Articles

Article

Original Research Article

Exp Neurobiol 2010; 19(3): 132-139

Published online December 31, 2010

https://doi.org/10.5607/en.2010.19.3.132

© The Korean Society for Brain and Neural Sciences

5-hydroxy-L-tryptophan Suppressed Food Intake in Rats Despite an Increase in the Arcuate NPY Expression

Young Wha Moon1, Si Ho Choi2, Sang Bae Yoo3, Jong-Ho Lee3 and Jeong Won Jahng3*

1Department of Natural Science, The Catholic University of Korea College of Medicine, Seoul 137-701, Korea, 2Center for Stem Cell and Regenerative Medicine, University of Southern California Keck School of Medicine, Los Angeles 90033, USA, 3Department of Oral and Maxillofacial Surgery, Dental Research Institute, Seoul National University School of Dentistry, Seoul 110-769, Korea

Correspondence to: *To whom correspondence should be addressed.
TEL: 82-2-2072-0739, FAX: 82-2-766-4948
e-mail: jwjahng@snu.ac.kr

This study was conducted to define the underlying mechanism of hypophagia induced by increased central serotonergic action. Rats received 3 daily injections of 5-hydroxy-L-tryptophan (5-HTP), a serotonin precursor, at a dose of 100 mg/kg/10 ml saline at 1 h before lights off. A significant suppression in food intake was observed shortly after the 5-HTP injection and persisted during 3 daily 5-HTP injections. Neuropeptide Y (NPY) expression in the arcuate nucleus increased after 3 days of 5-HTP treatment, as high as in the pair-fed group. Immunoreactivity of phosphorylated extracellular signal-regulated protein kinase (pERK1/2) in the hypothalamic paraventricular nucleus (PVN) was increased markedly by 3 days of 5-HTP treatment, but not by 3 days of pair-fed. mRNA expression levels of serotonin reuptake transporter (5-HTT) was increased in the dorsal raphe nucleus of the 5-HTP treated rats, but not in the pair-fed group. Results suggest that increased pERK1/2 in the PVN of 5-HTP injected rats may be a part of serotonergic anorectic signaling, perhaps blunting the orectic action of NPY; i.e., 5-HTP injected rats showed hypophagia despite of increased NPY expression in the arcuate nucleus.

Keywords: food intake, hypophagia, hypothalamus, serotonin

Serotonin, 5-hydroxytrypamine (5-HT), known to play a role in feeding behavior as an anorectic molecule (Curzon, 1990) has been implicated in the processes of within-meal satiation and post-meal satiety (Halford and Blundell, 2000). The hypothalamus appears to be where 5-HT exerts its anorectic effect in the central control of feeding, perhaps, at least partly, through its interaction with the hypothalamic feeding peptides. It has been reported that 5-HT exhibits a negative correlation with neuropeptide Y (NPY), a potent orexigenic molecule, in the hypothalamus (Dryden et al., 1995; 1996; Jahng et al., 1998b; Currie et al., 2002). We have previously reported that the hypothalamic expression of NPY was significantly decreased in anorectic (anx/anx) mouse showing drastic activation of the central 5-HT system (Jahng et al., 1998b). Previous studies reported that metergoline, a 5-HT1/5-HT2 receptor antagonist, and 8-hydroxy-2-(di-n-propylamino) tetralin, a 5-HT1A receptor agonist, enhances food consumption (Coscina et al., 1994; Currie and Coscina, 1996; Voigt et al., 2002), and that 5-HT1A receptor immunoreactivity is observed in the hypothalamic arcuate neurons containing NPY (Collin et al., 2002). Taken together, it is suggested that anorexic effects of the brain 5-HT system may comprise decreased NPYergic activity in the hypothalamus.

NPY dose-dependently increased cellular level of phosphorylated extracellular signal-regulated protein kinase (pERK1/2) in cultured cells (Gur et al., 2002). It has been shown that food deprivation increases neuronal level of pERK1/2 in the hypothalamic paraventricular nucleus (PVN) of mice (Ponsalle et al., 1992) and rat (Ueyama et al., 2004; Lee et al., 2010). Food deprivation increases not only NPY mRNA expression in the arcuate nucleus (Brady et al., 1990; Swart et al., 2002; Kim et al., 2005; Lee et al., 2010) but also release in the PVN (Dube et al., 1992; Yoshihara et al., 1996). Neurons in the PVN are richly supplied by axons of NPY neurons from the arcuate nucleus (Elmquist et al., 1998; 1999). Thus, if the PVN neurons are second order effectors located downstream of the arcuate nucleus, pERK1/2 could, possibly, be a part of NPY downstream signaling cascade in the PVN during food deprivation.

In order to determine if pERK1/2 is a putative downstream effecter of NPY signaling in the hypothalamic PVN, possibly related with increased brain 5-HT level, 5-hydroxy-L-tryptophan (5-HTP), a 5-HT precursor, was administrated to rats to increase the brain 5-HT level (Gartside et al., 1992; Yamada et al., 2000; Choi et al., 2003).

Animals

Adult male Sprague-Dawley rats (250~300 g, Daehanbiolink Co., Korea) were individually acclimated to the standard laboratory conditions (12 h light-dark cycle, light on at 9:00 AM) with free access to standard laboratory food (Purina Rodent Chow, Purina Co., Seoul, Korea) and water ad libitum. Animals were cared according to The Guideline for Animal Experiments, 2000, edited by The Korean Academy of Medical Sciences, which is consistent with NIH Guideline for the Care and Use of Laboratory Animals, 1996 revised.

Drug treatments

Rats were divided into three treatment groups (n=6/group/time point), such as the control, the 5-hydroxy-L-tryptophan (5-HTP; 100 mg/kg/10 ml, dissolved in sterile physiologic saline; Sigma Co., MO, USA) injected or the pair-fed group. The 5-HTP group received a single intraperitoneal injection of 5-HTP at 1 h before lights off or three daily injections at 9:00 AM every morning. The control group received the same volume of saline instead of 5-HTP at each time point. The pair-fed group was provided with the same amount of food consumed by 5-HTP rats. Rats were sacrificed at 2 or 8 h after the single injection of 5-HTP, or 24 h after the last injection of daily 5-HTP. Total 48 rats (18 control, 18 5-HTP, and 12 pair-fed) were hired for this study.

In situ hybridization

Rats were anesthetized with an overdose of sodium pentobarbital. Once unresponsive, transcardiac perfusion was performed with heparinized isotonic saline containing 0.5% NaNO2, then with 4% paraformaldehyde in 0.1 M sodium phosphate buffer. The brains were rapidly dissected, blocked, post-fixed for 3 h, and transferred into 30% sucrose for 24 h for cryoprotection. Forty-micron coronal sections were cut on a freezing sliding microtome. Every other sections through the rostral-caudal extent of the hypothalamus (between bregma -1.80 mm and -3.80 mm; Paxinos and Watson, 1986) and the raphe nucleus (between bregma -7.64 mm and -8.80 mm; Paxions and Watson, 1986) were collected into 20 ml glass scintillation vials containing ice-cold 2×SSC (0.3 M NaCl, 0.03 M Na Citrate) for in situ hybridization. The SSC was pipetted off, and sections were suspended in 1 ml of prehybridization buffer (50% formamide, 10% dextran sulfate, 2×SSC, 1×Denhardt's solution, 50 mM DTT, and 0.5 mg/ml denatured herring sperm DNA), incuated for 2 h at 48℃. In situ hybridization was performed with radioactively labeled cDNA probes of NPY (Jahng et al., 1998b; for the arcuate sections) or serotonin reuptake transporter (5-HTT, Jahng et al., 1998a; for the raphe sections) as we previously described (Choi et al., 2003). The tissue sections were then mounted on gelatin-subbed slides, air-dried, and apposed to Kodak BioMax film (Eastman Kodak Co., NY, USA) at 4℃. Exposure times varied from 12 to 48 h to obtain autoradiographic images within a linear range of optical density after development in Kodak D-19 developer. In situ hybridization was carried out on the representative members of each experimental group at the same time under identical conditions, allowing direct comparison of mRNA expression.

Immunohistochemistry

Free-floating tissue sections were washed twice for 15 min in 0.1 M sodium phosphate buffered saline (PBS), and then permeabilized in 0.2% Triton, 1% bovine serum albumin (BSA) in PBS for 30 min. After washing twice in PBS-BSA, sections were incubated overnight with anti-rabbit phosphop44/42 MAPK (Thr202/Tyr204) antibody (1:300 dilution, Cell signaling, Beverly, MA, USA). Sections were washed in PBS-BSA twice and incubated for 1 h with biotinylated anti-rabbit-goat antibody (Vector Laboratories, CA, USA); bound secondary antibody was then amplified with commercial ABC kit (Vectastain Elite Kit, Vector Laboratories, CA, USA). Antibody complexes were visualized by a 5 min 0.05% diaminobenzadine reaction. Immunostained sections were mounted onto gelatin-coated slides, air dried overnight, consequently dehydrated through a graded ethanol to xylene, and then coverslipped with Permount.

Quantitative and statistical analysis

Images on the autoradiographic films were digitized with a Zeiss Stemi-2000 stereoscope attached to a Dage-MTI CCD 72 camera and MCID image analysis system (MCID, Imaging Research Inc., Ontario, Canada). Tissue levels of NPY, 5-HTT mRNA, or pERK were determined by quantifying the mean relative optical density of pixels with densities of at least 2 S.D. above the mean density of the image background (mRNA or protein pixels). For each section, the mean background value was subtracted from the mean pixel value. The pixel values were averaged across three sections from each individual rat and then the average value of each rat averaged across all rats in each experimental group. All the data was analyzed by one way analysis of variance (ANOVA) and preplanned comparisons with the control were performed by post-hoc Fisher's PLSD test or unpaired t-test using StatView software (Abacus, Berkeley, CA). Significance was set at p<0.05, and all values were presented as means±SEM.

Rats received an intraperitoneal injection of 5-HTP (100 mg/kg/10 ml saline) or saline at 1 h before lights off, and the spontaneous feeding with ad libitum access to food (standard rodent chow) and water for 2 or 8 h were measured. Food intake of 5-HTP injected rats decreased significantly (p<0.05) compared with the saline injected controls at both time points (Fig. 1A). Cumulative food intake was suppressed persistently (p<0.05 vs. saline on each day) during 3 daily administrations of 5-HTP (Fig. 1B). Weight losses in 5-HTP rats compared with saline controls appeared to be more severe than in its pair-fed group (Fig. 1C).

mRNA expression levels of 5-HT reuptake transporter 5-HTT in the dorsal raphe nucleus, where most of 5-HT neurons in the brain are located, were examined after 3 days of 5-HTP treatment when not only the 5-HTP group but also the pairfed group showed significant reductions in body weight compared to their saline controls. 5-HTT mRNA levels increased in the 5-HTP treated group (p<0.05), but not in its pair-fed group, as compared with the free-fed saline group (Fig. 2), suggesting an increased 5-HTergic activity in the brain by 5-HTP injections, but not by pair-feeding.

A single injection of 5-HTP appeared not to acutely affect NPY mRNA expression levels in the arcuate nucleus; i.e., the arcuate NPY mRNA level did not differ from the saline group at 2 or 8 h after a single injection (Fig. 3). Three days of 5-HTP treatment significantly increased NPY expression levels in the arcuate nucleus (p<0.05 vs. saline), and this increase was also observed by 3 days of pair-fed (Fig. 3B), suggesting that the increased NPY expression is a consequence of chronic weight loss.

Rats were sacrificed 24 h after the last injection of 3 daily 5-HTP and the tissue sections of the paraventricular nucleus (PVN), where NPYergic fibers are richly innervated from the arcuate nucleus, were processed for pERK immunohistochemistry (Fig. 4A). pERK levels in the PVN markedly increased (p<0.05) in 5-HTP rats, but not in pair-fed rats, compared to their saline controls (Fig. 4B).

We have demonstrated that 5-HTP injections persistently suppresses food intake and induces weight loss, in accordance with our previous report suggesting that anorexia by 5-HTP injections is due to increased 5-HTergic activities in the brain regions (Choi et al., 2003). Weight losses in 5-HTP injected rats appeared to be bigger than in its pair-fed group, consistently with our previous report (Choi et al., 2003), suggesting an additional anorectic effect of the 5-HTP injection, other than decreasing energy intake. Previous studies have reported that 5-HT may increase the resting energy expenditure (Leibowitz and Alexander, 1998; Walsh et al., 1999). That is, not only decreased energy intake but also increased energy expenditure may contribute to the weight loss by systemic 5-HTP.

In this study, 5-HTT mRNA expression in the dorsal raphe nucleus was increased by 3 days of 5-HTP treatment, but not by 3 days of pair-fed (food restriction). Previous studies have reported that long-term food restriction decreases the brain density (Huether, 1999) and expression levels of 5-HTT (Haider and Haleem, 2000; Jahng et al., 2007), and that the depletion of brain 5-HT with chronic para-chlorophenylalanine treatment decreases 5-HTT mRNA expression in the raphe nucleus (Linnet et al., 1995; Yu et al., 1995). Also, we have reported that increased 5-HTT mRNA expression in the raphe nucleus by 3 daily 5-HTP injections is accompanied with increased 5-HT levels in the brain regions (Choi et al., 2003). Thus, it is concluded that increased 5-HTT mRNA expression in the dorsal raphe of 5-HTP treated rats may not be a consequence of reduced food intake and weight loss, and it reveals an increased 5-HTergic activity, likely due to increased 5-HT levels in the brain regions.

Previous studies have reported that 5-HT exhibits a negative correlation with NPY in the hypothalamus (Dryden et al., 1995; 1996; Jahng et al., 1998b; Currie et al., 2002), suggesting that anorexic effects of the brain 5-HT system may comprise decreased NPYergic activity in the hypothalamus. However, in this study, NPY mRNA expression the arcuate nucleus markedly increased after 3 daily injection of 5-HTP when the hypothalamic 5-HT level increased (Choi et al., 2003). Although a single injection of 5-HTP instantly increased the hypothalamic 5-HT levels (Choi et al., 2003), the arcuate NPY expression was not acutely affected by a single 5-HTP injection in this study, suggesting that increased NPY expression in the arcuate nucleus with 3 daily injections of 5-HTP is not a direct effect of increased 5-HT neurotransmission in the hypothalamus. Meanwhile, the arcuate NPY expression was increased in the pair-fed (food restriction) group as much as in the 3 daily 5-HTP group. A negative energy balance, such as food restriction or food deprivation, increases NPY mRNA expression in the hypothalamic arcuate nucleus (Ponsalle et al., 1992; Bi et al., 2003; Makimura et al., 2003; Jahng et al., 2005). Thus, it is concluded that the increased NPY expression in the arcuate nucleus of 5-HTP treated rats is a consequence of decreased food intake, a negative energy balance, rather than of increased 5-HTergic activity in the hypothalamus. The hypothalamic NPY, a potent orexic peptide, stimulates feeding (Stanley and Leibowitz, 1985; Kalra et al., 1999; Schwartz et al., 2000), and increased NPY expression in the arcuate nucleus correlates with obese phenotype; i.e., increased food intake and weight gain (Sancora et al., 1990; Kowalski et al., 1999). However, food intake of 5-HTP injected rats was persistently suppressed despite of the increased NPY expression in the arcuate nucleus, suggesting that a tentative orectic action by increased hypothalamic NPY is inhibited in the 5-HTP injected rats. Also, it should be noticed that a single injection of 5-HTP instantly suppressed food intake (Choi et al., 2003), but not acutely affected the arcuate NPY expression in this study. Thus, it is hypothesized that the anorectic action by increased 5-HTergic activity in the hypothalamus is not mediated by decreased NPY expression in the arcuate nucleus, but it may comprise a blunted orectic signaling of NPY in the paraventricular nucleus where the axons of the arcuate NPY neurons are richly supplied (Elmquist et al., 1998; 1999; Schwartz et al., 2000).

In vitro study demonstrated that NPY dose-dependently increases cellular level of pERK1/2 in cultured cells (Gur et al., 2002). In vivo studies have shown that food deprivation increases not only NPY release (Dube et al., 1992; Yoshihara et al., 1996) but also the neuronal level of pERK1/2 in the hypothalamic PVN (Ponsalle et al., 1992; Ueyama et al., 2004; Lee et al., 2010). These studies suggest that NPY signaling cascade in the PVN neurons may involve the activation of ERK1/2, and this idea seemed to be further supported by the present result demonstrating that pERK1/2 level is increased in the PVN when NPY expression increased in the arcuate nucleus following 3 daily injections of 5-HTP. However, in the pair-fed group, the PVN-pERK1/2 level did not increase despite a significant increase of NPY expression in the arcuate nucleus. We have previously shown that intracerebroventricular injection of NPY, although it stimulated feeding, did not increase pERK1/2 level in the PVN (Lee et al., 2010). Thus, it is suggested that pERK1/2 may not be a downstream signaling of increased NPYergic activity in the PVN of 5-HTP injected rats. Previous studies have supported the idea that increased 5-HTergic activity may be implicated in the pERK1/2 increase in the PVN of 5-HTP injected rats. That is, activation of the 5-HT1A receptor resulted in ERK activation in cell lines (Millan et al., 2001) and injections with 5-HT1A agonists increased pERK1/2 level in the rat PVN (Sullivan et al., 2005; Crane et al., 2007), suggesting that 5-HT1A receptors may stimulate pERK1/2 levels in the PVN. Neurons expressing 5-HT1A receptors are observed in the PVN (Marvin et. al., 2010). Currie and Coscina (1996) demonstrated that intra-PVN injections of metergoline, a 5-HT1/5-HT2 receptor antagonist, antagonize the hypophagia following 5-HT injections into the PVN. We have observed that ketanserin, a 5-HT2A/2C antagonist, although it abolished the hypophagia by 5-HTP injections, did not block the pERK1/2 increase in the PVN (unpublished data). A 5-HT2A/2C agonist DOI attenuated NPY-induced feeding and this was antagonized by ketanserin (Currie et al., 2002). Thus, it is concluded that increased pERK1/2 level in the PVN of 5-HTP injected rats may be a part of 5-HTergic signaling mediated by 5-HT1 receptors, but not by 5-HT2 receptors, possibly blunting the orectic NPYergic signal in the PVN.

It is speculated that 5-HT-induced hypophagia is predominantly mediated by central 5-HT pathways, although the mechanism has not been fully defined. Heisler and colleagues (2006) have suggested that 5-HT-induced hypophagia is mediated by downstream activation of melanocortin 4 receptor (Mc4r). They hypothesized that 5-HT action at the arcuate nucleus would lead to a decrease in the release of the endogenous melanocortin receptor (MCR) antagonist AgRP and an increase in the release of the endogenous MCR agonist α-MSH at downstream MCR-expressing target sites. Mc4rs are expressed in the hypothalamic PVN (Kishi et al., 2003), where the axons of AgRP and α-MSH neurons are richly innervated from the arcuated nucleus (Elmquist et al., 1998; 1999). Previous study has suggested that pERK1/2 is a downstream effecter of the central Mc4rs mediating hypophagia (Sutton et al., 2005). Thus, one can prospect that the increased pERK1/2 level in the PVN of 5-HTP injected rats may be a consequence of Mc4rs activation by increased release of its agonist α-MSH in the PVN. However, 5-HTP injections did not increase the expression of proopiomelanocortin (POMC), functional precursor of α-MSH, in the arcuate nucleus (our unpublished observation). We have previously reported that the arcuate POMC expression is decreased by chronic treatment with selective 5-HT reuptake inhibitor fluoxetine known to increase the brain 5-HT level (Myung et al., 2005). Thus, it is concluded that the increased pERK1/2 in the PVN of 5-HTP injected rats is less likely due to an activation of melanocortin pathways.

  1. Bi S, Robinson BM, Moran TH. Acute food deprivation and chronic food restriction differently affect hypothalamic NPY mRNA expression. Am J Physiol Regul Integr Comp Physiol 2003;285:R1030-R1036.
    Pubmed
  2. Brady LS, Smith MA, Gold PW, Herkenham M. Altered expression of hypothalamic neuropeptide mRNAs in food-restricted and food-deprived rats. Neuroendocrinology 1990;52:441-447.
    Pubmed
  3. Choi SH, Kwon BS, Lee S, Houpt TA, Lee HT, Jahng JW. Systemic 5-hydroxy-L-tryptophan down-regulates the arcuate CART mRNA level in rats. Regul Pept 2003;115:73-80.
    Pubmed
  4. Collin M, Bäckberg M, Onnestam K, Meister B. 5-HT1A receptor immunoreactivity in hypothalamic neurons involved in body weight control. Neuro Report 2002;13:945-951.
  5. Coscina DV, Feifel D, Nobrega JN, Currie PJ. Intraventricular but not intraparaventricular nucleus metergoline elicits feeding in satiated rats. Am J Physiol 1994;266:1562-1567.
  6. Crane JW, Shimizu K, Carrasco GA, Garcia F, Jia C, Sullivan NR, D'Souza DN, Zhang Y, Van de Kar LD, Muma NA, Battaglia G. 5-HT1A receptors mediate (+)8-OH-DPAT-stimulation of extracellular signal-regulated kinase (MAP kinase) in vivo in rat hypothalamus: time dependence and regional differences. Brain Res 2007;1183:51-59.
    Pubmed
  7. Currie PJ, Coiro CD, Niyomchai T, Lira A, Farahmand F. Hypothalamic paraventricular 5-hydroxytryptamine: receptor-specific inhibition of NPY-stimulated eating and energy metabolism. Pharmacol Biochem Behav 2002;71:709-716.
    Pubmed
  8. Currie PJ, Coscina DV. Metergoline potentiates natural feeding and antagonizes the anorectic action of medial hypothalamic 5-hydroxytryptamine. Pharmacol Biochem Behav 1996;53:1023-1028.
    Pubmed
  9. Curzon G. Serotonin and appetite. Ann NY Acad Sci 1990;600:521-530.
    Pubmed
  10. Dryden S, Frankish HM, Wang Q, Williams G. Increased feeding and neuropeptide Y (NPY) but not NPY mRNA level in the hypothalamus of the rat following central administration of the serotonin synthesis inhibitor p-chlorophenylalanine. Brain Res 1996;724:232-237.
    Pubmed
  11. Dryden S, Wang Q, Frankish HM, Pickavance L, Williams G. The serotonin (5-HT) antagonist methysergide increases neuropeptide Y (NPY) synthesis and secretion in the hypothalamus of the rat. Brain Res 1995;699:12-18.
    Pubmed
  12. Dube MG, Sahu A, Kalra PS, Kalra SP. Neuropeptide Y release is elevated from the microdissected paraventricular nucleus of food-deprived rats: an in vitro study. Endocrinology 1992;131:684-688.
    Pubmed
  13. Elmquist J, Elias C, Saper C. From lesions to leptin: hypothalamic control of food intake and body weight. Neuron 1999;22:221-232.
    Pubmed
  14. Elmquist J, Maratos-Flier E, Saper C, Flier J. Unraveling the central nervous system pathways underlying responses to leptin. Nature Neurosci 1998;1:445-450.
    Pubmed
  15. Gartside SE, Cowen PJ, Sharp T. Effect of 5-hydroxy-L-tryptophan on the release of 5-HT in rat hypothalamus in vivo as measured by microdialysis. Neuropharmacology 1992;31:9-14.
    Pubmed
  16. Gur G, Bonfil D, Safarian H, Naor Z, Yaron Z. Pituitary adenylate cyclase activating polypeptide and neuropeptide Y regulation of gonadotropin subunit gene expression in tilapia: role of PKC, PKA and ERK. Neuroendocrinology 2002;75:164-174.
    Pubmed
  17. Haider S, Haleem DJ. Decreases of brain serotonin following a food restriction schedule of 4 weeks in male and female rats. Med Sci Monit 2000;6:1061-1067.
    Pubmed
  18. Halford JC, Blundell JE. Separate systems for serotonin and leptin in appetite control. Ann Med 2000;32:222-232.
    Pubmed
  19. Heisler LK, Jobst EE, Sutton GM, Zhou L, Borok E, Thornton-Jones Z, Liu HY, Zigman JM, Balthasar N, Kishi T, Lee CE, Aschenasi CJ, Zhang CY, Yu J, Boss O, Mountjoy KG, Clifton PG, Lowell BB, Friedman JM, Horvath T, Butler AA, Elmquist JK, Cowley MA. Serotonin reciprocally regulates melanocortin neurons to modulate food intake. Neuron 2006;51:239-249.
    Pubmed
  20. Huether G. Acute regulation and long-term modulation of presynaptic serotonin output. Adv Exp Med Biol 1999;467:1-10.
    Pubmed
  21. Jahng JW, Houpt TA, Joh TH, Son JH. Differential expression of monoamine oxidase A, serotonin transporter, tyrosine hydroxylase and norepinephrine transporter mRNA by anorexia mutation and food deprivation. Dev Brain Res 1998a;107:241-246.
    Pubmed
  22. Jahng JW, Houpt TA, Kim SJ, Joh TH, Son JH. Neuropeptide Y mRNA and serotonin innervation in the arcuate nucleus of anorexia mutant mice. Brain Res 1998b;790:67-73.
    Pubmed
  23. Jahng JW, Kim JG, Kim HJ, Kim BT, Kang DW, Lee JH. Chronic food restriction in young rats results in depression- and anxiety-like behaviors with decreased expression of serotonin reuptake transporter. Brain Res 2007;1150:100-107.
    Pubmed
  24. Jahng JW, Lee JY, Yoo SB, Kim YM, Ryu V, Kang DW, Lee JH. Refeeding-induced expression of neuronal nitric oxide synthase in the rat paraventricular nucleus. Brain Res 2005;1048:185-192.
    Pubmed
  25. Kalra SP, Dube MG, Pu S, Xu B, Horvath TL, Kalra PS. Interacting appetite-regulating pathways in the hypothalamic regulation of body weight. Endocr Rev 1999;20:68-100.
    Pubmed
  26. Kim HJ, Lee JH, Choi SH, Lee YS, Jahng JW. Fasting-induced increases of arcuate NPY mRNA and plasma corticosterone are blunted in the rat experienced neonatal maternal separation. Neuropeptides 2005;39:587-594.
    Pubmed
  27. Kishi T, Aschkenasi CJ, Lee CE, Mountjoy KG, Saper CB, Elmquist JK. Expression of melanocortin 4 receptor mRNA in the central nervous system of the rat. J Comp Neurol 2003;457:213-235.
    Pubmed
  28. Kowalski TJ, Houpt TA, Jahng JW, Okada N, Liu SM, Chua SC, Smith GP. Neuropeptide Y overexpression in the preweanling Zucker (fa/fa) rat. Physiol Behav 1999;67:521-525.
    Pubmed
  29. Lee JH, Cha MJ, Yoo SB, Moon YW, Noh SJ, Jahng JW. Leptin blocks the fasting-induced increase of pERK1/2 in the paraventricular nucleus of rats. Regul Pept 2010;162:122-128.
    Pubmed
  30. Leibowitz SF, Alexander JT. Hypothalamic serotonin in control of eating behavior, meal size, and body weight. Biol Psychiatry 1998;44:851-864.
    Pubmed
  31. Linnet K, Koed K, Wiborg O, Gregersen N. Serotonin depletion decreases serotonin transporter mRNA levels in rat brain. Brain Res 1995;697:251-253.
    Pubmed
  32. Makimura H, Mizno TM, Isoda F, Beasley J, Silverstein JH, Mobbs CV. Role of glucocorticoids in mediating effects of fasting and diabetes on hypothalamic gene expression. BMC Physiol 2003;3:5.
    Pubmed
  33. Marvin E, Scrogin K, Dudas B. Morphology and distribution of neurons expressing serotonin 5-HT1A receptors in the rat hypothalamus and the surrounding diencephalic and telencephalic areas. J Chem Neuroanat 2010;39:235-241.
    Pubmed
  34. Millan MJ, Newman-Tancredi A, Duqueyroix D, Cussac D. Agonist properties of pindolol at h5-HT1A receptors coupled to mitogen-activated protein kinase. Eur J Pharmacol 2001;424:13-17.
    Pubmed
  35. Myung CS, Kim BT, Choi SH, Song GY, Lee SY, Jahng JW. Role of neuropeptide Y and proopiomelanocortin in fluoxtine-induced anorexia. Arch Pharm Res 2005;28:716-721.
    Pubmed
  36. Paxions G, Watson C. The Rat Brain in Stereotaxic Coordinate. San Diego, CA: Academic Press, 1986.
  37. Ponsalle P, Srivastava LS, Uht RM, White JD. Glucocorticoids are required for food deprivation-induced increases in hypothalamic neuropeptide Y expression. J Neuroendocrinol 1992;4:585-591.
    Pubmed
  38. Sancora G, Kershaw M, Finklestein JA, White JD. Increased hypothalamic content of preproneuropeptide Y messenger ribonucleic acid in genetically obese Zucker rats and its regulation by food deprivation. Endocrinology 1990;127:730-737.
    Pubmed
  39. Schwartz MW, Woods SC, Porte D, Seeley RJ, Baskin DG. Central nervous system control of food intake. Nature 2000;404:661-671.
    Pubmed
  40. Stanley BG, Leibowitz SF. Neuropeptide Y injected in the paraventricular hypothalamus: a powerful stimulant of feeding behavior. Proc Natl Acad Sci USA 1985;82:3940-3943.
    Pubmed
  41. Sullivan NR, Crane JW, Damjanoska KJ, Carrasco GA, D'Souza DN, Garcia F, Van de Kar LD. Tandospirone activates neuroendocrine and ERK (MAP kinase) signaling pathways specifically through 5-HT1A receptor mechanisms in vivo. Naunyn-Schmiedeberg's Arch Pharmacol 2005;371:18-26.
    Pubmed
  42. Sutton GM, Duos B, Patterson LM, Berthoud H-R. Melanocortinergic modulation of cholecystokinin-induced suppression of feeding through extracellular signal-regulated kinase signaling in rat solitary nucleus. Endocronology 2005;146:3739-3747.
  43. Swart I, Jahng JW, Overton JM, Houpt TA. Hypothalamic NPY, AGRP, and POMC mRNA responses to leptin and refeeding in mice. Am J Physiol Regul Integr Comp Physiol 2002;283:R1020-R1026.
    Pubmed
  44. Ueyama E, Morikawa Y, Yasuda T, Senba E. Attenuation of fasting-induced phosphorylation of mitogenactivated protein kinases (ERK/p38) in the mouse hypothalamus in response to refeeding. Neurosci Lett 2004;371:40-44.
    Pubmed
  45. Voigt JP, Schade R, Fink H, Hortnagl H. Role of 5-HT1A receptors in the control of food intake in obese Zucker rats of different ages. Pharmacol Biochem Behav 2002;72:403-409.
    Pubmed
  46. Walsh KM, Leen E, Lean ME. The effect of sibutramine on resting energy expenditure and adrenaline-induced thermogenesis in obese females. Int J Obes Relat Metab Disord 1999;23:1009-1015.
    Pubmed
  47. Yamada J, Ujikawa M, Sugimoto Y. Serum leptin levels after central and systemic injection of a serotonin precursor, 5-hydroxytryptophan, in mice. Eur J Pharmacol 2000;406:159-162.
    Pubmed
  48. Yoshihara T, Honma S, Katsuno Y, Honma K. Dissociation of paraventricular NPY release and plasma corticosterone levels in rats under food deprivation. Am J Physiol 1996;271:E239-E245.
    Pubmed
  49. Yu A, Yang J, Pawlyk AC, Tejani-Butt SM. Acute depletion of serotonin down-regulates serotonin transporter mRNA in raphe neurons. Brain Res 1995;688:209-212.
    Pubmed