Paula Abate

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 preweanlings 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.

Fetal Exposure to Moderate Ethanol Doses: Heightened Operant Responsiveness Elicited by Ethanol‐Related Reinforcers

BACKGROUNDnPrenatal exposure to moderate ethanol doses during late gestation modifies postnatal ethanol palatability and ingestion. The use of Pavlovian associative procedures has indicated that these prenatal experiences broaden the range of ethanol doses capable of supporting appetitive conditioning. Recently, a novel operant technique aimed at analyzing neonatal predisposition to gain access to ethanol has been developed. Experiment 1 tested the operant conditioning technique for developing rats described by Arias and colleagues (2007) and Bordner and colleagues (2008). In Experiment 2, we analyzed changes in the disposition to gain access to ethanol as a result of moderate prenatal exposure to the drug.nnnMETHODSnIn Experiment 1, newborn pups were intraorally cannulated and placed in a supine position that allowed access to a touch-sensitive sensor. Paired pups received an intraoral administration of a given reinforcer (milk or quinine) contingent upon physical contact with the sensor. Yoked controls received similar reinforcers only when Paired pups activated the circuit. In Experiment 2, natural reinforcers (water or milk) as well as ethanol (3% or 6% v/v) or an ethanol-related reinforcer (sucrose compounded with quinine) were tested. In this experiment, pups had been exposed to water or ethanol (1 or 2 g/kg) during gestational days 17 to 20.nnnRESULTSnExperiment 1 confirmed previous results showing that 1-day-old pups rapidly learn an operant task to gain access to milk, but not to gain access to a bitter tastant. Experiment 2 showed that water and milk were highly reinforcing across prenatal treatments. Furthermore, general activity during training was not affected by prenatal exposure to ethanol. Most importantly, prenatal ethanol exposure facilitated conditioning when the reinforcer was 3% v/v ethanol or a psychophysical equivalent of ethanols gustatory properties (sucrose-quinine).nnnCONCLUSIONSnThe present results suggest that late prenatal experience with ethanol changes the predisposition of the newborn to gain access to ethanol-related stimuli. In conjunction with prior literature, this study emphasizes the fact that intrauterine experience with ethanol not only augments ethanols palatability and ingestion, but also facilitates the acquisition of response-stimulus associations where the drug acts as an intraoral reinforcer.

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 drugs 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 with ethanol: Correlations between maternal hypothermia during pregnancy and neonatal responsiveness to chemosensory cues of the drug

BACKGROUNDnFetuses learn about ethanol odor when the drug is present in the amniotic fluid. Prenatal learning comprising ethanols chemosensory cues also suggests an acquired association between ethanols chemosensory and postabsorptive properties. Ethanol-related thermal disruptions have been implicated as a significant component of the drugs 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.nnnMETHODSnDuring 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.nnnRESULTSnEthanol 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.nnnCONCLUSIONSnIn conjunction with prior research, the present results indicate that fetal ethanol exposure may yield learning of an association between ethanols sensory and unconditioned properties. Ethanol-induced hypothermia during late gestation seems to represent a significant component of ethanols unconditioned consequences. Specifically, ethanol-related thermal disruptions in the womb are highly predictive of neonatal responsiveness to ethanols chemosensory cues that are known to be processed by the near-term fetus.

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

RationaleEarly ethanol exposure promotes ethanol reinforcement, mediated perhaps by ethanol’s motivational effects. The opioid system mediates ethanol reinforcement, at least in part.ObjectivesModulation of consummatory and seeking behaviors by the opioid system was tested in terms of ethanol or sucrose operant self-administration.MethodsWistar-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, 6xa0h before operant task, pups were re-exposed to ethanol after naloxone injection (0 or 1xa0mg/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.ResultsSucrose 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.ConclusionsSelf-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.

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.

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.

Maternal isolation during the first two postnatal weeks affects novelty-induced responses and sensitivity to ethanol-induced locomotor activity during infancy

Animals exposed to chronic maternal separation (MS) exhibit enhanced ethanol self-administration and greater hormonal and behavioral responsiveness to stress in adulthood. Whether the effects of MS are immediately evident in infancy or whether they appear only later on development is still an unanswered question This study tested sensitivity to ethanols behavioral stimulating effects in infant rats that experienced MS from postnatal Day 1-14. MS infants exhibited significantly greater reactivity to the motor stimulating effects of 1.25u2009g/kg ethanol than control animals, yet greater motor suppression after 2.5u2009g/kg ethanol. Baseline level of response to novelty was altered in MS infants, in a nor-binaltorphimine insensitive manner, that is, despite modified activity of the kappa-opioid system. These results indicate that the consequences of chronic maternal isolation emerge early in ontogeny, affecting ethanol sensitivity in infancy.

The role of acetaldehyde in ethanol reinforcement assessed by Pavlovian conditioning in newborn rats.

RationaleAnimal studies indicate that central acetaldehyde, dependent on catalase metabolism of ethanol (EtOH), modulates ethanol reinforcement. Brain catalase activity and acetaldehyde (ACD) production are significantly higher in rat pups compare d with adults. Interestingly, infant rats show high EtOH affinity for alcohol consumption and are particularly sensitive to the drug’s reinforcing effects.ObjectivesWe tested whether central ACD is necessary and sufficient to induce appetitive conditioning in newborn rats through the artificial nipple technique.MethodsVehicle, EtOH (100xa0mg%), and acetaldehyde (0.35xa0μmol) were administered into the cisterna magna (1xa0μl). Half of the animals also received a central administration of 75xa0μg (experiment 1) or 40xa0μg of d-penicillamine (experiment 2). Afterwards, pups were exposed to an olfactory cue (conditioned stimulus). One hour later, neonates were tested with an artificial nipple in the presence of the conditioned cue. Nipple attachment duration, mean grasp duration, and number of nipple disengagements served as dependent variables.ResultsPositive responses to the scented nipple occurred in neonates conditioned with EtOH or ACD (experiments 1 and 2). In experiment 1, there were indications that d-penicillamine weakened the reinforcing effects of EtOH and ACD. In experiment 2, d-penicillamine (40xa0μg) significantly inhibited appetitive conditioned responses dependent upon EtOH or ACD.ConclusionsAppetitive conditioning was observed when employing either central EtOH or ACD as unconditioned stimuli. Central abduction of ACD inhibited conditioned appetitive responsiveness to the surrogate nipple. Central ACD is involved in the determination or modulation of EtOH’s motivational properties during early stages in development.

Acetaldehyde involvement in ethanol's postabsortive effects during early ontogeny

Clinical and biomedical studies sustains the notion that early ontogeny is a vulnerable window to the impact of alcohol. Experiences with the drug during these stages increase latter disposition to prefer, use or abuse ethanol. This period of enhanced sensitivity to ethanol is accompanied by a high rate of activity in the central catalase system, which metabolizes ethanol in the brain. Acetaldehyde (ACD), the first oxidation product of ethanol, has been found to share many neurobehavioral effects with the drug. Cumulative evidence supports this notion in models employing adults. Nevertheless very few studies have been conducted to analyze the role of ACD in ethanol postabsorptive effects, in newborns or infant rats. In this work we review recent experimental literature that syndicates ACD as a mediator agent of reinforcing aspects of ethanol, during early ontogenetic stages. We also show a meta-analytical correlational approach that proposes how differences in the activity of brain catalase across ontogeny, could be modulating patterns of ethanol consumption.