Clinical use of progesterone in human sperm preparation media for increasing IVF success

RESEARCH QUESTION

Can the addition of progesterone and neurotensin, molecular agents found in the female reproductive tract, after sperm washing increase the fertilization potential of human spermatozoa?

DESIGN

(i) Cohort study of 24 men. Spermatozoa selected by swim-up were incubated in either progesterone or neurotensin (0.1-100 µM) for 1-4 h, and hyperactive motility and binding to hyaluronan (0.1-100 µM) were assessed. The effect of progesterone 10 µM on sperm function was assessed in a blinded manner, including: hyperactive motility, binding to hyaluronan, tyrosine phosphorylation, acrosome reaction and oxidative DNA damage. (i) Embryo safety testing [one-cell mouse embryo assay (MEA), endotoxin and sterility counts (n = 3)] in preclinical embryo models of IVF (murine and porcine, n = 7 each model) and a small preliminary human study (n = 4) of couples undergoing standard IVF with oocytes inseminated with spermatozoa ± 10 µM progesterone.

RESULTS

Progesterone 10 µM increased sperm binding to hyaluronan, hyperactive motility and tyrosine phosphorylation (all P < 0.05). Neurotensin had no effect (P > 0.05). Progesterone 10 µM in human embryo culture media passed embryo safety testing (MEA, endotoxin concentration and sterility plate count). In preclinical models of IVF, the exposure of spermatozoa to progesterone 10 µM and oocytes to progesterone 1 µM was not detrimental, and increased the fertilization rate in mice and the blastocyst cell number in mice and pigs (all P ≤ 0.03). In humans, every transferred blastocyst that had been produced from spermatozoa exposed to progesterone resulted in a live birth.

CONCLUSION

The addition of progesterone to sperm preparation media shows promise as an adjunct to current methods for increasing fertilization potential. Randomized controlled trials are required to determine the clinical utility of progesterone for improving IVF outcomes.

Neurotensin counteracts hair growth inhibition induced by chronic restraint stress

Stress has been considered as a potential trigger for hair loss through the neuroendocrine-hair follicle (HF) axis. Neurotensin (NTS), a neuropeptide, is known to be dysregulated in the inflammatory-associated skin diseases. However, the precise role of NTS in stress-induced hair loss is unclear. To investigate the function and potential mechanisms of NTS in stress-induced hair growth inhibition, we initially detected the expression of neurotensin receptor (Ntsr) and NTS in the skin tissues of stressed mice by RNA-sequencing and ELISA. We found chronic restraint stress (CRS) significantly decreased the expression of both NTS and Ntsr in the skin tissues of mice. Intracutaneous injection of NTS effectively counteracted CRS-induced inhibition of hair growth in mice. Furthermore, NTS regulated a total of 1093 genes expression in human dermal papilla cells (HDPC), with 591 genes being up-regulated and 502 genes being down-regulated. GO analysis showed DNA replication, cell cycle, integral component of plasma membrane and angiogenesis-associated genes were significantly regulated by NTS. KEGG enrichment demonstrated that NTS also regulated genes related to the Hippo signalling pathway, axon guidance, cytokine-cytokine receptor interaction and Wnt signalling pathway in HDPC. Our results not only uncovered the potential effects of NTS on stress-induced hair growth inhibition but also provided an understanding of the mechanisms at the gene transcriptional level.

Neurotensin receptor 1-biased ligand attenuates neurotensin-mediated excitation of ventral tegmental area dopamine neurons and dopamine release in the nucleus accumbens

Strong expression of the G protein-coupled receptor (GPCR) neurotensin receptor 1 (NTR1) in ventral tegmental area (VTA) dopamine (DA) neurons and terminals makes it an attractive target to modulate DA neuron activity and normalize DA-related pathologies. Recent studies have identified a novel class of NTR1 ligand that shows promising effects in preclinical models of addiction. A lead molecule, SBI-0654553 (SBI-553), can act as a positive allosteric modulator of NTR1 β-arrestin recruitment while simultaneously antagonizing NTR1 Gq protein signaling. Using cell-attached recordings from mouse VTA DA neurons we discovered that, unlike neurotensin (NT), SBI-553 did not independently increase spontaneous firing. Instead, SBI-553 blocked the NT-mediated increase in firing. SBI-553 also antagonized the effects of NT on dopamine D2 auto-receptor signaling, potentially through its inhibitory effects on G-protein signaling. We also measured DA release directly, using fast-scan cyclic voltammetry in the nucleus accumbens and observed antagonist effects of SBI-553 on an NT-induced increase in DA release. Further, in vivo administration of SBI-553 did not notably change basal or cocaine-evoked DA release measured in NAc using fiber photometry. Overall, these results indicate that SBI-553 blunts NT's effects on spontaneous DA neuron firing, D2 auto-receptor function, and DA release, without independently affecting these measures. In the presence of NT, SBI-553 has an inhibitory effect on mesolimbic DA activity, which could contribute to its efficacy in animal models of psychostimulant use.

Neurotensin modulation of lipopolysaccharide induced inflammation of gut-liver axis: Evaluation using neurotensin receptor agonist and antagonist

Lipopolysaccharide (LPS), a toxic component of the cell wall of Gram-negative bacteria, is a potent immune stressor. LPS-induced inflammation of the gut-liver axis is well demonstrated. Neurotensin (NTS), a tri-decapeptide present in the gastrointestinal tract, has anti-inflammatory, anti-oxidative, and growth-promoting properties. This study elucidated the efficacy of PD149163, the type I NTS receptor agonist (NTS₁) in the modulation of LPS-induced inflammation of the gut-liver axis of mice. Young-adult female mice (Age: 8 weeks; BW: 25 ± 2.5 g) were maintained in six groups (6/group); Group I as control and Group II, III & IV were exposed to LPS (1 mg/kg BW/Day; i.p.) for five days. LPS pre-exposed Group III and Group IV mice were treated with NTS₁ agonist PD149163 (100 μg/kg BW i.p.) and antagonist SR48692 (0.5 mg/kg BW i.p.) respectively for 28 days. Group V and Group VI mice were exposed to only PD149163 and only SR48692 respectively with the doses as mentioned above for 28 days. Group I and LPS-exposed Group II mice were also maintained four weeks without further treatment. Histopathology revealed LPS-induced inflammation of the gut and liver. Significant elevation of plasma TNF-α and IL-6 and serum ALT and AST reflected as biomarkers of inflammation. Oxidative stress on both organs was distinct from decreased glutathione reductase and increased lipid peroxidation. PD149163 but not SR48692 ameliorated LPS-induced inflammation in both gut and liver counteracting inflammatory responses and oxidative stress. The use of NTS agonists including PD149163 could be exploited for therapeutic intervention of inflammatory diseases including that of the gut-liver axis.

Intravenous administration of xenin-25 accelerates cyclic ruminal contractions in healthy conscious sheep

The present study aimed to determine the effect and mode of action of the intravenous injection of xenin-25 on cyclic contractions of the rumen in healthy conscious sheep and mode of its action. Clinically healthy male sheep were equipped with a rumen cannula by surgery under anesthesia, and ruminal contractions were recorded with manometry in conscious animals after the recovery period. Intravenous xenin-25 injection induced a cluster of premature ruminal phasic contractions in a dose-dependent manner between 0.03 and 1 nmol/kg, and the change at the highest dose was statistically significant. In contrast, intravenous neurotensin injection inhibited the amplitude of cyclic rumen contractions. The xenin-25 effect was not significantly altered by prior injection of the neurotensin receptor subtype-1 antagonist SR 48692 at 30 and 100 nmol/kg. After euthanasia the ruminal muscles were excised for in vitro experiments. A single xenin-25 application (0.3-10 μM) to the longitudinal and circular muscle strips of the rumen did not induce any change in tension or electric field stimulation-induced phasic contractions of the muscle strips. These results demonstrated that circulating xenin-25 stimulates rumen contractions by acting on sites except the intramural intrinsic nerve plexus or smooth muscles of the rumen, implying that xenin-25 acts on the gastric center and/or cholinergic efferent nerve innervated to the ovine rumen.

Neurotensin and xenin stimulates pancreatic exocrine secretion through the peripheral cholinergic nerves in conscious sheep

The present study aimed to clarify the effects of neurotensin and xenin on pancreatic exocrine secretion in conscious sheep and their mechanism of actions. The animals were equipped with two silastic cannulae in the common bile duct to separately collect pancreatic fluid and bile, and a silastic cannula in the proximal duodenum to continuously return the mixed fluids. NT and xenin were intravenously injected at range of 0.01-3.0 nmol/kg during the phase I of duodenal migrating motor complex. A single intravenous NT injection significantly and dose-dependently increased pancreatic fluid, protein, and bicarbonate outputs. The effect of NT at 1 nmol/kg was completely inhibited by a background intravenous infusion of atropine methyl nitrate at a dose of 10 nmol/kg/min, however, the effect was not altered by a prior injection of the neurotensin receptor subtype (NTR)-1 antagonist SR 48692 at 60 nmol/kg. Moreover, a single intravenous xenin-25 injection significantly and dose-dependently increased pancreatic fluid and protein output, whereas the effect of xenin-25 did not clearly show dose-dependence. The prior SR 48692 injection at 30 nmol/kg did not significantly alter the effects of xenin-25 at 0.3 nmol/kg, while the atropine infusion significantly inhibited the increase in fluid secretion. Under the atropine infusion, xenin-25 at 0.3 nmol/kg did not increase protein and bicarbonate outputs, whereas the inhibitory effect of the atropine was not significant compared to that of the single injection of xenin-25. A single intravenous injection of NTR-2 agonist levocabastine at 0.1-3 nmol/kg did not alter pancreatic exocrine secretion. These results suggest that both NT and xenin-25 effectively stimulates pancreatic exocrine secretion through the peripheral cholinergic system in sheep and that NTR-2 is not involved in the regulation of pancreatic exocrine secretion, however, we did not precisely determine the role of NTR-1 in the actions of both the peptides on pancreatic exocrine secretion.

Minimum biological domain of xenin-25 required to induce anion secretion in the rat ileum

Xenin-25 has a variety of physiological functions in the gastrointestinal tract, including ion transport and motility. Xenin-25 and neurotensin show sequence homology, especially near their C-terminal regions. The sequence similarity between xenin-25 and neurotensin indicates that the effects of xenin-25 is mediated by the neurotensin receptor but some biological actions of xenin-25 are independent. We have previously reported that xenin-25 modulates intestinal ion transport and colonic smooth muscle activity. However, minimal biological domain of xenin-25 to induce ion transport was not clear. To improve the mechanistic understanding of xenin-25 and to gain additional insights into the functions of xenin-25, the present study was designed to determine the minimal biological domain of xenin-25 required for ion transport in the rat ileum using various truncated xenin fragments and analogues in an Ussing chamber system. The present results demonstrate that the minimum biological domain of xenin-25 to induce Cl-/HCO3- secretion in the ileum contains the C-terminal pentapeptide. Furthermore, Arg at position 21 is important to retain the biological activity of xenin-25 and induces Cl-/HCO3- secretion in the rat ileum.

Diverse intracellular signaling pathways mediate the effects of neurotensin on the excitability of type II neurons in the rat dorsolateral bed nucleus of the stria terminalis

We examined the effects of neurotensin (NTS) on the excitability of type II neurons in the rat dorsolateral bed nucleus of the stria terminalis (dlBNST) using whole-cell patch-clamp electrophysiology. Bath-application of NTS depolarized type II dlBNST neurons. Analyses of the steady-state I-V relationships implied that the depolarizing effect of NTS is due to potassium conductance blocking. The depolarizing effect of NTS was abolished in the presence of a PLC inhibitor, but not affected by a protein kinase C inhibitor. In the presence of a CaMKII inhibitor, NTS showed depolarizing effects via the increase in non-selective cation conductance in addition to the decrease in potassium conductance. Unexpectedly, in the presence of a PKA inhibitor, NTS hyperpolarized type II dlBNST neurons. These results reveal that diverse signaling pathways mediate the effects of NTS on the excitability of type II dlBNST neurons. The elevation of intracellular Ca2+ levels via the inositol phosphate-mediated signaling activates both Ca2+-dependent adenylate cyclase (AC) and CaMKII. Activation of the AC-cAMP-PKA pathway exerts depolarizing effects on type II dlBNST neurons by decreasing potassium conductance and increasing non-selective cation conductance, whereas activation of the CaMKII pathway exerts hyperpolarizing effects on dlBNST neurons by decreasing non-selective cation conductance.

The effect of Xenin25 on spontaneous circular muscle contractions of rat distal colon in vitro

Xenin25 has a variety of physiological functions in the Gastrointestinal (GI) tract, including ion transport and motility. However, the motility responses in the colon induced by Xenin25 remain poorly understood. Therefore, the effect of Xenin25 on the spontaneous circular muscle contractions of the rat distal colon was investigated using organ bath chambers and immunohistochemistry. Xenin25 induced the inhibition followed by postinhibitory spontaneous contractions with a higher frequency in the rat distal colon. This inhibitory effect of Xenin25 was significantly suppressed by TTX but not by atropine. The inhibitory time (the duration of inhibition) caused by Xenin25 was shortened by the NTSR1 antagonist SR48692, the NK1R antagonist CP96345, the VPAC2 receptor antagonist PG99-465, the nitric oxide-sensitive guanylate-cyclase inhibitor ODQ, and the Ca2+ -dependent K+ channel blocker apamin. The higher frequency of postinhibitory spontaneous contractions induced by Xenin25 was also attenuated by ODQ and apamin. SP-, NOS-, and VIP-immunoreactive neurons were detected in the myenteric plexus (MP) of the rat distal colon. Small subsets of the SP-positive neurons were also Calbindin positive. Most of the VIP-positive neurons were also NOS positive, and small subsets of the NK1R-positive neurons were also VIP positive. Based on the present results, we propose the following mechanism. Xenin25 activates neuronal NTSR1 on the SP neurons of IPANs, and transmitters from the VIP and apamin-sensitive NO neurons synergistically inhibit the spontaneous circular muscle contractions via NK1R. Subsequently, the postinhibitory spontaneous contractions are induced by the offset of apamin-sensitive NO neuron activation via the interstitial cells of Cajal. In addition, Xenin25 also activates the muscular NTSR1 to induce relaxation. Thus, Xenin25 is considered to be an important modulator of post prandial circular muscle contraction of distal colon since the release of Xenin25 from enteroendocrine cells is stimulated by food intake.

Neurolysin substrates bradykinin, neurotensin and substance P enhance brain microvascular permeability in a human in vitro model

Increased brain microvascular permeability and disruption of blood-brain barrier (BBB) function are among hallmarks of several acute neurodegenerative disorders, including stroke. Numerous studies suggest the involvement of bradykinin (BK), neurotensin (NT) and substance P (SP) in BBB impairment and oedema formation after stroke; however, there is paucity of data in regard to the direct effects of these peptides on the brain microvascular endothelial cells (BMECs) and BBB. The present study aimed to evaluate the direct effects of BK, NT and SP on the permeability of BBB in an in vitro model based on human induced pluripotent stem cell (iPSC)-derived BMECs. Our data indicate that all three peptides increase BBB permeability in a concentration-dependent manner in an in vitro model formed from two different iPSC lines (CTR90F and CTR65M) and widely used hCMEC/D3 human BMECs. The combination of BK, NT and SP at a sub-effective concentration also resulted in increased BBB permeability in the iPSC-derived model indicating potentiation of their action. Furthermore, we observed abrogation of BK, NT and SP effects with pretreatment of pharmacological blockers targeting their specific receptors. Additional mechanistic studies indicate that the short-term effects of these peptides are not mediated through alteration of tight-junction proteins claudin-5 and occludin, but likely involve redistribution of F-actin and secretion of vascular endothelial growth factor. This is the first experimental study to document the increased permeability of the BBB in response to direct action of NT in an in vitro model. In addition, our study confirms the expected but not well-documented, direct effect of SP on BBB permeability and adds to the well-recognised actions of BK on BBB. Lastly, we demonstrate that peptidase neurolysin can neutralise the effects of these peptides on BBB, suggesting potential therapeutic implications.

Ψ-Xenin-6 enhances sitagliptin effectiveness, but does not improve glucose tolerance

Recent studies have characterised the biological properties and glucose-dependent insulinotropic polypeptide (GIP) potentiating actions of an enzymatically stable, C-terminal hexapeptide fragment of the gut hormone xenin, namely Ψ-xenin-6. Given the primary therapeutic target of clinically approved dipeptidyl peptidase-4 (DPP-4) inhibitor drugs is augmentation of the incretin effect, the present study has assessed the capacity of Ψ-xenin-6 to enhance the antidiabetic efficacy of sitagliptin in high fat fed (HFF) mice. Individual administration of either sitagliptin or Ψ-xenin-6 alone for 18 days resulted in numerous metabolic benefits and positive effects on pancreatic islet architecture. As expected, sitagliptin therapy was associated with elevated circulating GIP and GLP-1 levels, with concurrent Ψ-xenin-6 not elevating these hormones or enhancing DPP-4 inhibitory activity of the drug. However, combined sitagliptin and Ψ-xenin-6 therapy in HFF mice was associated with further notable benefits, beyond that observed with either treatment alone. This included body weight change similar to lean controls, more pronounced and rapid benefits on circulating glucose and insulin as well as additional improvements in attenuating gluconeogenesis. Favourable effects on pancreatic islet architecture and peripheral insulin sensitivity were more apparent with combined therapy. Expression of hepatic genes involved in gluconeogenesis and insulin action were partially, or fully, restored to normal levels by the treatment regimens, with beneficial effects more prominent in the combination treatment group. These data demonstrate that combined treatment with Ψ-xenin-6 and sitagliptin did not alter glucose tolerance but does offer some metabolic advantages, which merit further consideration as a therapeutic option for type 2 diabetes.

Effects of long-acting GIP, xenin and oxyntomodulin peptide analogues on alpha-cell transdifferentiation in insulin-deficient diabetic GluCreERT2;ROSA26-eYFP mice

Enzyme-resistant long-acting forms of the gut-derived peptide hormones, glucose-dependent insulinotropic polypeptide (GIP), xenin and oxyntomodulin (Oxm) have been generated, and exert beneficial effects on diabetes control and pancreatic islet architecture. The current study has employed alpha-cell lineage tracing in Glu^CreERT2;ROSA26-eYFP transgenic mice to investigate the extent to which these positive pancreatic effects are associated with alpha- to beta-cell transdifferentiation. Twice-daily administration of (D-Ala²)GIP, xenin-25[Lys¹³PAL] or (D-Ser²)-Oxm[Lys³⁸PAL] for 10 days to streptozotocin (STZ)-induced diabetic mice did not affect body weight, food intake or blood glucose levels, but (D-Ser²)-Oxm[Lys³⁸PAL] reduced (P < 0.05 to P < 0.001) fluid intake and circulating glucagon. (D-Ala²)GIP and (D-Ser²)-Oxm[Lys³⁸PAL] also augmented (P < 0.05 and P < 0.01, respectively) pancreatic insulin content. Detrimental changes of pancreatic morphology induced by STZ in Glu^CreERT2;ROSA26-eYFP mice were partially reversed by all treatment interventions. This was associated with reduced (P < 0.05) apoptosis and increased (P < 0.05 to P < 0.01) proliferation of beta-cells, alongside opposing effects on alpha-cells, with (D-Ala²)GIP and (D-Ser²)-Oxm[Lys³⁸PAL] being particularly effective in this regard. Alpha-cell lineage tracing revealed that induction of diabetes was accompanied by increased (P < 0.01) transdifferentiation of glucagon positive alpha-cells to insulin positive beta-cells. This islet cell transitioning process was augmented (P < 0.01 and P < 0.001, respectively) by (D-Ala²)GIP and (D-Ser²)-Oxm[Lys³⁸PAL]. (D-Ser²)-Oxm[Lys³⁸PAL] also significantly (P < 0.05) promoted loss of alpha-cell identity in favour of other endocrine islet cells. These data highlight intra-islet benefits of (D-Ala²)GIP, xenin-25[Lys¹³PAL] and (D-Ser²)-Oxm[Lys³⁸PAL] in diabetes with beta-cell loss induced by STZ. The effects appear to be independent of glycaemic change, and associated with alpha- to beta-cell transdifferentiation for the GIP and Oxm analogues.

Neurotensin receptors regulate transactivation of the EGFR and HER2 in a reactive oxygen species-dependent manner

Neurotensin is a 13 amino acid peptide which is present in many lung cancer cell lines. Neurotensin binds with high affinity to the neurotensin receptor 1, and functions as an autocrine growth factor in lung cancer cells. Neurotensin increases tyrosine phosphorylation of the epidermal growth factor receptor (EGFR) and the neurotensin receptor 1 antagonist SR48692 blocks the transactivation of the EGFR. Here the effects of reactive oxygen species on the transactivation of the EGFR and HER2 were investigated. Using non-small cell lung cancer (NSCLC) cell lines, neurotensin receptor 1 mRNA and protein were present. Using NCI-H838 cells, neurotensin or neurotensin^8-13 but not neurotensin^1-8 increased EGFR, ERK and HER2 tyrosine phosphorylation which was blocked by SR48692. Neurotensin addition to NCI-H838 cells increased significantly reactive oxygen species which was inhibited by SR48692, Tiron (superoxide scavenger) and diphenylene iodonium (DPI inhibits the ability of NADPH oxidase and dual oxidase enzymes to produce reactive oxygen species). Tiron or DPI impaired the ability of neurotensin to increase EGFR, ERK and HER2 tyrosine phosphorylation. Neurotensin stimulated NSCLC cellular proliferation whereas the growth was inhibited by SR48692, DPI or lapatinib (lapatinib is tyrosine kinase inhibitor of the EGFR and HER2). Lapatinib inhibited the ability of the neurotensin receptor 1 to transactivate the EGFR and HER2. The results indicate that neurotensin receptor 1 regulates the transactivation of the EGFR and HER2 in a reactive oxygen species-dependent manner.

Effects of an enzymatically stable C-terminal hexapseudopeptide fragment peptide of xenin-25, ψ-xenin-6, on pancreatic islet function and metabolism

Xenin-25 undergoes rapid enzyme metabolism following secretion. Early studies demonstrated bioactivity of a C-terminal hexapeptide fragment of xenin-25, namely xenin-6, which were enhanced through introduction of a reduced N-terminal peptide bond, to yield Ψ-xenin-6. The present study was undertaken to define the biological actions and potential antidiabetic properties of Ψ-xenin-6. In vitro enzymatic stability, insulin and glucagon secretory activity, as well as effects on beta-cell survival were determined. Studies in mice were used to assess the impact of Ψ-xenin-6 on glucose homeostasis and satiety. Ψ-xenin-6 was resistant to murine plasma degradation. In BRIN-BD11 cells and isolated murine islets, Ψ-xenin-6 significantly stimulated insulin secretion, and prominently enhanced the insulinotropic actions of GIP. Xenin-6 and Ψ-xenin-6 had no impact on glucagon secretion, although xenin-6 partially reversed the glucagonotropic action of GIP. Further in vitro investigations revealed that, similar to GLP-1, Ψ-xenin-6 significantly augmented proliferation of human and rodent clonal beta-cells, whilst also fully protecting against cytokine-induced beta-cell cytotoxicity, with greater potency than xenin-25 and xenin-6. When administered to mice in combination with glucose, Ψ-xenin-6 significantly reduced glucose levels and enhanced glucose-induced insulin release, with a duration of biological action beyond 8 h. Ψ-xenin-6 also significantly enhanced the glucose-lowering action of GIP in vivo. In overnight fasted mice, Ψ-xenin-6 exhibited satiety actions at both 25 and 250 nmol/kg. These data demonstrates that Ψ-xenin-6 is a metabolically stable C-terminal fragment analogue of xenin-25, with a metabolic action profile that merits further study as a potential antidiabetic compound.

Long-Acting Neurotensin Synergizes With Liraglutide to Reverse Obesity Through a Melanocortin-Dependent Pathway

Neurotensin (NT), a gut hormone and neuropeptide, increases in circulation after bariatric surgery in rodents and humans and inhibits food intake in mice. However, its potential to treat obesity and the subsequent metabolic dysfunctions have been difficult to assess owing to its short half-life in vivo. Here, we demonstrate that a long-acting, pegylated analog of the NT peptide (P-NT) reduces food intake, body weight, and adiposity in diet-induced obese mice when administered once daily for 6 days. Strikingly, when P-NT was combined with the glucagon-like peptide 1 mimetic liraglutide, the two peptides synergized to reduce food intake and body weight relative to each monotherapy, without inducing a taste aversion. Further, P-NT and liraglutide coadministration improved glycemia and reduced steatohepatitis. Finally, we show that the melanocortin pathway is central for P-NT-induced anorexia and necessary for the full synergistic effect of P-NT and liraglutide combination therapy. Overall, our data suggest that P-NT and liraglutide combination therapy could be an enhanced treatment for obesity with improved tolerability compared with liraglutide monotherapy.

Central action of xenin affects the expression of lipid metabolism-related genes and proteins in mouse white adipose tissue

Xenin is a gastrointestinal hormone that reduces food intake when administered centrally and it has been hypothesized that central action of xenin participates in the regulation of whole-body metabolism. The present study was performed to address this hypothesis by investigating the central effect of xenin on the expression of genes and proteins that are involved in the regulation of lipid metabolism in white adipose tissue (WAT). Male obese ob/ob mice received intracerebroventricular (i.c.v.) injections of xenin (5μg) twice 12h apart. Food intake and body weight change during a 24-h period after the first injection were measured. Epididymal WAT was collected at the end of the 24-h treatment period and levels of lipid metabolism-related genes and proteins were measured. Xenin treatment caused significant reductions in food intake and body weight compared to control vehicle treatment. Levels of fatty acid synthase (FASN) protein were significantly reduced by xenin treatment, while levels of adipose triglyceride lipase (Atgl) and beta-3 adrenergic receptor (Adrb3) mRNA and phosphorylated hormone sensitive lipase (Ser⁶⁶⁰-pHSL and Ser⁵⁶³-pHSL) were significantly increased by xenin treatment. These findings suggest that central action of xenin causes alterations in lipid metabolism in adipose tissue toward reduced lipogenesis and increased lipolysis, possibly contributing to xenin-induced body weight reduction. Thus, enhancing central action of xenin and its downstream targets may be possible targets for the treatment of obesity by reducing the amount of stored fat in adipose tissue.

Hormonal Responses to Cholinergic Input Are Different in Humans with and without Type 2 Diabetes Mellitus

Peripheral muscarinic acetylcholine receptors regulate insulin and glucagon release in rodents but their importance for similar roles in humans is unclear. Bethanechol, an acetylcholine analogue that does not cross the blood-brain barrier, was used to examine the role of peripheral muscarinic signaling on glucose homeostasis in humans with normal glucose tolerance (NGT; n = 10), impaired glucose tolerance (IGT; n = 11), and type 2 diabetes mellitus (T2DM; n = 9). Subjects received four liquid meal tolerance tests, each with a different dose of oral bethanechol (0, 50, 100, or 150 mg) given 60 min before a meal containing acetaminophen. Plasma pancreatic polypeptide (PP), glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), glucose, glucagon, C-peptide, and acetaminophen concentrations were measured. Insulin secretion rates (ISRs) were calculated from C-peptide levels. Acetaminophen and PP concentrations were surrogate markers for gastric emptying and cholinergic input to islets. The 150 mg dose of bethanechol increased the PP response 2-fold only in the IGT group, amplified GLP-1 release in the IGT and T2DM groups, and augmented the GIP response only in the NGT group. However, bethanechol did not alter ISRs or plasma glucose, glucagon, or acetaminophen concentrations in any group. Prior studies showed infusion of xenin-25, an intestinal peptide, delays gastric emptying and reduces GLP-1 release but not ISRs when normalized to plasma glucose levels. Analysis of archived plasma samples from this study showed xenin-25 amplified postprandial PP responses ~4-fold in subjects with NGT, IGT, and T2DM. Thus, increasing postprandial cholinergic input to islets augments insulin secretion in mice but not humans.

Trial Registration: ClinicalTrials.gov NCT01434901

Dose-Dependent AMPK-Dependent and Independent Mechanisms of Berberine and Metformin Inhibition of mTORC1, ERK, DNA Synthesis and Proliferation in Pancreatic Cancer Cells

Natural products represent a rich reservoir of potential small chemical molecules exhibiting anti-proliferative and chemopreventive properties. Here, we show that treatment of pancreatic ductal adenocarcinoma (PDAC) cells (PANC-1, MiaPaCa-2) with the isoquinoline alkaloid berberine (0.3-6 µM) inhibited DNA synthesis and proliferation of these cells and delay the progression of their cell cycle in G1. Berberine treatment also reduced (by 70%) the growth of MiaPaCa-2 cell growth when implanted into the flanks of nu/nu mice. Mechanistic studies revealed that berberine decreased mitochondrial membrane potential and intracellular ATP levels and induced potent AMPK activation, as shown by phosphorylation of AMPK α subunit at Thr-172 and acetyl-CoA carboxylase (ACC) at Ser79. Furthermore, berberine dose-dependently inhibited mTORC1 (phosphorylation of S6K at Thr389 and S6 at Ser240/244) and ERK activation in PDAC cells stimulated by insulin and neurotensin or fetal bovine serum. Knockdown of α1 and α2 catalytic subunit expression of AMPK reversed the inhibitory effect produced by treatment with low concentrations of berberine on mTORC1, ERK and DNA synthesis in PDAC cells. However, at higher concentrations, berberine inhibited mitogenic signaling (mTORC1 and ERK) and DNA synthesis through an AMPK-independent mechanism. Similar results were obtained with metformin used at doses that induced either modest or pronounced reductions in intracellular ATP levels, which were virtually identical to the decreases in ATP levels obtained in response to berberine. We propose that berberine and metformin inhibit mitogenic signaling in PDAC cells through dose-dependent AMPK-dependent and independent pathways.

Mephedrone alters basal ganglia and limbic neurotensin systems

Mephedrone (4-methylmethcathinone) is a synthetic cathinone designer drug that alters pre-synaptic dopamine (DA) activity like many psychostimulants. However, little is known about the post-synaptic dopaminergic impacts of mephedrone. The neuropeptide neurotensin (NT) provides inhibitory feedback for basal ganglia and limbic DA pathways, and post-synaptic D1 -like and D2 -like receptor activity affects NT tissue levels. This study evaluated how mephedrone alters basal ganglia and limbic system NT content and the role of NT receptor activation in drug consumption behavior. Four 25 mg/kg injections of mephedrone increased NT content in basal ganglia (striatum, substantia nigra and globus pallidus) and the limbic regions (nucleus accumbens core), while a lower dosage (5 mg/kg/injection) only increased striatal NT content. Mephedrone-induced increases in basal ganglia NT levels were mediated by D1 -like receptors in the striatum and the substantia nigra by both D1 -like and D2 -like receptors in the globus pallidus. Mephedrone increased substance P content, another neuropeptide, in the globus pallidus, but not in the dorsal striatum or substantia nigra. Finally, the NT receptor agonist PD149163 blocked mephedrone self-administration, suggesting reduced NT release, as indicated by increased tissue levels, likely contributing to patterns of mephedrone consumption.

Role of context in neurotensin-induced sensitization to the locomotor stimulant effect of amphetamine

Previous studies have shown that repeated central injections of neurotensin, or its active analog, D-Tyr([11])neurotensin, sensitize to the locomotor stimulant effect of amphetamine. The development of sensitization to amphetamine can be modulated by contextual stimuli associated with the drug and as a consequence the expression of sensitization becomes context-dependent. The present study was thus aimed at determining whether the induction of amphetamine sensitization by neurotensin is modulated by the context in which neurotensin is administered. Different groups of adult male Long Evans rats were injected on four occasions with D-Tyr([11])neurotensin (18 nmol/10 μl; i.c.v.) in the locomotor activity cages (paired group) or in their home cage (unpaired group); control group received vehicle injection in both environments. One week after the last central injection, the locomotor response to a single dose of amphetamine (0.75 mg/kg; i.p.) was measured in all the rats. Results show that amphetamine induced higher ambulatory, non-ambulatory and vertical activity in the paired group than in the control group confirming the sensitization effect. The paired group also displayed significant higher ambulatory activity than those in the unpaired group, confirming that the expression of sensitization was context-dependent. This context-dependency was not found however for amphetamine-induced non-ambulatory and vertical activity suggesting that neurotensin can induce both a context-dependent and context-independent sensitization.

Characterisation of the biological activity of xenin-25 degradation fragment peptides

Xenin-25, a peptide co-secreted with the incretin hormone glucose-dependent insulinotropic polypeptide (GIP), possesses promising therapeutic actions for obesity-diabetes. However, native xenin-25 is rapidly degraded by serum enzymes to yield the truncated metabolites: xenin 9-25, xenin 11-25, xenin 14-25 and xenin 18-25. This study has examined the biological activities of these fragment peptides. In vitro studies using BRIN-BD11 cells demonstrated that native xenin-25 and xenin 18-25 possessed significant (P<0.05 to P<0.001) insulin-releasing actions at 5.6 and 16.7 mM glucose, respectively, but not at 1.1  mM glucose. In addition, xenin 18-25 significantly (P<0.05) potentiated the insulin-releasing action of the stable GIP mimetic (D-Ala²)GIP. In contrast, xenin 9-25, xenin 11-25 and xenin 14-25 displayed neither insulinotropic nor GIP-potentiating actions. Moreover, xenin 9-25, xenin 11-25 and xenin 14-25 significantly (P<0.05 to P<0.001) inhibited xenin-25 (10⁻⁶ M)-induced insulin release in vitro. I.p. administration of xenin-based peptides in combination with glucose to high fat-fed mice did not significantly affect the glycaemic excursion or glucose-induced insulin release compared with controls. However, when combined with (D-Ala²)GIP, all xenin peptides significantly (P<0.01 to P<0.001) reduced the overall glycaemic excursion, albeit to a similar extent as (D-Ala²)GIP alone. Xenin-25 and xenin 18-25 also imparted a potential synergistic effect on (D-Ala²)GIP-induced insulin release in high fat-fed mice. All xenin-based peptides lacked significant satiety effects in normal mice. These data demonstrate that the C-terminally derived fragment peptide of xenin-25, xenin 18-25, exhibits significant biological actions that could have therapeutic utility for obesity-diabetes.

The combination of GIP plus xenin-25 indirectly increases pancreatic polypeptide release in humans with and without type 2 diabetes mellitus

Xenin-25 (Xen) is a 25-amino acid neurotensin-related peptide that activates neurotensin receptor-1 (NTSR1). We previously showed that Xen increases the effect of glucose-dependent insulinotropic polypeptide (GIP) on insulin release 1) in hyperglycemic mice via a cholinergic relay in the periphery independent from the central nervous system and 2) in humans with normal or impaired glucose tolerance, but not type 2 diabetes mellitus (T2DM). Since this blunted response to Xen defines a novel defect in T2DM, it is important to understand how Xen regulates islet physiology. On separate visits, subjects received intravenous graded glucose infusions with vehicle, GIP, Xen, or GIP plus Xen. The pancreatic polypeptide response was used as an indirect measure of cholinergic input to islets. The graded glucose infusion itself had little effect on the pancreatic polypeptide response whereas administration of Xen equally increased the pancreatic polypeptide response in humans with normal glucose tolerance, impaired glucose tolerance, and T2DM. The pancreatic polypeptide response to Xen was similarly amplified by GIP in all 3 groups. Antibody staining of human pancreas showed that NTSR1 is not detectable on islet endocrine cells, sympathetic neurons, blood vessels, or endothelial cells but is expressed at high levels on PGP9.5-positive axons in the exocrine tissue and at low levels on ductal epithelial cells. PGP9.5 positive nerve fibers contacting beta cells in the islet periphery were also observed. Thus, a neural relay, potentially involving muscarinic acetylcholine receptors, indirectly increases the effects of Xen on pancreatic polypeptide release in humans.

Neurotensin-loaded collagen dressings reduce inflammation and improve wound healing in diabetic mice

Impaired wound healing is an important clinical problem in diabetes mellitus and results in failure to completely heal diabetic foot ulcers (DFUs), which may lead to lower extremity amputations. In the present study, collagen based dressings were prepared to be applied as support for the delivery of neurotensin (NT), a neuropeptide that acts as an inflammatory modulator in wound healing. The performance of NT alone and NT-loaded collagen matrices to treat wounds in streptozotocin (STZ) diabetic induced mice was evaluated. Results showed that the prepared dressings were not-cytotoxic up to 72h after contact with macrophages (Raw 264.7) and human keratinocyte (HaCaT) cell lines. Moreover, those cells were shown to adhere to the collagen matrices without noticeable change in their morphology. NT-loaded collagen dressings induced faster healing (17% wound area reduction) in the early phases of wound healing in diabetic wounded mice. In addition, they also significantly reduced inflammatory cytokine expression namely, TNF-α (p<0.01) and IL-1β (p<0.01) and decreased the inflammatory infiltrate at day 3 post-wounding (inflammatory phase). After complete healing, metalloproteinase 9 (MMP-9) is reduced in diabetic skin (p<0.05) which significantly increased fibroblast migration and collagen (collagen type I, alpha 2 (COL1A2) and collagen type III, alpha 1 (COL3A1)) expression and deposition. These results suggest that collagen-based dressings can be an effective support for NT release into diabetic wound enhancing the healing process. Nevertheless, a more prominent scar is observed in diabetic wounds treated with collagen when compared to the treatment with NT alone.

VPAC receptor signaling modulates grouping behavior and social responses to contextual novelty in a gregarious finch: a role for a putative prefrontal cortex homologue

In both mammals and birds, vasoactive intestinal polypeptide (VIP) neurons and fibers are present in virtually every brain area that is important for social behavior. VIP influences aggression in birds, social recognition in rodents, and prolactin secretion in both taxa, but other possible functions in social modulation remain little explored. VIP effects are mediated by VPAC receptors, which bind both VIP and pituitary adenylate cyclase activating peptide. Within the lateral septum and medial bed nucleus of the stria terminalis, VPAC receptors are found at higher densities in gregarious finch species relative to territorial species, suggesting that VPAC receptor activation promotes social contact and/or preference for larger groups. Here we here test this hypothesis in zebra finches (Taeniopygia guttata), and also examine the relevance of VPAC receptors to anxiety-like processes. Intraventricular infusions of the VPAC receptor antagonist, neurotensin6-11 mouseVIP7-28, strongly reduce social contact when animals are tested in a novel environment, and exert sex-specific effects on grouping behavior. Specifically, VPAC receptor antagonism reduces gregariousness in females but increases gregariousness in males. Interestingly, VPAC antagonism in the medial pallium (putative prefrontal cortex homologue) significantly reduces gregariousness in both sexes, suggesting site-specific effects of VIP signaling. However, VPAC antagonism does not modulate novel-familiar social preferences in a familiar environment or general anxiety-like behaviors. The current results suggest that endogenous activation of VPAC receptors promotes social contact under novel environmental conditions, a function that may be accentuated in gregarious species. Moreover, endogenous VIP modulates gregariousness in both males and females.

Different patterns of Akt and ERK feedback activation in response to rapamycin, active-site mTOR inhibitors and metformin in pancreatic cancer cells

The mTOR pathway is aberrantly stimulated in many cancer cells, including pancreatic ductal adenocarcinoma (PDAC), and thus it is a potential target for therapy. However, the mTORC1/S6K axis also mediates negative feedback loops that attenuate signaling via insulin/IGF receptor and other tyrosine kinase receptors. Suppression of these feed-back loops unleashes over-activation of upstream pathways that potentially counterbalance the antiproliferative effects of mTOR inhibitors. Here, we demonstrate that treatment of PANC-1 or MiaPaCa-2 pancreatic cancer cells with either rapamycin or active-site mTOR inhibitors suppressed S6K and S6 phosphorylation induced by insulin and the GPCR agonist neurotensin. Rapamycin caused a striking increase in Akt phosphorylation at Ser(473) while the active-site inhibitors of mTOR (KU63794 and PP242) completely abrogated Akt phosphorylation at this site. Conversely, active-site inhibitors of mTOR cause a marked increase in ERK activation whereas rapamycin did not have any stimulatory effect on ERK activation. The results imply that first and second generation of mTOR inhibitors promote over-activation of different pro-oncogenic pathways in PDAC cells, suggesting that suppression of feed-back loops should be a major consideration in the use of these inhibitors for PDAC therapy. In contrast, metformin abolished mTORC1 activation without over-stimulating Akt phosphorylation on Ser(473) and prevented mitogen-stimulated ERK activation in PDAC cells. Metformin induced a more pronounced inhibition of proliferation than either KU63794 or rapamycin while, the active-site mTOR inhibitor was more effective than rapamycin. Thus, the effects of metformin on Akt and ERK activation are strikingly different from allosteric or active-site mTOR inhibitors in PDAC cells, though all these agents potently inhibited the mTORC1/S6K axis.

Xenin-25 increases cytosolic free calcium levels and acetylcholine release from a subset of myenteric neurons

Xenin-25 (Xen) is a 25 amino acid neurotensin-related peptide reportedly produced with glucose-dependent insulinotropic polypeptide (GIP) by a subset of K cells in the proximal gut. We previously showed exogenously administered Xen, with GIP but not alone, increases insulin secretion in humans and mice. In mice, this effect is indirectly mediated via a central nervous system-independent cholinergic relay in the periphery. Xen also delays gastric emptying, reduces food intake, induces gall bladder contractions, and increases gut motility and secretion from the exocrine pancreas, suggesting that some effects of Xen could be mediated by myenteric neurons (MENs). To determine whether Xen activates these neurons, MENs were isolated from guinea pig proximal small intestines. Cells expressed neuronal markers and exhibited typical neuron-like morphology with extensive outgrowths emanating from cell bodies. Cytosolic free Ca(2+) levels ([Ca(2+)](i)) were measured using Fura-2. ATP/UTP, KCl, and forskolin increased [Ca(2+)](i) in 99.6%, 92%, and 23% of the MENs imaged, respectively, indicating that they are functional and activated by nucleotide receptor signaling, direct depolarization, and cAMP. [Ca(2+)](i) increased in only 12.7% of MENs treated with Xen. This rise was blocked by pretreatment with EGTA, diazoxide, SR48692, and neurotensin. Thus the Xen-mediated increase in [Ca(2+)](i) involves influx of extracellular Ca(2+) and activation of neurotensin receptor-1 (NTSR1). Xen also increased acetylcholine release from MENs. Amylin, produced by β-and enteroendocrine cells, delays gastric emptying and increased [Ca(2+)](i) almost exclusively in Xen-responsive MENs. Immunohistochemistry demonstrated NTSR1 expression in human duodenal MENs. Thus myenteric rather than central neurons could mediate some effects of Xen and amylin.

Neurotensin and CRH interactions augment human mast cell activation

Stress affects immunity, but the mechanism is not known. Neurotensin (NT) and corticotropin-releasing hormone (CRH) are secreted under stress in various tissues, and have immunomodulatory actions. We had previously shown that NT augments the ability of CRH to increase mast cell-dependent skin vascular permeability in rodents. Here we show that NT triggered human mast cell degranulation and significantly augmented CRH-induced vascular endothelial growth factor (VEGF) release. Investigation of various signaling molecules indicated that only NF-κB activation was involved. These effects were blocked by pretreatment with the NTR antagonist SR48692. NT induced expression of CRH receptor-1 (CRHR-1), as shown by Western blot and FACS analysis. Interestingly, CRH also induced NTR gene and protein expression. These results indicate unique interactions among NT, CRH, and mast cells that may contribute to auto-immune and inflammatory diseases that worsen with stress.

Intrathecal administration of NTS1 agonists reverses nociceptive behaviors in a rat model of neuropathic pain

Chronic neuropathic pain arising from peripheral nerve damage is a severe clinical issue where there is a major unmet medical need. We previously demonstrated that both neurotensin (NT) receptor subtypes 1 (NTS1) and 2 (NTS2) are involved in mediating the naloxone-insensitive antinociceptive effects of neurotensin in different analgesic tests including hotplate, tail-flick, and tonic pain. However, the role of these receptors in neuropathic pain management has been poorly investigated. In the present study, we therefore examined whether intrathecal delivery of NTS1 agonists was effective in reducing neuropathic pain symptoms in rats. Neuropathy was induced by sciatic nerve constriction (CCI model), and the development of mechanical allodynia and thermal hyperalgesia on the ipsi- and contralateral hind paws was examined 3, 7, 14, 21, and 28 days post-surgery. CCI-operated rats exhibited significant increases in thermal and mechanical hypersensitivities over a 28-day testing period. Spinal injection of NT to CCI rats alleviated the behavioral responses to radiant heat and mechanical stimuli, with a maximal reversal of 91% of allodynia at 6 μg/kg. Intrathecal administration of the NTS1-selective agonist, PD149163 (30-90 μg/kg) also produced potent anti-allodynic and anti-hyperalgesic effects in nerve-injured rats. Likewise, heat hyperalgesia and tactile allodynia produced by CCI of the sciatic nerve were fully reversed by the NTS1 agonist, NT69L (5-25 μg/kg). Altogether, these results support the idea that the NTS1 receptor subtype is involved in pain modulation, and the potential use of NTS1 agonists for the treatment of painful neuropathies.

Neurotensin modulates pacemaker activity in interstitial cells of Cajal from the mouse small intestine

Neurotensin, a tridecapeptide localized in the gut to discrete enteroendocrine cells of the small bowel mucosa, is a hormone that plays an important role in gastrointestinal secretion, growth, and motility. Neurotensin has inhibitory and excitatory effects on peristaltic activity and produces contractile and relaxant responses in intestinal smooth muscle. Our objective in this study is to investigate the effects of neurotensin in small intestinal interstitial cells of Cajal (ICC) and elucidate the mechanism. To determine the electrophysiological effects of neurotensin on ICC, whole-cell patch clamp recordings were performed in cultured ICC from the small intestine. Exposure to neurotensin depolarized the membrane of pacemaker cells and produced tonic inward pacemaker currents. Only neurotensin receptor1 was identified when RT-PCR and immunocytochemistry were performed with mRNA isolated from small intestinal ICC and c-Kit positive cells. Neurotensin-induced tonic inward pacemaker currents were blocked by external Na⁺-free solution and in the presence of flufenamic acid, an inhibitor of non-selective cation channels. Furthermore, neurotensin-induced action is blocked either by treatment with U73122, a phospholipase C inhibitor, or thapsigargin, a Ca²⁺-ATPase inhibitor in ICC. We found that neurotensin increased spontaneous intracellular Ca²⁺ oscillations as seen with fluo4/AM recording. These results suggest that neurotensin modulates pacemaker currents via the activation of non-selective cation channels by intracellular Ca²⁺-release through neurotensin receptor1.

Changes in CNS response to neurotensin accompany the postpartum period in mice

Neurotensin (NT) is a highly conserved neuropeptide in mammals. Recent studies suggest that altered NT neurotransmission in postpartum females could promote the emergence of some maternal behaviors, including offspring protection. Here we evaluated how virgin and postpartum brains from mice selected for high maternal defense differ in response to NT. Virgin and postpartum mice were injected with either vehicle or 0.1 μg NT icv and brains were evaluated for c-Fos immunoreactivity, an indirect marker of neuronal activity. Using ANOVA analysis, common significant responses to NT were found in both female groups in four brain regions, including supraoptic nucleus, ventromedial nucleus, bed nucleus of stria terminalis dorsal, and a subregion of lateral septum (LS). For postpartum mice, only one additional region showed a significant response to NT relative to vehicle, whereas for virgin mice seven unique brain regions showed a significant c-Fos response: nucleus accumbens shell, paraventricular nucleus, central amygdala, and substantia nigra. Using a principal components analysis of c-Fos, we identified regions within each group with highly correlated activity. As expected, virgin and postpartum mice (vehicle conditions) showed different activity hubs and in the postpartum group the hubs matched regions linked to maternal care. The response to injected NT was different in the maternal and virgin groups with maternal mice showing a stronger coordinated activity in periaqueductal gray whereas virgin mice showed a stronger septal and amygdala linking of activity. Together, these results indicate neuronal responses of virgin and postpartum mice to NT and highlight pathways by which NT can alter maternal responses.

The role of NTS2 in the development of tolerance to NT69L in mouse models for hypothermia and thermal analgesia

NT69L is a neurotensin (NT)(8-13) analog that binds the two major NT receptors, NTS1 and NTS2, and elicits similar behavioral effects as endogenous NT. Tolerance develops rapidly to some, but not to all of NT69L's effects, and to date, little is known about the mechanisms responsible for this tolerance. The development of tolerance appears to be more prevalent in behavioral effects mediated by NTS1 than by those mediated by NTS2, including hypothermia and thermal analgesia. However, we hypothesize that both NTS1 and NTS2 have important roles in mediating the effects of NT69L. Here, we investigate the role of NTS2 on NT69L-mediated hypothermia and thermal analgesia with the use of NTS2 knock-out mice. We show that tolerance develops to NT69L-mediated hypothermia and thermal analgesia following sub-chronic treatment in wild-type (WT) mice, and that NTS2 is necessary for the development of that tolerance. Additionally, we suggest potential means by which NTS2 influences these NT69L-mediated behaviors.

Pancreatic cancer bears overexpression of neurotensin and neurotensin receptor subtype-1 and SR 48692 counteracts neurotensin induced cell proliferation in human pancreatic ductal carcinoma cell line PANC-1

The presence of neurotensin and neurotensin receptors has been demonstrated in human pancreatic carcinomas using autoradiography and Northern blot analysis. In vitro studies have reported that the neurotensin antagonist SR 48692 could inhibit the growth of MIA PaCa-2 cells in a neurotensin mediated fashion, and neurotensin could overcome this inhibition or stimulate proliferation. However, it is currently unknown whether such actions are exerted on PANC-1 cells. In addition, the immunolocation of neurotensin and neurotensin receptors is still unclear in human pancreatic ductal carcinoma tissues. Immunohistochemistry was applied to detect the distribution of neurotensin and neurotensin receptor subtype-1 in human pancreatic ductal carcinoma and normal pancreatic tissues. Furthermore, an in vitro study was carried out to test the pharmacological profile of neurotensin and SR 48692 in human pancreatic ductal carcinoma cell line PANC-1. Compared with normal pancreatic tissues, pancreatic ductal carcinoma tissues have higher neurotensin and neurotensin receptor subtype-1 expression rates. Pancreatic ductal carcinomas (32/40) bear the expression of both neurotensin and neurotensin receptor subtype-1. We observed that neurotensin (10⁻¹¹-10⁻⁷ M) significantly stimulated the proliferation of PANC-1 and SR 48692 (10⁻¹¹-10⁻⁷ M) alone had no effect on the growth of PANC-1 cells; however, SR 48692 (10⁻¹⁰-10⁻⁶ M) inhibited the stimulatory effect of neurotensin (10⁻⁹ M). Considering the overexpression of both neurotensin and neurotensin receptor subtype-1 in pancreatic ductal carcinomas, it could enable us to develop markers for pancreatic cancer diagnosis. As SR 48692 could inhibit neurotensin induced cell growth, neurotensin receptor subtype-1 may serve as a therapeutic target for the therapy of pancreatic carcinomas. Furthermore, our study indicates that the counteraction of neurotensin and neurotensin receptor subtype-1 regulates the genesis and development of pancreatic carcinomas.

Neurotensin triggers dopamine D2 receptor desensitization through a protein kinase C and beta-arrestin1-dependent mechanism

The peptide neurotensin (NT) is known to exert a potent excitatory effect on the dopaminergic system by inhibiting D2 dopamine (DA) receptor (D2R) function. This regulation is dependent on activation of PKC, a well known effector of the type 1 NT receptor (NTR1). Because PKC phosphorylation of the D2R has recently been shown to induce its internalization, we hypothesized that NT acts to reduce D2R function through heterologous desensitization of the D2R. In the present study, we first used HEK-293 cells to demonstrate that NT induces PKC-dependent D2R internalization. Furthermore, internalization displayed faster kinetics in cells expressing the D2R short isoform, known to act as an autoreceptor in DA neurons, than in cells expressing the long isoform, known to act as a postsynaptic D2R. In patch clamp experiments on cultured DA neurons, overexpression of a mutant D2S lacking three key PKC phosphorylation sites abrogated the ability of NT to reduce D2R-mediated cell firing inhibition. Short interfering RNA-mediated inhibition of β-arrestin1 and dynamin2, proteins important for receptor desensitization, reduced agonist-induced desensitization of D2R function, but only the inhibition of β-arrestin1 reduced the effect of NT on D2R function. Taken together, our data suggest that NT acutely regulates D2 autoreceptor function and DA neuron excitability through PKC-mediated phosphorylation of the D2R, leading to heterologous receptor desensitization.

Molecular characterization of structure and tissue distribution of chicken neurotensin receptor

Neurotensin, a tridecapeptide, is distributed in a wide range of tissues and exhibits multiple functions through its receptors. Hitherto molecular characterization of the neurotensin receptor has been reported in mammalian, amphibian, and fish species but not in avian species. In this study, we cloned the cDNA encoding chicken neurotensin receptor from the duodenum and characterized its primary structure, biological activity and distribution in the gastrointestinal tract. The cDNA encoded a protein consisting of 399 amino acids that had significant overall sequence homology to other vertebrate neurotensin receptor 1 with higher extent in the seven transmembrane domains. Chicken neurotensin increased intracellular Ca(2+) concentrations in human embryonic kidney 293 cells transiently expressing the chicken neurotensin receptor 1. Real-time PCR analysis showed that chicken neurotensin receptor 1 mRNA is expressed throughout the gastrointestinal tract with markedly higher level in the colon/rectum. These results indicate that the chicken neurotensin receptor 1 is involved in gastrointestinal functions through an intracellular signaling pathway accompanied by an increase in Ca(2+) levels.

A neurotensin analog, NT69L, attenuates intravenous nicotine self-administration in rats

NT69L is a neurotensin analog that blocks nicotine-induced locomotor activity and has sustained efficacy in a rat model of nicotine-induced sensitization when administered peripherally. Additionally, NT69L attenuates food-reinforcement in rats. The present study tested the effect of acute administration of NT69L on nicotine self-infusion in Sprague-Dawley rats. Rats were trained to self-infuse nicotine intravenously (0.03mg/kg per infusion) following operant training. Once the rats acquired stable responding to nicotine self-infusion they were pretreated with NT69L (1mg/kg, i.p.) or saline 30min before being assessed for nicotine self-infusion. Pretreatment with NT69L significantly attenuated nicotine self-infusion under FR1 (fixed ratio of 1) and FR5 schedule of reinforcement as compared to saline pretreatment. Control rats that were response-independent "yoked" as well as rats that self-infused saline or NT69L showed minimal responses, indicating that nicotine served as a reinforcer. Additionally, NT69L modulated serum corticosterone; brain norepinephrine serotonin; and dopamine receptors mRNA levels altered in the nicotine self-infused rats after a 24h withdrawal period. Pretreatment with NT69L significantly decreased the nicotine-induced increase in serum corticosterone levels and striatal norepinephrine and increased the nicotine-induced reduction in serotonin in both the striatum and the prefrontal cortex (PFC). NT69L might modulate dopamine neurotransmission implicated in the reinforcing effects of nicotine by modulating tyrosine hydroxylase and dopamine receptor mRNA levels in the PFC and striatum. These data support further study of the effects of NT analogs on attenuating the reinforcing effects of psychostimulants.

Bombesin and neurotensin exert antiproliferative effects on oval cells and augment the regenerative response of the cholestatic rat liver

The regenerative capacity of the cholestatic liver is significantly attenuated. Oval cells are hepatic stem cells involved in liver's regeneration following diverse types of injury. The present study investigated the effect of the neuropeptides bombesin (BBS) and neurotensin (NT) on oval cell proliferation as well as on hepatocyte and cholangiocyte proliferation and apoptosis in the cholestatic rat liver. Seventy male Wistar rats were randomly divided into five groups: controls, sham operated, bile duct ligated (BDL), BDL+BBS (30 μg/kg/d), BDL+NT (300 μg/kg/d). Ten days later, alpha-fetoprotein (AFP) mRNA (in situ hybridization), cytokeratin-19 and Ki67 antigen expression (immunohistochemistry) and apoptosis (TUNEL) were evaluated on liver tissue samples. Cells with morphologic features of oval cells that were cytokeratin-19(+) and AFP mRNA(+) were scored in morphometric analysis and their proliferation was recorded. In addition, the proliferation and apoptotic rates of hepatocytes and cholangiocytes were determined. Alanine aminotransferase (ALT) levels and hepatic oxidative stress (lipid peroxidation and glutathione redox state) were also estimated. The neuropeptides BBS and NT significantly reduced ALT levels and hepatic oxidative stress. Both agents exerted similar and cell type-specific effects on oval cells, hepatocytes and cholangiocytes: (a) oval cell proliferation and accumulation in the cholestatic liver was attenuated, (b) hepatocyte proliferation was increased along with a decreased rate of their apoptosis and (c) cholangiocyte proliferation was attenuated and their apoptosis was increased. These observations might be of potential value in patients with extrahepatic cholestasis.

[Effect of dipeptide neurotensin analog dilept on extracellular concentrations of glutamate, GABA and HVA in N. accumbens of rat brain]

The influence of dilept (GZR-123, N-caproyl-L-prolyl-L-tyrosine methyl ester)--a dipeptide analog of neurotensin (NT)--on extracellular concentration of glutamate, gamma-aminobutyric acid (GABA) and homovanillic acid (HVA) in n. accumbens of Wistar rats has been studied. By means of microdialysis, it was shown that dilept increases the concentrations of glutamate and GABA and decreases the HVA content in n. accumbens. These effects of dilept are similar to those produced by NT introduced into n. accumbens. Thus, dilept can be considered as a systemically active dipeptide analog of NT, which is capable of modulating the dysbalance of glutamate-, GABA-, and dopaminergic systems of n. accumbens. These neurochemical data taken together with previously established behavioral effects of dilept suggest that this dipeptide is a potential antipsychotic drug.

[Emotional state variations in rats during recall of passive avoidance reactions after neurotensin administration into nucleus accumbens of the brain]

Behavioral effects of neurotensin administration into the nucleus accumbens were studied in rats with neurotoxic lesions of serotoninergic structures of the dorsal raphe nucleus or periaqueductal grey matter. Changes in recall of passive avoidance conditioned reactions and aftereffects of painful stimulation in the locomotor activity were studied in the "open field" and elevated plus-maze and T-maze tests. The toxin administration into the dorsal raphe nucleus did not impair the recall of the passive avoidance reactions, but enhanced the oppressive aftereffects of painful stimulation, which can specify the development of anxiety in rats. The toxin administration into the periaqueductal grey matter had an opposite effect, which can be considered as a manifestation of the panic state. Neurotensin weakened the above mentioned effects of the toxin and, depending on the evoked emotional disorders, produced the anxiolytic or antipanic effects.

Evaluation of the degradation and metabolic effects of the gut peptide xenin on insulin secretion, glycaemic control and satiety

Recently, glucagon-like peptide 1 (GLP1) and glucose-dependent insulinotropic polypeptide (GIP) have received much attention regarding possible roles in aetiology and treatment of type 2 diabetes. However, peptides co-secreted from the same enteroendocrine cells are less well studied. The present investigation was designed to characterise the in vitro and in vivo effects of xenin, a peptide co-secreted with GIP from intestinal K-cells. We examined the enzymatic stability, insulin-releasing activity and associated cAMP production capability of xenin in vitro. In addition, the effects of xenin on satiety, glucose homoeostasis and insulin secretion were examined in vivo. Xenin was time dependently degraded (t(1/2)=162±6 min) in plasma in vitro. In clonal BRIN-BD11 cells, xenin stimulated insulin secretion at 5.6 mM (P<0.05) and 16.7 mM (P<0.05 to P<0.001) glucose levels compared to respective controls. Xenin also exerted an additive effect on GIP, GLP1 and neurotensin-mediated insulin secretion. In clonal β-cells, xenin did not stimulate cellular cAMP production, alter membrane potential or elevate intra-cellular Ca(2)(+). In normal mice, xenin exhibited a short-acting (P<0.01) satiety effect at high dosage (500 nmol/kg). In overnight fasted mice, acute injection of xenin enhanced glucose-lowering and elevated insulin secretion when injected concomitantly or 30 min before glucose. These effects were not observed when xenin was administered 60 min before the glucose challenge, reflecting the short half-life of the native peptide in vivo. Overall, these data demonstrate that xenin may have significant metabolic effects on glucose control, which merit further study.

Activation of Na+/H+ exchanger 1 by neurotensin signaling in pancreatic cancer cell lines

Acidosis commonly observed in solid tumors like pancreatic cancer promotes genetic instability and selection of a more malignant phenotype of cancer cells. Overexpression or activation of integral membrane proteins mediating H+ efflux may contribute to extracellular acidification. Neurotensin (NT) induces intracellular alkalinization and stimulates interleukin-8 production in pancreatic cancer cells and, as demonstrated here, the stable NT analog Lys(8)-psi-Lys(9)NT(8-13) enhances the amiloride-sensitive, Na+-dependent transmembrane H+ flux by a factor of 2.05+/-0.28 and 2.69+/-0.07 in BxPC-3 and PANC-1 pancreatic cancer cells, respectively, by phosphorylation of the Na+/H+ exchanger 1 (NHE1). Human genome-wide gene expression analysis was performed to detect effects of Lys(8)-psi-Lys(9)NT(8-13) on BxPC-3 cells. Results indicated upregulation of genes involved in regulation of NHE1, hypoxic response and glycolysis in response to Lys(8)-psi-Lys(9)NT(8-13) even under normoxic conditions. Therefore, our findings suggest that growth factors like NT may be implicated in the early progression of pancreatic cancer by localized acidification and induction of an aerobic glycolytic phenotype with higher metastatic potential in small cell aggregates.

Effect of intracerebroventricular infusion of neurotensin in glucose-dependent insulinotropic peptide secretion in dogs

GIP is a major physiological component of the enteroinsular axis. Several researchers have pointed to a neural regulation of GIP secretion. We have previously studied the effect of intracerebroventricular (icv) infusion of insulin, NPY and bombesin in the regulation of GIP secretion. The aim of the present study is to evaluate a possible role of neurotensin in neural regulation of GIP secretion. Thirty-two adult dogs were used in this study. In a dose-response study (experiment 1) we used 3 different doses of neurotensin (25, 50 and 100microg) in a bolus icv infusion. In experiment 2 the animals received a bolus icv infusion of 50microg neurotensin and an equivalent amount of artificial cerebrospinal fluid (aCSF) at 1-week interval. In experiment 3 the animals received a continuous icv infusion of neurotensin at a constant rate of 1microg/kg/h and aCSF over a 3-h period, at 1-week interval. In experiment 4 the experiment of group 3 was repeated with a simultaneous intraduodenal infusion of a glucose load through the Mann-Bollman fistula. Plasma levels of glucose, insulin and GIP were assayed.

RESULTS

Bolus and continuous icv infusion of neurotensin produced a significant increase in glucose, GIP and insulin levels. In the 4th experiment icv infusion of neurotensin produced a more prominent increase of glucose and insulin levels compare to infusion of aCSF. GIP levels were lower after infusion of neurotensin compared to aCSF.

CONCLUSIONS

Our data suggest a differential effect of neurotensin on GIP secretion, dependent on the energy load.

Physiological studies on neurotensin in rat small bowel isografts

BACKGROUND/AIMS

The cause of dysmotility in the small intestine of patients with small bowel transplantation (SBT) is still unknown. It is established that neurotensin (NT) is released by stimulation of non-adrenergic non-cholinergic (NANC) excitatory nerves. It is considered that the ileum is more important than the jejunum in regard to digestive functions. In order to evaluate the intestinal function of rat ileal isografts, this study examined the enteric nerve responses to electrical field stimulation (EFS) and NT in the isografted rat ileum, using the normal ileum as a control.

METHODOLOGY

Orthotopic entire small bowel transplantation (SBT) with portocaval drainage was performed from Lewis rats to Lewis rats. Grafted tissue specimens were obtained 130 days after SBT (n = 8). As controls, normal segments of the ileum were obtained from untransplanted Lewis rats (n = 20). A mechanograph was used to evaluate in vitro ileal responses to electrical field stimulation (EFS) of the adrenergic and cholinergic nerve before and after treatments with various autonomic nerve blockers and NT.

RESULTS

All ileal muscle strips used in the present studies responded to EFS before and after the blockade of both the adrenergic and cholinergic nerves. The intrinsic innervation contains both excitatory (cholinergic and NANC excitatory nerves) and inhibitory nerves (adrenergic and NANC inhibitory nerves) in the normal and isografted ileum of LEW rats. Excitatory nerves, especially NANC excitatory nerves, were more dominant in the isografted ileum than in the normal ileum (P < 0.001). NANC inhibitory nerves were found to act on the normal ileum and to a greater extent in the isografted ileum (P < 0.05). NT mediates the contraction reaction of NANC excitatory nerve in the normal ileum and to a greater extent in the isografted ileum (P < 0.05).

CONCLUSIONS

Contraction reactions of NT were observed in both the normal and isografted ileum, but were increased in the isografted ileum. The increase of the NT in mediating NANC excitatory nerves and decrease of the NANC inhibitory nerves may be largely related to the peristaltic abnormalities seen in the isografted LEW rat ileum.

Neurotensin modulation of acetylcholine, GABA, and aspartate release from rat prefrontal cortex studied in vivo with microdialysis

The effects of the peptide transmitter neurotensin (NT) on the release of acetylcholine (ACh), gamma-aminobutyric acid (GABA), glutamate (Glu), aspartate (Asp), and taurine from the prefrontal cortex (PFC) of freely moving rats were studied by transversal microdialysis. Neurotensin (0.2 and 1 microM) administered locally in the PFC produced a concentration-dependent increase in the extracellular levels of ACh, GABA, and Asp, but not of Glu or taurine. The increase produced by 1 microM NT reached a maximum of about 240% for ACh, 370% for GABA, and 380% for Asp. Lower doses of NT (0.05 microM) did not cause a significant change in ACh, GABA, or Asp output in the PFC. Higher concentrations of NT (2 microM) did not induce further increases in the level of neurotransmitters. A high-affinity selective neurotensin receptor (NTR1) antagonist SR 48692 (0.5 microM) perfused locally blocked neurotensin (1 microM)-evoked ACh, GABA, and Asp release. Local infusion of the sodium channel blocker tetrodotoxin (TTX) (1 microM) decreased the release of ACh, had no significant effect on GABA or Asp release, and prevented the 1 microM neurotensin-induced increase in ACh, GABA, and Asp output. Removal of calcium from the Ringer's solution prevented the peptide from having any effects on the neurotransmitters. Thus, in vivo NT plays a modulatory role in the PFC by interacting with cortical neurons releasing GABA and Asp and with ACh-containing neurons projecting to the PFC. The NT effects are of neural origin, as they are TTX-sensitive, and mediated by the NTR1 receptor, as they are antagonized by SR 48692.

Neurotensin in the ventral pallidum increases extracellular gamma-aminobutyric acid and differentially affects cue- and cocaine-primed reinstatement

Cocaine-primed reinstatement is an animal model of drug relapse. The neurocircuitry underlying cocaine-primed reinstatement includes a decrease in GABA in the ventral pallidum (VP) that is inhibited by a mu opioid receptor antagonist, suggesting that opioid peptides colocalized with GABA in the projection from the nucleus accumbens to the VP may mediate this effect. Neurotensin is also colocalized with GABA and has been shown to increase GABA release in several brain regions. Therefore, the present study determined whether neurotensin increases GABA release in the VP, antagonizes cocaine-induced decreases in GABA, and prevents reinstatement of cocaine seeking. In vivo microdialysis revealed that the neurotensin agonist neurotensin peptide fragment 8-13 [NT(8-13)] increased GABA in the VP in a neurotensin receptor and tetrodotoxin-dependent manner and blocked the cocaine-induced decrease in GABA. NT(8-13) (3 nmol) microinjected into the VP prevented cue-induced reinstatement without affecting cocaine self-administration. In contrast, 3 nmol NT(8-13) potentiated cocaine-primed reinstatement. The neurotensin antagonist SR142948 (2-[[[5-(2,6-dimethoxyphenyl)-1-[4-[[[3-(dimethylamino)propyl]methylamino]carbonyl]-2-(1-methylethyl)phenyl]-1H -pyrazol-3-yl]carbonyl]amino]-tricyclo-[3.3.1.13,7]decane-2-carboxylic acid) had no effect on any behavioral measure when infused in the VP at the dose tested but attenuated cocaine-primed reinstatement when administered systemically. In contrast to reinstatement, NT(8-13) did not alter the motor response to acute cocaine or the development of motor sensitization by chronic cocaine. Three conclusions can be drawn from these data: 1) neurotensin promotes GABA release in the VP and correspondingly inhibits cue-induced reinstatement, 2) neurotensin and cocaine interact in a manner that countermands the neurotensin-induced increase in GABA and promotes reinstatement, and 3) endogenous release of neurotensin in the VP is not necessary for reinstatement.

PKD, PKD2, and p38 MAPK mediate Hsp27 serine-82 phosphorylation induced by neurotensin in pancreatic cancer PANC-1 cells

It is widely recognized that Hsp27 is a downstream substrate of the p38 MAPK cascade whereas the role of PKD family members in mediating receptor-stimulated Hsp27 Ser-82 phosphorylation has not been evaluated. Here, we show that neurotensin induced a rapid and striking increase in Hsp27 Ser-82 phosphorylation in PANC-1 cells, which was closely correlated with stimulation of activation loop phosphorylation of PKDs and p38 MAPK Thr180/Tyr182 phosphorylation. Treatment of PANC-1 cells with either the selective PKC inhibitor GF-I or the p38 MAPK inhibitor SB202190 partially reduced neurotensin-induced Hsp27 Ser-82 phosphorylation. However, treatment of the cells with a combination of GF-I and SB202190 virtually abolished neurotensin-induced Hsp27 Ser-82 phosphorylation. Overexpression of PKD in stably transfected PANC-1 cells increased the magnitude and prolonged the duration of Hsp27 Ser-82 phosphorylation in response to neurotensin. Either PKD or PKD2 gene silencing utilizing siRNAs targeting distinct PKD or PKD2 sequences reduced neurotensin-stimulated Hsp27 Ser-82 phosphorylation, but cotransfection of siRNAs targeting both, PKD and PKD2, markedly decreased neurotensin-induced Hsp27 Ser-82 phosphorylation. Knockdown of PKD and PKD2 abolished Hsp27 phosphorylation in cells treated with SB202190. Thus, neurotensin induces Hsp27 Ser-82 phosphorylation through p38 MAPK- and PKC/PKD-dependent pathways in PANC-1 cells. Our results demonstrate, for the first time, that neurotensin induces a striking increase in Hsp27 phosphorylation on Ser-82 in PANC-1 cells through convergent p38 MAPK, PKD, and PKD2 signaling.

Neurotensin is a versatile modulator of in vitro human pancreatic ductal adenocarcinoma cell (PDAC) migration

Background: While the neurotensin (NT) roles in pancreatic cancer growth are well documented, its effects on pancreatic cancer cell migration have not been described. Methods: The NT-induced effects on the migration process of human pancreatic ductal adenocarcinoma cells (PDACs) were characterized by means of various assays including computer-assisted video-microscopy, fluorescence microscopy, ELISA-based, small GTPase pull-down and phosphorylation assays. Results: The NT-induced modifications on in vitro PDACs migration largely depended on the extra-cellular matrix environment and cell propensity to migrate collectively or individually. While NT significantly reduced the level of migration of collectively migrating PDACs on vitronectin, it significantly increased the level of individually migrating PDACs. These effects were mainly mediated through the sortilin/NTR3 receptor. Neurotensin both induced altered expression of αV and β5 integrin subunits in PDACs cultured on vitronectin resulting in modified adhesion abilities, and caused modifications to the organization of the actin cytoskeleton through the NT-mediated activation of small Rho GTPases. While the NT effects on individually migrating PDACs were mediated at least through the EGFR/ERK signaling pathways, those on collectively migrating PDACs appeared highly dependent on the PI 3-kinase pathway. Conclusion: This study strongly suggests the involvement of neurotensin in the modulation of human PDAC migration.

Time course of the hypothermic response to continuously administered neurotensin

Intracerebroventricular administration of the tridecapeptide neurotensin is known to elicit hypothermia in rodents for few hours. In the present study, we investigated a continuous intracerebroventricular infusion regimen for prolongation of the hypothermic effect. Male Wistar-Han rats (n=13) received neurotensin 10-50 microg/h for 48 h, while their body temperature was monitored continuously. This protocol led to a dose-dependent decrease of body temperature down to 35-36 degrees C. The nadir of hypothermia lasted for approximately 4h and normothermia was re-established after 12-24h. Furthermore, abundance of neurotensin in the hypothalamus was determined after 6 and 30 h by western blotting. High levels were still found at 30 h, while the rats had already become normothermic at that time. In summary, continuous infusion of neurotensin led to prolongation of the known hypothermic response, however resulted in development of tolerance.

Evidence that neurotensin mediates postprandial intestinal hyperemia in the python, Python regius

Digestion of large meals in pythons produces substantial increases in heart rate and cardiac output, as well as a dilation of the mesenteric vascular bed leading to intestinal hyperemia, but the mediators of these effects are unknown. Bolus intra-arterial injections of python neurotensin ([His3, Val4, Ala7]NT) (1 − 1,000 pmol/kg) into the anesthetized ball python Python regius ( n = 7) produced a dose-dependent vasodilation that was associated with a decrease in systemic pressure (Psys) and increase in systemic blood flow (Qsys). There was no effect on pulmonary pressure and conductance. A significant ( P < 0.05) increase in heart rate ( fH) and total cardiac output (Qtot) was seen only at high doses (>30 pmol/kg). The systemic vasodilation and increase in Qtot persisted after β-adrenergic blockade with propranolol, but the rise in fH was abolished. Also, the systemic vasodilation persisted after histamine H2-receptor blockade. In unanesthetized pythons ( n = 4), bolus injection of python NT in a dose as low as 1 pmol/kg produced a significant increase in blood flow to the mesenteric artery (177% ± 54%; mean ± SE) and mesenteric conductance (219% ± 74%) without any increase in Qsys, systemic conductance, Psys, and fH. The data provide evidence that NT is an important hormonal mediator of postprandial intestinal hyperemia in the python, but its involvement in mediating the cardiac responses to digestion may be relatively minor.

Neurotensin-produced antinociception in the rostral ventromedial medulla is partially mediated by spinal cord norepinephrine

Microinjection of neurotensin (NT) into the rostral ventromedial medulla (RVM) produces dose-dependent antinociception. Here we show that antinociception produced by intra-RVM microinjection of neurotensin (NT) or the selective NT receptor subtype 1 (NTR1) agonist PD149163 can be partially blocked by intrathecal (i.t.) yohimbine, an alpha2-adrenoceptor antagonist and by methysergide, a serotonin receptor antagonist. Antinociception produced by the NTR2 agonist beta-lactotensin (beta-LT) is blocked by intrathecal (i.t.) yohimbine, but not by methysergide i.t. It is not known which noradrenergic cell group is involved in this newly identified noradrenergic component of NTR-mediated antinociception. These experiments provide the first evidence that selective activation of NTR2 in the RVM produces antinociception. These results also provide evidence that activation of NTR1 in the RVM produces antinociception through spinal release of norepinephrine (NE) and serotonin, and that activation of NTR2 in the RVM produces antinociception mediated by spinal release of NE.