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

C57BL/6J offspring mice reared by a single-mother exhibit, compared to mice reared in a biparental parenting structure, distinct neural activation patterns and heightened ethanol-induced anxiolysis

RATIONALE

Parenting experiences with caregivers play a key role in neurodevelopment. We recently reported that adolescents reared by a single-mother (SM) display an anxiety-prone phenotype and drink more alcohol, compared to peers derived from a biparental (BP) rearing condition.

OBJECTIVES

To investigate if SM and BP offspring infant mice exhibit differential sensitivity to ethanol-induced locomotor activity and differential activity patterns in brain areas related to anxiety response. We also analyzed anxiety response and ethanol-induced anxiolysis in SM and BP adolescents.

METHODS

Mice reared in SM or BP conditions were assessed for (a) ethanol-induced locomotor activity at infancy, (b) central expression of Fos-like proteins (likely represented mostly by FosB, a transcription factor that accumulates after chronic stimuli exposure and serves as a molecular marker of neural plasticity) and cathecolaminergic activity, and (c) anxiety-like behavior and ethanol-induced anxiolysis in adolescence.

RESULTS

Infant mice were sensitive to the stimulating effects of 2.0 g/kg alcohol, regardless parenting structure. SM mice exhibited, relative to BP mice, a significantly greater number of Fos-like positive cells in the central amygdala and basolateral amygdala nuclei. Ethanol treatment, but not parenting condition, induced greater activation of dopaminergic neurons in ventral tegmental area. SM, but not BP, adolescent mice were sensitive to ethanol-induced anxiolysis.

CONCLUSIONS

These results highlight the complex relationship between parenting experiences and neurodevelopment. The SM parenting may result in greater neural activation patterns in brain areas associated with anxiety response, potentially contributing to increased basal anxiety and alcohol sensitivity.

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.

Brief ethanol exposure and stress-related factors disorganize neonatal breathing plasticity during the brain growth spurt period in the rat

RATIONALE

The effects of early ethanol exposure upon neonatal respiratory plasticity have received progressive attention given a multifactorial perspective related with sudden infant death syndrome or hypoxia-associated syndromes. The present preclinical study was performed in 3-9-day-old pups, a stage in development characterized by a brain growth spurt that partially overlaps with the 3rd human gestational trimester.

METHODS

Breathing frequencies and apneas were examined in pups receiving vehicle or a relatively moderate ethanol dose (2.0 g/kg) utilizing a whole body plethysmograph. The experimental design also considered possible associations between drug administration stress and exteroceptive cues (plethysmographic context or an artificial odor). Ethanol exposure progressively exerted a detrimental effect upon breathing frequencies. A test conducted at PD9 when pups were under the state of sobriety confirmed ethanol's detrimental effects upon respiratory plasticity (breathing depression).

RESULTS

Pre-exposure to the drug also resulted in a highly disorganized respiratory response following a hypoxic event, i.e., heightened apneic episodes. Associative processes involving drug administration procedures and placement in the plethysmographic context also affected respiratory plasticity. Pups that experienced intragastric administrations in close temporal contiguity with such a context showed diminished hyperventilation during hypoxia. In a 2nd test conducted at PD9 while pups were intoxicated and undergoing hypoxia, an attenuated hyperventilatory response was observed. In this test, there were also indications that prior ethanol exposure depressed breathing frequencies during hypoxia and a recovery normoxia phase.

CONCLUSION

As a whole, the results demonstrated that brief ethanol experience and stress-related factors significantly disorganize respiratory patterns as well as arousal responses linked to hypoxia in neonatal rats.

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 exposure alters met-enkephalin expression in brain regions related with reinforcement: possible mechanism for ethanol consumption in offspring

The endogenous opioid system is involved in ethanol reinforcement. Ethanol-induced changes in opioidergic transmission have been extensively studied in adult organisms. However, the impact of ethanol exposure at low or moderate doses during early ontogeny has been barely explored. We investigated the effect of prenatal ethanol exposure on alcohol intake and Methionine-enkephalin (Met-enk) content in rat offspring. Met-enk content was assessed in the ventral tegmental area [VTA], nucleus accumbens [NAcc], prefrontal cortex [PFC], substantia nigra [SN], caudate-putamen [CP], amygdala, hypothalamus and hippocampus. Pregnant rats were treated with ethanol (2g/kg) or water during GDs 17-20. At PDs 14 and 15, preweanlings were evaluated in an intake test (5% and 10% ethanol, or water). Met-enk content in brain regions of infants prenatally exposed to ethanol was quantitated by radioimmunoassay. Ethanol consumption was facilitated by prenatal experience with the drug, particularly in females. Met-enk content in mesocorticolimbic regions - PFC and NAcc - was increased as a consequence of prenatal exposure to ethanol. Conversely, Met-enk levels in the VTA were reduced by prenatal ethanol manipulation. Prenatal ethanol also increased peptide levels in the medial-posterior zone of the CP, and strongly augmented Met-enk content in the hippocampus and hypothalamus. These findings show that prenatal ethanol exposure stimulates consumption of the drug in infant rats, and induces selective changes in Met-enk levels in regions of the mesocorticolimbic and nigrostriatal systems, the hypothalamus and hippocampus. Our results support the role of mesocorticolimbic enkephalins in ethanol reinforcement in offspring, as has been reported in adults.

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.

Role of mu, delta and kappa opioid receptors in ethanol-reinforced operant responding in infant rats

We recently observed that naloxone, a non-specific opioid antagonist, attenuated operant responding to ethanol in infant rats. Through the use of an operant conditioning technique, we aimed to analyze the specific participation of mu, delta, and kappa opioid receptors on ethanol reinforcement during the second postnatal week. In Experiment 1, infant rats (PDs 14-17) were trained to obtain 5, 7.5, 10, or 15% ethanol, by operant nose-poking. Experiment 2 tested blood ethanol levels (BELs) attained by operant behavior. In Experiment 3, at PDs 16-18, rats received CTOP (mu antagonist: 0.1 or 1.0 mg/kg), naltrindole (delta antagonist: 1.0 or 5.0 mg/kg) or saline before training. In Experiment 4, rats received nor-binaltorphimine (kappa antagonist: 10.0 or 30.0 mg/kg, a single injection after completion of PD 15 operant training), spiradoline mesylate (kappa agonist: 1.0 or 5.0 mg/kg; at PDs 16-18) or saline (PDs 16-18), before the conditioning. Experiments 5 and 6 assessed possible side effects of opioid drugs in locomotor activity (LA) and conditioned taste aversion (CTA). Ethanol at 7.5 and 10% promoted the highest levels of operant responding. BELs were 12-15 mg/dl. In Experiment 3 naltrindole (dose-response effect) and CTOP (the lowest dose) were effective in decreasing operant responding. Nor-binaltorphimine at 10.0 mg/kg and spiradoline at 5.0 mg/kg also blocked ethanol responding. The effects of opioid drugs on ethanol reinforcement cannot be explained by effects on LA or CTA. Even though particular aspects of each opioid receptor require further testing, a fully functional opioid system seems to be necessary for ethanol reinforcement, during early ontogeny.

Naloxone attenuation of ethanol-reinforced operant responding in infant rats in a re-exposure paradigm

RATIONALE

Early ethanol exposure promotes ethanol reinforcement, mediated perhaps by ethanol's motivational effects. The opioid system mediates ethanol reinforcement, at least in part.

OBJECTIVES

Modulation of consummatory and seeking behaviors by the opioid system was tested in terms of ethanol or sucrose operant self-administration.

METHODS

Wistar-derived infant rats were tested in an operant conditioning task. (1) Infants were trained on postnatal days (PDs) 14-17 to obtain 5% sucrose and 3.75% ethanol or water, and evaluated in an extinction session at PD 18. (2) Ethanol (3.75%) was used as reinforcer. At PDs 16-17, 6 h before operant task, pups were re-exposed to ethanol after naloxone injection (0 or 1 mg/kg). (3) Sucrose (5%) acted as reinforcer. Pups were re-exposed to sucrose after naloxone injection. (4) A PD 18 re-exposure trial in which pups were injected with naloxone and re-exposed to ethanol was added.

RESULTS

Sucrose and ethanol promoted higher levels of operant responding than water during training and extinction. Re-exposure to ethanol preceded by naloxone decreased nose-poking. A similar profile was observed towards sucrose. No seeking behavior was observed in pups re-exposed to ethanol following naloxone injection during PDs 16-18.

CONCLUSIONS

Self-administration of ethanol was established in terms of operant responding in preweanling rats with no previous exposure to the drug. Pairing of naloxone with ethanol, at a point separate in time from operant responding, reduced ethanol reinforcement. This indicated participation of the opioid system in ethanol reinforcement. This effect seems not to be unique to ethanol but also is observable when sucrose acts as reinforcer.

Alcohol-induced neuronal death in central extended amygdala and pyriform cortex during the postnatal period of the rat

Mothers who consume alcohol during pregnancy may cause a neurotoxic syndrome defined as fetal alcohol spectrum disorder (FASD) in their offspring. This disorder is characterized by reduction in brain size, cognitive deficits and emotional/social disturbances. These alterations are thought to be caused by an alcohol-induced increase in apoptosis during neurodevelopment. Little is known about neuroapoptosis in the central extended amygdala and the pyriform cortex, which are key structures in emotional/social behaviors. The goal of this study was to determine the vulnerability of neuroapoptotic alcohol effects in those areas. Rats were administered alcohol (2.5g/kg s.c. at 0 and 2h) or saline on postnatal day (PND) 7, 15 and 20. The Amino-cupric-silver technique was used to evaluate neurodegeneration and immunohistochemistry to detect activated caspases 3-8 and 9 at 2h, 4, 6, 8, 12 and 24h after drug administration. We measured blood alcohol levels each hour, from 2 to 8h post second administration of alcohol in each of the ages studied. Results showed alcohol induced apoptotic neurodegeneration in the central extended amygdala on PND 7 and 15, and pyriform cortex on PND 7, 15 and 20. These structures showed activation of caspase 3 and 9 but not of caspase 8 suggesting that alcohol-induced apoptosis could occur by the intrinsic pathway. The pharmacokinetic differences between ages did not associate with the neurodegeneration age dependence. In conclusion, these limbic areas are damaged by alcohol, and each one has their own window of vulnerability during the postnatal period. The possible implications in emotional/social features in FASD are discussed.

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.

Participation of the endogenous opioid system in the acquisition of a prenatal ethanol-related memory: effects on neonatal and preweanling responsiveness to ethanol

The present study tested the involvement of the opioid system in the acquisition and expression of prenatal ethanol-related memories. We evaluated how this prenatal experience modulates ethanol self-administration in newborn rats, and preweanling's ingestion of the drug. During Gestational Days (GDs) 17-20, four groups of dams were treated with ethanol (2 g/kg) or water, followed immediately by naloxone (10 mg/kg) or saline administration. A fifth group received a similar dose of naloxone 20min before ethanol administration. On PD 1, pups were tested on an operant learning procedure to obtain milk or 3% ethanol. One hour later, an extinction session was performed. At Postnatal Days (PDs) 14 and 15, preweanlings representing each prenatal treatment were evaluated in an intake test with infusions of 5% ethanol or water. Prior to the intake test on PD14, preweanlings were administered naloxone (1 mg/kg), saline or remained untreated. In both tests, animals representative of both genders were utilized. One-day-old pups rapidly learned the operant behavior to gain access to milk. In contrast, only pups prenatally treated with ethanol (administered immediately before naloxone or saline injection) increased operant responding to gain access to ethanol. On an intake test at PDs 14 and 15, those animals prenatally exposed to naloxone 20 min before ethanol administration consumed significantly lower ethanol levels than the remaining prenatal ethanol groups. Postnatal treatment with naloxone diminished intake of all solutions at PD14. These results suggest that prenatal ethanol exposure facilitates neonatal operant learning reinforced by intraoral administration of ethanol and increases ethanol consumption during PDs 14-15. The endogenous opioid system apparently is involved in the acquisition of prenatal ethanol memories, which can modulate the reinforcing attributes of the drug in neonatal and preweanling rats.

Binge ethanol exposure in late gestation induces ethanol aversion in the dam but enhances ethanol intake in the offspring and affects their postnatal learning about ethanol

Previous studies show that exposure to 1 or 2g/kg of ethanol during the last days of gestation increases ethanol acceptance in infant rats. We tested whether prenatal exposure to 3g/kg, a relatively high ethanol dose, generates an aversion to ethanol in both the dam and offspring, and whether this prenatal experience affects the expression of learning derived from ethanol exposure postnatally. The answer was uncertain, because postnatal administration of a 3-g/kg ethanol dose induces an aversion to ethanol after postnatal day (PD) 10 but increases ethanol acceptance when administered during the first postnatal week. In the present study, pregnant rats received intragastric administrations of water or ethanol (3g/kg) on gestation days 17-20. On PDs 7-8 or 10-11, the offspring were administered water or ethanol (3g/kg). Intake of ethanol and water, locomotor activity in an open field, and ethanol odor preference were evaluated in the pups, whereas the mothers were evaluated in terms of ethanol intake. Results indicated an aversion to ethanol in dams that had been administered ethanol during gestation, despite a general increase in ethanol intake observed in their pups relative to controls. The prenatal ethanol exposure also potentiated the increase in ethanol intake observed after intoxication on PDs 7-8. Ethanol intoxication on PDs 10-11 reduced ethanol consumption; this ethanol aversion was still evident in infant rats exposed prenatally to ethanol despite their general increase in ethanol intake. No effects of prenatal ethanol exposure were observed in terms of motor activity or odor preference. It is concluded that prenatal exposure to ethanol, even in a dose that induces ethanol aversion in the gestating dam, increases ethanol intake in infant rats and that this experience modulates age-related differences in subsequent postnatal learning about ethanol.

Effects of maternal alcohol consumption during breastfeeding on motor and cerebellar Purkinje cells behavior in mice

Purkinje cells (PCs) are the sole output from the cerebellar cortex. Their electrophysiological behavior may serve as indicator of chronic ethanol effects on the cerebellum. Here, we studied the effects of ethanol consumption through breastfeeding on motor behavior, histology and PCs electrophysiology. Mice with different maternal drinking regimen (ethanol, E or sucrose, S) during prenatal (E/and S/) and postnatal period (/E and/S) were compared. Motor performance in the runway and rotarod tests was significantly worse in mice exposed to ethanol prenatally (E/E and E/S) than in mice exposed to sucrose (S/S), with a limited influence, if any, of mother regimen during lactation (E/S vs E/E). A loss of 20-25% of PCs was found for both E/S and E/E compared to S/S mice but PC numbers were similar in S/E and S/S. Mean PC spontaneous simple spike firing rate and rhythmicity were higher in E/S and E/E than in S/S but there was no difference between S/E and S/S. Complex spike frequency was similar in all groups. In contrast, complex spike duration and the related pause induced on the simple spike firing were shorter in E/E and in E/S, but no difference was found between S/E and S/S. We conclude that cerebellar dysfunction induced by maternal ethanol consumption in mice depends upon the drinking regimen during pregnancy and not during lactation.

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.

Differential motivational properties of ethanol during early ontogeny as a function of dose and postadministration time

While appetitive reinforcement effects of ethanol are easily detected in rat neonates, such phenomena rarely have been observed in older infants. Recently, Molina et al. [Molina, J. C., Ponce L. F., Truxell, E., & Spear N. E. (2006). Infantile sensitivity to ethanol's motivational effects: ethanol reinforcement during the third postnatal week. Alcohol Clin Exp Res 30, 1506-1519] reported such effects of ethanol in 14-day-olds using a second-order conditioning procedure. Infants also appear to be sensitive to biphasic reinforcement or general motivational effects of ethanol, with appetitive effects seeming to occur early in the state of intoxication and aversive effects predominant during late stages, but tests have been inconclusive. The present study examined the possibility of biphasic motivational effects of ethanol during infancy through the use of second-order conditioning procedures. Preweanling rats (14 days old) experienced intraoral water infusions (conditioned stimulus, CS) either 5-20 or 30-45 min after administration of 0.5 or 2.0 g/kg i.g. ethanol. Pups were then exposed to the CS while over a novel texture (second-order phase). Tests of tactile preference for that texture followed. Locomotive, thermal, hormonal (corticosterone release), and pharmacokinetic patterns likely to underlie the acquisition of ethanol-mediated conditioning were also examined in subsequent experiments. Intraoral CSs paired with either early or late effects of low-dose ethanol (0.5 g/kg, blood ethanol concentration: 40 mg%) became positive second-order reinforcers. Appetitive effects were also exhibited by pups exposed to the CS during commencement of the toxic episode induced by a 2.0 g/kg ethanol dose, 5-20 min after administration of ethanol, whereas aversions emerged when CS presentation occurred 30-45 min postadministration time (blood ethanol concentrations: 157 and 200 mg%, respectively). Overall, the results indicate that infants rapidly detect differential motivational properties of ethanol as a function of dose or drug postadministration time. Relatively neutral stimuli associated with these properties are later capable of acting as either positive or aversive reinforcers. Thermal and motor responses that accompany ethanol intoxication do not seem to be directly associated with differential hedonic properties of the drug at this stage of development.

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.

Alcohol levels in Chinese lactating mothers after consumption of alcoholic diet during postpartum "doing-the-month" ritual

This study examined the effects of exposure to ethanol through cultural practices by lactating mothers. Specifically, the pharmacokinetics of alcohol in Chinese lactating mothers was investigated after they consumed chicken soup flavored with sesame oil and rice wine (CSSR), a typically prescribed diet during the postpartum "doing-the-month" period. Experimental findings were employed to estimate the potential ethanol dose to neonates and determine associated health risks. Twenty-three lactating mothers were examined. Informed consent was obtained from each subject. The target alcohol dosage was 0.3g/kg. Milk and blood samples were collected at fixed time intervals from each subject following exposure to CSSR, and alcohol levels were determined. Acute health risks to infants were estimated by comparing the potential infant dosage to an established criterion dose. Blood alcohol level peaked at 20 min after exposure to CSSR and decreased almost linearly thereafter. Alcohol in milk reached a plateau roughly at 20-40 min after exposure to CSSR and then decreased. Alcohol pharmacokinetics among subjects varied widely. The coefficients of variation in subject alcohol concentrations were 16.5-46.2% (mean, 30.0%) for blood and 32.8-57.6% (mean, 44.4%) for milk. Mean maximal alcohol concentration in blood (30.2+/-5.0 mg/dl) was achieved at 23.5+/-7.6 min and in milk (31.6+/-10.3 mg/dl) at 31.7+/-12.7 min. Potential infant doses were 3.0-58.8 mg (mean, 13.4 mg), and the predicted time required for milk alcohol level to return to zero level was 175 min. The acute health risks for infants exposed to alcohol through their mothers' milk under the current exposure scenario are low (hazard index<0.2). Nursing infants at least 3h after ingesting a diet containing alcohol would further reduce potential health risks.

Fetal or Infantile Exposure to Ethanol Promotes Ethanol Ingestion in Adolescence and Adulthood: A Theoretical Review

BACKGROUND

Despite good evidence that ethanol abuse in adulthood is more likely the earlier human adolescents begin drinking, it is unclear why the early onset of drinking occurs in the first place. A review of experimental studies with animals complemented by clinical, epidemiologic and experimental studies with humans supports the idea that precipitating conditions for ethanol abuse occur well before adolescence, in terms of very early exposure to ethanol as a fetus or infant. Experimental studies with animals indicate, accordingly, that ethanol intake during adolescence or adulthood is potentiated by much earlier exposure to ethanol as a fetus or infant.

METHODS

Two broad theoretical frameworks are suggested to explain the increase in affinity for ethanol that follows very early exposure to ethanol, one based on effects of mere exposure and the other on associative conditioning. Studied for 50 years or more in several areas of psychology, "effects of mere exposure" refers to enhanced preference expressed for flavors, or just about any stimuli, that are relatively familiar. An alternative framework, in terms of associative conditioning, is guided by this working hypothesis: During ethanol exposure the fetus or infant acquires an association between ethanol's orosensory (odor/taste) and pharmacological consequences, causing the animal subsequently to seek out ethanol's odor and taste.

RESULTS AND CONCLUSIONS

The implication that ethanol has rewarding consequences for the fetus or young infant is supported by recent evidence with perinatal rats. Paradoxically, several studies have shown that such early exposure to ethanol may in some circumstances make the infant treat ethanol-related events as aversive, and yet enhanced intake of ethanol in adolescence is nevertheless a consequence. Alternative interpretations of this paradox are considered among the varied circumstances of early ethanol exposure that lead subsequently to increased affinity for ethanol.

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.

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.

Fetal learning with ethanol: correlations between maternal hypothermia during pregnancy and neonatal responsiveness to chemosensory cues of the drug

BACKGROUND

Fetuses learn about ethanol odor when the drug is present in the amniotic fluid. Prenatal learning comprising ethanol's chemosensory cues also suggests an acquired association between ethanol's chemosensory and postabsorptive properties. Ethanol-related thermal disruptions have been implicated as a significant component of the drug's unconditioned properties. In the present study, ethanol-induced thermal changes were analyzed in pregnant rats subjected to a moderate ethanol dose. This thermal response was later tested for its correlation with the responsiveness of the progeny to ethanol and nonethanol chemosensory stimuli.

METHODS

During gestational day (GD) 14, pregnant rats were subjected to a minor surgical procedure to place a subcutaneous telemetric thermal sensor in the nape of the neck. During GDs 17 to 20, females received a daily intragastric administration of ethanol (2 g/kg) or water, using solutions kept at room temperature. Maternal body temperatures were recorded before and after (4 consecutive hours) the administration of water or ethanol. Newborns representative of both prenatal treatments were tested in terms of behavioral activity elicited by the smell of ethanol or of a novel odorant (cineole). A third group of pups were tested in response to unscented air stimulation.

RESULTS

Ethanol administration during late gestation induced reliable maternal hypothermia, a thermal disruption greater than that observed in water-treated females. It was systematically observed that maternal ethanol-induced hypothermia negatively correlated with neonatal motor reactivity elicited by ethanol olfactory stimulation. No other significant correlations were observed in terms of responsiveness to cineole or to unscented air in animals prenatally exposed to ethanol or water.

CONCLUSIONS

In conjunction with prior research, the present results indicate that fetal ethanol exposure may yield learning of an association between ethanol's sensory and unconditioned properties. Ethanol-induced hypothermia during late gestation seems to represent a significant component of ethanol's unconditioned consequences. Specifically, ethanol-related thermal disruptions in the womb are highly predictive of neonatal responsiveness to ethanol's chemosensory cues that are known to be processed by the near-term fetus.

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.

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.

Interactions between perinatal and neonatal associative learning defined by contiguous olfactory and tactile stimulation

Tactile stimulation of the neonate, as performed by the mother during and after delivery, has been described as an effective unconditioned stimulus during early ontogeny (Leon, 1987; Ronca & Alberts, 1994). The present experiments examined the interaction between perinatal and neonatal learning determined by the explicit association between alcohol odor and vigorous body stimulation of the perinatal organism. In Experiment 1, rat fetuses were exposed to either alcohol or saline 10 min prior to cesarean delivery. The alcohol administration procedure here employed was sufficient to provide sensory contamination of the amniotic fluid but avoid fetal alcohol intoxication. Pups in the two prenatal treatments later experienced the smell of alcohol, tactile stimulation, or both stimuli explicitly paired or unpaired. Other postnatal groups were composed of pups that had no explicit experience with either experimental stimulus. Pups subjected to alcohol odor in utero displayed more overall motor activity in response to that odor than saline controls. The increased motor responses were further potentiated in pups that experienced additional postnatal alcohol odor paired with tactile stimulation. In Experiment 2, pups were exposed to alcohol in the amniotic fluid 10 or 30 min prior to birth. As previously demonstrated the memory acquired in utero appears highly dependent upon contingency between exposure to this particular scent and delivery procedures. Pups in both prenatal treatment groups were then exposed to alcohol odor paired or unpaired with tactile stimulation. Some control animals received no further experience with either stimuli. Those pups exposed to alcohol odor paired with tactile stimulation both pre- and postnatally later showed maximum motor activity elicited by the odor of alcohol. The results support the notion of fetal associative learning comprising alcohol's chemosensory cues and behaviorally activating stimuli. Furthermore, the conditioned response under analysis is potentiated whenever neonates are reexposed to contingent presentations of the elements that defined the original associative memory.