Age-dependent effects of stress on ethanol-induced motor activity in rats

Experimental Evidence on Age-related Differential Outcomes Associated With Substance Abuse

Growing evidence indicates that adolescent substance abuse is now an alarming concern that imposes a considerable socio-economic burden on societies. On the other hand, numerous studies have shown that due to specific neurophysiological features, the brain is more vulnerable to the adverse effects of psychoactive drugs at an early age. Unfortunately, these negative effects are not limited to the period of drug use, but can persistently affect the brain's responsiveness to future exposures to the same or other types of drug. For researchers to develop pharmacological strategies for managing substance abuse disorders, they need to gain a deep understanding of the differences in behavioral outcomes associated with each type of drug across different age groups. The present study was conducted to review the experimental evidence revealing the mentioned differential effects with an emphasis on common drugs of abuse, including cocaine, nicotine, cannabis, and opioids. Although the cellular mechanisms underlying age-related effects have not been exclusively addressed for each drug, the most recent results are presented and discussed. Future studies are required to focus on these mechanisms and reveal how molecular changes during brain development can result in differential responses to drugs at the behavioral level.

Gestational hypoxia in late pregnancy differentially programs subcortical brain maturation in male and female rat offspring

BACKGROUND

Hypoxia is associated with pregnancy complications, such as preeclampsia, placental abruption, and gestational sleep apnea. Hypoxic insults during gestation can impact the brain maturation of cortical and subcortical pathways, such as the nigrostriatal pathway. However, the long-term effects of in utero hypoxic stress exposure on brain maturation in offspring are unclear, especially exposure during late gestation. The purpose of this study was to determine the impact of gestational hypoxia in late pregnancy on developmental programming of subcortical brain maturation by focusing on the nigrostriatal pathway.

METHODS

Timed pregnant Long-Evans rats were exposed to chronic intermittent hypoxia or room air normoxia from gestational day (GD) 15-19 (term 22-23 days). Male and female offspring were assessed during two critical periods: puberty from postnatal day (PND) 40-45 or young adulthood (PND 60-65). Brain maturation was quantified by examining (1) the structural development of the nigrostriatal pathway via analysis of locomotor behaviors and the substantia nigra dopaminergic neuronal cell bodies and (2) the refinement of the nigrostriatal pathway by quantifying ultrasonic vocalizations (USVs).

RESULTS

The major findings of this study are gestational hypoxia has age- and sex-dependent effects on subcortical brain maturation in offspring by adversely impacting the refinement of the nigrostriatal pathway in the absence of any effects on the structural development of the pathway. During puberty, female offspring were impacted more than male offspring, as evidenced by decreased USV call frequency, chirp USV call duration, and simple call frequency. In contrast, male offspring were impacted more than female offspring during young adulthood, as evidenced by increased latency to first USV, decreased simple USV call intensity, and increased harmonic USV call bandwidth. No effects of gestational hypoxia on the structural development of the nigrostriatal pathway were observed.

CONCLUSIONS

These novel findings demonstrate hypoxic insults during pregnancy mediate developmental programming of the cortical and subcortical pathways, in which male offspring exhibit long-term adverse effects compared to female offspring. Impairment of cortical and subcortical pathways maturation, such as the nigrostriatal pathway, may increase risk for neuropsychiatric disorders (e.g., mood disorders, cognitive dysfunction, brain connectivity dysfunction).

Effect of intermittent access to alcohol mixed in energy drink during adolescence on alcohol self-administration, anxiety, and memory during adulthood in rats

BACKGROUND

Mixing alcohol with caffeinated energy drinks is a common practice among young people. Consumption of alcohol mixed in energy drink is associated with increased risk of binge drinking and alcohol dependence. The purpose of this study was to determine whether voluntary intermittent access to alcohol mixed in energy drink in adolescent rats alters adult self-administration of alcohol, anxiety, and memory.

METHODS

For 10 weeks in the home-cage, two groups of adolescent female Sprague-Dawley rats had intermittent access to energy drink (ED) or 10% alcohol mixed in energy drink (AmED) with water concurrently available. Other rat groups had daily continuous access to ED or AmED. Anxiety was measured with an open field test and memory was assessed with a novel place recognition test. For self-administration, rats pressed levers for 10% alcohol alone on a fixed ratio (FR1) and on a progressive ratio (PR).

RESULTS

Intermittent access to AmED generated greater intake during the initial 30 min of access (AmED 1.70 ± 0.04 g/kg vs. ED 1.01 ± 0.06 g/kg) and during the subsequent 24 h (AmED 7.04 ± 0.25 g/kg vs. ED 5.60 ± 0.29 g/kg). Intermittent AmED caused a significant but small decrease in anxiety while neither ED nor AmED altered memory. During alcohol self-administration, group differences emerged only during PR testing during which intermittent AmED rats responded more than all other groups.

CONCLUSIONS

These findings suggest that intermittent access to AmED generates binge-like consumption that supports human findings that AmED generates greater alcohol consumption. Furthermore, experience with AmED may alter the motivational properties of alcohol into adulthood without necessarily causing a major impact on anxiety or memory.

Adolescent exposure to delta-9-tetrahydrocannabinol and ethanol heightens sensitivity to fear stimuli

Cannabis use disorder (CUD) has doubled in prevalence over the past decade as a nation-wide trend toward legalization allows for increased drug accessibility. As a result, marijuana has become the most commonly used illicit drug in the United States particularly among the adolescent population. This is especially concerning since there is greater risk for the harmful side effects of drug use during this developmental period due to ongoing brain maturation. Increasing evidence indicates that CUD often occurs along with other debilitating conditions including both alcohol use disorder (AUD) and anxiety disorders such post-traumatic stress disorder (PTSD). Additionally, exposure to cannabis, alcohol, and stress can induce alterations in glutamate regulation and homeostasis in the prefrontal cortex (PFC) that may lead to impairments in neuronal functioning and cognition. Therefore, in order to study the relationship between drug exposure and the development of PTSD, these studies utilized rodent models to determine the impact of adolescent exposure to delta-9-tetrahydrocannabinol (THC) and ethanol on responses to fear stimuli during fear conditioning and used calcium imaging to measure glutamate activity in the prelimbic cortex during this behavioral paradigm. The results from these experiments indicate that adolescent exposure to THC and ethanol leads to enhanced sensitivity to fear stimuli both behaviorally and neuronally. Additionally, these effects were attenuated when animals were treated with the glutamatergic modulator N-acetylcysteine (NAC). In summary, these studies support the hypothesis that adolescent exposure to THC and ethanol leads to alterations in fear stimuli processing through glutamatergic reliant modifications in PFC signaling.

Prediction of ethanol self-administration in pre-weanling, adolescent, and young adult rats

Alcohol (ethanol) use is almost normative by late adolescence, in most western countries. It is important to identify factors that distinguish those who progress from alcohol initiation to sustained use of the drug, from those that keep a controlled pattern of drinking. The factors precipitating this transition may change across development. This study analyzed associations between behavioral endophenotypes and ethanol intake at three developmental periods. Exp. 1 measured ethanol drinking at postnatal day 18, via an intraoral infusion procedure, in male or female pre-weanling rats screened for anxiety response in the light-dark box test and for distance traveled in a novel open field. Exp. 2 measured, in juvenile/adolescent or young adult rats, the association between shelter seeking, exploratory/risk-taking behaviors, anxiety or hedonic responses, and ethanol intake. Ethanol intake in pre-weanlings was explained by distance traveled in a novel environment, whereas anxiety responses, measured in the multivariate concentric square field apparatus (MSCF), selectively predicted ethanol intake at adolescence, but not at adulthood. Those juvenile/adolescents with lower mean duration of visit to areas of the MSCF that evoke anxiogenic responses exhibited heightened ethanol intake. These findings suggest that the association between anxiety and ethanol intake may be specifically relevant during adolescence.

Effect of lacosamide on ethanol induced conditioned place preference and withdrawal associated behavior in mice: Possible contribution of hippocampal CRMP-2

BACKGROUND

Excessive consumption of ethanol is known to activate the mTORC1 pathway and to enhance the Collapsin Response Mediator Protein-2 (CRMP-2) levels in the limbic region of brain. The latter helps in forming microtubule assembly that is linked to drug taking or addiction-like behavior in rodents. Therefore, in this study, we investigated the effect of lacosamide, an antiepileptic drug and a known CRMP-2 inhibitor, which binds to CRMP-2 and inhibits the formation of microtubule assembly, on ethanol-induced conditioned place preference (CPP) in mice.

METHODS

The behavior of mice following ethanol addiction and withdrawal was assessed by performing different behavioral paradigms. Mice underwent ethanol-induced CPP training with alternate dose of ethanol (2 g/kg, po) and saline (10 ml/kg, po). The effect of lacosamide on the expression of ethanol-induced CPP and on ethanol withdrawal associated anxiety and depression-like behavior was evaluated. The effect of drug on locomotor activity was also assessed and hippocampal CRMP-2 levels were measured.

RESULTS

Ethanol-induced CPP was associated with enhanced CRMP-2 levels in the hippocampus. Lacosamide significantly reduced the expression of ethanol-induced CPP and alleviated the levels of hippocampal CRMP-2 but aggravated withdrawal-associated anxiety and depression in mice.

CONCLUSION

The present study demonstrated the beneficial effect of lacosamide in attenuation of expression of ethanol induced conditioned place preference via reduction of hippocampal CRMP-2 level. These findings suggest that lacosamide may be investigated further for ethanol addiction but not for managing withdrawal.

The impact of low to moderate chronic intermittent ethanol exposure on behavioral endpoints in aged, adult, and adolescent rats

The average age of the population in the United States and other countries is increasing. Understanding the health consequences in the aged population is critical. Elderly individuals consume ethanol, often at elevated rates, and in some cases in a binge episode. The present study sought to investigate whether binge-like ethanol exposure in aged male rats produced differential health and behavioral effects compared to adult male and adolescent male rats. Subjects were exposed to either 1.0 g/kg or 2.0 g/kg ethanol every other day via intraperitoneal injection for 20 days, and tested on a variety of behavioral measures and body weight. Binge-like ethanol exposure produced differential effects on body weight between aged and adolescent and adult rats. In addition, aged rats had a significantly longer loss of righting reflex and demonstrated a trend toward tolerance following the 2.0-g/kg exposure. No significant effects on anxiety-like behavior as measured by open arm entries, depressive-like symptoms as measured by immobility in the forced swim test, or cognitive performance as measured by latency and path length in the Morris water maze were found. These results demonstrate that aged animals are differentially sensitive to the impact of chronic intermittent ethanol exposure in some, but not all behaviors. Future research is needed to understand the mechanisms of these differential effects.

Interaction Between Stress and Addiction: Contributions From Latin-American Neuroscience

Drug addiction is a chronic neuropsychiatric disorder that escalates from an initial exposure to drugs of abuse, such as cocaine, cannabis, or heroin, to compulsive drug-seeking and intake, reduced ability to inhibit craving-induced behaviors, and repeated cycles of abstinence and relapse. It is well-known that chronic changes in the brain’s reward system play an important role in the neurobiology of addiction. Notably, environmental factors such as acute or chronic stress affect this system, and increase the risk for drug consumption and relapse. Indeed, the HPA axis, the autonomic nervous system, and the extended amygdala, among other brain stress systems, interact with the brain’s reward circuit involved in addictive behaviors. There has been a growing interest in studying the molecular, cellular, and behavioral mechanisms of stress and addiction in Latin-America over the last decade. Nonetheless, these contributions may not be as strongly acknowledged by the broad scientific audience as studies coming from developed countries. In this review, we compile for the first time a series of studies conducted by Latin American-based neuroscientists, who have devoted their careers to studying the interaction between stress and addiction, from a neurobiological and clinical perspective. Specific contributions about this interaction include the study of CRF receptors in the lateral septum, investigations on the neural mechanisms of cross-sensitization for psychostimulants and ethanol, the identification of the Wnt/β-catenin pathway as a critical neural substrate for stress and addiction, and the emergence of the cannabinoid system as a promising therapeutic target. We highlight animal and human studies, including for instance, reports coming from Latin American laboratories on single nucleotide polymorphisms in stress-related genes and potential biomarkers of vulnerability to addiction, that aim to bridge the knowledge from basic science to clinical research.

Repeated Cycles of Binge-Like Ethanol Intake in Adolescent Female Rats Induce Motor Function Impairment and Oxidative Damage in Motor Cortex and Liver, but Not in Blood

Moderate ethanol consumption (MEC) is increasing among women. Alcohol exposure usually starts in adolescence and tends to continue until adulthood. We aimed to investigate MEC impacts during adolescence until young adulthood of female rats. Adolescent female Wistar rats received distilled water or ethanol (3 g/kg/day), in a 3 days on-4 days off paradigm (binge drinking) for 1 and 4 consecutive weeks. We evaluate liver and brain oxidative damage, peripheral oxidative parameters by SOD, catalase, thiol contents, and MDA, and behavioral motor function by open-field, pole, beam-walking, and rotarod tests. Our results revealed that repeated episodes of binge drinking during adolescence displayed lipid peroxidation in the liver and brain. Surprisingly, such oxidative damage was not detectable on blood. Besides, harmful histological effects were observed in the liver, associated to steatosis and loss of parenchymal architecture. In addition, ethanol intake elicited motor incoordination, bradykinesia, and reduced spontaneous exploratory behavior in female rats.

Alcohol, psychomotor-stimulants and behaviour: methodological considerations in preclinical models of early-life stress

BACKGROUND

In order to assess the risk associated with early-life stress, there has been an increase in the amount of preclinical studies investigating early-life stress. There are many challenges associated with investigating early-life stress in animal models and ensuring that such models are appropriate and clinically relevant.

OBJECTIVES

The purpose of this review is to highlight the methodological considerations in the design of preclinical studies investigating the effects of early-life stress on alcohol and psychomotor-stimulant intake and behaviour.

METHODS

The protocols employed for exploring early-life stress were investigated and summarised. Experimental variables include animals, stress models, and endpoints employed.

RESULTS

The findings in this paper suggest that there is little consistency among these studies and so the interpretation of these results may not be as clinically relevant as previously thought.

CONCLUSION

The standardisation of these simple stress procedures means that results will be more comparable between studies and that results generated will give us a more robust understanding of what can and may be happening in the human and veterinary clinic.

Ethanol-induced autonomic responses and risk taking increase in young adults with a positive family history of alcohol problems

The mechanisms that underlie the greater prevalence of alcohol use disorders in individuals with a positive family history (FH+) of alcohol abuse are still under investigation. These subjects may exhibit differential sensitivity to alcohol's effects on psychomotor stimulation and impulsivity. Alcohol-induced psychomotor stimulation, measured as the heart rate (HR) response, is a proxy for the positive rewarding effects of the drug. We analyzed alcohol-induced effects on time perception (Time Production Task), risk taking (Balloon Analogue Risk Task [BART]), and HR in FH+ and FH- participants. In the FH+ and FH- groups, women and men received 0.6 and 0.7g/kg alcohol, respectively. The alcohol dose yielded a breath alcohol concentration of 0.08% throughout the experiment. The control groups received placebo, and the subjective perception of alcohol intoxication was assessed. Alcohol intoxication significantly increased HR and the adjusted average number of pumps on the BART (a measure of risk taking) in FH+ men and women but not in FH- participants. Behavioral impulsivity was unaffected by alcohol or a FH of alcohol abuse. FH- but not FH+ participants who received alcohol reported significantly greater subjective perception of alcohol's effects than their placebo counterparts. These results indicate that FH+ individuals presented heightened sensitivity to alcohol-induced HR stimulation and alcohol-induced risk taking compared with their FH- counterparts. FH+ subjects, however, were insensitive to the subjective effects of alcohol. This idiosyncratic response pattern may be a likely pathway by which a FH of alcohol problems promotes alcohol drinking.

Short-term selection for high and low ethanol intake yields differential sensitivity to ethanol's motivational effects and anxiety-like responses in adolescent Wistar rats

Alcohol use disorders are modulated by genetic factors, but the identification of specific genes and their concomitant biological changes that are associated with a higher risk for these disorders has proven difficult. Alterations in the sensitivity to the motivational effects of ethanol may be one way by which genes modulate the initiation and escalation of ethanol intake. Rats and mice have been selectively bred for high and low ethanol consumption during adulthood. However, selective breeding programs for ethanol intake have not focused on adolescence. This phase of development is associated with the initiation and escalation of ethanol intake and characterized by an increase in the sensitivity to ethanol's appetitive effects and a decrease in the sensitivity to ethanol's aversive effects compared with adulthood. The present study performed short-term behavioral selection to select rat lines that diverge in the expression of ethanol drinking during adolescence. A progenitor nucleus of Wistar rats (F₀) and filial generation 1 (F₁), F₂, and F₃ adolescent rats were derived from parents that were selected for high (STDRHI) and low (STDRLO) ethanol consumption during adolescence and were tested for ethanol intake and responsivity to ethanol's motivational effects. STDRHI rats exhibited significantly greater ethanol intake and preference than STDRLO rats. Compared with STDRLO rats, STDRHI F₂ and F₃ rats exhibited a blunted response to ethanol in the conditioned taste aversion test. F₂ and F₃ STDRHI rats but not STDRLO rats exhibited ethanol-induced motor stimulation. STDRHI rats exhibited avoidance of the white compartment of the light-dark box, a reduction of locomotion, and a reduction of saccharin consumption, suggesting an anxiety-prone phenotype. The results suggest that the genetic risk for enhanced ethanol intake during adolescence is associated with lower sensitivity to the aversive effects of ethanol, heightened reactivity to ethanol's stimulating effects, and enhanced innate anxiety.

Effects of environmental enrichment upon ethanol-induced conditioned place preference and pre-frontal BDNF levels in adolescent and adult mice

Environmental enrichment (EE) provides a non-pharmacological tool to alter drug-induced reward, yet its effects on ethanol-induced reward remain controversial. We analyzed adolescent vs. adult (mice) differences in the influence of EE on ethanol-induced conditioned place preference (CPP). The effects of these treatments on brain-derived neurotrophic factor (BDNF) levels in the prefrontal cortex were examined in a separate group of animals. Ethanol-induced CPP was found in adults, and it was similar in EE and in animals reared under standard housing conditions (SC). Adolescents kept under EE, but not those in SC, exhibited CPP. Among SC, but not among EE, adolescents, BDNF levels were significantly lower in those treated with ethanol than in those given vehicle. These results indicate that, compared to adults, adolescent exhibited reduced sensitivity to ethanol’s rewarding effects, yet the youth but not the adults exhibited sensitivity to the promoting effect of EE upon CPP by ethanol. Ethanol significantly reduced BDNF levels in adolescents reared under standard housing conditions, but not in adult mice nor in adolescents given EE housing conditions. The present results add to the plethora of adolescent-specific responses to ethanol or to environmental stimuli that may put the youth at risk for escalation of ethanol intake.

Prenatal ethanol exposure modifies locomotor activity and induces selective changes in Met-enk expression in adolescent rats

Several studies suggest that prenatal ethanol exposure (PEE) facilitates ethanol intake. Opioid peptides play a main role in ethanol reinforcement during infancy and adulthood. However, PEE effects upon motor responsiveness elicited by an ethanol challenge and the participation of opioids in these actions remain to be understood. This work assessed the susceptibility of adolescent rats to prenatal and/or postnatal ethanol exposure in terms of behavioral responses, as well as alcohol effects on Met-enk expression in brain areas related to drug reinforcement. Motor parameters (horizontal locomotion, rearings and stereotyped behaviors) in pre- and postnatally ethanol-challenged adolescents were evaluated. Pregnant rats received ethanol (2g/kg) or water during gestational days 17-20. Adolescents at postnatal day 30 (PD30) were tested in a three-trial activity paradigm (habituation, vehicle and drug sessions). Met-enk content was quantitated by radioimmunoassay in several regions: ventral tegmental area [VTA], nucleus accumbens [NAcc], prefrontal cortex [PFC], substantia nigra [SN], caudate-putamen [CP], amygdala, hypothalamus and hippocampus. PEE significantly reduced rearing responses. Ethanol challenge at PD30 decreased horizontal locomotion and showed a tendency to reduce rearings and stereotyped behaviors. PEE increased Met-enk content in the PFC, CP, hypothalamus and hippocampus, but did not alter peptide levels in the amygdala, VTA and NAcc. These findings suggest that PEE selectively modifies behavioral parameters at PD30 and induces specific changes in Met-enk content in regions of the mesocortical and nigrostriatal pathways, the hypothalamus and hippocampus. Prenatal and postnatal ethanol actions on motor activity in adolescents could involve activation of specific neural enkephalinergic pathways.

Age-Dependent Susceptibility to Alcohol-Induced Cerebral Artery Constriction

BACKGROUND

Age has been recognized as an important contributor into susceptibility to alcohol-driven pathology.

PURPOSE

We aimed at determining whether alcohol-induced constriction of cerebral arteries was age-dependent.

STUDY DESIGN

We used rat middle cerebral artery (MCA) in vitro diameter monitoring, patch-clamping and fluorescence labeling of myocytes to study an age-dependent increase in the susceptibility to alcohol in 3 (50 g), 8 (250 g), and 15 (440 g) weeks-old rats.

RESULTS

An age-dependent increase in alcohol-induced constriction of MCA could be observed in absence of endothelium, which is paralleled by an age-dependent increase in both protein level of the calcium-/voltage-gated potassium channel of large conductance (BK) accessory β1 subunit and basal BK channel activity. Ethanol-induced BK channel inhibition is increased with age.

CONCLUSIONS

We demonstrate an increased susceptibility of MCA to ethanol-induced constriction in a period equivalent to adolescence and early adulthood when compared to pre-adolescence. Our work suggests that BK β1 constitutes a significant contributor to age-dependent changes in the susceptibility of cerebral arteries to ethanol.

Dose-dependent effects of alcohol administration on behavioral profiles in the MCSF test

The acute effects of alcohol administration are age-, dose-, time- and task-dependent. Although generally considered to be a sedative drug, alcohol has both stimulatory and depressant effects on behavior, depending on dose and time. Alcohol-induced motor activating effects are consistently shown in mice but rarely demonstrated in adult, outbred rats using conventional behavioral tests. The aim of the present experiment was to study acute alcohol-induced effects on behavioral profiles in a more complex environment using the novel multivariate concentric square field™ (MCSF) test, designed for assessing different behaviors in the same trial including locomotor activity. Adult male Wistar rats (Sca:WI) were administered one intraperitoneal (i.p.) injection of alcohol (0.0 g/kg, 0.5 g/kg, 1.0 g/kg, or 1.5 g/kg) 5 min prior to the 30-min MCSF test. The two highest doses induced marked motor-suppressing effects. A significant interaction between group and time was found in general activity when comparing rats exposed to alcohol at 0.0 g/kg and 0.5 g/kg. In contrast to the 0.0 g/kg dose that increased the activity over time, animals administered the low dose (0.5 g/kg) demonstrated an initial high activity followed by a decline over time. No indications for acute alcohol-induced anxiolytic-like effects were found. The multivariate setting in the MCSF test appears to be sensitive for detecting motor-activating effects of low doses of alcohol as well as reduced locomotion at doses lower than in other behavioral tasks. The detection of subtle changes in behavior across time and dose is important for understanding alcohol-induced effects. This approach may be useful in evaluating alcohol doses that correspond to different degrees of intoxication in humans.

Pharmacological characterization of the nociceptin/orphanin FQ receptor on ethanol-mediated motivational effects in infant and adolescent rats

Activation of nociceptin/orphanin FQ (NOP) receptors attenuates ethanol drinking and prevents relapse in adult rodents. In younger rodents (i.e., infant rats), activation of NOP receptors blocks ethanol-induced locomotor activation but does not attenuate ethanol intake. The aim of the present study was to extend the analysis of NOP modulation of ethanol's effects during early ontogeny. Aversive and anxiolytic effects of ethanol were measured in infant and adolescent rats via conditioned taste aversion and the light-dark box test; whereas ethanol-induced locomotor activity and ethanol intake was measured in adolescents only. Before these tests, infant rats were treated with the natural ligand of NOP receptors, nociceptin (0.0, 0.5 or 1.0 μg) and adolescent rats were treated with the specific agonist Ro 64-6198 (0.0, 0.1 or 0.3 mg/kg). The activation of NOP receptors attenuated ethanol-induced anxiolysis in adolescents only, and had no effect on ethanol's aversive effects. Administration of Ro 64-6198 blocked ethanol-induced locomotor activation but did not modify ethanol intake patterns. The attenuation of ethanol stimulating and anxiolytic effect by activation of NOP receptors indicates a modulatory role of this receptor on ethanol effects, which is expressed early in ontogeny.

Adolescent rats are resistant to the development of ethanol-induced chronic tolerance and ethanol-induced conditioned aversion

The analysis of chronic tolerance to ethanol in adult and adolescent rats has yielded mixed results. Tolerance to some effects of ethanol has been reported in adolescents, yet other studies found adults to exhibit greater tolerance than adolescents or comparable expression of the phenomena at both ages. Another unanswered question is how chronic ethanol exposure affects subsequent ethanol-mediated motivational learning at these ages. The present study examined the development of chronic tolerance to ethanol's hypothermic and motor stimulating effects, and subsequent acquisition of ethanol-mediated odor conditioning, in adolescent and adult male Wistar rats given every-other-day intragastric administrations of ethanol. Adolescent and adult rats exhibited lack of tolerance to the hypothermic effects of ethanol during an induction phase; whereas adults, but not adolescents, exhibited a trend towards a reduction in hypothermia at a challenge phase (Experiment 1). Adolescents, unlike adults, exhibited ethanol-induced motor activation after the first ethanol administration. Adults, but not adolescents, exhibited conditioned odor aversion by ethanol. Subsequent experiments conducted only in adolescents (Experiment 2, Experiment 3 and Experiment 4) manipulated the context, length and predictability of ethanol administration. These manipulations did not promote the expression of ethanol-induced tolerance. This study indicated that, when moderate ethanol doses are given every-other day for a relatively short period, adolescents are less likely than adults to develop chronic tolerance to ethanol-induced hypothermia. This resistance to tolerance development could limit long-term maintenance of ethanol intake. Adolescents, however, exhibited greater sensitivity than adults to the acute motor stimulating effects of ethanol and a blunted response to the aversive effects of ethanol. This pattern of response may put adolescents at risk for early initiation of ethanol intake.

Response to stress in Drosophila is mediated by gender, age and stress paradigm

All living organisms must maintain equilibrium in response to internal and external challenges within their environment. Changes in neural plasticity (alterations in neuronal populations, dendritic remodeling, and synaptic turnover) are critical components of the homeostatic response to stress, which has been strongly implicated in the onset of affective disorders. However, stress is differentially perceived depending on the type of stress and its context, as well as genetic background, age and sex; therefore, an individual's maintenance of neuronal homeostasis must differ depending upon these variables. We established Drosophila as a model to analyze homeostatic responses to stress. Sexually immature and mature females and males from an isogenic wild-type strain raised under controlled environmental conditions were exposed to four reproducible and high-throughput translatable stressors to facilitate the analysis of a large number of animals for direct comparisons. These animals were assessed in an open-field arena, in a light-dark box, and in a forced swim test, as well as for sensitivity to the sedative effects of ethanol. These studies establish that immature and mature females and males represent behaviorally distinct populations under control conditions as well as after exposure to different stressors. Therefore, the neural substrates mediating the stress response must be differentially expressed depending upon the hormonal status of the brain. In addition, an adaptive response to a given stressor in one paradigm was not predictive for outcomes in other paradigms.

Stress in adolescence and drugs of abuse in rodent models: role of dopamine, CRF, and HPA axis

RATIONALE

Research on adolescence and drug abuse increased substantially in the past decade. However, drug-addiction-related behaviors following stressful experiences during adolescence are less studied. We focus on rodent models of adolescent stress cross-sensitization to drugs of abuse.

OBJECTIVES

Review the ontogeny of behavior, dopamine, corticotropin-releasing factor (CRF), and the hypothalamic-pituitary-adrenal (HPA) axis in adolescent rodents. We evaluate evidence that stressful experiences during adolescence engender hypersensitivity to drugs of abuse and offer potential neural mechanisms.

RESULTS AND CONCLUSIONS

Much evidence suggests that final maturation of behavior, dopamine systems, and HPA axis occurs during adolescence. Stress during adolescence increases amphetamine- and ethanol-stimulated locomotion, preference, and self-administration under many conditions. The influence of adolescent stress on subsequent cocaine- and nicotine-stimulated locomotion and preference is less clear. The type of adolescent stress, temporal interval between stress and testing, species, sex, and the drug tested are key methodological determinants for successful cross-sensitization procedures. The sensitization of the mesolimbic dopamine system is proposed to underlie stress cross-sensitization to drugs of abuse in both adolescents and adults through modulation by CRF. Reduced levels of mesocortical dopamine appear to be a unique consequence of social stress during adolescence. Adolescent stress may reduce the final maturation of cortical dopamine through D2 dopamine receptor regulation of dopamine synthesis or glucocorticoid-facilitated pruning of cortical dopamine fibers. Certain rodent models of adolescent adversity are useful for determining neural mechanisms underlying the cross-sensitization to drugs of abuse.

Relationship between ethanol-induced activity and anxiolysis in the open field, elevated plus maze, light-dark box, and ethanol intake in adolescent rats

It is yet unclear if ethanol-induced motor stimulation in the open field (OF) merely reflects psychomotor stimulating effects of the drug or if this stimulation is driven or modulated by ethanol's antianxiety properties. In the present study, adolescent rats were administered with different ethanol doses or remained untreated. They were sequentially assessed in the OF, elevated plus maze (EPM), and light-dark box (LDB) and then assessed for ethanol intake. The aims were to assess the relationship between measures of ethanol-induced activity and anxiolysis, analyze ethanol intake as a function of prior ethanol exposure, and associate behavioral responsiveness in these apparatus with ethanol intake during adolescence. The results suggested that the enhanced exploration of the OF observed after 2.5 and 3.25 g/kg ethanol reflected a motor-stimulating effect that appeared to be relatively independent of anxiolysis. The 1.25 g/kg dose induced motor stimulation in the OF and anti-anxiety effects in the EPM, but these effects were relatively independent. The 0.5 g/kg ethanol dose exerted significant anxiolytic effects in the EPM in the absence of stimulating effects in the OF. A multivariate regression analysis indicated that adolescents with a higher frequency of rearing behavior in the OF, higher percentage of open arm entries in the EPM, and lower propensity to enter the central area of the OF exhibited greater ethanol intake. These results indicate that the OF is a valid procedure for the measurement of ethanol-induced stimulation, and provide information toward characterizing subpopulations of adolescents at risk for initiating alcohol drinking.