anatomical substrate for observed neurotensin-dopamine interactions in the mesocorticolimbic and nigrostriatal projection systems.

Heterogeneity of [3H]neurotensin bindings: studies with dynorphin, L-156,903 and levocabastine

The binding of [3H]neurotensin (NT) to membranes from rat forebrain was complex, exhibiting 'high' affinity (Kd approximately 0.5 nM) and 'low' affinity (Kd approximately 5.0 nM) binding components. Dynorphin A(1-13) (DYN A(1-13] and L-156,903 (N-oxo-3-(10H-phenothiazine-10-yl)propyl-1- arginyl-1-prolyl-1-phenylalanine) potently inhibited [3H]NT binding to brain with shallow biphasic competition curves. Saturation binding studies conducted in the presence or absence of DYN A(1-13) or L-156,903 indicated that these compounds, like levocabastine, exhibited substantial selectivity for 'low' affinity NT site. Structure-activity studies indicated rigid structural requirements for the NT binding activity of DYN A(1-13) and L-156,903. In contrast to the results using brain tissue, DYN A(1-13), L-156,903 and levocabastine were very weak or inactive to inhibit [3H]NT binding to rat uterus. These studies further characterize the heterogeneity of [3H]NT binding in vitro and demonstrate clear tissue differences in binding within a given species.

Extensive co-localization of neurotensin with dopamine in rat meso-cortico-frontal dopaminergic neurons

In mammalian brain, dopaminergic (DA) cell bodies located in the ventral mesencephalon give rise to meso-cortical, meso-limbic and meso-striatal systems. Among these, the meso-cortical DA pathway is particularly involved in the processing of emotional and cognitive responses. We demonstrate that the rat meso-cortical neurons specifically contain, in addition to DA, another transmitter, Neurotensin. If this co-localization exists in man, it may provide an anatomical substratum for the biological theory of schizophrenia as well as an indication that potential anti-psychotic drugs which act differentially on the DA ascending transmissions can be developed.

Characterization of neurotensin binding sites in intact and solubilized bovine brain membranes

Analysis of the equilibrium binding of [3H]-neurotensin(1-13) at 25 degrees C to its receptor sites in bovine cortex membranes indicated a single population of sites with an apparent equilibrium dissociation constant (KD) of 3.3 nM and a density (Bmax) of 350 fmol/mg protein (Hill coefficient nH = 0.97). Kinetic dissociation studies revealed the presence of a second class of sites comprising less than 10% of the total. KD values of 0.3 and 2.0 nM were obtained for the higher and lower affinity classes of sites, respectively, from association-dissociation kinetic studies. The binding of [3H]neurotensin was decreased by cations (monovalent and divalent) and by a nonhydrolysable guanine nucleotide analogue. Competition studies gave a potency ranking of [Gln4]neurotensin greater than neurotensin(8-13) greater than neurotensin(1-13). Smaller neurotensin analogues and neurotensin-like peptides were unable to compete with [3H]neurotensin. Stable binding activity for [3H]neurotensin in detergent solution (Kd = 5.5 nM, Bmax = 250 fmol/mg protein, nH = 1.0) was obtained in 2% digitonin/1 mM Mg2+ extracts of membranes which had been preincubated (25 degrees C, 1 h) with 1 mM Mg2+ prior to solubilization. Association-dissociation kinetic studies then revealed the presence of two classes of sites (KD1 = 0.5 nM, KD2 = 3.6 nM) in a similar proportion to that found in the membranes. The solubilized [3H]-neurotensin activity retained its sensitivity to cations and guanine nucleotide.

[3H]neurotensin(8-13) binds in human brain to the same sites as does [3H]neurotensin but with higher affinity

The binding of [3H]neurotensin(8-13) to membranes from human frontal cortex at 0 degree C was time dependent, specific, saturable, and reversible. Saturation isotherms provided an equilibrium dissociation constant (KD) of 0.52 nM, and the maximal number of binding sites (Bmax) was 3.5 pmol/g original wet weight of tissue. Scatchard analysis yielded a straight line, and the Hill coefficient was equal to 1, a result indicating that [3H]neurotensin(8-13) bound to single, noncoopertive sites. The KD values of several analogs of neurotensin determined in competition with [3H]neurotensin(8-13) were similar to those previously determined in competition with [3H]neurotensin. The regional distribution of binding sites for [3H]neurotensin(8-13) was also similar to that for [3H]neurotensin. These results suggest that [3H]neurotensin(8-13) binds to the same sites as [3H]neurotensin and that [3H]neurotensin(8-13) has a higher affinity than [3H]neurotensin for these sites in human brain.

Two populations of neurotensin binding sites in murine brain: discrimination by the antihistamine levocabastine reveals markedly different radioautographic distribution

Monoiodo-[125I-Tyr3]neurotensin (NT) bound to a high affinity, low capacity binding component and a lower affinity, high capacity component in rat brain synaptic membranes. The antihistamine H1 agent levocabastine, which bears no structural relationship to NT, selectively and totally inhibited NT binding to its low affinity binding sites. The IC50 for levocabastine was 7 nM. Lowering the temperature of the binding assay from 25 to 4 degrees C markedly reduced the affinity of the high affinity NT binding site but did not affect the ability of levocabastine to discriminate between high and low affinity NT binding sites in rat brain membranes and tissue sections. Radioautographic studies of [125I-Tyr3]NT binding to rat brain tissue sections in the absence and presence of levocabastine revealed markedly different regional distributions of the two NT binding components. The levocabastine-sensitive NT binding site was present in membranes from rat and mouse brain but absent from rabbit brain membranes and from human brain tissue sections. It was also absent from mouse neuroblastoma N1E115 and human colonic adenocarcinoma HT29 cell membranes, two cell lines which have previously been shown to possess NT receptors functionally coupled to intracellular second messenger-generating systems. These findings are discussed in the light of the known properties of the high and low affinity NT binding sites in rat brain.

Neurotensin in the human brain

The localization of neurotensin-immunoreactive sites in the adult human brain was investigated by the indirect immunoperoxidase method of Sternberger [Sternberger (1979) Immunocytochemistry. Wiley, New York]. Our results demonstrate a widespread, albeit uneven occurrence of neurotensin-immunoreactive cells and processes throughout the central nervous system. Immunoreactive cells are prominent in the medial hypothalamus and in various regions of the limbic system, including the amygdaloid body, septal area, bed nucleus of the stria terminalis and piriform cortex. A few cells were also found in the dorsal synencephalon, superior colliculus, periaqueductal grey and spinal trigeminal nucleus. The distribution of immunoreactive fibres corresponds well with that reported for rodents. Areas with the highest concentration of neurotensin-immunoreactive processes included all the areas where immunoreactive neurons were found and, in addition, periventricular thalamic nuclei, the sublenticular region, lateral parts of the brainstem reticular formation and the vagus-solitarius complex. Comparison mapping studies of melanin-containing neurons on sections treated with neurotensin antiserum revealed an anatomical relation between almost all the catecholaminergic cell clusters with peptide-containing fibres.

Distribution of neurotensin binding sites in rat brain: a light microscopic radioautographic study using monoiodo [125I]Tyr3-neurotensin

The topographic distribution of specifically labeled neurotensin binding sites was examined by light microscopic radioautography in rat brain sections incubated with monoiodo [125I]Tyr3-neurotensin. Preliminary experiments indicated that under the present experimental conditions [125I]neurotensin specifically binds to a single apparent population of sites with a dissociation constant of 7.7 +/- 0.3 nM, and that fixation of the labeled sections with glutaraldehyde ensures regionally proportional retention of more than 70% of bound [125I]neurotensin molecules. High concentrations of [125I]neurotensin binding sites were detected in the olfactory bulb and tubercle, parts of the neocortex, the lateral septum, the diagonal band of Broca, the caudate putamen, the amygdala, the dentate gyrus, the anterior dorsal nucleus of the thalamus, the suprachiasmatic nucleus of the hypothalamus, the medial habenula, the zona incerta, the substantia nigra and the ventral tegmental area. In certain areas, such as in the diagonal band of Broca, the substantia innominata, the nucleus basalis and the pars compacta of the substantia nigra, discrete accumulations of silver grains were apparent over neuronal perikarya and their proximal dendrites. In most areas, however, the label appeared more or less uniformly distributed over nerve cell bodies and surrounding neuropil. In several instances, the labeling conformed with the distribution of cell bodies of origin and terminal aborizations of specific projection systems, suggesting that neurotensin receptors might be distributed both proximally and distally on the plasma membrane of certain neurons. Such putative "neurotensinoceptive" projection systems might involve part of the mesostriatal, mesocortical and mesolimbic dopamine systems, as well as the raphe-prosencephalic serotonin system and the habenulo-interpeduncular and basal forebrain-cortical cholinergic systems. Finally, areas of dense [125I]neurotensin labeling often corresponded to zones previously shown to exhibit intense acetylcholinesterase staining, suggesting the existence of a possible link between the expression of neurotensin binding sites and that of acetylcholinesterase in certain neuronal populations.

Neurotensin receptors on the rat liver plasma membranes

Neurotensin (NT) is now classified as a brain-gut peptide in the central nervous system and gastrointestinal tract. In the present study, we characterized the NT receptors on the rat liver plasma membranes. The specific binding of [3H]NT was time dependent, reversible, and saturable. Scatchard analysis of the specific binding data yielded two classes of binding sites, a high affinity site and a low affinity site. The average maximum number of binding sites (Bmax) amounted to 13.3 +/- 1.1 fmol/mg protein at high affinity site and 122.3 +/- 21.5 fmol/mg protein at low affinity site, respectively. The dissociation constant (Kd) had values of 0.39 +/- 0.01 nM at high affinity site and 8.1 +/- 1.1 nM at low affinity site, respectively. The amount of specifically bound [3H]NT was significantly reduced in the presence of mono and divalent cations, EDTA, EGTA and a peptidase inhibitor bacitracin, NT1-13 competed with [3H]NT for its binding site with an IC50 of 0.19 nM at high affinity site (0.2 nM concentration of [3H]NT) and 0.7 nM at low affinity site (4.0 nM concentration of [3H]NT). Xenopsin, a NT analogue separated from the skin of Xenopus laevis, was equipotent (IC50 0.75 nM) with NT1-13 at 4.0 nM concentration of [3H]NT. C-terminal sequence of NT contains the structure necessary for interaction with NT binding sites whereas N-terminal sequence had no binding activity. Since NT has a hyperglysemic and a hypercholesterolemic effects in rats, these NT receptors on the rat liver plasma membranes may be involved in the hyperglycemia and/or hypercholesteroremia induced by NT.

Neurotensin receptors in canine intestinal smooth muscle: preparation of plasma membranes and characterization of (Tyr3-125I)-labelled neurotensin binding

To study the binding of (Tyr3-125I)-labelled neurotensin to intestinal muscle, plasma membranes have been purified from dog intestinal circular smooth muscle. Purification was done by differential centrifugation followed by separation on a sucrose gradient. Electron microscopic study revealed that the dissected circular muscles used as the source of membranes were free of myenteric plexus and that the plasma membrane fraction obtained was free of any mitochondria or synaptosomes. The fraction used was obtained at the interface of 14%-33% sucrose density on the gradient and was 25-times enriched in the plasma membrane marker enzyme 5'-nucleotidase activity as compared to post-nuclear supernatant. This fraction contained negligible activity of mitochondrial membrane marker enzyme cytochrome c oxidase and low activity of a putative endoplasmic reticulum marker enzyme NADPH-cytochrome-c reductase. This membrane fraction contained a high density of neurotensin binding sites. This binding was studied by kinetic and by saturation approaches. Analysis of data from saturation binding studies by the computer programs (EBDA and LIGAND) suggested the presence of a two-site model (Kd1 = 0.118 nM, Kd2 = 3.18 nM, Bmax1 = 9.73 fmol/mg and Bmax2 = 129.8 fmol/mg). A part of specifically bound neurotensin was rapidly dissociated. No cooperativity between the two receptor types could be detected. A kinetic analysis of binding gave the Kd value equal to 0.107 nM. Carboxy terminal amino acid residues 8-13 were found to be essential for the binding activity and replacement of Tyr11 by tryptophan reduced the affinity of the peptide by 10 times in displacement studies. Binding was modulated by sodium ions and a guanine nucleotide Gpp[NH]p. MgCl2, CaCl2 and KCl were also found to reduce the specific binding. Evidence was found of a high specific binding to another membrane fraction poor in plasma membranes and rich in synaptosomes. We concluded that plasma membrane of canine intestinal circular muscle contains neurotensin receptors with recognition properties distinct from those obtained in previous studies of neurotensin binding sites in murine tissues. Another neurotensin binding site may be present on neuronal membranes.

Neurotensin receptor binding sites in monkey and human brain: autoradiographic distribution and effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment

Neurotensin (NT) receptor binding sites were characterized and localized by using membrane binding assay and in vitro receptor autoradiography in monkey and human brain. Additionally, the effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment on NT binding sites were investigated in monkey. [125I]Tyr3-NT ([125I]NT) apparently binds to a single class of high-affinity sites (Kd in nanomolar range) in both species. Ligand selectivity patterns strongly suggest that the structural requirements of both monkey and human brain NT receptors are very similar to those previously reported in other tissues, such as those of the rat brain and rat stomach. In monkey brain, [125I]NT binding sites are discretely distributed with high densities of sites found in the cingulate cortex, amygdala, hippocampus, ventral tegmental area, substantia nigra, and periaqueductal gray matter. A similar pattern is observed in the human brain. However, the laminar distribution of [125]NT binding sites in cortex varies between monkey and human brain. In monkey brain, [125I]NT binding sites are mostly concentrated in deep cortical layers while the laminar distribution of NT sites changes with cortical areas in human brain. The densities of [125I]NT binding sites are markedly decreased in the caudate, putamen, and substantia nigra in MPTP-treated monkeys. These results suggest strong interactions between NT and dopaminergic systems in both monkey and human brain tissues.

Functional properties and molecular structure of central and peripheral neurotensin receptors

Membranes prepared from mammalian brain or intestine contain two types of specific binding sites for neurotensin that differ by their affinity and by their sensitivity to sodium ions, GTP, and the antihistamine drug levocabastine. Only the high affinity sites are present in cell cultures and in soluble extracts of CHAPS-treated membranes. These sites represent functional neurotensin receptors coupled to GTP-binding proteins that regulate intracellular levels of cAMP, cGMP and inositol phosphates in neuroblastoma N1E115 cells. The molecular weight of neurotensin receptors in cells and membrane preparations of various origin is about 110,000.

Evidence for a displaceable non-specific [3H]neurotensin binding site in rat brain

Levocabastine is a potent antihistamine drug, structurally unrelated to neurotensin. In rat and mouse brain but not in other animal species, it inhibited 60% of the [3H]neurotensin binding displaced by unlabelled neurotensin or neurotensin(8-13). The levocabastine-sensitive site or "site 1" displayed high affinity properties for levocabastine (IC50 = 25 nM) and was highly sterospecific (IC50-value higher than 10 microM for one of the isomers). Binding to the "site 1" in rat brain corresponded to the [3H]neurotensin binding displaceable by 1 microM levocabastine, whereas binding to the "site 2" corresponded to the binding displaced by 1 microM neurotensin when the "site 1" was occluded by 1 microM levocabastine. Both "site 1" and "site 2" appeared to be saturable. Scatchard plots obtained in rat bulbus olfactorius allowed to calculate a KD-values of 7.1 nM and a Bmax-values of 37.2 fmol/mg original tissue for "site 1", while "site 2" displayed a KD-value of 0.7 nM and a Bmax-value of 16.3 fmol/mg original tissue. The regional distributions of both sites showed marked differences. The "site 1" was homogeneously distributed throughout all rat brain areas, whereas the amount of "site 2" binding was markedly different in separate brain areas: bulbus olfactorius and substantia nigra had the highest amounts (8.9 and 7.8 fmol/mg tissue) while cerebellum had the lowest (0.4 fmol/mg tissue). In spite of its high affinity and stereospecificity, "site 1" has to be considered as an acceptor or recognition site for [3H]neurotensin because of its species-link, low saturability and homogeneous distribution in all rat brain areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopaminergic control of 125I-labeled neurotensin binding site density in corticolimbic structures of the rat brain

In the rat brain, destruction of dopaminergic cell groups by injections of 6-hydroxydopamine into the ventral mesencephalic tegmentum results in large decreases in the number of neurotensin binding sites in the mesencephalon and the striatum. In contrast, these lesions produce an increase in the number of 125I-labeled neurotensin binding sites in the lateral part of the prefrontal cortex despite a large decrease in cortical dopamine levels. Increases in the number of 125I-labeled neurotensin binding sites in this cortical area as well as in the entorhinal cortex, the nucleus accumbens, and the central part of the striatum were also obtained after chronic blockade of dopamine neurotransmission by a long-acting neuroleptic pipotiazine palmitic ester. We propose that dopamine inputs regulate the density of postsynaptic neurotensin binding sites through cortical and subcortical dopamine receptors. Therefore, some of the clinical effects of neuroleptics in schizophrenic patients could be partly related to changes in neurotensin neurotransmission.

Binding of [3H]neurotensin in human brain: properties and distribution

The binding of [3H]neurotensin to membranes from human brain at 0 degrees C was specific, saturable, and reversible. In the frontal cortex, the equilibrium dissociation constant (KD) for [3H]neurotensin determined from the ratio of rate constants (k-1/k1), saturation isotherms, and inhibition binding experiments was 0.80, 2.0, and 2.0 nM, respectively, and the maximum number of binding sites (Bmax) from the saturation isotherms and the competitive binding experiments was 2.4 and 2.2 pmol/g of tissue, respectively. Hill coefficients for binding were equal to 1, indicating the presence of single, noncooperative binding sites. Inhibition of specific binding of [3H]-neurotensin by several analogs of neurotensin showed that [Gln4]neurotensin and neurotensin(8-13) had the highest affinities for these binding sites in human frontal cortex, with each analog being approximately 13-fold more potent than neurotensin. In addition, these data showed that the carboxy-terminal portion of neurotensin played an important part in the binding of this neuropeptide in human brain, a result described for other species. Regional distribution of binding sites was different from that reported for animal brains. Of the 33 different regions investigated, the uncus and substantia nigra showed the highest specific binding of [3H]neurotensin, whereas such areas as the pineal body, medulla, and corpus callosum had few binding sites.

Neurotensin and its analogs--correlation of specific binding with stimulation of cyclic GMP formation in neuroblastoma clone N1E-115

The receptors which mediate neurotensin-stimulated intracellular cyclic GMP formation in murine neuroblastoma clone N1E-115 [J. A. Gilbert and E. Richelson, Eur. J. Pharmac. 99, 245 (1984)] were further characterized. The binding of [3H]neurotensin to intact N1E-115 cells at 0 degree displayed specificity, saturability, reversibility, and tissue linearity. A single class of neurotensin receptors was demonstrated with an apparent KD of 9-11 nM and a Bmax of 180-250 fmoles/10(6) cells, determined by the type of serum employed in the cellular culture medium. A number of neurotensin analogs and fragments were compared for their ability to inhibit [3H]neurotensin binding and stimulate intracellular cyclic GMP formation with intact N1E-115 cells. A direct correlation was found to exist between the KD and EC50 for each peptide. The carboxyl-terminal portion of neurotensin proved to be responsible for the binding and biochemical activities of this peptide with clone N1E-115. Neurotensin(8-13) was, in fact, fifty times more potent than native neurotensin in stimulating intracellular cyclic GMP formation and had an 18-fold higher affinity for the neurotensin receptor on this neuronal cell type.

Characterization and autoradiographic distribution of neurotensin binding sites in the human brain

The characteristics and topographical distribution of monoiodo 125I-Tyr3-neurotensin (NT) binding sites in normal human brain tissue were studied on brain sections and by quantitative autoradiography. Sections at the level of the substantia nigra show a dissociation constant and maximal binding capacity of 4.8 +/- 0.8 nM and 70 +/- 7 fmol/mg protein, respectively. High density of 125I-NT binding sites were mainly found in dopaminergic (DA)-rich areas such as the substantia nigra, the ventral tegmental area, the striatum and the nucleus accumbens, further supporting an interaction between NT and DA neurons in human brain.

Interactions between neuropeptides and dopamine neurons in the ventromedial mesencephalon

Cholecystokinin (CCK), enkephalin, neurotensin (NT), substance P (SP) and substance K (SK) are five neuropeptides that exist in neuronal perikarya or fibers in the vicinity of the A10 dopamine neurons in the ventromedial mesencephalon. Based upon this anatomical proximity, many investigations have been evaluating the possibility that these peptides may influence the function of the A10 dopamine neurons. A variety of experimental techniques have been employed in this regard, including anatomical, electrophysiological, neurochemical and behavioral methodologies. Measurement of immunoreactive peptide levels with radioimmunoassay, and visualization of peptidergic neurons and fibers with immunocytochemistry has demonstrated not only that peptides exist in the vicinity of A10 dopamine neurons, but using double labeling techniques NT and CCK have been found to coexist with dopamine in the same neuron. Further, by combining retrograde tracing technique with immunocytochemistry, the origin of some peptidergic afferents to the ventromedial mesencephalon has been determined. With the exception of CCK-8, microinjection into the ventromedial mesencephalon of rats with all the peptides or potent analogues produces a dose-related increase in spontaneous motor activity. For SP, NT and enkephalin the motor response has been blocked by dopamine antagonists. Further, an increase in dopamine metabolism in mesolimbic dopamine terminal fields is produced concurrent with the behavioral hyperactivity. These data indicate that SP, SK, enkephalin and NT can activate dopamine neurons in the ventromedial mesencephalon. This postulate is supported by electrophysiological studies showing an excitatory action by iontophoretic administration of peptide onto dopamine neurons. However, in some studies, excitatory electrophysiological effects were not observed. While some observations are contradictory, sufficient data has accumulated that tentative postulates and conclusions can be made about how these peptides may influence the A10 dopamine neurons. Further, speculations are offered as to the role this modulatory action may play in the many behaviors and pathologies thought to involve these dopamine neurons.

Covalent labeling of neurotensin receptors in rat gastric fundus plasma membranes

Neurotensin receptors from plasma membranes of rat gastric fundus smooth muscle were specifically and covalently labeled either by using the photoreactive analogue 125I-labeled azidobenzoyl (Trp11)-neurotensin or by cross-linking (monoiodo-Tyr3)neurotensin to the membrane preparation by means of disuccinimidyl suberate. Analysis of plasma membranes by sodium dodecylsulfate-polyacrylamide gel electrophoresis and autoradiography revealed that the same protein band with an apparent molecular weight of 110,000 was specifically labeled by both methods. This band consisted of a single chain protein since its apparent size was found to be the same with or without reduction of membrane samples before electrophoresis. Only neurotensin and its biologically active analogues were able to protect plasma membranes against specific labeling of the protein band of molecular weight 110,000. Comparison of these results with those obtained from rat brain synaptic membranes shows that although rat central and peripheral neurotensin receptors exhibit similar specificities towards a series of neurotensin analogues, their subunit structures are different.

Loss of high affinity neurotensin receptors in substantia nigra from parkinsonian subjects

Monoiodo [125I-Tyr3]-Neurotensin binding was studied in post mortem substantia nigra from 17 control and 15 parkinsonian subjects. Binding to individual homogenates was decreased by 58%, 49% and 26% at 0.36, 1.4, 5.5 M(-9) concentration of ligand, respectively. Saturation analysis using pooled substantia nigra demonstrated an almost complete loss of the high affinity component of the neurotensin receptor complex, yielding a 24% loss of the total binding capacity, with no alteration of the low affinity component. Similarly an important loss of binding was observed in monoiodo[125I-Tyr3]-Neurotensin autoradiograms of two substantia nigra from parkinsonian subjects. These results support the hypothesis of neurotensin receptors occurring on dopamine cell bodies and/or dendrites in human substantia nigra. Role of neurotensin may be of importance in the regulation of dopamine pathway involved in parkinsonism.