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Effects of Γ-Aminobutyric Acid on Food Intake and Appetite in Mandarin Fish Siniperca Chuatsi

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Effects of Γ-Aminobutyric Acid on Food Intake and Appetite in Mandarin Fish Siniperca Chuatsi 第 41 卷 第 6 期 水 生 生 物 学 报 Vol. 41, No. 6 2017 年 11 月 ACTA HYDROBIOLOGICA SINICA Nov., 2017 doi: 10.7541/2017.162 EFFECTS OF γ-AMINOBUTYRIC ACID ON FOOD INTAKE AND APPETITE IN MANDARIN FISH SINIPERCA CHUATSI HUANG Dong1, 2, LIANG Xu-Fang1, 2, YUAN Xiao-Chen1, 2, CAI Wen-Jing1, 2, LI Ai-Xuan1, 2, HE Shan1, 2 and XUE Min3 (1. College of Fisheries, Chinese Perch Research Center, Huazhong Agricultural University, Wuhan 430070, China; 2. Freshwa- ter Aquaculture, Key Lab of Freshwater Animal Breeding, Ministry of Agriculture, Wuhan 430070, China; 3. National Aquafeed Safety Assessment Station, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, China) Abstract: γ-Aminobutyric acid (GABA) has been established as an important regulator of food intake in mammals, but its role in fish remains scant. The aim of this study was to investigate the effects of GABA on food intake in mandarin fish (Siniperca chuatsi). Fish received intracerebroventricular (ICV) injection of sa- line and different doses of GABA (50, 125, 500 and 2000 μg). Food intake increased significantly in 125 μg GABA group within 2h. The RT-qPCR data demonstrated that up-regulation of NPY and AgRP, and down- regulation of CART and POMC were consistent with higher food intake of mandarin fish. The mRNA expres- sion of Leptin-R decreased significantly at all the four doses of GABA at 0.5h and 2h compared to the saline injected fish. These results indicated that GABA could affect the appetite by regulating leptin signaling path- way and thus resulting in alteration of food intake. Our findings could provide theory basis for GABA applica- tion in aquaculture feeds. Key words: γ-Aminobutyric acid; Mandarin fish; Food intake; Gene expression; Leptin signaling path- way CLC number: S965.1 Document code: A Article ID: 1000-3207(2017)06-1311-07 γ-Aminobutyric acid (GABA), a non-protein were observed following injections of the agonist or amino acid, distributes widely in nature and serves as antagonists of GABA into the hypothalamus[2, 11—15]. a major inhibitory neurotransmitter in the central Likewise, GABA is also involved in the regulation of nervous system[1, 2]. It has been implicated in several a number of physiological functions in fish. It was centrally mediated physiological functions such as found that injecting GABA intraperitoneally caused neurotransmission[3], blood pressure regulator[4], hor- an increase of serum GTH levels in regressed or early monal regulator[5], relaxation regulator[6] and sleep- maturing fish, rather in late maturing animals[16]. An lessness and depression regulator[7]. Moreover, it has ICV injection of muscimol caused an acute and dose been established as an important regulator of food in- dependent increase in locomotor activity of juvenile take in mammals[8—10]. Many previous studies were spring chinook salmon[17]. Interactions in goldfish carried out by using commercial GABA, GABA recep- were found between feeding behaviors and ORXR-β- [18] tor agonist or GABA receptor antagonist in mamma- GABAAR subunit . However, effects of GABA on lian species. It was reported that injection of GABA into food intake of teleost remain largely unknown. There- the ventromedial hypothalamus of satiated rats in- fore, further studies are needed to elucidate the poten- duced further consumption of food. Similar effects tial role of GABA on food intake of fish. Received date: 2016-11-24; Accepted date: 2017-04-27 Foundation item: Supported by the National Basic Research Program of China (2014CB138601); the Fundamental Research Funds for the Central Universities (2015PY041) Brief introduction of author: Huang Dong (1991—), Male, born in Shanxi; Master student; major in molecular nutrition of fish. E-mail: [email protected] Corresponding author: Liang Xu-Fang, E-mail: [email protected] 1312 水 生 生 物 学 报 41 卷 As is known to us, the regulation of appetite mrigola (initial body weight: 0.16±0.02 g) (Wuhan, which controls food intake is a complex phenomenon China) at 8:00 am and 17:00 pm every day. Animals involving interactions between the brain and periphe- were acclimated to these conditions for at least 2 weeks ral signals. A few peptides are now recognized to play before the experiment. an important role in the regulation of appetite, which 1.3 Drug and treatment exist in the same neuron or may have interactions The GABA was purchased from Sigma Bio- with GABA. Neuropeptide Y (NPY) neurons coex- chemicals, Dorset, UK. The drug was dissolved in pressing GABA and agouti-related protein (AgRP) teleost saline (20 mg Na2CO3 per 100 mL of 0.6% [19] stimulate appetite . In addition, NPY, AgRP, and NaCl). Doses of drug were selected based on previ- GABA released in the ARC suppress the restraint of ous studies[24—26], which were chosen for the follow- proopiomelanocortin (POMC) neurons coexpressing ing experiments. The ICV injections were carried out α-melanocyte stimulating hormone (α-MSH) and co- using a 0.5 mm Microlance needle connected to a 5 μL caine and amphetamine regulated transcript (CART) [19] Hamilton microsyringe. The needle was performed on appetite . Leptin, a product of the obese (ob) freehand through the central junction between the gene, bindings with leptin receptor (Leptin-R) and frontal and parietal bones. The procedure of ICV in- acts directly on the hypothalamus to inhibit nore- jection and accuracy of injection placement into the pinephrine efflux (NE) efflux through GABA[20]. Al- ventricular regions of the fish brain followed the though information about the feeding regulation [27] method of De Pedro et al . After injection, the mechanism of these peptides is increasing, the intera- wounds were covered immediately with vaseline. ctions of GABA with them on food intake of fish are 1.4 Effects of ICV administration of GABA on food still limited. intake Mandarin fish (Siniperca chuatsi), a demersal After the acclimation period, 30 food-deprived piscivore, is one of the most valuable food fish native (24h) fish were anesthetized with MS-222 (1鲶10000) to the freshwaters of China. It is one of the chief eco- and weighted when they lost equilibrium, which were nomic edible fish in China and in other countries due [21, 22] divided into five groups that received ICV injection, to its large size, fast growth and delicious flesh . respectively. GABA at 50 μg, 125 μg, 500 μg and In addition, it has distinct food preference. In the 2000 μg, and one control group, which received ICV wild, it feed solely on live fry of other fish species once the fry start feeding[23]. injection of the same volume of teleost saline (5 μL). In the present study, we investigated food intake The fish were habituated in anaesthetic-free water and mRNA expression profiles of five representative within 1—2min to help them recovered equilibrium appetite-related genes in the brain of mandarin fish and normal swimming activity after injection. Every after GABA administration. This study will provide a mandarin fish was then transferred to a aquaria which better understanding of GABA in mediating food in- contained enough pre-weighted prey fish (average take of fish. body weight: 0.16 g) immediately. The food intake was measured by directly observing and recording the 1 Materials and methods number of prey fish eaten by individual mandarin fish 1.1 Ethics statement after 0.5h, 2h and 4h. The formula is as follows: This study was carried out in strict accordance FI=Wi–(Wf×F) where Wi=initial food weight, Wf=re- with the recommendations in the Guide for the Care maining food weight and F=correction factor[27]. and Use of Laboratory Animals of the National Vete- 1.5 Effects of ICV administration of GABA on gene rinary and Quarantine Service. The protocol was ap- expression proved by the Committee on the Ethics of Animal Ex- In order to examine effects of GABA on brain periments of the Huazhong Agricultural University. NPY, AgRP, CART, POMC and Leptin-R mRNA ex- 1.2 Animals pressions, another experiment was performed using The mandarin fish were obtained from Wuhan the uninjectd stock of mandarin fish, which received Freshwater Fish Farm (Wuhan, China). Prior to the the same treatment without giving prey fish. Fish initiation of the experiment, 100 mandarin fish were were then sampled at 0.5h and 2h after injection carried out in 2 cylindrical plastic tanks (350 L) and without feeding. Brains of both groups were dissec- were kept under controlled light-dark conditions (12 ted and immediately snap-frozen in liquid nitrogen Light /12 Dark) with a constant flow of filtered water and stored at –80℃ for RNA isolation and sub- and the water temperature was regulated to 23—25℃. sequent analyses. The fish were fed with (2% of bodyweight) Cirrhina Total RNA was extracted using Trizol reagent 6 期 黄 东等: γ-氨基丁酸对鳜摄食和食欲的影响 1313 (TaKaRa, Japan), treated with RQI RNase-Free DNase value method[29]. All amplifications were performed (TaKaRa, Japan) to remove DNA contaminant, and in triplicate for each RNA sample. then spectrophotometrically quantified. For each re- 1.6 Statistical analyses verse transcription reaction, RNA was subjected to All data were presented as mean±SEM (standard cDNA synthesis by SuperScriptTM II RT reverse tran- error of the mean). Statistical analysis was performed scriptase (TaKaRa, Japan) according to reagent’s in- by a one-way analysis of variance (one-way AN- structions. The selected gene coding sequence were OVA) using SPSS 19.0 with Duncan’s multiple com- based on the results of transcriptome sequencing of parisons test. Statistical significance was determined mandarin fish which were mapped to the mandarin at the 5% level. fish genome by the Short Oligonucleotide Analysis 2 Results [28] Package SOAP aligner/soap2 .
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