Manifesto for an ECNP Neuromodulation Thematic Working Group (TWG): Non-invasive brain stimulation as a new Super-subspecialty

Non-Invasive Brain Stimulation (NIBS) techniques and in particular, repetitive Transcranial Magnetic Stimulation (rTMS), are developing beyond mere clinical application. Although originally purposed for the treatment of resistant neuropsychiatric disorders, NIBS is also contributing to a deeper understanding of psychiatric disorders. rTMS is also changing the model of the disorder itself, from "mental" to one of neural connectivity. TMS allows the assessment of brain circuit excitability and eventually, of plastic changes affecting these circuits. While a clinical translational approach is, at the present time, the most adequate to meet the dimensional-circuit base model of the disorder, it refines the standard categorical classification of psychiatric disorders. The discovery of the fundamental importance of the balance between neuroplasticity and inflammation is also now explored through neuro-modulation findings consistently with the evidence of anti-inflammatory actions of the magnetic pulses. rTMS may activate, inhibit, or otherwise interfere with the activity of neuronal cortical networks, depending on stimulus frequency and intensity of brain-induced electric field. Of particular interest, yet still unclear, is how the relatively unspecific nature of TMS stimulation may lead to specific neuronal reorganization, as well as a definition of the TMS-triggered reorganization of functional brain modules, raising attention on the importance of the active participation of the patient to the treatment.. Configuration and state of consciousness of the subject have made subjective experience under treatment regain importance in the neuro-scientific Psychiatry based on the requirement of United States National Institute of Health (NIH) and the substantial importance of the consciousness state in the efficacy of the TMS treatment. By focusing on the subjective experience, a renaissance of the phenomenology offers Psychiatry an opportunity to become proficient and to distinguish itself from other disciplines. For all these reasons, TMS should be included in the cluster of the sub-specialties as a new "Super-Specialty" and an appropriate training course has to be inaugurated. Psychiatrists are nowadays multi-specialists, moving from a specialty to another, vs super-specialist. The cultivation of a properly trained cohort of TMS psychiatrists will better meet the challenges of treatment-resistant psychiatric conditions (disorders of connectivity), through appropriate and ethical practice, meanwhile facilitating an informed development and integration of additional emerging neuro-modulation techniques. The aim of this consensus paper is to underline the interdisciplinary nature of NIBS, that also encompasses the subjective experience and to point out the necessity of a neuroscience-applied approach to NIBS in the context of the European College of Neuro-psychopharmacology (ECNP).

Developmental differences in the brain response to unhealthy food cues: an fMRI study of children and adults

BACKGROUND

Food cues are omnipresent and may trigger overconsumption. In the past 2 decades, the prevalence of childhood obesity has increased dramatically. Because children's brains are still developing, especially in areas important for inhibition, children may be more susceptible than adults to tempting food cues.

OBJECTIVE

We examined potential developmental differences in children's and adults' responses to food cues to determine how these responses relate to weight status.

DESIGN

We included 27 children aged 10-12 y and 32 adults aged 32-52 y. Functional magnetic resonance imaging data were acquired during a food-viewing task in which unhealthy and healthy food pictures were presented.

RESULTS

Children had a stronger activation in the left precentral gyrus than did adults in response to unhealthy compared with healthy foods. In children, unhealthy foods elicited stronger activation in the right inferior temporal and middle occipital gyri, left precentral gyrus, bilateral opercular part of the inferior frontal gyrus, left hippocampus, and left middle frontal gyrus. Adults had stronger activation in the bilateral middle occipital gyrus and the right calcarine sulcus for unhealthy compared with healthy foods. Children with a higher body mass index (BMI) had lower activation in the bilateral dorsolateral prefrontal cortex while viewing unhealthy compared with healthy foods. In adults there was no correlation between BMI and neural response to unhealthy compared with healthy foods.

CONCLUSIONS

Unhealthy foods might elicit more attention both in children and in adults. Children had stronger activation while viewing unhealthy compared with healthy foods in areas involved in reward, motivation, and memory. Furthermore, children activated a motivation and reward area located in the motor cortex more strongly than did adults in response to unhealthy foods. Finally, children with a higher BMI had less activation in inhibitory areas in response to unhealthy foods, which may mean they are more susceptible to tempting food cues. This trial was registered at www.trialregister.nl as NTR4255.

NPY receptor subtype specification for behavioral adaptive strategies during limited food access

The neuropeptide Y (NPY) system in the brain regulates a wide variety of behavioral, metabolic and hormonal homeostatic processes required for energy balance control. During times of limited food availability, NPY promotes behavioral hyperactivity necessary to explore and prepare for novel food resources. As NPY can act via 5 different receptor subtypes, we investigated the path through which NPY affects different behavioral components relevant for adaptation to such conditions. We tested NPY Y1 and Y2 receptor knockout mice and their wild-type littermate controls in a daily scheduled limited food access paradigm with unlimited access to running wheel. Here we show that NPY Y1 receptor deficient mice lack the expression of appetitive behavior and that NPY Y2 receptors control the level of hyperactive behavior under these conditions. Thus, receptor specificity determines the differential expression of NPY-mediated behavioral adaptations to overcome a negative energy status.

Obesity genes identified in genome-wide association studies are associated with adiposity measures and potentially with nutrient-specific food preference

BACKGROUND

New genetic loci, most of which are expressed in the brain, have recently been reported to contribute to the development of obesity. The brain, especially the hypothalamus, is strongly involved in regulating weight and food intake.

OBJECTIVES

We investigated whether the recently reported obesity loci are associated with measures of abdominal adiposity and whether these variants affect dietary energy or macronutrient intake.

DESIGN

We studied 1700 female Dutch participants in the European Prospective Investigation into Cancer and Nutrition (EPIC). Their anthropometric measurements and intake of macronutrients were available. Genotyping was performed by using KASPar chemistry. A linear regression model, with an assumption of an additive effect, was used to analyze the association between genotypes of 12 single nucleotide polymorphisms (SNPs) and adiposity measures and dietary intake.

RESULTS

Seven SNPs were associated (P < 0.05) with weight, body mass index (BMI), and waist circumference (unadjusted for BMI). They were in or near to 6 loci: FTO, MC4R, KCTD15, MTCH2, NEGR1, and BDNF. Five SNPs were associated with dietary intake (P < 0.05) and were in or near 5 loci: SH2B1 (particularly with increased fat), KCTD15 (particularly with carbohydrate intake), MTCH2, NEGR1, and BDNF.

CONCLUSIONS

We confirmed some of the findings for the newly identified obesity loci that are associated with general adiposity in a healthy Dutch female population. Our results suggest that these loci are not specifically associated with abdominal adiposity but more generally with obesity. We also found that some of the SNPs were associated with macronutrient-specific food intake.

Chronic blockade of melanocortin receptors alleviates allodynia in rats with neuropathic pain

We investigated the involvement of the spinal cord melanocortin (MC) system in neuropathic pain. Because we recently demonstrated that MC receptor ligands acutely alter nociception in an animal model of neuropathic pain, in this study we tested whether chronic administration was also effective. We hypothesized that chronic blockade of the spinal MC system might decrease sensory abnormalities associated with this condition. The effects of the MC receptor antagonist SHU9119 (0.5 microg/d) and agonist MTII (0.1 microg/d) were evaluated in rats with a chronic constriction injury of the sciatic nerve. Drugs were continuously infused into the cisterna magna. Antinociceptive effects were measured with tests involving temperature (10 degrees C or 47.5 degrees C) or mechanical (von Frey) stimulation. The administration of MTII increased mechanical allodynia, whereas SHU9119 produced a profound cold and mechanical antiallodynia, altering responses to control levels. The antiallodynic effects of SHU9119 were very similar to those produced by the alpha(2)-adrenergic agonist tizanidine (50 microg/d). The effects of SHU9119 and MTII are most likely mediated through the MC4 receptor, because this is the only MC-receptor subtype present in the spinal cord. We conclude that the chronic administration of MC4-receptor antagonists might provide a promising tool in the treatment of neuropathic pain.

IMPLICATIONS

In this study we demonstrated that continuous intrathecal infusion of the melanocortin-receptor antagonist SHU9119 reduces cold and mechanical allodynia in rats with a chronic constriction injury of the sciatic nerve, a lesion producing neuropathic pain.

Drug target discovery by pharmacogenetics: mutations in the melanocortin system and eating disorders

The identification of the genetic defect underlying the obese phenotype of the viable yellow mouse, ectopic overexpression of the agouti protein which acts as antagonist at the melanocortin-4 receptor, together with the demonstration that the brain melanocortin system was one major downstream effector pathway of leptin signaling has put forward melanocortin receptors as drug targets for obesity. The lack of compounds acting as melanocortin receptor antagonists was the reason why pharmacological studies had not recognized melanocortin receptors as important drug targets earlier. Blockade of brain melanocortin receptors results in increased food intake and body weight, whereas stimulation of the brain melanocortin system results in decreased food intake and activation of the hypothalamo-pituitary-adrenal axis. Anorexia nervosa is characterized by decreased body weight and food intake accompanied by changes in neuroendocrine systems such as strong activation of the hypothalamo-pituitary-adrenal axis. Since agouti-related protein suppresses the activity of the melanocortin system, the AgRP gene was investigated as candidate gene in anorexia nervosa. One variant of the AgRP gene was associated with anorexia nervosa, thus putting forward melanocortin receptor blockade as putative pharmacotherapy. Investigating variations in candidate genes in disease populations appears to be a fruitful approach towards the identification of drug targets.

Neuropathic pain: a possible role for the melanocortin system?

In humans, damage to the nervous system can lead to a pain state referred to as neuropathic pain. Here, we give a short overview of the clinical picture and classification of neuropathic pain and highlight some of the currently known pathophysiological mechanisms involved, with special emphasis on neuropeptide plasticity. In this context, we discuss a specific group of neuropeptides, the melanocortins. These peptides have been demonstrated to play a role in nociception and to functionally interact with the opiate system. Recently, we demonstrated that spinal melanocortin receptors are upregulated in a rat model of neuropathic pain and that blockade of the melanocortin MC(4) receptor has anti-allodynic effects in this condition, suggesting that the melanocortin system plays a role in neuropathic pain. A natural agonist of melanocortin receptors is alpha-melanocyte-stimulating hormone (alpha-MSH), derived from the precursor molecule pro-opiomelanocortin (POMC). Cleavage of this precursor also yields beta-endorphin, which is co-released with alpha-MSH in nociception-associated areas of the spinal cord. We hypothesise that melanocortin receptor blockade attenuates a tonic influence of alpha-MSH on nociception, thus allowing the analgesic effects of beta-endorphin to develop, resulting in the alleviation of allodynia. In this way, treatment with melanocortin receptor antagonists might enhance opioid efficacy in neuropathic pain, which would be of great benefit in clinical practice.

Hypothalamic, metabolic, and behavioral responses to pharmacological inhibition of CNS melanocortin signaling in rats

The CNS melanocortin (MC) system is implicated as a mediator of the central effects of leptin, and reduced activity of the CNS MC system promotes obesity in both rodents and humans. Because activation of CNS MC receptors has direct effects on autonomic outflow and metabolism, we hypothesized that food intake-independent mechanisms contribute to development of obesity induced by pharmacological blockade of MC receptors in the brain and that changes in hypothalamic neuropeptidergic systems known to regulate weight gain [i.e., corticotropin-releasing hormone (CRH), cocaine-amphetamine-related transcript (CART), proopiomelanocortin (POMC), and neuropeptide Y (NPY)] would trigger this effect. Relative to vehicle-treated controls, third intracerebroventricular (i3vt) administration of the MC receptor antagonist SHU9119 to rats for 11 d doubled food and water intake (toward the end of treatment) and increased body weight ( approximately 14%) and fat content ( approximately 90%), hepatic glycogen content ( approximately 40%), and plasma levels of cholesterol ( approximately 48%), insulin ( approximately 259%), glucagon ( approximately 80%), and leptin ( approximately 490%), whereas spontaneous locomotor activity and body temperature were reduced. Pair-feeding of i3vt SHU9119-treated animals to i3vt vehicle-treated controls normalized plasma levels of insulin, glucagon, and hepatic glycogen content, but only partially reversed the elevations of plasma cholesterol ( approximately 31%) and leptin ( approximately 104%) and body fat content ( approximately 27%). Reductions in body temperature and locomotor activity induced by i3vt SHU9119 were not reversed by pair feeding, but rather were more pronounced. None of the effects found can be explained by peripheral action of the compound. The obesity effects occurred despite a lack in neuropeptide expression responses in the neuroanatomical range selected across the arcuate (i.e., CART, POMC, and NPY) and paraventricular (i.e., CRH) hypothalamus. The results indicate that reduced activity of the CNS MC pathway promotes fat deposition via both food intake-dependent and -independent mechanisms.

Association between an agouti-related protein gene polymorphism and anorexia nervosa

Anorexia nervosa (AN) is a life threatening disorder affecting mostly adolescent women. It is a dramatic psychiatric syndrome accompanied by severe weight loss, hyperactivity and neuroendocrine changes (reviewed in Refs 1 and 2). Several studies have shown a strong genetic component in AN (reviewed in Ref 3). Recent advances in unraveling the mechanisms of weight control point to a crucial role of the melanocortin-4 receptor (MC4-r) system in regulating body weight. The orexigenic neuropeptide agouti-related protein (AGRP), a MC4-r antagonist, plays a crucial role in maintaining body weight, by inducing food intake. The sequence of the coding region of the human AGRP gene (AGRP) was determined and the AGRP of 100 patients with AN was screened for variations. Three single nucleotide polymorphisms (SNPs) were identified and screened in a further 45 patients and 244 controls. Two alleles were in complete linkage disequilibrium and were significantly enriched in anorectic patients (11%; P = 0.015) compared to controls (4.5%). These data indicate that variations of AGRP are associated with susceptibility for AN. This is possibly caused by defective suppression of the MC4-r by the variant AGRP, leading to a decreased feeding signal, increasing the risk of developing AN. These results implicate that antagonism of the MC4-r might be considered as pharmacotherapy for patients with AN.

Common requirements for melanocortin-4 receptor selectivity of structurally unrelated melanocortin agonist and endogenous antagonist, Agouti protein

The activity of melanocortin receptors (MCR) is regulated by melanocortin peptide agonists and by the endogenous antagonists, Agouti protein and AgRP (Agouti-related protein). To understand how the selectivity for these structurally unrelated agonists and antagonist is achieved, chimeric and mutants MC3R and MC4R were expressed in cell lines and pharmacologically analyzed. A region containing the third extracellular loop, EC3, of MC4R was essential for selective Agouti protein antagonism. In addition, this part of MC4R, when introduced in MC3R, conferred Agouti protein antagonism. Further mutational analysis of this region of MC4R demonstrated that Tyr(268) was required for the selective interaction with Agouti protein, because a profound loss of the ability of Agouti protein to inhibit (125)I-labeled [Nle(4),d-Phe(7)]alpha-melanocyte-stimulating hormone (MSH) binding was observed by the single mutation of Tyr(268) to Ile. This same residue conferred selectivity for the MC4R selective agonist, [d-Tyr(4)]MT-II, whereas it inhibited interaction with the MC3R-selective agonist, [Nle(4)]Lys-gamma(2)-MSH. Conversely, mutation of Ile(265) in MC3 (the corresponding residue of Tyr(268)) to Tyr displayed a gain of affinity for [d-Tyr(4)]MT-II, but not for Agouti protein, and a loss of affinity for [Nle(4)]Lys-gamma(2)-MSH as compared with wild-type MC3R. This single amino acid mutation thus confers the selectivity of MC3R toward a pharmacological profile like that observed for MC4R agonists but not for the antagonist, Agouti protein. Thus, selectivity for structurally unrelated ligands with opposite activities is achieved in a similar manner for MC4R but not for MC3R.

AgRP(83-132) acts as an inverse agonist on the human-melanocortin-4 receptor

The central melanocortin (MC) system has been demonstrated to act downstream of leptin in the regulation of body weight. The system comprises alpha-MSH, which acts as agonist, and agouti-related protein (AgRP), which acts as antagonist at the MC3 and MC4 receptors (MC3R and MC4R). This property suggests that MCR activity is tightly regulated and that opposing signals are integrated at the receptor level. We here propose another level of regulation within the melanocortin system by showing that the human (h) MC4R displays constitutive activity in vitro as assayed by adenylyl cyclase (AC) activity. Furthermore, human AgRP(83-132) acts as an inverse agonist for the hMC4R since it was able to suppress constitutive activity of the hMC4R both in intact B16/G4F melanoma cells and membrane preparations. The effect of AgRP(83-132) on the hMC4R was blocked by the MC4R ligand SHU9119. Also the hMC3R and the mouse(m)MC5R were shown to be constitutively active. AgRP(83-132) acted as an inverse agonist on the hMC3R but not on the mMC5R. Thus, AgRP is able to regulate MCR activity independently of alpha-MSH. These findings form a basis to further investigate the relevance of constitutive activity of the MC4R and of inverse agonism of AgRP for the regulation of body weight.

Antagonism of the melanocortin system reduces cold and mechanical allodynia in mononeuropathic rats

The presence of both pro-opiomelanocortin-derived peptides and melanocortin (MC) receptors in nociception-associated areas in the spinal cord suggests that, at the spinal level, the MC system might be involved in nociceptive transmission. In the present study, we demonstrate that a chronic constriction injury (CCI) to the rat sciatic nerve, a lesion that produces neuropathic pain, results in changes in the spinal cord MC system, as shown by an increased binding of (125)I-NDP-MSH to the dorsal horn. Furthermore, we investigated whether intrathecal administration (in the cisterna magna) of selective MC receptor ligands can affect the mechanical and cold allodynia associated with the CCI. Mechanical and cold allodynia were assessed by measuring withdrawal responses of the affected limb to von Frey filaments and withdrawal latencies upon immersion in a 4.5 degrees C water bath, respectively. We show that treatment with the MC receptor antagonist SHU9119 has a profound anti-allodynic effect, suggesting that the endogenous MC system has a tonic effect on nociception. In contrast, administration of the MC4 receptor agonists MTII and d-Tyr-MTII primarily increases the sensitivity to mechanical and cold stimulation. No antinociceptive action was observed after administration of the selective MC3 receptor agonist Nle-gamma-MSH. Together, our data suggest that the spinal cord MC system is involved in neuropathic pain and that the effects of MC receptor ligands on the responses to painful stimuli are exerted through the MC4 receptor. In conclusion, antagonism of the spinal melanocortin system might provide a new approach in the treatment of neuropathic pain.

The effect of leptin on luteinizing hormone release is exerted in the zona incerta and mediated by melanin-concentrating hormone

The adipose hormone, leptin, not only restrains appetite, but also influences energy expenditure. One such influence is to promote sexual maturation and fertility. The neuromodulatory circuits that mediate this effect are not well known but the present study suggests that one mediator could be melanin-concentrating hormone (MCH). We show that the long-form receptor (Ob-Rb) is expressed in the zona incerta of the rat and that administration of leptin (both 0.5 microg and 1.0 microg/side) into this area of ovariectomized, oestrogen-primed rats stimulated the release of luteinizing hormone (LH) within 1 h, the effect enduring for a further 1 h. Injections of leptin into the arcuate nucleus induced a smaller, transient rise in LH while injections into the paraventricular and ventromedial nuclei were without effect. MCH neurones are present in the zona incerta and administration of this hormone into the medial preoptic area (mPOA) stimulates LH release, therefore we investigated the possibility that MCH might mediate this effect of leptin. An injection of MCH antiserum into mPOA prevented the rise in LH normally induced by leptin injected into the zona incerta. In addition, melanocortin receptor antagonists ([D-Arg8]ACTH(4-10) and [Ala6]ACTH(4-10)), previously shown to inhibit the stimulatory effect of MCH on LH release, also inhibited the effect of leptin. We propose that one route by which leptin may promote reproductive activity is by enhancing MCH release from fibres within the mPOA. Speculative mechanisms for the action of MCH include the following possibilities: MCH may be acting on the specific MCH receptor which in turn interacts with a melanocortin or melanocortin-like receptor; MCH may bind directly to one of the melanocortin receptors; or melanocortin antagonists may interact with the MCH receptor.

Melanocortins and the brain: from effects via receptors to drug targets

The lack of specific receptors (and antagonists) has hampered the research on the neural mechanism of action of adrenocorticotropic hormone (ACTH)- and melanocyte-stimulating hormone (MSH)-like peptides. Yet the original observations in the 1970s already pointed to cAMP as a possible mediator of ACTH/MSH effects in neurons. The cloning of melanocortin receptors since 1992, the identification of at least two subtypes (melanocortin MC(3) and MC(4) receptors) that are present in neural tissue and the development of selective and potent agonists as well as antagonists have markedly furthered the position of melanocortins as important neuropeptides. In this paper we discuss the role of especially the receptor subtype melanocortin MC(4) in various behaviors including grooming behavior and feeding behavior and consider new insights in the interaction between the opioid and the melanocortin system at the level of the spinal cord (i.e. pain perception). Finally, based on new data obtained in molecular pharmacological studies on brain melanocortin receptors, we suggest a general concept for selective receptor-ligand interaction: ligand residues outside the peptide core-sequence may direct the conformation of the residues in the ligand core-sequence that interact directly with the receptor-binding pocket and thereby determine selectivity.

Melanin-concentrating hormone, melanocortin receptors and regulation of luteinizing hormone release

Melanin-concentrating hormone (MCH) is a neuropeptide, identified by its ability to either mimic or antagonize the melanin-dispersing action of alpha-melanocyte stimulating hormone (alphaMSH) on skin melanophores. MCH and alphaMSH also have antagonistic actions in the brain affecting feeding behaviour, aggression, anxiety, arousal and reproductive function through the release of luteinizing hormone (LH). It is not clear, however, how they exert their opposite effects in the central nervous system (CNS). One possibility is that they act via a common receptor. In this study we have examined the effect of a number of MC receptor antagonists, with relative selectivity for the MC3, 4 and 5 subtypes, on the actions of MCH on LH release. We confirmed that bilateral administration of MCH (100 and 200 ng/side) into the medial preoptic area of oestrogen-primed (oestradiol benzoate 5 microgram) ovariectomized anaesthetized rats, stimulated the release of LH. This effect was blocked by the concomitant administration into the medial preoptic area of the MC4/5 antagonist ([D-Arg8]ACTH(4-10) and the MC3/5 antagonist ([Ala6]ACTH(4-10)-both at 500 ng/side-but not by the MC3/4 antagonist, SHU9119 (200 ng/side). Furthermore, the MC3 agonist [Nle3]-gamma2 MSH failed to affect LH release. These results indicate that the MC3 and MC4 receptors are not involved in mediating the action of MCH but are consistent with an action via the MC5 subtype. Preputial glands, which express MC5 receptors, were also stimulated by MCH which is in keeping with this idea. In HEK293 cells transfected with the MC5 receptor MCH increased the production of IP3. However, it was much less potent than alphaMSH and unlike alphaMSH, had no effect on the production of cAMP. MCH (10-10 to 10-5 M) also failed to displace I125NDP-MSH from cells transfected with MC5 receptors indicating that it was not acting as a competitive antagonist and its binding site was distinct from that of alphaMSH. Thus while MCH may function as an agonist at the MC5 receptor, its stimulation of LH release is more likely to be mediated via a specific MCH receptor that has common properties with the MC5 receptor.

Melanocortins and the treatment of nervous system disease. Potential relevance to the skin?

For several decades melanocortins have been implicated in the modulation of brain function. More recently, this idea has been supported by the identification and cloning of melanocortin (MC) receptors in the nervous system. MCs stimulate axonal growth in fetal neural tissue or in neural cell lines in culture. This feature was utilized in screening their neurotrophic or neuroprotection potential in animal studies of nervous system disease (peripheral nerve and spinal cord trauma, toxic and metabolic neuropathies, EAN, EAE, etc.). Some of these effects may be mediated by MC4 receptor activation, although as yet unknown receptors may also be involved (for instance, protection by Org 2766). To what extent MC-nervous system effects are related to known effects of MCs in skin- and neuro-immune systems, remains to be discovered. Nevertheless, it is of interest to note that activation of brain MC4 receptors profoundly affects care behavior for the body surface (skin and fur). The excessive grooming response in rodents exhibits a remarkable functional correlation with MSH activity in a brain-skin axis.

Characterization of melanocortin receptor ligands on cloned brain melanocortin receptors and on grooming behavior in the rat

Since the melanocortin MC3 and melanocortin MC4 receptors are the main melanocortin receptor subtypes expressed in rat brain, we characterized the activity and affinity of nine melanocortin receptor ligands using these receptors in vitro, as well as their activity in a well-defined melanocortin-induced behavior in the rat: grooming behavior. We report here that [D-Tyr4]melanotan-II and RMI-2001 (Ac-cyclo-[Cys4, Gly5, D-Phe7, Cys10]alpha-MSH-NH2) have significantly higher affinity and potency on the rat melanocortin MC4 receptor as compared to the rat melanocortin MC3 receptor. Nle-gamma-MSH (melanocyte-stimulating hormone) was the only ligand with higher affinity and potency on the rat melanocortin MC3 receptor. The potency order of melanocortin MC4 receptor agonists, but not that of melanocortin MC3 receptor agonists, fitted with the potency of these ligands to stimulate grooming behavior, when administered intracerebroventricularly. SHU9119 (Ac-cyclo-[Nle4, Asp5, D-Nal(2)7, Lys10]alpha-MSH-(4-10)-NH2) and RMI-2005 (Ac-cyclo-[Cys4, Gly5, D-Na](2)7, Nal(2)9, Cys10]alpha-MSH-(4-10)-NH2) were able to inhibit alpha-MSH-induced melanocortin receptor activity in vitro, as well as alpha-MSH-induced grooming behavior. Melanotan-II, [Nle4-D-Phe7]alpha-MSH and RMI-2001 were also effective in inducing grooming behavior when administered intravenously. In the absence of purely selective melanocortin MC(3/4) receptor ligands, we demonstrated that careful comparison of ligand potencies in vitro with ligand potencies in vivo, could identify which melanocortin receptor subtype mediated alpha-MSH-induced grooming behavior. Furthermore, blockade of novelty-induced grooming behavior by SHU9119 demonstrated that this physiological stress response is mediated via activation of the melanocortin system.

Conformation of the core sequence in melanocortin peptides directs selectivity for the melanocortin MC3 and MC4 receptors

Melanocortin peptides regulate a variety of physiological processes. Five melanocortin receptors (MC-R) have been cloned and the MC3R and MC4R are the main brain MC receptors. The aim of this study was to identify structural requirements in both ligand and receptor that determine gamma-melanocyte-stimulating hormone (MSH) selectivity for the MC3R versus the MC4R. Substitution of Asp10 in [Nle4]Lys-gamma2-MSH for Gly10 from [Nle4]alpha-MSH, increased both activity and affinity for the MC4R while the MC3R remained unaffected. Analysis of chimeric MC3R/MC4Rs and mutant MC4Rs showed that Tyr268 of the MC4R mainly determined the low affinity for [Nle4]Lys-gamma2-MSH. The data demonstrate that Asp10 determines selectivity for the MC3R, however, not through direct side chain interactions, but probably by influencing how the melanocortin core sequence is presented to the receptor-binding pocket. This is supported by mutagenesis of Tyr268 to Ile in the MC4R which increased affinity and activity for [Nle4]Lys-gamma2-MSH, but decreased affinity for two peptides with constrained cyclic structure of the melanocortin core sequence, MT-II and [D-Tyr4]MT-II, that also displayed lower affinity for the MC3R. This study provides a general concept for peptide receptor selectivity, in which the major determinant for a selective receptor interaction is the conformational presentation of the core sequence in related peptides to the receptor-binding pocket.

Expression of melanocortin receptors and pro-opiomelanocortin in the rat spinal cord in relation to neurotrophic effects of melanocortins

Although neurotrophic effects of alpha-melanocyte-stimulating hormone (alpha-MSH) are well established, the mechanism underlying these effects is unknown. To identify candidate components of the signaling system that may mediate these effects, in the present study rat spinal cord, dorsal root ganglia, sciatic nerve and soleus muscle were analysed for the expression of the neural MC3, MC4 and MC5 receptors and for the expression of the melanocortin precursor pro-opiomelanocortin (POMC). In rat lumbar spinal cord, the MC4 receptor was the only MC receptor subtype for which mRNA was detectable using RNAse protection assays. In situ binding studies using 125I-NDP-MSH, a synthetic alpha-MSH analogue, demonstrated MC receptor protein in the rat spinal cord, predominantly localised in substantia gelatinosa and area X, surrounding the central canal. Furthermore, POMC mRNA was demonstrated in rat spinal cord and dorsal root ganglia. These findings suggest a functional melanocortin system in the rat spinal cord, that might be involved in peripheral nerve repair. Regulation of POMC or MC receptor transcripts does not appear to be involved in the response to peripheral nerve crush in rats, since no change in mRNA expression patterns was detected after sciatic nerve crush, using quantitative RNAse protection assays. Nevertheless, subtle changes in melanocortin receptor binding did occur postsurgically in several regions of the spinal cord in both sham-operated and sciatic nerve-lesioned rats. The robust expression of MC receptor protein in spinal cord regions that are generally associated with nociception suggests a potentially broader involvement of endogenous melanocortins in spinal pathways which mediate the responses to peripheral injury, in addition to any direct melanocortin effects on sprouting and neurite outgrowth.

Melanocortins and cardiovascular regulation

The melanocortins form a family of pro-opiomelanocortin-derived peptides that have the melanocyte-stimulating hormone (MSH) core sequence, His-Phe-Arg-Trp, in common. Melanocortins have been described as having a variety of cardiovascular effects. We review here what is known about the sites and mechanisms of action of the melanocortins with respect to their effects on cardiovascular function, with special attention to the effects of the gamma-melanocyte-stimulating hormones (gamma-MSHs). This is done in the context of present knowledge about agonist selectivity and localisation of the five melanocortin receptor subtypes cloned so far. gamma2-MSH, its des-Gly12 analog (= gamma1-MSH) and Lys-gamma2-MSH are 5-10 times more potent than adrenocorticotropic hormone-(4-10)(ACTH-(4-10)) to induce a pressor and tachycardiac effect following intravenous administration. The Arg-Phe sequence near the C-terminal seems to be important for full in vivo intrinsic activity. Related peptides with a C-terminal extension with (gamma3-MSH) or without the Arg-Phe sequence (alpha-MSH, as well as the potent alpha-MSH analog, [Nle4,D-Phe7]alpha-MSH), are, however, devoid of these effects. In contrast, ACTH-(1-24) has a depressor effect combined with a tachycardiac effect, effects which are not dependent on the presence of the adrenals. Although the melanocortin MC3 receptor is the only melanocortin receptor subtype for which gamma2-MSH is selective, in vivo and in vitro structure-activity data indicate that it is not via this receptor that this peptide and related peptides exert either their pressor and tachycardiac effects or their extra- and intracranial blood flow increasing effect. We review evidence that the pressor and tachycardiac effects of the gamma-MSHs are due to an increase of sympathetic outflow to the vasculature and the heart, secondary to activation of centrally located receptors. These receptors are most likely localised in the anteroventral third ventricle (AV3V) region, a brain region situated outside the blood-brain barrier, and to which circulating peptides have access. These receptors might be melanocortin receptors of a subtype yet to be identified. Alternatively, they might be related to other receptors for which peptides with a C-terminal Arg-Phe sequence have affinity, such as the neuropeptide FF receptor and the recently discovered FMRFamide receptor. Melanocortin MC4 receptors and still unidentified receptors are part of the circuitry in the medulla oblongata which is involved in the depressor and bradycardiac effect of the melanocortins, probably via interference with autonomic outflow. Regarding the effects of the gamma-MSHs on cortical cerebral blood flow, it is not yet clear whether they involve activation of the sympathetic nervous system or activation of melanocortin receptors located on the cerebral vasculature. The depressor effect observed following intravenous administration of ACTH-(1-24) is thought to be due to activation of melanocortin MC2 receptors whose location may be within the peripheral vasculature. Melanocortins have been observed to improve cardiovascular function and survival time in experimental hemorrhagic shock in various species. Though ACTH-(1-24) is the most potent melanocortin in this model, alpha-MSH and [Nle4,D-Phe7]alpha-MSH and ACTH-(4-10) are quite effective as well. As ACTH-(4-10) is a rather weak agonist of all melanocortin receptors, it is difficult to determine via which of the melanocortin receptors the melanocortins bring about this effect. Research into the nature of the receptors involved in the various cardiovascular effects of the melanocortins would greatly benefit from the availability of selective melanocortin receptor antagonists.

Asp10 in Lys-gamma2-MSH determines selective activation of the melanocortin MC3 receptor

The melanocortin MC3 and MC4 receptors are the main melanocortin receptors expressed in brain. Of the endogenous melanocortins, gamma2-melanocortin stimulating hormone (MSH) selectively activates the melanocortin MC3 receptor, whereas alpha- and beta-MSH activate all melanocortin receptors. The aim was to gain an insight into the contribution of amino acids in positions 5 and 10 of melanocortins to the selectivity of [Nle4]Lys-gamma2-MSH for the melanocortin MC3 receptor versus the melanocortin MC4 receptor. Introduction of Asp10 into [Nle4]alpha-MSH as in [Nle4,Gly5,Asp10]alpha-MSH selectively increased the EC50 value for the melanocortin MC4 receptor. Conversely, removal of Asp10, as in [Nle4,Gly10]Lys-gamma2-MSH, selectively decreased the EC50 value for the melanocortin MC4 receptor. Thus, Asp10 in Lys-gamma2-MSH determined selectivity for the melanocortin MC3 receptor versus the melanocortin MC4 receptor.

Expression of melanocortin-5 receptor in secretory epithelia supports a functional role in exocrine and endocrine glands

Melanocortins (alphaMSH and ACTH-related peptides) influence the physiological functions of certain peripheral organs, including exocrine and endocrine glands. This study was designed to determine the identity and anatomical localization of the melanocortin receptors (MC-R) expressed in these organs in the rat. MC5-R messenger RNA was found in exocrine glands, including lacrimal, Harderian, preputial, and prostate glands and pancreas, as well as in adrenal gland, esophagus, and thymus, as demonstrated by ribonuclease protection assays. In exocrine glands, MC5-R messenger RNA expression was restricted to secretory epithelia. MC-R protein was likewise present in secretory epithelia of exocrine glands, as determined by 125I-labeled [Nle4,D-Phe7]alphaMSH ([125I]NDP-MSH) binding and autoradiography in tissue sections. Specific [125I]NDP-MSH binding was also observed in adrenal cortex, thymus, spleen, and esophageal and trachealis muscle. MC receptors in these sites are accessible to circulating MC-R agonists in vivo, as specific binding of [125I]NDP-MSH was observed in exocrine and adrenal glands after systemic injection in vivo. Taken together, these findings show that the MC5 receptor is commonly and selectively expressed in exocrine glands and other peripheral organs. Based on these findings and compelling evidence from other studies, a functional coherence is suggested between central and peripheral actions of melanocortins and melanocortin receptors in physiological functions, including thermoregulation, immunomodulation, and sexual behavior.

The role of central melanocortin receptors in the activation of the hypothalamus-pituitary-adrenal-axis and the induction of excessive grooming

1. In accord with previous studies intracerebroventricular (i.c.v.) injections of ACTH1-24 (1 microg) induced a display of excessive grooming, and increased the plasma concentrations of ACTH and corticosterone. Pituitary-adrenal activation was blocked by pretreatment with dexamethasone, indicating that the effect of the (i.c.v.) injected peptide was not caused by a peripheral effect on the adrenal cortex. 2. Doses of 1 and 3 microg of a non-selective melanocortin-3/4-receptor antagonist (SHU 9119), or of 5 and 10 microg of a selective melanocortin-4-receptor antagonist ([D-Arg8]ACTH4-10), coadministered (i.c.v.) with 1 microg ACTH1-24, inhibited the ACTH1-24-induced activation of the hypothalamus-pituitary-adrenal-axis and excessive grooming. 3. In addition, several doses of the selective melanocortin-3-receptor agonist Lys-gamma2-MSH were centrally administered, but neither neuroendocrine, nor excessive grooming responses were observed. 4. These results imply that the melanocortin-4-receptor, and not the melanocortin-3-receptor, is involved in the ACTH1-24-induced rise in plasma levels of ACTH and corticosterone, and excessive grooming.

Molecular pharmacology of neural melanocortin receptors

The cloning of melanocortin receptors opened new avenues to identify selective ligands for this receptor family. gamma-MSH was characterized as a melanocortin-3 receptor selective agonist, [D-Arg8]ACTH-(4-10) and [Pro8,10, Gly9]ACTH-(4-10) were characterized as melanocortin-4 receptor antagonists. The application of these ligands in vivo revealed that melanocortin-4 receptors mediate melanocortin-induced grooming behaviour in the rat. Since we still lack potent and selective melanocortin receptor ligands, we performed homology modelling and site directed mutagenesis of the melanocortin-4 receptor, in order to understand how melanocortins bind melanocortin receptors. A histidine at position 260 in the melanocortin-4 receptor is important for normal receptor function. However this residue is not forming a salt bridge with a glutamate at position 92 to keep the receptor in an inactive conformation, nor with the glutamate in the melanocortin peptides as had been suggested before.

Effects of estrogen on oxytocin receptor messenger ribonucleic acid expression in the uterus, pituitary, and forebrain of the female rat

Oxytocin receptors are regulated during parturition and lactation. Gonadal steroids are thought to be key players in this regulation. It is not well documented how oxytocin receptor gene expression is regulated in the CNS. In this study we analyzed potential estrogen effects on the oxytocin receptor mRNA levels in some areas integral to the limbic-hypothalamic system, namely the ventromedial nucleus of the hypothalamus (VMH), posterior medial nucleus of amygdala (MeAmyg), and arcuate nucleus (ARC), as well as the caudate putamen (CPu), CA1 region of the hippocampus, anterior pituitary, and uterine tissue of ovariectomized (OVX) female rats. By in situ hybridization we observed a 4.4-fold increase in oxytocin receptor mRNA levels in the VMH after 48 h of estrogen treatment when compared to OVX rats. Smaller increases were observed in the MeAmyg, hippocampus, and anterior pituitary (3.18, 1.76, and 2.55, respectively). No changes in oxytocin receptor mRNA levels were observed in the CPu or ARC after estrogen treatment. A similar finding resulted from slot-blot analysis of total mRNA extracts. In uterine tissue, 48 h of estrogen treatment increased oxytocin receptor mRNA level in the myometrium (3.13-fold). No changes in oxytocin receptor mRNA levels were observed after 12 and 24 h of estrogen treatment. These findings suggest that the estrogenic regulation of oxytocin receptor binding in both CNS and uterine tissues may in part be mediated by de novo synthesis of oxytocin receptor mRNA or by alterations in the stability of oxytocin receptor gene transcripts.

Brain melanocortin receptors: from cloning to function

The cloning of brain melanocortin (MC) receptors, the mapping of their expression pattern and the identification of MC receptor selective ligands have opened a new avenue towards elucidating the role of the melanocortin system in the brain. MC receptors have now been implicated in melanocortin-induced grooming behavior in rats, in the melanocortin-induced lowering of blood pressure and in the control of weight homeostasis. Functional opioid antagonism and the anti-pyretic and anti-inflammatory effects of melanocortins are probably also mediated via MC receptors. However, the effects of melanocortins on avoidance behavior and the effect of gamma 2-MSH on increasing blood pressure are not mediated via one of the cloned brain MC receptors. The structure of brain MC receptors, their expression pattern, the MC receptor selective ligands and the function of MC receptors are briefly reviewed.

Melanocortin receptors mediate alpha-MSH-induced stimulation of neurite outgrowth in neuro 2A cells

Melanocortins (MC), neuropeptides derived from pro-opiomelanocortin, have been implicated in enhancing neurite outgrowth via an as yet unknown mechanism. Recently, five MC receptors have been identified, three of which, the MC3-R, the MC4-R and the MC5-R, are expressed in the nervous system. In this study, alpha-MSH and the melanocortin analog [D-Phe7]ACTH (4-10) were able to stimulate neurite outgrowth in the neuroblastoma cell line Neuro 2A. ACTH (4-10), gamma2-MSH and ORG2766 were inactive. In addition, the MC4-R antagonist [D-Arg8]ACTH (4-10), inhibited the alpha-MSH effect, indicating that the MC4-R mediated stimulation of neurite outgrowth by alpha-MSH. Indeed, the presence of MC4-R mRNA in Neuro 2A cells was demonstrated by a RNase protection assay. Heterologous expression of the MC5-R in Neuro 2A cells lead to the recruitment of a responsiveness to gamma2-MSH, but did not increase the effect of alpha-MSH on neurite outgrowth. This finding indicated that the function of MC4-R can also be exerted by another MC receptor, suggesting that the coupling to Gs, which they have in common, plays an essential role in the neurite outgrowth promoting effect. This was further substantiated by the fact that forskolin treatment per se induced neurite outgrowth in a similar fashion. These data imply that the neurotrophic properties of alpha-MSH are likely to result from Gs-coupled MC receptor activity in neuronal cells.

Molecular neurobiology and pharmacology of the vasopressin/oxytocin receptor family

1. VP and OT mediate their wealth of effects via 4 receptor subtypes V1a, V1b, V2, and OT receptors. 2. We here review recent insights in the pharmacological properties, structure activity relationships, species differences in ligand specificity, expression patterns, and signal transduction of VP/OT receptor. 3. Furthermore, the existence of additional VP/OT receptor subtypes is discussed.

Rat oxytocin receptor in brain, pituitary, mammary gland, and uterus: partial sequence and immunocytochemical localization

Partial complementary DNAs of an oxytocin (OT) receptor were cloned from rat brain and uterus. The complementary DNAs encoded for the same amino acid sequence, which showed a high degree of homology with the human and porcine uterine OT receptors, except for a region in the third intracellular loop. Antibodies were raised against nonoverlapping sequences of the third intracellular loop of this rat OT receptor. Using these antisera, OT receptor expression was demonstrated in the brain, pituitary, mammary gland, and uterus by immunocytochemistry. In the brain, several areas including the ventromedial hypothalamus, the bed nucleus of the stria terminalis, the ventral pallidum, the paraventricular nucleus, and the dorsal part of the supraoptic nucleus, demonstrated OT-receptor immunoreactivity. However, no immunoreactivity was detected in two areas of the brain known to contain dense OT-binding sites by receptor autoradiography studies: the ventral hippocampus and the central nucleus of the amygdala. In the pituitary, both the anterior and posterior lobes were positive for OT receptor immunoreactivity, whereas the intermediate lobe was negative. These results demonstrate that the same receptor type is expressed in both peripheral OT target tissues and the brain, and also suggest the possibility that a different OT receptor subtype may be present in some areas of the brain.

Differential effects of melanocortin peptides on neural melanocortin receptors

Melanocortins (MCs) have various physiological actions on the brain. The recent cloning of neural MC receptors opened new avenues to study the effects of these neuropeptides on the nervous system. Here we investigated the structure-activity relationships (SARs) of peptides derived from adrenocorticotropic hormone (ACTH) with cloned MC3 and MC4 receptors in vitro and correlated these with central effects of MCs in vivo. Analysis of the effects of various MC peptides on cAMP accumulation in and binding to cells that expressed either the rat MC3 receptor or the human MC4 receptor demonstrated that ACTH-4-9-NH2 was the core sequence of ACTH able to activate these receptors. Furthermore, gamma-melanocyte-stimulating hormone (MSH) displayed selectivity for the MC3 receptor, whereas [D-Phe7]ACTH-4-10 more efficiently activated the MC4 receptor than the MC3 receptor. The activities of MC fragments that lacked the three carboxyl-terminal amino acids (residues 11-13) of ACTH-1-13 were much lower than that of alpha-MSH, for both receptors. Furthermore, the three amino-terminal amino acids (residues 1-3) of alpha-MSH were more important for full activation of the MC4 receptor, compared with the MC3 receptor. The SAR for the MC4 receptor resembled that for the induction of excessive grooming behavior by MC peptides. Therefore, we suggest that this behavioral response is mediated by MC4 receptors. The SAR for the MC3 receptor did not overlap with that for in vivo effects of MCs. ORG2766, an ACTH-4-9 analog that is very potent in an active avoidance task, did not activate, antagonize, or bind to the MC3 and MC4 receptors. This suggests the presence of still other MC receptors, in addition to the MC3 and MC4 receptors, in the brain. These data identify peptides with selectivity for either the MC3 receptor or the MC4 receptor, which may be used for development of novel MC receptor-specific ligands. Furthermore, this is the first report that discusses behavioral effects of MCs in light of data on cloned MC receptors.

Identification of antagonists for melanocortin MC3, MC4 and MC5 receptors

Antagonists for the melanocortin receptor family were identified by analysis of the effects of four melanocortin analogues on alpha-MSH(alpha-melanocyte-stimulating hormone)-induced cAMP accumulation in 293 human embryonal kidney (HEK) cells that expressed either the rat melanocortin MC3 receptor, the human melanocortin MC4 receptor or the ovine melanocortin MC5 receptor. Two peptides, [D-Arg8]ACTH(adrenocorticotrope hormone)-(4-10) and [Pro8,10,Gly9]ACTH-(4-10), antagonized the action of alpha-MSH on the melanocortin MC4 and MC5 receptors, but not the melanocortin MC3 receptor. [Ala6]ACTH-(4-10) inhibited the alpha-MSH activation of the melanocortin MC3 and MC5, but only weakly antagonized the activation of the melanocortin MC4 receptor. [Phe-I7]ACTH-(4-10) antagonized the melanocortin MC3, MC4 and MC5 receptors equally well. These antagonists were also tested to block a behavioral response induced by alpha-MSH. alpha-MSH-induced excessive grooming behavior in rats was inhibited by [Phe-I7]ACTH-(4-10), [D-Arg8]ACTH-(4-10) and [Pro8,10,Gly9]ACTH-(4-10), but not by [Ala6]ACTH-(4-10). This suggests that alpha-MSH-induced excessive grooming behavior is mediated by melanocortin MC4 receptors.

Repression of estrogen-dependent stimulation of the oxytocin gene by chicken ovalbumin upstream promoter transcription factor I

The orphan receptor chicken ovalbumin upstream promoter transcription factor I (COUP-TF I) fully prevented not only the activation of the oxytocin gene by retinoic acid and thyroid hormone but also completely repressed the estrogen-dependent stimulation in transfected P19 EC cells. DNase I footprinting showed that the COUP-TF I protein bound to the 5'-flanking region of the oxytocin gene at the site of the distal composite hormone response element, which mediates the responses to estrogen, retinoic acid, and thyroid hormone. Electrophoretic mobility shift assay using this composite hormone response element as probe showed that COUP-TF I and the estrogen receptor competed for binding but did not form a heterodimer. The binding by COUP-TF I was stronger than the binding of the estrogen receptor. Thus, the mechanism of repression involves occupancy of integrated binding sites. By mutagenesis of the composite hormone response element, the COUP-TF I binding site and the estrogen response element could be separated, resulting in functional dissociation of the repressive action of COUP-TF I and the induction by estrogen. The results show that repression of gene expression by COUP-TF I is not limited to receptors that act through heterodimerization but also extends to the homodimer-forming estrogen receptor in a context-dependent manner. This interaction between COUP-TF I and the estrogen receptor may provide a physiological mechanism of selective antagonism of gene regulation by estrogens.

A composite hormone response element mediates the transactivation of the rat oxytocin gene by different classes of nuclear hormone receptors

Transcription factors of the steroid/thyroid hormone receptor superfamily are mediators of development and regulation of the brain. Previous studies have shown that the hypothalamic oxytocin (OT) gene is a potential target of these receptors, since its promoter is stimulated by estrogens and thyroid hormone. Here it is shown that the rat OT promoter is stimulated (at least 20-fold) by retinoic acid through two distinct regions in the 5'-flanking region. The major retinoic acid response element was located between nucleotides -172 and -148 and a minor one between nucleotides -112 and -77, as concluded from the transactivation of 5'-deletion mutants and binding to promoter elements by the retinoic acid receptor. Since the -172/-148 element also conferred estrogen and thyroid hormone responsiveness, it can be considered a composite hormone response element. This element contains a natural variant of the direct repeat of the half-site AGGTCA with spacing zero (DR-0) as well as a palindrome. Analysis of the core sequences of this element by site-directed mutagenesis showed that each of the three TGACC motifs integral to this element contributes to the multihormone sensitivity, but the contribution of each motif is different for the individual receptors. In neonatal rats, vitamin A deficiency and retinoic acid supplementation did not cause changes in hypothalamic OT mRNA levels and OT peptide levels in the pituitary gland and plasma. Gel-retarded protein-DNA complexes were formed between the composite hormone response element and extracts of the hypothalamic supraoptic and paraventricular nuclei. The composite hormone response element has a unique configuration and integrates responses of multiple members of the steroid/thyroid hormone receptor superfamily.

The identification of a cis-acting element involved in cyclic 3',5'-adenosine monophosphate regulation of bovine vasopressin gene expression

Cyclic adenosine 3',5'-monophosphate (cAMP) has been implicated as an intracellular messenger mediating osmotic regulation of expression of the gene encoding the neuropeptide vasopressin (VP) in the hypothalamus. We have used a heterologous transient transfection system to demonstrate that cAMP regulates the bovine VP gene promoter following transfection into CV1 cells. Mutational analysis identified a bovine VP cAMP-responsive element (BVP-CRE) 120-112 base-pairs upstream of the start of transcription. DNase I footprint analysis using nuclear protein extract from CV1 cells showed protection at the site of the BVP-CRE. Protection of the BVP-CRE was also observed using purified AP1 protein, while there was a weak interaction with the BVP-CRE using purified rat CREB protein. Nuclear proteins purified from the rat supraoptic nucleus bind to the BVP-CRE. As transgenic mouse studies have shown that the bovine VP gene is subject to appropriate physiological regulation in the mouse hypothalamus (Ang, H. L., Funkhouser, J., Carter, D. A., Ho, M. Y., and Murphy, D. (1991) Soc. Neurosci. Abstr. 513, 12), these data indicate a role for the BVP-CRE element in mediating VP gene expression in vivo. These data demonstrate that cAMP regulates bovine VP gene expression in vitro via a cis-acting element within the VP promoter, and this activation may be mediated by members of the AP1/ATF/CREB family of transcription factors.

Thyroid hormone regulates the oxytocin gene

Endocrine factors involved in the transcriptional regulation of the oxytocin (OT) gene were investigated in heterologous expression systems. Plasmids having a 5'-flanking region of the rat OT gene (-363/+16) or the human OT gene (-382/+41) cloned in front of the firefly luciferase gene were co-transfected with an expression vector for the rat thyroid hormone receptor alpha in P19 embryonal carcinoma (EC) cells. Thyroid hormone (T3) stimulated the activity of the rat and human OT promoters about 10-fold. In MCF-7 breast tumor cells transfected with the human OT promoter-luciferase fusion gene, T3 stimulation through endogenous thyroid hormone receptors was about 5-fold. Co-transfection experiments in P19EC cells using 5' deletion mutants of the rat OT gene showed that thyroid hormone responsiveness was located in two regions, one located between nucleotides -195 and -172, the other between nucleotides -172 and -148. Each region accounted for about 3-fold T3 stimulation. Gel retardation analysis using extracts from HeLa cells over-producing the c-erbA/TR alpha protein showed specific binding to the -172/-148 element, while no binding occurred on the -195/-172 element. The -172/-148 element which contains the imperfect estrogen response element, GGTGACCTTGACC, has inverted as well as direct repeats of the TGACC motif. Mutagenesis of TGACC motifs separately reduced thyroid hormone responsiveness by about 50%. However, simultaneous mutation of two TGACC motifs abolished the responsiveness to T3 completely. There was no cooperativity between the activated thyroid hormone and estrogen receptors in transfected MCF-7 cells nor in thyroid hormone receptor and estrogen receptor co-transfected P19EC cells. Negative interactions between these two receptors were observed and gel retardation assays showed interaction between the two receptors proteins. It was shown in an in vivo experiment that treatment of rats with thyroid hormone increased hypothalamic OT mRNA levels, the pituitary OT content, as well as OT levels in blood. The results reveal thyroid hormone as a physiological regulator of OT gene expression, which stimulates OT promoter activity directly through interaction with a thyroid hormone-response element in the OT gene.

Comparison of the estrogen responsiveness of the rat and bovine oxytocin gene promoters

DNA sequences in the 5'-flanking region of rat and bovine oxytocin genes were examined for their capacity to confer estrogen responsiveness to their homologous promoters. In contrast to the 5'-flanking region of the rat oxytocin gene, upstream promoter sequences up to 3200 bp of the bovine gene linked to the chloramphenicol acetyltransferase (CAT) reporter gene which were transfected in estrogen receptor expressing MCF-7 cells did not respond to estrogen. Testing 5'-deletion mutants of the rat upstream region linked to the luciferase gene in P19 embryocarcinoma cells co-transfected with an estrogen receptor expression plasmid showed that two regions each associated with approximately 15-fold stimulation of promoter activity were located between nucleotides -172 and -149 and between -148 and +16 in the rat gene. The former region contains the imperfect palindrome GGTGACCTTGACC which differs in one nucleotide from the estrogen response element (ERE) consensus. It is concluded that the corresponding motive CATAACCTTGACC of the bovine gene is not a functional ERE. Thus, the estrogen responsiveness of oxytocin genes is species-dependent.

Vasopressin gene expression is stimulated by cyclic AMP in homologous and heterologous expression systems

The possible role of cyclic AMP (cAMP) in the regulation of the vasopressin (VP) gene was tested in two cellular expression systems: one cell line with endogenous VP expression and the other which was transiently with a VP promoter-luciferase fusion gene. 8,Bromo-cAMP stimulated the VP mRNA content about 4-fold in the human VP-expressing small cell lung carcinoma cell line GLC-8. The luciferase activity in P19 embryonal carcinoma cells which were transiently transfected with -174 to +44 of the 5'-flanking region of the human VP gene linked to the firefly luciferase gene, was stimulated about 2-fold by the cAMP analogue. The results indicate that cAMP plays a role in the upregulation of the VP gene and hence point to several putative nucleotide motives in the promoter functionally conferring this response.

Regulation of the rat oxytocin gene by estradiol

Abstract Oxytocin (OT) plays a role in reproduction at the level of the pituitary and mammary glands and uterus. This OT is synthesized in the hypothalamo-neurohypophyseal system (HNS). A number of observations have suggested that estrogens regulate the production of OT in the HNS. In this study the effect of 17beta-estradiol on the activity of the OT gene promoter was examined as well as the effect of 17beta-estradiol in vivo on OT messenger ribonucleic acid (mRNA) and peptide revels in the rat HNS. Vasopressin (VP) and its mRNA were also determined in the in vivo studies. The direct transcriptional stimulation of OT gene expression by 17beta-estradiol was studied in two different heterologous expression systems. When a plasmid having nucleotides -363 to +16 of the rat OT gene fused to the firefly luciferase reporter gene was co-transfected with an estrogen receptor expression vector in P19 embryonal carcinoma cells, luciferase activity was stimulated 80-fold by 17beta-estradiol. In estrogen receptor containing MCF-7 cells transfected with a plasmid having nucleotides -188 to +16 of the rat OT gene fused to the chloramphenicol acetyl transferase gene, 17beta-estradiol induced the expression of the chloramphenicol acetyl transferase gene through the cloned promoter element. After in vivo treatment of ovariectomized rats with 17beta-estradiol, levels of OT mRNA and VP mRNA were measured in microdissected supraoptic and paraventricular nuclei as well as VP and OT levels in these nuclei and the pituitary gland. As compared to non-treated ovariectomized rats there was no difference in contents of OT mRNA and VP mRNA in these hypothalamic nuclei and in levels of the peptides in paraventricular nuclei and the pituitary gland. A 30% reduction of the OT content of the supraoptic nuclei only was found, while the VP content did not change. To explain the results immunocytochemical analyses of the hypothalamus were performed, showing that the estrogen receptor was absent in the magnocellular neurons of the supraoptic and paraventricular nuclei. The results demonstrate that the 5'flanking region of the OT gene confers estrogen-sensitivity to transcription of the OT gene. This potential to respond to estrogens is not used in the OT-producing neurons of supraoptic and paraventricular nuclei probably due to the absence of the estrogen receptor.