neurotrophic factor regulates energy expenditure through...

Int. Jnl. Experimental Diab. Res., Vol. 2, pp. 201-209

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Brain-derived Neurotrophic Factor RegulatesEnergy Expenditure Through the Central NervousSystem in Obese Diabetic Mice

TAKESHI NONOMURAa, ATSUSHI TSUCHIDAa, MICHIKO ONO-KISHINOa,TSUTOMU NAKAGAWAa, MUTSUO TAIJIa’* and HIROSHI NOGUCHIa,b

aSumitomo Pharmaceuticals Co. Ltd., Discovery Research Laboratories II, 3-1-98 Kasugadenaka, Konohana-ku,Osaka 554-0022, Japan; bSumitomo Pharmaceuticals Co. Ltd., Business Development and Licensing Office,3-11 Kandasurugadai, Chiyoda-ku, Tokyo 101-8319, Japan

(Received 2 April 2001; Revised 29 June 2001; In finalform 30 July 2001)

It has been previously demonstrated that brain-derived neurotrophic factor (BDNF) regulates glu-cose metabolism and energy expenditure in rodentdiabetic models such as C57BL/KsJ-leprdb/leprab

(db/db) mice. Central administration of BDNF hasbeen found to reduce blood glucose in db/db mice,suggesting that BDNF acts through the central nerv-ous system. In the present study we have expandedthese investigations to explore the effect of centraladministration of BDNF on energy metabolism. In-tracerebroventricular administration of BDNF low-ered blood glucose and increased pancreatic insulincontent of db/db mice compared with vehicle-treatedpellet pair-fed db/db mice. While body temperaturesof the pellet pair-fed db/db mice given vehicle werereduced because of restricted food supply in thispair-feeding condition, BDNF treatment remarkablyalleviated the reduction of body temperature sug-gesting the enhancement of thermogenesis. BDNFenhanced norepinephrine turnover and increaseduncoupling protein-1 mRNA expression in the inter-scapular brown adipose tissue. Our evidence indi-cates that BDNF activates the sympathetic nervoussystem via the central nervous system and regulatesenergy expenditure in obese diabetic animals.

Keywords: Neurotrophic factor; Intracerebroventricular ad-ministration; Energy expenditure; Glucose metabolism;Norepinephrine turnover

Abbreviations: BDNF, brain-derived neurotrophic factor; NE,norepinephrine; UCP-1, uncoupling protein-i; BAT, brownadipose tissue

INTRODUCTION

Brain-derived neurotrophic factor (BDNF), a

member of the neurotrophin family, has beenwidely demonstrated to function in the centraland peripheral nervous systems and motor neu-

rons in the fetus and in adulthood.[1,2,3,4,5,6]

BDNF is known to regulate neural developmentand regeneration, promote neurite extensionand maintain neuronal survival. [7,8’9’1’11] In addi-tion to those diverse roles of BDNF in the nerv-

ous system, we have discovered that BDNFplays important roles in the endocrine systemand regulates glucose metabolism.I121

We have shown that systemic administration ofBDNF improves glucose metabolism in obese dia-betic C57BL/KsJ-lepreb/lepreb (db/db) mice.[12’13]

Although BDNF also suppresses food intake insuch hyperphagic obese mice, we developed a

novel apparatus to pair-feed vehicle-treated con-

trol mice precisely to BDNF-treated mice anddemonstrated that BDNF has a major hypo-glycemic effect independent of appetite.I41 Wehave clarified the unique profile of peripheralBDNF administration in regulating glucose me-tabolism: (1) BDNF enhances insulin sensitivity

*Corresponding author. Tel.: 81-6-6466-5299, Fax: 81-6-6466-5491, e-mail: [email protected]

201

202 T. NONOMURA et al.

and ameliorates insulin resistance; (2) the hypo-glycemic effect of BDNF lasts long after thecessation of treatment; and (3) insulin content in

pancreas is increased and in histological observa-tions, insulin-positive pancreatic beta cells are

regranulated by BDNF administration.I13,14,151 In-terestingly, in addition to its efficacy on glucosemetabolism, BDNF also prevents the reduction ofbody temperature in the db/db mice deprived offood supply. [141 This finding indicates that BDNFameliorates the impaired energy balance in dia-betic mice. However, the mechanism by whichBDNF regulates glucose metabolism and energyexpenditure still remains unclear. We have not yetobtained any evidence to show the direct effectsof BDNF on glucose metabolism in cultured cellsfrom peripheral tissues such as liver, muscle, andadipose tissue. Under the precise control of foodintake by means of our pellet pair-fed.apparatus,we have demonstrated that intracerebroventricu-lar administration of BDNF shows the similaranorectic and hypoglycemic effects as seen in

peripheral administration in db/db mice.[141 Wethus hypothesize that BDNF regulates glucosemetabolism by acting through the central nervoussystem. To evaluate this hypothesis we have ana-

lyzed the effects of intracerebroventricular BDNFadministration on energy expenditure in thepresent study. We explore the action of BDNFin regulating thermogenesis and demonstratethe involvement of the sympathetic nervous sys-tem in this process.

were performed basically as described in our pre-vious study.I141 The supply of pellets to the BDNF-treated mice was not limited, but the supply ofpellets to the vehicle-treated mice was limited tothe number of those consumed by the BDNF-treated mice. All animal experiments were doneaccording to the guidelines of the Sumitomo Phar-maceuticals Committee on Animal Research.

Intracerebroventricular Administrationof BDNF

Human recombinant BDNF (N-terminal methion-ine-free, Regeneron Pharmaceuticals, Tarrytown,NY) was administered using artificial cerebro-spinal fluid (aCSF; 0.166g/L CaCI2, 7.014g/LNaC1, 0.298g/L KC1, 0.203g/L MgCla/6H20and 2.10g/L NaHCO3) as a vehicle for in-tracerebroventricular administration. Mice wereanesthetized with diethyl ether, and fifteenmicrograms of BDNF (3txl/mouse) were injectedthrough a Hamilton syringe into the lateral cere-bral ventricle according to the following coordi-nates: 1.0mm lateral to the bregma and 3.0mmventral to the skull surface. For the pellet-pair feedexperiment, mice received a total of five injections,alternating sides of the head for each injection,with the injections being given every other day(three on one side of the head and two on theother side). Both sides of injection placement wereverified by injecting Evans Blue in the same man-

ner at the end of the experiment.

MATERIALS AND METHODS

Animals

Male C57BL/KsJ-db/db mice were obtained fromClea Japan Inc. (Tokyo, Japan). Mice were singlyhoused and the treatments started at 10-12 weeksof age. Animals were given food (CE-2, Clea JapanInc.) and water ad libitum except for the pair-feed-ing experiment. Pellet pair-fed mice were housedin the synchronized pellet pair-feeding apparatus(Sumitomo Pharmaceuticals and Osaka Micro

Systems, Osaka, Japan). Pair-feeding experiments

Measurement of Blood Glucoseand Insulin

Blood samples were collected from tail vein, andblood glucose was measured by the GLUCOSECII-TEST WAKO (Mutarotase-glucose oxidasemethod, Wako Chemical, Osaka, Japan). Plasmainsulin concentrations were measured by ELISA(Levis-insulin-mouse; Shibayagi, Gunma, Japan).At the end of the treatment, the whole pancreaswas resected from each mouse and dividedinto splenic and duodenal regions. Splenic re-

gions were weighed, minced, and homogenizedin acid-ethanol solution (75% ethanol, 23.5%

INTERNATIONAL JOURNAL OF EXPERIMENTAL DIABETES RESEARCH

BDNF CENTRALLY REGULATES ENERGY EXPENDITURE 203

distilled water, 1.5% conc. HC1). After overnightincubation at 4C the suspensions were cen-

trifuged, and the supernatants were collectedand assayed for insulin content.

Body Temperature and ThermographicImaging Analysis

Body temperature was measured using an elec-tron thermistor (Model BAT-12, Physitemp,Clifton, NJ) equipped with rectal probe (RET-3, Physitemp, Clifton, NJ). Skin temperaturewas imaged by thermography (TVS-8000MkII,Abionics, Tokyo, Japan) after shaving the backhair.

Measurement of Norepinephrine(NE) Turnover

The effect of BDNF on norepinephrine turnoverwas assessed using a slightly modified version ofthe method previously reported by Collins.[16]

db/db mice received intracerebroventricular ad-ministration of either BDNF (15 txg/mouse) or ve-hicle at the beginning of a dark cycle, and thenfood was removed. Two hours after BDNF or vehi-cle treatment, c-methyl-p-tyrosine methyl ester(250mg/kg, Sigma, St. Louise, MO), an inhibitorof tyrosine hydroxylase, was intraperitoneallyinjected to block de novo catecholamine synthesis.The mice were decapitated two hours after c-MTinjection and the interscapular brown adiposetissue (BAT) was immediately dissected, weighedand then frozen in liquid nitrogen. The BAT was

homogenized with 0.1N perchloric acid containing5mM EDTA. Homogenates were filtrated througha 0.22 xm mesh membrane to remove debris. Nore-pinephrine content in homogenates was measuredusing an HPLC system (LC-10A, Shimadzu Instru-mentation, Kyoto, Japan) equipped with a column(CA-5DS, Eicom, Kyoto, Japan).

Northern Blot Analysis

db/db mice were intracerebroventricularly injectedwith either BDNF or vehicle at the beginning of a

dark cycle and then food was removed. Animalswere sacrificed 4 hours after BDNF (15 Ixg/mouse)or vehicle treatment; interscapular BAT was ex-cised and frozen immediately. RNA was preparedfrom the tissues with Trizol (Gibco BRL Life Tech-nologies, Rockville, MD, USA) using the manufac-turer’s protocol. Yield and purity of RNA weredetermined by spectrophotometric absorptionanalysis at 260/280nm. 3g of total RNA was

electrophoresed in a 1% agarose gel containingformaldehyde and then transferred to GT probemembranes (Bio-Rad Laboratories, Hercules, CA,USA). A 1071-base pair rat uncoupling protein-1(UCP1) probe (nucleotides 84-1154 in Genebankaccession no. Ml1814) was obtained by reverse

transcriptase-polymerase chain reaction (RT-PCR)from rat BAT RNA using primers 5’-CCA CAGGAATTC GAAGTT GAG AGT TCG GTA and 5’-CCC AGC TCT AGA GCC CAG CAT AGG AGCCCA as reported previously.[71 A 349-base pairmouse ]3-actin probe (nucleotides 728-1076 inGenebank accession no. M12481) was obtained byRT-PCR from mouse liver RNA using primers 5’-TGG AAT CCT GTG GCA TCC ATG AAA Cand 5’-TAA AAC GCA GCT CAG TAA CAG TCCG. All probes were verified by sequencing. Probeswere randomly labeled using a BcaBest labelingkit (Takara, Ohtsu, Japan) with [c-32p]-deoxyCTP (Amersham Pharmacia Biotech, Bucking-hamshire, England). Hybridization was carriedout at 65C in 0.25M sodium phosphate (pH7.2)/7% SDS, and blots were washed twice with20mM sodium phosphate (pH 7.2)/5% SDSand then with 20mM sodium phosphate (pH7.2)/1% SDS. Hybridization signals were quanti-fied using a bio-imaging analyzer BAS2000 (FujiPhoto Film, Tokyo, Japan).

Statistical Analysis

All data are presented as means + SD. The statis-tical calculations were performed using SASsoftware (SAS Institute, Cary, NC), and differ-ences between individual groups were analyzedby the Student’s t-test, the Dunnett’s test or

Jonckheere-Terpstra test. P <0.05 was consideredstatistically significant.



RESULTS

Effect of IntracerebroventricularAdministration of BDNF on GlucoseMetabolism

15tg BDNF per mouse or the same volume (31/mouse) of vehicle solution was administered in-

tracerebroventricularly to db/db mice every otherday 5 times. After intracerebroventricular BDNFadministration, the food intake of db/db mice de-creased as shown in Figure 1A. Food intake ofthe vehicle-treated pellet pair-fed db/db mice wasvery well synchronized to the BDNF-treatedmice. Compared with such vehicle-treated con-trol mice, the repetitive intracerebroventricular

0 2 4 6 8 I0

(days)

5OO

-400

300

200

100

0 ,I ,I, I,,,

0 2 4 6 8 10(days)

10

00 5 10

(days)

-C]--vehicle

BDNF

vehicle

BDNF

FIGURE Effects of intracerebroventricular BDNF adminis-tration on food intake (A), blood glucose concentration (B) andbody weight (C) in db/db mice. BDNF (151g/mouse) or vehi-cle was administered on alternate days to db/db mice housedin the pellet pair-feeding apparatus. Data are presented asmean +_ SD (n =9). **P < 0.01 vs. vehicle by Student’s t-test.

administration of BDNF significantly loweredblood glucose concentrations in db/db mice (Fig.1B). There was no significant difference in bodyweight between BDNF-treated and the pellet pair-fed mice (Fig. 1C). To study the dose-dependencyof repetitive intracerebroventricular administra-tion, three different doses (0.15, 1.5 and15g/mouse) of BDNF were injected every otherday to db/db mice, respectively. BDNF was foundto be dose-dependently effective in loweringblood glucose concentration and reducing food in-take of db/db mice by Jonckheere-Terpstra test(blood glucose; P =0.002, food intake; P 0.009).15 ig/mouse of BDNF significantly reduced foodintake and lowered blood glucose concentration

(Figs. 2A, B).In addition to blood glucose, we next analyzed

the effect of intracerebroventricular administra-tion of BDNF on plasma insulin levels. As shownin Table I, plasma insulin concentrations of both

A

00 2 4 6 8

(days)

--D--- vehicle (n=7)

---4-- BDNF(0.15tg/mouse)(n=8)

+BDNF(1.5g/mouse)(n=8)

BDNF(15pg/mouse)(n=7)

500

" 400

300

200

100

vehicle (n=7)

BDNF(0.15tg/mouse)(n=8)BDNF(1.5g/mouse)(n=8)

BDNF(15gg/mouse)(n=7)

0 2 4 6 8

(days)

FIGURE 2 Dose-response effects of intracerebroventricularBDNF administration on food intake (A) and blood glucoseconcentration (B) in db/db mice. BDNF (0.15, 1.5, 15 bg/mouse)or vehicle was administered on alternate days to ad libitum-feddb/db mice. Data are presented as mean SD (n 7 or 8). *P <0.05, **P 0.01 vs. vehicle by Dunnett’s test. BDNF was foundto be dose-dependently effective in lowering blood glucoseconcentration and reducing food intake of db/db mice byJonckheere-Terpstra test (blood glucose; P=0.002, foodintake; P 0.009).



TABLE Effect of intracerebroventricular BDNF adminis-tration on plasma insulin concentration and pancreatic in-sulin content in db/db mice. BDNF (15g/shot) or vehiclewas administered on alternate days for a total of five injec-tions to db/db mice housed in the pellet pair-feeding appa-ratus. Plasma insulin concentration was measured at Days 0(baseline) and 10. Pancreases were removed from the mice atDay 10 and the pancreatic insulin content was measured.Data are presented as mean SD (n 9)

Day 1 10

Plasma insulin concentration

[ng/ml]Pair-feed + vehicleBDNF

45.1 _+ 20.9 30.4 16.149.0

___11.6 16.3 12.2

Pancreatic insulin content[ng/mg tissue]

Pair-feed + vehicle N.A.BDNF N.A.

P < 0.01 vs. vehicle by Student’s t-test.

92.9 47.3606.8 161.4"*

the BDNF-treated db/db mice and pellet pair-feddb/db mice decreased during the experimental pe-riod. However, the plasma insulin concentrationof BDNF-treated db/db mice tended to be lowerthan that of the pellet pair-fed mice after repetitiveintracerebroventricular administrations. Since wehave previously found that subcutaneous admin-istration of BDNF increases pancreatic insulin con-tents of db/db mice, we then analyzed pancreaticinsulin content after repetitive intracerebroventri-cular administration of BDNE The pancreatic in-sulin content of BDNF-treated mice was found tobe approximately 6-fold higher than that of thepellet pair-fed mice (Tab. I). These findings sug-gest that intracerebroventricular administrationas well as subcutaneous administration of BDNFregulates glucose metabolism in a similar fashion.

Effect of IntracerebroventricularAdministration of BDNF on BodyTemperature

To verify our hypothesis that BDNF regulates glu-cose metabolism by acting through the brain, weanalyzed the effect of intracerebroventricularBDNF administration on the rectal temperatureof db/db mice in this study. Compared with adlibitum-fed db/db mice (approximately 37-38C),

the rectal temperature of the vehicle-treated pelletpair-fed db/db mice was lower, probably due to thereduced food intake that was synchronized withBDNF-treated mice (Tab. II). The rectal tempera-ture of the BDNF-treated db/db mice at Days i and10 was significantly higher than the vehicle-treated pellet pair-fed db/db mice and almost com-parable to ad libitum-fed mice in spite of a reducedfood intake that was approximately the same asthe pair-fed mice. We then examined the skin’ tem-perature of these db/db mice by thermographyimaging analysis (Fig. 3). Whereas the skin tem-

perature of a typical vehicle-treated pellet pair-fedmouse was lower than an ad libitum-fed mouse,the skin temperature of the paired BDNF-treatedmouse recovered. A relatively higher temperaturewas observed in the interscapular region of theBDNF-treated mouse suggesting enhancement ofthermogenesis in the brown adipose tissue (BAT).

TABLE II Rectal temperature of db/db mice with intracere-broventricular BDNF administration. BDNF (15g/shot) orvehicle was administered on alternate days for a total of fiveinjections to db/db mice housed in the pellet pair-feeding appa-ratus. Rectal temperatures were measured at the next day af-ter the first injection (Day 1) and two days after the last (fifth)injection (Day 10). Data are presented as mean SD (n=9)

Day 10

Rectal temperature (C)Pair-feed + vehicle 34.6 1.8 35.0 _+ 1.1BDNF 37.0 0.4** 37.2 +_ 1.2"*

P < 0.01 vs. vehicle by Student’s t-test.

36.0

2g.O

FIGURE 3 Thermographic imaging analysis of the backskin temperature of db/db mice after intracerebroventricularBDNF administration. Thermographic imaging analysis of aBDNF (15g/mouse, on alternate days)-treated mouse (a),a vehicle-treated mouse pair-fed to the BDNF-treated mouse(b), and a vehicle-treated mouse fed ad libitum (c). Analysiswas performed at Day 10.



Enhancement of NorepinephrineTurnover in db/db Mice Treatedwith BDNF

In order to explore the effect of BDNF on sympa-thetic nerve activity, we examined NE utilization(i.e., NE turnover) in BAT of a BDNF-treated db/dbmouse. To assess NE turnover, NE contents inBAT were measured after blocking catecholaminesynthesis with administration of a-methyl-p-tyro-sine (a-MT), a tyrosine hydroxylase inhibitor. Twohours prior to c’MT administration, db/db micereceived a single intracerebroventricular adminis-tration of either BDNF or vehicle. After adminis-tration of a-MT there was a decrease in the NEcontents of the BAT in db/db mice that received ve-hicle intracerebroventricularly, indicating a block-age of catecholamine synthesis. Compared withsuch control animals, intracerebroventricular ad-ministration of BDNF elicited a larger reduction inNE contents in interscapular BAT, indicating en-hancement of NE turnover (Fig. 4).

Effects of a Single IntracerebroventricularAdministration of BDNF on mRNAExpression of Uncoupling Protein-1

To study the action mechanism by which BDNFenhances energy expenditure in greater detail weexamined the effect of intracerebroventricular

600

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0

vehicle BDNF vehicle BDNF

pre ct -MT

FIGURE 4 NE turnover in db/db mice treated with BDNF.Following a single intracerebroventricular administration ofBDNF (15g/mouse), the tyrosine hydroxylase inhibitor a-methyl-p-tyrosine (a-MT) was intraperitoneally injected. NEcontents were measured 2hr after injecting the blockingreagent. NE turnover was determined from the decrease inNE content after blockage of catecholamine biosynthesis.Data are presented as mean +SD (n =6 or 8). *P <0.05 vs.vehicle by Student’s t-test.

Vehicle BDNFii.:.,,.......i-.,.,:.o..i ..

-6 200

UCP’I (R)

150. lOO

-actin

Vehicle BDNF

FIGURE 5 Effects of a single intracerebro,entricular ad-ministration of BDNF on mRNA expression of uncouplingprotein-1 in brown adipose tissue.BDNF (15g/mouse) or vehicle was administered intra-

cerebroventricularly to db/db mice and then fasting wasstarted. Four hours after BDNF or vehicle administration, theinterscapular brown adipose tissue was dissected and totalRNA was isolated. Northern blot analysis (UCP1 and fi-actinprobes) of the total RNA (3g) was then performed. Dataare shown as means SD (n 4). *P <0.05 vs. vehicle byStudent’s t-test. The left panels show representative blots.

administration of BDNF on the expression of un-coupling protein (UCP)-I gene in BAT. db/dbmice were intracerebroventricularly adminis-trated with either BDNF (15g/mouse) or vehi-cle followed by food removal. Four hours afterBDNF or vehicle administration, total RNA wasprepared from BAT and subjected to Northernblot analysis using UCP-1 cDNA as a probe. Asshown in Figure 5, a single intracerebroventricu-lar administration of BDNF increased UCP-1mRNA in BAT by 1.5-fold.

DISCUSSION

We have previously shown that peripheral subcu-taneous administration of BDNF lowered food in-take and blood glucose concentration of diabeticdb/db mice with accompanying obesity and hyper-insulinemia.[12’131 We have also demonstratedthe hypoglycemic effect of BDNF on db/db miceeven under strict pellet pair-feeding conditionsusing our novel apparatus[141 which indicates thatblood glucose is actually being lowered by BDNFapart from the hypoglycemic effect ascribed tohypophagia. Since BDNF does not lower bloodglucose levels of normal rodents and streptozo-tocin-treated rodent models, it is unlikely that



BDNF enhances insulin secretion from the pan-creas.[12,141 In streptozotocin-treated mice, wehave found concomitant administration of BDNFwith insulin enhances the acute hypoglycemic ef-fect of insulin.I141 These data suggest that pe-ripheral subcutaneous administration of BDNFenhances insulin sensitivity or ameliorates insulinresistance or both in peripheral tissues.

In our studies so far with cultured adipocyteand myotubule cell lines we have observed no

direct action of BDNF on insulin stimulated2-deoxyglucose uptake (unpublished data), al-though peripheral tissues such as adipose tissueand muscle are involved in insulin-dependentglucose metabolism. Moreover, it was reportedelsewhere that intracerebroventricular infusion ofBDNF suppresses food intake and body weightgain but does not affect blood glucose level in

normoglycemic (Long-Evans) rats. [181 Therefore,we investigated the effect of central administra-tion of BDNF on glucose metabolism in hyper-glycemic animals. Our present study clearlydemonstrated that central BDNF administrationreduces blood glucose and also increases pancre-atic insulin contents in obese hyperglycemic db/dbmice under strict pellet pair-feeding conditions.In comparison with subcutaneous administration,a much lower dose (approximately 1/100) ofBDNF was found to be effective with central ad-ministration. These results indicate that BDNFregulates glucose metabolism and maybe pancre-atic function through the central nervous system.

Previously, we have found that subcutaneousadministration of BDNF raised rectal and skintemperatures in db/db mice,[141 indicating the regu-latory role of BDNF on energy metabolism. Inthe present study we were also able to repro-duce these effects of BDNF through central ad-ministration. It is well known that the sympatheticnervous system is involved in regulating thermo-genesis and maintaining body temperature inmammals.I191 In this study, we demonstrated thatcentral administration of BDNF rapidly enhancesNE turnover in thermogenic brown adipose tissue

(BAT) of db/db mice. This is consistent with thepresent thermographic data in which skin tem-

perature increased in the interscapular region that

abundantly contains BAT. BAT is a major sourceof non-shivering thermogenesis in rodents[21 andthe thermogenic ability of BAT is thought to bedue to UCP-1.[2] Intracerebroventricular adminis-tration of BDNF also rapidly increased UCP-1mRNA expression in BAT of db/db mice demon-strating the central regulation of BDNF in energyexpenditure. Taken together, the above indicatesthat BDNF regulates energy metabolism throughthe central nervous system and the auton’omicnervous system.

It is well known that the blood brain barrierrestricts the transport of peptides and proteinsbetween the blood and the brain. [221 It has beenreported however that BDNF passes through theblood brain barrier by a saturable transport sys-tem and quickly enters into brain. [23,24] In our

preliminary experiments, subcutaneous treat-ment of BDNF as well as intracerebroventriculartreatment rapidly showed anorexic effect in

db/db mice (data not shown). Since subcutaneousadministration of BDNF ameliorated the energyexpenditure in our previous study,[14] BDNF ad-ministered even peripherally may rapidly enterthe brain and regulate energy metabolism inobese diabetic animals.The pharmacological profiles of BDNF shown

in this study reminded us of leptin, an adipocyte-derived satiety hormone regulating body adi-

posity by modulating food intake and energymetabolism.[8,25,26] Peripheral administration ofleptin stimulates sympathetic nerve activity in in-

terscapular BAT and norepinephrine turnover[6,27]

and regulates the expression of UCP1 by modulat-ing the sympathetic nervous system.[28,29] Sincethe functional form of the leptin receptor (Ob-Rb)is expressed in the hypothalamus, a major site ofmetabolic regulation by the autonomic nervous

system,I31 intracerebroventricular or intrahypo-thalamic administration of leptin can reproducemost of the effects of peripheral leptin administra-tion.[26’31’32] Leptin administered peripherally mayaccess the hypothalamus via receptor-mediatedtransport, and regulate energy expenditure andfood intake primarily by interacting with Ob-Rbin the hypothalamus. Therefore, many of the thera-peutic profiles of leptin are very similar to BDNE



Since the functional full-length form of BDNF re-

ceptor, trkB is expressed in the hypothalamus,[33,34]

it is plausible that BDNF may act via the hypo-thalamic neuronal system. More studies will beneeded to clarify the action mechanisms of BDNFin comparison with leptin.

In conclusion, the present study has demon-strated that central administration of BDNFregulates the glucose metabolism and energyexpenditure of obese diabetic animals in a simi-lar fashion to peripheral administration. Theseresults further suggest that BDNF modulatessympathetic nerve activity through central regu-lation in the hypothalamus and affects energyexpenditure.

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