Neurotensin excites periaqueductal gray neurons projecting to the rostral ventromedial medulla

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

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

Emerging functions of neuronostatin in physiology, pathology, and potential therapeutics

Neuronostatin, a bioactive peptide hormone, was encoded by pro-somatostatin and discovered using a bioinformatic method in 2008. Neuronostatin is widely expressed in the central nervous system (CNS) and peripheral tissues, it is also highly conserved among humans, rodents, and even goldfish. The 13 and 19 amino acids and the C-terminal amidation type play important roles in physiological and pathological functions. The present study reviews the roles of neuronostatin in food intake and drinking of water, as well as in the neuroendocrine processes, pain regulation, cardiovascular and circulation function, memory and studies, depression-like effect, and energy metabolism in animals. However, the information on the physiology and pathology of neuronostatin, especially the molecular mechanism, remains scarce. Considering the broad functions of neuronostatin, this endogenous neuropeptide could be a promising therapeutic target for future research and drug design if the exact receptor could be found in humans.

Examination of pain threshold and neuropeptides in patients with acute suicide risk

INTRODUCTION

One of the main challenges in suicide prevention is the limited understanding of the biological mechanisms underlying suicide. Recent findings suggest impairments in pain processing in acutely suicidal patients. However, little is known about the biological factors that may drive these discrete physiological abnormalities. In this study, we examined plasma peptides involved in analgesic and inflammatory responses and physical pain threshold in acutely suicidal patients.

METHODS

Thirty-seven depressed patients of both sexes hospitalized for severe suicidal ideation or a recent suicide attempt were characterized clinically including history of suicidal ideation and behavior. Psychological and physical pain, and pressure pain threshold was also measured. Plasma levels of β-endorphin, neurotensin, agouti-related protein (AgRP), C-reactive protein (CRP), adrenocorticotropic hormone (ACTH), and brain-derived neurotrophic factor (BDNF) were run in Milliplex multiplex assays.

RESULTS

The number of lifetime suicide attempts was positively correlated with β-endorphin (r = 0.702; p = 0.007), and neurotensin (r = 0.728, p = 0.007) plasma levels. Higher pain threshold was measured in the suicide attempt group as compared to the suicidal ideation group. Pain threshold was strongly and negatively associated with CRP plasma levels (r = -0.548; p < 0.001). In patients reporting chronic pain, lower AgRP levels and lower pain threshold were observed (t = 4.472; p = 0.001).

CONCLUSION

Our results suggest that abnormalities in the opioid and neurotensin systems may underlie the increase in pain threshold found in suicide attempters, and possibly risk for suicidal behavior. Targeting pain circuits and systems may provide therapeutic mechanisms for suicide prevention.

Diverse actions of the modulatory peptide neurotensin on central synaptic transmission

Neurotensin (NT) is a 13 amino acid neuropeptide that is expressed throughout the central nervous system and is implicated in the etiology of multiple diseases and disorders. Many primary investigations of NT-induced modulation of neuronal excitability at the level of the synapse have been conducted, but they have not been summarized in review form in nearly 30 years. Therefore, the goal of this review is to discuss the many actions of NT on neuronal excitability across brain regions as well as NT circuit architecture. In the basal ganglia as well as other brain nuclei, NT can act through diverse intracellular signaling cascades to enhance or depress neuronal activity by modulating activity of ion channels, ionotropic and metabotropic neurotransmitter receptors, and presynaptic release of neurotransmitters. Further, NT can produce indirect effects by evoking endocannabinoid release, and recently has itself been identified as a putative retrograde messenger. In the basal ganglia, the diverse actions and circuit architecture of NT signaling allow for input-specific control of reward-related behaviors.

Gene-environment interactions in a rat model of depression. Maternal separation affects neurotensin in selected brain regions

Although the etiology of major psychiatric disorders has not been elucidated, accumulating evidence indicates that both genetic and early environmental factors play a role. We have previously demonstrated behavioral and neurochemical changes both in non-manipulated genetic rat models of depression, such as Flinders Sensitive Line (FSL) and Fawn Hooded (FH), and in normal rats following maternal separation (MS). The aim of the present study was to extend this work by exploring whether neurotensin (NT), a peptide implicated in several psychiatric disorders, is altered in a new animal model based on gene - environment interactions. More specifically, we used the FSL rats as a genetic model of depression and the Flinders Resistant Line (FRL) as controls and subjected them to MS. Pups randomly assigned to the MS procedure were separated from the dam as a litter for 180min daily between postnatal day 2 to 14. On postnatal day 90, rats were weighed and sacrificed by a two second high energy focused microwave irradiation and several brain regions were obtained by micropuncture. Neurotensin-like immunoreactivity (NT-LI) was measured by radioimmunoassay (RIA). The results showed that the FSL rats compared to the FRL rats have higher baseline NT-LI concentrations in the temporal cortex and periaqueductal gray and a markedly different response to maternal separation. The only observed change following maternal separation in the FRL rats was an NT-LI increase in the periaqueductal gray. In contrast, in the FSL significant increases were found in the nucleus accumbens, hippocampus, and entorhinal cortex and a decrease was seen in the temporal cortex after MS. The present study revealed baseline regional differences in NT-LI concentrations between the FSL and FRL strains and demonstrated that early MD differentially affects the two strains. The relevance of these alterations for depression as well as possible mechanisms underlying this gene-environment interaction are discussed.

Distribution of Neurotensin and Somatostatin-28 (1-12) in the Minipig Brainstem

Using an indirect immunoperoxidase technique, an in depth study has been carried out for the first time on the distribution of fibres and cell bodies containing neurotensin and somatostatin-28 (1-12) (SOM) in the minipig brainstem. The animals used were not treated with colchicine. The distribution of neurotensin- and SOM-immunoreactive fibres was seen to be quite similar and was moderate in the minipig brainstem: a close anatomical relationship between both neuropeptides was observed. The distribution of cell bodies containing neurotensin or SOM was quite different and restricted. Cell bodies containing neurotensin were found in four brainstem nuclei: nucleus centralis raphae, nucleus dorsalis raphae, in the pars centralis of the nucleus tractus spinalis nervi trigemini and in the nucleus ventralis raphae. Cell bodies containing SOM were found in six nuclei/regions of the brainstem: nucleus ambiguus, nucleus dorsalis motorius nervi vagus, formatio reticularis, nucleus parabrachialis medialis, nucleus reticularis lateralis and nucleus ventralis raphae. According to the observed anatomical distribution of the immunoreactive structures containing neurotensin or SOM, the peptides could be involved in sleep-waking, nociceptive, gustatory, motor, respiratory and autonomic mechanisms.

Neurotensin and neurotensin receptors: characteristic, structure-activity relationship and pain modulation--a review

Neurotensin (NT) is a tridecapeptide, which - since its discovery in 1973--has been demonstrated to be involved in the control of various physiological activities in both the central nervous system and in the periphery. Its biological effects are mediated by four receptor types. Exogenously administered NT exerts different behavioral effects, including antinociception. Structure-activity relationship studies performed in recent years resulted in development of several peptidomimetic receptor agonists and non-peptidic receptor antagonists that are useful tools for studies of NT mechanisms in tissue and on cellular level. This may result in design of new generation of analgesics based on neurotensin. NT antinociceptive effects are distinct from opioid analgesia. This creates opportunity of development of hybride analgesics that may simultaneously activate both opioid and NT antinociceptive pathways.

Neurotensin induced Egr-1 activity is altered in the postpartum period in mice

Neurotensin (NT) is a 13 amino acid neuropeptide that is identical in mice and humans and is released from and acts upon a number of social brain regions. Recent work indicates NT neurotransmission may be altered in postpartum females and support the onset of some maternal behaviors. In a recent study, we highlighted how virgin and postpartum brains from mice selected for high offspring protection differ in response to injected NT (0.1 μg) relative to vehicle when examining c-Fos profiles across the CNS. In this companion study we use a second marker for brain activity, Egr-1, and evaluate multiple brain regions. Common significant increased Egr-1 responses to NT (relative to vehicle) were found in both female groups only in ventromedial hypothalamus. In lateral periaqueductal gray, virgin mice showed a significant Egr-1 increase with NT (relative to vehicle), but maternal mice did not. When comparing NT injections, virgin (relative to maternal) mice had significantly higher activity in five regions, including anterior hypothalamus, lateral hypothalamus, somatosensory cortex, paraventricular nucleus, and zona incerta; no regions were higher in maternal mice. A Principal Components Analysis was also used for data mining and in virgin mice, greater changes in activity hubs were found with NT (relative to vehicle) than for maternal mice. Overall, a lower sensitivity to NT in terms of Egr-1 reactivity in the maternal state was highlighted and this is consistent with previous c-Fos results. These findings provide additional insight into the mechanisms by which NT functions in the CNS.

Central administration of neuronostatin induces antinociception in mice

Neuronostatin, a recently discovered endogenous bioactive peptide, was encoded by pro-mRNA of somatostatin that contributes to modulation of nociception. However, nociceptive effect of neuronostatin is still not fully known. The aim of this study was to evaluate effect of neuronostatin on nociception and elucidate its possible mechanism of action. Intracerebroventricular (i.c.v.) administration of neuronostatin (0.3, 3, 6, 12nmol/mouse) produced a dose- and time-related antinociceptive effect in the tail immersion assay in mice, an acute pain model. The antinociceptive effect of neuronostatin was significantly antagonized by naloxone, and was strongly inhibited by co-injection with β-funaltrexamine or nor-binaltorphimine, but not by naltrindole. Also, melanocortin 3/4 receptor antagonist, SHU9119, completely blocked the effect of neuronostatin. These data indicated the involvement of both μ- and κ-opioid receptors and central melanocortin system in the analgesic response induced by neuronostatin. In addition, neuronostatin (6nmol, i.c.v.) increased c-Fos protein expression in the periaqueductal gray (PAG) and the nucleus raphe magnus (NRM) that have a pivotal role in regulating descending pain pathways. Taken together, this study is the first to reveal that neuronostatin produces antinociceptive effect via opioid and central melanocortin systems, which is associated with an increase in neuronal activity the PAG and NRM.

Nocistatin excites rostral agranular insular cortex-periaqueductal gray projection neurons by enhancing transient receptor potential cation conductance via G(alphaq/11)-PLC-protein kinase C pathway

Rostral agranular insular cortex (RAIC) projects to periaqueductal gray (PAG) and inhibits spinal nociceptive transmission by activating PAG-rostral ventromedial medulla (RVM) descending antinociceptive circuitry. Despite being generated from the same precursor prepronociceptin, nocistatin (NST) and nociceptin/orphanin FQ (N/OFQ) produce supraspinal analgesic and hyperalgesic effects, respectively. Prepronociceptin is highly expressed in the RAIC. In the present study, we hypothesized that NST and N/OFQ modulate spinal pain transmission by regulating the activity of RAIC neurons projecting to ventrolateral PAG (RAIC-PAG). This hypothesis was tested by investigating electrophysiological effects of N/OFQ and NST on RAIC-PAG projection neurons in brain slice. Retrogradely labeled RAIC-PAG projection neurons are layer V pyramidal cells and express mRNA of vesicular glutamate transporter subtype 1, a marker for glutamatergic neurons. N/OFQ hyperpolarized 25% of RAIC-PAG pyramidal neurons by enhancing inwardly rectifying potassium conductance via pertussis toxin-sensitive G(alphai/o). In contrast, NST depolarized 33% of RAIC-PAG glutamatergic neurons by causing the opening of canonical transient receptor potential (TRPC) cation channels through G(alphaq/11)-phospholipase C-protein kinase C pathway. There were two separate populations of RAIC-PAG pyramidal neurons, one responding to NST and the other one to N/OFQ. Our results suggest that G(alphaq/11)-coupled NST receptor mediates NST excitation of RAIC-PAG glutamatergic neurons, which is expected to cause the supraspinal analgesia by enhancing the activity of RAIC-PAG-RVM antinociceptive pathway. Opposite effects of NST and N/OFQ on supraspinal pain regulation are likely to result from their opposing effects on RAIC-PAG pyramidal neurons.

Neurotensin inhibition of GABAergic transmission via mGluR-induced endocannabinoid signalling in rat periaqueductal grey

Neurotensin modulates pain via its actions within descending analgesic pathways which include brain regions such as the midbrain periaqueductal grey (PAG). The aim of this study was to examine the cellular actions of neurotensin on PAG neurons. Whole cell patch clamp recordings were made from rat midbrain PAG slices in vitro to examine the postsynaptic effects of neurotensin and its effects on GABA(A) mediated inhibitory postsynaptic currents (IPSCs). Neurotensin (100-300 nM) produced an inward current in subpopulations of opioid sensitive and insensitive PAG neurons which did not reverse over membrane potentials between -50 and -130 mV. The neurotensin induced current was abolished by the NTS1 and NTS1/2 antagonists SR48692 (300 nM) and SR142948A (300 nM). Neurotensin also produced a reduction in the amplitude of evoked IPSCs, but had no effect on the rate and amplitude of TTX-resistant miniature IPSCs. The neurotensin induced inhibition of evoked IPSCs was reduced by the mGluR5 antagonist MPEP (5microM) and abolished by the cannabinoid CB(1) receptor antagonist AM251 (3 microM). These results suggest that neurotensin produces direct neuronal depolarisation via NTS1 receptors and inhibits GABAergic synaptic transmission within the PAG. The inhibition of synaptic transmission is mediated by neuronal excitation and action potential dependent release of glutamate, leading to mGluR5 mediated production of endocannabinoids which activate presynaptic CB(1) receptors. Thus, neurotensin has cellular actions within the PAG which are consistent with both algesic and analgesic activity, some of which are mediated via the endocannabinoid system.

Nocistatin and nociceptin exert opposite effects on the excitability of central amygdala nucleus-periaqueductal gray projection neurons

Central amygdala nucleus (CeA)-periaqueductal gray (PAG) pathway is the component of descending antinociceptive circuitry. Nociceptin/orphanin FQ (N/OFQ) and nocistatin (NST) produce supraspinal pronociceptive and antinociceptive effects, respectively. We hypothesized that opposite effects of N/OFQ and NST on supraspinal pain modulation result from their opposing effects on the excitability of CeA-PAG projection neurons. This hypothesis was tested by investigating electrophysiological effects of N/OFQ and NST on medial CeA neurons that project to PAG (CeA(M)-PAG). N/OFQ hyperpolarized CeA(M)-PAG projection neurons by enhancing inwardly rectifying potassium conductance. In contrast, NST depolarized CeA(M)-PAG neurons by causing the opening of TRPC cation channels via G(alphaq/11)-PLC-PKC pathway. CeA(M)-PAG neurons hyperpolarized by N/OFQ express CRF or neurotensin mRNA. NST-responsive CeA(M)-PAG neurons contain CRF or substance P mRNA. Our study provides the evidence that the molecular and cellular basis for opposite effects of N/OFQ and NST on supraspinal pain regulation is their opposing effects on the excitability of peptidergic CeA(M)-PAG neurons.

Neural mechanism underlying acupuncture analgesia

Acupuncture has been accepted to effectively treat chronic pain by inserting needles into the specific "acupuncture points" (acupoints) on the patient's body. During the last decades, our understanding of how the brain processes acupuncture analgesia has undergone considerable development. Acupuncture analgesia is manifested only when the intricate feeling (soreness, numbness, heaviness and distension) of acupuncture in patients occurs following acupuncture manipulation. Manual acupuncture (MA) is the insertion of an acupuncture needle into acupoint followed by the twisting of the needle up and down by hand. In MA, all types of afferent fibers (Abeta, Adelta and C) are activated. In electrical acupuncture (EA), a stimulating current via the inserted needle is delivered to acupoints. Electrical current intense enough to excite Abeta- and part of Adelta-fibers can induce an analgesic effect. Acupuncture signals ascend mainly through the spinal ventrolateral funiculus to the brain. Many brain nuclei composing a complicated network are involved in processing acupuncture analgesia, including the nucleus raphe magnus (NRM), periaqueductal grey (PAG), locus coeruleus, arcuate nucleus (Arc), preoptic area, nucleus submedius, habenular nucleus, accumbens nucleus, caudate nucleus, septal area, amygdale, etc. Acupuncture analgesia is essentially a manifestation of integrative processes at different levels in the CNS between afferent impulses from pain regions and impulses from acupoints. In the last decade, profound studies on neural mechanisms underlying acupuncture analgesia predominately focus on cellular and molecular substrate and functional brain imaging and have developed rapidly. Diverse signal molecules contribute to mediating acupuncture analgesia, such as opioid peptides (mu-, delta- and kappa-receptors), glutamate (NMDA and AMPA/KA receptors), 5-hydroxytryptamine, and cholecystokinin octapeptide. Among these, the opioid peptides and their receptors in Arc-PAG-NRM-spinal dorsal horn pathway play a pivotal role in mediating acupuncture analgesia. The release of opioid peptides evoked by electroacupuncture is frequency-dependent. EA at 2 and 100Hz produces release of enkephalin and dynorphin in the spinal cord, respectively. CCK-8 antagonizes acupuncture analgesia. The individual differences of acupuncture analgesia are associated with inherited genetic factors and the density of CCK receptors. The brain regions associated with acupuncture analgesia identified in animal experiments were confirmed and further explored in the human brain by means of functional imaging. EA analgesia is likely associated with its counter-regulation to spinal glial activation. PTX-sesntive Gi/o protein- and MAP kinase-mediated signal pathways as well as the downstream events NF-kappaB, c-fos and c-jun play important roles in EA analgesia.

Genomic expression during human myelopoiesis

Background

Human myelopoiesis is an exciting biological model for cellular differentiation since it represents a plastic process where multipotent stem cells gradually limit their differentiation potential, generating different precursor cells which finally evolve into distinct terminally differentiated cells. This study aimed at investigating the genomic expression during myeloid differentiation through a computational approach that integrates gene expression profiles with functional information and genome organization.

Results

Gene expression data from 24 experiments for 8 different cell types of the human myelopoietic lineage were used to generate an integrated myelopoiesis dataset of 9,425 genes, each reliably associated to a unique genomic position and chromosomal coordinate. Lists of genes constitutively expressed or silent during myelopoiesis and of genes differentially expressed in commitment phase of myelopoiesis were first identified using a classical data analysis procedure. Then, the genomic distribution of myelopoiesis genes was investigated integrating transcriptional and functional characteristics of genes. This approach allowed identifying specific chromosomal regions significantly highly or weakly expressed, and clusters of differentially expressed genes and of transcripts related to specific functional modules.

Conclusion

The analysis of genomic expression during human myelopoiesis using an integrative computational approach allowed discovering important relationships between genomic position, biological function and expression patterns and highlighting chromatin domains, including genes with coordinated expression and lineage-specific functions.

Neurotensin: role in psychiatric and neurological diseases

Neurotensin (NT), an endogenous brain-gut peptide, has a close anatomical and functional relationship with the mesocorticolimbic and neostriatal dopamine system. Dysregulation of NT neurotransmission in this system has been hypothesized to be involved in the pathogenesis of schizophrenia. Additionally, NT containing circuits have been demonstrated to mediate some of the mechanisms of action of antipsychotic drugs, as well as the rewarding and/or sensitizing properties of drugs of abuse. NT receptors have been suggested to be novel targets for the treatment of psychoses or drug addiction.

Neurotensin and pain modulation

Neurotensin (NT) can produce a profound analgesia or enhance pain responses, depending on the circumstances. Recent evidence suggests that this may be due to a dose-dependent recruitment of distinct populations of pain modulatory neurons. NT knockout mice display defects in both basal nociceptive responses and stress-induced analgesia. Stress-induced antinociception is absent in these mice and instead stress induces a hyperalgesic response, suggesting that NT plays a key role in the stress-induced suppression of pain. Cold water swim stress results in increased NT mRNA expression in hypothalamic regions known to project to periaqueductal gray, a key region involved in pain modulation. Thus, stress-induced increases in NT signaling in pain modulatory regions may be responsible for the transition from pain facilitation to analgesia. This review focuses on recent advances that have provided insights into the role of NT in pain modulation.

Potent spinal analgesia elicited through stimulation of NTS2 neurotensin receptors

Intrathecal administration of the neuropeptide neurotensin (NT) was shown previously to exert antinociceptive effects in a variety of acute spinal pain paradigms including hotplate, tail-flick, and writhing tests. In the present study, we sought to determine whether some of these antinociceptive effects might be elicited via stimulation of low-affinity NTS2 receptors. We first established, using immunoblotting and immunohistochemical techniques, that NTS2 receptors were extensively associated with putative spinal nociceptive pathways, both at the level of the dorsal root ganglia and of the superficial layers of the dorsal horn of the spinal cord. We then examined the effects of intrathecal administration of NT or selective NTS2 agonists on acute thermal pain. Both NT and NTS2 agonists, levocabastine and Boc-Arg-Arg-Pro-Tyrpsi(CH2NH)Ile-Leu-OH (JMV-431), induced dose-dependent antinociceptive responses in the tail-flick test. The effects of levocabastine and of JMV-431 were unaffected by coadministration of the NTS1-specific antagonist 2-[(1-(7-chloro-4-quinolinyl)-5-(2,6-dimethoxy-phenyl)pyrazol-3-yl)carboxylamino]tricyclo)3.3.1.1.(3.7))-decan-2-carboxylic acid (SR48692), confirming that they were NTS2 mediated. In contrast, the antinociceptive effects of NT were partly abolished by coadministration of SR48692, indicating that NTS1 and NTS2 receptors were both involved. These results suggest that NTS2 receptors play a role in the regulation of spinal nociceptive inputs and that selective NTS2 agonists may offer new avenues for the treatment of acute pain.

Localization of neurotensin immunoreactivity in neurons and organ of corti of rat cochlea

The distribution of neurotensin-containing cell bodies and fibers has been observed in the central and peripheral nervous system, including sensory ganglia, but no description has been found in the peripheral auditory system. Here, we investigated the presence of neurotensin immunoreactivity in the cochlea of the adult Wistar rat. Strong neurotensin immunoreactivity was detected in the cytoplasm of the inner hair cells (IHC) and Deiters' cells of the organ of Corti. Outer hair cells (OHC) show weak immunoreaction. Neurotensin immunoreactivity was also found in the neurons and fibers of the spiral ganglia. Quantitative microdensitometric image analysis of the neurotensin immunoreactivity showed a strong immunoreaction in the hair cells of organ of Corti and a moderate to strong labeling in the spiral ganglion neurons. A series of double immunolabeling experiments demonstrated a strong neurotensin immunoreactivity in the parvalbumin immunoreactive IHC and also in the calbindin immunoreactive Deiters' cells. Weak neurotensin immunoreactivity was seen in the calbindin positive OHC. Neurofilament and parvalbumin immunoreactive neurons and fibers in the spiral ganglia showed neurotensin immunoreactivity. Calbindin immunoreactivity was not detected in the spiral ganglion neurons, which are labeled by neurotensin immunoreactivity. The presence of neurotensin in the cochlea may be related to its modulation of neurotransmission in the peripheral auditory pathway.

Glutamate transporter function of rat hippocampal astrocytes is impaired following the global ischemia

Astroglial glutamate transporters, GLT-1 and GLAST, play an essential role in removing released glutamate from the extracellular space and are essential for maintaining a low concentration of extracellular glutamate in the brain. It was hypothesized that impaired function of glial glutamate transporters induced by transient global ischemia may lead to an elevated level of extracellular glutamate and subsequent excitotoxic neuronal death. To test this hypothesis, in the present study, we performed whole-cell patch-clamp recording of hippocampal CA1 astrocytes in control or postischemic slices, and measured glutamate transporter activity by recording glutamate-evoked transporter currents. Six to 24 h after global ischemia, maximal amplitude of glutamate transporter currents recorded from postischemic CA1 astrocytes was significantly reduced. Western blotting analysis indicated that transient global ischemia decreased the protein level of GLT-1 in the hippocampal CA1 area without affecting GLAST protein level. Further real-time quantitative RT-PCR assays showed that global ischemia resulted in a decrease in GLT-1 mRNA level of hippocampal CA1 region. Global ischemia-induced reduction in GLT-1 expression and glutamate transporter function of CA1 astrocytes precedes the initiation of delayed neuronal death in CA1 pyramidal layer. The present study provides the evidence that transient global ischemia downregulates glutamate transporter function of hippocampal CA1 astrocytes by decreasing mRNA and protein levels of GLT-1.

Role of calcium in neurotensin-evoked enhancement in firing in mesencephalic dopamine neurons

Neurotensin (NT) increases neurotransmission within the mesolimbic dopamine system by enhancing the firing rate of dopaminergic (DAergic) neurons and by acting at the nerve terminal level. The signal transduction pathways involved in these effects have not been characterized, but NT receptors are coupled to the phospholipase C pathway and Ca(2+) mobilization. However, an enhancement of intracellular Ca(2+) concentration ([Ca(2+)](i)) evoked by NT in DAergic neurons has yet to be demonstrated. Furthermore, the hypothesis that the excitatory effects of NT in DAergic neurons are Ca(2+) dependent is currently untested. In whole-cell recording experiments, DAergic neurons in culture were identified by their selective ability to express a cell-specific green fluorescent protein reporter construct. These experiments confirmed that NT increases firing rate in cultured DAergic neurons. This effect was Ca(2+) dependent because it was blocked by intracellular dialysis with BAPTA. Using Ca(2+) imaging, we showed that NT caused a rapid increase in [Ca(2+)](i) in DAergic neurons. Most of the Ca(2+) originated from the extracellular medium. NT-induced excitation and Ca(2+) influx were blocked by SR48692, an antagonist of the type 1 NT receptor. Blocking IP(3) receptors using heparin prevented the excitatory effect of NT. Moreover, Zn(2+) and SKF96365 both blocked the excitatory effect of NT, suggesting that nonselective cationic conductances are involved. Finally, although NT can also induce a rise in [Ca(2+)](i) in astrocytes, we find that NT-evoked excitation of DAergic neurons can occur independently of astrocyte activation.

Neurotensin depolarizes globus pallidus neurons in rats via neurotensin type-1 receptor

The globus pallidus is a major component in the indirect pathway of the basal ganglia. There is evidence that neurotensin receptors exist in this nucleus. To determine the electrophysiological effects of neurotensin on pallidal neurons, whole-cell patch-clamp recordings were performed in the acutely prepared brain slices. Under current-clamp recordings, neurotensin at 1 microM depolarized pallidal neurons. Voltage-clamp recordings also showed an inward current induced by neurotensin. The depolarizing effect of neurotensin could be mimicked by the C-terminal fragment, neurotensin (8-13), but not by the N-terminal fragment, neurotensin (1-8). Both SR 142948A, a non-selective neurotensin receptor type-1 and type-2 antagonist, and SR 48692, a selective type-1 receptor antagonist, blocked the depolarizing effect of neurotensin, and which themselves had no effect on membrane potential. Thus, neurotensin type-1 receptors appear to mediate the effect of neurotensin. The depolarization evoked by neurotensin persisted in the presence of tetrodotoxin, ionotropic and metabotropic glutamate and GABA receptor antagonists, indicating that neurotensin excited the pallidal neurons by activating the receptor expressed on the neurons recorded. Current-voltage relationship revealed that both the suppression of a potassium conductance and the activation of a cationic conductance are involved in the neurotensin-induced depolarization. Based on the action of neurotensin in the globus pallidus we hypothesize that alterations of the striatopallidal neurotensin system contribute to symptoms of basal ganglia motor disorders.

Antinociception induced by beta-lactotensin, a neurotensin agonist peptide derived from beta-lactoglobulin, is mediated by NT2 and D1 receptors

In this study, we examined the antinociceptive effect of beta-lactotensin, a neurotensin agonist that has been isolated from the chymotrypsin digest of beta-lactoglobulin as an ileum-contracting peptide. Beta-lactotensin showed naloxone-insensitive antinociceptive activity by the tail-pinch test after i.c.v. (200 nmol/mouse) or s.c. (300 mg/kg) administration in ddY mice. Tolerance was not developed to antinociception induced by beta-lactotensin after repeated s.c. administration for 5 days. The antinociceptive activity of beta-lactotensin was blocked by treatment with the neurotensin NT2 receptor antisense ODN, while treatment with the NT1 receptor antisense ODN had no effect. The antinociceptive activity was also blocked by a dopamine D1 receptor antagonist, SCH23390 (1 microg/mouse, i.c.v.), while a D2 receptor antagonist, raclopride (0.5 microg/mouse, i.c.v.), did not block the activity. These results indicate that the antinociceptive activity of beta-lactotensin is mediated by NT2 and D1 receptors.

Receptor subtype-specific modulation by dopamine of glutamatergic responses in striatal medium spiny neurons

The output of GABAergic medium-sized spiny neurons in the dorsal striatum is controlled in part by glutamatergic input from the neocortex and the thalamus, and dopaminergic input from ventral midbrain. We acutely isolated these neurons from juvenile (P14-24) rats to study the consequences of the interaction between glutamate and dopamine for neuronal excitability. Single-cell RT-PCR analysis was used to identify the expression patterns of dopamine receptors. D1 and D2 dopamine receptor mRNA was detected in 11/22 and 3/22 of isolated neurons, respectively. Receptor mRNA co-expression was detected in 1/22 cells tested. Whole-cell voltage clamp recording (V(h)=-70 mV) was combined with local or bath application of dopaminergic and glutamatergic agonists to explore dopamine receptor modulation of glutamatergic excitation. Glutamate-evoked inward currents (5 microM, Mg(2+)-free, 1 microM glycine) were attenuated by dopamine (5 microM) to 83.2+/-3.6% (n=31). NMDA-evoked (20 microM), APV-sensitive currents were attenuated by dopamine to 80.9+/-4.5% (n=24). NMDA-induced responses were also attenuated by the D1 receptor agonist SKF 38393 (1 microM; n=28), while the D2/3 receptor agonist quinpirole (10 microM) had no effect. The currents evoked by application of AMPA (5 microM) displayed a steady rundown. Application of dopamine abolished or significantly reduced the rundown in the cells tested (n=17). A similar effect was observed after the application of SKF 38393 (1 microM), while quinpirole (10 microM) had no significant effect. Our results provide direct evidence for modulation by dopamine of glutamatergic responses of striatal medium spiny neurons, and demonstrate that the effects of this neuromodulator are receptor subtype specific. Disruption of this modulatory effect is likely to contribute to movement disorders associated with Parkinson's disease.

Endogenous opiates and behavior: 2001

This paper is the twenty-fourth installment of the annual review of research concerning the opiate system. It summarizes papers published during 2001 that studied the behavioral effects of the opiate peptides and antagonists. The particular topics covered this year include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology(Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).