Effects of sweetened ethanol solutions on ethanol self-administration and blood ethanol levels

The enhancement of voluntary self-administration of ethanol by sucrose or saccharin was tested in conjunction with measurements of blood ethanol levels. Adult male rats were given access to both tap water and one of five solutions: 0.125% saccharin, 10% sucrose, ethanol, saccharin+ethanol, or sucrose+ethanol. The rats receiving the sucrose+ethanol solution drank consistently more ethanol (>5 g/kg/day) than did the rats receiving the saccharin+ethanol solution (<3 g/kg/day) or ethanol only (<2 g/kg/day). Both sweetened solutions produced higher ethanol consumption during these periods than ethanol alone. However, no significant differences in blood ethanol levels were found between the sucrose+ethanol and saccharin+ethanol conditions, when tested at different intervals on Day 44 or Day 45 of ethanol consumption. Following 45 days of consumption, no change in the bicuculline seizure threshold was observed in the ethanol-consuming rats compared to the controls. In a separate study using 90 naive rats, rats were gavaged with ethanol (1, 2, or 3 g/kg) containing either 10% sucrose (n=10 for each dose of ethanol), 0.125% saccharin (n=10 for each dose of ethanol), or ethanol alone (n=10 for each dose of ethanol), and blood was collected from the tip of the tail 30, 60, 180, 300, and 540 min later and analyzed for ethanol concentrations. Sucrose significantly decreased the resultant blood ethanol levels at several time points following gavage. These results indicate that sucrose can significantly alter blood ethanol levels and that chronic self-administration of a sweetened ethanol solution for 6 weeks does not produce ethanol dependence.     

Effects of ethanol on cocaine discrimination in rats

Ethanol and cocaine are frequently abused in combination, but little is known about how the subjective effects of the two drugs interact. The ability of ethanol and other GABA(A)-active compounds to alter the discriminative stimulus effects of cocaine was tested. Male Sprague-Dawley rats were trained to discriminate cocaine (10 mg/kg ip) from saline using either single- or cumulative-dosing methods. In single-dose testing, ethanol (0.1-0.5 g/kg) dose-dependently decreased cocaine-appropriate responding following the training dose of cocaine. Ethanol (0.5 g/kg) produced a rightward shift in the cocaine cumulative dose-effect curve. Ethanol (0.1-1.0 g/kg) failed to substitute for the discriminative stimulus effects of cocaine and the higher doses (1-2 g/kg) completely suppressed responding. Indirect GABA(A) agonists diazepam (benzodiazepine site) and pentobarbital (barbiturate site) did not block the discriminative stimulus effects of cumulative doses of cocaine. The GABA(A) antagonist pentylenetetrazol (PTZ) (10-40 mg/kg) did not substitute for cocaine. These findings suggest that ethanol can modulate the discriminative stimulus effects of cocaine, and that these effects may not be mediated by the actions of ethanol at the GABA(A) receptor.     

Schedule-induced ethanol polydipsia: Function of ethanol concentration

Rats were maintained in cages with automatic food dispensers that provided a 24 hr feeding regimen known to produce schedule-induced ethanol polydipsia. For ten days water was the only available fluid; then for 17 days either 5% or 10% ethanol replaced water. The ethanol concentrations were then switched between groups for a final 13 days. Ethanol intake increased for both groups over the first seven days and then reached asymptote. The daily intake (ml) of 5% ethanol was two times that of 10%, resulting in no difference between groups in g/kg ethanol consumed. When the concentrations were switched, g/kg/day dropped, but returned to previous levels within seven days. Again intake (ml) of 5% was two times that of 10% but groups did not differ in g/kg/day. Mean blood ethanol concentration at 9:30 hr was 75.0 mg/100 ml with 5% ethanol and 127.8 mg/100 ml with 10% ethanol.     

Ethanol does not affect discriminative-stimulus effects of nicotine in rats

The effects of ethanol were evaluated in rats trained to discriminate 0.4 mg/kg of nicotine from saline under a fixed-ratio 10 schedule of food delivery. Ethanol (0.1-1 g/kg, i.p.) did not produce any nicotine-like discriminative effects and did not produce any shift in the dose-response curve for nicotine discrimination. Thus, the ability to discriminate nicotine's effects does not appear to be altered by ethanol administration. However, the high dose of 1 g/kg ethanol, given either alone or in combination with nicotine, markedly depressed food-maintained responding. This later effect was associated in some rats with an attenuation of the discriminative-stimulus effects of the training dose of nicotine. This suggests that previous reports of increased tobacco smoking following ethanol consumption in humans are connected, in some way, with an increase in motivation to consume nicotine that is produced by ethanol, rather than with a decrease in the subjective response to nicotine.     

Ethanol-induced inhibition of the drinking response to hypertonic saline in the rat

The effects of ethanol, in doses of 0.05, 0.1 and 0.2 ml/100 g, on the drinking responses of rats to subcutaneous injection of hypertonic saline (1 mEq/100 g) were examined. Rats were also studied for the effects of ethanol (0.1 ml/100 g) on drinking responses to intraperitoneal injection of dextran (20% w/v, 1.5 ml/100 g). After injection of hypertonic saline, rats given ethanol drank less than those administered water or isocalorific glucose. Ethanol inhibited the drinking responses to hypertonic saline dose-dependently with higher doses having a greater inhibitory effect. Ethanol administration had no effect on water consumption stimulated by intraperitoneal injection of dextran. It is concluded that administration of ethanol to rats has a dose-dependent inhibitory effect on thirst and fluid consumption stimulated by injection of hypertonic saline but is without effect on thirst and drinking stimulated by intraperitoneal injection of dextran.     

Induction of high voluntary ethanol intake in dependent rats

The experimental conditions under which oral high intake may be induced in previously intoxicated rats have been investigated. Seventeen rats were administered intragastrically with 10 g/kg/day of ethanol for 15 days. At cessation of treatment, they were presented a single bottle of alcoholic solution (10% v/v) during 24 hr. For the following 6 days, they received either an ethyl alcohol solution or water in alternation for 8 hours each. Ethanol treated rats exhibited a high oral intake of ethanol equivalent to the previously injected doses. Controls displayed a significantly lower intake of ethanol. It is concluded that the suppression of the withdrawal state by an initial priming oral intake of ethanol in physically dependent rats is a condition for the development of a conditioned taste preference for ethanol as a basis for the behavioral dependence.     

Maternal ethanol consumption by pregnant guinea pigs causes neurobehavioral deficits and increases ethanol preference in offspring

The objective of this study was to test the hypothesis that prenatal exposure to ethanol, through maternal consumption of an aqueous ethanol solution, induces neurobehavioral deficits and increases ethanol preference in offspring. Pregnant Dunkin-Hartley-strain guinea pigs were given 24-h access to an aqueous ethanol solution (5%, v/v) sweetened with sucralose (1 g/l), or water sweetened with sucralose (1 g/l), throughout gestation. Spontaneous locomotor activity was measured in the offspring on postnatal day (PD) 10. The offspring underwent either ethanol preference testing using a two-bottle-choice paradigm beginning on PD 40 or Morris water maze testing using a hidden moving platform design beginning on PD 60. Maternal consumption of a 5% (v/v) ethanol solution (average daily dose of 2.3±0.1 g of ethanol/kg maternal body weight; range: 1.8-2.8 g/kg) decreased offspring birth weight, increased spontaneous locomotor activity, and increased preference for an aqueous ethanol solution. In the Morris water maze test, sucralose-exposed offspring decreased escape latency on the second day of testing, whereas the ethanol-exposed offspring showed no improvement. These data demonstrate that moderate maternal consumption of ethanol produces hyperactivity, enhances ethanol preference, and impairs learning and memory in guinea pig offspring.     

The High-Ethanol Preferring rat as a model to study the shift between alcohol abuse and dependence

The High-Ethanol Preferring line of rats (HEP), recently selected by R.D. Myers, is characterised by a high voluntary consumption of alcohol (3-4 g/kg/day for males and 6-8 g/kg/day for females, when a 10% ethanol solution is available as a choice vs. water) and a high sensitivity to taste reinforcement (saccharin, quinine). Our previous data obtained with HEP rats showed no evidence of development of dependence after long-term sustained alcohol intake. In this study, we subjected these rats to several long-term administration protocols suggested to favour the development of alcohol dependence, including multiple alcohol concentrations or sweetened alcohol solutions (ethanol 10% or 20%+saccharin), and deprivation periods. The results showed no increase in alcohol consumption, no shift of preference for alcohol solutions when offered as a free choice vs. a preferred saccharin solution, and a very limited alcohol-deprivation effect when alcohol is made available after a period of deprivation, the three criteria used to demonstrate the development of dependence. Regardless of the method used, HEP rats failed to show dependence after long-term, heavy ethanol consumption. Resistance to ethanol dependence may in fact be genetically influenced and the HEP rat appears as a valuable model to search for factors involved in the transition from alcohol abuse to dependence.     

Nicotine-induced conditioned taste aversion in the rat: effects of ethanol

It has been shown that small doses of ethanol antagonise the discriminative stimulus properties of nicotine in the rat. The aim of the present study was to evaluate whether ethanol could antagonise the aversive stimulus effects of nicotine. Wistar rats were trained to associate nicotine injections with a novel tasting fluid (0.1% saccharin) in the conditioned taste aversion procedure. Nicotine (0.3 mg/kg, s.c.) was injected 5 min after the end of a 20-min exposure to the saccharin solution. Ethanol (0.25-0.5 g/kg, i.p.) was administered 5 or 50 min before nicotine. In general, ethanol did not inhibit nicotine-induced conditioned taste aversion. Contrary to the findings in drug discrimination studies, a slight but significant enhancement of nicotine-induced taste aversion conditioning was observed after ethanol pre-treatment. Blood ethanol levels were measured in a separate group of rats. Maximal blood ethanol levels after i.p. administration of 0.25 or 0.5 g/kg ethanol exceeded 20 and 80 mg%, respectively. Concluding, the present results may indicate that ethanol does not attenuate nicotine-induced conditioned taste aversion in the rat.     

Induction and maintenance of ethanol self-administration without food deprivation in the rat

Rats were trained to lick at a drinking tube containing 5% ethanol to obtain access to a 0.1-ml dipper containing 20% sucrose. Following 20 of these drinking sessions, a lever press response was shaped and maintained with ethanol presentation in the dipper. This induction procedure resulted in rats responding on a FR 8 schedule of reinforcement to receive 40% (v/v) ethanol. Ethanol intakes over 0.5 g/kg in 30 min were obtained when ethanol concentrations over 10% were available. These intakes frequently resulted in blood ethanol levels over 100 mg ethanol/dl blood. This contingent sucrose induction procedure did not use food deprivation at any time. It is suggested that this procedure can be used to investigate the processes involved with the initiation of ethanol as a reinforcer independent of food restriction procedures.     

Consumption of intoxicating beverages by rats and mice exhibiting high and low preferences for ethanol

Lines of rats selectively bred for alcohol consumption or avoidance (AA and ANA, ALKO, Finland) as well as inbred strains of mice (C57/BL/6J and DBA/2J) and common female Wistar rats (Charles River) exhibiting high and low preferences for ethanol were tested under free-choice conditions for their consumption of solutions of ethanol (5, 10, or 15 g/100 ml tap water), sodium pentobarbital (0.19, 0.038, 0.076 g/100 ml tap water), and different beverages containing ethanol in the range of 8.1–9.6% (red and white wine, Scotch, ethanol in Hawaiian Punch). The Wistar rats and the mice classified as alcohol-preferring also tended to consume more of the pentobarbital solution than did alcohol-avoiding animals. Alcohol-nonaccepting (ANA) rats, however, consumed considerably more of all three pentobarbital solutions than did the alcohol-accepting (AA) rats. The intake of pentobarbital by the ANA rats and C57/BL/6J mice was in the range of 25–40 mg/kg/day, quantities that might be expected to produce pharmacological effects discriminable by those animals. The intake of ethanol by ANA rats was markedly elevated when the ethanol was contained in white wine or in punch.     

Effects of peripheral neurotensin on behavior of the rat.

Neurotensin (NT), a tridecapeptide found in brain and gut neurons, inhibits feeding and grooming, increases drinking, and enhances ethanol-induced sedation in rats after central injection. We tested the behavioral effects of IP injection of NT (0.1-100 micrograms/kg) in water-deprived rats given access to 5 or 10% ethanol for 30 min, followed by 30-min access to water. Behaviors during alcohol access were quantified with an instantaneous time-sampling observational technique. Food intake and observed feeding and grooming behaviors were significantly inhibited by large doses of NT (10-100 micrograms/kg) and water intake and resting behavior were increased. When the "limited access procedure" was used to induce ethanol selection in nondeprived rats, NT did not affect ethanol or water intake. Peripheral NT affects intake of food and water and observed feeding, grooming, and resting after peripheral injection in deprived rats, but does not affect ethanol consumption. These actions suggest physiological roles for endogenous neurotensin and its receptors in regulation of specific behaviors.     

Dose and route dependency of metabolism and toxicity of chloroform in ethanol-treated rats

 The effects of a single dose of ethanol on the metabolism and toxicity of chloroform administered to rats per os (p.o.), intraperitoneally (i.p.), or by inhalation (inh) at different doses were investigated. Rats that had been given either ethanol (2 g/kg) or vehicle (water) alone at 4 p.m. on the previous day were challenged with chloroform at 10 a.m. p.o. (0, 0.1, 0.2, or 0.4 g/kg), i.p. (0, 0.1, 0.2, or 0.4 g/kg), or inh (for 6 h each at 0, 50, 100, or 500 ppm). The ethanol treatment, which had no influence on the intake of food and water, increased chloroform metabolism in vitro about 1.5-fold with no significant influence on liver glutathione content. The treatment had a dose-dependent effect on the metabolism and toxicity of chloroform, and the effect differed depending on the route of administration. Compared at the same dose level, the area under the curve (AUC) of blood chloroform concentration was invariably smaller following p.o. than i.p. administration. In accordance with this, chloroform administered p.o. caused more deleterious hepatic damage than the same amount of chloroform administered i.p. Although ethanol treatment had no significant influence on the AUC at any dose by any route of administration, the toxicity of p.o.-administered chloroform was significantly higher in ethanol-treated rats than in control rats at a dose as low as 0.1 g/kg, whereas no significant difference was observed in toxicity between both groups of rats at such a low dose administered i.p. When rats were exposed inh to air containing chloroform vapor, ethanol consumption had no effect on hepatotoxicity until the exposure concentration was raised to 500 ppm, a finding which suggests that a single dose of ethanol (2 g/kg) affects the toxicokinetics of inhaled chloroform in rats only at a concentration as high as 500 ppm. Received: 6 December 1993 / Accepted: 25 May 1994     

Differences in response to the aversive properties of ethanol in rats selectively bred for oral ethanol preference

A conditioned taste aversion (CTA) paradigm was used to determine whether aversion to the pharmacological effects of ethanol, apart from orosensory cues, can contribute to genetic differences in voluntary ethanol consumption. Four doses of ethanol, administered IP, were paired with the consumption of a 0.1% saccharin solution in rats from the alcohol-preferring (P) and alcohol-nonpreferring (NP) lines. Repeated pairing of saccharin and ethanol in a dose of 1.0 g/kg produced stronger and more prolonged aversion to saccharin in NP rats, compared with P rats, at comparable blood ethanol levels. A low dose of ethanol (0.25 g/kg) produced transient conditioned facilitation of saccharin consumption in P rats, but not in NP rats, at comparable blood ethanol levels. The results suggest that rats of the NP line find the postingestional effects of high-dose ethanol more aversive, and low-dose ethanol less reinforcing, than do rats of the P line. Genetic differences in voluntary ethanol consumption may be due, in part, to differences in aversion to the postingestional effects of ethanol.     

Induction of dependence on ethanol by free-choice drinking in alcohol-preferring rats

Studies were performed to examine whether chronic, voluntary consumption of ethanol by the selectively-bred, alcohol-preferring P-rats produces physical dependence. Body weight reduction, food restriction and flavoring the 10% ethanol solution increased ethanol consumption from 7 to 14 g ethanol/kg body weight/day when water was freely available. Under similar conditions, consumption by selectively-bred, alcohol-nonpreferring NP-rats increased from 1 to 12 g/kg/day. Removal of ethanol after eight weeks induced physical signs of withdrawal in both lines of animals. In two subsequent studies, P-rats were given food, water and unflavored 10% ethanol ad lib for 15 and 20 weeks; ethanol consumption was 7.2 and 5.6 g/kg/day, respectively. Upon removal of ethanol, manifestations of withdrawal, scored blind in one experiment, developed in 85% of the animals and persisted for 72 hours. Importantly, none in the control groups of P and NP rats given water only exhibited these signs. The ethanol withdrawn groups were hyperactive in both the open-field and the head-poke apparatus. These results indicate that sufficient ethanol was voluntarily consumed by the selectively-bred alcohol-preferring P-rats under free-feeding conditions to produce physical dependence.     

Effect of addition of ethanol and NaCl on saccharin + glucose polydipsia.

Rats received an ad lib choice of food, water, and a solution containing saccharin, glucose, and NaCl solutes either as single stimuli or in combinations. Ethanol was gradually added to these vehicles or water from 0.5--15% w/v. Ethanol intakes of all groups with vehicles containing glucose were higher than intakes of the water vehicle group. Ethanol intakes of the 0.125% saccharin + 3.0% glucose + 1.0% NaCl + ethanol group were highest, peaking at greater than 9.0 g/kg/day, and this group displayed the highest blood ethanol levels. However, there was no evidence of withdrawal syndrome, nor of increased intake of unflavored ethanol by groups previously receiving flavored ethanol. It is suggested that ethanol eliminative capacity limits free-choice ethanol intake when maximized by the addition of sapid congeners.     

Effects of restraint stress on voluntary ethanol intake and ulcer proliferation in rats

The present study examined the effect of exposure to a schedule of predictable restraint stress on voluntary ethanol consumption and ulcer proliferation in rats. Following ethanol screening rats were divided into high, medium and low ethanol consuming groups on the basis of daily ethanol intake (g/kg/day) and exposed to daily 1 hr restraint stress for 10 consecutive days. Voluntary ethanol consumption was monitored both during the stress period and for an additional 25 days post-stress. Stomach pathology was assessed on days 1, 5 and 10 of the stress period as well as at the conclusion of the post-stress period. Results indicated a differential effect of stress on ethanol intake in that high ethanol preferring rats consumed less ethanol in the first 5 days of the post-stress period as compared to non-stressed controls. In contrast, the medium ethanol preferring group drank more ethanol than controls during days 1-5 of the post-stress period. Ethanol consumption for the low ethanol groups did not change during the entire experiment. Stomach pathology data revealed no ulcer formation in the stressed groups during the stress period. At the end of the post-stress period, however, stressed animals exhibited a significantly greater ulcer severity (mean cumulative ulcer length) and ulcer frequency (mean number of ulcers per rat) than non-stressed groups. Stomach pathology for ethanol consuming groups did not differ from controls, indicating that ethanol did not, by itself, affect ulcer development.     

Chronic ethanol tolerance as a result of free-choice drinking in alcohol-preferring rats of the WHP line

The development of tolerance to alcohol with chronic consumption is an important criterion for an animal model of alcoholism and may be an important component of the genetic predisposition to alcoholism. The aim of this study was to determine whether the selectively bred Warsaw High Preferring (WHP) line of alcohol-preferring rats would develop behavioral and metabolic tolerance during the free-choice drinking of ethanol. Chronic tolerance to ethanol-induced sedation was tested. The loss of righting reflex (LRR) paradigm was used to record sleep duration in WHP rats. Ethanol (EtOH)-naive WHP rats received a single intraperitoneal (i.p.) injection of 5.0 g ethanol/kg body weight (b.w.), and sleep duration was measured. Subsequently, rats had access to a 10% ethanol solution under a free-choice condition with water and food for 12 weeks. After 12 weeks of the free-choice intake of ethanol, the rats received another single i.p. injection of 5.0 g ethanol/kg b.w., and sleep duration was reassessed. The blood alcohol content (BAC) for each rat was determined after an i.p. injection of 5 g/kg of ethanol in naive rats and again after chronic alcohol drinking at the time of recovery of the righting reflex (RR). The results showed that the mean ethanol intake was 9.14 g/kg/24 h, and both sleep duration and BAC were decreased after chronic ethanol intake. In conclusion, WHP rats exposed to alcohol by free-choice drinking across 12 weeks exhibited increased alcohol elimination rates. Studies have demonstrated that WHP rats after chronic free-choice drinking (12 weeks) of alcohol develop metabolic tolerance. Behavioral tolerance to ethanol was demonstrated by reduced sleep duration, but this decrease in sleep duration was not significant.     

Blood alcohol level and caloric intake in the gravid rat as a function of diurnal period, trimester, and vehicle

Blood ethanol levels, caloric intake and weight gain were monitored over the 21-day gestational period in the gravid Sprague-Dawley rat as a function of the administration of ethanol in either a liquid diet (Ensure) or an aqueous saccharin solution. The mean daily percentage of ethanol consumed (38% vs 31%), and g/Kg of ethanol consumed (11.9 vs 9.7 g/Kg) were higher for the liquid diet group than the aqueous solution group. Ethanol consumption varied by the trimester in the Ensure but not in the saccharin solution rats. Proportional maternal weight gain, live litter size, and live litter weight did not vary as a function of the method of ethanol administration. Both groups exhibited significant diurnal periodicity in ethanol consumption, and the greatest caloric intake during the second trimester. The implications of these results for ethanol administration in gravid rats is discussed.     

A single oral dose of ethanol can alter transdermal absorption of topically applied chemicals in rats.

Topical ethanol is used as a dermal penetration enhancer in some commercial products. Previous studies have demonstrated that chronic ethanol consumption can also disrupt skin barrier function, leading to increased transdermal penetration. This observation becomes much more relevant if a single drinking episode induces similar changes. The purpose of this study was thus to examine the transdermal penetration of three model chemicals after acute ethanol consumption. Wistar rats were gavaged with either 10, 6, 4.3, 3, 1.5 g/kg ethanol or saline and allowed to recover for 2 or 24 h. Blood and skin ethanol levels were determined and in vitro penetration experiments performed. The herbicide paraquat, industrial solvent N,N-dimethylformamide (DMF), and insect repellent N,N-diethyl-m-toluamide (DEET) were used as is model chemicals. Absorption was determined and directly compared between ethanol- and saline-treated skin by calculating enhancement ratios. Blood ethanol levels range from 0.25 to 0.015% at 2 h with skin levels at 12-18% of blood values. Ethanol enhances the absorption of paraquat, DMF, and DEET in a dose-dependent fashion. Paraquat and DEET showed no appreciable reduction in enhancement between 2 and 24 h postgavage for the 10-g/kg dose, but DMF did. Enhancement ratios were higher at 24 h for 10 than for 6 g/kg animals, demonstrating a dose-response relationship for recovery time. These studies imply that increased absorption of topical chemical occurs after alcohol ingestion. Both acute and chronic ethanol consumption can compromise the dermal barrier.