The synthesis of neurotensin

Hungry for relief: Potential for neurotensin to address comorbid obesity and pain

Chronic pain and obesity frequently occur together. An ideal therapy would alleviate pain without weight gain, and most optimally, could promote weight loss. The neuropeptide neurotensin (Nts) has been separately implicated in reducing weight and pain but could it be a common actionable target for both pain and obesity? Here we review the current knowledge of Nts signaling via its receptors in modulating body weight and pain processing. Evaluating the mechanism by which Nts impacts ingestive behavior, body weight, and analgesia has potential to identify common physiologic mechanisms underlying weight and pain comorbidities, and whether Nts may be common actionable targets for both.

Stable Gastric Pentadecapeptide BPC 157 May Recover Brain-Gut Axis and Gut-Brain Axis Function

Conceptually, a wide beneficial effect, both peripherally and centrally, might have been essential for the harmony of brain-gut and gut-brain axes' function. Seen from the original viewpoint of the gut peptides' significance and brain relation, the favorable stable gastric pentadecapeptide BPC 157 evidence in the brain-gut and gut-brain axes' function might have been presented as a particular interconnected network. These were the behavioral findings (interaction with main systems, anxiolytic, anticonvulsive, antidepressant effect, counteracted catalepsy, and positive and negative schizophrenia symptoms models). Muscle healing and function recovery appeared as the therapeutic effects of BPC 157 on the various muscle disabilities of a multitude of causes, both peripheral and central. Heart failure was counteracted (including arrhythmias and thrombosis), and smooth muscle function recovered. These existed as a multimodal muscle axis impact on muscle function and healing as a function of the brain-gut axis and gut-brain axis as whole. Finally, encephalopathies, acting simultaneously in both the periphery and central nervous system, BPC 157 counteracted stomach and liver lesions and various encephalopathies in NSAIDs and insulin rats. BPC 157 therapy by rapidly activated collateral pathways counteracted the vascular and multiorgan failure concomitant to major vessel occlusion and, similar to noxious procedures, reversed initiated multicausal noxious circuit of the occlusion/occlusion-like syndrome. Severe intracranial (superior sagittal sinus) hypertension, portal and caval hypertensions, and aortal hypotension were attenuated/eliminated. Counteracted were the severe lesions in the brain, lungs, liver, kidney, and gastrointestinal tract. In particular, progressing thrombosis, both peripherally and centrally, and heart arrhythmias and infarction that would consistently occur were fully counteracted and/or almost annihilated. To conclude, we suggest further BPC 157 therapy applications.

Neuroprotection by Therapeutic Hypothermia

Hypothermia therapy is an old and important method of neuroprotection. Until now, many neurological diseases such as stroke, traumatic brain injury, intracranial pressure elevation, subarachnoid hemorrhage, spinal cord injury, hepatic encephalopathy, and neonatal peripartum encephalopathy have proven to be suppressed by therapeutic hypothermia. Beneficial effects of therapeutic hypothermia have also been discovered, and progress has been made toward improving the benefits of therapeutic hypothermia further through combination with other neuroprotective treatments and by probing the mechanism of hypothermia neuroprotection. In this review, we compare different hypothermia induction methods and provide a summarized account of the synergistic effect of hypothermia therapy with other neuroprotective treatments, along with an overview of hypothermia neuroprotection mechanisms and cold/hypothermia-induced proteins.

Therapeutic effects of pharmacologically induced hypothermia against traumatic brain injury in mice

Preclinical and clinical studies have shown therapeutic potential of mild-to-moderate hypothermia for treatments of stroke and traumatic brain injury (TBI). Physical cooling in humans, however, is usually slow, cumbersome, and necessitates sedation that prevents early application in clinical settings and causes several side effects. Our recent study showed that pharmacologically induced hypothermia (PIH) using a novel neurotensin receptor 1 (NTR1) agonist, HPI-201 (also known as ABS-201), is efficient and effective in inducing therapeutic hypothermia and protecting the brain from ischemic and hemorrhagic stroke in mice. The present investigation tested another second-generation NTR1 agonist, HPI-363, for its hypothermic and protective effect against TBI. Adult male mice were subjected to controlled cortical impact (CCI) (velocity=3 m/sec, depth=1.0 mm, contact time=150 msec) to the exposed cortex. Intraperitoneal administration of HPI-363 (0.3 mg/kg) reduced body temperature by 3-5°C within 30-60 min without triggering a shivering defensive reaction. An additional two injections sustained the hypothermic effect in conscious mice for up to 6 h. This PIH treatment was initiated 15, 60, or 120 min after the onset of TBI, and significantly reduced the contusion volume measured 3 days after TBI. HPI-363 attenuated caspase-3 activation, Bax expression, and TUNEL-positive cells in the pericontusion region. In blood-brain barrier assessments, HPI-363 ameliorated extravasation of Evans blue dye and immunoglobulin G, attenuated the MMP-9 expression, and decreased the number of microglia cells in the post-TBI brain. HPI-363 decreased the mRNA expression of tumor necrosis factor-α and interleukin-1β (IL-1β), but increased IL-6 and IL-10 levels. Compared with TBI control mice, HPI-363 treatments improved sensorimotor functional recovery after TBI. These findings suggest that the second generation NTR-1 agonists, such as HPI-363, are efficient hypothermic-inducing compounds that have a strong potential in the management of TBI.

A novel stroke therapy of pharmacologically induced hypothermia after focal cerebral ischemia in mice

Compelling evidence from preclinical and clinical studies has shown that mild to moderate hypothermia is neuroprotective against ischemic stroke. Clinical applications of hypothermia therapy, however, have been hindered by current methods of physical cooling, which is generally inefficient and impractical in clinical situations. In this report, we demonstrate the potential of pharmacologically induced hypothermia (PIH) by the novel neurotensin receptor 1 (NTR1) agonist ABS-201 in a focal ischemic model of adult mice. ABS-201 (1.5-2.5 mg/kg, i.p.) reduces body and brain temperature by 2-5°C in 15-30 min in a dose-dependent manner without causing shivering or altering physiological parameters. Infarct volumes at 24 h after stroke are reduced by ∼30-40% when PIH therapy is initiated either immediately after stroke induction or after 30-60 min delay. ABS-201 treatment increases bcl-2 expression, decreases caspase-3 activation, and TUNEL-positive cells in the peri-infarct region, and suppresses autophagic cell death compared to stroke controls. The PIH therapy using ABS-201 improves recovery of sensorimotor function as tested 21 d after stroke. These results suggest that PIH induced by neurotensin analogs represented by ABS-201 are promising candidates for treatment of ischemic stroke and possibly for other ischemic or traumatic injuries.

Cancer, chemistry, and the cell: molecules that interact with the neurotensin receptors

The literature covering neurotensin (NT) and its signalling pathways, receptors, and biological profile is complicated by the fact that the discovery of three NT receptor subtypes has come to light only in recent years. Moreover, a lot of this literature explores NT in the context of the central nervous system and behavioral studies. However, there is now good evidence that the up-regulation of NT is intimately involved in cancer development and progression. This Review aims to summarize the isolation, cloning, localization, and binding properties of the accepted receptor subtypes (NTR1, NTR2, and NTR3) and the molecules known to bind at these receptors. The growing role these targets are playing in cancer research is also discussed. We hope this Review will provide a useful overview and a one-stop resource for new researchers engaged in this field at the chemistry-biology interface.

Brain neurotensin, psychostimulants, and stress--emphasis on neuroanatomical substrates

Neurotensin (NT) is a peptide that is widely distributed throughout the brain. NT is involved in locomotion, reward, stress and pain modulation, and in the pathophysiology of drug addiction and depression. In its first part this review brings together relevant literature about the neuroanatomy of NT and its receptors. The second part focuses on functional-anatomical interactions between NT, the mesotelencephalic dopamine system and structures targeted by dopaminergic projections. Finally, recent data about the actions of NT in processes underlying behavioral sensitization to psychostimulant drugs and the involvement of NT in the regulation of the hypothalamo-pituitary-adrenal gland axis are considered.

Effects of NT on gastrointestinal motility and secretion, and role in intestinal inflammation

It is well established that interactions of neuropeptides with several cell types at various parts of the intestine are critically involved in intestinal pathophysiology. Among them, neurotensin has been identified as an important mediator in the development and progress of several gastrointestinal functions and disease conditions, exerting its effects by interacting with specific receptors that exert direct and indirect effects on nerves, epithelial cells, and cells of the immune and inflammatory systems. This review summarizes our recent understanding on the participation of neurotensin in the physiology and pathophysiology of the small and large intestine, and discusses various mechanisms that could be involved in these actions.

Neurotensin-induced Cl(-) current in guinea-pig dorsal root ganglion cells

In guinea-pig dorsal root ganglion cells held under voltage-clamp at -80 mV, neurotensin elicited an inward current (I(NT)) whose amplitude increased with increasing neurotensin concentration (40-4000 nM). The effect was blocked by a nonpeptide neurotensin antagonist. I(NT) occurred in the absence of the extracellular Na(+), but not in the absence of the intracellular Cl(-), and it was outward directed by reversing the driving force for Cl(-). I(NT), like the gamma-amino-butyric acid (GABA)-induced Cl(-) current (I(GABA)), remained little changed after virtual elimination of cytosolic free-ionized Ca(2+) or after treatment with a Ca(2+)-activated Cl(-) channel blocker, but, in contrast to I(GABA) it was resistant to the I(GABA) blocker picrotoxin, slower in time course and more easily desensitized when repeatedly elicited. I(NT) and I(GABA) were additive to each other. AG-protein inhibitor markedly reduced I(NT), and a G-protein activator produced an inward current during which no current could be elicited by neurotensin. These results show that neurotensin exerts an effect to activate Ca(2+)-insensitive Cl(-) channels distinct from those activated by GABA in guinea-pig dorsal root ganglion cells, and the effect may arise through a G-protein-dependent mechanism.

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.

Peripheral axotomy induces increased expression of neurotensin in large neurons in rat lumbar dorsal root ganglia

In normal rat lumbar 4 and 5 dorsal root ganglia (DRGs) a few large neurons expressed neurotensin-like immunoreactivity (LI). Twenty hours after crushing the lumbar 4 and 5 dorsal roots or the sciatic nerve, accumulations of neurotensin-LI were seen in many nerve fibers on the ganglionic side of both crushes, indicating a significant centrifugal transport of neurotensin under normal circumstances. A distinct increase in expression of neurotensin (peptide and mRNA) was observed in many large neuron profiles in the ipsilateral lumbar 4 and 5 DRGs two days after unilateral sciatic nerve transection. Two weeks after axotomy the number of neurotensin-positive neuron profiles was reduced and had almost reached normal levels. In the superficial dorsal horn of the lesion side the number of neurotensin immunoreactive fibers in laminae I-II was markedly reduced 7 days after peripheral axotomy. There was no detectable increase in neurotensin-L1 in laminae III-IV of spinal dorsal horn, in the dorsal column nuclei or in the peripheral neuroma (2-28 days after axotomy), suggesting that the amounts of neurotensin transported centrifugally from DRG neurons after axotomy are low. Neurotensin-LI only sometimes colocalized with neuropeptide Y-LI, another peptide known to be upregulated in large DRG neurons. These two peptides may therefore partly be localized in different populations of large DRG neurons. The present results show that, in contrast to the nerve injury-induced general downregulation of neurotensin systems in the superficial dorsal horn and of neurotensin receptor mRNA expression in DRGs as shown in previous studies, axotomy causes upregulation of expression of neurotensin peptide in some large DRG neurons.

Functional activity of new C-terminal cyclic-neurotensin fragment analogs

Neurotensin (NT, pGlu-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu) is a tridecapeptide that displays a wide spectrum of biological actions. Cyclic derivatives of a hexapeptide NT [(8-13)] (N alpha MeArg-Lys-Pro-Trp-Tle-Leu, Tle = tert-leucine) were designed and prepared by a combination of solution and solid-phase peptide synthetic methodologies. As reported previously, several analogs possessed nanomolar binding affinities for NT receptors in newborn (10-day-old) mouse brain membrane preparations. In this study, we determined the functional ability of these analogs to mobilize intracellular free calcium, [Ca2+]i, in HT-29 cells (human colonic adenocarcinoma). Of greatest interest were the cyclic compounds 2, 6 and 9 that had Ki values of 0.19, 3.50 and 4.18 microM for [3H]NT labeled receptors in the HT-29 cell membrane assay, respectively. In the functional assay, compounds 2 and 6 mobilized [Ca2+] with EC50 values of 0.13 and 20 microM, respectively. In comparison, Compound 9 blocked the NT-induced mobilization of [Ca2+]i, with an IC50 of 1.70 microM. The present findings indicate that small molecule cyclic analogs, that possess functional activity, can be designed and may have therapeutic utility in the treatment of schizophrenia and possibly other neurological disorders.

Neuroactive peptides: unique phases in research on mammalian brain over three decades

Because of the enormous growth over the last three decades of research on the role of peptides in the brain, the need became apparent to determine the status of these compounds in terms of their current research interest. Since 1965, over a quarter of a million research papers have been published on peptides that have since been classified as neuroactive. The present study was undertaken to analyze systematically the yearly trends of research emphasis in neuroactive peptides as reflected by their individual frequency of publication by year, beginning in 1966. A computer analysis of the publication characteristics was carried out using the Medline data base in which the citation search was limited to the topic brain crossed with the topic mammal. One criterion for the inclusion of a given peptide in the analysis was a frequency of 25 or more citations following its discovery, as related to the mammalian brain. The 42 peptides that met this criterion were: adrenocorticotropic hormone, angiotensin II, atrial natriuretic factor, bombesin, bradykinin, calcitonin, calcitonin gene-related peptide, carnosine, beta-casomorphin, cholecystokinin, corticotropin-releasing factor, delta sleep-inducing peptide, dynorphin, beta-endorphin, Leu-enkephalin, Met-enkephalin, galanin, gastrin, glucagon, growth hormone, growth hormone-releasing factor, insulin, kyotorphin, beta-lipotropin, luteinizing hormone-releasing factor, melanocyte-stimulating hormone release inhibitory factor-1, alpha-melanocyte-stimulating hormone, motilin, neurokinin A, neurokinin B, neuropeptide Y, neurotensin, oxytocin, pituitary adenylate cyclase activating polypeptide, peptide HI, prolactin, secretin, somatostatin, substance P, thyroid-releasing hormone, vasopressin, and vasoactive intestinal peptide. An overall analysis of the 298,105 papers published on these 42 peptides since 1965 revealed that the research activity of 24,742, or 8.30%, of the studies, focused on their neuroactive properties. Taken as a whole, the research on neuroactive peptides reached a peak in 1986, as reflected by the total of 1793 papers published during that year. Although the level of publication has fluctuated between 1548 and 1774 research papers over the last 6 years, it is now clear that the trend in research on neuroactive peptides has reached an asymptote today that shows no sign of deviation. A temporal analysis year by year of individual publication profiles revealed three distinct trends: 1) peptides showed a slow development in research interest and did not exceed more than 15-30 publications per year; 2) peptides exhibited a steady increase in research activity over the years that continues today; and 3) peptides displayed an initial, often intense, research emphasis that inexplicably declined, in some cases precipitously, in the mid 1980s.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibitory effect of neurotensin on proline

The effect of neurotensin (NT) on proline absorption across rat jejunum was investigated using the single-pass perfusion technique. This study showed that intravenous administration of NT produced a dose-dependent inhibition of proline absorption. Thus, NT at a 0.16 pmol/kg/min concentration gave 10% decrease in proline absorption while 0.32 and 1.6 pmol/kg/min concentration gave 31% and 45% decrease, respectively. In the absence of Na, proline absorption decreased to 77% from control values. No change in proline absorption was noticed when NT at a concentration of 0.32 pmol/kg/min was intravenously injected in the absence of sodium from the perfusion solution. Water absorption did not show significant changes (P > 0.05) in presence or absence of NT. Moreover, NT did not produce a significant change (P > 0.2) in intracellular proline accumulation. NT inhibited proline absorption through an indirect mechanism that is Na-dependent and independent of changes in water absorption.

Subsets of neurotensin-immunoreactive neurons revealed following antagonism of the dopamine-mediated suppression of neurotensin immunoreactivity in the rat striatum

The distribution of neurotensin-immunoreactive structures in the rat striatum was evaluated after blockade of dopamine neurotransmission by drugs that act presynaptically (6-hydroxydopamine, reserpine) and postsynaptically, preferentially at the D2 (eticlopride, haloperidol) and D1 [(R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepi n-7-ol, SCH-23390] receptor sites. Calbindin-D (mol. wt 28,000) immunoreactivity was used to delineate patch (striosome) and matrix in the caudate-putamen and core and shell in the nucleus accumbens. Antagonism at the D2 dopamine receptor and 6-hydroxydopamine lesions caused dense axonal immunoreactivity and moderate numbers of neurotensin-immunoreactive neurons to be distributed preferentially in the matrix of the caudate-putamen. D1 receptor antagonism was significantly less effective at eliciting neurotensin-immunoreactive neurons in the caudate-putamen. Reserpine or co-administration of the D1 and D2 receptor antagonists produced many neurotensin-immunoreactive neurons in both striatal compartments throughout the caudate-putamen and dense axonal neurotensin immunoreactivity in the medial patch compartment. To varying degrees, with SCH-23390 being least effective and reserpine most effective, all of the drug treatments elicited neurotensin immunoreactivity in neurons in the olfactory tubercle, rostral nucleus accumbens, accumbal shell and ventrolateral caudate-putamen, i.e. most of the ventral striatum.

Postnatal development of striatal neurotensin immunoreactivity in relation to clusters of substance P immunoreactive neurons and the "dopamine islands" in the rat

Conventional immunoperoxidase preparations of the coronally sectioned brains of rats killed at various times during the early postnatal period revealed the distributions of tyrosine hydroxylase, substance P, and neurotensin immunoreactivities. At birth, patches of dense tyrosine hydroxylase immunoreactivity were present across the breadth of the rostral striatum, whereas patches displaying substance P immunoreactivity were present only in its lateral half, appearing in its medial half by about postnatal day 3. Neuronal neurotensin immunoreactivity was absent in the rostral striatum at birth, although some neurotensin immunoreactive cells were present in the tail of the caudate-putamen. Rostrally, neurotensin immunoreactive cells appeared first along the lateral margin of the caudate-putamen on postnatal day 3, became numerous there about day 5, spread medially into the striatum by day 7, and achieved their medialmost distribution by about day 10. Their numbers and those of substance P immunoreactive neurons diminished thereafter. Substance P immunoreactive patches, which contained numerous labeled neurons and "puncta," shared coextensive distributions with patches of dense tyrosine hydroxylase immunoreactivity, but interdigitated with neurotensin immunoreactive cell clusters. The neurotensin immunoreactive cell clusters lacked puncta, the light microscopic representation of axon terminals, or swellings. It is concluded that the patchy infrastructure of the striatum, which is established prior to birth, is substrate for the progression of separate "waves" of elevated neuronal peptide content, one reflecting substance P and a later one reflecting neurotensin. These proceed along rostromedialward trajectories to involve interdigitating neuronal domains.

Synaptic organization of neurotensin immunoreactive amacrine cells in the chicken retina

Immunohistochemistry was utilized to investigate the light and electron microscopic localization of neurotensinlike immunoreactive (NT) amacrine cells in the chicken retina. The NT cells possess oval cell bodies (7 microns in diameter) that are located in either the second or third tier of cells from the border of the inner nuclear and inner plexiform layers. The processes of such cells extend into the inner plexiform layer where they ramify as a narrow plexus in sublamina 1 and as a broad plexus in sublaminas 3 and 4. Additionally, stained processes are observed occasionally within sublamina 5. At the ultrastructural level, NT-positive somas exhibit a rather dense and evenly distributed peroxidase reaction product throughout their cytoplasm. The nucleus of NT amacrine cells possess a round, unindented nuclear membrane. NT-immunoreactive processes in the inner plexiform layer interact synaptically only with non-NT cells. NT processes receive synaptic input mainly from the processes of amacrine cells and to a lesser degree from bipolar cells. The large majority of NT-stained varicosities form presynaptic contacts onto the processes of amacrine cells, but are also presynaptic to bipolar cell axon terminals. Moreover, each of the above synaptic relationships can be identified in each of sublaminas 1 and 3 to 4 of the inner plexiform layer. In addition, NT processes are presynaptic to processes devoid of synaptic vesicles that may originate from ganglion cells. Finally, NT processes occasionally form synaptic contacts onto somas situated in the most proximal row of the inner nuclear layer.

Retrograde axonal transport of neurotensin in the dopaminergic nigrostriatal pathway in the rat

Although the existence of receptor transport has been clearly demonstrated in peripheral nerves, there is no clear cut evidence in the brain of such a process for neuropeptide receptors. Because of the localization of neurotensin receptors on dopaminergic terminals, the dopaminergic nigrostriatal pathway appears to be the system of choice for studying the axonal transport of neuropeptide receptors in the brain. When labelled neurotensin was injected into the rat striatum, a delayed accumulation of radioactivity in the ipsilateral substantia nigra was observed about 2 h after injection. An essential requirement to clearly observe this phenomenon was the pretreatment of animals with kelatorphan in order to prevent the labelled neurotensin degradation. The appearance of this labelling was prevented by injection of an excess of unlabelled neurotensin or of neurotensin 8-13, an active neurotensin fragment, but not by neurotensin 1-8, which had no affinity for neurotensin receptors. This process was saturable, microtubule-dependent and occurred only in mesostriatal and nigrostriatal dopaminergic neurons as identified after 6-hydroxydopamine lesion and by autoradiography. These results demonstrate that neurotensin was retrogradely transported by a process involving neurotensin receptors. The retrograde transport of receptor-bound neuropeptide may represent an important dynamic process which conveys information molecules from the synapse towards the cell body.

Heterologous desensitization of bradykinin-induced phosphatidylinositol response and Ca2+ mobilization by neurotensin in NG108-15 cells

The heterologous desensitization of the bradykinin (BK)-induced increase in intracellular Ca2+ concentration ([Ca2+]i) by neurotensin was studied in neuroblastoma x glioma hybrid NG108-15 cells. The addition of neurotensin to the cells resulted in an increase in [Ca2+]i and an increase in the formation of inositol phosphates in Ca2+-free medium. Pretreatment of the cells with neurotensin resulted in 43% decrease in the BK-induced increase of [Ca2+]i. The increase in [Ca2+]i induced by ionomycin, which causes Ca2+ release from the intracellular pool, was not decreased by pretreatment with neurotensin. This indicates that the inhibitory effect of neurotensin on the BK-induced increase of [Ca2+]i was not due to depletion of the intracellular Ca2+ pool. Pretreatment with neurotensin also caused a 47% decrease in the BK-induced formation of inositol trisphosphates (IP3). This decrease was not due to depletion of phosphatidylinositol bisphosphates. Neurotensin did not inhibit [3H]BK binding to cell membranes. These results show that neurotensin desensitizes the BK responses of NG108-15 cells, heterologously, perhaps by changes in phospholipase C and/or guanine nucleotide-binding protein (G-protein).

Effects of ICV administration of neurotensin and analogs on EEG in rats

The electroencephalographic (EEG) effects of the ICV administration of neurotensin (NT 1-13), NT 1-8 (an inactive neurotensin fragment) and D TYR-11 NT (a long-lasting analog of neurotensin) were studied in rats. In awake rats, NT 1-13 (30 micrograms) and D TYR-11 NT (10 micrograms) induced an increase of the power spectrum in the theta range activity (4-7 Hz). In rats recorded during the sleep-wakefulness cycles, NT 1-13 (10 and 30 micrograms) and D TYR-11 NT (10 micrograms) had an awakening effect and also induced an increase of latency to the first episode of the different sleep stages (intermediate stage and slow wave sleep). NT 1-8 (30 and 90 micrograms in awake rats, 10 and 90 micrograms for sleep-wakefulness cycles) was inactive in all these experiments. Thus, it seems that all these effects can be linked to neurotensin receptors; indeed only fragments which recognize receptors possess an EEG activity.

Numbers of neurotensin-immunoreactive neurons selectively increased in rat ventral striatum following acute haloperidol administration

The effect of haloperidol (HAL) on neurotensin (NT) levels in various structures of the rat brain was evaluated using an immunoperoxidase method. Adult, male Sprague-Dawley rats were given intraperitoneal injections of either HAL (2 mg/kg) or vehicle at twenty-four and four hours prior to sacrifice. The brains were fixed, cut at 50 micron on the vibratome, and prepared to demonstrate NT immunoreactivity, or its absence following appropriate control incubations. The distributions of NT-immunoreactive (IR) cell bodies were plotted using the camera lucida, and the numbers of NT-IR neurons in various structures were recorded. The numbers of NT-IR perikarya in striatal and ventral striatal structures of HAL-treated rats greatly exceeded those observed in the same structures of control animals. In other NT-IR rich regions including the bed nucleus of the stria terminalis, central amygdala, hypothalamus and septum, HAL and control values did not differ. Conversely, HAL treatment appeared to effect a decrease in the number of immunoreactive perikarya in the medial amygdala and caudal part of the endopiriform area. It was noted that in brain regions where D-2 receptors are reported to be numerous, the number of NT-stained cells increased following HAL treatment, whereas in regions where D-1 receptors predominate, the number remained stable or decreased. Subjective evaluation of axon terminal immunoreactivity revealed a change only in the globus pallidus, where the proportional area of that structure exhibiting NT-immunoreactivity expanded following HAL.

Projection of neurotensin-like immunoreactive neurons from the lateral parabrachial area to the central amygdaloid nucleus of the rat with reference to the coexistence with calcitonin gene-related peptide

The origin of neurotensin-like immunoreactive (NTI) fibers in the central amygdaloid nucleus (AC) in the rat was examined using indirect immunofluorescence and retrograde tracing combined with immunocytochemistry. Destruction of the external subdivision of the lateral parabrachial nucleus, which contains a group of NTI neurons, resulted in a marked reduction of these fibers in the ipsilateral AC, which suggests that most of these fibers are of extrinsic origin. This was also supported by the finding that injection of fast blue dye into the AC labeled many neurons in the external subdivision of the lateral parabrachial nucleus ipsilaterally, and that simultaneous treatment with antiserum against NT stained some of these neurons. Subsequent immunohistochemical staining of alternate sections revealed that many of these NTI neurons were also labeled by calcitonin gene-related peptide antiserum.

Precursor forms of neurotensin (NT) in cat: processing with pepsin yields NT-(3-13) and NT-(4-13)

Basic proteins present in 0.1 N HCl extracts of feline CNS and intestine were found to liberate immunoreactive neurotensin (iNT) when treated with hog pepsin. These protein substrates were separated using Sephadex G-25, Sephadex G-75 and reverse-phase HPLC. In a calibrated SDS-polyacrylamide gel electrophoresis system, the major substrate from cat ileum exhibited a molecular weight of ca 16 kDa and minor substrates were observed at 30, 40 and 65 kDa. As shown previously for synthetic NT, pepsin-treatment of feline ileal NT converted it into the fully immunoreactive NT-(4-13) fragment (yield, 95%). When treated with pepsin, the partially purified ileal substrates gave rise to 4 immunoreactive peptides, one of which (ca 15% of total) eluted with the same retention time as NT-(4-13) while the major peptide formed (ca 40% of total) eluted near to the position of NT-(3-13). Both these products reacted equally well with two different antisera towards the C-terminal 5- and 8-residues of NT and were not recognized by an N-terminal antiserum. Experiments using various proteases demonstrated that the NT-related sequence(s) were located internally in each substrate and suggested that they were bounded by double basic residues. Substrate activity in isotonic homogenates of feline spinal cord, brain, adrenal and ileum cosedimented with iNT during equilibrium centrifugation, apparently in association with vesicle and/or synaptosomal particles. These findings indicate that basic proteins, colocalized with NT in vesicle-like particles of CNS, adrenals and ileum, could serve as precursors to this peptide, being liberated by pepsin-related enzyme(s).

Neurotensin immunoreactive neurons in the human infant diencephalon

Neurotensin-like immunoreactive (NT-IR) neurons are present in discrete subregions of the anterior, medial and lateral thalamic nuclear groups of the human infant brain. The pulvinar is notably rich in such cells. Smaller numbers of cells are present in the ventral group, centromedian nucleus, reticular nuclei and intralaminar nuclei. Neurotensin immunoreactive axons accumulate dorsally in the thalamus and cross the deep white matter. The cerebral cortex contains a rich network of NT-IR axons. The subthalamic nucleus is rich in NT-IR neurons. Within the hypothalamus NT-IR perikarya are present in parts of the lateral and tuberal regions and in the lateral mammillary area. NT-IR axons are widespread being particularly prominent in parts of the tuberal region and the mammillary body.

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-like immunoreactivity in the pituitary and hypothalamus of bony fishes

Using an antiserum raised against synthetic neurotensin (NT), the distribution of immunoreactivity in the pituitary and hypothalamus has been examined by immunocytochemistry at light and electron microscope level in a number of species of bony fishes. In most species immunoreactive perikarya were found in the preoptic region of the hypothalamus, with fibres throughout the tuberal hypothalamus and neurohypophysis (neural lobe and median eminence). In the neurohypophysis of teleosts NT-like immunoreactivity was seen in a dense band of fibres bordering the ACTH cells of the rostral pars distalis: absorption controls showed that this was due to the presence of an NT(8-13)-like or xenopsin-like sequence, which, according to electron microscopic observations, was contained in small dense cored vesicles. The antiserum also stained the pituitary ACTH cells of some species, apparently due to cross-reaction with the 17-19 sequence of ACTH. These results suggest that an NT-like peptide may have a role in control of the adenohypophysis in fishes.

Neurotensin immunoreactive structures in the human infant striatum, septum, amygdala and cerebral cortex

Neurotensin immunoreactive (NT-IR) neuronal perikarya are present in small numbers in the bed nucleus of the stria terminalis, lateral olfactory stria, substantia innominata, caudate nucleus and putamen of the human infant forebrain. Larger numbers of perikarya are present in the amygdala and related structures. NT-IR axons are present in the medial septal area, bed nucleus of the stria terminalis, caudate nucleus, putamen and amygdala. The cerebral cortex contains a rich network of NT axons with an accentuation in layer II. This network appears to be derived from bundles of axons which traverse the deep white matter from the thalamus.

Neurotensinlike immunoreactive neurons in the hedgehog (Erinaceus europaeus) and the sheep (Ovis aries) central nervous system

Neurotensin-containing neurons in the hedgehog and sheep central nervous system were studied immunohistochemically. In both species, mapping of neurotensin neurons was achieved only after pretreatment with colchicine injected intracerebroventricularly 2 days prior to perfusion. Bipolar or multipolar neurotensin neurons, 10-30 micron in diameter, were observed in the following regions of the central nervous system of both species: medial amygdaloid nucleus, lateral septal nucleus, interstitial nucleus of the stria terminals, caudate nucleus, preoptic area, and hypothalamus. On the contrary, while immunoreactive neurons were found in the central amygdaloid nucleus, nucleus accumbens, nucleus of the diagonal band, subthalamus, superior central nucleus, dorsal raphe nucleus, central gray substance of the pons, and dorsal horn of the spinal cord of the hedgehog, respective regions of the sheep appeared to be devoid of immunoreactive perikarya. Also, in some regions, namely the hippocampal formation, the central gray substance of the midbrain, the locus coeruleus, and the nucleus of the solitary tract, neurotensin neurons were found exclusively in the latter species. The existence of these differences in the distribution pattern of neurotensin-immunoreactive neurons between the two species as well as between them and others already examined is briefly discussed.

Light and electron microscopic immunocytochemistry of neurotensin-like immunoreactive neurons in the rat hypothalamus

Neurotensin-like immunoreactive neuronal perikarya, fibers and terminals in the rat hypothalamus, particularly in the arcuate nucleus, the paraventricular nucleus and the median eminence, were investigated by light and electron microscopic immunocytochemistry. The main distributional areas of immunoreactive neuronal perikarya were found to be the arcuate nucleus, the periventricular nucleus and the paraventricular nucleus by light microscopic immunocytochemistry. Immunoreactive neuronal perikarya showed a characteristic distributional pattern in the arcuate nucleus. In the paraventricular nucleus they were distributed in both the magnocellular and parvocellular portions. A large number of immunoreactive terminals were observed throughout the external layer of the median eminence, particularly its lateral portion. A moderate number of immunoreactive terminals were also observed in the internal layer of the median eminence. By electron microscopic immunocytochemistry immunoreactive neuronal perikarya both in the arcuate and paraventricular nuclei showed generally well-developed cell organelles such as mitochondria, r-ER, and Golgi complex. In addition, immunoreactive dense granules were dispersed throughout the perikarya. A large number of immunoreactive terminals containing immunoreactive dense granules, clear vesicles and mitochondria were observed in the vicinity of pericapillary spaces of the external layer of the median eminence. This observation strongly suggests that neurotensin-like immunoreactive substance is released into the portal capillaries.

Occurrence of neurotensinlike immunoreactivity in subpopulations of hypothalamic, mesencephalic, and medullary catecholamine neurons

By using indirect immunofluorescence histochemistry combined with the elution-restaining technique, the presence of a neurotensinlike peptide in some catecholamine neurons in the rat brain has been demonstrated. At the level of the medulla oblongata neurotensinlike immunoreactivity was observed in most of the small-sized catecholamine (adrenaline) cell bodies in the dorsolateral part of the nucleus of the solitary tract and in some catecholamine (noradrenaline) cells in the medial part. Neurotensin-positive fibers were found throughout the solitary tract nucleus with increasing concentrations in the rostral direction. Very few neurotensin fibers were seen in the vagal dorsal motor nucleus, which contained a dense network of adrenaline fibers. In the ventral mesencephalon, neurotensinlike immunoreactivity was seen mainly in dopamine cell bodies in the ventral tegmental area, including midline structures, with only single examples of coexistence in the substantia nigra. The dopamine cell bodies of both the A9 and A10 cell groups were surrounded by dense to medium-dense networks of neurotensin fibers. In the hypothalamus numerous dopamine neurons in the arcuate nucleus exhibited neurotensinlike immunoreactivity. Neurotensin-positive nerve terminals, partially overlapping catecholamine (mainly dopamine) fibers, were seen in the external layer of the median eminence. The present results demonstrate coexistence of neurotensinlike immunoreactivity and catecholamines in populations of neurons in some of the central catecholamine cell groups and provide a morphological basis for interactions between the peptide and amines.

Neurotensin: a new 'reward peptide'

oeurotensin (NT) is a tridecapeptide which is thought to bind to receptors located on dopamine cells in the ventral tegmental area (VTA). Rats with cannulas implanted in the VTA showed a significant increase in time spent in an environment in which they had received bilateral injections of neurotensin on previous days. This is indicative of conditioned reinforcement in which the neuropeptide was the primary reinforcer. In order to determine the specificity of neurotensin receptor interactions, 3 fragments of the peptide were examined at 2 doses. NT1-8 and NT8-13 were found to be inactive while NT1-11 demonstrated significant activity. The results suggest that NT in the VTA is capable of inducing reinforcing effects. This is the first evidence for a non-opiate 'reward peptide'.

Morphological survey of neurotensin-like immunoreactive neurons in the hypothalamus

Neurotensin-like immunoreactive neuronal perikarya, fibers and terminals in in the rat hypothalamus were investigated by light and electron microscopic immunocytochemistry. Distributional density and pattern of these elements were clarified. Fine structure of immunoreactive neuronal perikarya with respect to development of cell organellae and immunoreactive dense granules was also elucidated. Features of immunoreactive processes, dendrites and preterminal axons were examined electron microscopically. In addition to the above findings by light and electron microscopic immunocytochemistry, we examined the coexistence of dopamine and neurotensin-like immunoreactive substances in these same neurons in the arcuate and periventricular nuclei. This was proved by the application of fluorescence histochemistry and immunocytochemistry on the same sections. Moreover, we speculated that the ascending noradrenergic neurons influence the neurotensin immunoreactive neurons in the paraventricular nucleus since a marked decrease in the number of neurotensin-like immunoreactive neuronal perikarya was observed after transection of ascending noradrenergic pathway.

Distribution and origins of neurotensin-containing fibers in the nucleus ventromedialis hypothalami of the rat: an experimental immunohistochemical study

The distribution and origins of neurotensin (NT)-containing fibers in the nucleus ventromedialis hypothalami (VM) of the rat were investigated experimentally using an indirect immunofluorescence technique. A dense plexus of NT-like immunoreactive (NTI) fibers which was composed of very fine varicosities was identified in the VM. Although they were distributed throughout its entire rostrocaudal extent, the distribution was uneven. The highest density was identified in the dorsomedial part of the VM. In the central part, a less numerous but still moderate number of NTI fibers was detected in its dorsal part. But in a ventrolateral direction, they decreased in number and in the ventrolateral part only a few NTI fibers were seen. The present study demonstrated experimentally that these fibers originate from the medial nucleus of the amygdaloid complex (AM), since destruction of the AM resulted in a marked reduction of NTI fibers ipsilaterally in the VM. These findings suggest that the AM influences the VM's functions via neurotensin-like immunoreactive fibers.

Action of neurotensin on spinal cord neurons in the rat

Histochemical, biochemical and pharmacological data suggest that the tridecapeptide neurotensin (NT) may play a role as an intercellular messenger in the spinal cord of rats. In the present study the response of spinal cord neurons to NT was investigated employing conventional extra- and intracellular recording techniques in combination with iontophoresis or a microperfusion system which permits the control of the maximal concentration of NT reached near the neuron. Recordings were obtained from motoneurons, interneurons and from neurons in the dorsal horn receiving synaptic input from low and high threshold mechanoreceptors activated in their peripheral cutaneous receptive fields. The most commonly observed action of NT applied by either mode was an excitation after a dose-dependent delay. The response was dose-dependent, repeatable and reversible. The intracellular recordings revealed that these excitatory responses were due to a depolarizing action of NT associated with an increase in input resistance, not attributable to non-linearities in the current-voltage relationship. The present data are in agreement with most previous investigations reporting excitatory actions of NT on neurons in various neuronal structures in the peripheral and central nervous system. It seems unlikely that these excitatory effects are indirect actions mediated by an inhibition of other neurons in the vicinity.

Ontogeny of neurotensin-containing neuron system of the rat: immunohistochemical analysis--II. Lower brain stem

The ontogeny of the neurotensin neuron system in the lower brain stem of the rat was investigated by means of indirect immunofluorescent method. Neurotensin-like immunoreactivity-containing cells first appear in the primordium of the n. tractus solitarii, n. tractus spinalis nervi trigemini, reticular formation just medial to the latter nucleus, n. reticularis parvocellularis, n. laterodorsalis tegmenti, and midbrain reticular formation of the fetus at gestational day 17. At gestional day 18, neurotensin-immunoreactive cells newly appear in the n. raphe dorsalis. Between gestational day 19 and postnatal day 7, the animals show a remarkable increase in number of immunoreactive cells and fibers in various lower brain stem areas except for n. tractus spinalis nervi trigemini and n. tractus solitarii. Moreover, during this stage, neurotensin-immunoreactive cells located in the n. prepositus hypoglossi and n. vestibularis lateralis appear for the first time at birth and postnatal day 5, respectively. Since postnatal day 7, although the majority of immunoreactive cells located in the lower brain stem decrease in number as the rats grow, immunoreactive cells in the n. tractus spinalis nervi trigemini, on the contrary, increase in number from after birth until postnatal day 10, and maintain more or less their immunoreactivity even in the adult rat. In addition, neurotensin-immunoreactive cells in the nucleus of the solitary tract increase in number during the fetal period, reach the maximum content at postnatal day 7-10, and maintain their immunoreactivity even in the adult rats. Thus, the present study demonstrated that neurotensin-like immunoreactive structures appear at a very early ontogenetical stage, suggesting that neurotensin plays an important role in the development of the lower brain stem of the rat. In addition, the present study further showed that neurotensin-immuno-reactivity shows various fluctuations during the ontogeny, suggesting multiple functions of neurotensin in the central nervous system.