Enhanced ethanol intake in preweanling rats following exposure to ethanol in a nursing context

Moderate ethanol exposure during early ontogeny of the rat alters respiratory plasticity, ultrasonic distress vocalizations, increases brain catalase activity, and acetaldehyde-mediated ethanol intake

Early ontogeny of the rat (late gestation and postnatal first week) is a sensitive period to ethanol’s positive reinforcing effects and its detrimental effects on respiratory plasticity. Recent studies show that acetaldehyde, the first ethanol metabolite, plays a key role in the modulation of ethanol motivational effects. Ethanol brain metabolization into acetaldehyde via the catalase system appears critical in modulating ethanol positive reinforcing consequences. Catalase system activity peak levels occur early in the ontogeny. Yet, the role of ethanol-derived acetaldehyde during the late gestational period on respiration response, ultrasonic vocalizations (USVs), and ethanol intake during the first week of the rat remains poorly explored. In the present study, pregnant rats were given a subcutaneous injection of an acetaldehyde-sequestering agent (D-penicillamine, 50 mg/kg) or saline (0.9% NaCl), 30 min prior to an intragastric administration of ethanol (2.0 g/kg) or water (vehicle) on gestational days 17–20. Respiration rates (breaths/min) and apneic episodes in a whole-body plethysmograph were registered on postnatal days (PDs) 2 and 4, while simultaneously pups received milk or ethanol infusions for 40-min in an artificial lactation test. Each intake test was followed by a 5-min long USVs emission record. On PD 8, immediately after pups completed a 15-min ethanol intake test, brain samples were collected and kept frozen for catalase activity determination. Results indicated that a moderate experience with ethanol during the late gestational period disrupted breathing plasticity, increased ethanol intake, as well brain catalase activity. Animals postnatally exposed to ethanol increased their ethanol intake and exerted differential affective reactions on USVs and apneic episodes depending on whether the experience with ethanol occur prenatal or postnatally. Under the present experimental conditions, we failed to observe, a clear role of acetaldehyde mediating ethanol’s effects on respiratory plasticity or affective states, nevertheless gestational acetaldehyde was of crucial importance in determining subsequent ethanol intake affinity. As a whole, results emphasize the importance of considering the participation of acetaldehyde in fetal programming processes derived from a brief moderate ethanol experience early in development, which in turn, argues against “safe or harmless” ethanol levels of exposure.

The presence of chemosensory cues transmitted through the mother's milk increases the search and ingestion responses toward bitter and sour solutions

Olfaction is of major importance during early stages of life in altricial species. This sense allows newborns to develop different behaviors that will allow them to survive. Odors tend to be associated to contextual stimuli (such as warmth); this, in turn, enables the pups to recognize when to withdraw or approach. At the same time, olfaction modulates the acceptance of aversive flavors. The increase of approach responses toward a bitter substance during early life is enhanced by stimulation with familiar, pre-exposed odors. Newborn rats exhibit heightened grasp responses toward an artificial nipple dispensing quinine, and drink more of this bitter solution, in the presence of a pre-exposed odor (lemon or the mother's odor). The present research assessed the replicability of previous results by pre-exposing the subjects to the scent through maternal milk and using solutions with different aversive tastes. Half of the subjects (3 day-old Wistar rats) were pre-exposed to lemon odor through the maternal milk (the mother had previously ingested the lemon essence via an intragastric injection); 4 h later, all the rats were evaluated in the presence of the lemon odor with an artificial nipple containing quinine, citric acid, saline solution, or water. The results showed enhanced seeking and intake of the bitter (quinine) and sour solution (citric acid). However, this did not occur when the nipple contained water or saline solution. The evidence suggests that: During the early stages of development, familiar odors regulate the acceptance of non-palatable, otherwise rejected, flavors; and that the route of transmission of the pre-exposed odor can be through air, or through food (amniotic fluid in previous studies and, in this case, breast milk), that is, via the retronasal and orthonasal routes.

Effects of ethanol exposure in a familiar or isolated context during infancy on ethanol intake during adolescence

Early exposure to ethanol affects ethanol intake later in life. This early experience encompasses exposure to social stimuli and the pharmacological and orosensory properties of ethanol. The specific contribution of each type of stimulus to subsequent ethanol intake remains unknown. We assessed the intake of various concentrations of ethanol in a familiar or isolated context during infancy and the lingering effects of this experience on ethanol intake during adolescence. On postnatal day 3 (PD3), PD7, and PD11, rats were given 5% ethanol or water in a nursing or isolated context (Experiments 1 and 2). Intake tests (ethanol vs. water) were conducted during adolescence. Experiment 2 matched the amount of fluid ingested during infancy in both contexts and subsequently tested ethanol consumption during adolescence. The results revealed a facilitative effect of the nursing context on fluid intake during the tests in infancy. Pups stimulated with ethanol but not water in the isolated context exhibited an increase in ethanol consumption during adolescence. This effect disappeared when the isolated infants were matched to receive the same amount of ethanol ingested by their nursed counterparts. In Experiment 3, isolated infant rats were exposed to different ethanol concentrations (.0%, 2.5%, 5.0%, and 10.0%), and drug consumption was tested during adolescence. This exposure increased adolescent ethanol intake, regardless of the alcohol concentration (Experiment 3). The common denominators that resulted in enhanced ethanol intake during adolescence were preexposure to ethanol via active consumption of the drug that induced a low-to-moderate level of intoxication in an isolated context.

Prenatal ethanol increases sucrose reinforcement, an effect strengthened by postnatal association of ethanol and sucrose

Late prenatal exposure to ethanol recruits sensory processing of the drug and of its motivational properties, an experience that leads to heightened ethanol affinity. Recent studies indicate common sensory and neurobiological substrates between this drug and sweet tastants. Using a recently developed operant conditioning technique for infant rats, we examined the effects of prenatal ethanol history upon sucrose self-administration (postnatal days, PDs 14-17). Prior to the last conditioning session, a low (0.5 g/kg) or a high (2.5 g/kg) ethanol dose were paired with sucrose. The intention was to determine if ethanol would inflate or devalue the reinforcing capability of the tastant and if these effects are dependent upon prenatal ethanol history. Male and female pups prenatally exposed to ethanol (2.0 g/kg) responded more when reinforced with sucrose than pups lacking this antenatal experience. Independently of prenatal status, a low ethanol dose (0.5 g/kg) enhanced the reinforcing capability of sucrose while the highest dose (2.5 g/kg) seemed to ameliorate the motivational properties of the tastant. During extinction (PD 18), two factors were critical in determining persistence of responding despite reinforcement omission. Pups prenatally exposed to ethanol that subsequently experienced the low ethanol dose paired with sucrose, showed higher resistance to extinction. The effects here reported were not associated with differential blood alcohol levels across prenatal treatments. These results indicate that fetal ethanol experience promotes affinity for a natural sweet reinforcer and that low doses of ethanol are also capable of enhancing the positive motivational consequences of sucrose when ethanol and sucrose are paired during infancy.

A comparison between taste avoidance and conditioned disgust reactions induced by ethanol and lithium chloride in preweanling rats

Adult rats display taste avoidance and disgust reactions when stimulated with gustatory stimuli previously paired with aversive agents such as lithium chloride (LiCl). By the second postnatal week of life, preweanling rats also display specific behaviors in response to a tastant conditioned stimulus (CS) that predicts LiCl-induced malaise. The present study compared conditioned disgust reactions induced by LiCl or ethanol (EtOH) in preweanling rats. In Experiment 1 we determined doses of ethanol and LiCl that exert similar levels of conditioned taste avoidance. After having equated drug dosage in terms of conditioned taste avoidance, 13-day-old rats were given a single pairing of a novel taste (saccharin) and either LiCl or ethanol (2.5 g/kg; Experiment 2). Saccharin intake and emission of disgust reactions were assessed 24 and 48 hr after training. Pups given paired presentations of saccharin and the aversive agents (ethanol or LiCl) consumed less saccharin during the first testing day than controls. These pups also showed more aversive behavioral reactions to the gustatory CS than controls. Specifically, increased amounts of grooming, general activity, head shaking, and wall climbing as well as reduced mouthing were observed in response to the CS. Conditioned aversive reactions but not taste avoidance were still evident on the second testing day. In conclusion, a taste CS paired with postabsorptive effects of EtOH and LiCl elicited a similar pattern of conditioned rejection reactions in preweanling rats. These results suggest that similar mechanisms may be underlying CTAs induced by LiCl and a relatively high EtOH dose.

Maternal care alterations induced by repeated ethanol leads to heightened consumption of the drug and motor impairment during adolescence: a dose-response analysis

Maternal ethanol exposure during lactation induces behavioral alterations in offspring, including disruptions in motor skills and heightened ethanol ingestion during adolescence. These behavioral outcomes appear to partially depend on ethanol-induced disruptions in maternal care. The present study assessed motor skills and ethanol intake in adolescent rats raised by dams that had been repeatedly given ethanol during lactation. Female rats (postpartum days [PDs] 3-13) were administered ethanol (0.5, 1.5, or 2.5 g/kg) or vehicle every other day and allowed to freely interact with their pups. During adolescence, the offspring were evaluated for motor coordination (accelerating rotarod test) and oral ethanol self administration. The lowest maternal ethanol dose (0.5 g/kg) mildly affected motor performance, whereas the higher doses (1.5 and 2.5 g/kg) resulted in motor coordination impairment and greater ethanol intake. Maternal care behavior was affected by ethanol in a dose-dependent fashion. These results indicate that early experience with ethanol during lactation, even when the drug dosage is kept relatively low, leads to long-term consequences in offspring. Dose-response effects on maternal care behavior (i.e., nest building, crouching) may underlie disruptions in motor development and greater ethanol intake resulting from these early ethanol experiences.

Prenatal and postnatal ethanol experiences modulate consumption of the drug in rat pups, without impairment in the granular cell layer of the main olfactory bulb

The effect of moderate exposure to ethanol during late gestation was studied in terms of its interaction with moderate exposure during nursing from an intoxicated dam. A further issue was whether behavioral effects of ethanol, especially the enhanced ethanol intake known to occur after moderate ethanol prenatally or during nursing, depend upon teratological effects that may include death of neurons in the main olfactory bulb (MOB). During gestational days 17-20 rats were given 0, 1 or 2g/kg ethanol doses intragastrically (i.g.). After parturition these dams were given a dose of 2.5g/kg ethanol i.g. each day and allowed to perform regular nursing activities. During postnatal days (PDs) 15 and 16, ethanol intake of pups was assessed along with aspects of their general activity. In a second experiment pups given the same prenatal treatment as above were tested for blood ethanol concentration (BEC) in response to an ethanol challenge on PD6. A third experiment (Experiment 2b) assessed stereologically the number of cells in the granular cell layer of the MOB on PD7, as a function of analogous pre- and postnatal ethanol exposures. Results revealed that ethanol intake during the third postnatal week was increased by prenatal as well as postnatal ethanol exposure, with a few interesting qualifications. For instance, pups given 1g/kg prenatally did not have increased ethanol intake unless they also had experienced ethanol during nursing. There were no effects of ethanol on either BECs or conventional teratology (cell number). This increases the viability of an explanation of the effects of prenatal and early postnatal ethanol on later ethanol intake in terms of learning and memory.

Ethanol exposure during late gestation and nursing in the rat: effects upon maternal care, ethanol metabolism and infantile milk intake

Ethanol experiences, during late gestation as well as during nursing, modify the behavioral dynamics of the dam/pup dyad, and leads to heightened ethanol intake in the offspring. This study focuses on: a) behavioral and metabolic changes in intoxicated dams with previous exposure to ethanol during pregnancy and b) infantile consumption of milk when the dam is either under the effects of ethanol or sober. Pregnant rats received water, 1.0 or 2.0 g/kg ethanol, and were administered with water or ethanol during the postpartum period. Intoxication during nursing disrupted the capability of the dam to retrieve the pups and to adopt a crouching posture. These disruptions were attenuated when dams had exposure to ethanol during pregnancy. Ethanol experiences during gestation did not affect pharmacokinetic processes during nursing, whereas progressive postpartum ethanol experience resulted in metabolic tolerance. Pups suckling from intoxicated dams, with previous ethanol experiences, ingested more milk than did infants suckling from ethanol-intoxicated dams without such experience. Ethanol gestational experience results in subsequent resistance to the drug's disruptions in maternal care. Consequently, better maternal care by an intoxicated dam with ethanol experience during gestation facilitates access of pups to milk which could be contaminated with ethanol.

Fetal learning about ethanol and later ethanol responsiveness: evidence against "safe" amounts of prenatal exposure

Near-term fetuses of different mammalian species, including humans, exhibit functional sensory and learning capabilities. The neurobiological literature indicates that the unborn organism processes sensory stimuli present in the amniotic fluid, retains this information for considerable amounts of time, and is also capable of associating such stimuli with biologically relevant events. This research has stimulated studies aimed at the analysis of fetal and neonatal learning about ethanol, a topic that constitutes the core of the present review. Ethanol has characteristic sensory (olfactory, taste, and trigeminal) attributes and can exert pharmacologic reinforcing effects. The studies under examination support the hypothesis that low to moderate levels of maternal ethanol intoxication during late pregnancy set the opportunity for fetal learning about ethanol. These levels of prenatal ethanol exposure do not generate evident morphologic or neurobehavioral alterations in the offspring, but they exert a significant impact upon later ethanol-seeking and intake behaviors. Supported by preclinical and clinical findings, this review contributes to strengthening the case for the ability of prenatal ethanol exposure to have effects on the postnatal organism.

The effect of gestational ethanol exposure on voluntary ethanol intake in early postnatal and adult rats

Clinical and epidemiological studies provide strong data for a relationship between prenatal ethanol exposure and the risk for abuse in adolescent and young adult humans. However, drug-acceptance results in response to fetal exposure have differed by study, age at evaluation, and experimental animal. In the present study, the authors tested whether voluntary ethanol intake was enhanced in both the infantile and adult rat (15 and 90 days of age, respectively), as a consequence of chronic fetal drug experience. Experimental rats were exposed in utero by administering ethanol to a pregnant dam in a liquid diet during gestational Days 6-20. Compared with those for isocaloric pair-fed and ad lib chow control animals, the results for experimental animals demonstrated that fetal exposure significantly increased infantile affinity for ethanol ingestion without affecting intake patterns of an alternative fluid (water). Heightened affinity for ethanol was absent in adulthood. Moreover, the results argue against malnutrition as a principal factor underlying the infantile phenomenon. These data add to a growing literature indicative of heightened early postnatal acceptance patterns resulting from maternal use or abuse of ethanol during pregnancy.

Heightened Ethanol Intake in Infant and Adolescent Rats After Nursing Experiences With an Ethanol-Intoxicated Dam

BACKGROUND

Preweanling rats detect ethanol (175 mg/100 ml) in maternal milk when the dam is moderately intoxicated. Repeated experiences with the intoxicated dam facilitate subsequent recognition of ethanol's chemosensory attributes and promote ethanol-related memories with a negative hedonic content. This memory has been attributed to the infant's acquired association between ethanol's chemosensory attributes and its disruptive effects on maternal care. In this study, infant and adolescent ethanol intake patterns were analyzed as a function of prior interactions, during early infancy, with their intoxicated dams.

METHODS

During postpartum days 3, 5, 7, 9, 11, and 13, breast-feeding dams received an intragastric administration of either 2.5 g/kg of ethanol or water. Pups whose dams had been given one of these two maternal treatments were tested on postnatal day 15 for ingestion of 0% (water), 2.5, 5.0, or 10% v/v ethanol solution. During adolescence, remaining animals from these litters were first adapted to ingest water from drinking tubes and then were given simultaneous access to tap water and a given ethanol solution. The first day, a 3% v/v ethanol solution was used. This solution was increased by 1% ethanol each following day until the solution was 6% v/v ethanol.

RESULTS

Maternal drug treatment did not affect the body weights of dams, infants, or adolescents. Water intake during infancy and adolescence also was unaffected by prior maternal treatment. However, infants that had previously interacted with ethanol-intoxicated dams exhibited heightened ethanol intake scores (grams per kilogram and percentage body weight gains), especially when tested with 5 or 10% v/v ethanol solutions. Similarly, adolescent males (but not females) that had interacted with an intoxicated dam during infancy also had higher ethanol consumption levels than those that had interacted with a nonintoxicated dam.

CONCLUSIONS

Contrary to what might be expected in animals that acquire an aversive memory for ethanol's chemosensory cues as a function of prior interactions with an intoxicated mother, these results indicate that such interactions promote a long-lasting increase in ethanol intake. These results suggest that rats reared by intoxicated dams become sensitive to the negative reinforcing properties of ethanol.

National Institute on Alcohol Abuse and Alcoholism Report on Moderate Drinking

In support of the 2005 update of the U.S. Department of Agriculture/U.S. Department of Health and Human Services Dietary Guidelines, the National Institute on Alcohol Abuse and Alcoholism was asked to assess the strength of the evidence related to health risks and potential benefits of moderate alcohol consumption, with particular focus on the areas of cardiovascular disease, breast cancer, obesity, birth defects, breastfeeding, and aging. The findings were reviewed by external researchers with extensive research backgrounds on the consequences and benefits of alcohol consumption. This report now serves as the National Institutes of Health's formal position paper on the health risks and potential benefits of moderate alcohol use.

Socially mediated alcohol preferences in adolescent rats following interactions with an intoxicated peer

This study focuses on "passive social influences" (alcohol-related information acquired by an organism that interacts with an intoxicated counterpart) that can potentially affect alcohol preference in adolescent rats. Five experiments were conducted to investigate whether repeated social interactions with an intoxicated peer can generate alcohol-related memories that lead an animal to exhibit heightened alcohol olfactory preference patterns. Juvenile experiences with alcohol were operationalized as follows: interactions with an alcohol-intoxicated peer (Experiment 1), with an alcohol-scented cotton surrogate (Experiment 2) or with an anesthetized alcohol-intoxicated partner (Experiments 3-5). Periadolescents were then evaluated in a two-way location olfactory test where they had the opportunity to investigate a hole scented with alcohol odor or vanilla (an odorant naturally preferred by the strain of rats here utilized). Only juveniles that interacted with an alcohol-intoxicated peer were found to exhibit a significant change in alcohol odor preferences when compared to appropriate controls that interacted with a non-intoxicated peer. Alcohol odor exposure alone or interactions with an anesthetized alcohol-intoxicated peer were not sufficient to establish changes in preference for alcohol sensory cues. Results indicate that social interactions with an intoxicated peer determine heightened preference for alcohol cues in periadolescents. The establishment of this preference seems to require behavioral manifestations of the intoxicated counterpart, instead of just being dependent on an olfactory pre-exposure to alcohol cues.

Long lasting effects of rearing by an ethanol-consuming dam on voluntary ethanol consumption by rats

For exposure to alcohol early in life to potentiate alcohol abuse in adolescence or adulthood, consequences of early exposure to alcohol must be of considerable duration. In two experiments using Norway rats as subjects, we examined effects of exposure during weaning to a dam consuming ethanol on adolescents' later affinity for ethanol. In a preliminary experiment, we offered rat pups a choice between 8% ethanol and water for 7 days immediately after they were weaned at 26 days of age. Pups whose dam had ingested 8% ethanol for 6 days either immediately or 1 week before we weaned them drank more ethanol than pups whose dam drank only water during the same period. Independent groups of rats reared by a dam consuming 8% ethanol from postnatal days 18 to 26 and tested 1, 2, 4 or 6 weeks later all drank significantly more 8% ethanol at testing than did pups whose dam drank only water. Our data also provided confirmation of previous reports of an experience-independent greater affinity for ethanol in younger rats.

Nursing from an ethanol-intoxicated dam induces short- and long-term disruptions in motor performance and enhances later self-administration of the drug

RATIONALE

During interactions with an ethanol-intoxicated dam, preweanling rats encode ethanol-related chemosensory information. These experiences have been observed to enhance subsequent recognition of ethanol's chemosensory properties and to modulate learning about ethanol.

OBJECTIVE

The present study tested the effects of ethanol-related nursing experiences on motor function in later infancy and adolescence and on ethanol intake during adolescence.

METHODS

Wistar-derived rats were reared by dams intragastrically administered with ethanol (2.5 g/kg) or with water during postnatal days (PDs) 3, 5, 7, 9, 11, and 13. Later in infancy or in adolescence, these rats were tested on a motor coordination task (Accelerod) while either sober or acutely intoxicated with ethanol (1 g/kg). During adolescence, animals had simultaneous access to varying ethanol concentrations (3, 4, 5, or 6% v/v) and water.

RESULTS

Both infants and adolescents that had been reared by ethanol-intoxicated dams exhibited dramatic behavioral impairments in the Accelerod task when compared with the offspring of water control dams. Ethanol intoxication disrupted motor performance in both age groups, but this effect was independent of prior maternal treatment. When tested for voluntary ethanol intake as adolescents, those with prior nursing experiences with an intoxicated dam ingested more ethanol than adolescents reared by sober dams.

CONCLUSIONS

Early experiences with alcohol comprising interactions with an alcohol-intoxicated dam result in motor impairment and enhanced ethanol intake later in life.

Effects of ethanol consumption by adult female rats on subsequent consumption by adolescents

We used a two-bottle choice test to measure voluntary ethanol consumption by adolescent rats that had lived with ethanol-consuming or water-consuming adult conspecifics. We found that housing weanlings with either a virgin or a lactating adult female rat that ingested ethanol increased the weanlings' subsequent voluntary intake of ethanol when they were fluid-deprived and provided with choices between 8% ethanol solution and water for 2 h/day. Rats housed with both an ethanol-consuming virgin female and their water-consuming dam drank more ethanol than did rats housed with a dam and virgin female, both consuming water. Rats housed with an ethanol-consuming dam and ethanol consuming adult virgin did not drink more ethanol than did rats housed with an ethanol-consuming dam and a water-consuming virgin female. In sum: (1) young rats learned socially to consume ethanol. (2) Exposure to ethanol in mother's milk was not necessary for such social learning to occur, and (3) living with an ethanol-consuming unfamiliar, virgin female conspecific resulted in enhanced ethanol intake by adolescent rats, even if a water-consuming dam was also present.

Ethanol consumption by rat dams during gestation, lactation and weaning increases ethanol consumption by their adolescent young

In two experiments, we examined effects of ethanol consumption in rat dams during gestation, lactation, and weaning on voluntary ethanol consumption by their adolescent young. We found that exposure to an ethanol-ingesting dam throughout gestation, lactation, and weaning enhanced voluntary ethanol consumption by 26- to 33-day-old adolescents. We systematically examined effects on adolescent ethanol intake or requiring dams to drink ethanol during various periods in their pups' development. We found that exposure to an ethanol-consuming dam during weaning enhanced adolescent ethanol consumption and exposure to a dam drinking ethanol during either gestation or while nursing enhanced adolescents' ethanol consumption only if pups also had access to ethanol during the weaning period.

Chemosensory factors influencing alcohol perception, preferences, and consumption

This article presents the proceedings of a symposium at the 2002 RSA/ISBRA Meeting in San Francisco, California, co-organized by Julie A. Mennella and Alexander A. Bachmanov of the Monell Chemical Senses Center. The goal of this symposium was to review the role that chemosensory factors (taste, smell, and chemical irritation) play in the perception, preference, and consumption of alcohol. The presented research focused on both humans and laboratory animals and used a variety of approaches including genetic, developmental, pharmacological, behavioral, and psychophysical studies. The presentations were as follows: (1) Introduction and overview of the chemical senses (Julie A. Mennella and Alexander A. Bachmanov); (2) Taste reactivity as a measure of alcohol palatability and its relation to alcohol consumption in rats (Stephen W. Kiefer); (3) Early learning about the sensory properties of alcohol in laboratory animals (Juan Carlos Molina); (4) Early learning about the sensory properties of alcohol in humans (Julie A. Mennella); (5) Genetic dissection of the ethanol-sweet taste relationship in mice (Alexander A. Bachmanov and Michael Tordoff); and (6) Human genetic variation in taste: connections with alcohol sensation and intake (Valerie B. Duffy and Linda M. Bartoshuk). The symposium concluded with a general discussion.

Increases in ethanol ingestion by young rats following interaction with intoxicated siblings: a review

Although there are a variety of animal models used in alcoholism research, there has been very little experimental investigation into possible environmental/experiential factors leading to an initial bout of alcohol ingestion. Adolescent alcohol abuse is a major problem in today's society and research is beginning to focus on the predisposing conditions toward alcohol consumption, particularly in this vulnerable age group. The results of recent research from our laboratory are reviewed in which voluntary ingestion of ethanol by preweanling and adolescent rats is increased following exposure to an intoxicated sibling. This paradigm centers on the notion that rodents, and perhaps other mammalian species as well, acquire information about foods to ingest based in part on interaction with a conspecific that has recently ingested a novel diet (e.g. Galef, 1981). Smelling food-derived cues on the breath of another animal is known to affect later food choice. The procedures described in this paper represent a potential new model for examining the effects of early exposure to ethanol through social interactions on the initiation of voluntary alcohol ingestion.

Social interaction with an intoxicated sibling can result in increased intake of ethanol by periadolescent rats

A novel procedure for enhancing voluntary intake of ethanol in periadolescent rats is described. The procedure is a modification of Galef et al.'s (e.g., Galef, Kennett, & Stein, 1985; Anim Learn Behave 13:25-30) demonstrator-observer procedure. Subjects were Sprague-Dawley rats, 28-35 days of age. The experimental subject (observer) interacted with a same-sex conspecific (demonstrator) previously administered (a) 1.5 g/kg ethanol, (b) an equal volume of water, or (c) 2.1% Sanka coffee intragastrically. Observers were tested with 24-hour access to ethanol and coffee solutions. Observers that had interacted with demonstrators administered ethanol ingested significantly more ethanol during the test than observers in the other two groups. In Experiment 2 demonstrators were administered one of several doses of ethanol (0.0, 1.0, 1.5, or 3.0 g/kg) and observers' ethanol intakes were assessed. Only those observers that interacted with 1.5 g/kg demonstrators increased their ingestion of ethanol, relative to water controls. The lower (1.0 g/kg) and higher (3.0 g/kg) dose groups did not show altered ethanol ingestion. These results are discussed with respect to threshold levels of respired ethanol cues and the ability of observers to detect these cues from demonstrators. The demonstrator-observer procedure appears to be effective for the social transmission of preferences for ethanol in periadolescent rats.

Infant rats respond differently to alcohol after nursing from an alcohol-intoxicated dam

Our previous studies indicate that rat pups are able to detect the low levels of ethanol (175 mg %) found in the milk of a moderately intoxicated dam. The present study tested the effect of infantile interactions (including suckling) with ethanol-treated mothers on later behavioral responsiveness to ethanol's sensory properties. In Experiment 1, pups suckled from dams subjected to a 2.5 g/kg ethanol dose (i.g.) or water-treated females during postnatal days (PDs) 3, 5, 7, 9, 11, and 13. During PD 15, these pups were exposed to procedures to induce a conditioned aversion to the low level of ethanol (175 mg % in water), with lithium chloride as the unconditioned stimulus. Conditioning was more effective for pups with the prior ethanol experience within the nursing context. Greater responsiveness to ethanol in milk also was found for conditioning control pups that had interacted with intoxicated dams than for those that had interacted with water-treated dams. Experiment 2 determined that interaction with an intoxicated dam was sufficient for altered responsiveness to ethanol, in that the additional conditioning procedures of Experiment 1 were not needed for the effect. Generally, a relatively brief history of infantile interaction with ethanol-intoxicated dams increased later responsiveness to ethanol's orosensory properties. The results suggest that moderately intoxicated dams within the nursing context provide information to the progeny that may lead to the establishment of ethanol-related memories.

Chronic alcohol administration in the rat pup: effects upon later consumption of alcohol and other palatable solutions

Previous studies indicate that in rats, chronic alcohol exposure during the first weeks of life markedly affect subsequent ethanol consumption patterns. The present study examined the impact of different alcohol doses (0.5-3.0 g/kg), administered between postnatal days 6-12, upon subsequent infantile consumption of an ethanol solution as well as upon intake of various non-ethanol solutions (water, sucrose, quinine or sucrose mixed with quinine). Alcohol administration did not strongly affect consumption scores of water, sucrose or quinine. In contrast, 15-day-old pups pretreated with 2.0 and 3.0 g/kg alcohol doses showed significant increases in terms of alcohol consumption when compared to saline controls. Furthermore, a positive significant correlation was observed between alcohol intake patterns and alcohol dose administered during early ontogeny. Intake of sucrose mixed with quinine was also significantly and positively correlated with pretreatment ethanol dosage. Interestingly, this taste configuration has been shown to mimic psychophysical properties of ethanol in the rat. The results appear not to be explained by teratological effects of the drug upon sensory processing of distinctive tastants. It appears that chronic alcohol exposure during early ontogeny provides specific sensory-related alcohol information that later modulates alcohol intake patterns.

Behavioral detection of low concentrations of ethanol in milk in the preweanling rat

Previous animal models testing infantile reactivity to ethanol (EtOH) in maternal milk used EtOH doses that vastly exceeded levels actually encountered in a mildly or moderately intoxicated dam. The present study assessed whether 12- and 16-day-old rats are capable of detecting EtOH in milk at levels actually recorded in an intoxicated dam. Experiment 1 determined representative levels of EtOH in maternal milk as a function of maternal intragastric administration of EtOH (0.5-3.0 g/kg). Experiment 2A assessed generalization of conditioned taste aversions accrued with a high level of EtOH (6%) in either water or milk vehicles towards lower, more representative EtOH levels obtained from Experiment 1. With body weight gain as the dependent measure, conditioned aversions to milk were evident with the milk vehicle, but there was no detection of EtOH at any level at either age. Detection of the high level of EtOH (6%) in milk, however, was observed by 16 day olds within an habituation paradigm (Exp. 2b) via cardiac and behavioral (locomotion, mouthing) indexes. In Experiment 3 application of Experiment 2's more sensitive, behavioral index to assess generalization of the conditioned taste aversions revealed detection of a lower, more representative concentration of EtOH (175 mg%) in milk in 16-day-old rats. Overall the results show that the unweaned rat is capable of detecting very low concentrations of EtOH in milk and can modify their behavior accordingly. The expression of this capability is not, however, homogeneous across different response indexes. In conjunction with prior research it is clear that the infant rat's perception of EtOH in milk, including the very low levels of EtOH found in maternal milk during mild or moderate intoxication, is a relevant experience for generating new responses towards EtOH.

Effects of preweanling ethanol odor exposure on ethanol preference

Preweaning exposure to a foreign odor has been shown to alter later responding to that odor. Early experience with ethanol odor may alter not only responding to ethanol odor, but also intake of ethanol solutions. The present study tested the effects of exposure to ethanol odor prior to weaning on ethanol odor preference and ethanol consumption. Sprague-Dawley-derived rats were exposed to the odor of 100% ethanol from postnatal day 1 to 22 in the home cage. An odor preference test was conducted on postnatal day 14 and a two-bottle ethanol intake test was conducted after weaning. In both odor preference and intake tests, animals previously exposed to ethanol odor exhibited a greater preference for ethanol than controls. The results demonstrate that early experience with the odor of ethanol can increase ingestion of ethanol later in life.

Prenatal and postnatal ethanol exposure influences preweanling rats' behavioral and autonomic responding to ethanol odor

The specific question was how prenatal and/or postnatal experience with ethanol influences cardiac and behavioral responses to the odor of ethanol on postnatal day (PD) 16. In each of two experiments, pregnant rats were given ethanol or water on gestational days 17-20. Offspring were exposed on PD12 to one of three conditions: intragastric administration of 6% ethanol, indirect exposure to ethanol from littermates, or no treatment. Results of Experiment 1 indicated that, regardless of prenatal ethanol exposure, 16-day-olds exposed on PD12 either directly or indirectly to ethanol expressed a greater increase in HR in response to ethanol odor than pups not postnatally exposed to ethanol. In Experiment 2, in which a lower ethanol dose was used postnatally, an interaction between pre- and postnatal ethanol exposure was observed; that is, pups exposed pre- and postnatally to ethanol showed the greatest increases in HR and the smallest increases in motor activity in response to ethanol odor. In both experiments motor activity was dissociated from increases in HR. The results are discussed in terms of what is learned, prenatally and postnatally, in association with the chemosensory properties of ethanol.

Mother's milk: a medium for early flavor experiences

For centuries, many believed that the lactating woman's diet could influence the composition and flavor of her milk and that substances in human milk could be transmitted from the wet nurse or mother and have long-lasting effects on the child. The research described herein focuses on mother's milk as a medium of early sensory experiences for the human infant and establishes several points. First, human milk is not a food of invariant flavor. Rather, like the milk of other mammals, human milk is flavored by ingested compounds such as garlic, mint, vanilla, and alcohol and provides the potential for a rich source of varying chemosensory experiences to the infant. Second, the infants' response to a particular flavor in milk may depend upon the recency and duration of past exposures. That is, the prior diet of mothers, and consequently their infants, may modify the infants' responses to these flavors during breastfeeding.