Ontogeny of ethanol intake in alcohol preferring (P) and alcohol nonpreferring (NP) rats

There is a scarcity of research on ethanol affinity in alcohol‐preferring (P) rats before weaning and it is unknown if neonate P rats exhibit ethanol intake preferences comparable to those observed in adult P rats. This study examined ethanol intake in P and alcohol‐nonpreferring (NP) rats 3 hr after birth (Experiment 1, surrogate nipple test), at postnatal days (PD) 8, 12, and 18 (Experiment 2, consumption from the floor procedure) and at adolescence (Experiment 3, two‐bottle choice test at PD32). The high‐preference genotype was readily expressed 3 hr after birth. P neonates drank twice as much ethanol as their NP counterparts. This heightened ethanol preference transiently reversed at P8, reemerged as weaning approached (P18) and was fully expressed during adolescence. These results help to clarify the ontogeny of genetic predisposition for ethanol. Genetic predisposition for higher ethanol intake in P than in NP rats seems to be present immediately following birth. © 2010 Wiley Periodicals, Inc. Dev Psychobiol 53:234–245, 2011.     

Ethanol‐induced locomotor activity in adolescent rats and the relationship with ethanol‐induced conditioned place preference and conditioned taste aversion

Adolescent rats exhibit ethanol‐induced locomotor activity (LMA), which is considered an index of ethanol's motivational properties likely to predict ethanol self‐administration, but few studies have reported or correlated ethanol‐induced LMA with conditioned place preference (CPP) by ethanol at this age. The present study assessed age‐related differences in ethanol's motor stimulating effects and analyzed the association between ethanol‐induced LMA and conventional measures of ethanol‐induced reinforcement. Experiment 1 compared ethanol‐induced LMA in adolescent and adult rats. Subsequent experiments analyzed ethanol‐induced CPP and conditioned taste aversion (CTA) in adolescent rats evaluated for ethanol‐induced LMA. Adolescent rats exhibit a robust LMA after high‐dose ethanol. Ethanol‐induced LMA was fairly similar across adolescents and adults. As expected, adolescents were sensitive to ethanol's aversive reinforcement, but they also exhibited CPP. These measures of ethanol reinforcement, however, were not related to ethanol‐induced LMA. Spontaneous LMA in an open field was, however, negatively associated with ethanol‐induced CTA. © 2012 Wiley Periodicals, Inc. Dev Psychobiol 55: 429–442, 2013     

Alcohol exposure during adolescence impairs auditory fear conditioning in adult Long-Evans rats

Few studies have examined long-term effects of ethanol on auditory fear conditioning, and fewer still have examined whether adolescence represents a unique period of vulnerability. We investigated the impact of ethanol consumption during adolescence and adulthood on fear conditioning, following an extended abstinence period. Male and female Long-Evans rats (N = 80) consumed 10% ethanol or water (control) in a limited-access drinking paradigm (1 h) between postnatal (P) days 28-45 (adolescent) and P80-97 (adult). After the abstinence period (30 days), ethanol and control groups were assessed on the auditory fear-conditioning task. Alcohol consumption impaired tone conditioning in the male and female adolescent group. There were no persisting effects of adult dosing. In addition, adolescent rats consumed more ethanol than adults. These data provide evidence that ethanol consumption during adolescence produces enduring effects on auditory fear conditioning. The age-specific effect of ethanol may be attributable to an interplay of higher ethanol intake and the unique neurobiological characteristics of adolescents.     

Effects of prenatal and postnatal maternal ethanol on offspring response to alcohol and psychostimulants in long evans rats

An important factor that may influence addiction liability is exposure during the early life period. Exposure to ethanol, early in life, can have long-lasting implications on brain function and drugs of abuse response later in life. In the present study we investigated the behavioral responses to ethanol and to psychostimulants in Long Evans rats that have been exposed to pre- and postnatal ethanol. Since a relationship between heightened drug intake and susceptibility to drug-induced locomotor activity/sensitization has been demonstrated, we tested these behavioral responses, in control and early life ethanol-exposed animals. The young adult male and female progeny were tested for locomotor response to alcohol, cocaine and d-amphetamine. Sedative, rewarding effects of alcohol and alcohol consumption were measured. Our results show that early life ethanol exposure behaviorally sensitized animals to subsequent ethanol and psychostimulants exposure. Ethanol-exposed animals were also more sensitive to the hyperlocomotor effects of all drugs of abuse tested and to those of the dopamine receptor agonist apomorphine. Locomotor sensitization to repeated injections of cocaine was facilitated in ethanol-exposed animals. Ethanol-induced conditioned place preference was also facilitated in ethanol-exposed animals. Ethanol consumption and preference were increased after early life ethanol exposure and this was associated with decreased sensitivity to the sedative effects of ethanol. The altered behavioral responses to drugs of abuse were associated with decreased striatal dopamine transporter and hippocampal NMDAR binding. Our results outline an increased vulnerability to rewarding and stimulant effects of ethanol and psychostimulants and support the epidemiological and clinical data that suggested that early chronic exposure to ethanol may increase the propensity for later self-administration of ethanol or other substances.     

Differential role of mu, delta and kappa opioid receptors in ethanol-mediated locomotor activation and ethanol intake in preweanling rats

The opioid system modulates ethanol intake and reinforcement in adult and preweanling rodents. While adult heterogeneous rats normally do not show ethanol-mediated locomotor stimulation, preweanling rats show it quite clearly. We recently observed that naloxone, a non-specific opioid antagonist, attenuated ethanol-induced locomotor activation in preweanling rats. In the present study we tested the role of specific opioid receptors (mu, delta and kappa) in ethanol-mediated locomotor stimulation and ethanol intake. In Experiment 1 13-day-old rats received naloxonazine (mu antagonist: 0, 7.5 or 15 mg/kg), naltrindole (delta antagonist: 0, 2 or 4 mg/kg) or nor-binaltorphimine (kappa antagonist: 0, 2, 4 or 8 mg/kg) before an intragastric administration of ethanol (0 or 2.5 g/kg), and subsequent locomotor activity assessment. In Experiment 2, the same opioid antagonists were administered on postnatal days 13 and 14 before consumption of ethanol (6%), saccharin (0.05%) or distilled water. In Experiment 1 only naloxonazine reduced ethanol-mediated locomotor stimulation. None of the opioid antagonists affected locomotor activity in water controls. In Experiment 2 naloxonazine and naltrindole suppressed ingestion of all the solutions tested. Similar to what has been reported in adult rodents, mu-opioid receptors seem to modulate ethanol-activating effects during early ontogeny. Hence, there seems to be a partial overlap of neurochemical mechanisms involved in the rewarding and stimulating effects of ethanol in preweanling rats. Mu-receptor antagonists reduced both ethanol-induced activity and ethanol intake, but it is unclear whether the latter effect is specific to ethanol or only a reflection of an effect on consummatory behavior generally, since mu and delta receptor antagonists also suppressed ingestion of water and sacccharin.     

Social learning about ethanol in preweanling rats: role of endogenous opioids

The role of the endogenous opioid system in social learning about ethanol was examined in three experiments using preweanling rats. Experiment 1 showed that interactions with intoxicated siblings in the home cage on postnatal Days (PD) 12, 14, and 16 results in increased voluntary intake of ethanol when subjects are tested 24 hr after the final exposure. The results also suggested that the endogenous opioid system is not involved in acquisition. Administration of naloxone during social exposure to ethanol had no effect on later ethanol intake. Experiment 2 examined the effects of receptor‐selective antagonists administered prior to test. For subjects that had social exposure to ethanol, intake of ethanol was completely suppressed by either naloxone or the δ antagonist naltrindole. For ethanol‐naïve subjects, intake also was completely suppressed by naloxone. However, intake was partially blocked by naltrindole or the μ antagonist β‐FNA. Experiment 3 confirmed the differential involvement of μ and δ receptors in ethanol intake through a more comprehensive dose–response analysis of β‐FNA and naltrindole. Collectively, these data reveal that learning about ethanol from intoxicated conspecifics not only affects voluntary intake of ethanol but also alters the opioidergic response to ethanol consumption. © 2004 Wiley Periodicals, Inc. Dev Psychobiol 44: 132–139, 2004.     

Dopamine receptors modulate ethanol's locomotor‐activating effects in preweanling rats

Near the end of the second postnatal week motor activity is increased soon after ethanol administration (2.5 g/kg) while sedation‐like effects prevail when blood ethanol levels reach peak values. This time course coincides with biphasic reinforcement (appetitive and aversive) effects of ethanol determined at the same age. The present experiments tested the hypothesis that ethanol‐induced activity during early development in the rat depends on the dopamine system, which is functional in modulating motor activity early in ontogeny. Experiments 1a and 1b tested ethanol‐induced activity (0 or 2.5 g/kg) after a D1‐like (SCH23390; 0, .015, .030, or .060 mg/kg) or a D2‐like (sulpiride; 0, 5, 10, or 20 mg/kg) receptor antagonist, respectively. Ethanol‐induced stimulation was suppressed by SCH23390 or sulpiride. The dopaminergic antagonists had no effect on blood ethanol concentration (Experiments 2a and 2b). In Experiment 3, 2.5 g/kg ethanol increased dopamine concentration in striatal tissue as well as locomotor activity in infant Wistar rats. Adding to our previous results showing a reduction in ethanol induced activity by a GABA B agonist or a nonspecific opioid antagonist, the present experiments implicate both D1‐like and D2‐like dopamine receptors in ethanol‐induced locomotor stimulation during early development. According to these results, the same mechanisms that modulate ethanol‐mediated locomotor stimulation in adult rodents seem to regulate this particular ethanol effect in the infant rat. © 2009 Wiley Periodicals, Inc. Dev Psychobiol 52: 13–23, 2010     

Adolescent social stress and social context influence the intake of ethanol and sucrose in male rats soon and long after the stress exposures

Social instability stress in adolescent rats (SS; postnatal day 30–45, daily 1 hr isolation +new cage partner) alters behavioural responses to psychostimulants, but differences in voluntary consumption of natural and drug rewards are unknown. SS also is associated with an atypical behavioural repertoire, for example reduced social interactions. Here, we investigated whether SS rats differ from control (CTL) rats in ethanol (EtOH) or sucrose intake in experiments involving different social contexts: alone, in the presence of an unfamiliar peer, in the presence of its cage partner, or in competition against its cage partner. SS rats drank more EtOH than CTL rats irrespective of social context, although the effects were driven primarily by those tested soon after the test procedure rather than weeks later in adulthood. SS and CTL rats did not differ in sucrose intake, except in adulthood under conditions of competition for limited access (SS>CTL). Adolescent rats drank more sucrose than adults, in keeping with evidence that adolescents are more sensitive to natural rewards than adult animals. Overall, adolescent SS modified the reward value of EtOH and sucrose, perhaps through stress/glucocorticoids modifying the development of the mesocorticolimbic system.     

Differences in the social consequences of ethanol emerge during the course of adolescence in rats: social facilitation, social inhibition, and anxiolysis

The present experiments explored social consequences of ethanol during adolescence by examining dose-dependent ethanol-induced social facilitation and inhibition in a non-anxiogenic (familiar) environment, and ethanol-related anxiolysis in an anxiogenic (unfamiliar) environment in early (P28) and late (P42) adolescent rats. Pronounced age-related differences in the social consequences of ethanol emerged during the course of adolescence, with early adolescents being uniquely sensitive to activating effects of low doses of ethanol when tested in the familiar context in terms of play fighting-an adolescent-characteristic form of social interactions, but conversely less sensitive than late adolescents to ethanol-associated social suppression when tested at higher ethanol doses in this context. Early adolescents were also less sensitive than late adolescents to the anxiolytic effects of ethanol revealed in the unfamiliar test situation, when indexed in terms of increases in social investigation and the ethanol-induced transformation of social avoidance into social preference. Anti-anxiety properties of ethanol were found to be sex-dependent in older animals, with late adolescent females being more sensitive to ethanol anxiolysis than their male counterparts. Considerable ontogenetic differences in the social consequences of ethanol are evident even within the adolescent period, with early adolescence being a time of particularly pronounced adolescent-typical sensitivities to ethanol.     

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.     

Concomitant stress potentiates the preference for,and consumption of, ethanol induced by chronic pre-exposure to ethanol

Ethanol abuse is linked to several acute and chronic injuries that can lead to health problems. Ethanol addiction is one of the most severe diseases linked to the abuse of this drug. Symptoms of ethanol addiction include compulsive substance intake and withdrawal syndrome. Stress exposure has an important role in addictive behavior for many drugs of abuse (including ethanol), but the consequences of stress and ethanol in the organism when these factors are concomitant results in a complex interaction. We investigated the effects of concomitant, chronic administration of ethanol and stress exposure on the withdrawal and consumption of, as well as the preference for, ethanol in mice. Male Swiss mice (30–35 g, 8-10 per group) were exposed to an ethanol liquid diet as the only source of food for 15 days. In the final 5 days, they were exposed to forced swimming stress. Twelve hours after removal of the ethanol liquid diet, animals were evaluated for ethanol withdrawal by measuring anxiety-related behaviors and locomotor activity. Twenty-four hours after evaluation of ethanol withdrawal, they were evaluated for voluntary consumption of ethanol in a “three-bottle choice” paradigm. Mice exposed to chronic consumption of ethanol had decreased locomotor activity during withdrawal. Contrary to our expectations, a concomitant forced swimming stress did not aggravate ethanol withdrawal. Nevertheless, simultaneous ethanol administration and stress exposure increased voluntary consumption of ethanol, mainly solutions containing high concentrations of ethanol. These results showed that stressful situations during ethanol intake may aggravate specific addiction-related behaviors.     

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.     

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. © 2010 Wiley Periodicals, Inc. Dev Psychobiol 52: 545–557, 2010.     

Persisting changes in basolateral amygdala mRNAs after chronic ethanol consumption

Adolescent alcohol use is common and evidence suggests that early use may lead to an increased risk of later dependence. Persisting neuroadaptions in the amygdala as a result of chronic alcohol use have been associated with negative emotional states that may lead to increased alcohol intake. This study assessed the long-term impact of ethanol consumption on levels of several basolateral amygdala mRNAs in rats that consumed ethanol in adolescence or adulthood. Male Long-Evans rats were allowed restricted access to ethanol or water during adolescence (P28, n = 11, controls = 11) or adulthood (P80, n = 8, controls = 10) for 18 days. After a sixty day abstinent period, the brain was removed and sections containing the basolateral amygdala were taken. In situ hybridization was performed for GABA_A α₁, glutamic acid decarboxylase (GAD₆₇), corticotropin releasing factor (CRF), and N-methyl-d-aspartate (NMDA) NR2A mRNAs. A significant decrease was observed in GABA_A α₁, GAD₆₇, and CRF, but not NR2A, mRNAs in adult rats that consumed ethanol in comparison to controls. No significant changes were seen in adolescent consumers of ethanol for any of the probes tested. A separate analysis for each probe in the piriform cortex ascertained that the changes after ethanol consumption were specific to the basolateral amygdala. These results indicate that chronic ethanol consumption induces age-dependent alterations in basolateral amygdala neurochemistry.     

Low and moderate doses of acute ethanol do not impair spatial cognition but facilitate accelerating rotarod performance in adolescent and adult rats

Adolescents and adult rodents have differing sensitivities to the acute effects of ethanol on a variety of behavioral and electrophysiological measures. Often, these differences are revealed using high ethanol doses and consequently little is known about these age-related effects using lower ethanol doses. We sought to determine if low-dose ethanol produces differential effects on cognition and motor behavior in adolescent and adult rats. Adolescent (postnatal day PD 30–32) and adult (PD 70–72) male Sprague Dawley rats were trained on the standard version of the Morris Water Maze (MWM) for 5 days or received 5 training trials on an accelerating rotarod (ARR). Adolescents learned the location of the submerged platform in the MWM significantly slower than adults during training and, acute ethanol administration (0.5 g/kg, 0.75 g/kg, or 1.0 g/kg) 30 min before testing did not impair spatial memory in either age group. On the ARR test, adolescent rats spent significantly more time on the rotarod compared to adults and, alcohol exposure (1.0 g/kg) significantly increased ARR performance 30 min following administration. Our findings address the utility of investigating low and moderate doses of ethanol during different developmental stages in rats.     

Magnitude and ethanol sensitivity of tonic GABAA receptor-mediated inhibition in dentate gyrus changes from adolescence to adulthood

Ethanol consumption by adolescents is a public health problem of striking importance. Educational and clinical efforts to address this problem have been aided by recent neurobehavioral studies indicating that ethanol disrupts memory and memory-related brain functions more powerfully in adolescent animals than in adults. Still, the mechanisms underlying this developmental sensitivity remain unclear. GABA(A) receptor (GABA(A)R)-mediated neurotransmission in the hippocampal formation, particularly that which is driven by extrasynaptic GABA(A)Rs, is enhanced by pharmacologically relevant concentrations of ethanol, and may be, in part, responsible for the modulation of memory and memory-related circuit plasticity. Using hippocampal slices from adolescent and adult rats, we have shown that tonic current mediated by extrasynaptic GABA(A)Rs is larger in dentate gyrus granule cells from adult animals than in those from adolescents and that 30 mM ethanol enhances inhibitory tonic current more in cells from adolescent rats than in those from adults. It is possible that more powerful promotion of tonic GABA(A)R-mediated inhibition by ethanol in the dentate gyrus of adolescent rats, compared with adults, contributes to the developmental differences that have previously been observed with respect to ethanol-induced memory impairment and reduction of synaptic plasticity.     

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 2 g/kg ethanol doses intragastrically (i.g.). After parturition these dams were given a dose of 2.5 g/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 1 g/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.     

Stress during adolescence alters behavioral sensitization to amphetamine

In humans, chronic intermittent and uncontrollable stress during adolescence is viewed as a key factor for vulnerability to drug abuse and development of psychopathologies later in life. Less is known about the long-term effects of chronic stress in animals during the juvenile period. Although there is evidence of cross sensitization during prenatal period and adulthood between chronic stress and amphetamine-induced behavioral sensitization in the rat, no studies have been conducted on cross sensitization between chronic variable stress in adolescence and behavioral sensitization to amphetamine. To address this question, at the onset of adolescence (28 days) male rats were subjected to 28 days of intermittent non-habituating social stress (isolation, novel environment, crowding, litter-shifting, subordination), or physical stress (restraint, swim, cold, ether, noise), or were handled as controls. Twenty-four hours after the last stressor or handling, all groups were exposed to a novel environment for 1 h, after which they underwent a regimen of behavioral sensitization to amphetamine. Our results showed that socially stressed rats have low locomotor activity in the novel environment, when compared to the control and physical groups who were identical in the same test. Even though socially stressed rats had lower locomotor activity in response to amphetamine injections, there were no significant differences during the training phase between the three groups at this dose of amphetamine. However, when tested for behavioral sensitization to amphetamine control and physically stressed rats showed a robust sensitization, socially stressed rats were significantly inhibited. We conclude that our chronic variable social stress protocol during adolescence inhibits behavioral sensitization to amphetamine during adulthood.