Neurotensin Concentrations Research Articles

The effects of glutamate receptor agonists on neurotensin release using in vivo microdialysis

In the present study, extracellular concentrations of neurotensin were measured from the striatum, nucleus accumbens and the medial prefrontal cortex in the awake, freely moving rat. Using a highly sensitive solid phase radioimmunoassay, basal concentrations of neurotensin were 2–5 pg/sample. In each region, glutamate receptor agonists, N-methyl-d-aspartate (NMDA) and kainic acid, increased neurotensin release 2–3-fold. Preincubation with the Na+ channel blocker tetrodotoxin abolished the glutamate receptor agonist-induced increases except in the striatum following kainic acid infusion. These findings indicate that activation of glutamate receptors may indirectly stimulate neurotensin release.

The effects of acute antipsychotic drug administration on the neurotensin system of the developing rat brain

The effects of antipsychotic drugs on the neurotensin (NT) system have been well characterized in adult male animals. There is considerable evidence that the NT system undergoes distinct age-related changes during development of the rat brain. This observation in conjunction with antipsychotic pharmacotherapy in children and breast feeding women led us to characterize the effects of antipsychotic drug administration in neonatal rats. The effects of a single subcutaneous injection of haloperidol (2.0 mg/kg) on the developing NT system were determined between postnatal days 10 and 21. Haloperidol significantly increased NT/neuromedin N (NT/NN) mRNA expression and NT concentrations in the caudate/putamen as early as postnatal day 10. Haloperidol did not increase NT/NN mRNA expression in the nucleus accumbens until postnatal day 15 and did not increase NT concentrations in this brain region until postnatal day 21. These results demonstrate that there is a critical time point in development before which the NT system does not respond to antipsychotic drug administration in the same manner as the mature rat.

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 γ-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.

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

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

Effect of chronic intraperitoneal injections of leptin on hypothalamic neurotensin content and food intake

This study was intended for the investigation of the effects of chronic injections of leptin for 7 days on food intake and hypothalamic neurotensin (NT). Leptin treatment significantly reduced food intake [144.3±2.5 g (L) vs. 156.7±2.5 g (C); P=0.002] and body weight gain [23.7 g±1.0 g (L) vs. 31.5±1.3 g (C); P=0.003]. NT concentration was lower in the lateral hypothalamus (LH) of leptin-treated rats than in the control ad libitum fed rats (−30%; P<0.05). The same diminution was observed in pair-fed rats (−27%; P<0.05). This diminution was therefore related to the decrease in food intake rather than to a direct effect of leptin. As the LH was the only area where NT was modified, it appears that among the hypothalamic nuclei involved in the regulation of feeding behavior it is the most sensitive area to a low energy depletion. Therefore, it might play a specific role in triggering the mechanisms necessary to restore body weight and/or energy balance.

Neurotensin inhibits neuronal Na +, K +-ATPase activity through high affinity peptide receptor

Neurotensin is a peptide present in mammalian CNS and peripheral tissues, which may play a major role in neurotransmission or neuromodulation, subserving diverse physiological functions. We studied the effect of added neurotensin on ATPase activities in synaptosomal membranes isolated from rat cerebral cortex. Neurotensin at 3 × 10 −8–3 × 10 −6 M concentration decreased 20–44% Na +, K +-ATPase activity but failed to modify Mg 2+-ATPase activity; lower neurotensin concentrations (3 × 10 −14–3 × 10 −10 M) had no effect on enzyme activities. This inhibitory effect was abolished by neurotensin heating, by enzyme preincubation with neurotensin during periods exceeding 10 min, or by adding 1 × 10 −6 M SR 48692, a high affinity neurotensin receptor antagonist. Levocabastine, which blocks low affinity neurotensin receptor, failed to alter enzyme inhibition by the peptide. It is suggested that the sodium pump may be a target for neurotensin effects at neuronal level involving the participation of high affinity neurotensin receptor.

G protein-coupled receptor signaling in human ductal pancreatic cancer cells: Neurotensin responsiveness and mitogenic stimulation

Neuropeptides and their corresponding G protein-coupled receptors (GPCRs) are increasingly implicated in the autocrine/paracrine stimulation of growth of human cancers. We report that neurotensin induced rapid Ca2+ mobilization from intracellular stores followed by Ca2+ influx in five human ductal pancreatic cancer cell lines: HPAF-II, Capan-1, Capan-2, PANC-1, and MIA PaCa-2. In addition, most cell lines exhibited Ca2+ responses to multiple neuropeptides including bombesin, bradykinin, cholecystokinin, and vasopressin and to bioactive lipids, including lysophosphatidic acid (LPA), that also act via GPCRs. The well-differentiated line HPAF-II responded to at least seven independent GPCR agonists. The concentrations of neurotensin required to induce half-maximal effects (EC50) in HPAF-II and PANC-1 cells were 5 and 8nM, respectively. Digital fluorescence image analysis to measure Ca2+ responses in single cells revealed that 90% or more of HPAF-II and PANC-1 cells responded to 10nM neurotensin. Addition of neurotensin to PANC-1 cells also induced rapid and dose-dependent extracellular-regulated protein kinase (ERK-1 and ERK-2) activation and subsequently, stimulated DNA synthesis. The signaling complexity of GPCRs uncovered by these studies reveals a new aspect in the biology of human pancreatic cancer and could offer the basis for new approaches to the treatment of this disease.

On the role of gastrin-releasing peptide in meal-stimulated exocrine pancreatic secretion.

The contribution of gastrin-releasing peptide (GRP) in the physiologic pancreatic response to a meal is unknown. We therefore investigated whether immunoneutralization of GRP could influence the exocrine pancreatic response to a meal as well as plasma concentrations of the peptide hormones neurotensin (NT) and cholecystokinin (CCK). Modified Herrera fistulas were implanted in five mongrel dogs. After a standard meal, we analyzed plasma NT, CCK, and GRP, and protein and enzyme (amylase, lipase, trypsin) content of exocrine pancreatic juice. An unspecific rabbit immunoglobulin solution was administered intravenously as a control. This experiment was repeated with a specific anti-GRP-immunoglobulin. The i.v. administration of the anti-GRP-antibody significantly inhibited meal-stimulated pancreatic secretion. Integrated protein output decreased from 58.4 to 36.8 g/180 min (p < 0.05), as did amylase (2,102 to 1,145 KU/180 min; p < 0.05), lipase (2,258 to 1,172 KU/180 min; p < 0.05), and trypsin (5,321 to 4,990 U/180 min). Postprandially released NT decreased from 8,271 to 5,825 pmol/180 min (p < 0.05). In contrast, integrated amounts of CCK remained relatively stable with 473 to 611 pmol/180 min. The neuropeptide GRP is one of the biologically important regulatory factors influencing meal-stimulated pancreatic secretion, as well as the postprandial plasma level of the peptide hormone NT in the dog. These mentioned effects of postprandially released GRP seem not to be mediated by CCK in an endocrine manner.

Neurotensin studies in alcohol naive, preferring and non-preferring rats

Neurotensin is a tridecapeptide, present in the central nervous system and the gastrointestinal tract in man and animals. Previous studies in mice selectively bred for differences in hypnotic sensitivity to ethanol have provided data to suggest that neurotensinergic systems may mediate differences in ethanol's actions in these animals. The present study sought to determine if brain neurotensin levels differed between two lines of rats which have been selectively bred for alcohol preferring or non-preferring behaviors. In addition, electroencephalographic and event-related potential responses to intracerebroventricular saline and neurotensin (10 or 30 μg) were evaluated between the rat lines. Similar to human subjects at high genetic risk for alcoholism, preferring rats were found to have more electroencephalographic fast frequency activity and lowered amplitude of the P3 component of the event-related potential in cortical sites under the saline condition. Overall, electrophysiological response to neurotensin, in the two rats lines, was substantially similar to what has been reported previously in outbred Wistar rats, and consisted of dose-related decreases in overall electroencephalographic spectral power concomitant with increases in amplitude and decreases in the latency of the N1 component of the event-related potential. However, differences in neurotensin responses between the preferring and non-preferring rat lines were also found. The differences in electroencephalographic high-frequency activity and in P3 amplitude seen between the rat lines under control conditions were eliminated by administration of neurotensin. In addition, preferring rats appeared to be more sensitive to neurotensin-induced increases in N1 amplitude. Brain neurotensin concentrations were also found to differ between the lines. Significantly lower concentrations of neurotensin were found in the frontal cortex of preferring rats when compared to non-preferring rats or outbred Wistars. Taken together, these studies suggest that differences in the regulation of neurotensin neurons may contribute to the expression of behavioral preference for ethanol consumption in selective rat lines. Additionally, drugs targeting the neurotensinergic system may plausibly be of utility in the treatment of alcoholism.

Neuroendocrine Peptides in Stomach and Colon of an Animal Model for Human Diabetes Type I

Twelve prediabetic and 12 diabetic non-obese diabetic (NOD) mice, all females aged 22–24 weeks, were investigated. As controls, 12 BLAB/cJ Bom mice of the same age and gender as the NOD mice were used. The concentration of several neuroendocrine peptides was determined by radioimmunoassay of tissue extracts of transmural specimens of antrum and distal colon. The neuroendocrine peptides investigated were peptide YY (PYY), somatostatin, vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), neurotensin, and galanin. In the antrum, VIP, NPY, and galanin concentrations were all significantly lower in prediabetic and diabetic NOD mice than in controls. There was no statistical difference between NOD mice and controls regarding neurotensin content. In the colon, the concentrations of PYY, somatostatin, VIP, NPY, and galanin were lower in prediabetic and diabetic NOD mice than in controls. The concentration of neurotensin in prediabetic, but not in diabetic NOD mice was lower than that of controls. The present observations support the previously reported studies on animal models for human type I diabetes that the neuroendocrine system of the gut is disturbed. It also shows that the neuroendocrine system of the stomach and large intestine is affected. The present findings may have some implications for the gastrointestinal dysfunction observed in patients with human type I diabetes.

Differential responses by neurotensin systems in extrapyramidal and limbic structures to ibogaine and cocaine

Ibogaine (Endabuse™) is a psychoactive indole alkaloid found in the West African shrub, Tabernanthe iboga. This drug interrupts cocaine and amphetamine abuse and has been proposed for treatment of addiction to these stimulants. However, the mechanism of action that explains its pharmacological properties is unclear. Since previous studies demonstrated differential effects of psychotomimetic drugs (cocaine and methamphetamine) on neuropeptides such as neurotensin (NT), the present study was designed to determine: (1) the effects of ibogaine on striatal, nigral, cortical, and accumbens neurotensin-like immunoreactivity (NTLI); (2) the effects of selective dopamine antagonists on ibogaine-induced changes in NT concentrations in these brain areas; and (3) the effects of ibogaine pretreatment on cocaine-induced changes in striatal, nigral, cortical and accumbens NTLI content. Ibogaine treatments profoundly affected NT systems by increasing striatal, nigral, and accumbens NTLI content 12 h after the last drug administration. In contrast, NTLI concentrations were not significantly increased in the frontal cortex after ibogaine treatment. The ibogaine-induced increases in NTLI in striatum, nucleus accumbens and substantia nigra were blocked by coadministration of the selective D 1 receptor antagonist, SCH 23390. The D 2 receptor antagonist, eticlopride, blocked the ibogaine-induced increase in nigral NTLI, but not in striatum and nucleus accumbens. Ibogaine pretreatment significantly blocked the striatal and nigral increases of NTLI resulting from a single cocaine administration. Whereas many of the responses by NT systems to ibogaine resembled those which occur after cocaine, there were also some important differences. These data suggest that NT may contribute to an interaction between ibogaine and the DA system and may participate in the pharmacological actions of this drug.

How Age Changes the Content of Neuroendocrine Peptides in the Murine Gastrointestinal Tract

Background: Motility disorders in the gastrointestinal tract increase with ageing, and colorectal carcinoma is a tumor of the middle-aged and elderly. Gastrointestinal secretion, absorption, motility, cell proliferation, local immune defense and blood flow are all regulated by the neuroendocrine peptides. It is conceivable that gastrointestinal disorders at an advanced age may be accompanied by changes in this regulatory system. Objective: To ascertain possible age-related changes in neuroendocrine peptides in a rodent animal model. Methods: The concentrations of various neuroendocrine peptides were determined by radioimmunoassays in tissue extracts from the antrum, duodenum and colon of mice in four different age groups: 1, 3, 12 and 24 months. The neuroendocrine peptides investigated were: secretin, gastric inhibitory polypeptide (GIP), gastrin, motilin, peptide YY (PYY), somatostatin, vasoactive intestinal polypeptide (VIP), substance P, neuropeptide Y (NPY), galanin and neurotensin. Results: Antrum: Concentrations of somatostatin, VIP and substance P decreased significantly in 1-month-old mice (but that of neurotensin increased) compared with 3-month-old mice. In 12-month-old and 24-month-old mice, concentrations of gastrin, somatostatin, VIP, substance P, NPY, galanin and neurotensin all decreased vis-à-vis 3-month-old mice. Duodenum: Whereas the levels of secretin, GIP and neurotensin increased, those of gastrin, motilin, somatostatin, VIP, substance P, NPY and galanin decreased in 1-month-old mice vis-à-vis 3-month-old mice. In both 12-month-old and 24-month-old mice, the concentrations of secretin and GIP increased, compared with those of 3-month-old mice. The levels of gastrin, motilin, somatostatin, VIP, NPY and galanin decreased in both 12-month-old and 24-month-old mice vis-à-vis 3-month-old mice. Substance P and neurotensin concentrations decreased in 12-month-old mice, but not in 24-month-old mice. Colon: In 1-month-old mice the levels of PYY, somatostatin, VIP, substance P and galanin decreased vis-à-vis 3-month-old mice. In 12-month-old mice, the concentrations of PYY, somatostatin, VIP, NPY, galanin and neurotensin decreased compared with those in 3-month-old mice. In 24-month-old mice, the VIP level decreased, whereas the substance P level increased. Conclusion: The changes in neuroendocrine peptides observed in the gastrointestinal tract of this murine animal model could be of some relevance for the increased gastrointestinal dysfunction in the elderly human. They may also be involved in the development of colorectal cancer.

Neuroendocrine peptides of the gastrointestinal tract of an animal model of human type 2 diabetes mellitus.

We studied ten obese diabetic mice (Umeå/ Bom-ob) and 10 homozygous lean controls aged 21 weeks. The concentration of several neuroendocrine peptides was determined by radioimmunoassay of tissue extracts of antrum, duodenum and distal colon. The neuroendocrine peptides that we investigated were: secretin, gastric inhibitory polypeptide (GIP), gastrin, motilin, peptide YY (PYY), somatostatin, vasoactive intestinal polypeptide (VIP), substance P, neurotensin, neuropeptide Y (NPY) and galanin. In the antrum, gastrin, somatostatin, VIP, substance P and NPY concentrations were significantly lower in obese diabetic mice than in the lean controls. There was no statistical difference between the obese mice and lean controls for neurotensin and galanin content. In the duodenum, the concentration of substance P was lower in the obese diabetic mice than in lean mice. There was no statistical difference between obese diabetic mice and lean controls regarding the concentration of secretin, GIP, motilin, gastrin, somatostatin, VIP, neurotensin, NPY or galanin. In the colon, the levels of PYY, somatostatin, VIP, substance P, NPY and galanin were significantly lower in the obese diabetic mice than the lean controls. The concentration of neurotensin in the obese mice did not differ from that in the lean controls. The present study showed that the neuroendocrine system is disturbed in an animal model of human type 2 diabetes and that this disturbance differs from that observed in other animal models of human type 1 diabetes. The present findings may have some implications for the gastrointestinal dysfunction observed in patients with type 2 diabetes.

Distinct and interactive effects of d-amphetamine and haloperidol on levels of neurotensin and its mRNA in subterritories in the dorsal and ventral striatum of the rat.

Striatal tissue concentrations of neurotensin, expression of neurotensin/neuromedin N (NT/N) mRNA, and numbers of neurotensin-immunoreactive neurons are increased by d-amphetamine (amph), which stimulates dopamine release in the striatum, and haloperidol (hal), a dopamine receptor antagonist with high affinity for D2-like receptors. The possibility that the effects of these drugs involve distinct subpopulations of striatal neurons was addressed in this study, in which the relative numbers and distributions of striatal neuron profiles containing neurotensin immunoreactivity and/or NT/N mRNA were compared following administrations of hal, amph, hal and amph co-administered, and vehicle. Fourteen striatal subterritories in caudate-putamen, nucleus accumbens, and olfactory tubercle were evaluated. Amph produced increases in the expression of neurotensin preferentially in the ventromedial and caudodorsal subterritories of the caudate-putamen, the rostrobasal cell cluster and lateral shell of the nucleus accumbens, and the olfactory tubercle. Haloperidol produced increased neurotensin expression in much of dorsal and ventral striatum, most prominently in the rostral, dorsomedial and ventrolateral quadrants of the caudate-putamen, and in the rostrobasal cell cluster, rostral pole, medial and lateral shell of the nucleus accumbens and the olfactory tubercle. The numbers of neurons responding to amph and hal in all subterritories following co-administration of the two drugs were significantly less than the summed numbers responding individually to amph and hal. Furthermore, in the subterritories where immunohistochemically detectable responses elicited by amph exceeded those produced by hal, co-administration of the two drugs resulted in responses comparable to those elicited by hal given alone. It is suggested that some of the reported anti-dopaminergic behavioral effects of basal ganglia neurotensin may be attenuated in conditions of reduced dopamine neurotransmission.

Evidence That Hypothalamic Neurotensin Signals Leptin Effects on Feeding Behavior in Normal and Fat-Preferring Rats

Leptin inhibits food intake when it is injected in the periphery or in the central nervous system. It is likely that its action is not only mediated by the inhibition of orexigenic peptides such as neuropeptide Y. Therefore, we characterized the pharmacological and physiological relationships of leptin with neurotensin (NT), a central feeding inhibitor. Firstly, we investigated the central interactions of leptin and NT. Intracerebro-ventricular (ICV) injection were done in normal Long-Evans rats. NT had a short lasting (30 minutes; p<0.01) inhibitory effect on spontaneous food intake measured at the beginning of the dark phase whereas the effect of ICV leptin was observed after 24 hours (p<0.001). Co-injection with leptin potentiated NT effect at 30 minutes (p<0.001) and prolonged it for 30 additional minutes (p<0.01). In addition, NT potentiated the effect of leptin at 30 and 60 minutes (p<0.02 and p<0.001 respectively) but not at 24 hours. Secondly, we observed that NT concentrations were augmented in selective brain areas in fat-preferring rats (+ 34% for hypothalamic NT; p<0.03). This increase was observed in the parvocellular part of the paraventricular nucleus (PVNp) only and was associated with an increase in circulating leptin levels (+ 75%; p<0.003). Interestingly, plasma leptin and NT in the PVNp were strongly correlated (r=0.57; p<0.003), suggesting changes of NT processing or release in this nucleus. These results strongly suggest that the short-term anorexigenic effects of leptin in normal rats are at least partly mediated by changes in NT processing or release. They also suggest that these processes take place in the hypothalamus, most probably in the PVNp and that they might be sensitive to fat ingestion. Therefore, the neurotensin increase observed in fat-preferring rats would limit the overconsumption of energy, a physiological mechanism translated by leptin.

Differential effects of neurotensin on dopamine release in the caudal and rostral nucleus accumbens: A combined in vivo electrochemical and electrophysiological study

The time-course of variations in extracellular dopamine concentration following local pressure ejection of 10 −7 to 10 −3 M neurotensin into the ventral tegmental area of the rat was determined in the minute range in the nucleus accumbens by means of differential normal pulse voltammetry associated with carbon fibre electrodes. The effects of neurotensin ejection into the ventral tegmental area were further investigated on the firing activity of the corresponding dopaminergic neurons. The lowest concentration of neurotensin (10 −7 M) enhanced the extracellular dopamine concentration throughout the nucleus accumbens and stimulated the discharge activity of ventral tegmental area dopaminergic neurons. The two highest concentrations of neurotensin (10 −5 M and 10 −3 M) evoked two patterns of responses on the extracellular dopamine concentration and on the discharge activity of dopaminergic neurons. The extracellular dopamine concentration was increased above basal levels in the caudal part of the nucleus accumbens. In the rostral part, the evoked changes exhibited a multiphasic time-course characterized by a decreasing phase below baseline. The firing rate of dopaminergic neurons was either increased or decreased, depending on the neuron being tested. In fact, neurotensin ejection was always followed by an exacerbation of bursting activity, the resulting effect on the mean firing rate being related to the duration of the interburst intervals. Indeed, short interburst intervals permitted an increase in mean firing rate whereas long interburst intervals, indicative of excessive depolarization, led to a decrease in mean firing rate. These results suggest that variations in extracellular dopamine concentration evoked by neurotensin administration into the ventral tegmental area are the result of neurotensin-evoked changes in dopaminergic activity. Moreover, the differential effects evoked by high concentrations of neurotensin could be attributable to two subpopulations of ventral tegmental area dopaminergic neurons which could project differentially to the caudal and the rostral parts of the nucleus accumbens.

Role of the ileocecal junction in the motor response to intestinal resection

Extensive resections of the distal small intestine are associated with motor disruption in the proximal remnant. Luminal contents such as bacteria and short-chain fatty acids may play a role. We evaluated the effect of bypass of the ileocecal junction (ICJ) on the motor response to a 50% distal resection. Thirty-five dogs were divided into three groups: transection control (TC, n = 11); 50% distal resection with intact ICJ (DR, n = 12), and 50% distal resection with jejunocolostomy to bypass the ICJ (DRBP, n = 12). Motor activity, intestinal transit, nutrition, absorption, and motor active hormones were studied over a 3-month period. Caloric intake was reduced and nutritional status similarly impaired in both resected groups. Steatorrhea, however, was significantly greater after DRBP. Intestinal structural adaptation was similar in both resected groups at 12 weeks. Animals in the bypass group demonstrated elevated intraluminal short-chain fatty acid and anaerobic bacterial counts. Migrating motor complex frequency was similar in the three groups; distal starts, however, were more frequent in both resected groups. Clustered contractile activity was prominent in the remnant after both DR and DRBP (50% and 32% recording time occupied by clusters, respectively [not significant]). Basal levels of peptide YY were increased following resection and this increase was unaffected by ICJ bypass. Postprandial neurotensin concentrations were transiently increased after distal bowel resection. In contrast, the postprandial neurotensin response was abolished following resection with bypass of the ICJ. Basal motilin levels were reduced following resection alone but not after resection with ICJ bypass. The motor response to resection does not appear to be related to alterations in circulating levels of hormones localized to the distal ileum; neither does it seem to be influenced by luminal bacteria and short-chain fatty acids or retention of a sphincteric mechanism at the ICJ. These findings also raise questions about the role of short-chain fatty acids and bacteria in the generation of the various distinctive motor patterns of the distal ileum. Resection of the distal ileum through loss of the receptor site for either retarding reflexes or bile salt absorption may be of greater importance in determining the motor response to resection.

Mesolimbic expression of neurotensin and neurotensin receptor during stress-induced gastric mucosal injury.

Neurotensin is a neurotransmitter present in the brain and gastrointestinal tract. Intracerebroventricular injection of neurotensin protects rats from gastric mucosal injury caused by cold water restraint (CWR). Direct injection of neurotensin into the nucleus accumbens (NACB), part of the mesolimbic dopamine system, reduces gastric mucosal injury, suggesting that neurotensin confers protection on the mucosa through interaction with the mesolimbic system. The hypothesis is that the concentration of neurotensin in the mesolimbic system decreases during CWR, affecting the expression of neurotensin and the neurotensin receptor. After 1 h of CWR, neurotensin concentration significantly decreased 41% in the NACB and returned toward control concentrations after 2 h of CWR. The concentration of neurotensin mRNA significantly decreased 46% after 1 h CWR and returned toward control after 2 h. In contrast, neurotensin binding sites in the NACB increased from 159 to 228 fmol/mg protein after 1 h of CWR and increased significantly to 280 fmol/mg protein after 2 h CWR, whereas the level of neurotensin receptor mRNA significantly decreased 51 and 50% at 1 and 2 h, respectively. These studies show that neurotensin concentration within the mesolimbic system is transiently reduced by CWR stress and that the number of neurotensin binding sites increases, presumably in response to the decrease in neurotensin.

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

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

Reduced food intake after jejunoileal bypass: a possible association with prolonged gastric emptying and altered gut hormone patterns

The object of this study was to examine whether eating behavior, food preference, gastric emptying, and gut hormone patterns are altered after jejunoileal bypass (JIB) in patients with severe obesity. Eight obese [mean (+/- SD) body mass index (BMI; in kg/m2) 42.9 +/- 4] subjects were studied prospectively before and 9 mo after JIB with eight age- and sex-matched normal-weight control subjects. Total energy intake, data from the universal eating monitor (VIKTOR), eating motivation measured by visual analog scales, a food-preference checklist, a forced-choice list, solid-phase gastric emptying, and postprandial concentrations of cholecystokinin, motilin, and neurotensin were studied. BMI was reduced by 29% after JIB. Compared with normal subjects, the JIB patients showed a reduced desire to eat, decreased hunger, and reduced prospective consumption before a test meal. After surgery, obese subjects selected fewer food items and showed a reduced preference for high-carbohydrate and high-fat items before a test meal. There was a trend from an accelerated toward a decelerated eating pattern in obese subjects after JIB. After JIB, gastric emptying of obese subjects was slowed and similar to that in control subjects. Obese subjects had lower postprandial cholecystokinin concentrations that were lower than those of control subjects both before and after JIB. Postprandial concentrations of neurotensin were higher after JIB. We conclude that after JIB, the desire to eat and preference for high-carbohydrate and high-fat items is reduced, resulting in decreased energy intake. That gastric emptying is prolonged and gut hormone patterns are altered with low postprandial plasma cholecystokinin and high neurotensin plasma concentrations may at least partly account for these observations.