A CreER mouse to study melanin concentrating hormone signaling in the developing brain.

The neuropeptide, melanin concentrating hormone (MCH), and its G protein-coupled receptor, melanin concentrating hormone receptor 1 (Mchr1), are expressed centrally in adult rodents. MCH signaling has been implicated in diverse behaviors such as feeding, sleep, anxiety, as well as addiction and reward. While a model utilizing the Mchr1 promoter to drive constitutive expression of Cre recombinase (Mchr1-Cre) exists, there is a need for an inducible Mchr1-Cre to determine the roles for this signaling pathway in neural development and adult neuronal function. Here, we generated a BAC transgenic mouse where the Mchr1 promotor drives expression of tamoxifen inducible CreER recombinase. Many aspects of the Mchr1-Cre expression pattern are recapitulated by the Mchr1-CreER model, though there are also notable differences. Most strikingly, compared to the constitutive model, the new Mchr1-CreER model shows strong expression in adult animals in hypothalamic brain regions involved in feeding behavior but diminished expression in regions involved in reward, such as the nucleus accumbens. The inducible Mchr1-CreER allele will help reveal the potential for Mchr1 signaling to impact neural development and subsequent behavioral phenotypes, as well as contribute to the understanding of the MCH signaling pathway in terminally differentiated adult neurons and the diverse behaviors that it influences.

Melanin-Concentrating Hormone and Its MCH-1 Receptor: Relationship Between Effects on Alcohol and Caloric Intake.

BACKGROUND: Reward and energy homeostasis are both regulated by a network of hypothalamic neuropeptide systems. The melanin-concentrating hormone (MCH) and its MCH-1 receptor (MCH1-R) modulate alcohol intake, but it remains unknown to what extent this reflects actions on energy balance or reward. Here, we evaluated the MCH1-R in regulation of caloric intake and motivation to consume alcohol in states of escalated consumption. METHODS: Rats had intermittent access (IA) to alcohol and were divided into high- and low-drinking groups. Food and alcohol consumption was assessed after administration of an MCH1-R antagonist, GW803430. Next, GW803430 was evaluated on alcohol self-administration in protracted abstinence induced by IA in high-drinking rats. Finally, the effect of GW803430 was assessed on alcohol self-administration in acute withdrawal in rats exposed to alcohol vapor. Gene expression of MCH and MCH1-R was measured in the hypothalamus and nucleus accumbens (NAc) in both acute and protracted abstinence. RESULTS: High-drinking IA rats consumed more calories from alcohol than chow and GW803430 decreased both chow and alcohol intake. In low-drinking rats, only food intake was affected. In protracted abstinence from IA, alcohol self-administration was significantly reduced by pretreatment with GW803430 and gene expression of both MCH and the MCH1-R were dysregulated in hypothalamus and NAc. In contrast, during acute withdrawal from vapor exposure, treatment with GW803430 did not affect alcohol self-administration, and no changes in MCH or MCH1-R gene expression were observed. CONCLUSIONS: Our data suggest a dual role of MCH and the MCH1-R in regulation of alcohol intake, possibly through mechanisms involving caloric intake and reward motivation. A selective suppression of alcohol self-administration during protracted abstinence by GW803430 was observed and accompanied by adaptations in gene expression of MCH and MCH1-R. Selective suppression of escalated consumption renders the MCH1-R an attractive target for treatment of alcohol use disorders.

Immunohistochemical distribution of somatostatin and somatostatin receptor subtypes (SSTR1-5) in hypothalamus of ApoD knockout mice brain.

In the present study, the expression of somatostatin (SST) and somatostatin receptor subtypes (SSTR1-5) was determined in the hypothalamus of wild-type (wt) and apolipoprotein D knockout (ApoD(-/-)) mice brain. SST-like immunoreactivity, while comparable in most regions of hypothalamus, diminished significantly in arcuate nucleus of ApoD(-/-) mice. SSTR1 strongly localized in all major hypothalamic nuclei as well as in the median eminence and ependyma of the third ventricle of wt mice brain. SSTR1-like immunoreactivity increases in hypothalamus except in paraventricular nucleus of ApoD(-/-) mice. SSTR2 was well expressed in most of the hypothalamic regions whereas it decreases significantly in ventromedial and arcuate nucleus of ApoD(-/-) mice. SSTR3 and SSTR4-like immunoreactivity increases in ApoD(-/-) mice in all major nuclei of hypothalamus, median eminence, and ependymal cells of third ventricle. SSTR5 is well expressed in ventromedial and arcuate nucleus whereas weakly expressed in paraventricular nucleus. In comparison to wt, ApoD(-/-) mice exhibit increased SSTR5-like immunoreactivity in paraventricular nuclei and decreased receptor expression in ventromedial hypothalamus and arcuate nucleus. In conclusion, the changes in hypothalamus of ApoD(-/-) mice may indicate potential role of ApoD in regulation of endocrine functions of somatostatin in a receptor-dependent manner.

[Effect of somatostatin on functions of acupuncture meridians].

Our previous studies have showed that analogue electroacupuncture (EA) could induce a transmission of electrical signals along meridians, and excitatory neurotransmitters such as substance P and glutamate were involved in the transmission process. In recent studies, our results showed that somatostatin and its receptors played a dose-dependent tonic inhibition on the discharge rates of original and adjacent nerves innervating the acupoints. In addition, there existed an interaction between somatostatin and glutamate. These results suggest that the balance between excitatory and inhibitory neurotransmitters plays an important role in the function activities of acupoints and meridians.

Electrophysiological effect of ghrelin and somatostatin on rat hypothalamic arcuate neurons in vitro.

Growth hormone (GH) secretion from the pituitary gland is partly regulated by GH releasing hormone (GHRH)-containing neurons located in the hypothalamic arcuate nucleus (ARC). GHRH-containing neurons express the GH secretagogue (GHS) receptor (GHS-R) and the somatostatin (SRIF) receptor. Recently, an endogenous ligand for the GHS-R named ghrelin was found. Therefore, it seems that both ghrelin and SRIF are involved in the hypothalamic regulation of GH release via GHRH-containing neurons in the ARC. In extracellular single unit recordings from in vitro hypothalamic slice preparations from rats, application of 100 nM ghrelin substantially excited ARC neurons (82.5%), whereas 1 microM SRIF substantially inhibited them (81.8%). The ghrelin-induced excitatory and SRIF-induced inhibitory effects on ARC neurons were dose-dependent and persisted during synaptic blockade using low-Ca(2+)/high-Mg(2+) solution. In addition, the effects were antagonized by [D-Lys(3)]-GHRP-6, a GHS-R antagonist, and CYN154806, a SRIF receptor subtype sst2 antagonist, respectively. When ghrelin and SRIF were sequentially applied to ARC neurons, 95.2% were excited by ghrelin and inhibited by SRIF. Similarly, 85.0% of ARC neuroendocrine cells that project to the median eminence were excited by ghrelin and inhibited by SRIF. These results indicate that ARC neuroendocrine cells projecting to the median eminence are dose-dependently, postsynaptically and oppositely regulated by ghrelin through GHS-R and SRIF via the SRIF sst2 receptor subtype. Our results also suggest that most of these ARC neuroendocrine cells are presumably GHRH-containing neurons and are involved in the cellular processes through which ghrelin and SRIF participate in the hypothalamic regulation of GH release.

Melanin-concentrating hormone receptor-1 antagonists as antiobesity therapeutics: current status.

There is compelling genetic and pharmacologic evidence to indicate that melanin-concentrating hormone receptor-1 (MCHR1) signaling is involved in the regulation of food intake and energy expenditure. The medical need for novel therapies to treat obesity and related metabolic disorders has led to a great deal of interest by pharmaceutical companies in the discovery of MCHR1 antagonists. Recent publications describing preclinical studies have demonstrated that small-molecule MCHR1 antagonists decrease food intake, bodyweight, and adiposity in rodent models of obesity. Results from ongoing early-stage clinical trials with MCHR1 antagonists are eagerly awaited, as is the movement of other MCHR1 antagonists into the clinic.

Biological examination of melanin concentrating hormone receptor 1: multi-tasking from the hypothalamus.

Since its discovery as the first receptor for the orexigenic neuropeptide melanin-concentrating hormone (MCH), the MCH receptor, MCHR1, has been actively pursued for therapeutic intervention in the treatment of obesity. Mice with targeted deletion of MCHR1 or its cognate ligand, MCH, generally have decreased body weight and fat mass and are resistant to diet-induced obesity compared with their wild-type counterparts. Mice treated via intracerebroventricular infusion with MCH, or that overexpress MCH or MCHR1, exhibit weight gain compared with control animals. MCHR1 is also a central target of leptin signaling and appears to be a mediator of insulin resistance. The distribution of MCH and MCHR1 in rat brain, outside of regions that control appetite and satiety, has led to the finding that MCH signaling participates in other functions such as emotion and stress. This review will describe in detail the biological studies that show how MCH and MCHR1 control numerous physiological functions. The current status of the development of MCHR1 antagonists for clinical use will also be assessed. Given the substantial link between obesity and its many associated afflictions, a single pharmaceutical agent that could be used to treat multiple pathologies would be welcome.

Effect of electro-acupuncture at Foot-Yangming Meridian on somatostatin and expression of somatostatin receptor genes in rabbits with gastric ulcer.

AIM: To discuss the protective effect of electroacupuncture at the Foot-Yangming Meridian on gastric mucosal lesion, somatostatin (SS) and the expression of SS receptor genes (SSR(1)mRNA ) in rabbits with gastric ulcer and to further explore the relative specificity of meridians and viscera at gene expression level. METHODS: Forty rabbits were randomly divided into control group (A), gastric ulcer model group (B), Foot-Yangming Meridian group (C), Foot-Shaoyang Meridian group (D) and Foot-Taiyang Meridian group (E). The gastric ulcer model was prepared by infusing alcohol into stomach. Groups C-E were treated with electro-acupuncture at points along the above meridians using meridian stimulating instruments for 7 d respectively. By the end of treatment, the index of gastric ulcer was determined, the amount of epidermal growth factor(EGF) and somatostatin was measured by radioimmunoassay (RIA). SS-R(1)mRNA expression in gastric mucosa was determined by RT-PCR. RESULTS: The value of EGF in model group was obviously lower (73.6+/-14.8 vs 91.3+/-14.9 pg/mL, P<0.01) than that in control group. The index of gastric ulcer, content of SS and expression of SSR1mRNA in gastric mucosa were significantly higher than those in control group (24.88+/-6.29 vs 8.50+/-2.98 scores, P<0.01; 2978.6+/-587.6 vs 1852.4+/-361.7 mIU/mL, P<0.01; 2.56+/-0.25 vs 1.04+/-0.36, P<0.01). The value of EGF in Foot-Yangming Meridian group was higher than that in model group (92.2+/-6.7 vs 73.6+/-14.8 pg/mL, P<0.01). The index of gastric ulcer, content of SS and expression of SS-R(1)mRNA in gastric mucosa were significantly lower than those in control group (10.88+/-3.23 vs 24.88+/-6.29 scores, P<0.01; 1800.2+/-488 vs 2978.6+/-587.6 mIU/mL, P<0.01; 1.07+/-0.08 vs 2.56+/-0.25 mIU/mL, P<0.01). Compared to the model group, the content of SS and expression of SSR1mRNA in gastric mucosa in Foot-Shaoyang Meridian group decreased (2441.0+/-488.vs 2978.6+/-587.6 mIU/mL, P<0.05;1.73+/-0.16 vs 2.56+/-0.25 mIU/mL, P<0.01). But the above parameters in Foot-Taiyang Meridian group did not improve and were significantly different from those in Foot-Yangming Meridian group (P<0.05). CONCLUSION: Electro-acupuncture at Foot-Yangming Meridian can protect gastric mucosa against injury. The mechanism may be related to the regulation of brain-gut peptides and the expression of SSR(1)mRNA.

Evidence for a stimulatory action of melanin-concentrating hormone on luteinising hormone release involving MCH1 and melanocortin-5 receptors.

The present series of studies aimed to further our understanding of the role of melanin-concentrating hormone (MCH) neurones in the central regulation of luteinising hormone (LH) release in the female rat. LH release was stimulated when MCH was injected bilaterally into the rostral preoptic area (rPOA) or medial preoptic area (mPOA), but not when injected into the zona incerta (ZI), of oestrogen-primed ovariectomised rats. In rats that were steroid-primed to generate a surge-like release of LH, MCH administration into the ZI blocked this rise in LH release: no such effect occurred when MCH was injected into the rPOA or mPOA. In vitro, MCH stimulated gonadotrophin-releasing hormone (GnRH) release from hypothalamic explants. Double-label immunohistochemistry showed GnRH-immunoreactive neurones in the vicinity of and intermingled with immunoreactive MCH processes. MCH is the endogenous ligand of the MCH type 1 receptor (MCH1-R). Previously, we have shown a role for melanocortin-5 receptors (MC5-R) in the stimulatory action of MCH, so we next investigated the involvement of both MCH1-R and/or MC5-R in mediating the actions of MCH on GnRH and hence LH release. The stimulatory action of MCH in the rPOA was inhibited by administration of antagonists for either MCH1-R or MC5-R. However, in the mPOA, the action of MCH was blocked only by the MC5-R antagonist. LH release was stimulated by an agonist for MC5-R injected into the rPOA or mPOA; this was blocked by the MC5-R antagonist but not the MCH1-R antagonist. These results indicate that both MCH1-R and MC5-R are involved in the central control of LH release by MCH.

Involvement of the Sst1 somatostatin receptor subtype in the intrahypothalamic neuronal network regulating growth hormone secretion: an in vitro and in vivo antisense study.

Five somatostatin (SRIH) receptors (sst1-5) have been cloned. Recent anatomical evidence suggests that sst1 and sst2 may be involved in the central regulation of GH secretion. Given the lack of specific receptor antagonists, we used selective antisense oligodeoxynucleotides (ODNs) to test the hypothesis that one or both of these subtypes are involved in the intrahypothalamic network regulating pulsatile GH secretion. In mouse neuronal hypothalamic cultures the proportion of GHRH neurons coexpressing sst1 or sst2 messenger RNAs (mRNAs) was identical. In contrast, sst1 mRNAs were more often present than sst2 in SRIH-expressing neurons. Firstly, sst1 antisense ODN in vitro treatment abolished sst1, but not sst2, receptor modulation of glutamate sensitivity and decreased sst1, but not sst2, mRNAs. The reverse was true after treatment with sst2 antisense. Sense ODNs did not alter the effects of SRIH agonists. In a second series of experiments, nonanaesthetized adult male rats were infused for 120 h intracerebroventricularly with ODNs. Only the sst1 antisense ODN diminished the amplitude of ultradian GH pulses without modifying their frequency. In parallel, sst1 antisense ODN strongly diminished sst1 immunoreactivity in the anterior periventricular nucleus and median eminence, as well as sstl periventricular nucleus mRNA levels. The effectiveness of the sst2 antisense ODN was attested by the inhibition of hypothalamic binding of [125I]Tyr0-D-Trp8-SRIH. Scrambled ODNs had no effect on GH secretion or on sst mRNAs or SRIH binding levels. These results favor a preferential involvement of sst1 receptors in the intrahypothalamic regulation of GH secretion by SRIH.

Rat somatostatin receptor subtype 4 can be made sensitive to agonist-induced internalization by mutation of a single threonine (residue 331).

A sequence motif of 20 amino acid residues within the C-terminal portion of the rat somatostatin receptor subtype 4 (SSTR4) has been shown to prevent rapid agonist-dependent receptor internalization in transfected human embryonic kidney (HEK) cells. Molecular dissection of this motif by biochemical ligand-binding assays revealed that the block was released by mutating a single residue (threonine 331) to an alanine. These data are in line with confocal microscopic analysis of cultured primary neurons microinjected with cDNA constructs encoding either SSTR4 or the mutant T331A. Immunocytochemical analysis showed that the mutant receptor, but not SSTR4, was internalized. However, internalized T331A was not recycled to the cell surface, suggesting that it lacks sequence elements that determine intracellular sorting after endocytosis. Neither wildtype SSTR nor the mutant T331A exhibited functional desensitization when assayed for their ability to inhibit adenylate cyclase. In agreement with this, the wt receptor and its mutant were not phosphorylated in response to agonist treatment. Lack of desensitization of SSTR4 has been electrophysiologically verified by coexpressing the receptor with a G-protein-gated, inwardly rectifying potassium channel in Xenopus oocytes. A strong somatostatin 14 (SST14)-activated inward potassium current was observed that was long-lasting and which decayed only slowly after washout of the agonist. This is in contrast to another somatostatin receptor subtype, SSTR3, which mediates rapidly desensitizing currents. Binding experiments on HEK cells transfected with either SSTR3 or 4 indicated that this difference is not attributable to slow dissociation of the agonist from the receptor, suggesting that SSTR4 mediates long-lasting signalling, a property which may be relevant for clinical therapy.