Effects of rearing conditions on behaviour and endogenous opioids in rats with alcohol access during adolescence.

Causal links between early-life stress, genes and later psychiatric diagnoses are not possible to fully address in human studies. Animal models therefore provide an important complement in which conditions can be well controlled and are here used to study and distinguish effects of early-life stress and alcohol exposure. The objective of this study was to investigate the impact of rearing conditions on behaviour in young rats and if these changes could be followed over time and to examine interaction effects between early-life environment and adolescent alcohol drinking on behaviour and immunoreactive levels of the opioid peptides dynorphin B, met-enkephalin-Arg(6)Phe(7) and beta-endorphin. We employed a rodent model, maternal separation, to study the impact of rearing conditions on behaviour, voluntary alcohol consumption and alcohol-induced effects. The consequences of short, 15 min (MS 15), and long, 360 min (MS 360), maternal separation in combination with adolescent voluntary alcohol consumption on behaviour and peptides were examined. A difference in the development of risk taking behaviour was found between the MS15 and MS360 while the development of general activity was found to differ between intake groups. Beta-endorphin levels in the pituitary and the periaqueductal gray area was found to be higher in the MS15 than the MS360. Adolescent drinking resulted in higher dynorphin B levels in the hippocampus and higher met-enkephalin-Arg(6)Phe(7) levels in the amygdala. Amygdala and hippocampus are involved in addiction processes and changes in these brain areas after adolescent alcohol drinking may have consequences for cognitive function and drug consumption behaviour in adulthood. The study shows that individual behavioural profiling over time in combination with neurobiological investigations provides means for studies of causality between early-life stress, behaviour and vulnerability to psychiatric disorders.

The response to naltrexone in ethanol-drinking rats depends on early environmental experiences.

The opioid receptor antagonist naltrexone is currently used in the treatment of alcohol addiction. However, substantial individual differences have been reported for the efficacy of naltrexone. Genetic factors are known to contribute to these differences; however, little is known about the impact of early environmental influences. Based on previous findings that have suggested a link between ethanol, endogenous opioids and the early environment, it was hypothesised that early environmental factors affect naltrexone efficacy later in life. A population of Wistar rats was subjected to three different rearing conditions where the pups experienced a daily separation from the dam, for either 15 min or 360 min, or were just briefly handled. On postnatal day 26, the rats were given intermittent access to ethanol (5% and 20%) and water for six weeks before naltrexone (0.3mg/kg or 3.0mg/kg) or saline treatment using a randomised injection schedule with a one-week washout period between injections. Naltrexone reduced ethanol consumption, but there was high variability in the efficacy. In addition, there was an association between the rearing condition and the effectiveness of naltrexone. Naltrexone reduced ethanol intake in rats experiencing postnatal conditions that contrasted normal wildlife conditions, i.e., prolonged absence or continuous presence of the dam, and naltrexone had no effect on the total ethanol consumption in rats reared under naturalistic conditions, i.e., short absences of the dam. These rats reduced their intake of 5% ethanol but increased their preference for 20% ethanol. We conclude that rats with a history of early adversity responded well to naltrexone treatment, whereas rats reared in a social context similar to that found in nature did not benefit from treatment. The present study highlights the importance of not only considering genetics but also environmental factors when identifying individual responses to naltrexone.

Early environmental factors differentially affect voluntary ethanol consumption in adolescent and adult male rats.

BACKGROUND: Previous studies using the maternal separation (MS) model have shown that environmental factors early in life affect adult ethanol consumption. Prolonged MS is related to enhanced propensity for high adult ethanol intake when compared to short MS. Less is known about the environmental impact on adolescent ethanol intake. In this study, the aim was to compare establishment of voluntary ethanol consumption in adolescent and adult rats subjected to different rearing conditions. METHODS: Wistar rat pups were separated from their mother 0 minutes (MS0), 15 minutes (MS15), or 360 minutes (MS360) daily during postnatal days (PNDs) 1 to 20. After weaning, the male rats were divided into two groups; rats were given free access to water, 5 and 20% ethanol at either PND 26 or 68. Ethanol was provided in 24-hour sessions three times per week for 5 weeks. RESULTS: MS resulted in altered ethanol consumption patterns around the pubertal period but otherwise the rearing conditions had little impact on ethanol consumption in adolescents. In adults, the establishment of ethanol consumption was dependent on the rearing condition. The adult MS0 and MS15 rats had a stable ethanol intake, whereas the MS360 rats increased both their ethanol intake and preference over time. CONCLUSIONS: With the use of intermittent access to ethanol, new data were provided, which confirm the notion that MS360 represents a risk environment related to higher ethanol intake compared to MS15. The adolescent rats had higher ethanol intake than adult rats but the consumption was independent of rearing condition. Experiences during the first three postnatal weeks thus affect the establishment of voluntary ethanol consumption differently in adolescent and adult rats. Further studies are now warranted to examine the consequences of a combination of early environmental influence and high adolescent ethanol intake.

Postpartum Behavioral Profiles in Wistar Rats Following Maternal Separation - Altered Exploration and Risk-Assessment Behavior in MS15 Dams.

The rodent maternal separation (MS) model is frequently used to investigate the impact of early environmental factors on adult neurobiology and behavior. The majority of MS studies assess effects in the offspring and few address the consequences of repeated pup removal in the dam. Such studies are of interest since alterations detected in offspring subjected to MS may, at least in part, be mediated by variations in maternal behavior and the amount of maternal care provided by the dam. The aim of this study was to investigate how daily short (15 min; MS15) and prolonged (360 min; MS360) periods of MS affects the dam by examining postpartum behavioral profiles using the multivariate concentric square field (MCSF) test. The dams were tested on postpartum days 24-25, i.e., just after the end of the separation period and weaning. The results reveal a lower exploratory drive and lower risk-assessment behavior in MS15 dams relative to MS360 or animal facility reared dams. The present results contrast some of the previously reported findings and provide new information about early post-weaning behavioral characteristics in a multivariate setting. Plausible explanations for the results are provided including a discussion how the present results fit into the maternal mediation hypothesis.