Impact of adolescent alcohol use across the lifespan: Long-lasting tolerance to high-dose alcohol coupled with potentiated spatial memory impairments to moderate-dose alcohol.

Understanding how alcohol exposure during adolescence affects aging is a critical but understudied area. In the present study, male rats were exposed to either alcohol or saline during adolescence, then tested every 4 months following either an ethanol or saline challenge; animals were tested until postnatal day (PD) 532. It was found that long-lasting tolerance to high-dose ethanol exists through the test period, as measured by loss of righting reflex, while tolerance to lower doses of ethanol is not found. In addition, alcohol exposure during adolescence facilitated spatial memory impairments to acute ethanol challenges later in life. The current work demonstrates that exposure to ethanol during adolescent development can produce long-lasting detrimental impairments.

Differences in Behavioral Responding in Adult and Aged Rats Following Chronic Ethanol Exposure.

BACKGROUND: Research suggests symptoms of chronic alcoholism, and withdrawal may be more severe in elderly compared with younger adults. However, examination of the effects of long-term ethanol (EtOH) consumption and withdrawal is limited in aged rodents. We thus investigated EtOH withdrawal and potential deficits in cognitive and motor behavior in young adult and aged rats. We also examined the effects of acute allopregnanolone as a potential mechanism contributing to age-related differences in EtOH's cognitive-impairing effects. METHODS: Male young adult (postnatal days 70 to 72) and aged (approximately 18 months) Sprague-Dawley rats were treated with liquid EtOH diet in a modified chronic intermittent EtOH (modified-CIE) paradigm. The severity of EtOH withdrawal was determined using a 4-item rating scale, and withdrawal-induced anxiety-like behavior was assessed in the elevated plus maze (EPM) and open field. After a 14-day EtOH-free period, spatial performance was assessed in the Morris water maze (MWM) during sober acquisition and in response to a subsequent EtOH and allopregnanolone challenge. RESULTS: Modified-CIE adults consumed more EtOH during treatment and exhibited robust EtOH withdrawal using a behavioral rating scale compared to aged rats. In the EPM, adult and aged modified-CIE groups spent increased time in the closed arms, while aged animals also made significantly more closed arm entries, fewer open arm entries, and spent less time in the open arms during withdrawal compared to controls. Modified-CIE decreased MWM performance of adult and aged rats, but did not result in motor impairments in either age group. Finally, acute allopregnanolone increased time to the MWM platform in adults but not aged animals. CONCLUSIONS: The elderly may be vulnerable to EtOH withdrawal as modified-CIE aged rats displayed anxiety-like behavior compared to controls during withdrawal despite achieving lower blood EtOH concentrations during treatment than younger adults. Our data also indicate that modified-CIE and EtOH withdrawal cause persistent cognitive impairments in both age groups. The results from this study provide further evidence indicating the elderly may be sensitive to the effects of alcohol.

Alcohol use across the lifespan: An analysis of adolescent and aged rodents and humans.

Adolescence and old age are unique periods of the lifespan characterized by differential sensitivity to the effects of alcohol. Adolescents and the elderly appear to be more vulnerable to many of alcohol's physiological and behavioral effects compared to adults. The current review explores the differential effects of acute alcohol, predominantly in terms of motor function and cognition, in adolescent and aged humans and rodents. Adolescents are less sensitive to the sedative-hypnotic, anxiolytic, and motor-impairing effects of acute alcohol, but research results are less consistent as it relates to alcohol's effects on cognition. Specifically, previous research has shown adolescents to be more, less, and similarly sensitive to alcohol-induced cognitive deficits compared to adults. These equivocal findings suggest that learning acquisition may be differentially affected by ethanol compared to memory, or that ethanol-induced cognitive deficits are task-dependent. Older rodents appear to be particularly vulnerable to the motor- and cognitive-impairing effects of acute alcohol relative to younger adults. Given that alcohol consumption and abuse is prevalent throughout the lifespan, it is important to recognize age-related differences in response to acute and long-term alcohol. Unfortunately, diagnostic measures and treatment options for alcohol dependence are rarely dedicated to adolescent and aging populations. As discussed, although much scientific advancement has been made regarding the differential effects of alcohol between adolescents and adults, research with the aged is underrepresented. Future researchers should be aware that adolescents and the aged are uniquely affected by alcohol and should continue to investigate alcohol's effects at different stages of maturation.

Chronic intermittent ethanol exposure produces persistent anxiety in adolescent and adult rats.

BACKGROUND: Ethanol (EtOH) dependence and tolerance in the adult are marked by increased function of NMDA receptors and decreased function of GABAA receptors, which coincide with altered receptor subunit expression in specific brain regions. Adolescents often use EtOH at levels greater than adults, yet the receptor subunit expression profiles following chronic intermittent EtOH (CIE) exposure in adolescents are not known. Persistent age-dependent changes in receptor subunit alterations coupled with withdrawal-related anxiety may help explain the increase in alcohol abuse following adolescent experimentation with the drug. METHODS: Adolescent and adult rats received 10 intraperitoneal administrations of 4.0 g/kg EtOH or saline every 48 hours. At either 24 hours or 12 days after the final exposure, anxiety-like behavior was assessed on the elevated plus maze and tissue was collected. Western blotting was used to assess changes in selected NMDA and GABAA receptor subunits in whole cortex and bilateral hippocampus. RESULTS: CIE exposure yields a persistent increase in anxiety-like behavior in both age groups. However, selected NMDA and GABAA receptor subunits were not differentially altered by this CIE exposure paradigm in adolescents or adults. CONCLUSIONS: CIE exposure produced persistent anxiety-like behavior, which has important implications for alcohol cessation. Given the reported behavioral and neuropeptide expression changes in response to this dose of EtOH, it is important for future work to consider the circumstances under which these measures are altered by EtOH exposure.

The effects of acute alcohol on motor impairments in adolescent, adult, and aged rats.

Acute alcohol exposure has been shown to produce differential motor impairments between aged and adult rats and between adolescent and adult rats. However, the effects of acute alcohol exposure among adolescent, adult, and aged rats have yet to be systematically investigated within the same project using a dose-dependent analysis. We sought to determine the age- and dose-dependent effects of acute alcohol exposure on gross and coordinated motor performance across the rodent lifespan. Adolescent (PD 30), adult (PD 70), and aged (approximately 18 months) male Sprague-Dawley rats were tested on 3 separate motor tasks: aerial righting reflex (ARR), accelerating rotarod (RR), and loss of righting reflex (LORR). In a separate group of animals, blood ethanol concentrations (BEC) were determined at multiple time points following a 3.0 g/kg ethanol injection. Behavioral tests were conducted with a Latin square repeated-measures design in which all animals received the following doses: 1.0 g/kg or 2.0 g/kg alcohol or saline over 3 separate sessions via intraperitoneal (i.p.) injection. During testing, motor impairments were assessed on the RR 10 min post-injection and on ARR 20 min post-injection. Aged animals spent significantly less time on the RR when administered 1.0 g/kg alcohol compared to adult rats. In addition, motor performance impairments significantly increased with age after 2.0 g/kg alcohol administration. On the ARR test, aged rats were more sensitive to the effects of 1.0 g/kg and 2.0 g/kg alcohol compared to adolescents and adults. Seven days after the last testing session, animals were given 3.0 g/kg alcohol and LORR was examined. During LORR, aged animals slept longer compared to adult and adolescent rats. This effect cannot be explained solely by BEC levels in aged rats. The present study suggests that acute alcohol exposure produces greater motor impairments in older rats when compared to adolescent and adult rats and begins to establish a procedure to determine motor effects by alcohol across the lifespan.

Acute alcohol produces ataxia and cognitive impairments in aged animals: a comparison between young adult and aged rats.

BACKGROUND: Aging in both humans and rodents appears to be accompanied by physiological changes that increase biologic sensitivity to ethanol (EtOH) intoxication. However, animal models designed to investigate this increased alcohol sensitivity have yet to be established. For this reason, we sought to determine whether acute EtOH administration produces differential effects on motor coordination and spatial cognition in young adult and aged rats. METHODS: Male young adult (postnatal day 70 to 72) and aged (~18 months) Sprague-Dawley rats were assessed on 2 motor tasks (the accelerating rotarod [RR] and the aerial righting reflex [ARR]) and a single cognitive performance task (the Morris water maze [MWM]). Following acute EtOH exposure via intraperitoneal injection, animals' performance was reassessed. RESULTS: Aged rats showed a dramatic increase in EtOH-induced ataxia on the RR and the ARR relative to young adult animals. Similarly, results from the MWM revealed that aged animals had slightly greater EtOH-induced impairments compared with young adult animals. Importantly, the increased impairments produced by EtOH were not due to differential blood EtOH levels. CONCLUSIONS: We demonstrate for the first time that aged rats show greater EtOH-induced deficits compared with young adults in tasks of motor and cognitive performance. The possible role of protein kinase C as a mechanism for increased sensitivity to the motor-impairing effects of EtOH is discussed. Given the high prevalence of alcohol use among the elderly, increased vulnerability to alcohol-induced deficits may have a profound effect on injury in this population.

The effect of chronic intermittent ethanol exposure on spatial memory in adolescent rats: the dissociation of metabolic and cognitive tolerances.

Using a rapid chronic intermittent ethanol (CIE) vapor exposure paradigm, we demonstrate the dissociability of metabolic tolerance from cognitive tolerance in adolescent rats. Adolescent rats were trained to spatially navigate in the Morris Water Maze and then exposed to CIE vapor or air 16 h a day for 4 days. After a final 28 h withdrawal, all rats received a saline or ethanol challenge, followed by a test of spatial memory 30 min after administration. Results indicate that CIE vapor exposure did not significantly impair adolescent spatial memory. Although CIE-exposed rats developed metabolic tolerance to a subsequent ethanol administration, CIE exposure did not alter dose-dependent ethanol-induced spatial memory impairments. These data indicate that metabolic ethanol tolerance can be distinguished from cognitive ethanol tolerance during adolescence and suggest that blood alcohol levels alone do not fully explain ethanol-induced spatial memory impairments.

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.

Behavioral effects of ethanol in cerebellum are age dependent: potential system and molecular mechanisms.

BACKGROUND: Adolescent rats are less sensitive to the motor-impairing effects of ethanol than adults. However, the cellular and molecular mechanisms underlying this age-dependent effect of ethanol have yet to be fully elucidated. METHOD: Male rats of various ages were used to investigate ethanol-induced ataxia and its underlying cellular correlates. In addition, Purkinje neurons from adolescent and adult rats were recorded both in vivo and in vitro. Finally, protein kinase C (PKCγ) expression was determined in 3 brain regions in both adolescent and adult rats. RESULTS: The present multi-methodological investigation confirms that adolescents are less sensitive to the motor-impairing effects of ethanol, and this differential effect is not because of differential blood ethanol levels. In addition, we identify a particular cellular correlate that may underlie the reduced motor impairment. Specifically, the in vivo firing rate of cerebellar Purkinje neurons recorded from adolescent rats was insensitive to an acute ethanol challenge, while the firing rate of adult cerebellar Purkinje neurons was significantly depressed. Finally, it is demonstrated that PKCγ expression in the cortex and cerebellum mirrors the age-dependent effect of ethanol: adolescents have significantly less PKCγ expression compared to adults. CONCLUSIONS: Adolescents are less sensitive than adults to the motor-impairing effects of ethanol, and a similar effect is seen with in vivo electrophysiological recordings of cerebellar Purkinje neurons. While still under investigation, PKCγ expression mirrors the age effect of ethanol and may contribute to the age-dependent differences in the ataxic effects of ethanol.

The influence of a chronic adolescent nicotine exposure on ethanol withdrawal severity during adulthood in C3H mice.

Animal and human studies have shown tolerance, consumption, relapse, and behavioral interactions between ethanol and nicotine, but little is understood about their interaction, especially as it relates to ethanol withdrawal in adulthood for subjects who have an adolescent history of using these drugs. This study investigated nicotine's influence on ethanol withdrawal seizures in two different age groups of male C3H mice. Adolescent and adult male C3H mice, beginning at postnatal day 28 or 70, respectively, were subjected to a 7-day chronic exposure to ethanol only, ethanol plus nicotine, nicotine only, or vehicle treatment. Six weeks later, all the groups were subjected to chronic exposure to ethanol vapors and the severity of their ethanol withdrawal seizures was assessed by handling-induced convulsions. An adolescent exposure to chronic nicotine resulted in an exacerbation of ethanol withdrawal seizures in adulthood. Given this, adolescence may contain a neurophysiological critical period that is sensitive to nicotine and which may result in an altered response to ethanol dependency in adulthood. These findings have serious implications for the long-term consequences following co-abuse of these drugs during adolescence.

The role of GABA(A) receptors in the acute and chronic effects of ethanol: a decade of progress.

The past decade has brought many advances in our understanding of GABA(A) receptor-mediated ethanol action in the central nervous system. We now know that specific GABA(A) receptor subtypes are sensitive to ethanol at doses attained during social drinking while other subtypes respond to ethanol at doses attained by severe intoxication. Furthermore, ethanol increases GABAergic neurotransmission through indirect effects, including the elevation of endogenous GABAergic neuroactive steroids, presynaptic release of GABA, and dephosphorylation of GABA(A) receptors promoting increases in GABA sensitivity. Ethanol's effects on intracellular signaling also influence GABAergic transmission in multiple ways that vary across brain regions and cell types. The effects of chronic ethanol administration are influenced by adaptations in GABA(A) receptor function, expression, trafficking, and subcellular localization that contribute to ethanol tolerance, dependence, and withdrawal hyperexcitability. Adolescents exhibit altered sensitivity to ethanol actions, the tendency for higher drinking and longer lasting GABAergic adaptations to chronic ethanol administration. The elucidation of the mechanisms that underlie adaptations to ethanol exposure are leading to a better understanding of the regulation of inhibitory transmission and new targets for therapies to support recovery from ethanol withdrawal and alcoholism.

Investigation of ethanol-induced impairment of spatial memory in gamma2 heterozygous knockout mice.

GABA(A) receptors, the major inhibitory receptors in the mammalian central nervous system, are affected by a number of drug compounds, including ethanol. The pharmacological effects of certain drugs have been shown to be dependent upon specific GABA(A) receptor subunits. Because benzodiazepines and ethanol have similar effect signatures, it has been hypothesized that these drugs share the gamma2-containing GABA(A) receptors as a mechanism of action. To probe the involvement of the gamma2 subunit in ethanol's actions, spatial memory for the Morris water maze task was tested in gamma2 heterozygous knockout mice and wild type littermate controls following ethanol administration at the following doses: 0.0, 1.25, 1.75, and 2.25 g/kg. While baseline learning and memory were unaffected by reduction of gamma2 containing GABA(A) receptors, ethanol dose-dependently impaired spatial memory equally in gamma2 heterozygous knockouts and wild type littermate controls.

Chronic intermittent exposure to ethanol during adolescence produces tolerance to the hypnotic effects of ethanol in male rats: a dose-dependent analysis.

Adolescence is a time period when distinct behavioral and neurophysiological changes occur. Novelty seeking is common during this developmental period, and binge alcohol consumption by adolescents is prevalent. Adolescents, as compared to adults, have been shown to display decreased sensitivity to many effects of ethanol, including effects that may serve as cues to moderate consumption. Consequently, reduction of these factors could facilitate drinking behaviors in adolescents, which may disrupt normal developmental processes. Chronic intermittent ethanol exposure (CIEE) to high doses of ethanol in rats has been shown to prevent normal developmental increases in sensitivity to ethanol-induced loss of righting reflex (LORR). However, it is unknown whether the same disruptions would occur following CIEE to more moderate and low alcohol doses. The present study was designed to evaluate the effects of CIEE in rats to several different doses during adolescence on ethanol-induced LORR in adulthood. Male rats were weighed and treated intraperitoneal with 1.0, 2.0, 3.0, or 4.0 g/kg ethanol or equivolume saline (equivalent to 4.0 g/kg dosings) every 48 hours for 20 days beginning on postnatal day (PN) 30. LORR was measured following each ethanol exposure. Finally, LORR was measured in both ethanol and saline-exposed animals following 4.0 g/kg ethanol challenge on PN 50 and following a 12-day withdrawal period (PN62). Duration of LORR remained unchanged throughout the adolescent exposure period. However, when LORR was measured on PN50 and PN62, 4.0 and 3.0 g/kg treatment groups displayed significantly less LORR compared to the free feeding and 1.0 g/kg ethanol treated groups. Animals displayed no tolerance development to LORR throughout the chronic exposure period even though moderate and high doses of ethanol were used. CIEE to high (3.0 or 4.0 g/kg) doses of ethanol disrupted the expected developmental increase in sensitivity to ethanol-induced LORR. These results may have implications for human adolescent drinkers. Specifically due to adolescents' relative resistance to the hypnotic effects of alcohol and their tendency to intake alcohol in an intermittent, or binge-like, manner such tolerance might lead to increases in alcohol abuse in this population of drinkers.

The effects of continuous and intermittent ethanol exposure in adolesence on the aversive properties of ethanol during adulthood.

BACKGROUND: Alcohol abuse among adolescents is prevalent. Epidemiological studies suggest that alcohol abuse during the adolescent developmental period may result in long-term changes such as an increased susceptibility to alcohol-related problems in adulthood. Laboratory findings suggest that alcohol exposure during the adolescent developmental period, as compared with adulthood, may differentially impact subsequent neurobehavioral responses to alcohol. The present study was designed to examine whether ethanol exposure, continuous versus intermittent, during the adolescent developmental period would alter the aversive properties of ethanol in adult C3H mice. METHODS: Periadolescent (PD28) male C3H mice were exposed to 64 hours of continuous or intermittent ethanol vapor. As a comparison, adult (PD70) C3H mice were also exposed to 64 hours of continuous or intermittent ethanol vapor. Six weeks after ethanol exposure, taste aversion conditioning was carried out on both ethanol pre-exposed and ethanol-naive animals using a 1-trial, 1-flavor taste-conditioning procedure. RESULTS: Ethanol exposure during the periadolescent period significantly attenuated a subsequent ethanol-induced conditioned taste aversion, as compared with control animals. Adult animals exposed to chronic ethanol vapor during adolescence showed less of an aversion to an ethanol-paired flavor than ethanol-naive adults. Intermittent exposure to ethanol vapor during periadolescence produced a greater attenuation. CONCLUSION: It is suggested that ethanol exposure during the periadolescent period results in long-term neurobehavioral changes, which lessen a conditioned aversion to ethanol in adulthood. It is suggested that this age-related effect may underlie the increased susceptibility to alcohol-related problems which is negatively correlated with the age of onset for alcohol abuse.

Periadolescent exposure to ethanol and diazepam alters the aversive properties of ethanol in adult mice.

Evidence suggests that the developing adolescent brain may be especially vulnerable to long-term neurobehavioral consequences following ethanol exposure and withdrawal. In the present study, we examined the long-term effect of adolescent ethanol withdrawal on a subsequent EtOH-induced conditioned taste aversion (CTA). Periadolescent and adult C3H mice were exposed to 64 h of continuous (single withdrawal) or intermittent (multiple withdrawal) ethanol vapor. Following each ethanol exposure, animals received either 0, 1, 2, or 3 mg/kg diazepam (DZP) in an attempt to counteract the possible effect of ethanol withdrawal. About 6 weeks following ethanol and DZP treatment, animals were tested for an EtOH-induced CTA. As expected, exposure to EtOH during adolescence attenuated the EtOH-induced CTA as compared to controls. Unexpectedly, administration of DZP during withdrawal did not spare but rather mimicked the attenuation of the EtOH-induced CTA seen in animals exposed to ethanol in adolescence. This attenuation was not evident when EtOH and/or DZP was administered in adulthood. Given the similar mode of action of EtOH and DZP on the GABA system, the principal implication of the present findings is that the intoxicating effect of ethanol on the developing brain can result in long-term changes in the aversive properties of EtOH.