- Email: [email protected]
Intracerebroventricular injection of muscimol, baclofen or nipecotic acid stimulates food intake in layer-type, but not meat-type, chicks
Brain Research 993 (2003) 235 – 238 www.elsevier.com/locate/brainres
Short communication
Intracerebroventricular injection of muscimol, baclofen or nipecotic acid stimulates food intake in layer-type, but not meat-type, chicks Takashi Bungo a,*, Tomofumi Izumi a, Kazuya Kawamura a, Tomo Takagi b, Hiroshi Ueda a, Mitsuhiro Furuse b a
Laboratory of Animal Science, Department of Agrobiological Science, Faculty of Agriculture, Ehime University, 3-5-7 Tarumi, Matsuyama 790-8566, Japan b Department of Animal and Marine Bioresource Sciences, Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan Accepted 10 September 2003
Abstract This study was designed to compare the effects of muscimol (GABAA agonist), baclofen (GABAB agonist) and nipecotic acid (GABA uptake inhibitor) on food intake in two chicken strains (meat-type and layer-type chicks). The intracerebroventricular (ICV) injection of all GABA agents induced hyperphagia in layer-type chicks. However, in broiler chicks, there were similar tendencies with muscimol and nipecotic acid but not significantly different. Conversely, ICV injection of baclofen depressed feeding of broiler chicks. These results suggest that there are some differences in central GABAergic systems between these strains of chicks, but GABAergic systems have an important role in the regulation of food intake in neonatal chicks. D 2003 Elsevier B.V. All rights reserved. Theme: Neurotransmitters, modulators, transporters, and receptors Topic: GABA Keywords: Food intake; Muscimol; Baclofen; Nipecotic acid; GABAergic system; Chick
Research over the past several decades has examined the brain neurochemical systems that regulate food intake in mammalian species, and has identified a number of neurotransmitters that appear to contribute to this behavior. gAminobutyric acid (GABA), the most widely distributed inhibitory neurotransmitter in the vertebrate central nervous system [23], is found in high concentrations in brain areas known to be involved in the control of ingestive behavior [7]. Additionally, numerous studies using pharmacological treatments have investigated the role of GABA in the regulation of appetitive behavior of mammals: intracerebroventricular (ICV) administration of GABAA agonist [1,21] or GABAB agonist [10,11] induced hyperphagia. Conversely, Olgiati et al. [20] demonstrated that GABA decreased food consumption when injected into the lateral ventricles of rats. In addition, it is reported that ICV injection of GABA did not alter eating response in sheep [22]. The reasons for these different responses are likely to be species
* Corresponding author. Tel./fax: +81-89-946-9820. E-mail address: [email protected] (T. Bungo). 0006-8993/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2003.09.017
specific or the site acted on in the brain. Thus, many researchers have also investigated a number of major central sites in rats [17,19,21,25,28]. In avian species, similar to mammalian, GABA has been shown to exist in various regions of the chick brain [5,14,24]. It is reported that ICV injection of GABAA receptor agonist muscimol increased food intake in turkeys [8] and meat-type (broiler) chickens [16]. On the other hand, baclofen, a GABAB receptor agonist, did not affect food intake in broiler chickens [16]. However, comparable data in avian species are controversial and limited. Therefore, the purpose of this study is to examine the acute effect of central injection of GABA agonists and GABA uptake inhibitor on the feeding of both meat- and layer-type chicks. Day-old male Single Comb White Leghorn (SCWL) chicks (Kudoh-sha, Ehime, Japan) and broiler chicks (Cobb; Fresh Foods, Ehime, Japan) were maintained in a room with 24-h light and at a temperature of 30 jC. They were given free access to a commercial starter diet (Nihon Nosan Kogyo, Yokohama, Japan) and water during the pre-experimental period. Before each experiment, chicks were distributed into experimental groups based on body weight so
236
T. Bungo et al. / Brain Research 993 (2003) 235–238
At the end of the experiments, birds were sacrificed by decapitation, followed by brain sectioning to identify the location of the drug injection. Data were deleted from individuals in which the presence of Evans Blue dye in the lateral ventricle was not verified. The number of birds used for data analysis is shown in each figure. ANOVA was used to determine overall statistical significance due to treatment. When a treatment effect was significant, the Fisher’s protected LSD test was used to compare the significance among means. Dose of significance was set at p < 0.05. Results are presented as means F S.E.M. Regression equations were fitted to the data. The results of the effect of central injection of muscimol are shown in Fig. 1. Each level of muscimol failed to stimulate food intake in broiler chicks at 30 min when compared with control (Fig. 1A: p>0.05). On the other hand, food intake in SCWL chicks increased significantly with 0.1 and 0.2 Ag muscimol when compared with control at 30 min post-injection (Fig. 1B; F(3,20) = 3.181, p < 0.05). The results of the effect of ICV administration of baclofen are shown in Fig. 2. Food intake in broiler chicks decreased significantly with 0.1 and 0.2 Ag baclofen when compared with control at 30 min post-injection (Fig. 2A; F(3,30) = 3.219, p < 0.05). In contrast to broiler chicks, the Fig. 1. Food intake of (A) broiler and (B) Leghorn chicks injected ICV with saline or one of three doses of muscimol (0.1, 0.2 or 0.5 Ag). Values are means F S.E.M. The number of chicks used is shown in parentheses. *P < 0.05, compared with saline control. (B) Food intake (g/30 min) = 0.41(S.E. 0.10) + 3.67(S.E. 1.18)X 6.38(S.E. 2.15)X 2 , R2 = 0.318, P < 0.05.
that the average body weight was as uniform as possible for each treatment. The birds were reared individually in experimental cages and had ad libitum access to food up to the time of treatments. Birds were given free access to food for 30 min immediately after each treatment. In Experiments 1 (Cobb; 2-day-old) and 2 (SCWL; 3-day-old), saline or muscimol (GABAA agonist; 0.1, 0.2 or 0.5 Ag) was injected once intracerebroventricularly (ICV) into the lateral ventricle. In Experiments 3 (Cobb; 3-day-old) and 4 (SCWL; 4-dayold), birds were injected by the ICV route with four levels (0, 0.05, 0.1 and 0.2 Ag) of baclofen (GABAB agonist). In Experiments 5 (Cobb; 3-day-old) and 6 (SCWL; 3-dayold), birds were injected by the ICV route with three levels (0, 0.2 and 0.4 mg) of nipecotic acid (GABA uptake inhibitor). Muscimol and baclofen were both purchased from Sigma (St. Louis, MO, USA). ( F )-Nipecotic acid was purchased from Research Biochemicals International (Natick, MA, USA). Drugs were dissolved in a 0.1% Evans Blue solution, which was prepared in a 0.85% saline. Saline containing Evans Blue was used as a control. The birds were injected ICV using a microsyringe according to the methods used by Davis et al. [6] and Furuse et al. [13].
Fig. 2. Food intake of (A) broiler and (B) Leghorn chicks injected ICV with saline or one of three doses of baclofen (0.05, 0.1 or 0.2 Ag). Values are means F S.E.M. The number of chicks used is shown in parentheses. *P < 0.05, compared with saline control. (A): Food intake (g/30 min) = 0.71(S.E. 0.12) 2.59(S.E. 0.94)X, R2 = 0.192, P < 0.01. (B) Food intake (g/ 30 min) = 0.29(S.E. 0.10) + 3.47(S.E. 0.93)X, R2 = 0.303, P < 0.001.
T. Bungo et al. / Brain Research 993 (2003) 235–238
ICV injection of baclofen stimulated food consumption in a dose-dependent manner and food intake in SCWL chicks increased significantly with 0.2 Ag baclofen when compared with control at 30 min post-injection (Fig. 2B; F(3,30) = 4.354, p < 0.05). The effect of ICV administration of nipecotic acid (0.2 or 0.4 mg) on food consumption in chicks fed ad libitum over a 30-min period is shown in Fig. 3. Each level of nipecotic acid failed to stimulate food intake in broiler chicks during the 30-min period when compared with control (Fig. 3A: p>0.05). On the other hand, the ICV injection of nipecotic acid stimulated food consumption in a dose-dependent manner and food intake in SCWL chicks increased significantly with 0.4 mg nipecotic acid when compared with control at 30 min post-injection (Fig. 3B; F(2.14) = 4.185, p < 0.05). The present results show that central injection of muscimol, GABAA agonist, stimulated feeding behavior in SCWL chicks (Fig. 1B), which is in good agreement with other reports in mammals [1,21] and avians [6,16]. On the other hand, muscimol tended to stimulate feeding, but no significant difference was obtained in broiler chicks (Fig. 1A). However, GABAA antagonist (bicuculline) decreased food intake in broiler chicks (unpublished data). Additionally, although there was no systematic attempt to quantify
Fig. 3. Food intake of (A) broiler and (B) Leghorn chicks injected ICV with saline or one of two doses of baclofen (0.2 or 0.4 mg). Values are means F S.E.M. The number of chicks used is shown in parentheses. *P < 0.05, compared with saline control. (B): Food intake (g/30 min) = 0.43(S.E. 0.12) + 1.30(S.E. 0.45)X, R2 = 0.359, P < 0.05.
237
other behavioral measurement, frequency of pecking in broiler chicks accelerated with muscimol for a short span of time. It seemed that there may be GABAA receptormediated feeding regulation in broiler chicks and duration of efficacy of muscimol in broilers may be shorter than that in layers. Similar to this, we found that duration of efficacy of glutamate in broilers was shorter than that in layers [3]. It is reported that the injection of baclofen, GABAB agonist, induced an eating response in mammals [10,11]. Central injection of baclofen stimulated feeding in SCWL chicks (Fig. 2B), which was similar to that observed in mammals. However, a diametrically opposed effect was observed in broiler chicks (Fig. 2A). As for the difference between broiler and layer chicks on GABAB receptormediated feeding regulation, it has been reported also that the anorexic effect of L-pipecolic acid, GABA uptake inhibitor, was attenuated significantly by co-injection of GABAB antagonist in fasted broiler chicks, but not layer chicks [26]. These results indicated that the role of GABAB receptor might be influenced by genetic selection. The reason for these different responses is not clear, but some hypotheses are proposed. First, it is likely that distribution and/or number of GABAB receptors in broiler chicks may differ from SCWL chicks. It has been demonstrated that the action site of GABAB agonist in the central nervous system has different effects, e.g. microinjection of baclofen into the amygdala [19] and the lateral hypothalamus [17] decreased food intake while injections into the nucleus accumbens shell [25,29] increased food intake in the rat. Second, it was supposed that the effect of baclofen on the release and/or synthesis of neurotransmitters (or neuromodulators) which affect feeding regulation in broiler chicks may differ from that in SCWL chicks. It is reported that GABAB receptors might be present presynaptically to reduce evoked release of transmitters such as GABA, glutamate, and substance P [2,15]. As regards synthesis, Coscina et al. [4] reported that intracisternal injection of GABA agent elevated levels of taurine in the brain of obese, but not of lean Zucker rats. Actually, it is known that taurine may have a neurotransmitter (or neuromodulatory) role in some parts of the nervous system [18]. Recently, it was reported that food intake in SCWL chicks was increased by L-pipecolic acid under ad libitum feeding [27]. Additionally, the orexigenic effect of L-pipecolic acid is mediated by both GABA A and GABAB receptors [27]. The central injection of nipecotic acid, which inhibits uptake of GABA [9,18] and leads to higher extracellular concentration of GABA, in SCWL chicks was the induction of hyperphagia (Fig. 3B). Similar to L-pipecolic acid, it seemed that the higher concentration of GABA by nipecotic acid might contribute to this effect via both GABA receptors. On the other hand, nipecotic acid failed to stimulate feeding behavior in broiler chicks (Fig. 3B). The cause may be the difference between broiler and layer chicks on GABAB receptor-mediated feeding regulation, as mentioned above.
238
T. Bungo et al. / Brain Research 993 (2003) 235–238
In meat-type (broiler) chickens, it has been demonstrated that muscimol increased food intake but baclofen did not have any affect [16]. There is the possibility that the density of GABA receptors in the brain may alter with age. Furthermore, handling of chicks has been shown to decrease forebrain GABA receptors and in vitro GABA release from brain tissues [12]. In the case of chicken study [16], a surgical procedure to attach the guide cannula for ICV injection was done before the experiments. This procedure may alter the potency of GABA agents between chickens and neonatal chicks. Further research on the density of GABA receptors and the concentration of GABA at each site in chick brains is needed to understand the role of GABA in central regulation of appetite in avian species. However, the results described here suggest that both GABA receptors play important roles in the control of neonatal chicks with strain differences.
Acknowledgements This work was supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science.
References [1] B.A. Baldwin, I.S. Ebenezer, C. De La Riva, Effects of intracerebroventricular injection of muscimol or GABA on operant feeding in pigs, Physiol. Behav. 48 (1990) 417 – 421. [2] N.G. Bowery, S.J. Enna, g-Aminobutyric acidB receptors: first of the functional metabotropic heterodimers, J. Pharmacol. Exp. Ther. 292 (2000) 2 – 7. [3] T. Bungo, S. Yoshinaga, H. Ueda, Intracerebroventricularly administered excitatory amino acids: effects on feeding behavior in chicks, J. Appl. Anim. Res. 22 (2002) 161 – 168. [4] D.V. Coscina, T.W. Castonguay, J.S. Stern, Effect of increasing brain GABA on the meal patterns of genetically obese vs. lean Zucker rats, Int. J. Obes. 16 (1992) 425 – 433. [5] A. Csillag, M.G. Stewart, E.M. Curtis, GABAergic structures in the chick telencephalon: GABA immunocytochemistry combined with light and electron microscope autoradiography and golgi impregnation, Brain Res. 437 (1987) 283 – 297. [6] J.L. Davis, D.T. Masuoka, J.F. Gerbrandt, A. Cherkin, Autoradiographic distribution of L-proline in chicks after intracerebral injection, Physiol. Behav. 22 (1979) 693 – 695. [7] C. Decavel, A.N. Van den Pol, GABA: a dominant neurotransmitter in the hypothalamus, J. Comp. Neurol. 302 (1990) 1019 – 1037. [8] D.M. Denbow, Induction of food intake by a GABAergic mechanism in the turkey, Physiol. Behav. 49 (1990) 485 – 488. [9] J.L. do Nascimento, A.L. Ventura, R. Paes de Carvalho, Veratridineand glutamate-induced release of [3H]-GABA from cultured chick retina cells: possible involvement of a GAT-1-like subtype of GABA transporter, Brain Res. 798 (1998) 217 – 222.
[10] I.S. Ebenezer, The effect of intracerebroventricular administration of baclofen on food intake in rats, NeuroReport 1 (1990) 73 – 76. [11] I.S. Ebenezer, B.A. Baldwin, Effect of intracerebroventricular administration of GABAB receptor agonist baclofen on operant feeding in satiated pigs, Br. J. Pharmacol. 101 (1990) 559 – 562. [12] E. Fluck, S. Hogg, R.B. Jones, R. Bourne, S.E. File, Changes in Tonic immobility and the GABA-benzodiazepine system in response to handling in the chick, Pharmacol. Biochem. Behav. 58 (1997) 269 – 274. [13] M. Furuse, R. Ando, T. Bungo, R. Ao, M. Shimojo, Y. Masuda, Intracerebroventricular injection of orexins does not stimulate food intake in neonatal chicks, Br. Poult. Sci. 40 (1999) 698 – 700. [14] R.H. Granda, W.J. Grossland, GABA-like immunoreactivity of neurons in the chicken diencephalon and mesencephalon, J. Comp. Neurol. 287 (1989) 455 – 469. [15] J.S. Isaacson, J.M. Solis, R.A. Nicoll, Local and diffuse synaptic action of GABA in the hippocampus, Neuron 10 (1993) 165 – 175. [16] H. Jonaidi, V. Babapour, D.M. Denbow, GABAergic control of food intake in the meat-type chickens, Physiol. Behav. 76 (2002) 465 – 468. [17] J. Kelly, J. Rothstein, S.P. Grossman, GABA and hypothalamic feeding system: 1. Topographic analysis of the effects of microinjections of muscimol, Physiol. Behav. 23 (1979) 1123 – 1134. [18] Z.L. Kruk, C.J. Pycock (Eds.), Inhibitory Amino Acids: GABA, Glycine and Taurine, 3rd ed., Neurotransmitters and Drugs, Chapman & Hall, New York, 1991, pp. 142 – 158. [19] F.G. Minano, S.M.S. Meneres, M. Sancibrian, P. Salinas, GABAA receptor in amygdala: role in feeding in fasted and satiated rats, Brain Res. 586 (1992) 104 – 110. [20] V.R. Olgiati, C. Netti, F. Guidobono, A. Pecile, The central GABAergic system and control of food intake under different experimental conditions, Psychopharmacology (Berlin) 68 (1980) 163 – 167. [21] S. Pu, M.R. Jain, T.L. Horvath, S. Diano, P.S. Kalra, S.P. Kalra, Interactions between neuropeptide Y and gamma-aminobutyric acid in stimulation of feeding: a morphological and pharmacological analysis, Endocrinology 140 (1999) 933 – 940. [22] J.R. Seone, F. Dumont, C.L. Girard, L. Bedard, J.J. Matte, Effects of intraventricular injections of gamma-aminobutyric acid and related substances on feeding behavior in satiated sheep, Can. J. Physiol. Pharm. 62 (1984) 1296 – 1299. [23] L. Sivilotti, A. Nistri, GABA receptor mechanisms in the central nervous system, Prog. Neurobiol. 36 (1991) 35 – 92. [24] M.G. Stewart, R.C. Bourne, J. Chmielowska, M. Kalman, A. Csillag, D. Stanford, Quantitative autoradiographic analysis of the distribution of [3H] muscimol binding to GABA receptors in chick brain, Brain Res. 456 (1988) 387 – 391. [25] T.R. Stratford, A.E. Kelley, GABA in the nucleus accumbens shell participates in the central regulation of feeding behavior, J. Neurosci. 17 (1997) 4434 – 4440. [26] T. Takagi, T. Bungo, E.-S. Saito, T. Tachibana, S. Saito, I. Yamasaki, S. Tomonaga, D.M. Denbow, M. Furuse, Intracerebroventricular administration of GABA-A and GABA-B receptor antagonists attenuate feeding and sleeping-like behavior induced by L-pipecolic acid in the neonatal chicks, J. Neurosci. Res. 73 (2003) 270 – 275. [27] T. Takagi, T. Tachibana, E.-S. Saito, S. Tomonaga, S. Saito, T. Bungo, D.M. Denbow, M. Furuse, Central pipecolic acid increases food intake under ad libitum feeding conditions in the neonatal chicks, Neurosci. Lett. 347 (2003) 93 – 96. [28] S. Tsujii, G.A. Bray, GABA-related feeding control in genetically obese rats, Brain Res. 540 (1991) 48 – 54. [29] B.O. Ward, E.M. Somerville, P.G. Clifton, Intraaccumbens baclofen selectively enhances feeding behavior in the rat, Physiol. Behav. 68 (2000) 463 – 468.
Short communication
Intracerebroventricular injection of muscimol, baclofen or nipecotic acid stimulates food intake in layer-type, but not meat-type, chicks Takashi Bungo a,*, Tomofumi Izumi a, Kazuya Kawamura a, Tomo Takagi b, Hiroshi Ueda a, Mitsuhiro Furuse b a
Laboratory of Animal Science, Department of Agrobiological Science, Faculty of Agriculture, Ehime University, 3-5-7 Tarumi, Matsuyama 790-8566, Japan b Department of Animal and Marine Bioresource Sciences, Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan Accepted 10 September 2003
Abstract This study was designed to compare the effects of muscimol (GABAA agonist), baclofen (GABAB agonist) and nipecotic acid (GABA uptake inhibitor) on food intake in two chicken strains (meat-type and layer-type chicks). The intracerebroventricular (ICV) injection of all GABA agents induced hyperphagia in layer-type chicks. However, in broiler chicks, there were similar tendencies with muscimol and nipecotic acid but not significantly different. Conversely, ICV injection of baclofen depressed feeding of broiler chicks. These results suggest that there are some differences in central GABAergic systems between these strains of chicks, but GABAergic systems have an important role in the regulation of food intake in neonatal chicks. D 2003 Elsevier B.V. All rights reserved. Theme: Neurotransmitters, modulators, transporters, and receptors Topic: GABA Keywords: Food intake; Muscimol; Baclofen; Nipecotic acid; GABAergic system; Chick
Research over the past several decades has examined the brain neurochemical systems that regulate food intake in mammalian species, and has identified a number of neurotransmitters that appear to contribute to this behavior. gAminobutyric acid (GABA), the most widely distributed inhibitory neurotransmitter in the vertebrate central nervous system [23], is found in high concentrations in brain areas known to be involved in the control of ingestive behavior [7]. Additionally, numerous studies using pharmacological treatments have investigated the role of GABA in the regulation of appetitive behavior of mammals: intracerebroventricular (ICV) administration of GABAA agonist [1,21] or GABAB agonist [10,11] induced hyperphagia. Conversely, Olgiati et al. [20] demonstrated that GABA decreased food consumption when injected into the lateral ventricles of rats. In addition, it is reported that ICV injection of GABA did not alter eating response in sheep [22]. The reasons for these different responses are likely to be species
* Corresponding author. Tel./fax: +81-89-946-9820. E-mail address: [email protected] (T. Bungo). 0006-8993/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2003.09.017
specific or the site acted on in the brain. Thus, many researchers have also investigated a number of major central sites in rats [17,19,21,25,28]. In avian species, similar to mammalian, GABA has been shown to exist in various regions of the chick brain [5,14,24]. It is reported that ICV injection of GABAA receptor agonist muscimol increased food intake in turkeys [8] and meat-type (broiler) chickens [16]. On the other hand, baclofen, a GABAB receptor agonist, did not affect food intake in broiler chickens [16]. However, comparable data in avian species are controversial and limited. Therefore, the purpose of this study is to examine the acute effect of central injection of GABA agonists and GABA uptake inhibitor on the feeding of both meat- and layer-type chicks. Day-old male Single Comb White Leghorn (SCWL) chicks (Kudoh-sha, Ehime, Japan) and broiler chicks (Cobb; Fresh Foods, Ehime, Japan) were maintained in a room with 24-h light and at a temperature of 30 jC. They were given free access to a commercial starter diet (Nihon Nosan Kogyo, Yokohama, Japan) and water during the pre-experimental period. Before each experiment, chicks were distributed into experimental groups based on body weight so
236
T. Bungo et al. / Brain Research 993 (2003) 235–238
At the end of the experiments, birds were sacrificed by decapitation, followed by brain sectioning to identify the location of the drug injection. Data were deleted from individuals in which the presence of Evans Blue dye in the lateral ventricle was not verified. The number of birds used for data analysis is shown in each figure. ANOVA was used to determine overall statistical significance due to treatment. When a treatment effect was significant, the Fisher’s protected LSD test was used to compare the significance among means. Dose of significance was set at p < 0.05. Results are presented as means F S.E.M. Regression equations were fitted to the data. The results of the effect of central injection of muscimol are shown in Fig. 1. Each level of muscimol failed to stimulate food intake in broiler chicks at 30 min when compared with control (Fig. 1A: p>0.05). On the other hand, food intake in SCWL chicks increased significantly with 0.1 and 0.2 Ag muscimol when compared with control at 30 min post-injection (Fig. 1B; F(3,20) = 3.181, p < 0.05). The results of the effect of ICV administration of baclofen are shown in Fig. 2. Food intake in broiler chicks decreased significantly with 0.1 and 0.2 Ag baclofen when compared with control at 30 min post-injection (Fig. 2A; F(3,30) = 3.219, p < 0.05). In contrast to broiler chicks, the Fig. 1. Food intake of (A) broiler and (B) Leghorn chicks injected ICV with saline or one of three doses of muscimol (0.1, 0.2 or 0.5 Ag). Values are means F S.E.M. The number of chicks used is shown in parentheses. *P < 0.05, compared with saline control. (B) Food intake (g/30 min) = 0.41(S.E. 0.10) + 3.67(S.E. 1.18)X 6.38(S.E. 2.15)X 2 , R2 = 0.318, P < 0.05.
that the average body weight was as uniform as possible for each treatment. The birds were reared individually in experimental cages and had ad libitum access to food up to the time of treatments. Birds were given free access to food for 30 min immediately after each treatment. In Experiments 1 (Cobb; 2-day-old) and 2 (SCWL; 3-day-old), saline or muscimol (GABAA agonist; 0.1, 0.2 or 0.5 Ag) was injected once intracerebroventricularly (ICV) into the lateral ventricle. In Experiments 3 (Cobb; 3-day-old) and 4 (SCWL; 4-dayold), birds were injected by the ICV route with four levels (0, 0.05, 0.1 and 0.2 Ag) of baclofen (GABAB agonist). In Experiments 5 (Cobb; 3-day-old) and 6 (SCWL; 3-dayold), birds were injected by the ICV route with three levels (0, 0.2 and 0.4 mg) of nipecotic acid (GABA uptake inhibitor). Muscimol and baclofen were both purchased from Sigma (St. Louis, MO, USA). ( F )-Nipecotic acid was purchased from Research Biochemicals International (Natick, MA, USA). Drugs were dissolved in a 0.1% Evans Blue solution, which was prepared in a 0.85% saline. Saline containing Evans Blue was used as a control. The birds were injected ICV using a microsyringe according to the methods used by Davis et al. [6] and Furuse et al. [13].
Fig. 2. Food intake of (A) broiler and (B) Leghorn chicks injected ICV with saline or one of three doses of baclofen (0.05, 0.1 or 0.2 Ag). Values are means F S.E.M. The number of chicks used is shown in parentheses. *P < 0.05, compared with saline control. (A): Food intake (g/30 min) = 0.71(S.E. 0.12) 2.59(S.E. 0.94)X, R2 = 0.192, P < 0.01. (B) Food intake (g/ 30 min) = 0.29(S.E. 0.10) + 3.47(S.E. 0.93)X, R2 = 0.303, P < 0.001.
T. Bungo et al. / Brain Research 993 (2003) 235–238
ICV injection of baclofen stimulated food consumption in a dose-dependent manner and food intake in SCWL chicks increased significantly with 0.2 Ag baclofen when compared with control at 30 min post-injection (Fig. 2B; F(3,30) = 4.354, p < 0.05). The effect of ICV administration of nipecotic acid (0.2 or 0.4 mg) on food consumption in chicks fed ad libitum over a 30-min period is shown in Fig. 3. Each level of nipecotic acid failed to stimulate food intake in broiler chicks during the 30-min period when compared with control (Fig. 3A: p>0.05). On the other hand, the ICV injection of nipecotic acid stimulated food consumption in a dose-dependent manner and food intake in SCWL chicks increased significantly with 0.4 mg nipecotic acid when compared with control at 30 min post-injection (Fig. 3B; F(2.14) = 4.185, p < 0.05). The present results show that central injection of muscimol, GABAA agonist, stimulated feeding behavior in SCWL chicks (Fig. 1B), which is in good agreement with other reports in mammals [1,21] and avians [6,16]. On the other hand, muscimol tended to stimulate feeding, but no significant difference was obtained in broiler chicks (Fig. 1A). However, GABAA antagonist (bicuculline) decreased food intake in broiler chicks (unpublished data). Additionally, although there was no systematic attempt to quantify
Fig. 3. Food intake of (A) broiler and (B) Leghorn chicks injected ICV with saline or one of two doses of baclofen (0.2 or 0.4 mg). Values are means F S.E.M. The number of chicks used is shown in parentheses. *P < 0.05, compared with saline control. (B): Food intake (g/30 min) = 0.43(S.E. 0.12) + 1.30(S.E. 0.45)X, R2 = 0.359, P < 0.05.
237
other behavioral measurement, frequency of pecking in broiler chicks accelerated with muscimol for a short span of time. It seemed that there may be GABAA receptormediated feeding regulation in broiler chicks and duration of efficacy of muscimol in broilers may be shorter than that in layers. Similar to this, we found that duration of efficacy of glutamate in broilers was shorter than that in layers [3]. It is reported that the injection of baclofen, GABAB agonist, induced an eating response in mammals [10,11]. Central injection of baclofen stimulated feeding in SCWL chicks (Fig. 2B), which was similar to that observed in mammals. However, a diametrically opposed effect was observed in broiler chicks (Fig. 2A). As for the difference between broiler and layer chicks on GABAB receptormediated feeding regulation, it has been reported also that the anorexic effect of L-pipecolic acid, GABA uptake inhibitor, was attenuated significantly by co-injection of GABAB antagonist in fasted broiler chicks, but not layer chicks [26]. These results indicated that the role of GABAB receptor might be influenced by genetic selection. The reason for these different responses is not clear, but some hypotheses are proposed. First, it is likely that distribution and/or number of GABAB receptors in broiler chicks may differ from SCWL chicks. It has been demonstrated that the action site of GABAB agonist in the central nervous system has different effects, e.g. microinjection of baclofen into the amygdala [19] and the lateral hypothalamus [17] decreased food intake while injections into the nucleus accumbens shell [25,29] increased food intake in the rat. Second, it was supposed that the effect of baclofen on the release and/or synthesis of neurotransmitters (or neuromodulators) which affect feeding regulation in broiler chicks may differ from that in SCWL chicks. It is reported that GABAB receptors might be present presynaptically to reduce evoked release of transmitters such as GABA, glutamate, and substance P [2,15]. As regards synthesis, Coscina et al. [4] reported that intracisternal injection of GABA agent elevated levels of taurine in the brain of obese, but not of lean Zucker rats. Actually, it is known that taurine may have a neurotransmitter (or neuromodulatory) role in some parts of the nervous system [18]. Recently, it was reported that food intake in SCWL chicks was increased by L-pipecolic acid under ad libitum feeding [27]. Additionally, the orexigenic effect of L-pipecolic acid is mediated by both GABA A and GABAB receptors [27]. The central injection of nipecotic acid, which inhibits uptake of GABA [9,18] and leads to higher extracellular concentration of GABA, in SCWL chicks was the induction of hyperphagia (Fig. 3B). Similar to L-pipecolic acid, it seemed that the higher concentration of GABA by nipecotic acid might contribute to this effect via both GABA receptors. On the other hand, nipecotic acid failed to stimulate feeding behavior in broiler chicks (Fig. 3B). The cause may be the difference between broiler and layer chicks on GABAB receptor-mediated feeding regulation, as mentioned above.
238
T. Bungo et al. / Brain Research 993 (2003) 235–238
In meat-type (broiler) chickens, it has been demonstrated that muscimol increased food intake but baclofen did not have any affect [16]. There is the possibility that the density of GABA receptors in the brain may alter with age. Furthermore, handling of chicks has been shown to decrease forebrain GABA receptors and in vitro GABA release from brain tissues [12]. In the case of chicken study [16], a surgical procedure to attach the guide cannula for ICV injection was done before the experiments. This procedure may alter the potency of GABA agents between chickens and neonatal chicks. Further research on the density of GABA receptors and the concentration of GABA at each site in chick brains is needed to understand the role of GABA in central regulation of appetite in avian species. However, the results described here suggest that both GABA receptors play important roles in the control of neonatal chicks with strain differences.
Acknowledgements This work was supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science.
References [1] B.A. Baldwin, I.S. Ebenezer, C. De La Riva, Effects of intracerebroventricular injection of muscimol or GABA on operant feeding in pigs, Physiol. Behav. 48 (1990) 417 – 421. [2] N.G. Bowery, S.J. Enna, g-Aminobutyric acidB receptors: first of the functional metabotropic heterodimers, J. Pharmacol. Exp. Ther. 292 (2000) 2 – 7. [3] T. Bungo, S. Yoshinaga, H. Ueda, Intracerebroventricularly administered excitatory amino acids: effects on feeding behavior in chicks, J. Appl. Anim. Res. 22 (2002) 161 – 168. [4] D.V. Coscina, T.W. Castonguay, J.S. Stern, Effect of increasing brain GABA on the meal patterns of genetically obese vs. lean Zucker rats, Int. J. Obes. 16 (1992) 425 – 433. [5] A. Csillag, M.G. Stewart, E.M. Curtis, GABAergic structures in the chick telencephalon: GABA immunocytochemistry combined with light and electron microscope autoradiography and golgi impregnation, Brain Res. 437 (1987) 283 – 297. [6] J.L. Davis, D.T. Masuoka, J.F. Gerbrandt, A. Cherkin, Autoradiographic distribution of L-proline in chicks after intracerebral injection, Physiol. Behav. 22 (1979) 693 – 695. [7] C. Decavel, A.N. Van den Pol, GABA: a dominant neurotransmitter in the hypothalamus, J. Comp. Neurol. 302 (1990) 1019 – 1037. [8] D.M. Denbow, Induction of food intake by a GABAergic mechanism in the turkey, Physiol. Behav. 49 (1990) 485 – 488. [9] J.L. do Nascimento, A.L. Ventura, R. Paes de Carvalho, Veratridineand glutamate-induced release of [3H]-GABA from cultured chick retina cells: possible involvement of a GAT-1-like subtype of GABA transporter, Brain Res. 798 (1998) 217 – 222.
[10] I.S. Ebenezer, The effect of intracerebroventricular administration of baclofen on food intake in rats, NeuroReport 1 (1990) 73 – 76. [11] I.S. Ebenezer, B.A. Baldwin, Effect of intracerebroventricular administration of GABAB receptor agonist baclofen on operant feeding in satiated pigs, Br. J. Pharmacol. 101 (1990) 559 – 562. [12] E. Fluck, S. Hogg, R.B. Jones, R. Bourne, S.E. File, Changes in Tonic immobility and the GABA-benzodiazepine system in response to handling in the chick, Pharmacol. Biochem. Behav. 58 (1997) 269 – 274. [13] M. Furuse, R. Ando, T. Bungo, R. Ao, M. Shimojo, Y. Masuda, Intracerebroventricular injection of orexins does not stimulate food intake in neonatal chicks, Br. Poult. Sci. 40 (1999) 698 – 700. [14] R.H. Granda, W.J. Grossland, GABA-like immunoreactivity of neurons in the chicken diencephalon and mesencephalon, J. Comp. Neurol. 287 (1989) 455 – 469. [15] J.S. Isaacson, J.M. Solis, R.A. Nicoll, Local and diffuse synaptic action of GABA in the hippocampus, Neuron 10 (1993) 165 – 175. [16] H. Jonaidi, V. Babapour, D.M. Denbow, GABAergic control of food intake in the meat-type chickens, Physiol. Behav. 76 (2002) 465 – 468. [17] J. Kelly, J. Rothstein, S.P. Grossman, GABA and hypothalamic feeding system: 1. Topographic analysis of the effects of microinjections of muscimol, Physiol. Behav. 23 (1979) 1123 – 1134. [18] Z.L. Kruk, C.J. Pycock (Eds.), Inhibitory Amino Acids: GABA, Glycine and Taurine, 3rd ed., Neurotransmitters and Drugs, Chapman & Hall, New York, 1991, pp. 142 – 158. [19] F.G. Minano, S.M.S. Meneres, M. Sancibrian, P. Salinas, GABAA receptor in amygdala: role in feeding in fasted and satiated rats, Brain Res. 586 (1992) 104 – 110. [20] V.R. Olgiati, C. Netti, F. Guidobono, A. Pecile, The central GABAergic system and control of food intake under different experimental conditions, Psychopharmacology (Berlin) 68 (1980) 163 – 167. [21] S. Pu, M.R. Jain, T.L. Horvath, S. Diano, P.S. Kalra, S.P. Kalra, Interactions between neuropeptide Y and gamma-aminobutyric acid in stimulation of feeding: a morphological and pharmacological analysis, Endocrinology 140 (1999) 933 – 940. [22] J.R. Seone, F. Dumont, C.L. Girard, L. Bedard, J.J. Matte, Effects of intraventricular injections of gamma-aminobutyric acid and related substances on feeding behavior in satiated sheep, Can. J. Physiol. Pharm. 62 (1984) 1296 – 1299. [23] L. Sivilotti, A. Nistri, GABA receptor mechanisms in the central nervous system, Prog. Neurobiol. 36 (1991) 35 – 92. [24] M.G. Stewart, R.C. Bourne, J. Chmielowska, M. Kalman, A. Csillag, D. Stanford, Quantitative autoradiographic analysis of the distribution of [3H] muscimol binding to GABA receptors in chick brain, Brain Res. 456 (1988) 387 – 391. [25] T.R. Stratford, A.E. Kelley, GABA in the nucleus accumbens shell participates in the central regulation of feeding behavior, J. Neurosci. 17 (1997) 4434 – 4440. [26] T. Takagi, T. Bungo, E.-S. Saito, T. Tachibana, S. Saito, I. Yamasaki, S. Tomonaga, D.M. Denbow, M. Furuse, Intracerebroventricular administration of GABA-A and GABA-B receptor antagonists attenuate feeding and sleeping-like behavior induced by L-pipecolic acid in the neonatal chicks, J. Neurosci. Res. 73 (2003) 270 – 275. [27] T. Takagi, T. Tachibana, E.-S. Saito, S. Tomonaga, S. Saito, T. Bungo, D.M. Denbow, M. Furuse, Central pipecolic acid increases food intake under ad libitum feeding conditions in the neonatal chicks, Neurosci. Lett. 347 (2003) 93 – 96. [28] S. Tsujii, G.A. Bray, GABA-related feeding control in genetically obese rats, Brain Res. 540 (1991) 48 – 54. [29] B.O. Ward, E.M. Somerville, P.G. Clifton, Intraaccumbens baclofen selectively enhances feeding behavior in the rat, Physiol. Behav. 68 (2000) 463 – 468.