Tachykinin signaling inhibits task-specific behavioral responsiveness in honeybee workers.

Behavioral specialization is key to the success of social insects and leads to division of labor among colony members. Response thresholds to task-specific stimuli are thought to proximally regulate behavioral specialization, but their neurobiological regulation is complex and not well understood. Here, we show that response thresholds to task-relevant stimuli correspond to the specialization of three behavioral phenotypes of honeybee workers in the well-studied and important Apis mellifera and Apis cerana. Quantitative neuropeptidome comparisons suggest two tachykinin-related peptides (TRP2 and TRP3) as candidates for the modification of these response thresholds. Based on our characterization of their receptor binding and downstream signaling, we confirm a functional role of tachykinin signaling in regulating specific responsiveness of honeybee workers: TRP2 injection and RNAi-mediated downregulation cause consistent, opposite effects on responsiveness to task-specific stimuli of each behaviorally specialized phenotype but not to stimuli that are unrelated to their tasks. Thus, our study demonstrates that TRP signaling regulates the degree of task-specific responsiveness of specialized honeybee workers and may control the context specificity of behavior in animals more generally.

Androgen Suppresses In Vivo and In Vitro LH Pulse Secretion and Neural Kiss1 and Tac2 Gene Expression in Female Mice.

Androgens can affect the reproductive axis of both sexes. In healthy women, as in men, elevated exogenous androgens decrease gonad function and lower gonadotropin levels; such circumstances occur with anabolic steroid abuse or in transgender men (genetic XX individuals) taking androgen supplements. The neuroendocrine mechanisms by which endogenous or exogenous androgens regulate gonadotropin release, including aspects of pulsatile luteinizing hormone (LH) secretion, remain unknown. Because animal models are valuable for interrogating neural and pituitary mechanisms, we studied effects of androgens in the normal male physiological range on in vivo LH secretion parameters in female mice and in vitro LH secretion patterns from isolated female pituitaries. We also assessed androgen effects on hypothalamic and gonadotrope gene expression in female mice, which may contribute to altered LH secretion profiles. We used a nonaromatizable androgen, dihydrotestosterone (DHT), to isolate effects occurring specifically via androgen receptor (AR) signaling. Compared with control females, DHT-treated females exhibited markedly reduced in vivo LH pulsatility, with decreases in pulse frequency, amplitude, peak, and basal LH levels. Correlating with reduced LH pulsatility, DHT-treated females also exhibited suppressed arcuate nucleus Kiss1 and Tac2 expression. Separate from these neural effects, we determined in vitro that the female pituitary is directly inhibited by AR signaling, resulting in lower basal LH levels and reduced LH secretory responses to gonadotropin-releasing hormone pulses, along with lower gonadotropin gene expression. Thus, in normal adult females, male levels of androgen acting via AR can strongly inhibit the reproductive axis at both the neural and pituitary levels.

Sexual Dimorphic Distribution of Hypothalamic Tachykinin1 Cells and Their Innervations to GnRH Neurons in the Zebrafish.

Substance P (SP) and neurokinin A (NKA), encoded by TAC1/Tac1 gene are members of the tachykinin family, which exert their neuromodulatory roles in vertebrate reproduction. In mammals, SP and NKA have been shown to regulate gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion via kisspeptin neurons. On the other hand, the role of SP/NKA in the regulation of reproduction in non-mammalian vertebrates is not well known. In the present study, we first localized expression of tac1 mRNA in the brain of male and female zebrafish, Danio rerio. Next, using an antibody against zebrafish tachykinin1 (Tac1), we examined the neural association of SP/NKA neural processes with GnRH3 neurons, and with kisspeptin (kiss2) neurons, in the brains of male and female zebrafish. In situ hybridization showed an apparent male-dominant tac1 expression in the ventral telencephalic area, the anterior and posterior parts of the parvocellular preoptic nucleus, and the suprachiasmatic nucleus. On the other hand, there was female-dominant tac1 expression in the ventral periventricular hypothalamus. Confocal images of double-labeled zebrafish Tac1 and GnRH3 showed associations between Tac1-immunoreactive processes and GnRH3 neurons in the ventral telencephalic area. In contrast, there was no apparent proximity of Tac1 processes to kiss2 mRNA-expressing neurons in the hypothalamus. Lastly, to elucidate possible direct action of SP/NKA on GnRH3 or Kiss2 neurons, expression of SP/NKA receptor, tacr1a mRNA was examined in regions containing GnRH3 or Kiss2 neurons by in situ hybridization. Expression of tacr1a mRNA was seen in several brain regions including the olfactory bulb, preoptic area and hypothalamus, where GnRH3 and Kiss2 cells are present. These results suggest that unlike in mammals, Tac1 may be involved in male reproductive functions via direct action on GnRH3 neurons but independent of kisspeptin in the zebrafish.

Hypothalamic mechanisms associated with neuropeptide K-induced anorexia in Japanese quail (Coturnix japonica).

Central administration of neuropeptide K (NPK), a 36-amino acid peptide, is associated with anorexigenic effects in rodents and chickens. The mechanisms underlying the potent anorexigenic effects of NPK are still poorly understood. Thus, the aim of the present study was to identify the hypothalamic nuclei and neuropeptides that mediate anorexic effects of NPK in 7 day-old Japanese quail (Coturnix japonica). After a 6 h fast, intracerebroventricular (ICV) injection of NPK decreased food and water intake for 180 min post-injection. Quail injected with NPK had more c-Fos immunoreactive cells in the arcuate nucleus (ARC), lateral hypothalamus, and paraventricular nucleus (PVN) compared to the birds that were injected with the vehicle. In the ARC of NPK-injected quail, there was decreased neuropeptide Y (NPY), NPY receptor sub-type 1, and agouti-related peptide mRNA, and increased CART, POMC, and neurokinin receptor 1 mRNA. NPK-injected quail expressed greater amounts of corticotropin-releasing factor (CRF), CRF receptor sub-type 2, melanocortin receptors 3 and 4, and urocortin 3 mRNA in the PVN. In conclusion, results provide insights into understanding NPK-induced changes in hypothalamic physiology and feeding behavior, and suggest that the anorexigenic effects of NPK involve the ARC and PVN, with increased CRF and melanocortin and reduced NPY signaling.

Glucose, some amino acids and a plant secondary metabolite, chlorogenic acid induce the secretion of a regulatory hormone, tachykinin-related peptide, from the silkworm midgut.

Enteroendocrine cells in the insect midgut are thought to secrete peptide hormones in response to the nutritional state. However, the role of dietary compounds in inducing peptide hormone secretion from enteroendocrine cells in insects remains unknown. In the present study, we demonstrated that several dietary compounds from mulberry leaves, including glucose, amino acids, and the secondary metabolite chlorogenic acid, induced significant secretion of tachykinin-related peptides from isolated silkworm midguts at the luminal concentrations measured in fed larvae. This study provides evidence that the insect midgut senses a non-nutritious secondary metabolite in addition to nutrient metabolites to monitor luminal food status and secretes a feeding regulatory hormone, suggesting that a unique dietary sensory system modulates insect feeding via enteroendocrine control.

The role of melatonin, neurokinin, neurotrophic tyrosine kinase and glucocorticoid receptors in antidepressant-like effect.

Over the last few decades, depression has become one of the major public health problems in our society. This problem is connected not only with morbidity, but also with treatment, specifically with the effectiveness of the therapy as well as the concomitant side effects of available antidepressants. Major depressive disorder is a complex clinical entity, including different molecular mechanisms and neurological processes. This complexity is a challenge for scientists seeking to discover an innovatory antidepressant drug with multiple and complementary mechanisms of action. In this review, we discuss the role of melatonin, neurokinin, neurotrophic tyrosine kinase and glucocorticoid receptors in depression and antidepressant-like effects.

ERα in Tac2 Neurons Regulates Puberty Onset in Female Mice.

A variety of data suggest that estrogen action on kisspeptin (Kiss1)-containing arcuate nucleus neurons (which coexpress Kiss1, neurokinin B (the product of Tac2) and dynorphin (KNDy) neurons restrains reproductive onset and function, but roles for estrogen action in these Kiss1 neurons relative to a distinct population of rostral hypothalamic Kiss1 neurons (which does not express Tac2 or dynorphin) have not been directly tested. To test the role for estrogen receptor (ER)α in KNDy cells, we thus generated Tac2(Cre) and Kiss1(Cre) knock-in mice and bred them onto the Esr1(flox) background to ablate ERα specifically in Tac2-expressing cells (ERα(Tac2)KO mice) or all Kiss1 cells (ERα(Kiss1)KO mice), respectively. Most ERα-expressing Tac2 neurons represent KNDy cells. Arcuate nucleus Kiss1 expression was elevated in ERα(Tac2)KO and ERα(Kiss1)KO females independent of gonadal hormones, whereas rostral hypothalamic Kiss1 expression was normal in ERα(Tac2)KO but decreased in ERα(Kiss1)KO females; this suggests that ERα in rostral Kiss1 cells is crucial for control of Kiss1 expression in these cells. Both ERα(Kiss1)KO and ERα(Tac2)KO females displayed early vaginal opening, early and persistent vaginal cornification, increased gonadotropins, uterine hypertrophy, and other evidence of estrogen excess. Thus, deletion of ERα in Tac2 neurons suffices to drive precocious gonadal hyperstimulation, demonstrating that ERα in Tac2 neurons typically restrains pubertal onset and hypothalamic reproductive drive.

Involvement of spinal glutamate in nociceptive behavior induced by intrathecal administration of hemokinin-1 in mice.

The most recently identified tachykinin, hemokinin-1, was cloned from mouse bone marrow. While several studies indicated that hemokinin-1 is involved in pain and inflammation, the physiological functions of hemokinin-1 are not fully understood. Our previous research demonstrated that the intrathecal (i.t.) administration of hemokinin-1 (0.00625-1.6 nmol) dose-dependently induced nociceptive behaviors, consisting of scratching, biting and licking in mice, which are very similar with the nociceptive behaviors induced by the i.t. administration of substance P. Low-dose (0.0125 nmol) hemokinin-1-induced nociceptive behavior was inhibited by a specific NK1 receptor antagonist; however, high-dose (0.1 nmol) hemokinin-1-induced nociceptive behavior was not affected. In the present study, we found that the nociceptive behaviors induced by hemokinin-1 (0.1 nmol) were inhibited by the i.t. co-administration of MK-801 or D-APV, which are NMDA receptor antagonists. Moreover, we measured glutamate in the extracellular fluid of the mouse spinal cord using microdialysis. The i.t. administration of hemokinin-1 produced a significant increase in glutamate in the spinal cord, which was significantly reduced by co-administration with NMDA receptor antagonists. These results suggest that hemokinin-1-induced nociceptive behaviors may be mediated by the NMDA receptor in the spinal cord.

Protective effect of fenspiride on the bronchi in rats with chronic obstructive pulmonary disease.

We studied the effect of a non-steroidal anti-inflammatory drug fenspiride on contractive activity of bronchial smooth muscles on the model of chronic obstructive pulmonary disease of rats induced by 60-day exposure to nitrogen dioxide. The administration of fenspiride during the acute stage of the disease (day 15) abolished the constricting effect of the pollutant on the bronchial smooth muscles. Dilatation effect of fenspiride in a low dose (0.15 mg/kg) was mediated by its interaction with nerve endings of bronchial capsaicin-sensitive nerve C-fibers. The interaction of drug with receptors of C-fibers prevented neurogenic inflammation, which was confirmed by the absence of structural changes in the lungs typical of this pathology. The broncholytic effect of fenspiride in a high dose (15 mg/kg) was mediated by not only afferent pathways, but also its direct relaxing action on smooth muscle cells. The observed anti-inflammatory and bronchodilatation effect of fenspiride in very low doses can be used for prevention of chronic obstructive pulmonary disease in risk-group patients contacting with aggressive environmental factors.

Autocrine regulation of human sperm motility by tachykinins.

BACKGROUND: We examined the presence and function of tachykinins and the tachykinin-degrading enzymes neprilysin (NEP) and neprilysin-2 (NEP2) in human spermatozoa. METHODS: Freshly ejaculated semen was collected from forty-eight normozoospermic human donors. We analyzed the expression of substance P, neurokinin A, neurokinin B, hemokinin-1, NEP and NEP2 in sperm cells by reverse-transcriptase polymerase chain reaction (RT-PCR), western blot and immunocytochemistry assays and evaluated the effects of the neprilysin and neprilysin-2 inhibitor phosphoramidon on sperm motility in the absence and presence of tachykinin receptor-selective antagonists. Sperm motility was measured using WHO procedures or computer-assisted sperm analysis (CASA). RESULTS: The mRNAs of the genes that encode substance P/neurokinin A (TAC1), neurokinin B (TAC3), hemokinin-1 (TAC4), neprilysin (MME) and neprilysin-2 (MMEL1) were expressed in human sperm. Immunocytochemistry studies revealed that tachykinin and neprilysin proteins were present in spermatozoa and show specific and differential distributions. Phosphoramidon increased sperm progressive motility and its effects were reduced in the presence of the tachykinin receptor antagonists SR140333 (NK1 receptor-selective) and SR48968 (NK2 receptor-selective) but unmodified in the presence of SR142801 (NK3 receptor-selective). CONCLUSION: These data show that tachykinins are present in human spermatozoa and participate in the regulation of sperm motility. Tachykinin activity is regulated, at least in part, by neprilysins.

Tachykinin receptors as therapeutic targets in stress-related disorders.

The first report demonstrating the therapeutic efficacy of an orally applied neurokinin-1 (NK1) receptor antagonist in depression was published 10 years ago. Although there were difficulties to reproduce this particular finding, a huge amount of data has been published since this time, supporting the potential therapeutic value of various tachykinin ligands as promising novel tools for the management of stress-related disorders including anxiety disorders, schizophrenia and depression. The present review summarizes evidence derived from anatomical, neurochemical, pharmacological and behavioral studies demonstrating the localization of tachykinin neuropeptides including substance P (SP), neurokinin A, neurokinin B and their receptors (NK1, NK2, NK3) in brain areas known to be implicated in stress-mechanisms, mood/anxiety regulation and emotion-processing; their role as neurotransmitters and/or neuromodulators within these structures and their interactions with other neurotransmitter systems including dopamine, noradrenaline and serotonin (5-hydroxytryptamine, 5-HT). Finally, there is clear functional evidence from animal and human studies that interference with tachykinin transmission can modulate emotional behavior. Based on these findings and on evidence of upregulated tachykinin transmission in individuals suffering from stress-related disorders, several diverse tachykinin receptor antagonists, as well as compounds with combined antagonist profile have been developed and are currently under clinical investigation revealing evidence for anxiolytic, antidepressant and antipsychotic efficacy, seemingly characterized by a low side effect profile. However, substantial work remains to be done to clarify the precise mechanism of action of these compounds, as well as the potential of combining them with established and experimental therapies in order to boost efficacy.

An extract (THC-002) of Ba-Wei-Die-Huang-Wan inhibits expression of tachykinins, and P2X3 and TRPV1 receptors, and inhibits ATP-induced detrusor overactivity in spontaneously hypertensive rats.

AIMS: To investigate possible mechanisms of action of THC-002 (HARNCARE), a galenical produced from the traditional Chinese herbal mixture Ba-Wei-Die-Huang-Wan, which has been reported to improve lower urinary tract symptoms (LUTS) in patients. METHODS: Forty-five female SHRs were randomly separated into three groups. Two groups were given 20 ml physiological saline solution (PSS) per kg-body weight orally daily for 1 week. An hour after the administration of PSS, one of the groups received 20 mg THC-002 per kg body weight, and the other a similar volume of THC-002-free saline. The third group received no treatments. The bladders were analyzed by real time RT-PCR (n = 6) and immunohistochemistry (n = 3) for the expression of tachykinins and P2X3 and TRPV1 receptors. Cystometric investigation (n = 6) was conducted after intravesical instillation of saline followed by 5 mg/ml ATP solution. RESULTS: Treatment with PSS caused and upregulation of tachykinins and P2X3 and TRPV1 receptors, which was prevented in the group treated with THC-002. In the normal (non-treated) and non-THC-002-treated SHRs, instillation of the ATP solution decreased voiding interval, micturition volume, and bladder capacity compared to the instillation of saline. However, in the THC-002-treated SHRs, ATP instillation had no effect. CONCLUSIONS: In SHRs, THC-002 reduced the bladder expression of tachykinins and P2X3 and TRPV1 receptors, and inhibited ATP-induced detrusor overactivity. These effects may explain part of its beneficial effects on LUTS.

Quantitative peptidomics reveal brain peptide signatures of behavior.

The honey bee genome predicts approximately 100 peptides from 36 prohormones, but the functions of many of these peptides are unknown. We used differential isotope labeling combined with mass spectrometric analysis to quantify approximately 50% of known bee brain peptides in the context of foraging, with 8 showing robust and dynamic regulation. Some showed differences in brain abundance as a function of experience; specifically, nectar and pollen collection led to quick changes in abundance. These changes were related to the act of food collection, not ingestion, because foragers bring food back to the hive for storage rather than eating it themselves. Other peptide differences in brain abundance were seen in bees that either flew to a nectar feeder or a pollen feeder, but did not yet collect any food. These differences likely reflect well-known predispositions of some bees to collect either nectar or pollen, but not both. Tachykinin, PBAN, and sNPF were among the peptides with the strongest changes in association with nectar and pollen foraging. These peptides are known to be involved in regulating food intake in solitary insects, suggesting an evolutionary connection between that behavior and social foraging. These results demonstrate that it is now possible to use quantitative peptidomics to help determine which brain peptides are bioactive and to elucidate their function in the regulation of behavior.

Important roles of tachykinins in the development of allergic nasal hyperresponsiveness in guinea-pigs.

BACKGROUND: Although it has been suggested that the use of tachykinin receptor antagonists might prove to be an effective treatment for allergic rhinitis (AR), they are not used clinically. Therefore, we decided to examine the effects of tachykinin receptor antagonists on AR symptoms in an appropriate experimental model. OBJECTIVE: To evaluate newly developed tachykinin receptor antagonists in a Japanese cedar pollen-induced AR model and to determine their effect on allergen-induced sneezing, nasal blockage, and nasal hyperresponsiveness (NHR). METHODS: Sensitized guinea-pigs were challenged by forced inhalation of pollen once every week. Sneezing and nasal blockage were observed after pollen challenges. NHR (nasal blockage) to an intranasal application of leukotriene D(4) was assessed 2 days after an antigen challenge. We also evaluated whether intranasal dosing with a tachykinin causes NHR. NK(1) and NK(2) receptor antagonists were administered before an intranasal treatment with antigen or tachykinin. Amounts of tachykinins present in nasal cavity lavage fluid were measured by an enzyme immunoassay. RESULTS: Although an NK(1) and NK(2) receptor dual antagonist showed no effect on pollen-induced sneezing and biphasic nasal blockage, it did completely suppress the development of NHR. Experiments using specific NK(1) or NK(2) receptor antagonists revealed that NK(2) receptor activation was preferentially involved in the development of hyperresponsiveness. Increases in the levels of substance P (SP) and neurokinin A (NKA) in the nasal tissue were noted 20 min-1 h after the challenge. Intranasal instillation of either SP or NKA-induced NHR, which was almost completely inhibited by NK(2) receptor antagonists and partially inhibited by NK(1) receptor antagonists. CONCLUSIONS: SP and NKA, which are released early after the challenge, mediate the development of NHR by preferentially activating NK(2) receptors. Therefore, NK(2) receptor antagonists might prove to be effective treatment of AR.

Gosha-jinki-gan reduces transmitter proteins and sensory receptors associated with C fiber activation induced by acetic acid in rat urinary bladder.

AIM: We determined if Gosha-jinki-gan, a traditional Chinese herbal mixture, reduced the presence of the tachykinins neurokinin A, neurokinin B, and substance P, as well as the transient receptor potential vanilloid 1 (TRPV1) and P2X3 purine receptors that are functionally associated with C fibers in the urinary bladder. METHODS: Thirty-six female rats were fed with either a standard diet or one supplemented with 1.08% Gosha-jinki-gan. After 4 weeks, the urinary bladders were instilled with either saline or 0.1% acetic acid. After 30 min, the bladders were removed and expression of the tachykinins and the TRPV1 and P2X3 receptors was determined by immunohistochemistry and mRNA expression. RESULTS: In rats fed with the standard diet, the tachykinins and the TRPV1 and P2X3 receptors expressed nearby or within urothelium of the acetic acid-treated rats increased compared with the saline-instilled rats. In rats pretreated with Gosha-jinki-gan, the tachykinins and the TRPV1 and P2X3 receptors in the acetic acid-treated rats also increased compared with the saline-instilled rats. However, with the instillation of acetic acid, the tachykinins and the TRPV1 and P2X3 receptors of Gosha-jinki-gan pretreated rats decreased compared with standard diet fed rats. The mRNA expression levels of neurokinin A, substance P, and the TRPV1 receptor in acetic acid-treated Gosha-jinki-gan pretreated rats were lower than that in acetic acid-treated standard diet fed rats. Gosha-jinki-gan did not destroy nerve fibers within the bladders. CONCLUSIONS: Gosha-jinki-gan partially reduced the tachykinins and TRPV1 and P2X3 purine receptors without destroying the nerve fibers.

Effects of neonatal capsaicin treatment in the neutrophil production, and expression of preprotachykinin-I and tachykinin receptors in the rat bone marrow.

Bone marrow is richly innervated with both myelinated and non-myelinated nerve fibers, but the role of this innervation on hemopoiesis is poorly understood. Therefore, the aim of this study was to investigate the role of C-fibers on hematopoiesis. Wistar rats were neonatally injected with either capsaicin or its vehicle, and used at adult ages (8-10 weeks). In capsaicin-pretreated rats, the levels of substance P (SP) in bone marrow fluid were markedly reduced in comparison with the vehicle group (13.1+/-4.5 pg/ml versus 47.3+/-5.5 pg/ml, p<0.05). In bone marrow, the number of total leukocytes was 28% higher (p<0.05) in capsaicin-pretreated group, and this accompanied by a higher number of neutrophils, particularly of the immature forms. The mononuclear cell and eosinophils counts did not differ significantly among vehicle and capsaicin groups. In peripheral blood, the number of circulating neutrophils in the capsaicin group increased by 53.8% (p<0.05), whereas the number of mononuclear cells did not change significantly among groups. Eosinophils were virtually absent in the circulating blood in both groups. Semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) showed that both preprotachykinin (PPT)-I mRNA and the tachykinin neurokinin (NK)-1 mRNA expression in bone marrow cells significantly increased in capsaicin group, whereas the NK-2 mRNA expression was unchanged after capsaicin pretreatment. In conclusion, our data show that chronic neuropeptide depletion enhance the neutrophil proliferation and differentiation in the rat bone marrow by mechanisms involving upregulation of PPT-I gene and NK-1 receptors.

Tachykinins and the control of prolactin secretion.

Tachykinins are present in the pituitary gland and in brain areas involved in the control of the secretion of pituitary hormones. Tachykinins have been demonstrated to stimulate prolactin release acting directly on the anterior pituitary gland. These peptides have also been revealed to be able to act at the hypothalamic level, interacting with neurotransmitters and neuropeptides that have the potential to affect prolactin secretion. Tachykinins seem to act by stimulating or inhibiting the release of the factors that affect prolactin secretion. Among them, tachykinins have been demonstrated to stimulate oxytocin and vasopressin release, which in turn results in prolactin release. Tachykinins also potentiated the response to vasoactive intestinal peptide (VIP) and reinforced the action of glutamate, which in turn result in prolactin release. They have also been shown to interact with serotonin, a neurotransmitter involved in the control of prolactin secretion. In addition, tachykinins have been shown to inhibit GABA release, a neurotransmitter with prolactin-release inhibiting effect. This inhibition may result in an increased prolactin secretion by removal of the GABA inhibition. On the other hand, tachykinins have also been shown to stimulate dopamine release by the hypothalamus, an action that results in an inhibition of prolactin release. Dopamine is a well known inhibitor of prolactin secretion. In conclusion, although tachykinins have been shown to have a predominantly stimulatory effect on prolactin secretion, especially at the pituitary level, under some circumstances they may also exert an inhibitory influence on prolactin release, by stimulating dopamine release at the hypothalamic level.

Tachykinins and tachykinin receptors in the gut, with special reference to NK2 receptors in human.

Tachykinins (TKs), substance P (SP), neurokinin A (NKA) and B (NKB) are important peptide modulators of intestinal motility in animal species studied so far, including humans. Modulation of motility by TKs can occur at various levels, since these peptides are expressed in cholinergic excitatory motor neurons projecting to both circular and longitudinal muscle, interneurons, and intramural and extramural sensory neurons. The effects of SP, NKA and NKB are preferentially mediated through the stimulation of NK1, NK2 and NK3 receptors, respectively; however, the selectivity of natural TKs for their preferred receptors is relative. In addition, SP and NKA are expressed in similar quantities in the human intestine and adequate stimuli can release similar amount of these TKs from enteric nerves. Furthermore, a single anatomical substrate can express more than one TK receptor type, so that the blockade of a single receptor type may not reveal functional effects in integrated models of motility. In isolated human small intestine and colon circular muscle strips, both NK1 and NK2 receptors mediate contractile effects. Indeed, in the human small intestine, smooth muscle electrical and motor events induced by electrical field stimulation (EFS) can involve either or both NK1 and NK2 receptors or these latter receptors predominantly, depending on the experimental conditions. In contrast, in the human colonic smooth muscle, only the NK2 receptor-mediated component of the response to EFS is prominent and some evidence would suggest that this component is the main excitatory motor mechanism at this level. Furthermore, a NK2 receptor-mediated secretory component in the human colonic mucosa has been recently demonstrated. Thus, it could be speculated that the blockade of both NK1 and NK2 receptors will be necessary to antagonise motor effects induced by exogenous administration or endogenous release of TKs in the small intestine, whereas the blockade of the NK2 receptors would be sufficient to disrupt physiological motor and, possibly, secretory activity at the colonic level. Available evidence indicates that, in healthy volunteers, the infusion of NKA (25 pmol/kg/min i.v.) stimulated small intestine motility and precipitated a series of intestinal and non-intestinal adverse events. Nepadutant (8 mg i.v.), a selective NK2 receptor antagonist, antagonised small intestine motility induced by NKA and prevented associated intestinal adverse events. In another study, the same dose of nepadutant increased colo-rectal compliance during isobaric balloon distension in healthy volunteers pretreated with a glycerol enema, disclosing a NK2 receptor-mediated component in the regulation of colonic smooth muscle tone. However, the prolonged blockade of NK2 receptors by nepadutant (16 mg i.v. b.i.d. for 8 days) did not affect bowel habits, neither in term of movements nor of stool consistency. Altogether, these results indicate that, even when there is a significant redundance in the effects of TKs and in the role of their receptors, the selective blockade of tachykinin NK2 receptors can have functional consequences on human intestinal motility and perception, but this can occur without the disruption of the physiological functions.

Dysfunction of the cortico-basal ganglia-cortical loop in a rat model of early parkinsonism is reversed by metabotropic glutamate receptor 5 antagonism.

This study examined the cellular correlates of the akinetic deficits produced in Wistar rats by discrete bilateral 6-hydroxydopamine (6-OHDA) striatal infusions in the dorsolateral striatum, mimicking the preferential denervation of the motor striatal territory in early symptomatic stage of Parkinson's disease (PD). Intraneuronal gene expression of cytochrome oxidase subunit I (COI), a metabolic index of neuronal activity, was increased in the subthalamic nucleus, substantia nigra pars reticulata and decreased in frontal cortical areas, but paradoxically unchanged in the striatum, globus pallidus, entopeduncular nucleus and ventrolateral thalamic nucleus. Neither preproenkephalin A nor preprotachykinin mRNA expression, markers of striatal projection neurons, were modified in the denervated striatal area despite 90% loss of dopamine (DA) terminals. Preproenkephalin A mRNA expression was however, decreased in the nondepleted striatal region, suggesting compensatory increase of dopamine tone from those spared areas. A chronic treatment with the metabotropic glutamate receptor 5 (mGluR5) antagonist 2-methyl-6-(phenylethylnyl)-pyridine (MPEP), which alleviated the akinetic disorders produced by the lesion, reversed the lesion-induced variations of COI gene expression, moderately increased this marker in the structures unaffected by the lesion and did not modify the striatal neuropeptides gene expression. These data suggest that the expression of akinetic deficits in early parkinsonism is associated with focused metabolic changes in the cortico-basal ganglia-cortical loop downstream of the striatum and pallidal complex.

The Kell protein of the common K2 phenotype is a catalytically active metalloprotease, whereas the rare Kell K1 antigen is inactive. Identification of novel substrates for the Kell protein.

The Kell blood group is a highly polymorphic system containing over 20 different antigens borne by the protein Kell, a 93-kDa type II glycoprotein that displays high sequence homology with members of the M13 family of zinc-dependent metalloproteases whose prototypical member is neprilysin. Kell K1 is an antigen expressed in 9% of the Caucasian population, characterized by a point mutation (T193M) of the Kell K2 antigen, and located within a putative N-glycosylation consensus sequence. Recently, a recombinant, non-physiological, soluble form of Kell was shown to cleave Big ET-3 to produce the mature vasoconstrictive peptide. To better characterize the enzymatic activity of the Kell protein and the possible differences introduced by antigenic point mutations affecting post-translational processing, the membrane-bound forms of the Kell K1 and Kell K2 antigens were expressed either in K562 cells, an erythroid cell line, or in HEK293 cells, a non-erythroid system, and their pharmacological profiles and enzymatic specificities toward synthetic and natural peptides were evaluated. Results presented herein reveal that the two antigens possess considerable differences in their enzymatic activities, although not in their trafficking pattern. Indeed, although both antigens are expressed at the cell surface, Kell K1 protein is shown to be inactive, whereas the Kell K2 antigen binds neprilysin inhibitory compounds such as phosphoramidon and thiorphan with high affinity, cleaves the precursors of the endothelin peptides, and inactivates members of the tachykinin family with enzymatic properties resembling those of other members of the M13 family of metalloproteases to which it belongs.