| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Department of Veterinary Physiology (T.I., Y.E., S.A., K.N., N.M.), Faculty of Agriculture, University of Miyazaki, Miyazaki 889-2155; Department of Biochemistry (K.M., M.M., K.K.), National Cardiovascular Center Research Institute, Fujishirodai, Suita, Osaka 565-8565; and Laboratory of Veterinary Physiology (M.N.), Veterinary Medical Science, The University of Tokyo, Tokyo 113-8657, Japan
Address all correspondence and requests for reprints to: Noboru Murakami, Ph.D., Department of Veterinary Physiology, Faculty of Agriculture University of Miyazaki, Miyazaki 889-2155, Japan. E-mail: a0d201u{at}cc.miyazaki-u.ac.jp.
| Abstract |
|---|
|
|
|---|
-MSH) and
-helical corticotropin-releasing factor-(941) (antagonist for CRH) attenuated NMS-induced suppression of 24-h food intake. After icv injection of NMS, Fos-immunoreactive cells were detected in both the PVN and Arc. When neuronal multiple unit activity was recorded in the PVN before and after icv injection of NMS, a significant increase in firing rate was observed 5 min after administration, and this increase continued for 100 min. These results suggest that the novel peptide, NMS, may be a potent anorexigenic hormone in the hypothalamus, and that expression of proopiomelanocortin mRNA in the Arc and CRH mRNA in the PVN may be involved in NMS action on feeding. | Introduction |
|---|
|
|
|---|
NMU1R is located in a wide range of peripheral tissues such as intestine, testis, pancreas, uterus, lung, and kidney. On the other hand, expression of NMU2R is limited to areas of the brain such as the paraventricular nucleus (PVN), along the wall of the third ventricle in the hypothalamus and the CA1 region of the hippocampus (2, 5, 8, 9). Immunohistochemical and in situ analysis has revealed NMU-immunoreactive neurons or NMU mRNA expression in the ventromedial hypothalamic region including the arcuate nucleus (Arc), pituitary, caudal brainstem region including the nucleus of the solitary tract, area postrema, dorsal motor nucleus of the vagus nerve and inferior olive, and spinal cord (2, 10, 11). NMU-immunoreactive fibers project prominently into the PVN, ventromedial nucleus, dorsomedial nucleus, and Arc. It has been well documented that the PVN and Arc of the hypothalamus play pivotal roles in the regulation of feeding behavior through a complex neuronal network composed of several orexigenic neuropeptides such as neuropeptide Y (NPY), agouti-related protein (AGRP) and ghrelin, and anorexigenic neuropeptides such as
-MSH, cocaine- and amphetamine-regulated transcript, CRH, and leptin (12, 13). Icv administration of NMU suppresses both dark-phase food intake and fasting-induced feeding, suggesting that NMU acts as anorexigenic hormone (2, 3). Conversely, disruption of the NMU gene in mice [NMU knockout (KO) mice] resulted in severe obesity (14). Although ob/ob mice (mutant leptin-deficient mice) are known to be obese through a decrease in proopiomelanocortin (POMC) mRNA and an increase of NPY and AGRP mRNA in the Arc (15, 16, 17), obesity in NMU KO mice results specifically from a decrease of CRH mRNA in the PVN. Therefore, NMU and leptin share the mechanism of feeding suppression (14).
The fact that receptors for NMU have a high affinity for NMS suggests that NMS may also act on feeding. The NMS gene was mapped to chromosome 2q11.2 in humans, and this locus is consistent with one potential location of the quantitative trait loci implicated in obesity (18). These data also lead to speculation that NMS may play an important role in central regulation of feeding.
To examine whether NMS is involved in feeding regulation, the effects of central administration of NMS and NMU on food intake were investigated in rats, and the cellular mechanisms involved were analyzed.
| Materials and Methods |
|---|
|
|
|---|
Feeding experiments
Cannulation for icv injection was performed described previously (19). After surgery, all rats were housed individually in Plexiglas cages. During a 6-d postoperative recovery, the rats became accustomed to the handling procedure. In the first experiment, various doses of rat NMS and NMU were dissolved in saline, and 10 µl of solution was injected through a 27-gauge injection cannula connected to a 50-µl Hamilton syringe into each free-moving rat at 1845 h; 12-h food intake was then examined. We also examined the diurnal effect of NMS on food intake by icv injection of NMS at 0900 h. Rat NMS and NMU were synthesized by an Fmoc solid-phase method on a peptide synthesizer (433A; Applied Biosystems, Foster City, CA). In the second experiment, rats were fasted for 8 h from 0100 h at night, and then centrally injected with NMS or NMU (0.5 or 1 nmol) at 0845 h. In the third experiment, single NPY (0.5 nmol), ghrelin (0.5 nmol) or AGRP (1 nmol), and mixed NPY, ghrelin or AGRP + NMS (0.5 or 1 nmol) or NMU (0.5 or 1 nmol) (each peptide was mixed in 10 µl of saline solution) was administered to free-feeding rats at 0845 h and 2-h food intake was measured. NPY, ghrelin and AGRP were purchased from the Peptide Institute, Inc. (Osaka, Japan). In the fourth experiment, 1 nmol NMS was injected 1 h after pretreatment with 1, 5, or 10 µg
-helical corticotropin-releasing factor-(941) (
-hCRF) (Sigma, St. Louis, MO) or 0.1, 0.5, or 1 nmol SHU9119 (Bachem, Budendorfm, Switzerland) at 0745 h to 8-h fasted rats or intact rats, and 2-h and 24-h food intake was examined, respectively.
c-Fos immunohistochemistry
Ninety minutes before perfusion, rats were injected with NMS, NMU (1 nmol per rat) or saline (n = 3 per group) in the lateral ventricle to study the immunostaining of c-Fos-expressing neurons. After the rats had been perfused with fixative [4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.4)], the brain was removed immediately, fixed in fixative and embedded in O.C.T. compound (Tissue-Tek, Tokyo, Japan) at 20 C. Frozen serial brain sections (40 µm thick) were incubated for 1 d with goat anti-c-Fos antiserum (Santa Cruz Biotechnology, Santa Cruz, CA; final dilution 1:1500) and visualized by the avidin-biotin complex method (Vectastain Elite ABC kit; Vector Laboratories, Inc., Burlingame, CA) using 0.02% 3,3'-diaminobenzidine tetrahydrochloride (Sigma) and 0.005% hydrogen peroxide in 50 mM Tris-HCl (pH 7.6).
Quantitative RT-PCR
To quantify POMC and CRH mRNA in the Arc and PVN after icv injection of NMS, 1 nmol NMS was injected into rats at 1845 h, 4 h before collection of Arc and PVN tissue for mRNA extraction. After the brain tissues had been frozen, the Arc and PVN were dissected out. Total RNA was extracted from the Arc and PVN using an RNeasy Mini kit (QIAGEN, Hilden, Germany) and then synthesized into first-strand cDNA. Quantitative RT-PCR was conducted with a LightCycler system (Roche, Basel, Switzerland) using a LightCycler-FastStart DNA Master SYBR Green I kit (Roche). The primer set used for rat POMC was 5'-GACCTCACCACGGAAAGCAACCTG-3' and 5'-ACTTCCGGGGATTTTCAGTCAAGGG-3', and for rat CRH was 5'-ATCTCACCTTCCACCTTCTG-3' and 5'-GTGTGCTAAATGCAGAATCG-3'. Known amounts of rat POMC and CRH cDNA were used to obtain a standard curve. Rat glyceraldehyde-3-phosphate dehydrogenase mRNA was also measured as an internal control. The primer set used for rat glyceraldehyde-3-phosphate dehydrogenase was 5'-CGGCAAGTTCAACGGCACA-3' and 5'-AGACGCCAGTAGACTCCACGACA-3'.
Multiple unit activity (MUA) recording
Rats were fitted with chronically implanted electrode arrays as described previously (20). Briefly, the electrode assembly consisted of four 75-mm Teflon-insulated platinum (90%)-iridium (10%) wires (A-M Systems, Inc., Sequim, WA) encased in a stainless steel guide tube (650 mm diameter; Inter Medical, Fukuoka, Japan). The stainless steel tube served as a ground. The impedance of each platinum-iridium electrode measured at 1 kHz was 50100 k
. According to the stereotaxic atlas of the rat brain (Paxinos and Watson, Ref.27) described by Albe-Fessard et al., the electrodes were implanted unilaterally into the left side of the PVN and fixed to the skull with anchor screws and dental cement. At the same time, an icv cannula was implanted slantingly into the right lateral cerebral ventricle. After a recovery period of 5 d, MUA was recorded as follows: signals were passed through a buffer amplifier, amplified by a biophysical amplifier (MEG-2100; Nihon Kohden, Tokyo, Japan) with low and high cutoff frequencies of 500 Hz and 10 kHz, respectively, and displayed on an oscilloscope (DS-8812; Iwatsu, Tokyo, Japan). Neural spikes were discriminated by their amplitude, and the number of spikes was counted with a pulse counter (ET-612J; Nihon Kohden) and integrated for 1 sec. Outputs were recorded as a histogram on a thermal recorder (WR8500; Graphtec, Tokyo, Japan) and with a powerLab (AD Instrument, Castle Hill, Australia), respectively. On the day of the experiment, the MUA electrode was attached to the buffer amplifier under isoflurane inhalation anesthesia (Univentor 400; Univentor, Zejtun, Malta). Rats were maintained under anesthesia with 1.5% isoflurane (Abbott Laboratories, Abbott Park, IL). At 15 min after the beginning of stable MUA volley, rats received icv administration of 1 nmol NMS, NMU, or saline. At 120 min after administration, electrical stimulation was applied for 1 sec through the MUA electrode with pulses (1 mA) from an electric stimulator (RGF-4A; Radionics, Burlington, MA) to check the site of the electrode.
Statistical analysis
The data (mean ± SEM) were analyzed statistically by ANOVA with the post hoc Fishers test. P < 0.05 was considered statistically significant.
| Results |
|---|
|
|
|---|
|
To understand the cellular mechanisms involved in NMS-induced suppression of feeding, POMC and CRH mRNA expression and the expression of c-Fos protein were investigated. Icv administration of NMS augmented the levels of Arc POMC and PVN CRH mRNA (Fig. 2
, A and B). The involvement of POMC and CRH in NMS-induced suppression of feeding was therefore investigated using an antagonist for these peptides. Pretreatment with both SHU9119 (an antagonist for
-MSH) and
-hCRF (an antagonist for CRH) attenuated NMS-induced suppression of food intake in a dose-dependent manner in fasted rats. Whereas only SHU9119 significantly blocked the effect of NMS on 2-h food intake (Fig. 2C
), both
-hCRF and SHU9119 blocked the effect of NMS on 24-h food intake (Fig. 2D
). The central distributions of c-Fos immunoreactive cell were similar in NMS- and NMU-injected rats. The hypothalamic PVN (Fig. 3
, A and D), Arc (Fig. 3
, B and E), supraoptic nucleus (Fig. 3
, C and F) and SCN (data not shown) expressed the c-Fos protein strongly. In saline-treated rats, no c-Fos immunoreactivity was observed in any of these regions (data not shown).
|
|
|
| Discussion |
|---|
|
|
|---|
When the NMS was injected at 0900 h, there was no significant difference in food intake during the 12-h light period, suggesting the diurnal variation in the anorexigenic effect of NMS. Although the interpretation of these data is difficult because of the very low feeding activity in the beginning of the light period, this diurnal difference may be due to diurnal variation of NMU receptors in SCN (21) or diurnal variation of NMS secretion (6) in autocrine regulation.
It is not known why NMS-induced suppression of food intake is more potent and continues for a longer time than with NMU. There was no difference in the distribution of c-Fos expression between NMS- and NMU-injected rats. However, neural MUA records showed a clear difference between the rats. There was a greater increase in firing rate of PVN neurons in NMS-treated rats than in NMU-treated rats, and this increased effect continued for a long period of time after NMS injection. This potent and long-term increase of firing rate by NMS may cause the powerful and long-term suppression of food intake. Alternatively, the possibility that NMS may act on another unknown receptor cannot be excluded.
NPY, ghrelin, and AGRP-induced food intake was counteracted by coadministration of NMS, suggesting that the NPY, ghrelin, and AGRP are independently antagonistic with NMS for feeding regulation.
Hanada et al. (14) reported that icv injection of NMU in rats did not affect POMC mRNA expression in the Arc but augmented CRH mRNA expression in the PVN. In addition, CRH KO mice did not show any reduction in food intake after NMU injection (22). Therefore, it has been speculated that an increase in CRH, but not
-MSH, is the primary cause of NMU-induced suppression of food intake. In the present study, NMS increased both POMC and CRH mRNA expression. These results indicate that the cellular mechanism of suppression of food intake by NMS may be different from that by NMU, and both CRH and
-MSH may be involved in NMS-induced suppression of food intake. This hypothesis is supported by the following results: pretreatment with antagonists for
-MSH and CRH blocked NMS-induced suppression of food intake.
It is questionable why receptors for NMS and NMU are the same; nevertheless, the downstream mechanism of feeding regulation by NMS and NMU is different. Recent studies demonstrate that NMU, NMS, NMU1R, and NMU2R mRNA each have an intrinsic rhythmic expression in the SCN with a different circadian pattern (6, 21). Because the SCN sends neural projections into the PVN and Arc (23, 24), these different rhythmic expressions may relate to the different effects of NMS and NMU. Of course, as mentioned above, NMS may act on a receptor other than NMU1R and NMU2R. Either way, it is unknown why NMS, but not NMU, stimulates the POMC system in the Arc, but a different downstream mechanism may explain the difference in effectiveness and duration of action between NMU and NMS.
Wren et al. (25) reported that leptin was able to stimulate NMU release in hypothalamic explants in vitro. In contrast, Hanada et al. (14). showed that the anorexigenic effect of NMU is independent of leptin in NMU KO mice because NMU and leptin reduced food intake in ob/ob mice and NMU KO mice, respectively. Wren et al. measured NMU content using an antibody raised in a rabbit immunized with synthetic NMU-8. Because NMU-8 is the core active C terminus of NMS and NMU, the antibody must recognize both NMS and NMU. We had also raised antiserum against synthetic NMU-8 and established a RIA for NMU (26). Rat NMS and NMU were equally recognized with the serum on a molar basis (data not shown) and could not separate NMS and NMU in this RIA system. Therefore, NMU release stimulated by leptin in hypothalamic explants presented by Wren et al. might be NMS. If this is the case, NMS is the downstream signal pathway for leptin. NMS is a novel anorexigenic hormone, and further investigation of the function of NMS will help in our understanding of weight control mechanisms and should facilitate the study of eating disorders.
| Footnotes |
|---|
First Published Online June 23, 2005
Abbreviations: AGRP, Agouti-related protein; Arc, arcuate nucleus;
-hCRF,
-helical corticotropin-releasing factor-(941); icv, intracerebroventricular; KO, knockout; MUA, multiple-unit activity; NMS, neuromedin S; NMU, neuromedin U; NPY, neuropeptide Y; POMC, proopiomelanocortin; PVN, paraventricular nucleus; SCN, suprachiasmatic nucleus.
Received January 27, 2005.
Accepted for publication June 13, 2005.
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
E. Vigo, J. Roa, R. Pineda, J. M. Castellano, V. M. Navarro, E. Aguilar, L. Pinilla, and M. Tena-Sempere Novel role of the anorexigenic peptide neuromedin U in the control of LH secretion and its regulation by gonadal hormones and photoperiod Am J Physiol Endocrinol Metab, November 1, 2007; 293(5): E1265 - E1273. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. Melcher, R. Bader, and M. J Pankratz Amino acids, taste circuits, and feeding behavior in Drosophila: towards understanding the psychology of feeding in flies and man J. Endocrinol., March 1, 2007; 192(3): 467 - 472. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. Vigo, J. Roa, M. Lopez, J. M. Castellano, R. Fernandez-Fernandez, V. M. Navarro, R. Pineda, E. Aguilar, C. Dieguez, L. Pinilla, et al. Neuromedin S as Novel Putative Regulator of Luteinizing Hormone Secretion Endocrinology, February 1, 2007; 148(2): 813 - 823. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Endocrinology | Endocrine Reviews | J. Clin. End. & Metab. |
| Molecular Endocrinology | Recent Prog. Horm. Res. | All Endocrine Journals |