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Ž . Brain Research 846 1999 164–170 www.elsevier.comrlocaterbres Research report Investigation of the feeding effects of melanin concentrating hormone on food intake — action independent of galanin and the melanocortin receptors Michela Rossi ) , Sarah A. Beak, Sang-Jeon Choi, Caroline J. Small, David G.A. Morgan, Mohammad A. Ghatei, David M. Smith, Stephen R. Bloom ICSM Endocrine Unit, 6th Floor Commonwealth Bldg., Hammersmith Hospital, DuCane Road, London W12 0NN, UK Accepted 17 August 1999 Abstract Ž . Melanin concentrating hormone MCH is recognised as a hypothalamic appetite stimulant. The mechanism of action of MCH is undetermined largely due to lack of identification of hypothalamic MCH receptors. We designed in vivo and in vitro studies to further Ž . characterise the feeding effects of MCH in the rat. MCH was injected directly into the paraventricular nucleus PVN at the beginning of Ž . Ž . the light phase. PVN MCH 0.5 mg produced an increase in 2 h food intake of 272 "60% vs. saline control 0.7 "0.2 g , p -0.05. The Ž . time course of the effect of intracerebroventricular i.c.v. administration of 5 mg MCH on food intake was investigated. An increase in feeding was observed within 15 min from the time of injection and was not sustained beyond half an hour following administration. To investigate a possible interaction with galanin, 5 mg of MCH was injected i.c.v. with or without 10 mg of galanin. The two peptides Ž . together increased 1 h feeding above that of either peptide alone, 768 "62% compared with the saline group, 0.47 "0.2 g , p -0.05 vs. 585 "36%, galanin alone and 317 "72%, MCH alone. Finally, to investigate if MCH bound to the brain melanocortin receptors, w 125 x 4 7 receptor autoradiography was performed on rat brain sections with the stable analogue of alpha MSH, I Nle , D-Phe -a MSH and w 125 x 4 7 unlabeled MCH. MCH did not compete with I Nle , D-Phe -a MSH binding. Results demonstrate that MCH stimulates feeding via the PVN, has a short onset and duration of action and activates feeding by mechanisms independent to galanin and the melanocortin receptors. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Melanin concentrating hormone; Appetite; Hypothalamus; Intracerebroventricular; Melanocortin receptor 1. Introduction Ž . Melanin concentrating hormone MCH was first iso- w x lated and sequenced from salmon pituitaries in 1983 13 . Rat MCH was identified 6 years later as a cyclic 19 amino acid peptide differing from salmon MCH by only six w x amino acids 35 . This was later found to be identical to w x human MCH 19 . This high conservation of sequence suggests a critical physiological role. In mammals, there is now good evidence to support the role of MCH in the central regulation of feeding behaviour. In mammals, the CNS MCH perikarya are prominent in w x the lateral hypothalamus and the zona incerta 9,29 . Qu et w x al. 20 found MCH mRNA levels to be increased in the hypothalamus of obrob mice compared to wild type and obrq controls. Expression was further enhanced in all ) Corresponding author. Fax: q44-181-383-3142; e-mail: [email protected] groups of mice in the fasted state. Hypothalamic MCH mRNA expression was also examined in Wistar rats by Bluet Pajot et al. They found a diurnal rhythm, with expression being highest during the beginning of the dark wx phase, a time when rodents begin their feeding period 4 . The obese fat r fat mouse has a hypothalamic MCH pep- tide content three-fold higher than their wild type control w x 24 . Our laboratory has also found hypothalamic MCH peptide content to be elevated in the obese leptin receptor w x defective Zucker fa r fa rat 22 . A dose-dependent increase of MCH on food intake was Ž . seen when administered intracerebroventricularly i.c.v. in w x Wistar rats 23 . With twice daily administration, MCH repeatedly caused a 2 h increase in food intake for 5 consecutive days, after which time the effect was lost. Daily food intake and body weights were not altered, suggesting a reproducible but short-term effect on feeding, with possible down regulation of the receptor involved. Despite identification of specific MCH receptors on mouse 0006-8993r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0006-8993 99 02005-3

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Page 1: Investigation of the feeding effects of melanin concentrating hormone on food intake — action independent of galanin and the melanocortin receptors

Ž .Brain Research 846 1999 164–170www.elsevier.comrlocaterbres

Research report

Investigation of the feeding effects of melanin concentrating hormone onfood intake — action independent of galanin and the melanocortin receptors

Michela Rossi ) , Sarah A. Beak, Sang-Jeon Choi, Caroline J. Small, David G.A. Morgan, MohammadA. Ghatei, David M. Smith, Stephen R. Bloom

ICSM Endocrine Unit, 6th Floor Commonwealth Bldg., Hammersmith Hospital, DuCane Road, London W12 0NN, UK

Accepted 17 August 1999

Abstract

Ž .Melanin concentrating hormone MCH is recognised as a hypothalamic appetite stimulant. The mechanism of action of MCH isundetermined largely due to lack of identification of hypothalamic MCH receptors. We designed in vivo and in vitro studies to further

Ž .characterise the feeding effects of MCH in the rat. MCH was injected directly into the paraventricular nucleus PVN at the beginning ofŽ . Ž .the light phase. PVN MCH 0.5 mg produced an increase in 2 h food intake of 272"60% vs. saline control 0.7"0.2 g , p-0.05. The

Ž .time course of the effect of intracerebroventricular i.c.v. administration of 5 mg MCH on food intake was investigated. An increase infeeding was observed within 15 min from the time of injection and was not sustained beyond half an hour following administration. Toinvestigate a possible interaction with galanin, 5 mg of MCH was injected i.c.v. with or without 10 mg of galanin. The two peptides

Ž .together increased 1 h feeding above that of either peptide alone, 768"62% compared with the saline group, 0.47"0.2 g , p-0.05 vs.585"36%, galanin alone and 317"72%, MCH alone. Finally, to investigate if MCH bound to the brain melanocortin receptors,

w125 x 4 7receptor autoradiography was performed on rat brain sections with the stable analogue of alpha MSH, I Nle , D-Phe -aMSH andw125 x 4 7unlabeled MCH. MCH did not compete with I Nle , D-Phe -aMSH binding. Results demonstrate that MCH stimulates feeding via the

PVN, has a short onset and duration of action and activates feeding by mechanisms independent to galanin and the melanocortinreceptors. q 1999 Elsevier Science B.V. All rights reserved.

Keywords: Melanin concentrating hormone; Appetite; Hypothalamus; Intracerebroventricular; Melanocortin receptor

1. Introduction

Ž .Melanin concentrating hormone MCH was first iso-w xlated and sequenced from salmon pituitaries in 1983 13 .

Rat MCH was identified 6 years later as a cyclic 19 aminoacid peptide differing from salmon MCH by only six

w xamino acids 35 . This was later found to be identical tow xhuman MCH 19 . This high conservation of sequence

suggests a critical physiological role. In mammals, there isnow good evidence to support the role of MCH in thecentral regulation of feeding behaviour.

In mammals, the CNS MCH perikarya are prominent inw xthe lateral hypothalamus and the zona incerta 9,29 . Qu et

w xal. 20 found MCH mRNA levels to be increased in thehypothalamus of obrob mice compared to wild type andobrq controls. Expression was further enhanced in all

) Corresponding author. Fax: q44-181-383-3142; e-mail:[email protected]

groups of mice in the fasted state. Hypothalamic MCHmRNA expression was also examined in Wistar rats byBluet Pajot et al. They found a diurnal rhythm, withexpression being highest during the beginning of the dark

w xphase, a time when rodents begin their feeding period 4 .The obese fatr fat mouse has a hypothalamic MCH pep-tide content three-fold higher than their wild type controlw x24 . Our laboratory has also found hypothalamic MCHpeptide content to be elevated in the obese leptin receptor

w xdefective Zucker far fa rat 22 .A dose-dependent increase of MCH on food intake was

Ž .seen when administered intracerebroventricularly i.c.v. inw xWistar rats 23 . With twice daily administration, MCH

repeatedly caused a 2 h increase in food intake for 5consecutive days, after which time the effect was lost.Daily food intake and body weights were not altered,suggesting a reproducible but short-term effect on feeding,with possible down regulation of the receptor involved.Despite identification of specific MCH receptors on mouse

0006-8993r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.Ž .PII: S0006-8993 99 02005-3

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( )M. Rossi et al.rBrain Research 846 1999 164–170 165

w xmelanoma cells and human keratinocytes 7,5 , the absenceof a satisfactory radioligand has hindered research on

Ž .MCH receptor s structure and function.Recently, an MCH knockout mouse has been produced

which has a markedly altered energy balance phenotypew x28 . This mouse has a 25% reduction in body weight andfood intake, with virtually no fat deposits seen. It has aparadoxical increase in metabolic rate for its size but hasno other reported changes in behaviour or physiology. Thephenotype of this MCH knockout mouse is unique due toits leanness. Knockout models of orexigenic peptides in-volved in the hypothalamic feeding circuit have been

Ž . w xgenerated for neuropeptide Y NPY and galanin 8,37 .None of these mice had an altered feeding pattern or bodyweight.

In lower vertebrates, MCH is of functional importancein causing skin paling, by antagonising the melanin dis-persing action of a-melanocyte stimulating hormoneŽ . w xaMSH 21 . Although the mechanism of action of MCHis undetermined, an interaction with aMSH has beenreported in mammals as well as in fish. i.c.v. studies withMCH and aMSH in rodents have found they have oppo-site effects and act as functional antagonists when measur-

w xing food intake and auditory-gating paradigms 16,18 .When behavioural changes were examined, the effects ofdiscrete intranuclear injections of aMSH were antago-nised by prior administration of MCH, even though theMCH had no effect on these behaviours when given alonew x11 . Likewise Sanchez et al. found i.c.v. aMSH inducedexcessive grooming behaviour was blocked by prior ad-

w xministration of MCH 25 . To determine if MCH is actingcentrally through one of the brain melanocortin receptors,we performed receptor autoradiography on rat brains using

w 4 7 x Ž .iodinated Nle , D-Phe aMSH NDP-MSH with additionof unlabeled MCH to compete for the 125I NDP-MSHbinding sites.

Our aim was to investigate the site and time course ofaction of hypothalamic MCH stimulation of feeding and apossible interaction with the other neuropeptide feedingsystems. We report that MCH increases feeding when

Ž .injected into the paraventricular nucleus PVN and actswithin 15 min of an i.c.v. injection. This is very similar tothe feeding stimulus with galanin and we therefore investi-gated a possible interaction with MCH but found none. Wealso report that MCH does not bind to the currentlyidentified brain melanocortin receptors.

2. Materials and methods

2.1. Peptides

ŽRat MCH was obtained from Bachem Walden, Essex,. w 4 7 xUK and porcine galanin aMSH and Nle , D-Phe -aMSH

Ž .NDP-MSH were purchased from Penninsula LaboratoriesŽ .Merseyside, UK .

[125 ]2.2. Preparation of I NDP-MSH

Ž .NDP-MSH 5 nmol was radio-iodinated by the Iodogenw xmethod 2 and purified by reverse phase high performance

liquid chromatography using a C column and an 80 min18

25%–35% acetonitrile gradient in waterr0.05% trifluoro-acetic acid. The specific activity of the label was 7.7Bqrfmol determined by calculation from saturation andcompetition binding experiments.

2.3. Animals

Male Wistar rats weighing 200–250 g were maintainedŽin individual cages under controlled temperature 218C–

. Ž238C and light 12:12 h light: dark cycle, lights on 0700. Ž .h with ad libitum access to food RM1 diet, SDS UK and

water. Animal procedures undertaken were all approved bythe British Home Office Animals Scientific Procedures

Ž .Act 1986 Project Licence No. 90r1077 .

2.4. IntracerebroÕentricular and intranuclear cannulationand injections

Animal surgical procedures and handling was carriedw xout as previously described 23 . Animals were anaes-

Ž . Žthetized with i.p. xylazine 20 mgrkg Rompun, Bayer,. Ž . ŽSuffolk, UK and ketamine 100 mgrkg Ketalar, Parke

.Davis, Pontypool, Gwent, UK . Animals were placed in aKopf stereotactic frame with 3 mm skull tilt. Permanent

Ž .22-gauge Plastics One, Roanoke, VA were stereotacti-cally placed 0.8 mm posterior to the bregma in the midlineand implanted 6.5 mm below the outer surface of the skullinto the third cerebral ventricle for i.c.v. cannulation. ForPVN cannulation, 26-gauge stainless steel cannulae wereplaced 1.8 mm posterior to the bregma and 0.5 mm lateralto the midline and implanted 7 mm below the outer surfaceof the skull to approximately 1 mm above the PVN. Allcompounds were dissolved in 0.9% saline and each study

Žinvolved an injection of 10 ml over 1 min for i.c.v.. Ž .studies or 1 ml for PVN studies over 1 min of peptide or

Žsaline. Substances were administered by a 27-gauge for. Ž .i.c.v. studies or 31-gauge for PVN studies stainless steel

injector, placed in and projecting 1 mm below the tip ofthe cannulae. Following injection, animals were returnedto cages containing pre-weighed chow and observed.

At the end of the study period, animals were killed byŽ .decapitation after injection of 10 ml for i.c.v. studies or 1

Ž .ml for PVN studies of black ink. Brains were immedi-ately examined for presence of dye in the ventricles for thei.c.v. cannulated animals. For the PVN cannulated animals,brains were snap frozen, cryostat sliced into 15 mm coro-nal sections and stained with Cresyl violet for histologicalconfirmation of correct cannula placement. Only thoseanimals with correct cannula placement were included inthe data analysis.

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( )M. Rossi et al.rBrain Research 846 1999 164–170166

2.5. Injection of MCH into the PVN

ŽThree groups of satiated animals 11 to 14 rats per.group were studied at the beginning of the light phase and

injected with saline, 0.15 or 0.5 mg of MCH. Food intakewas measured at 2, 4 and 24 h after each injection.

2.6. ObserÕation of animals in time course study

ŽTwo groups of satiated i.c.v. cannulated animals ns9.per group were studied at the beginning of the light phase

and injected with saline or 5 mg of MCH. Immediatelyafter injection, animals were monitored by an observerwho was blind to the treatment. At 1 min intervals for aperiod of 2 h, it was noted whether each animal was eatingor not. Food intake was measured at the end of this period.

2.7. Injection of MCH andror galanin i.c.Õ.

ŽFour groups of satiated i.c.v. cannulated animals ns9.to 10 per group were studied at the beginning of the light

phase and injected with saline, 5 mg of MCH, 10 mg ofgalanin or both peptides together. These doses were chosensince these were the lowest doses above which no furtherincrease in feeding was seen in previous dose–responsestudies performed in our laboratory under identical circum-

Ž w x .stances Ref. 23 and unpublished findings . Food intakewas measured at 1 h after each injection.

2.8. Receptor autoradiography studies

Brains were removed from Wistar rats, snap frozen and15 mm cryosections were taken. Sections were taken seri-

ally in groups of five slides. Every fifth slide taken fromthe cryosections was stained with Cresyl violet to allow

w125 xorientation of the rat brain. Buffer preparations for Iw xNDP-MSH binding were taken from Tatro 32 . Slide-

mounted tissue sections were pre-incubated for 15 min atŽ .238C in a buffer consisting of Tris–HCl 50 mM , NaCl

Ž . Ž . Ž .140 mM , CaCl 2.5 mM , MgCl 1.2 mM , pH 7.2.2 2

Incubation was then performed in the above buffer plus0.25% bovine serum albumin, 0.6% ascorbic acid, apro-

Ž . w125 x Ž 4tonin 500 KIUrml and I NDP-MSH 8.5 to 9.5=10.c.p.m.rml . Nonspecific binding was determined in a quar-

ter of the slides by the addition of 200 nM aMSH. TheŽ .ability of MCH 10 nM and 1 mM to compete for the

binding sites was investigated by addition to half of theslides. The remaining quarter had no further peptide added

Ž .to the incubation buffer total binding . Slides were left toincubate for 2 h and reaction terminated by washing in thebuffer solution at 48C four times for 30 s, rinsed inice-cold distilled water and dried overnight at 48C undervacuum. Labeled sections were dry apposed to 3H-Hyper-

Ž .film Amersham International, Amersham, Bucks, UK ina light proof cassette which was stored at for 10 days aty808C.

2.9. Statistical analysis

Food intake is expressed as mean"S.E.M. on graphsand in the text referred to as a percentage increase com-pared with the control. Results for analysis of the PVN andi.c.v. MCH with galanin studies were analysed by ANOVA

Ž .followed by the Least Significant Difference LSD forpairwise comparison. In the time course study, unpairedtwo sample Student’s t-test was used to compare time

Fig. 1. Effect of increasing doses of MCH or saline into the PVN on 2 h food intake at the beginning of the light phase. U p-0.05 vs. saline group.

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( )M. Rossi et al.rBrain Research 846 1999 164–170 167

Table 1Effect of MCH on food intake following i.c.v. administration. This table shows the time course effects of 5 mg of MCH on food intake following i.c.v.

Ž . U UUadministration at the beginning of the light phase. Time is expressed in minutes min , means"S.E.M. p-0.05, p-0.005 vs. saline

Time to onset Time spent eating Time spent eating Time spent eating Time spent eatingof eating over 120 min between ts0 and ts30 between ts30 and ts60 between ts60 and ts120

Saline 59"16 4"1 2"1 2"1 0U U UUMCH 13"2 11"2 8"1 2"1 1"1

differences between the saline and MCH groups. Values ofp-0.05 were considered significant.

3. Results

3.1. InÕestigation of the direct intranuclear injection ofMCH into the PVN

At the beginning of the light phase, MCH increasedfeeding when injected directly into the PVN, by ANOVA,

Ž .F s3.356, ps0.045, Fig. 1 . The 0.5 mg dose of2,39

MCH increased 2 h food intake to 272"60%, p-0.05,Ž .compared with the saline group 0.7"0.2 g . Food intake

was no longer increased when measured at 4 or 24 hŽ .results not shown .

3.2. InÕestigation of the time course effect of i.c.Õ. MCHon feeding

The animals injected with 5 mg MCH had an increaseof food intake of 286"31%, p-0.01, compared with the

Ž .saline group 0.8"0.2 g . The mean onset of first startingto eat the chow provided was 13"2 min in the MCHgroup compared to 59"16 min in the saline group, p-

Ž .0.05 Table 1 . During the 2-h period, the animals thatreceived MCH ate for a total of 11"2 min compared to4"1 min in the saline group, p-0.05. This was furtheranalysed to determine the time the animals spent eatingfrom the time of injection to 30 min later, between 30 and

Ž .60 min and between 60 and 120 min Table 1 . A signifi-cant difference between the MCH and the saline group wasseen only from the time of injection to 30 min later, 8"1min vs. 2"1, p-0.005. This indicates that the effect ofi.c.v. MCH on food intake occurs within 15 min from thetime of injection and is not sustained beyond 30 to 60 minfollowing administration.

3.3. InÕestigation of simultaneous administration of MCHwith galanin

Ž .Both MCH and galanin alone increased feeding Fig. 2 ,317"72%, MCH group, p-0.01 and 585"36%, galanin

Žgroup, p-0.001 compared with the saline group 0.47"

Fig. 2. Effect of i.c.v. saline, 5 mg of MCH alone, 10 mg of galanin alone or both peptides together on 1 h food intake at the beginning of the light phase.U p-0.01, UU p-0.001 vs. saline group; v p-0.05, vv p-0.001 vs. MCHqgalanin group.

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( )M. Rossi et al.rBrain Research 846 1999 164–170168

w125 xFig. 3. Receptor autoradiography on coronal rat brain slices using I NDP-MSH. Total binding is shown in the first column. Binding is seen in areasw125 xincluding BST, MPO, MHB, PVN, VMN and the ME. The second column shows the nonspecific binding of I NDP-MSH, after addition of 200 nM of

w125 xunlabeled aMSH. The binding of I NDP-MSH was completely inhibited. The third column shows binding after addition of 1 mM of unlabeled MCH,w125 xthe I NDP-MSH binding was not affected.

.0.2 g . Simultaneous administration of both peptides causeda further increase of feeding 768"62%, p-0.05 vs.galanin alone or p-0.001 MCH alone groups.

3.4. InÕestigation of MCH binding to brain melanocortinreceptors

w125 xI NDP-MSH binding sites were seen in areas previ-w xously described by Tatro 32 , including the bed nucleus of

Ž . Ž .stria terminalis BST , medial preoptic nucleus MPO ,Ž .medial habuncular nucleus MHB , PVN, ventromedial

Ž . Ž . Ž .nucleus VMN and the median eminence ME Fig. 3 .w125 xWith addition of unlabeled aMSH the binding of the I

NDP-MSH was completely inhibited. With unlabeledw125 xMCH, even at the higher concentrations of 1 mM, I

NDP-MSH binding was not affected. This suggests thatMCH does not bind to any of the currently knownmelanocortin receptors in the rat brain.

4. Discussion

We have demonstrated that the PVN is sensitive to thefeeding effects of MCH, has a short onset and duration ofaction and activates feeding by mechanisms that appear tobe independent to galanin and the melanocortin receptors.

Several lines of evidence suggest that neuronal elementsin the PVN participate in the control of feeding andappetite control. Microinjection of several orexigenic pep-tides including NPY, galanin and the opioids have been

w xshown to increase feeding at the PVN 31,14,15 . Simi-larly, anorexigenic peptides such as glucagon-like peptide

Ž . w x1 GLP-1 and leptin reduce feeding here 17,12 . ThePVN is also an area found to exhibit dense expression ofthe early gene marker c-fos in response to injection of

w xpeptides implicated in appetite control 34,36 . In the mostdetailed study of MCH immunoreactivity in the rat brainby Bittencourt et al., localisation was seen to encircle all

w xthree parts of the PVN 3 . Our findings indicate that MCHis yet another player in PVN-mediated control of feeding.We have not examined feeding stimulation at other hy-pothalamic or cortical areas, and other nuclei may beinvolved. However, it is unlikely that the PVN is diffusingto another nucleus within the hypothalamus to stimulate

Ž .feeding, since the maximum dose of MCH used 0.5 mgw xdoes not stimulate feeding when injected i.c.v. 23 . It is

possible that all these peptides are interacting at the PVNto finely control food intake at mealtimes. It would alsosuggest that the PVN is a hypothalamic area where MCHreceptors will be found to exist.

We have shown that the onset of action of MCHhypothalamic activation causing a feeding stimulus is verybrief. The mean onset of initiation of the feeding occurs at13 min post-injection. The feeding period is started andfinished within half an hour of administration of the MCH.This is in keeping with the feeding time course seen with

w xpeptides such as galanin rather than NPY 14,6 . The MCHfeeding stimulus is, in fact, very similar to that seen withgalanin in terms of not only onset and duration of feeding,but also magnitude of the feeding response, demonstrationof tachyphylaxis to this response and stimulation of feed-

w xing following administration into the PVN 14,30 . It wasfor this reason that we went on to examine the feedingresponse to simultaneous administration of both galanin

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( )M. Rossi et al.rBrain Research 846 1999 164–170 169

and MCH using the lowest doses above which no furtherincrease in feeding was seen in previous dose–response

w xstudies performed in our laboratory 23 . If these peptideswere activating feeding through similar mechanisms, afurther increase in the amount of food consumed wouldnot be expected. Our findings that galanin and MCHtogether increased 1 h feeding above either peptide alonewould suggest that, despite the similarity in their stimula-tory effect on feeding, these peptides may be affectingseparate hypothalamic appetite neuronal circuits.

Functional interaction studies between MCH and otherorexigenic and anorexigenic peptides have been reported

w xby Tritos et al. 33 . They carried out a series of i.c.v.feeding studies and demonstrated the ability of GLP-1 andneurotensin to inhibit MCH-induced feeding. The samegroup previously reported that despite i.c.v. MCH andaMSH behaving as functional antagonists when observingfood intake, MCH did not block aMSH binding or cAMPproduction on cell lines expressing the MC3 or MC4

w xreceptors 16 . Our studies took these investigations onestep further by using receptor autoradiography on rat brainslices, thereby allowing direct examination of any bindinginteraction between MCH and brain melanocortin recep-tors to be determined. Although MC5 receptor mRNA inrat brain was not visualised by means of in situ hybridisa-tion, it is detected by means of RNAase protection assays,

w xRT-PCR and northern blotting 1,10 . In addition, thepossibility of future discoveries of new unidentified brainmelanocortin receptors still exists. NDP-MSH is a goodligand for this purpose since it is a potent analogue ofaMSH and binds with high affinity to all the clonedMC-Rs apart from MC2-R, the specific ACTH receptorw x26,27 . Our studies indicate that MCH does not bind inany appreciable amount to the currently identified rat brainmelanocortin receptors.

Substantial evidence now supports a major role forMCH in the hypothalamic control of feeding. Manipulationof MCH regulation may lead to a treatment for humanobesity. Before this can occur, it is vital that we continueto research the mechanisms underlying the stimulatoryeffect of this peptide.

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