Changes in the composition of the urine of yellow-vented bulbuls (Pycnonotus xanthopygos): the effects of ambient temperature, nitrogen, and water intake.

Uricotely (uric acid >50% of urinary nitrogen) in birds was once considered ubiquitous. However, Anna's hummingbirds (Calypte anna) have been shown to be an exception to this rule; under conditions of low ambient temperature (T(a)) and on a nitrogen-free diet, they increased their water intake and often became ammonotelic (ammonia >50% of urinary nitrogen). Our aim was to identify the effects of nitrogen intake, water intake, and T(a) on the ammonia excretion of yellow-vented bulbuls (Pycnonotus xanthopygos). We chose this predominantly frugivorous species because many of the characteristics of nectarivores that were used to explain increased ammonia excretion by C. anna are also characteristics of frugivorous birds. We assayed ureteral urine composition in eight yellow-vented bulbuls (P. xanthopygos), each randomly allocated a diet of 20% (0.6 M) sucrose solution supplemented by either 1.03 g/L or 7.23 g/L soy protein and held at a T(a) of either 28 degrees C or 10 degrees C. Food, and therefore water, intake rates varied with nitrogen intake but not with T(a). Food intake increased significantly with decreased nitrogen intake, while concentrations of all the excretory compounds in the urine (P<0.05) decreased; yet their proportions in the urine did not change significantly. The lower T(a) had no significant effect on food intake or on the concentration of uric acid. However, at 10 degrees C, the ammonia and urea concentrations increased (P<0.05), and this led to a significant increase in the proportion of ammonia in the urine. Our results demonstrate that, when bulbuls are exposed to low T(a), they are able to save energy by increasing the proportion of the ammonia in their urine.     

Effects of temperature acclimation on body mass and energy budget in the Chinese bulbul Pycnonotus sinensis

Chinese bulbuls(Pycnonotus sinensis) are small passerine birds that inhabit areas of central, southern and eastern China. Previous observations suggest that free–living individuals of this species may change their food intake in response to seasonal changes in ambient temperature. In the present study, we randomly assigned Chinese bulbuls to either a 30 °C or 10 °C group, and measured their body mass(BM), body temperature, gross energy intake(GEI), digestible energy intake(DEI), and the length and mass of their digestive tracts over 28 days of acclimation at these temperatures. As predicted, birds in the 30 °C group had lower body mass, GEI and DEI relative to those in the 10 °C group. The length and mass of the digestive tract was also lower in the 30 °C group and trends in these parameters were positively correlated with BM, GEI and DEI. These results suggest that Chinese bulbuls reduced their absolute energy demands at relatively high temperatures by decreasing their body mass, GEI and DEI, and digestive tract size.     

乙醇浓度对圈养长舌果蝠摄食糖水量的影响

正在自然生境中,果蝠主要以果实或者花蜜为食,成熟果实或花蜜由于微生物发酵而含一定量的乙醇。乙醇在生态系统中是一种常见物质,它是生物厌氧代谢的终端产物之一(Van Waarde,1991)。一旦果实成熟,它们中的糖分就会被微生物或者自身发酵代谢成乙醇(Battcock and Azam-Ali,1998;Dudley,2000,2004)。果实中的乙醇浓度主要是由这些以糖分为能源的发酵微生物的扩增状态来决定     

Physiological and biochemical thermoregulatory responses of Chinese bulbuls Pycnonotus sinensis to warm temperature: Phenotypic flexibility in a small passerine

Temperature is an important environmental cue for the regulation of thermogenesis in small birds. We tested the hypothesis that a small passerine, the Chinese bulbul Pycnonotus sinensis can decrease thermogenesis in response to warmer temperatures by decreasing body mass, the organ mass and changing physiological and biochemical processes in the liver and muscle. Captive Chinese bulbuls decreased in body mass and basal metabolic rate (BMR) during 4 weeks of acclimation to 30±1 °C. They also showed a decrease in liver, kidney and small intestine mass and reduced mitochondrial state-4 respiration and cytochrome C oxidase (COX) activity in the liver and muscle compared to 10±1 °C. Furthermore, BMR was positively correlated with body mass, organ mass (liver, kidney, small intestine and entire digestive tract), and mitochondrial state-4 respiration and cytochrome C oxidase (COX) activity in the liver and muscle. These results indicate that changes in body mass, organ mass and respiratory enzyme activity are mechanisms by which Chinese bulbuls adapt to warmer temperatures. The data support the hypothesis that such physiological flexibility is ubiquitous in birds.     

浙江温州地区4种雀形目鸟类消化道形态特征比较

食性是影响鸟类消化系统形态结构的重要因子之一.本文对丝光椋鸟Sturnus sericeus、白头鹎Pycnonotus sinensis、小鹀Emberiza pusilla及红头长尾山雀Aegithalos concinnus 4种雀形目鸟类的消化道形态结构进行了比较研究.结果发现,4种雀形目鸟类总消化道及各消化器...     

Ingestion patterns and daily energy intake on a sugary diet: the Red Lory Eos bornea and the Malachite Sunbird Nectarinia famosa

This study examines whether nectarivorous birds regulate daily energy intake as proposed by Lloyd in 1991. Two Old World nectarivorous species, a large non-passerine, the Red Lory Eos bornea, and a small passerine, the Malachite Sunbird Nectarinia famosa, were fed 0.25 mol/1 sucrose (9%), 0.73 mol/1 sucrose [24%] or 0.73 mol/1 glucose in separate laboratory trials to determine hourly and overall daily rate of sugar intake and consumption. Overall daily energy intake rates of the Malachite Sunbird and the Red Lory support the hypothesis of regulated energy intake for nectarivorous Old World birds. However, the species differ in their ingestion patterns through the day. The Red Lory ingests large volumes initially, regardless of sugar type. This is possibly a consequence of their large size and having a crop in which food can be stored. The Malachite Sunbird showed more regular hourly consumption through the day, and no change in mass during the day. Intake rates of both species were greater on lower sugar concentrations.     

The possible roles of ethanol in the relationship between plants and frugivores: first experiments with egyptian fruit bats

In this paper we discuss how yeast, fungi ubiquitously presentin sugar-rich fruit, can influence the interaction between frugivoresand fleshy-fruited plants via ethanol. We suggest that plants,the seeds of which are mostly dispersed by vertebrates, exploitthe ethanol from alcoholic fermentation by yeast in their seeddispersal strategy. Moderate consumption of ethanol, i.e., atconcentrations close to those in naturally ripening fruit, byfrugivores may have beneficial short- and long-term effectsfor these potential dispersers, whereas consumption of largerquantities may have negative short- and long-term effects. Ethanolvapor emanating from palatable fruit may act as an odor cue,guiding bats and other frugivores to the fruit, and aiding themto assess its quality. In addition, we suggest that ingestedethanol may be an appetitive stimulant. We also evaluate thepossibility that ethanol within fruit may be used as a sourceof energy by frugivorous vertebrates. Our preliminary data indicatethat Egyptian fruit bats (Rousettus aegyptiacus) can use theodor of ethanol to assess food suitability, but also that itmay not serve as an attractant over short distances (i.e., <1m). Instead, ethanol is avoided at concentrations greater than1%, a value which might typically characterize overripe andotherwise unpalatable fruit. Our initial results further indicatethat Egyptian fruit bats significantly decrease their food consumptionif it contains 1 or 2% ethanol. Overall, ethanol may play diverseroles in the nutritional ecology and behavior of fruit-eatingbats, and in the interaction between frugivores and plants,in general.     

Food choice by Blue-gray Tanagers in relation to protein content

We tested discriminatory ability and food choice in relation to protein content of the diet in wild-caught Blue-gray Tanagers (Thraupis episcopus), a generalist tropical frugivorous bird. In two sets of experiments we offered to five individual birds in pair-wise choice trials two nearly iso-caloric experimental diets differing in their protein content only. Protein contents of the experimental diets were 4.6 vs. 1.4% in the first experiment and 3.2 and 1.5% (dry matter basis) in the second experiment. Response varied among individual tanagers, but 6 of the 10 birds showed a clear preference for the food highest in protein. Two individuals displayed a strong positional preference. When testing each treatment group, birds ate daily significantly more of the food that had higher protein content. We conclude that Blue-gray Tanagers prefer richer nitrogen foods. Our results also demonstrate that Blue-gray Tanagers have remarkable discriminatory abilities, they reacted to differences in protein content as small as 0.09% fresh matter. We show for the first time discriminatory ability and preference of wild frugivorous birds for foods richer in protein under controlled conditions. Our findings support the hypothesis that frugivorous birds can act as selective agents for fruit pulp composition.     

Effects of ethanol on food consumption and skin temperature in the Egyptian fruit bat (Rousettus aegyptiacus)

Since mammalian frugivores generally choose to eat ripe fruit in which ethanol concentration ([EtOH]) increases as the fruit ripens, we asked whether ethanol acts as an appetitive stimulant in the Egyptian fruit bat, Rousettus aegyptiacus, and also studied the effects of ethanol on their skin temperature (T(s)). We hypothesized that the responses of fruit bats to dietary ethanol are concentration dependent and tested the predictions that the bats' response is positive, i.e., they eat more when [EtOH] in the food is in the range found in naturally ripe fruit, while it negatively affects them at higher concentrations. We also tested the prediction that in winter, even when availability of fruit is low and thermoregulatory costs are high, ingestion of ethanol by fruit bats is low because assimilated ethanol reduces shivering thermogenesis and peripheral vasodilation; these, alone or together, are detrimental to the maintenance of body temperature (T(b)). In summer, captive bats offered food containing 0.1% ethanol significantly increased consumption over food with no ethanol; they did not change consumption when food contained 0.01, 0.3, or 0.5% ethanol; but significantly decreased consumption at higher levels of ethanol [EtOH], i.e., 1 and 2%. In winter, captive bats ate significantly less when their food contained 0.1% ethanol than when it contained 0, 0.3, or 0.5%. During summer, freshly caught bats ate significantly more ethanol-containing food than freshly caught bats in winter. Skin temperature (T(s)) in Egyptian fruit bats decreased significantly at an ambient temperature (T(a)) of 12 °C (winter conditions) after gavage with liquid food containing 1% ethanol. The effect was clearly temperature-dependent, since ethanol did not have the same effect on bats gavaged with food containing 1% or no ethanol at a T(a) of 25 °C (summer conditions). In conclusion, ethanol may act as an appetitive stimulant for Egyptian fruit bats at low concentrations, but only in summer. Bats are deterred by food containing [EtOH] corresponding to that in overripe, unpalatable fruit (1 and 2%). Furthermore, during winter, Egyptian fruit bats are deterred by ethanol-rich fruit, possibly due to the potential thermoregulatory consequences of ethanol consumption.     

Comparisons of Dispersal Success between the Species Fruiting Prior to and Those at the Peak of Migrant Frugivore Abundance

I evaluated whether plants gain high dispersal success by synchronizing their fruiting with frugivore abundance. Fruiting phenologies, seasonal fluctuations in the abundance of frugivorous birds, and consumption of fruits by birds and Japanese macaques, Macaca fuscata Blyth, were studied in the montane forest of Yakushima for two years. At the community level, fruiting phenologies and seasonal fluctuations in frugivorous bird abundance were asynchronous because Zosterops japonica Temminck et Schlegel, a resident frugivore, decreased in number during the fruiting season. In addition, Symplocos myrtacea Sieb. et Zucc. fruited in September, before the migration of frugivorous birds (Turdus spp. and brown-eared bulbuls Hypsypetes amaurotis Temminck) in November and December. The phenology of other fruit species (Eurya japonica Thunb. and Cleyera japonica Thunb.p.p.emend. Sieb. et Zucc) were synchronized with migrant frugivorous birds. Fruit species with phenologies that are synchronized with migrant frugivore abundances have higher dispersal success either by birds (C. japonica) or macaques (E. japonica). Macaques predated most of the seeds of S. myrtacea. Dispersal success of S. myrtacea is low both by birds and macaques, thus the early fruiting by S. myrtacea does not seem to be an adaptation to maximize dispersal success by depending on resident dispersers or by avoiding intense competition for dispersers.     

Bird pollinators differ in their tolerance of a nectar alkaloid

Although the function of nectar is to attract and reward pollinators, secondary metabolites produced by plants as anti‐herbivore defences are frequently present in floral nectars. Greater understanding is needed of the effects of secondary metabolites in nectar on the foraging behaviour and performance of pollinators, and on plant–pollinator interactions. We investigated how nectar‐feeding birds, both specialist (white‐bellied sunbirds Cinnyris talatala) and generalist (dark‐capped bulbuls Pycnonotus tricolor and Cape white‐eyes Zosterops virens), respond to artificial nectar containing the alkaloid nicotine, present in nectar of Nicotiana species. Preference tests were carried out with a range of nicotine concentrations (0.1–300 μM) in two sucrose concentrations (0.25 and 1 M), and for bulbuls also in two sugars (sucrose and hexose). In addition, we measured short‐term feeding patterns in white‐bellied sunbirds that were offered nicotine (0–50 μM) in 0.63 M sucrose. Both nicotine and sugar concentrations influenced the response of bird pollinators to nicotine. The birds showed dose‐dependent responses to nicotine; and their tolerance of high nicotine concentrations was reduced on the dilute 0.25 M sucrose diet, on which they increased consumption to maintain energy intake. White‐bellied sunbirds decreased both feeding frequency and feeding duration as the nicotine concentration in artificial nectar increased. Of the three species, bulbuls showed the highest tolerance for nicotine, and sugar type (sucrose or hexose) had no effect. The indifference of bulbuls to nicotine may be related to their primarily frugivorous diet. However, the response of white‐eyes to nicotine in the dilute sucrose solution was very similar to that of sunbirds, even though white‐eyes are generalist nectar‐feeders. Additional testing of other avian nectarivores and different secondary metabolites is required to further elucidate whether generalist bird pollinators, which utilise dilute nectars in which secondary metabolites have stronger deterrent effects, are more tolerant of ‘toxic’ nectar.     

Preferences and apparent digestibilities of sugars by fruit damaging birds in Japan

Gray starlings Sturnus cineraceus, azure-winged magpies Cyanopica cyana and brown-eared bulbuls Hypsipetes amaurotis are among the main bird pests in commercial fruit orchards in central Japan. Recently Brugger & Nelms (1991) suggested that developing high-sucrose fruit cultivars could reduce crop damage, because some pest birds lack the enzyme sucrase and can develop an aversion to sucrose. Preferences for, and digestibilities of, the monosaccharides glucose and fructose and the disaccharide sucrose by these pests species were therefore studied to assess whether this idea would be applicable in central Japan. Gray starlings and brown-eared bulbuls were able to detect glucose, fructose, a mixture of glucose and fructose, and sucrose at a concentration of 12% w/v. Azure-winged magpies also detected glucose and fructose, but failed to detect sucrose at the same concentration. In pairwise preference trials gray starlings and azure-winged magpies selected the monosaccharides over sucrose, but brown-eared bulbuls did not. To estimate the digestibility of the sugars the apparent assimilated mass coefficient, AMC*, was calculated for each species eating each sugar by measuring intake and faecal output. Monosaccharides had mean AMC*s of 0.77, 0.96 and 0.92 when consumed by gray starlings, azure-winged magpies and brown-earned bulbuls respectively. AMC* values for sucrose were 0.82 and 0.49 for brown-eared bulbuls and azure-winged magpies respectively, but gray starlings were shown to be unable to digest sucrose. As AMC* values varied from 0.75 to 0.97, consumption rates of sugars increased as digestibility decreased. Although increasing sucrose contents of commercial fruits may deter sucrase-deficient birds such as gray starlings from depredating fruits, it may also lead to increased crop damage by species such as the azure-winged magpie and brown-eared bulbul which may have to consume more of the less digestible fruit in order to meet their energy requirements.     

Discrimination abilities for nutrients: which difference matters for choosy birds and why?

Fine-tuned discrimination abilities are a prerequisite for optimal diet theory (ODT) and the concept of nutrient regulation as alternative models of food choice. These abilities have rarely been determined, and neither has been applied to frugivorous consumers. We investigated nutrient choices of four tanagers (Tachyphonus cristatus, Dacnis cayana, Chlorophanes spiza and Cyanerpes nitidus) for different lipid or carbohydrate concentrations, and determined discrimination abilities by reducing in steps the difference between two foods ranging from 2.5 to 12%. Three species detected differences in sugar concentrations of only 1% and differences in lipid content of 2%. Hence, frugivorous tanagers were able to select the more rewarding food based on fine-scale differences in nutritional content. Tanagers also consumed more carbohydrates than proteins or lipids in isocaloric trials, but were indifferent to equicaloric solutions of 20% of either glucose or sucrose. In contrast to foods with low sugar contents, intake of foods high in lipids or carbohydrates was limited to a protein intake of 0.75 g/7 h. Lipid and carbohydrates were treated as though they were interchangeable nutrients for birds at low, but not at high, sugar concentrations. Furthermore, the tanagers discriminated foods containing the same amount of protein but differing in the type of protein. Preference for boviserine serum albumin (BSA) over casein was not related to moult. We supplemented the food consisting of casein with the essential amino acid cysteine to match cysteine concentrations of BSA. The birds then consumed more of the casein food than of the cysteine-supplemented casein food. Overall, the birds' consistent choices in the experiments with foods of different energy density are interpretable by both ODT and the nutrient regulation theory. However, only the latter accounts for the birds' choices of isocaloric foods differing in macro- or micronutritional content. Models of food selection should therefore focus on nutrient geometry and consumer-specific requirements. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

The influence of ambient temperature and the energy and protein content of food on nitrogenous excretion in the Egyptian fruit bat (Rousettus aegyptiacus)

The diets of frugivorous and nectarivorous vertebrates contain much water and generally have high energy but low protein contents. Therefore, we tested the prediction that to save energy under conditions of high energy demands and high water intake, frugivorous Egyptian fruit bats (Rousettus aegyptiacus) will increase both the absolute quantity and the proportion of ammonia in their urine. We also examined whether such changes occur when protein intake is low and water intake is high. We did three feeding trials. In trials 1 and 2, bats were fed one of four liquid diets containing constant soy protein concentrations but varying in sucrose concentration and were kept at ambient temperatures (T(a)) of 30 degrees Celsius and 12 degrees Celsius, respectively. In trial 3, bats were kept at Ta=12 degrees Celsius and fed one of four liquid diets with equal sucrose concentrations but varying protein concentrations. In trial 1, food intake at a sucrose concentration of 256 mmol/kg H(2)O was initially high but decreased to a constant rate with further increases in sucrose concentration, while in trial 2, food intake decreased exponentially with increasing sucrose concentration. As predicted, at 12 degrees Celsius with varying sucrose concentration, both the absolute quantity and the fraction of ammonia in the bats' urine increased significantly with food intake (P<0.02), while the absolute quantity of urea and the fraction of urea nitrogen excreted decreased significantly with food intake (P<0.03). Varying sucrose concentration had no significant effect on nitrogen excretion at Ta=30 degrees Celsius. Varying protein concentration had no significant effect on nitrogen excretion at Ta=12 degrees Celsius. We suggest that Egyptian fruit bats can increase ammonia excretion in response to increased energetic demands, and we calculate that they can save energy equal to approximately 2% of their daily metabolic rate by doing so.     

Neuropeptide-Y in the paraventricular nucleus increases ethanol self-administration

The paraventricular nucleus (PVN) of the hypothalamus is known to modulate feeding, obesity, and ethanol intake. Neuropeptide-Y (NPY), which is released endogenously by neurons projecting from the arcuate nucleus to the PVN, is one of the most potent stimulants of feeding behavior known. The role of NPY in the PVN on ethanol self-administration is unknown. To address this issue, rats were trained to self-administer ethanol via a sucrose fading procedure and injector guide cannulae aimed at the PVN were surgically implanted. Microinjections of NPY and NPY antagonists in the PVN were conducted prior to ethanol self-administration sessions. All doses of NPY significantly increased ethanol self-administration and preference, and decreased water intake. The NPY antagonist D-NPY partially reduced ethanol self-administration and completely blocked the effects of an intermediate dose of NPY (10 fmol) on ethanol intake, preference, and water intake. The competitive non-peptide Y1 receptor antagonist BIBP 3226 did not significantly alter ethanol self-administration or water intake when administered alone in the PVN but it completely blocked the effect of NPY (10 fmol) on ethanol intake. NPY infused in the PVN had no effect on ethanol self-administration when tested in rats that did not have a long history of ethanol self-administration. The doses of NPY tested produced no effect on food intake or body weight measured during the 24-h period after infusion in either ethanol-experienced or ethanol-inexperienced rats. These results indicate that elevation of NPY levels in the PVN potently increases ethanol self-administration and that this effect is mediated through NPY Y1 receptors.     

Nutritional requirements for maintenance of body weight and fat deposition in the long-distance migratory garden warbler, Sylvia borin (Boddaert)

Intake of food, protein, fat and carbohydrates and their fecal output and the birds' weights were recorded during different feeding trials with specific nutrient reduced diets in the old-world long-distance migratory garden warbler. The birds' body weights were affected by low dietary protein as well as low dietary fat levels. Low dietary protein and fat levels were associated with significant changes in daily gross and net food intake and in the efficiency of food and nutrient utilization. Birds fed on diets with low nutrient levels for an extended length of time recovered in weight after an initial weight loss. They obviously compensated the restricted nutrient levels primarily by increasing the daily food intake and by changing the efficiency of food and nutrient utilization. Effects of restricted dietary nutrient levels on body weight and adaptation depended on the previous composition of the food. The average daily net fat intake was much higher than the average daily net protein intake, both for maintenance of a constant body weight and for successful regain of weight. The data were further discussed with respect to the role of a fruit diet in omnivorous passerine birds.     

Do southern African songbirds live longer than their European counterparts?

Understanding life history evolution in tropical and southern hemisphere birds has been hindered by a paucity of knowledge of key life history traits and this is particularly true of African songbirds. Here we use a unique long-term mark-recapture data set collected over 16 years in Malawi (latitude 16°S) to estimate adult survival rates for 28 African passerine species. Survival of these and 11 other African songbirds (taken from the literature) showed a bi-modal distribution with annual survival of insectivores and nectarivores (bulbuls, thrushes, warblers and sunbirds) averaging 72% (quartiles 63–80%) compared to 54% (50–62%) in granivores (weavers, finches and canaries). The mean adult life expectancy of African insectivores and nectarivores (3.1 yr) was more than twice that of related European insectivores (1.4 yr) and nearly twice that of African granivores (1.6 yr). These marked differences in survival were highly significant after controlling for body mass and phylogeny. Among African songbirds there was a strong negative correlation between adult survival and clutch size with granivores laying relatively large clutches and living relatively short lives. We hypothesize that these differing life history trade-offs reflect variation in the seasonality of food resources whereby survival rates of northern temperate songbirds may be limited by food availability and cold weather during winter, while survival of southern African granivores may be limited by the influence of a variable and unpredictable rainfall regime on seed availability.     

Incorporating dispersal distance into the disperser effectiveness framework: frugivorous birds provide complementary dispersal to plants in a patchy environment

Fleshy-fruited plants are usually dispersed by an array of frugivores, differing in the effectiveness of the dispersal service they provide to the plant. Body size differences among frugivores are hypothesized to affect seed dispersal distances and consequently their effectiveness as dispersers. We tested this hypothesis by comparing the effectiveness of two passerine birds, grackles ( Onychognathus tristramii ) and bulbuls ( Pycnonotus xanthopygos ), dispersing the desert shrub Ochradenus baccatus . Laboratory experiments, quantifying gut retention time and the effect on germination, were combined with field observations quantifying bird movements and fruit consumption rates. An empirically parameterized mechanistic model showed that the two dispersers switch roles as a function of spatial-scale: while most seeds within the local habitat were dispersed by bulbuls, the larger grackles were exclusively responsible for between-patches, long-distance dispersal. We suggest that distance-related differences are common and important to plant fitness, and thus should explicitly be considered in studies of disperser effectiveness.     

Seasonal shifts in odor acuity by starlings

A passerine bird, the European Starling Sturnus vulgaris, demonstrated a seasonal ability to respond to odor cues. Cardiac conditioned responses were most evident when birds were in breeding condition. Once birds were in nonbreeding condition, responding to odors all but ceased. For birds in breeding condition, threshold sensitivity to the odor cyclohexanone was comparable to levels reported for nonpasserine birds (0.3% vapor saturation or 3.778 x 10(14) molecules/ml). In contrast, the threshold level during the postreproductive phase of the annual cycle was 10% vapor saturation (1.256 x 10(16) molecules/ml), a level high enough to implicate the trigeminal system as the modality mediating chemosensory perception. The strong cyclic responding pattern suggests links between photoperiodically controlled endocrine production, breeding behavior, and olfactory sensitivity.     

“Binge” drinking experience in adolescent mice shows sex differences and elevated ethanol intake in adulthood

Binge drinking, defined as achieving blood ethanol concentrations (BEC) of 80 mg%, has been increasing in adolescents and was reported to predispose later physical dependence. The present experiments utilized an animal model of binge drinking to compare the effect of ethanol “binge” experience during adolescence or adulthood on subsequent ethanol intake in male and female C57BL/6 mice. Adolescent and adult mice were initially exposed to the scheduled high alcohol consumption procedure, which produces BECs that exceed the levels for binge drinking following a 30-min ethanol session every third day. Ethanol intake and BECs were significantly higher in the adolescent (∼ 3 g/kg, 199 mg%) versus adult (∼ 2 g/kg, 135 mg%) mice during the first three ethanol sessions, but were more equivalent during the final two ethanol sessions (1.85-2.0 g/kg, 129-143 mg%). Then, separate groups of the ethanol-experienced mice were tested with ethanol naïve adolescent and adult mice for 2-h limited access (10% and 20% solutions) or 24-h (5%, 10% and 20% solutions) ethanol preference drinking. Limited access ethanol intake was significantly higher in female versus male mice, but was not altered by age or ethanol experience. In contrast, 24-h ethanol intake was significantly higher in the adolescent versus adult mice and in female versus male mice. Furthermore, binge drinking experience in the adolescent mice significantly increased subsequent ethanol intake, primarily due to intake in female mice. Thus, adolescent binge drinking significantly increased unlimited ethanol intake during adulthood, with female mice more susceptible to this effect.