- Email: [email protected]
Sucrose intake: Increase in non-stressed rats and reduction in chronically stressed rats are both prevented by the gamma-hydroxybutyrate (GHB) analogue, GET73
Pharmacological Research 57 (2008) 464–468
Contents lists available at ScienceDirect
Pharmacological Research journal homepage: www.elsevier.com/locate/yphrs
Sucrose intake: Increase in non-stressed rats and reduction in chronically stressed rats are both prevented by the gamma-hydroxybutyrate (GHB) analogue, GET73 Raffaella Tacchi a , Anna Ferrari a , Antonella Loche b , Alfio Bertolini a,∗ a b
Department of Diagnostic Services, Section of Clinical Pharmacology, School of Medicine, University of Modena and Reggio Emilia, Largo del Pozzo 71, 41100 Modena, Italy Laboratorio Farmaceutico CT, 18038 Sanremo, Italy
a r t i c l e
i n f o
Article history: Accepted 15 May 2008 Keywords: Chronic stress Gamma-hydroxybutyrate (GHB) analogue N-(4-Trifluoromethylbenzyl)-4methoxybutanamide (GET73) Rat Sucrose preference Sucrose intake
a b s t r a c t It has been previously shown that the gamma-hydroxybutyrate analogue N-(4-trifluoromethylbenzyl)4-methoxybutanamide (GET73) inhibits consumption and reinforcing effect of palatable food, in rats, at doses that have no detrimental effect on open-field behaviour. Here we show that GET73 is also able to prevent both the development of preference for a sucrose solution in non-stressed rats, and the reduction of preference for a sucrose solution induced by the daily exposure to continuously varied mildly stressful situations. Adult male Wistar Kyoto rats (180–190 g) were subjected to chronic unpredictable mild stress. Other rats of the same sex and strain were used to study the development of preference for a sucrose solution. Daily exposure to continuously varied mildly stressful situations produced a reduction of sucrose solution intake that started the 3rd week, and such reduction became highly significant during the 5th week. Treatment with GET73 (10 mg kg−1 , 50 mg kg−1 or 100 mg kg−1 once daily per os) produced a more evident reduction of sucrose solution intake during the 2nd and 3rd week, but during the 4th and 5th weeks the intake dose-dependently increased to values that, for the dose of 100 mg kg−1 , were not significantly different from those of non-stressed, vehicle-treated rats. In the same range of doses GET73 dose-dependently prevented the development of preference for a sucrose solution in non-stressed rats. The present data indicate that rats treated with GET73 do not develop the “depression-like” condition produced by the daily exposure, for several weeks, to continuously and unpredictably varied stressful situations in a valid (face, predictive, and construct validity) “depression” model. Moreover, GET73 prevents the development of preference for a sucrose solution in non-stressed rats. Concurrently, present and previous data suggest that GET73 “stabilize” the behaviour of rats, either preventing the development of a “depression-like” condition in a continuously stressful environment, or the rewarding effect of alcohol, sucrose, and palatable food. © 2008 Elsevier Ltd. All rights reserved.
1. Introduction Gamma-hydroxybutyric acid (GHB), a short-chain fatty acid, is an endogenous constituent of the mammalian brain, mostly deriving from a small portion of GABA metabolism [1]. Abundant data indicate that GHB functions as a neurotransmitter in the central nervous system, where it is unevenly distributed [2]. High affinity GHB binding sites have been localized in specific brain structures, including hippocampus, cortex, thalamus, amygdala, as well as dopaminergic nuclei (substantia nigra and ventral tegmental area) and regions receiving dopaminergic terminals (olfactory bulbs and
∗ Corresponding author. Tel.: +39 0594224064; fax: +39 0594224069. E-mail address: alfi[email protected] (A. Bertolini). 1043-6618/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.phrs.2008.05.004
tubercles, nucleus accumbens and caudate putamen) [3,4]. The GHB receptor has been cloned [4]. At higher concentrations, GHB also binds GABA B receptors [5,6]. When exogenously administered in pharmacological doses, GHB exerts different effects, including anxiolysis and protection against head injuries and global or focal brain ischemia [7–11]. Moreover, GHB has long been used for the treatment of alcohol dependence [12,13]. Indeed, treatment with GHB has been reported to effectively decrease alcohol craving and consumption as well as alcohol withdrawal symptoms in alcoholics [12]. Several lines of evidence indicate that GHB exerts its antialcohol effects by a substitution mechanism [13]. We have recently reported that a gamma-hydroxybutyrate (GHB) analogue, the N-(4-trifluoromethylbenzyl)-4-methoxybutanamide (GET73), besides producing a stronger and longer-lasting
R. Tacchi et al. / Pharmacological Research 57 (2008) 464–468
inhibition of alcohol intake than GHB, specifically attenuates the rewarding and incentive properties of varied and highly palatable food, and its consumption [14]. In a dose range (50–200 mg kg−1 , orally) that produced no detrimental effect on open-field behaviour (but rather an increase in ambulation and rearing and a decrease of fecal boluses: a picture that is considered expression of disinhibition) GET73 inhibited in fact both acquisition and expression of palatable food-induced conditioned place preference. Moreover, it reduced the consumption of palatable food, while that of standard (and hence humdrum and not particularly palatable) chow was increased. Palatability (particularly taste and smell), pleasantness and variety of foods are strong modulators of food reward. They are the main responsible for the gratification produced by palatable food and “snack foods” and are considered to be the major reason for overeating, and hence for overweight and obesity [15–22]. The inability to experience gratification and pleasure from otherwise gratifying and rewarding stimuli of intrinsic hedonic value – as sweetened (or salty), high-fat, palatable and varied foods are – is considered to be one of the distinctive, cardinal symptoms of depression (DSM IV-R). Thus, the influence of GET73 on the consumption of alcohol and rewarding and incentive properties of palatable food might suggest a sort of “anhedonizing” effect of this drug, and prompted us to study its possible influence on the development of a “depressionlike” condition, using the “chronic mild stress-induced anhedonia” model [23-31]. We evaluated whether GET73 hastens the decrease of the consumption of a sucrose solution by rats subjected to the “chronic mild stress-induced anhedonia” model and, on the other hand, whether it prevents the development of preference for a sucrose solution in non-stressed rats. 2. Materials and methods 2.1. Animals Adult male rats of a Wistar Kyoto strain were purchased from Harlan Italy (Correzzana, Milano). Upon arrival their weight was 180–190 g. Before being used for the experiments they were housed two per cage (40 cm × 21 cm × 15 cm) with food in pellets (TRM, Harlan Tecklab) and tap water freely available, under the temperature (22 ± 1 ◦ C), humidity (60%) and ventilation conditions advised by the European Community Ethical Regulations on the care of animals for scientific research (CEE Council 86/609; Italian D.L. 27/01/92 no. 116), on a 12 h:12 h light/dark cycle (lights on at 05:00 a.m., and off at 05:00 p.m.). The research protocol was approved by the Animal Experimentation Ethical Committee of the University of Modena and Reggio Emilia. After 1 week of adaptation, rats were placed in sound-proof rooms, in single cages, for the behavioural experiments. 2.2. Drug N-(4-Trifluoromethylbenzyl)-4-methoxybutanamide, kindly provided by GET S.r.l. (Sanremo, Italy), was suspended in vehicle [0.5% solution of methylcellulose (methocell Sigma, Milano, Italy) in distilled water] shortly before administration. 2.3. Influence of GET73 on the chronic unpredictable mild stress-induced anhedonia model 2.3.1. Procedure We used an established model of depression, (the chronic unpredictable mild stress) [27] with minor modifications [32,36,37]. Rats
465
were first trained to experience and drink a sweet beverage, by presenting them simultaneously with two identical bottles: during the first 24 h both bottles contained a 1% sucrose solution; during the subsequent 24 h one bottle contained the sucrose solution, the other contained tap water. Following a 23 h food and water deprivation, rats received the first baseline sucrose preference test: each animal was presented simultaneously with two pre-weighed bottles, one containing the sucrose solution, the other tap water. Both bottles were removed and weighed at 60 min (end of the test). Then, animals were given food and water for 2 h. After another period (21 h) of food and water deprivation, animals received a second baseline sucrose preference test (24 h after the first one). Four days thereafter, following 24 h food and water deprivation, animals received a third baseline sucrose preference test. These baseline tests and the subsequent sucrose preference tests were timetabled at the start of the dark phase (05:00–06:00 p.m.) and always occurred in the home cage of the rat. Following the third baseline test, animals were divided into five groups, each consisting of 10 rats, matched on the basis of their mean sucrose intake in the second and third baseline tests, so that means ± S.E. mean of the sucrose intakes were not significantly different among the different groups. Four groups were exposed during the following weeks to the chronic mild stress regime; one group was not stressed, other than the food and water deprivation that preceded each sucrose preference test, and was housed in a separate sound-proof room. The stress regime used in the 1st week consisted of: one 15 h period of paired housing immediately after the third baseline sucrose preference test; one 8 h period of low intensity stroboscopic illumination; one 16 h period in a soiled cage (200 ml water in sawdust bedding); one 8 h period of food deprivation; one 16 h period of water deprivation (bottle withdrawal) followed by one 8 h period of exposure to an empty water bottle; one 16 h period of 45◦ cage tilt; one 8 h period of low intensity stroboscopic illumination; one 16 h period of continuous (also overnight) illumination; one 8 h period of paired housing; one 24 h period of intermittent lighting (off/on every 2 h); one 24 h period of food and water deprivation preceding the 1 h sucrose preference test. The same stressors were administered the following weeks, but their sequence was at random, in order to be completely unpredictable to the animal. Sucrose consumption was measured, with the above-described procedure, at weekly intervals, in 1 h tests following 24 h food and water deprivation. The protocol is shown in detail in Table 1
Table 1 Chronic unpredictable mild stress protocol Monday 18.00—commence 15 h of paired housing Tuesday 09.00—commence 8 h of low intensity stroboscopic illumination Tuesday 17.00—switch off strobe light: commence 16 h soil bedding Wednesday 09.00—dry bedding; commence 8 h of food deprivation Wednesday 17.00—restore food; commence 16 h of water deprivation Thursday 09.00—offer empty water bottle for 8 h Thursday 17.00- restore water; tilt cages for 16 h Friday 09.00—untilt cages; commence 8 h of low intensity stroboscopic illumination Friday 17.00—switch off strobe light; switch lights to on overnight Saturday 09.00—commence 8 h of paired housing Saturday 17.00—commence 24 h of intermittent lighting (off/on every 2 h) Sunday 17.00—switch off intermittent lighting; commence 24 h of food and water deprivation preceding the 1 h sucrose preference test Monday 17.00—commence the 1 h sucrose preference test Stressors’ sequence during the 1st week. The same stressors were administered the following weeks, but their sequence was at random, in order to be completely unpredictable to the animal.
466
R. Tacchi et al. / Pharmacological Research 57 (2008) 464–468
2.3.2. Treatment The four groups of rats exposed to the daily stresses were randomly assigned to one of the following daily treatments by oral gavage (p.o.) starting on the 1st day of exposure to the chronic mild stress regime: (1) GET73, 10 mg kg−1 ; (2) GET73, 50 mg kg−1 ; (3) GET73, 100 mg kg−1 ; (4) vehicle, 2 ml kg−1 . The group of non-stressed rats was treated daily p.o. with 2 ml kg−1 of the vehicle. The doses of GET73 were chosen on the basis of its activity on palatable food intake [14]. 2.4. Influence of GET73 on sucrose intake in non-stressed rats In order to assess the possible influence of GET73 per se on sucrose intake, its effect on non-stressed animals with daily access to a 1% sucrose solution was studied. 2.4.1. Procedure Rats of the above-quoted Wistar Kyoto strain were randomly assigned to three groups, each consisting of 10 animals, housed in single cages, in a sound-proof room, with food in pellets (TRM, Harlan Tecklab) freely available, and on a 12 h light/dark cycle (lights on at 06:00 a.m., and off at 06:00 p.m.). They had free access to two identical bottles, whose position in the cage was inverted every day, one containing tap water and the other a 1% sucrose solution. The two bottles were withdrawn at 06:00 p.m. and replaced at 08:00 a.m. of the following day, and the amount of water and of sucrose solution drunk during the first hour was measured by weighing the bottles at 09:00 a.m. 2.4.2. Treatment These three groups of non-stressed rats were randomly assigned to one of the following daily treatments (p.o.) for 8 consecutive days: (1) GET73, 10 mg kg−1 ; (2) GET73, 100 mg kg−1 ; (3) vehicle, 2 ml kg−1 . 2.5. Statistical analysis Data are presented as means ± S.E.M. of the percentage of sucrose solution intake with respect to total fluid intake (=sucrose solution + plain water), and were analyzed using repeated measures ANOVA followed by subsequent one-way ANOVA and Student–Newman–Keuls post-hoc test. In experiment 1 (influence of GET73 on the chronic unpredictable mild stress-induced anhedonia) data obtained in stressed rats treated with GET73 (10 mg kg−1 , 50 mg kg−1 or 100 mg kg−1 ) were compared either with data obtained in stressed rats treated with the vehicle or with data obtained in non-stressed rats treated with the vehicle. In experiment 2 (influence of GET73 on sucrose intake in nonstressed rats) data obtained in rats treated with GET73 (10 mg kg−1 or 100 mg kg−1 ) were compared with data obtained in rats treated with the vehicle. Results were considered statistically significant when p < 0.05. 3. Results 3.1. Influence of GET73 on the sucrose consumption, measured at weekly intervals, in rats exposed to daily unpredictable mild stressors The mean baseline consumption of the sucrose solution, calculated with the data obtained in the second and third baseline sucrose preference test, was 7.3 ± 0.3 g, while the mean consumption of water was 3.1 ± 0.2 g.
Fig. 1. Influence of GET73 on sucrose solution intake in Wistar Kyoto male rats exposed to chronic mild stress. GET73 (10 mg kg−1 , 50 mg kg−1 or 100 mg kg−1 ) or vehicle were orally administered daily starting on the 1st day of stress exposure. The intake of sucrose solution is expressed as % over the total amount of fluid intake (sucrose solution + plain water) (sucrose preference). One group of non-stressed rats were orally daily treated with vehicle. Data are means (±S.E.mean) from 10 animals per group. GET73, at any dosage, produced at first a decrease in the consumption of sucrose solution, that was significant after 3 weeks of daily exposure to mild stressors; starting from the 4th week, GET73 produced a dose-dependent restoration of sucrose preference that, in rats treated with the highest dose (100 mg kg−1 ), was not different from that observed in non-stressed rats treated with the vehicle. (*) p < 0.05 vs. vehicle non-stressed group; (䊉) p < 0.05 vs. vehicle + stress group; ANOVA followed by Student–Newman–Keuls test.
The preference for the sucrose solution tended to increase in non-stressed rats treated with the vehicle: at the end of the 5th week their mean consumption of sucrose solution was 8.6 ± 0.2 g while their mean consumption of water was 2.3 ± 0.1 g. On the other hand, in rats daily exposed to an unpredictable sequence of mild stressors and treated with the vehicle, the consumption of sucrose solution decreased starting after the 3rd week: at the end of the experiment (5th week) the mean consumption of sucrose solution of these rats was 4.9 ± 0.3 g, and that of water was 4.9 ± 0.2 g. (Fig. 1) The treatment with GET73 at any dosage (10 mg kg−1 , 50 mg kg−1 or 100 mg kg−1 ) produced at first a decrease in the consumption of sucrose solution that was significant after 3 weeks of exposure to chronic mild stressors; starting from the 4th week, however, GET73 produced a dose-dependent restoration of sucrose preference that, in rats treated with 100 mg kg−1 , was not significantly different from that observed in non-stressed, vehicle-treated rats starting from the 4th week [3rd week: F(4,45) = 24.53, p = 0.000; 4th week: F(4,45) = 38.18, p = 0.000; 5th week: F(4,45) = 206.85, p = 0.000] (Fig. 1). 3.2. Influence of GET73 on the sucrose consumption, measured daily, in non-stressed rats In non-stressed rats with free choice of tap water or 1% sucrose solution, the sucrose preference almost steadily increased during the 8 days of observation (Fig. 2). The mean consumption of the 1% sucrose solution, measured during the first hour after a 14 h deprivation, was 5.7 ± 1.0 g on day 1 and 8.8 ± 0.9 g on day 8; on the other hand, the mean consumption of water, still measured during the first hour after a 14 h deprivation, was 4.3 ± 0.8 g on day 1, and 2.4 ± 0.2 g on day 8. GET73, daily administered p.o. at the doses of 10 mg kg−1 or 100 mg kg−1 , dose-dependently prevented the development of the sucrose preference: the amount of sucrose solution intake was significantly reduced (in comparison to vehicle-treated rats) starting from day 2, and was 6.1 ± 0.4 g on day 8 in rats treated with the dose of 10 mg kg−1 , whereas in rats treated with the dose of 100 mg kg−1
R. Tacchi et al. / Pharmacological Research 57 (2008) 464–468
Fig. 2. Influence of GET73 on the intake of sucrose solution in male Wistar Kyoto non-stressed rats. GET73 (10 mg kg −1 or 100 mg kg −1 ) or vehicle were orally administered daily. Data are means ± S.E.M from 10 animals per group. GET73 dosedependently and significantly inhibited the acquisition of preference for the sucrose solution, compared with vehicle-treated rats, as evidenced by the lack of increase in % sucrose consumed over the 8-day test period. (*) p < 0.05 vs. the corresponding value of the vehicle-treated group; ANOVA followed by Student–Newman–Keuls test.
the amount of sucrose solution intake never increased: on day 8, it was 5.2 ± 0.4 g, quite similar to the intake of water (5.1 ± 0.4 g) [2nd day: F(2,27) = 27.76, p = 0.000; 3rd day: F(2,27) = 83.60, p = 0.000; 4th day: F(2,27) = 68.47, p = 0.000; 5th day: F(2,27) = 64.60, p = 0.000; 6th day: F(2,27) = 99.19, p = 0.000; 6th day = F(2,27) = 108.30, p = 0.000; 8th day: F(2,27) = 127.54, p = 0.000] (Fig. 2). 4. Discussion The data obtained in our present study show that the gammahydroxybutyrate analogue GET73 dose-dependently prevents the development of preference for sucrose in normal rats and, in the same dose range, the reduced preference for sucrose produced in a model of “depression” (the “chronic mild stress-induced anhedonia”) [27], that is widely used, albeit subject to some criticisms [33–35]. We introduced some modifications into the original model, on the basis of our previous experience [32,36]. So, we discarded some stressors (white noise, novel odours and presence of a foreign object in the home gage) that in our experimental conditions were too weak and insufficiently stressful, and concurrently reduced the density of food deprivation periods (that may cause weight loss that is not strictly stress-linked) (in the present experiments, the body weight of rats subjected to stressors, either treated with GET73 or with the vehicle, did not significantly change during the 5 weeks of observation). Moreover, according to D’Aquila et al. [37], sucrose preference tests were carried out at the start of the animals’ dark cycle. Previous studies performed in our laboratory and also in other laboratories have shown that GET73 potently and effectively inhibits, for several hours after administration, either alcohol intake [G. Colombo, personal communication] in a strain of alcohol-preferring rats (Sardinian alcohol preferring) [38] or the consumption of highly palatable and varied foods in normal rats [14]. These effects of GET73 are observed with doses in the range of those used in the present study, and that have been shown to produce no detrimental effect on the gross behaviour and motor activity of rats. The present research was undertaken in order to ascertain whether GET73 may have a sort of “anhedonizing” effect, that could explain the inhibition of alcohol intake and of palatable diet consumption. In fact, in the chronic mild stress model, dur-
467
ing the first 3 weeks, GET73 seems to favour the development of “anhedonia”: on the 3rd weekly test of sucrose intake, the rats treated with any dose of GET73 drink less sucrose solution than stressed and vehicle-treated rats. But while in the latter the amount of sucrose solution intake significantly and steadily decreases in the 4th and 5th weekly test of sucrose intake, in the former (in spite of the persistence of the daily exposure to unpredictable stressors) the amount of sweet solution intake dose-dependently increases starting from the 4th week and, in rats treated with the highest dose of GET73 (100 mg kg−1 ), becomes similar to that of non-stressed vehicle-treated rats. That is, in this test GET73 has a biphasic effect: “anhedonizing” during the first 3 weeks of treatment, and “antidepressant” starting from the 4th week of treatment. On the other hand, GET73 dose-dependently prevents the development of sucrose preference daily assessed in normal, nonstressed rats with free choice of sucrose solution or tap water: rats treated with the highest dose of GET73 (100 mg kg−1 ) indifferently drink water or sucrose solution, without any preference for the latter. This effect is consistent with the previous results concerning the effect of GET73 on palatable diet consumption [14]. Preliminary experiments performed in the course of that study had ruled out a possible effect of GET73 on taste. Thus, it would seem that for treatments lasting up to 3 weeks, GET73 inhibits the effect of rewarding stimuli and potentiates the anhedonizing effect of a steadily stressful environment, while when administered for a longer time an effect typical of antidepressant treatments is observed. So far available data on the neurochemical effects of GET73 have been obtained with acute administrations (Tanganelli et al, submitted). Studies on the effects of repeated administrations for several weeks, which would be suitable for an interpretation of our present behavioural results, are on the other hand still in progress. Thus, only a tentative explanation can be tried. Particularly intriguing is the fact that (i) for treatments not exceeding 2–3 weeks, GET73 dose-dependently inhibits the intake of a sucrose solution, either under normal conditions or in the presence of continuously varied mildly stressful situations (present data), as well as the consumption of palatable food under normal housing conditions (our previous data) [14]; whereas (ii) for treatments of longer duration (more than 3 weeks) the opposite effect is observed, at least as concerns the preference for a sucrose solution in an experimental condition that models a depression state (present data). As if short-lasting treatments with GET73 would inhibit reward systems (or activate aversive systems), while longer-lasting treatments would produce an opposite effect by up- (or down-) regulating the same systems. Concurrently, present and previous data suggest that GET73 “stabilize” the behaviour of rats, either preventing the development of a “depression-like” condition in a continuously stressful environment, or the rewarding effect of alcohol, sucrose, and palatable food. Acknowledgement The technical assistance of Alessandra Ottani is acknowledged. References [1] Roth RH, Doherty JD, Walters JR. Gamma-hydroxybutyrate: a role in the regulation of central dopaminergic neurons? Brain Res 1980;189:556–60. [2] Maitre M. The gamma-hydroxybutyrate signalling system in brain: organization and functional implications. Prog Neurobiol 1997;51:337–61. [3] Hechler V, Gobaille S, Maitre M. Selective distribution pattern of gammahydroxybutyrate receptors in the rat forebrain and midbrain as revealed by quantitative autoradiography. Brain Res 1992;572:345–8.
468
R. Tacchi et al. / Pharmacological Research 57 (2008) 464–468
[4] Andriamampandry C, Taleb O, Viry S, Muller C, Humbert JP, Gobaille S, et al. Cloning and characterization of a rat brain receptor that binds the endogenous neuromodulator gamma-hydroxybutyrate (GHB). FASEB J 2003;17:1691–3. [5] Castelli MP, Mocci I, Langlois X, Gommerendagger W, Luyten WH, Leysen JE, et al. Quantitative autoradiographic distribution of gamma-hydroxybutyric acid binding sites in human and monkey brain. Mol Brain Res 2000;78:91–9. [6] Mathivet P, Bernasconi R, De Barry J, Marescaux C, Bittiger H. Binding characteristics of gamma-hydroxybutyric acid as a weak but selective GABAB receptor agonist. Eur J Pharmacol 1997;321:67–75. [7] Escuret E, Roquefeuil B, Frerebeau P, Baldy-Moulinier M. Effect of hyperventilation associated with administration of central nervous depressants in brain injuries. Acta Neurol Scand Suppl 1977;64:154–5. [8] Lavyne MH, Hariri RJ, Tankosic T, Babiak T. Effect of low dose gammabutyrolactone therapy on forebrain neuronal ischemia in the unrestrained, awake rat. Neurosurgery 1983;12:430–4. [9] Vergoni AV, Ottani A, Botticelli AR, Zaffe D, Guano L, Loche A, et al. Neuroprotective effect of gamma-hydroxybutyrate in transient global cerebral ischemia in the rat. Eur J Pharmacol 2000;397:75–84. [10] Ottani A, Saltini S, Bartiromo M, Zaffe D, Botticelli AR, Ferrari A, et al. Effect of gamma-hydroxybutyrate in two rat models of focal cerebral damage. Brain Res 2003;986:181–90. [11] Ottani A, Vergoni AV, Saltini S, Mioni C, Giuliani D, Bartiromo M, et al. Effect of late treatment with gamma-hydroxybutyrate on the histological and behavioral consequences of transient brain ischemia in the rat. Eur J Pharmacol 2004;485:183–91. [12] Gallimberti L, Canton G, Gentile N, Ferri M, Cibin M, Ferrara SD, et al. Gammahydroxybutyric acid for treatment of alcohol withdrawal syndrome. Lancet 1989;2:787–9. [13] Agabio R, Carai MA, Lobina C, Pani M, Reali R, Vacca G, et al. Development of short-lasting alcohol deprivation effect in sardinian alcohol-preferring rats. Alcohol 2000;21:59–62. [14] Ottani A, Leone S, Garcia Vergara FB, Tacchi R, Loche A, Bertolini A. Preference for palatable food is reduced by the gamma-hydroxybutyrate analogue GET73, in rats. Pharmacol Res 2007;55:271–9. [15] Jacobson MF, Brownell KD. Small taxes on soft drinks and snack foods to promote health. Am J Public Health 2000;90:854–7. [16] McCrory MA, Suen VM, Roberts SB. Biobehavioral influences on energy intake and adult weight gain. J Nutr 2002;132:3830S–4S. [17] Berthoud HR. Mind versus metabolism in the control of food intake and energy balance. Physiol Behav 2004;81:781–93. [18] Erlanson-Albertsson C. How palatable food disrupts appetite regulation. Basic Clin Pharmacol Toxicol 2005;97:61–73. [19] Treit D, Spetch ML, Deutsch JA. Variety in the flavor of food enhances eating in the rat: a controlled demonstration. Physiol Behav 1983;30:207–11. [20] Sclafani A. Carbohydrate taste, appetite, and obesity: an overview. Neurosci Biobehav Rev 1987;11:131–53.
[21] Rolls BJ, Rowe EA, Rolls ET, Kingston B, Megson A, Gunary R. Variety in a meal enhances food intake in man. Physiol Behav 1981;26:215–21. [22] Sorensen LB, Moller P, Flint A, Martens M, Raben A. Effect of sensory perception of foods on appetite and food intake: a review of studies on humans. Int J Obes Relat Metab Disord 2003;27:1152–66. [23] McKinney WT, Bunney WE. Animal models of depression: review of evidence and implications for research. Arch Gen Psychiatr 1969;21:240–8. [24] Abramson LY, Seligman MEP. Modelling psychopathology in the laboratory: history and rationale. In: Maser JD, Seligman MEP, editors. Psychopatology: experimental models. San Francisco: Freeman; 1978. p. 1–26. [25] Willner P. The validity of animal models of depression. Psychopharmacology 1984;83:1–16. [26] Papp M, Willner P, Muscat R. An animal model of anhedonia: attenuation of sucrose consumption and place preference conditioning by chronic unpredictable mild stress. Psychopharmacology 1991;104:255–9. [27] Willner P, Muscat R, Papp M. Chronic mild stress-induced anhedonia: a realistic animal model of depression. Neurosci Biobehav Rev 1992;16:525–34. [28] Papp M, Moryl E, Willner P. Pharmacological validation of the chronic mild stress model of depression. Eur J Pharmacol 1996;296:129–36. [29] Willner P. Validity, reliability and utility of the chronic mild stress model of depression: a 10-year review and evaluation. Psychopharmacology 1997;134:319–29. [30] Bekris S, Antoniou K, Daskas S, Papadopoulou-Daifoti Z. Behavioural and neurochemical effects induced by chronic mild stress applied to two different rat strains. Behav Brain Res 2005;161:45–59. [31] Willner P. Chronic mild stress (CMS) revisited: consistency and behaviouralneurobiological concordance in the effects of CMS. Neuropsychobiology 2005;52:90–110. [32] Benelli A, Filaferro M, Bertolini A, Genedani S. Influence of S-adenosyl-Lmethionine on chronic mild stress-induced anhedonia in castrated rats. Br J Pharmacol 1999;127:645–54. [33] Matthews K, Forbes N, Reid IC. Sucrose consumption as an hedonic measure following chronic unpredictable mild stress. Physiol Behav 1995;57: 241–8. [34] Forbes NF, Stewart CA, Matthews K, Reid IC. Chronic mild stress and sucrose consumption: validity as a model of depression. Physiol Behav 1996;60:1481–4. [35] Pecoraro N, Reyes F, Gomez F, Bhargava A, Dallmann MF. Chronic stress promotes palatable feeding, which reduces sign of stress: feedforward and feedback effects of chronic stress. Endocrinology 2004;145:3754–62. [36] Genedani S, Saltini S, Benelli A, Filaferro M, Bertolini A. Influence of SAMe on the modifications of brain polyamine levels in an animal model of depression. Neuroreport 2001;12:3939–42. [37] D’Aquila PS, Newton J, Willner P. Diurnal variation in the effect of chronic mild stress on sucrose intake and preference. Physiol Behav 1997;62:421–6. [38] Colombo G. Ethanol drinking behaviour in Sardinian alcohol-preferring rats. Alcohol Alcoholism 1997;32:443–53.
Contents lists available at ScienceDirect
Pharmacological Research journal homepage: www.elsevier.com/locate/yphrs
Sucrose intake: Increase in non-stressed rats and reduction in chronically stressed rats are both prevented by the gamma-hydroxybutyrate (GHB) analogue, GET73 Raffaella Tacchi a , Anna Ferrari a , Antonella Loche b , Alfio Bertolini a,∗ a b
Department of Diagnostic Services, Section of Clinical Pharmacology, School of Medicine, University of Modena and Reggio Emilia, Largo del Pozzo 71, 41100 Modena, Italy Laboratorio Farmaceutico CT, 18038 Sanremo, Italy
a r t i c l e
i n f o
Article history: Accepted 15 May 2008 Keywords: Chronic stress Gamma-hydroxybutyrate (GHB) analogue N-(4-Trifluoromethylbenzyl)-4methoxybutanamide (GET73) Rat Sucrose preference Sucrose intake
a b s t r a c t It has been previously shown that the gamma-hydroxybutyrate analogue N-(4-trifluoromethylbenzyl)4-methoxybutanamide (GET73) inhibits consumption and reinforcing effect of palatable food, in rats, at doses that have no detrimental effect on open-field behaviour. Here we show that GET73 is also able to prevent both the development of preference for a sucrose solution in non-stressed rats, and the reduction of preference for a sucrose solution induced by the daily exposure to continuously varied mildly stressful situations. Adult male Wistar Kyoto rats (180–190 g) were subjected to chronic unpredictable mild stress. Other rats of the same sex and strain were used to study the development of preference for a sucrose solution. Daily exposure to continuously varied mildly stressful situations produced a reduction of sucrose solution intake that started the 3rd week, and such reduction became highly significant during the 5th week. Treatment with GET73 (10 mg kg−1 , 50 mg kg−1 or 100 mg kg−1 once daily per os) produced a more evident reduction of sucrose solution intake during the 2nd and 3rd week, but during the 4th and 5th weeks the intake dose-dependently increased to values that, for the dose of 100 mg kg−1 , were not significantly different from those of non-stressed, vehicle-treated rats. In the same range of doses GET73 dose-dependently prevented the development of preference for a sucrose solution in non-stressed rats. The present data indicate that rats treated with GET73 do not develop the “depression-like” condition produced by the daily exposure, for several weeks, to continuously and unpredictably varied stressful situations in a valid (face, predictive, and construct validity) “depression” model. Moreover, GET73 prevents the development of preference for a sucrose solution in non-stressed rats. Concurrently, present and previous data suggest that GET73 “stabilize” the behaviour of rats, either preventing the development of a “depression-like” condition in a continuously stressful environment, or the rewarding effect of alcohol, sucrose, and palatable food. © 2008 Elsevier Ltd. All rights reserved.
1. Introduction Gamma-hydroxybutyric acid (GHB), a short-chain fatty acid, is an endogenous constituent of the mammalian brain, mostly deriving from a small portion of GABA metabolism [1]. Abundant data indicate that GHB functions as a neurotransmitter in the central nervous system, where it is unevenly distributed [2]. High affinity GHB binding sites have been localized in specific brain structures, including hippocampus, cortex, thalamus, amygdala, as well as dopaminergic nuclei (substantia nigra and ventral tegmental area) and regions receiving dopaminergic terminals (olfactory bulbs and
∗ Corresponding author. Tel.: +39 0594224064; fax: +39 0594224069. E-mail address: alfi[email protected] (A. Bertolini). 1043-6618/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.phrs.2008.05.004
tubercles, nucleus accumbens and caudate putamen) [3,4]. The GHB receptor has been cloned [4]. At higher concentrations, GHB also binds GABA B receptors [5,6]. When exogenously administered in pharmacological doses, GHB exerts different effects, including anxiolysis and protection against head injuries and global or focal brain ischemia [7–11]. Moreover, GHB has long been used for the treatment of alcohol dependence [12,13]. Indeed, treatment with GHB has been reported to effectively decrease alcohol craving and consumption as well as alcohol withdrawal symptoms in alcoholics [12]. Several lines of evidence indicate that GHB exerts its antialcohol effects by a substitution mechanism [13]. We have recently reported that a gamma-hydroxybutyrate (GHB) analogue, the N-(4-trifluoromethylbenzyl)-4-methoxybutanamide (GET73), besides producing a stronger and longer-lasting
R. Tacchi et al. / Pharmacological Research 57 (2008) 464–468
inhibition of alcohol intake than GHB, specifically attenuates the rewarding and incentive properties of varied and highly palatable food, and its consumption [14]. In a dose range (50–200 mg kg−1 , orally) that produced no detrimental effect on open-field behaviour (but rather an increase in ambulation and rearing and a decrease of fecal boluses: a picture that is considered expression of disinhibition) GET73 inhibited in fact both acquisition and expression of palatable food-induced conditioned place preference. Moreover, it reduced the consumption of palatable food, while that of standard (and hence humdrum and not particularly palatable) chow was increased. Palatability (particularly taste and smell), pleasantness and variety of foods are strong modulators of food reward. They are the main responsible for the gratification produced by palatable food and “snack foods” and are considered to be the major reason for overeating, and hence for overweight and obesity [15–22]. The inability to experience gratification and pleasure from otherwise gratifying and rewarding stimuli of intrinsic hedonic value – as sweetened (or salty), high-fat, palatable and varied foods are – is considered to be one of the distinctive, cardinal symptoms of depression (DSM IV-R). Thus, the influence of GET73 on the consumption of alcohol and rewarding and incentive properties of palatable food might suggest a sort of “anhedonizing” effect of this drug, and prompted us to study its possible influence on the development of a “depressionlike” condition, using the “chronic mild stress-induced anhedonia” model [23-31]. We evaluated whether GET73 hastens the decrease of the consumption of a sucrose solution by rats subjected to the “chronic mild stress-induced anhedonia” model and, on the other hand, whether it prevents the development of preference for a sucrose solution in non-stressed rats. 2. Materials and methods 2.1. Animals Adult male rats of a Wistar Kyoto strain were purchased from Harlan Italy (Correzzana, Milano). Upon arrival their weight was 180–190 g. Before being used for the experiments they were housed two per cage (40 cm × 21 cm × 15 cm) with food in pellets (TRM, Harlan Tecklab) and tap water freely available, under the temperature (22 ± 1 ◦ C), humidity (60%) and ventilation conditions advised by the European Community Ethical Regulations on the care of animals for scientific research (CEE Council 86/609; Italian D.L. 27/01/92 no. 116), on a 12 h:12 h light/dark cycle (lights on at 05:00 a.m., and off at 05:00 p.m.). The research protocol was approved by the Animal Experimentation Ethical Committee of the University of Modena and Reggio Emilia. After 1 week of adaptation, rats were placed in sound-proof rooms, in single cages, for the behavioural experiments. 2.2. Drug N-(4-Trifluoromethylbenzyl)-4-methoxybutanamide, kindly provided by GET S.r.l. (Sanremo, Italy), was suspended in vehicle [0.5% solution of methylcellulose (methocell Sigma, Milano, Italy) in distilled water] shortly before administration. 2.3. Influence of GET73 on the chronic unpredictable mild stress-induced anhedonia model 2.3.1. Procedure We used an established model of depression, (the chronic unpredictable mild stress) [27] with minor modifications [32,36,37]. Rats
465
were first trained to experience and drink a sweet beverage, by presenting them simultaneously with two identical bottles: during the first 24 h both bottles contained a 1% sucrose solution; during the subsequent 24 h one bottle contained the sucrose solution, the other contained tap water. Following a 23 h food and water deprivation, rats received the first baseline sucrose preference test: each animal was presented simultaneously with two pre-weighed bottles, one containing the sucrose solution, the other tap water. Both bottles were removed and weighed at 60 min (end of the test). Then, animals were given food and water for 2 h. After another period (21 h) of food and water deprivation, animals received a second baseline sucrose preference test (24 h after the first one). Four days thereafter, following 24 h food and water deprivation, animals received a third baseline sucrose preference test. These baseline tests and the subsequent sucrose preference tests were timetabled at the start of the dark phase (05:00–06:00 p.m.) and always occurred in the home cage of the rat. Following the third baseline test, animals were divided into five groups, each consisting of 10 rats, matched on the basis of their mean sucrose intake in the second and third baseline tests, so that means ± S.E. mean of the sucrose intakes were not significantly different among the different groups. Four groups were exposed during the following weeks to the chronic mild stress regime; one group was not stressed, other than the food and water deprivation that preceded each sucrose preference test, and was housed in a separate sound-proof room. The stress regime used in the 1st week consisted of: one 15 h period of paired housing immediately after the third baseline sucrose preference test; one 8 h period of low intensity stroboscopic illumination; one 16 h period in a soiled cage (200 ml water in sawdust bedding); one 8 h period of food deprivation; one 16 h period of water deprivation (bottle withdrawal) followed by one 8 h period of exposure to an empty water bottle; one 16 h period of 45◦ cage tilt; one 8 h period of low intensity stroboscopic illumination; one 16 h period of continuous (also overnight) illumination; one 8 h period of paired housing; one 24 h period of intermittent lighting (off/on every 2 h); one 24 h period of food and water deprivation preceding the 1 h sucrose preference test. The same stressors were administered the following weeks, but their sequence was at random, in order to be completely unpredictable to the animal. Sucrose consumption was measured, with the above-described procedure, at weekly intervals, in 1 h tests following 24 h food and water deprivation. The protocol is shown in detail in Table 1
Table 1 Chronic unpredictable mild stress protocol Monday 18.00—commence 15 h of paired housing Tuesday 09.00—commence 8 h of low intensity stroboscopic illumination Tuesday 17.00—switch off strobe light: commence 16 h soil bedding Wednesday 09.00—dry bedding; commence 8 h of food deprivation Wednesday 17.00—restore food; commence 16 h of water deprivation Thursday 09.00—offer empty water bottle for 8 h Thursday 17.00- restore water; tilt cages for 16 h Friday 09.00—untilt cages; commence 8 h of low intensity stroboscopic illumination Friday 17.00—switch off strobe light; switch lights to on overnight Saturday 09.00—commence 8 h of paired housing Saturday 17.00—commence 24 h of intermittent lighting (off/on every 2 h) Sunday 17.00—switch off intermittent lighting; commence 24 h of food and water deprivation preceding the 1 h sucrose preference test Monday 17.00—commence the 1 h sucrose preference test Stressors’ sequence during the 1st week. The same stressors were administered the following weeks, but their sequence was at random, in order to be completely unpredictable to the animal.
466
R. Tacchi et al. / Pharmacological Research 57 (2008) 464–468
2.3.2. Treatment The four groups of rats exposed to the daily stresses were randomly assigned to one of the following daily treatments by oral gavage (p.o.) starting on the 1st day of exposure to the chronic mild stress regime: (1) GET73, 10 mg kg−1 ; (2) GET73, 50 mg kg−1 ; (3) GET73, 100 mg kg−1 ; (4) vehicle, 2 ml kg−1 . The group of non-stressed rats was treated daily p.o. with 2 ml kg−1 of the vehicle. The doses of GET73 were chosen on the basis of its activity on palatable food intake [14]. 2.4. Influence of GET73 on sucrose intake in non-stressed rats In order to assess the possible influence of GET73 per se on sucrose intake, its effect on non-stressed animals with daily access to a 1% sucrose solution was studied. 2.4.1. Procedure Rats of the above-quoted Wistar Kyoto strain were randomly assigned to three groups, each consisting of 10 animals, housed in single cages, in a sound-proof room, with food in pellets (TRM, Harlan Tecklab) freely available, and on a 12 h light/dark cycle (lights on at 06:00 a.m., and off at 06:00 p.m.). They had free access to two identical bottles, whose position in the cage was inverted every day, one containing tap water and the other a 1% sucrose solution. The two bottles were withdrawn at 06:00 p.m. and replaced at 08:00 a.m. of the following day, and the amount of water and of sucrose solution drunk during the first hour was measured by weighing the bottles at 09:00 a.m. 2.4.2. Treatment These three groups of non-stressed rats were randomly assigned to one of the following daily treatments (p.o.) for 8 consecutive days: (1) GET73, 10 mg kg−1 ; (2) GET73, 100 mg kg−1 ; (3) vehicle, 2 ml kg−1 . 2.5. Statistical analysis Data are presented as means ± S.E.M. of the percentage of sucrose solution intake with respect to total fluid intake (=sucrose solution + plain water), and were analyzed using repeated measures ANOVA followed by subsequent one-way ANOVA and Student–Newman–Keuls post-hoc test. In experiment 1 (influence of GET73 on the chronic unpredictable mild stress-induced anhedonia) data obtained in stressed rats treated with GET73 (10 mg kg−1 , 50 mg kg−1 or 100 mg kg−1 ) were compared either with data obtained in stressed rats treated with the vehicle or with data obtained in non-stressed rats treated with the vehicle. In experiment 2 (influence of GET73 on sucrose intake in nonstressed rats) data obtained in rats treated with GET73 (10 mg kg−1 or 100 mg kg−1 ) were compared with data obtained in rats treated with the vehicle. Results were considered statistically significant when p < 0.05. 3. Results 3.1. Influence of GET73 on the sucrose consumption, measured at weekly intervals, in rats exposed to daily unpredictable mild stressors The mean baseline consumption of the sucrose solution, calculated with the data obtained in the second and third baseline sucrose preference test, was 7.3 ± 0.3 g, while the mean consumption of water was 3.1 ± 0.2 g.
Fig. 1. Influence of GET73 on sucrose solution intake in Wistar Kyoto male rats exposed to chronic mild stress. GET73 (10 mg kg−1 , 50 mg kg−1 or 100 mg kg−1 ) or vehicle were orally administered daily starting on the 1st day of stress exposure. The intake of sucrose solution is expressed as % over the total amount of fluid intake (sucrose solution + plain water) (sucrose preference). One group of non-stressed rats were orally daily treated with vehicle. Data are means (±S.E.mean) from 10 animals per group. GET73, at any dosage, produced at first a decrease in the consumption of sucrose solution, that was significant after 3 weeks of daily exposure to mild stressors; starting from the 4th week, GET73 produced a dose-dependent restoration of sucrose preference that, in rats treated with the highest dose (100 mg kg−1 ), was not different from that observed in non-stressed rats treated with the vehicle. (*) p < 0.05 vs. vehicle non-stressed group; (䊉) p < 0.05 vs. vehicle + stress group; ANOVA followed by Student–Newman–Keuls test.
The preference for the sucrose solution tended to increase in non-stressed rats treated with the vehicle: at the end of the 5th week their mean consumption of sucrose solution was 8.6 ± 0.2 g while their mean consumption of water was 2.3 ± 0.1 g. On the other hand, in rats daily exposed to an unpredictable sequence of mild stressors and treated with the vehicle, the consumption of sucrose solution decreased starting after the 3rd week: at the end of the experiment (5th week) the mean consumption of sucrose solution of these rats was 4.9 ± 0.3 g, and that of water was 4.9 ± 0.2 g. (Fig. 1) The treatment with GET73 at any dosage (10 mg kg−1 , 50 mg kg−1 or 100 mg kg−1 ) produced at first a decrease in the consumption of sucrose solution that was significant after 3 weeks of exposure to chronic mild stressors; starting from the 4th week, however, GET73 produced a dose-dependent restoration of sucrose preference that, in rats treated with 100 mg kg−1 , was not significantly different from that observed in non-stressed, vehicle-treated rats starting from the 4th week [3rd week: F(4,45) = 24.53, p = 0.000; 4th week: F(4,45) = 38.18, p = 0.000; 5th week: F(4,45) = 206.85, p = 0.000] (Fig. 1). 3.2. Influence of GET73 on the sucrose consumption, measured daily, in non-stressed rats In non-stressed rats with free choice of tap water or 1% sucrose solution, the sucrose preference almost steadily increased during the 8 days of observation (Fig. 2). The mean consumption of the 1% sucrose solution, measured during the first hour after a 14 h deprivation, was 5.7 ± 1.0 g on day 1 and 8.8 ± 0.9 g on day 8; on the other hand, the mean consumption of water, still measured during the first hour after a 14 h deprivation, was 4.3 ± 0.8 g on day 1, and 2.4 ± 0.2 g on day 8. GET73, daily administered p.o. at the doses of 10 mg kg−1 or 100 mg kg−1 , dose-dependently prevented the development of the sucrose preference: the amount of sucrose solution intake was significantly reduced (in comparison to vehicle-treated rats) starting from day 2, and was 6.1 ± 0.4 g on day 8 in rats treated with the dose of 10 mg kg−1 , whereas in rats treated with the dose of 100 mg kg−1
R. Tacchi et al. / Pharmacological Research 57 (2008) 464–468
Fig. 2. Influence of GET73 on the intake of sucrose solution in male Wistar Kyoto non-stressed rats. GET73 (10 mg kg −1 or 100 mg kg −1 ) or vehicle were orally administered daily. Data are means ± S.E.M from 10 animals per group. GET73 dosedependently and significantly inhibited the acquisition of preference for the sucrose solution, compared with vehicle-treated rats, as evidenced by the lack of increase in % sucrose consumed over the 8-day test period. (*) p < 0.05 vs. the corresponding value of the vehicle-treated group; ANOVA followed by Student–Newman–Keuls test.
the amount of sucrose solution intake never increased: on day 8, it was 5.2 ± 0.4 g, quite similar to the intake of water (5.1 ± 0.4 g) [2nd day: F(2,27) = 27.76, p = 0.000; 3rd day: F(2,27) = 83.60, p = 0.000; 4th day: F(2,27) = 68.47, p = 0.000; 5th day: F(2,27) = 64.60, p = 0.000; 6th day: F(2,27) = 99.19, p = 0.000; 6th day = F(2,27) = 108.30, p = 0.000; 8th day: F(2,27) = 127.54, p = 0.000] (Fig. 2). 4. Discussion The data obtained in our present study show that the gammahydroxybutyrate analogue GET73 dose-dependently prevents the development of preference for sucrose in normal rats and, in the same dose range, the reduced preference for sucrose produced in a model of “depression” (the “chronic mild stress-induced anhedonia”) [27], that is widely used, albeit subject to some criticisms [33–35]. We introduced some modifications into the original model, on the basis of our previous experience [32,36]. So, we discarded some stressors (white noise, novel odours and presence of a foreign object in the home gage) that in our experimental conditions were too weak and insufficiently stressful, and concurrently reduced the density of food deprivation periods (that may cause weight loss that is not strictly stress-linked) (in the present experiments, the body weight of rats subjected to stressors, either treated with GET73 or with the vehicle, did not significantly change during the 5 weeks of observation). Moreover, according to D’Aquila et al. [37], sucrose preference tests were carried out at the start of the animals’ dark cycle. Previous studies performed in our laboratory and also in other laboratories have shown that GET73 potently and effectively inhibits, for several hours after administration, either alcohol intake [G. Colombo, personal communication] in a strain of alcohol-preferring rats (Sardinian alcohol preferring) [38] or the consumption of highly palatable and varied foods in normal rats [14]. These effects of GET73 are observed with doses in the range of those used in the present study, and that have been shown to produce no detrimental effect on the gross behaviour and motor activity of rats. The present research was undertaken in order to ascertain whether GET73 may have a sort of “anhedonizing” effect, that could explain the inhibition of alcohol intake and of palatable diet consumption. In fact, in the chronic mild stress model, dur-
467
ing the first 3 weeks, GET73 seems to favour the development of “anhedonia”: on the 3rd weekly test of sucrose intake, the rats treated with any dose of GET73 drink less sucrose solution than stressed and vehicle-treated rats. But while in the latter the amount of sucrose solution intake significantly and steadily decreases in the 4th and 5th weekly test of sucrose intake, in the former (in spite of the persistence of the daily exposure to unpredictable stressors) the amount of sweet solution intake dose-dependently increases starting from the 4th week and, in rats treated with the highest dose of GET73 (100 mg kg−1 ), becomes similar to that of non-stressed vehicle-treated rats. That is, in this test GET73 has a biphasic effect: “anhedonizing” during the first 3 weeks of treatment, and “antidepressant” starting from the 4th week of treatment. On the other hand, GET73 dose-dependently prevents the development of sucrose preference daily assessed in normal, nonstressed rats with free choice of sucrose solution or tap water: rats treated with the highest dose of GET73 (100 mg kg−1 ) indifferently drink water or sucrose solution, without any preference for the latter. This effect is consistent with the previous results concerning the effect of GET73 on palatable diet consumption [14]. Preliminary experiments performed in the course of that study had ruled out a possible effect of GET73 on taste. Thus, it would seem that for treatments lasting up to 3 weeks, GET73 inhibits the effect of rewarding stimuli and potentiates the anhedonizing effect of a steadily stressful environment, while when administered for a longer time an effect typical of antidepressant treatments is observed. So far available data on the neurochemical effects of GET73 have been obtained with acute administrations (Tanganelli et al, submitted). Studies on the effects of repeated administrations for several weeks, which would be suitable for an interpretation of our present behavioural results, are on the other hand still in progress. Thus, only a tentative explanation can be tried. Particularly intriguing is the fact that (i) for treatments not exceeding 2–3 weeks, GET73 dose-dependently inhibits the intake of a sucrose solution, either under normal conditions or in the presence of continuously varied mildly stressful situations (present data), as well as the consumption of palatable food under normal housing conditions (our previous data) [14]; whereas (ii) for treatments of longer duration (more than 3 weeks) the opposite effect is observed, at least as concerns the preference for a sucrose solution in an experimental condition that models a depression state (present data). As if short-lasting treatments with GET73 would inhibit reward systems (or activate aversive systems), while longer-lasting treatments would produce an opposite effect by up- (or down-) regulating the same systems. Concurrently, present and previous data suggest that GET73 “stabilize” the behaviour of rats, either preventing the development of a “depression-like” condition in a continuously stressful environment, or the rewarding effect of alcohol, sucrose, and palatable food. Acknowledgement The technical assistance of Alessandra Ottani is acknowledged. References [1] Roth RH, Doherty JD, Walters JR. Gamma-hydroxybutyrate: a role in the regulation of central dopaminergic neurons? Brain Res 1980;189:556–60. [2] Maitre M. The gamma-hydroxybutyrate signalling system in brain: organization and functional implications. Prog Neurobiol 1997;51:337–61. [3] Hechler V, Gobaille S, Maitre M. Selective distribution pattern of gammahydroxybutyrate receptors in the rat forebrain and midbrain as revealed by quantitative autoradiography. Brain Res 1992;572:345–8.
468
R. Tacchi et al. / Pharmacological Research 57 (2008) 464–468
[4] Andriamampandry C, Taleb O, Viry S, Muller C, Humbert JP, Gobaille S, et al. Cloning and characterization of a rat brain receptor that binds the endogenous neuromodulator gamma-hydroxybutyrate (GHB). FASEB J 2003;17:1691–3. [5] Castelli MP, Mocci I, Langlois X, Gommerendagger W, Luyten WH, Leysen JE, et al. Quantitative autoradiographic distribution of gamma-hydroxybutyric acid binding sites in human and monkey brain. Mol Brain Res 2000;78:91–9. [6] Mathivet P, Bernasconi R, De Barry J, Marescaux C, Bittiger H. Binding characteristics of gamma-hydroxybutyric acid as a weak but selective GABAB receptor agonist. Eur J Pharmacol 1997;321:67–75. [7] Escuret E, Roquefeuil B, Frerebeau P, Baldy-Moulinier M. Effect of hyperventilation associated with administration of central nervous depressants in brain injuries. Acta Neurol Scand Suppl 1977;64:154–5. [8] Lavyne MH, Hariri RJ, Tankosic T, Babiak T. Effect of low dose gammabutyrolactone therapy on forebrain neuronal ischemia in the unrestrained, awake rat. Neurosurgery 1983;12:430–4. [9] Vergoni AV, Ottani A, Botticelli AR, Zaffe D, Guano L, Loche A, et al. Neuroprotective effect of gamma-hydroxybutyrate in transient global cerebral ischemia in the rat. Eur J Pharmacol 2000;397:75–84. [10] Ottani A, Saltini S, Bartiromo M, Zaffe D, Botticelli AR, Ferrari A, et al. Effect of gamma-hydroxybutyrate in two rat models of focal cerebral damage. Brain Res 2003;986:181–90. [11] Ottani A, Vergoni AV, Saltini S, Mioni C, Giuliani D, Bartiromo M, et al. Effect of late treatment with gamma-hydroxybutyrate on the histological and behavioral consequences of transient brain ischemia in the rat. Eur J Pharmacol 2004;485:183–91. [12] Gallimberti L, Canton G, Gentile N, Ferri M, Cibin M, Ferrara SD, et al. Gammahydroxybutyric acid for treatment of alcohol withdrawal syndrome. Lancet 1989;2:787–9. [13] Agabio R, Carai MA, Lobina C, Pani M, Reali R, Vacca G, et al. Development of short-lasting alcohol deprivation effect in sardinian alcohol-preferring rats. Alcohol 2000;21:59–62. [14] Ottani A, Leone S, Garcia Vergara FB, Tacchi R, Loche A, Bertolini A. Preference for palatable food is reduced by the gamma-hydroxybutyrate analogue GET73, in rats. Pharmacol Res 2007;55:271–9. [15] Jacobson MF, Brownell KD. Small taxes on soft drinks and snack foods to promote health. Am J Public Health 2000;90:854–7. [16] McCrory MA, Suen VM, Roberts SB. Biobehavioral influences on energy intake and adult weight gain. J Nutr 2002;132:3830S–4S. [17] Berthoud HR. Mind versus metabolism in the control of food intake and energy balance. Physiol Behav 2004;81:781–93. [18] Erlanson-Albertsson C. How palatable food disrupts appetite regulation. Basic Clin Pharmacol Toxicol 2005;97:61–73. [19] Treit D, Spetch ML, Deutsch JA. Variety in the flavor of food enhances eating in the rat: a controlled demonstration. Physiol Behav 1983;30:207–11. [20] Sclafani A. Carbohydrate taste, appetite, and obesity: an overview. Neurosci Biobehav Rev 1987;11:131–53.
[21] Rolls BJ, Rowe EA, Rolls ET, Kingston B, Megson A, Gunary R. Variety in a meal enhances food intake in man. Physiol Behav 1981;26:215–21. [22] Sorensen LB, Moller P, Flint A, Martens M, Raben A. Effect of sensory perception of foods on appetite and food intake: a review of studies on humans. Int J Obes Relat Metab Disord 2003;27:1152–66. [23] McKinney WT, Bunney WE. Animal models of depression: review of evidence and implications for research. Arch Gen Psychiatr 1969;21:240–8. [24] Abramson LY, Seligman MEP. Modelling psychopathology in the laboratory: history and rationale. In: Maser JD, Seligman MEP, editors. Psychopatology: experimental models. San Francisco: Freeman; 1978. p. 1–26. [25] Willner P. The validity of animal models of depression. Psychopharmacology 1984;83:1–16. [26] Papp M, Willner P, Muscat R. An animal model of anhedonia: attenuation of sucrose consumption and place preference conditioning by chronic unpredictable mild stress. Psychopharmacology 1991;104:255–9. [27] Willner P, Muscat R, Papp M. Chronic mild stress-induced anhedonia: a realistic animal model of depression. Neurosci Biobehav Rev 1992;16:525–34. [28] Papp M, Moryl E, Willner P. Pharmacological validation of the chronic mild stress model of depression. Eur J Pharmacol 1996;296:129–36. [29] Willner P. Validity, reliability and utility of the chronic mild stress model of depression: a 10-year review and evaluation. Psychopharmacology 1997;134:319–29. [30] Bekris S, Antoniou K, Daskas S, Papadopoulou-Daifoti Z. Behavioural and neurochemical effects induced by chronic mild stress applied to two different rat strains. Behav Brain Res 2005;161:45–59. [31] Willner P. Chronic mild stress (CMS) revisited: consistency and behaviouralneurobiological concordance in the effects of CMS. Neuropsychobiology 2005;52:90–110. [32] Benelli A, Filaferro M, Bertolini A, Genedani S. Influence of S-adenosyl-Lmethionine on chronic mild stress-induced anhedonia in castrated rats. Br J Pharmacol 1999;127:645–54. [33] Matthews K, Forbes N, Reid IC. Sucrose consumption as an hedonic measure following chronic unpredictable mild stress. Physiol Behav 1995;57: 241–8. [34] Forbes NF, Stewart CA, Matthews K, Reid IC. Chronic mild stress and sucrose consumption: validity as a model of depression. Physiol Behav 1996;60:1481–4. [35] Pecoraro N, Reyes F, Gomez F, Bhargava A, Dallmann MF. Chronic stress promotes palatable feeding, which reduces sign of stress: feedforward and feedback effects of chronic stress. Endocrinology 2004;145:3754–62. [36] Genedani S, Saltini S, Benelli A, Filaferro M, Bertolini A. Influence of SAMe on the modifications of brain polyamine levels in an animal model of depression. Neuroreport 2001;12:3939–42. [37] D’Aquila PS, Newton J, Willner P. Diurnal variation in the effect of chronic mild stress on sucrose intake and preference. Physiol Behav 1997;62:421–6. [38] Colombo G. Ethanol drinking behaviour in Sardinian alcohol-preferring rats. Alcohol Alcoholism 1997;32:443–53.