Hypothalamic orexigenic peptides are overexpressed in young Long–Evans rats after early life exposure to fat-rich diets

BBRC Biochemical and Biophysical Research Communications 342 (2006) 452–458 www.elsevier.com/locate/ybbrc

Hypothalamic orexigenic peptides are overexpressed in young Long–Evans rats after early life exposure to fat-rich diets Bernard Beck a b

a,*

, Rouba Kozak a, Kim M. Moar b, Julian G. Mercer

b

UHP/EA 3453 Syste`mes Neuromodulateurs des Comportements Ingestifs, Nancy, France Energy Balance and Obesity Division, Rowett Research Institute, Aberdeen, Scotland, UK Received 4 January 2006 Available online 9 February 2006

Abstract Nutritional factors have a critical influence during prenatal life on the development and regulation of networks involved in body weight and feeding regulation. To establish the influence of the macronutrient type on feeding regulatory mechanisms and more particularly on stimulatory pathways (galanin and orexins), we fed female rats on either a high-carbohydrate (HC), a high-fat (HF), or a wellbalanced control diet during gestation and lactation, and measured peptide expression in the hypothalamus and important hormones (leptin, insulin) in their pups at weaning. HF weanlings were 30% lighter than control and HC pups (P < 0.001). They were characterized by reduced plasma glucose and insulin levels (P < 0.01 or less). Their galanin and orexin systems were upregulated as shown by the significant augmentation of mRNA expression in the paraventricular nucleus and lateral hypothalamus, respectively. Inhibitory peptides like corticotropin-releasing hormone and neurotensin were not affected by this dietary treatment during early life. There was, therefore, a more intense drive to eat in HF pups, perhaps to compensate for the lower body weight at weaning. HF diets during early life had meanwhile some positive consequences: the lower metabolic profile might be beneficial in precluding the development of obesity and metabolic syndrome later in life. This is however valid only if the orexigenic drive is normalized after weaning.
2006 Elsevier Inc. All rights reserved. Keywords: Orexins; Galanin; Leptin; Corticotropin-releasing hormone; Neurotensin; Fetal origin; Insulin; Metabolic syndrome; Diet composition

More and more palatable (high-fat, high-carbohydrate) food is available in our societies, and in parallel the prevalence of obesity is rapidly increasing, especially in young people [1,2]. Nutritional factors have a critical influence during prenatal life on the development and regulation of pathways and networks involved in body growth. These factors are particularly important for the development of the central nervous system both from the quantitative and qualitative points of view. In laboratory rats, global undernutrition during gestation leads to the development of delayed-onset hyperphagia and obesity in the male offspring [3–5]. Protein-calorie malnutrition in prenatal life can induce insulin resistance * Corresponding author. Present address: INSERM U724 Faculte´ de Me´decine, 9 avenue de la Foreˆt de Haye BP 184, 54505 Vandœuvre les Nancy Cedex, France. Fax: +33 383 68 32 79. E-mail address: [email protected] (B. Beck).

0006-291X/$ - see front matter
2006 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2006.01.158

in the adult offspring [6]. Perinatal hyperinsulinism or insulin deficiency induced in pregnant rat dams are also predisposing factors for the development of overweight and diabetes in the offspring at adulthood [7,8]. Overnutrition during the first days of life has similar long-term effects on body-weight regulation [9]. These early periods of life correspond largely to the period of neuronal differentiation and of central nervous system maturation. This is the case for some hypothalamic neuropeptides that are involved in the regulation of feeding behavior, including neuropeptide Y (NPY), galanin (GAL), and the orexins (OX) [10–17]. These peptides stimulate food ingestion [18–20] and also influence dietary preferences. NPY preferentially stimulates carbohydrate intake [21] whereas GAL and OX orient the food choice towards fats [22–24]. Each dietary preference can be associated with a specific neuropeptidergic profile [25]. Conversely, ingestion of high-fat (HF) or high-carbohydrate (HC) diets

B. Beck et al. / Biochemical and Biophysical Research Communications 342 (2006) 452–458

can influence the hypothalamic levels of these peptides [26–29]. Fat-to-carbohydrate ratio appears to be a critical factor in this influence. The differentiation of these systems takes place in part during the last week of gestation in the rat, with development continuing during the first days of life until weaning. During this period, hypothalamic systems are very sensitive to maternal factors, including both metabolic factors and nutritional environment. As indicated above, most experiments have studied the quantitative aspects of food intake either overnutrition through litter size manipulation [30] or food restriction [31]. Concerning the impact of macronutrients, protein-energy malnutrition has also been studied because of the importance of this problem in developing countries [32,33]. The direct impact of the other macronutrients (carbohydrates and fats) on the central feeding regulatory systems has been less studied. From a more general point of view, it is known that carbohydrates must provide a minimum of energy for a pregnancy to go to full term [34]. Offspring of dams fed 32% fat diet during gestation are lighter at birth and fatter at weaning than controls [35]. At adulthood, both fats and carbohydrates can induce obesity and insulin resistance ([26]; see [36,37] for review). We have previously shown that the offspring of dams fed on unbalanced (HF or HC) diets during the gestation and lactation periods exhibit persistent alterations in the functioning of the NPY system in adulthood [38–40]. The changes in sensitivity to NPY injection and an increased peptide release after a glucoprivic challenge are associated with delays in the establishment of dietary preferences [39,40]. To further determine the influence of these types of diets on feeding stimulatory pathways, we fed female rats on either an HC, an HF, or a well-balanced control (C) diet during gestation and lactation, and measured in their pups at weaning the expression of peptides that are more linked to fat intake, such as galanin and orexins [23,41]. These measures were associated with the measurement of some other important metabolic factors, including insulin, leptin, or blood glucose but also to anorexigenic peptides such as neurotensin (NT) and corticotropin-releasing hormone (CRH) [42,43]. The latter is also involved in the regulation of the hypothalamic–pituitary axis and therefore is linked to stress [44]. Materials and methods This experiment was conducted according to the guidelines edited by the Society For Neuroscience for the use and care of animals in neuroscience research. Animals and protocol Female Long–Evans non-primiparous rats weighing about 250 g and male Long–Evans rats were obtained from CERJ (Centre d’Elevage R. Janvier; Le Genest, St-Isle, France). All rats were placed in a temperatureregulated room with an automatic 12 h light/12 h dark rhythm with chow and tap water ad libitum. After 1 week of adaptation to the conditions of the vivarium, they were fed ad libitum either the C, HF, or HC diets for 2

453

weeks to control their good adaptation to these new diets. They were then weighed and put in a breeding cage (3 females for 1 male). From day 1 of gestation, the dams (n = 42) were installed in individual plastic cages for the whole duration of the gestation and suckling periods. At birth, the litter size was adjusted to 8–10 pups with pups of the same dietary group in order to avoid any litter size effect. The dams were fed their respective diets until weaning of the pups. Female weanlings were discarded and randomly chosen male rats were weighed and killed by decapitation 3 h after the beginning of the light period. Food was withdrawn from the dark-to-light transition until sacrifice in order to have all the animals in the same basal metabolic state without a long, stressful fast. Trunk blood and the brain were sampled. Diets The three diets contained the same quantity of protein (18% by weight) to avoid any confounding of results. Protein content was sufficient to allow a normal pregnancy. Wheat starch and sucrose (2/3–1/3) were the carbohydrates used for the three diets. Margarine was the only lipid source; it was used instead of oil to provide a consistent texture in the HF diet. The three diets were supplemented with 0.2% methionine. About 73.7% and 13.3% of the available energy resulted from lipids in the HF and HC diets, respectively. The detailed composition of the diets has been previously described [39]. Samples and assays All biochemical measurements were made at the beginning of the light period because physiologically, it is a period of relative inactivity for feeding behavior. We could therefore easily avoid potential interference of food ingestion with some peptides like leptin or insulin, which are sensitive to the feeding state. In addition, this choice also avoided interference with daily rhythms of peptides like galanin and leptin, which peak in the dark period [45,46]. Blood. Trunk blood was sampled in tubes containing aprotinin and EDTA. It was centrifuged at 2500g for 20 min at 4 C. The plasma was divided in aliquots and stored at 20 C for the determination of plasma glucose, immunoreactive insulin (IRI), and leptin. IRI was measured by a single antibody-charcoal radioimmunoassay technique using commercially available kits (INSIK, CIS, Gif sur Yvette, France) and rat insulin (Novo, Copenhagen) as standard. Leptin was measured with rat leptin RIA kit (Linco Research, St. Charles, USA). Plasma glucose was measured by an enzymatic technique using a commercially available kit (Boehringer–Mannheim, Meylan, France). Brain. After sampling, the brains were immediately frozen and stored at 80 C until processed for mRNA expression measurement (n = 6–8 per group) and peptide determination (n = 10–13 per group). Gene expression for galanin, orexin, and CRH was measured using in situ hybridization. The protocol used has been previously published [47,48] and is described briefly below. mRNA levels were quantified in 20 lm coronal sections. The CRF probe was generated from a rat cDNA generously provided by Dr. K. Mayo. Galanin and orexin probes were generated as described previously [47,48]. Hypothalamic sections were collected onto slides, with adjacent sections on consecutively numbered slides. This permitted a number of mRNAs of interest to be localized and quantified in brain sections that were representative of different hypothalamic regions. Slides were fixed, acetylated, and hybridized overnight at 58 C using 35S-labeled cRNA probes (1–2 · 107 cpm/ml). Autoradiographic images (Hyperfilm b-max; Amersham) were quantified using the Image-Pro Plus system. Data were manipulated using a standard curve generated from 14C autoradiographic micro-scales (Amersham), and the integrated intensity of the hybridization signal computed. For the peptide content determination, serial brain sections of 300 lm were cut, and discrete hypothalamic sites were micropunched with needles of various diameters, as previously detailed [49]. The arcuate (ARC), the paraventricular (PVN), and the ventromedial (VMN) nuclei were micropunched, as well as the lateral hypothalamus (LH). Bilateral tissue samples

454

B. Beck et al. / Biochemical and Biophysical Research Communications 342 (2006) 452–458

were immediately placed in 500 ll cold extraction solution (HCl 0.2 N–Iniprol/EDTA) and stored at 80 C until extraction and assay of galanin, orexin A, and neurotensin. Microdissections and assays were performed blind to the group to which each rat belonged. Galanin in microdissected brain areas was measured with a specific radioimmunoassay developed in our laboratory [50]. The antibody used was raised in rabbits against rat galanin. Cross-reactivities were 100% and 0.1% with rat and porcine galanin, respectively. No cross-reactions were observed with other peptides such as NPY, secretin, VIP, or substance P. Standard (rat galanin, Peninsula Laboratories, St Helens, UK) or lyophilized extract that were reconstituted with assay buffer: 0.04 M phosphate buffer, pH 7.4, containing bovine serum albumin (fraction V, Sigma Chemicals, La Verpillie`re, France), aprotinin (4000 IU/ml, IniprolR, Laboratoires Choay, Paris), and sodium azide (Merck, Darmstadt). One hundred microliters of antiserum diluted in assay buffer and 100 ll of standard or extract were preincubated for 24 h at 4 C. Then, 100 ll of 125 I-labeled rat galanin (Peninsula Y-7141; specific activity 808 Ci/mmol, Dositek, Orsay, France) was added and incubated for a further 24 h. Bound and free fractions were separated by the addition of 500 ll of a solution of 2% charcoal (Norit A, Kodak, Rochester, NY) and 0.2% dextran (T70, Pharmacia, Uppsala, Sweden) in assay buffer. The bound fraction was measured in a gamma counter coupled to a microcomputer (MDA 312 system, Kontron, Velizy, France) for the plotting of the standard curve and the calculation of the results. Under these conditions, maximal binding was 47.1 ± 2.2 %. A 50% decrease of the bound activity (IC50) was obtained with a concentration of 0.99 ± 0.10 ng/ml galanin. Assay sensitivity was in the range 15–25 pg/tube. NT was assayed on the neutralized extract with a specific radioimmunoassay developed in our laboratory and previously described [51]. Briefly, standard [bovine neurotensin 1–13 (Calbiochem, La Jolla, USA)] or samples were incubated with specific NT antiserum and 125I-labeled NT (Amersham IM 163, Les Ulis, France) for 48 h including a 24-h preincubation period without labeled NT. Bound and free fractions were separated by the addition of charcoal-dextran solution. Radioactivity of the bound fraction was measured in the same conditions as for the galanin assay. For this experiment, maximal binding was 40.9 ± 1.8% and nonspecific binding averaged 2.9 ± 0.7%. All tissue extracts and plasma samples were measured in duplicate. Statistics Results are given as means ± SEM. They were compared using StatviewR software by one-way analysis of variance, followed when necessary by the PLSD-Fisher test. Regression lines were also calculated. A probability of less than 5% was considered significant.

Results

weight at weaning (21 days of age) (F (2, 54) = 16.92; P < 0.001). There was no difference between HC and C rats, but the HF rats were significantly lighter than the two other groups ( 25.3% vs. control; P < 0.001 and 32.0% vs. HC; P < 0.001). There was a significant effect of treatment for plasma glucose (F (2, 54) = 5.56; P < 0.01) and for IRI (F (2, 54) = 10.96; P < 0.001). Plasma glucose of the HF rats was significantly lower than those of control rats (P < 0.03) and HC rats (P < 0.0025). IRI in the HF rats was also significantly lower than those in control rats ( 53%; P < 0.001) and HC rats ( 47%; P < 0.001). For leptin, F value did not reach statistical significance (P = 0.09). Hypothalamic peptide expression and content Galanin mRNA expression in the ARC and PVN is shown in Fig. 1. There was a significant effect of treatment in the PVN only (F (2, 19) = 4.28; P < 0.03). Galanin expression was significantly higher in the HF rats than in the HC rats (P < 0.01). No significant difference was observed between C and HF rats (P = 0.11). Galanin concentration in the same brain areas and in the VMN is shown in Fig. 2. There was no significant effect of treatment in any area except for the VMN (F (2, 33) = 3.77; P < 0.035). Galanin concentration in the VMN of the control rats was significantly lower than that of HF rats ( 45%; P < 0.01). Orexin and CRH expressions in the three groups of rats are shown in Fig. 3. There was no effect of treatment on CRH expression but a significant effect on orexin expression (F (2, 18) = 4.46; P < 0.03). Orexin mRNA expression in the HF rats was significantly higher than in control rats (P < 0.01). NT concentrations in the LH and PVN were not modified by the treatment (cf. Table 2).

GAL mRNA in the ARC

Body weight and plasma parameters 100

Table 1 Body weight (BW), blood glucose (BG), and hormone concentrations at weaning in pups born of dams fed on a control well-balanced diet (C; n = 16), a high-carbohydrate diet (HC; n = 21) or a high-fat diet (HF; n = 21) during the gestation and suckling periods

60

a b

C

HC

HF

44.0 ± 2.2 7.47 ± 0.42 4.19 ± 0.57 7.34 ± 1.10

48.3 ± 1.6 7.72 ± 0.17 3.80 ± 0.36 6.96 ± 1.06

32.8 ± 1.2b 6.62 ± 0.17a 1.72 ± 0.36b 4.29 ± 0.55

P < 0.01 or less vs. two other groups. P < 0.001 vs. two other groups.

**

140

Body weight and plasma parameters are shown in Table 1. There was a significant effect of treatment on body

BW (g) BG (mmol/L) Insulin (ng/ml) Leptin (ng/ml)

GAL mRNA in the PVN

100

60

20

20 C

HF

HC

C

HF

HC

Fig. 1. Galanin mRNA expression (means ± SEM) in the paraventricular (PVN) and arcuate (ARC) nuclei of weanling pups born of dams fed on a control well-balanced diet (C; n = 6), a high-carbohydrate diet (HC; n = 8) or a high-fat diet (HF; n = 8) during the gestation and suckling periods. **P < 0.01 vs. HC.

B. Beck et al. / Biochemical and Biophysical Research Communications 342 (2006) 452–458

Galanin

Galanin

Galanin

Leptin (ng/ml)

(ng/mg prot)

(ng/mg prot)

(ng/mg prot)

12

2.5

3.0

3.5

10

r= 0.57;p<0.02

8

2.0 2.5

2.0

1.5

6 4

1.5

1.0 1.0

2

0.5

0.5

0

0 C HC

HF

455

0 40

0 C

HC HF

ARC

60

C HC HF

PVN

VMN

Fig. 2. Galanin concentration (mean ± SEM in ng/mg protein) in the paraventricular (PVN), ventromedian (VMN), and arcuate (ARC) nuclei of weanling pups born of dams fed on a control well-balanced diet (C; n = 10), a high-carbohydrate diet (HC; n = 13) or a high-fat diet (HF; n = 13) during the gestation and suckling periods. **P < 0.01 vs. Control.

80

100

120

140

160

180

200

220

expression OA mRNA in the LH IRI (ng/ml) 9

r= 0.45;p<0.05

8 7 6 5 4

CRH mRNA in the PVN 140

OA mRNA in the LH

3

**

2

180

1 0

140

100

40

60

80

100

120

140

160

180

200

220

expression OA mRNA in the LH 100

Fig. 4. Regression curves between orexin mRNA expression in the lateral hypothalamus (LH) and plasma leptin or plasma insulin concentrations in weanling pups born of dams fed on a control well-balanced diet, a highcarbohydrate diet or a high-fat diet during the gestation and suckling periods.

60 60 20

20 C

HF

HC

C

HF

HC

Fig. 3. Orexin A mRNA expression in the lateral hypothalamus (LH) and corticotropin-releasing hormone (CRH) mRNA expression (mean ± SEM) in the paraventricular (PVN) nucleus of pups born of dams fed on a control well-balanced diet (C; n = 6), a high-carbohydrate diet (HC; n = 8) or a high-fat diet (HF; n = 8) during the gestation and suckling periods. ** P < 0.01 vs. Control.

Table 2 Neurotensin (NT) concentrations (means ± SEM) in the lateral hypothalamus (LH) and paraventricular nucleus (PVN) at weaning in pups born of dams fed on a control well-balanced diet (C), a high-carbohydrate diet (HC) or a high-fat diet (HF) during the gestation and suckling periods C (n = 10) HC (n = 13) HF (n = 13) NT in the LH (pg/mg protein) 536 ± 55 NT in the PVN (pg/mg protein) 757 ± 42

555 ± 55 645 ± 65

528 ± 50 656 ± 57

Relationship between neuropeptides and hormones Orexin A expression was inversely correlated with plasma leptin level (P < 0.015) and IRI concentration

(P < 0.05), as shown in Fig. 4. Galanin expression in the PVN was not correlated with leptin (r = 0.37; P = 0.12). Discussion The global increase in obesity in the last 30 years constitutes a major health and economic problem. Feeding habits resulting from the widespread availability of processed foods have dramatically changed. They are associated with a decrease in exercise leading to a positive energy balance, storage of ingested energy in adipose tissue, and overweight plus metabolic disorders. This is normal because our genetic background is set to allow survival in periods of food deprivation, and our physiological and behavioral mechanisms are oriented towards food seeking and energy storage. It is evident that giving an excess of energy-dense foods to an adult individual without requiring work to obtain it will lead to obesity. The recent expansion of the obesity epidemics in children reveals another disturbing trend: amplification of the phenomenon in the younger generations. This is likely linked to the continuous exposure of people from conception to

456

B. Beck et al. / Biochemical and Biophysical Research Communications 342 (2006) 452–458

birth and adulthood to these high energy levels and unbalanced diets. This idea is represented by the ‘‘fetal origin of obesity’’ hypothesis. In this experiment, we investigated whether regulatory mechanisms are modified early in life after exposure to different diets either rich in fat or in carbohydrate. We focused our attention on the important central pathways involved in the regulation of food intake. We have already shown that the NPY system is durably altered after dietary manipulation during fetal and early postnatal life [38–40]. In the present experiment, we targeted other orexigenic signals linked to fat ingestion, such as galanin and orexins [20,52], and their associated hormonal systems in the periphery. The first obvious sign of the existence of important changes in rats born to dams fed on energy-dense diets rich either in carbohydrates or fat was the difference in body weight at weaning. After perinatal exposure to a high-fat diet, the young rats weighed 30% less than pups born to dams fed on a high-carbohydrate diet or on a control diet. This finding does not agree with the results of others who have found an improved growth of the pups on an HF diet [53]. This disparity might be related to a much lower fat content in the diet used by these authors (20 g fat/100 g diet vs. 55 g/100 g in our case). Others have, however, reported decreased weight associated to increased fat intake in rats [54] or in humans [55]. This weight deficit was associated with important changes in metabolic parameters. Both low blood glucose and insulin on one hand and leptin on the other hand reflect this weight change. Similar changes have been described in the literature. In a population with high levels of fat intake, such as the Inuits [56], abnormal glucose tolerance or insulin resistance is inversely correlated with fat intake [57,58]. The nature of fats ingested by the Inuit population, derived from seal oil and salmon, might play a role [59] but we obtained similar results with margarine in the present experiment. A reduced insulin secretion was also noted in the offspring of women who had high intake of fat during late pregnancy [60]. All of these changes show that the HF diet was the less-efficient diet for development during gestation and early age, yet perhaps was the most favorable in terms of metabolism. In the brain, we measured specific variations in the neuropeptidergic pathways regulating feeding behavior. These variations depended on the type (inhibitory or stimulatory) of the peptides studied on one hand and on the type of macronutrient on the other. First, we detected an influence of the dietary treatment on orexigenic peptides only. The hypothalamic status of CRH or NT either in the PVN (CRH, NT) or in the lateral hypothalamus (NT) where they work to inhibit food intake was not modified. For CRH, this finding is in agreement with the unchanged basal levels of corticosterone measured in HF pups at 10 and 35 days of age [61]. The orexigenic peptides galanin and orexins were upregulated. This upregulation was observed after the HF diet

only and therefore in the smaller rats. The mRNA expression of both peptides was augmented in their respective main areas of biosynthesis: the lateral hypothalamus for orexins and the PVN for galanin. Galanin content was also augmented in the VMN of HF offspring. Both PVN and VMN are important areas for feeding regulation by galanin as injection of the peptide in these nuclei strongly stimulates food intake and changes macronutrient selection in satiated and fasted rats [18,22,62]. In the PVN of HF pups, increased GAL expression concurrent with unchanged GAL content suggests the existence of an increase in GAL release and therefore a greater stimulatory effect on food intake. Galanin is also largely synthesized in the arcuate nucleus [63] but in this area, the role of galanin in food intake regulation is probably minor when compared with its role in the PVN [23,28,50]. Accordingly, we did not detect any change in GAL expression in the ARC. The present data emphasize therefore the importance of the PVN and VMN in the orexigenic role of galanin. It is also particularly interesting to note the increase in expression of orexins. Indeed, orexins are not regulated as other orexigenic peptides are; orexins are generally diminished in hyperphagic rodents [64,65]. The HF pups, with their low metabolic and hormonal status, probably need a more intense drive to eat to recover a status similar to the control rats. This scenario is reflected by the inverse correlation between orexin expression and insulin or leptin. Therefore, both galanin and orexin variations reflect an augmentation in the orexigenic drive in the HF pups. As shown in our previous study on the NPY status in these rats [38], this increase allows rats at adulthood to diminish the weight deficit observed at weaning; however, they do not achieve a complete compensation when they are fed a control diet during their growth. The adult HF offspring remain lighter and leaner. Feeding the weaned rats with a palatable and energy-dense diet for a short period might have been beneficial, but in the long term with these dietary conditions, the increase in orexigenic drive might have adverse effects if not normalized. In conclusion, we have shown in this experiment that the type of diet ingested during gestation and lactation by the dams is a factor of primary importance for the development of the offspring. A very high supply of fat during these periods has the most marked effects on the pups both on the central nervous system and in the periphery. Their low body weight at weaning might be considered a negative point mainly when compared with offspring of dams fed the control diet. However, it was associated with low insulin and glucose status. This outcome could be considered a favorable effect that might preclude the development of the metabolic syndrome and obesity later in life. The nature of the fats provided to the dams is also an important factor to consider and feeding them a diet with a more favorable fatty acid balance than that present in margarine might attenuate weight deficit without adverse consequences on the metabolic profile. Further studies are necessary to confirm this point.

B. Beck et al. / Biochemical and Biophysical Research Communications 342 (2006) 452–458

The orexigenic pathways are globally activated in HF offspring, possibly to counteract the lower body weight. It remains to be established if and how the activated galanin and orexins systems adapt to the change in food (milk to solid food) after weaning. Acknowledgments The authors wish to thank Ms Franc¸oise Bergerot, Mrs Brigitte Fernette, and Mr. Francesco Giannangelli for their excellent technical help as well as Ms. Lydie Poirson for her help in the preparation of the present manuscript. This study was supported by the European Commission, Quality of Life and Management of Living Resources, Key action 1 ‘‘Food, nutrition and health’’ programme (QLK1-2000-00515). References [1] B.M. Popkin, C.M. Doak, The obesity epidemic is a worldwide phenomenon, Nutr. Rev. 56 (1998) 106–114. [2] A.A. Hedley, C.L. Ogden, C.L. Johnson, M.D. Carroll, L.R. Curtin, K.M. Flegal, Prevalence of overweight and obesity among US children, adolescents, and adults, 1999–2002, J. Am. Med. Assoc. 291 (2004) 2847–2850. [3] A. Jones, S. Assimon, M. Friedman, The effect of diet on food intake and adiposity in rats made obese by gestational undernutrition, Physiol. Behav. 37 (1986) 381–386. [4] A.P. Jones, M.I. Friedman, Obesity and adipocyte abnormalities in offspring of rats undernourished during pregnancy, Science 215 (1982) 1518–1519. [5] A. Jones, E. Simson, M. Friedman, Gestational undernutrition and the development of obesity in rats, J. Nutr. 114 (1984) 1484–1492. [6] J.M. Dollet, B. Beck, J.P. Max, G. Debry, Protein-energy malnutrition in pregnant rats improves adaptation of endocrine pancreas in malnourished offspring and induces insulin resistance after rehabilitation, Br. J. Nutr. 58 (1987) 415–425. [7] G. Dorner, A. Plagemann, Perinatal hyperinsulinism as possible predisposing factor for diabetes mellitus, obesity and enhanced cardiovascular risk in later life, Horm. Metab. Res. 26 (1994) 213–221. [8] A. Plagemann, I. Heidrich, W. Rohde, F. Gotz, G. Dorner, Hyperinsulinism during differentiation of the hypothalamus is a diabetogenic and obesity risk factor in rats, Neuroendocrinol. Lett. 14 (1992) 373–378. [9] A. Plagemann, I. Heidrich, F. Gotz, W. Rohde, G. Dorner, Obesity and enhanced diabetes and cardiovascular risk in adult rats due to early postnatal overfeeding, Exp. Clin. Endocrinol. 99 (1992) 154–158. [10] Y. Yamamoto, Y. Ueta, Y. Hara, R. Serino, M. Nomura, I. Shibuya, A. Shirahata, H. Yamashita, Postnatal development of orexin/ hypocretin in rats, Mol. Brain Res. 78 (2000) 108–119. [11] T.L. Steininger, T.S. Kilduff, M. Behan, R.M. Benca, C.F. Landry, Comparison of hypocretin/orexin and melanin-concentrating hormone neurons and axonal projections in the embryonic and postnatal rat brain, J. Chem. Neuroanat. 27 (2004) 165–181. [12] S. Giorgi, G. Forloni, G. Baldi, S. Consolo, Gene expression and in vitro release of galanin in rat hypothalamus during development, Eur. J. Neurosci. 7 (1995) 944–950. [13] P.L. Pearson, L.L. Anderson, C.D. Jacobson, The prepubertal ontogeny of galanin-like immunoreactivity in the male Meishan pig brain, Dev. Brain Res. 92 (1996) 125–139. [14] A.R. Sizer, A. Ro¨kaeus, G.A. Foster, Analysis of the ontogeny of galanin in the rat central nervous system bt immunochemistry and radioimmunoassay, Int. J. Dev. Neurosci. 8 (1990) 81–97.

457

[15] Y. Kagotani, T. Hashimoto, Y. Tsuruo, H. Kawano, S. Daikoku, K. Chihara, Development of the neuronal system containing neuropeptide Y in the rat hypothalamus, Int. J. Dev. Neurosci. 7 (1989) 359–374. [16] P.L. Woodhams, Y.S. Allen, J. Mc Govern, J.M. Allen, S.R. Bloom, R. Balazs, J.M. Polak, Immunohistochemical analysis of the early ontogeny of the neuropeptide Y system in rat brain, Neuroscience 15 (1985) 173–202. [17] S.G. Bouret, S.J. Draper, R.B. Simerly, Formation of projection pathways from the arcuate nucleus of the hypothalamus to hypothalamic regions implicated in the neural control of feeding behavior in mice, J. Neurosci. 24 (2004) 2797–2805. [18] S.E. Kyrkouli, B.G. Stanley, R.D. Seirafi, S.F. Leibowitz, Stimulation of feeding by galanin—anatomical localization and behavioral specificity of this peptides effects in the brain, Peptides 11 (1990) 995–1001. [19] J.T. Clark, P.S. Kalra, W.R. Crowley, S.P. Kalra, Neuropeptide Y and human pancreatic polypeptide stimulate feeding behavior in rats, Endocrinology 115 (1984) 427–429. [20] T. Sakurai, A. Amemiya, M. Ishii, I. Matsuzaki, R.M. Chemelli, H. Tanaka, S.C. Williams, J.A. Richardson, G.P. Kozlowski, S. Wilson, J.R.S. Arch, R.E. Buckingham, A.C. Haynes, S.A. Carr, R.S. Annan, D.E. McNulty, W.S. Liu, J.A. Terrett, N.A. Elshourbagy, D.J. Bergsma, M. Yanagisawa, Orexins and orexin receptors: a family of hypothalamic neuropeptides and G protein-coupled receptors that regulate feeding behavior, Cell 92 (1998) 573–585. [21] B.G. Stanley, D.R. Daniel, A.S. Chin, S.F. Leibowitz, Paraventricular nucleus injections of peptide YY and neuropeptide Y preferentially enhance carbohydrate ingestion, Peptides 6 (1985) 1205–1211. [22] D.L. Tempel, K.J. Leibowitz, S.F. Leibowitz, Effects of PVN galanin on macronutrient selection, Peptides 9 (1988) 309–314. [23] A. Akabayashi, J.I. Koenig, Y. Watanabe, J.T. Alexander, S.F. Leibowitz, Galanin-containing neurons in the paraventricular nucleus: a neurochemical marker for fat ingestion and body weight gain, Proc. Natl. Acad. Sci. USA 91 (1994) 10375–10379. [24] D.J. Clegg, E.L. Air, S.C. Woods, R.J. Seeley, Eating elicited by orexin-A, but not melanin-concentrating hormone, is opioid mediated, Endocrinology 143 (2002) 2995–3000. [25] B. Beck, A. Stricker-Krongrad, A. Burlet, F. Cumin, C. Burlet, Plasma leptin and hypothalamic neuropeptide Y and galanin levels in Long–Evans rats with marked dietary preferences, Nutr. Neurosci. 4 (2001) 39–50. [26] B. Beck, A. Stricker-Krongrad, A. Burlet, J.P. Max, N. Musse, J.P. Nicolas, C. Burlet, Macronutrient type independently of energy intake modulates hypothalamic neuropeptide Y in Long–Evans rats, Brain Res. Bull. 34 (1994) 85–91. [27] B. Beck, Quantitative and macronutrient-related regulation of hypothalamic neuropeptide Y, galanin and neurotensin, in: H.R. Berthoud, R.J. Seeley (Eds.), Neural and Metabolic Control of Macronutrient Intake, CRC Press, Boca Raton, USA, 1999, pp. 461–470. [28] S.F. Leibowitz, J.T. Dourmashkin, G.Q. Chang, J.O. Hill, E.C. Gayles, S.K. Fried, J. Wang, Acute high-fat diet paradigms link galanin to triglycerides and their transport and metabolism in muscle, Brain Res. 1008 (2004) 168–178. [29] B. Beck, A. Stricker-Krongrad, A. Burlet, J.P. Nicolas, C. Burlet, Influence of diet composition on food intake and hypothalamic neuropeptide Y (NPY) in the rat, Neuropeptides 17 (1990) 197–203. [30] A. Plagemann, T. Harder, A. Rake, M. Voits, H. Fink, W. Rohde, G. Dorner, Perinatal elevation of hypothalamic insulin, acquired malformation of hypothalamic galaninergic neurons, and syndrome Xlike alterations in adulthood of neonatally overfed rats, Brain Res. 836 (1999) 146–155. [31] C.T. Huizinga, C.B.M. Oudejans, H.A. Delemarre vandeWaal, Decreased galanin mRNA levels in growth hormone-releasing hormone neurons after perinatally induced growth retardation, J. Endocrinol. 170 (2001) 521–528.

458

B. Beck et al. / Biochemical and Biophysical Research Communications 342 (2006) 452–458

[32] A. Plagemann, F. Rittel, T. Harder, T. Waas, T. Ziska, W. Rohde, Hypothalamic galanin levels in weanling rats exposed to maternal low-protein diet, Nutr. Res. 20 (2000) 977–983. [33] P.J. Morgane, R. AustinLafrance, J. Bronzino, J. Tonkiss, S. DiazCintra, L. Cintra, T. Kemper, J.R. Galler, Prenatal malnutrition and development of the brain, Neurosci. Biobehav. Rev. 17 (1993) 91–128. [34] K.G. Koski, F.W. Hill, L.S. Hurley, Effect of low carbohydrate diets during pregnancy on embryogenesis and fetal growth and development in rats, J. Nutr. 116 (1986) 1922–1937. [35] D.B. Hausman, H.M. Mc Closkey, R.J. Martin, Maternal fat type influences the growth and fatty acid composition of newborn and weanling rats, J. Nutr. 121 (1991) 1917–1923. [36] Z.S. Warwick, S.S. Schiffman, Role of dietary fat in calorie intake and weight gain, Neurosci. Biobehav. Rev. 16 (1992) 585–596. [37] A. Sclafani, Carbohydrate-induced hyperphagia and obesity in the rat: effects of saccharide type, form, and taste, Neurosci. Biobehav. Rev. 11 (1987) 155–162. [38] R. Kozak, J.G. Mercer, A. Burlet, K.M. Moar, C. Burlet, B. Beck, Hypothalamic neuropeptide Y content and mRNA expression in weanling rats subjected to dietary manipulations during fetal and neonatal life, Regul. Pept. 75–76 (1998) 397–402. [39] R. Kozak, A. Burlet, C. Burlet, B. Beck, Dietary composition during fetal and neonatal life affects neuropeptide Y functioning in adult offspring, Dev. Brain. Res. 125 (2000) 75–82. [40] R. Kozak, S. Richy, B. Beck, Persistent alterations in neuropeptide Y release in the paraventricular nucleus of rats subjected to dietary manipulation during early life, Eur. J. Neurosci. 21 (2005) 2887– 2892. [41] K.E. Wortley, G.Q. Chang, Z. Davydova, S.F. Leibowitz, Peptides that regulate food intake—Orexin gene expression is increased during states of hypertriglyceridemia, Am. J. Physiol. 284 (2003) R1454– R1465. [42] S.C. Heinrichs, D. Richard, The role of corticotropin-releasing factor and urocortin in the modulation of ingestive behavior, Neuropeptides 33 (1999) 350–359. [43] B. Beck, Cholecystokinin, neurotensin and corticotropin-releasing factor—3 important anorexic peptides, Ann. Endocrinol. 53 (1992) 44–56. [44] T.L. Bale, W.W. Vale, CRF and CRF receptors: role in stress responsivity and other behaviors, Annu. Rev. Pharmacol. Toxicol. 44 (2004) 525–557. [45] R. Saladin, P. Devos, M. Guerre-Millo, A. Leturque, J. Girard, B. Staels, J. Auwerx, Transient increase in obese gene expression after food intake or insulin administration, Nature 377 (1995) 527–529. [46] A. Akabayashi, C.T.B.V. Zaia, J.I. Koenig, S.M. Gabriel, I. Silva, S.F. Leibowitz, Diurnal rhythm of galanin-like immunoreactivity in the paraventricular and suprachiasmatic nuclei and other hypothalamic areas, Peptides 15 (1994) 1437–1444. [47] J.G. Mercer, C.B. Lawrence, T. Atkinson, Regulation of galanin gene expression in the hypothalamic paraventricular nucleus of the obese Zucker rat by manipulation of dietary macronutrients, Mol. Brain Res. 43 (1996) 202–208. [48] J.G. Mercer, K.M. Moar, A.W. Ross, N. Hoggard, P.J. Morgan, Photoperiod regulates arcuate nucleus POMC, AGRP, and leptin receptor mRNA in Siberian hamster hypothalamus, Am. J. Physiol. 278 (2000) R271–R281.

[49] B. Beck, A. Burlet, J.P. Nicolas, C. Burlet, Hypothalamic neuropeptide Y (NPY) in obese Zucker rats: implications in feeding and sexual behaviors, Physiol. Behav. 47 (1990) 449–453. [50] B. Beck, A. Burlet, J.P. Nicolas, C. Burlet, Galanin in the hypothalamus of fed and fasted lean and obese Zucker rats, Brain Res. 623 (1993) 124–130. [51] B. Beck, A. Burlet, J.P. Nicolas, C. Burlet, Neurotensin in microdissected brain nuclei and in the pituitary of the lean and obese Zucker rats, Neuropeptides 13 (1989) 1–7. [52] A.L. Gundlach, Galanin/GALP and galanin receptors: role in central control of feeding, body weight/obesity and reproduction? Eur. J. Pharmacol. 440 (2002) 255–268. [53] M. DelPrado, G. Delgado, S. Villalpando, Maternal lipid intake during pregnancy and lactation alters milk composition and production and litter growth in rats, J. Nutr. 127 (1997) 458–462. [54] L. Agius, B.J. Rolls, E.A. Rowe, D.H. Williamson, Impaired lipogenesis in mammary glands of lactating rats fed on a cafeteria diet. Reversal of inhibition of glucose metabolism in vitro by insulin, Biochem. J. 186 (1980) 1005–1008. [55] M. Furuta, S. Matsuda, Ecological study of mean birth weight and nutritional intake in Japan, Hum. Biol. 70 (1998) 1057–1071. [56] E. Nobmann, S. Ebbesson, R. White, C. Schraer, A. Lanier, L.R. Bulkow, Dietary intakes among Siberian Yupiks of Alaska and implications for cardiovascular disease, Int. J. Circumpolar. Health 57 (1998) 4–17. [57] C. Schraer, P. Risica, S. Ebbesson, O. Go, B. Howard, A. Mayer, Low fasting insulin levels in Eskimos compared to American Indians: are Eskimos less insulin resistant? Int. J. Circumpolar. Health 58 (1999) 272–280. [58] J. Naylor, C. Schraer, A. Mayer, A. Lanier, C. Treat, N. Murphy, Diabetes among Alaska Natives: a review, Int. J. Circumpolar. Health 62 (2003) 363–387. [59] A.I. Adler, E.J. Boyko, C.D. Schraer, N.J. Murphy, Lower prevalence of impaired glucose tolerance and diabetes associated with daily seal oil or salmon consumption among Alaska Natives, Diabetes Care 17 (1994) 1498–1501. [60] A.W. Shiell, D.M. Campbell, M.H. Hall, D.J. Barker, Diet in late pregnancy and glucose-insulin metabolism of the offspring 40 years later, BJOG 107 (2000) 890–895. [61] G. Trottier, K.G. Koski, T. Brun, D.J. Toufexis, D. Richard, C.D. Walker, Increased fat intake during lactation modifies hypothalamicpituitary-adrenal responsiveness in developing rat pups: a possible role for leptin, Endocrinology 139 (1998) 3704–3711. [62] R.R. Schick, S. Samsami, J.P. Zimmermann, T. Eberl, C. Endres, V. Schusdziarra, M. Classen, Effect of galanin on food intake in rats involvement of lateral and ventromedial hypothalamic sites, Am. J. Physiol. 264 (1993) R355–R361. [63] G. Skofitsch, D.M. Jacobowitz, Immunohistochemical mapping of galanin-like neurons in the rat nervous system, Peptides 6 (1985) 509–546. [64] A. StrickerKrongrad, S. Richy, B. Beck, Orexins/hypocretins in the ob/ob mouse: hypothalamic gene expression, peptide content and metabolic effects, Regul. Pept. 104 (2002) 11–20. [65] B. Beck, S. Richy, T. Dimitrov, A. StrickerKrongrad, Opposite regulation of hypothalamic orexin and neuropeptide Y receptors and peptide expressions in obese Zucker rats, Biochem. Biophys. Res. Commun. 286 (2001) 518–523.