A novel hypothalamic neuroendocrine peptide: URP (urotensin-II-related peptide)?

Microinjection of urotensin II into the pedunculopontine tegmentum leads to an increase in the consumption of sweet tastants

The pedunculopontine tegmentum (PPTg) plays a role in processing multiple sensory inputs and innervates brain regions associated with reward-related behaviors. The urotensin II receptor, activated by the urotensin II peptide (UII), is selectively expressed by the cholinergic neurons of the PPTg. Although the exact function of cholinergic neurons of the PPTg is unknown, they are thought to contribute to the perception of reward magnitude or salience detection. We hypothesized that the activation of PPTg cholinergic neurons would alter sensory processing across multiple modalities (ex. taste and hearing). Here we had three aims: first, determine if cholinergic activation is involved in consumption behavior of palatable solutions (sucrose). Second, if so, distinguish the impact of the caloric value by using saccharin, a zero calorie sweetener. Lastly, we tested the UII-mediated effects on perception of acoustic stimuli by measuring acoustic startle reflex (ASR). Male Sprague-Dawley rats were bilaterally cannulated into the PPTg, then placed under food restriction lasting the entire consumption experiment (water ad lib.). Treatment consisted of a microinjection of either 1 μL of aCSF or 1 μL of 10 μM UII into the PPTg, and the rats were immediately given access to either sucrose or saccharin. For the remaining five days, rats were allowed one hour access per day to the same sweet solution without any further treatments. During the saccharin experiment rats were tested in a contact lickometer which recorded each individual lick to give insight into the microstructure of the consumption behavior. ASR testing consisted of a baseline (no treatment), treatment day, and two additional days (no treatment). Immediately following the microinjection of UII, consumption of both saccharin and sucrose increased compared to controls. This significant increase persisted for days after the single administration of UII, but there was no generalized arousal or increase in water consumption between testing sessions. The effects on ASR were not significant. Activating cholinergic PPTg neurons may lead to a miscalculation of the salience of external stimuli, implicating the importance of cholinergic input in modulating a variety of behaviors. The long-lasting effects seen after UII treatment support further research into the role of sensory processing on reward related-behaviors at the level of the PPTg cholinergic neurons.

The G Protein-Coupled Receptor UT of the Neuropeptide Urotensin II Displays Structural and Functional Chemokine Features

The urotensinergic system was previously considered as being linked to numerous physiopathological states, including atherosclerosis, heart failure, hypertension, pre-eclampsia, diabetes, renal disease, as well as brain vascular lesions. Thus, it turns out that the actions of the urotensin II (UII)/G protein-coupled receptor UT system in animal models are currently not predictive enough in regard to their effects in human clinical trials and that UII analogs, established to target UT, were not as beneficial as expected in pathological situations. Thus, many questions remain regarding the overall signaling profiles of UT leading to complex involvement in cardiovascular and inflammatory responses as well as cancer. We address the potential UT chemotactic structural and functional definition under an evolutionary angle, by the existence of a common conserved structural feature among chemokine receptorsopioïdergic receptors and UT, i.e., a specific proline position in the transmembrane domain-2 TM2 (P2.58) likely responsible for a kink helical structure that would play a key role in chemokine functions. Even if the last decade was devoted to the elucidation of the cardiovascular control by the urotensinergic system, we also attempt here to discuss the role of UII on inflammation and migration, likely providing a peptide chemokine status for UII. Indeed, our recent work established that activation of UT by a gradient concentration of UII recruits Gαi/o and Gα13 couplings in a spatiotemporal way, controlling key signaling events leading to chemotaxis. We think that this new vision of the urotensinergic system should help considering UT as a chemotactic therapeutic target in pathological situations involving cell chemoattraction.

Intra-ventral tegmental area microinjections of urotensin II modulate the effects of cocaine

Although the peptide urotensin II (UII) has well studied direct actions on the cardiovascular system, the UII receptor (UIIR) is expressed by neurons of the hindbrain. Specifically, the UIIR is expressed by the cholinergic neurons of the laterodorsal tegmentum (LDTg) and the pedunculopontine tegmentum (PPTg). These neurons send axons to the ventral tegmental area (VTA), for which the PPTg and LDTg are the sole source of acetylcholine. Therefore, it was hypothesized that UIIR activation within the VTA would modulate reward-related behaviors, such as cocaine-induced drug seeking. Intra-VTA microinjections of UII at high concentrations (1 nmole) established conditioned place preference (CPP), but also blocked cocaine-mediated CPP (10 mg/kg). When rats received systemic sub-effectual doses of cocaine (7.5 mg/kg) with intra-VTA injections of 1 or 10 pmole of UII CPP was formed. Furthermore, the second endogenous ligand for the UIIR, urotensin II-related peptide, had the same effect at the 10 pmole dose. The effects of low doses of UII were blocked by pretreatment with the UIIR antagonist SB657510. Furthermore, it was found that intra-VTA UII (10 pmole) further increased cocaine-mediated (7.5 mg/kg) rises in electrically evoked dopamine in the nucleus accumbens. Our study has found that activation of VTA-resident UIIR produces observable behavioral changes in rats, and that UIIR is able to modulate the effects of cocaine. In addition, it was found that UIIR activation within the VTA can potentiate cocaine-mediated neurochemical effects. Therefore, the coincident activation of the UII-system and cocaine administration may increase the liability for drug taking behavior.

Direct evidence for the co-expression of URP and GnRH in a sub-population of rat hypothalamic neurones: anatomical and functional correlation

Urotensin-II-related peptide (URP) is an eight amino-acid neuropeptide recently isolated from rat brain and considered as the endogenous ligand for the GPR14 receptor. Using single and double immunohistochemical labelling, in situ hybridization and ultrastructural immunocytochemistry, we explored the cellular and subcellular localization of URP in the male rat brain. URP peptide was detected in numerous varicose fibres of the median eminence (ME) and organum vasculosum laminae terminalis (OVLT) as well as in neuronal cell bodies of the medial septal nucleus and diagonal band of Broca where corresponding mRNA were also detected. Combining in situ hybridization with immunohistochemistry, we showed that cell bodies of the rat anterior hypothalamus contained both URP mRNA and GnRH peptide. In addition, double ultrastructural immunodetection of URP and GnRH peptides clearly revealed, in the median eminence, the co-localization of both peptides in the same neuronal processes in the vicinity of fenestrated portal vessels. This remarkable cellular and subcellular distribution led us to test the effect of URP on the GnRH-induced gonadotrophins release in the anterior pituitary, and to discuss its putative role at the level of the median eminence.

[Endocrine neurons and neurotransmission: 40 years of cytochemical studies]

Conceptual advances about chemical neurotransmission during the last 40 years have benefited a lot from histocytochemical approaches and from a particular experimental model, the endocrine hypothalamic neurons. New concepts like cotransmission, neuronal versatility, somatodendritic release of neurotransmitters, volume transmission, differential routing or cooperative synthesis of mediators, have often been issued from this set of methodologies and from their application to neurosecretory neurons. This review, mainly based on the results of our group, is aiming at illustrating how the peculiar metabolism of these neurons and their location at the neuro-endocrine interface have allowed discovering new aspects of neurotransmission, first considered as exceptions but then generalized to the whole nervous system. These new concepts shed lights on the normal functioning of the brain and definitely contribute to diversify pharmacological approaches of pathological neurotransmission.

[André Calas, the original path of a neuroendocrinologist]

This talk, given as an introduction to a symposium organised to honor André Calas, calls forth his personality, recalls the major events in his career and summarizes the evolution of his research.

Characterization of urotensin II, distribution of urotensin II, urotensin II-related peptide and UT receptor mRNAs in mouse: evidence of urotensin II at the neuromuscular junction

Urotensin II (UII) and UII-related peptide (URP) are paralog neuropeptides whose existence and distribution in mouse have not yet been investigated. In this study, we showed by HPLC/RIA analysis that the UII-immunoreactive molecule in the mouse brain corresponds to a new UII(17) isoform. Moreover, calcium mobilization assays indicated that UII(17) and URP were equally potent in stimulating UII receptor (UT receptor). Quantitative RT-PCR and in situ hybridization analysis revealed that in the CNS UII and URP mRNAs were predominantly expressed in brainstem and spinal motoneurons. Besides, they were differentially expressed in the medial vestibular nucleus, locus coeruleus and the ventral medulla. In periphery, both mRNAs were expressed in skeletal muscle, testis, vagina, stomach, and gall bladder, whereas only URP mRNA could be detected in the seminal vesicle, heart, colon, and thymus. By contrast, the UT receptor mRNA was widely expressed, and notably, very high amounts of transcript occurred in skeletal muscle and prostate. In the biceps femoris muscle, UII-like immunoreactivity was shown to coexist with synaptophysin in muscle motor end plate regions. Altogether these results suggest that (i) UII and URP may have many redundant biological effects, especially at the neuromuscular junction; (ii) URP may more specifically participate to autonomic, cardiovascular and reproductive functions.

Another ligand fishing for G protein-coupled receptor 14. Discovery of urotensin II-related peptide in the rat brain

Urotensin II (UII), which was originally isolated from the teleost urophysis, was identified as an endogenous ligand for orphan G protein-coupled receptor 14 (GPR14). The structure of mammalian UII was confirmed by isolation from spinal cord in porcine, or was easily predicted from the sequence of prepro-UII in human. For rat and mouse, however, only the tentative sequences of UII peptides have been demonstrated because the typical processing sites are absent from the amino-terminal region of the mature peptides. Isolation of UII-like immunoreactivity in rat brain revealed the presence of a novel peptide, designated urotensin II-related peptide (URP). URP binds and activates the human and rat urotensin II receptors (GPR14) and has a hypotensive effect when administrated to anesthetized rats. Based on the DNA sequences of the cloned prepro-URP gene, the amino acid sequences of mature URP for mouse and human are identical to that for rat URP. These results suggest that URP is the endogenous and functional ligand for urotensin II receptor in the rat and mouse, and possibly in the human.

Form-deprivation myopia in chick induces limited changes in retinal gene expression

PURPOSE

Evidence has implicated the retina as a principal controller of refractive development. In the present study, the retinal transcriptome was analyzed to identify alterations in gene expression and potential signaling pathways involved in form-deprivation myopia of the chick.

METHODS

One-week-old white Leghorn chicks wore a unilateral image-degrading goggle for 6 hours or 3 days (n = 6 at each time). Total RNA from the retina/(retinal pigment epithelium) was used for expression profiling with chicken gene microarrays (Chicken GeneChips; Affymetrix, Santa Clara, CA). To identify gene expression level differences between goggled and contralateral nongoggled eyes, normalized microarray signal intensities were analyzed by the significance analysis of microarrays (SAM) approach. Differentially expressed genes were validated by real-time quantitative reverse transcription-polymerase chain reaction (qPCR) in independent biological replicates.

RESULTS

Small changes were detected in differentially expressed genes in form-deprived eyes. In chickens that had 6 hours of goggle wear, downregulation of bone morphogenetic protein 2 and connective tissue growth factor was validated. In those with 3 days of goggle wear, downregulation of bone morphogenetic protein 2, vasoactive intestinal peptide, preopro-urotensin II-related peptide and mitogen-activated protein kinase phosphatase 2 was validated, and upregulation of endothelin receptor type B and interleukin-18 was validated.

CONCLUSIONS

Form-deprivation myopia, in its early stages, is associated with only minimal changes in retinal gene expression at the level of the transcriptome. While the list of validated genes is short, each merits further study for potential involvement in the signaling cascade mediating myopia development.

Urotensin-II expression in the mouse spinal cord

Urotensin-II (UII), a 12 amino acid peptide, was discovered in the teleost fish neurosecretory cells located in the caudal portion of the spinal cord and which project to a neurohemal gland called the urophysis. The distribution of UII and of its prepro-UII mRNA is not limited to fish and was found for example in the rat spinal cord. In view of the potential interest of obtaining transgenic mice, we have therefore characterized the distribution of mouse pro-UII mRNA and UII immunoreactivity, by in situ hybridization and immunohistochemistry, respectively, in the mouse spinal cord. A population of UII-like immunoreactive cell bodies was located in the ventral horn of the different segments. These cells displayed all the features of motoneurons, as confirmed by a double immunohistochemical labelling showing the co-occurrence of UII and vesicular acetylcholine transporter, and by electron microscope immunocytochemistry. Retrograde labelling of motoneurons innervating the bulbocavernosus penile muscle showed that some of them contained UII. In situ hybridization histochemistry revealed that pro-UII mRNA was located in some ventral horn neuronal perikarya. The pro-UII mRNA-containing cell bodies possessed the same motoneuron characteristics, confirming the results of the immunohistochemical studies and showing that the gene of mouse UII is expressed in a subpopulation of motoneurons in the spinal cord. Our results support the assumption that UII peptide characterized as endocrine in fish is also expressed within mammalian motoneurons.