Acute ethanol exposure during pregnancy in rats: effects upon a multiple learning task

Attention, impulsivity, and cognitive flexibility in adult male rats exposed to ethanol binge during adolescence as measured in the five-choice serial reaction time task: the effects of task and ethanol challenges

RATIONALE

Alcohol abuse is prevalent in adolescent humans, but the long-term behavioral consequences of binge alcohol drinking are unknown.

OBJECTIVES

This study investigated the long-term effects of adolescent intermittent ethanol (AIE) exposure on attention and impulsivity.

METHODS

Adolescent male rats were exposed to 5 g/kg of 25% (v/w) ethanol every 8 h for 4 days. During adulthood, rats were tested in the five-choice serial reaction time task (5-CSRTT) assessing attention, impulsivity and cognitive flexibility.

RESULTS

There was no metabolic tolerance to ethanol in adolescent rats during AIE exposure. In the 5-CSRTT under baseline conditions, there were no differences between AIE-exposed and control rats in accuracy, omissions, or premature responses, although AIE-exposed rats tended to make more timeout responses than control rats. The short-duration stimulus challenge decreased accuracy and increased omissions and timeout responses in both AIE-exposed and control rats. The long intertrial interval challenge increased premature responses in all rats. An ethanol challenge decreased correct responses, and increased omissions in control, but not in AIE-exposed, rats. Control, but not AIE-exposed, rats exhibited decreased premature and timeout responses after ethanol administration. Response latencies were not affected in AIE-exposed or control rats indicating no sedative effects of ethanol challenge.

CONCLUSIONS

The results indicate that ethanol binge exposure during adolescence has long-lasting neurobehavioral consequences, which persist into adulthood and can be revealed after re-exposure to ethanol. AIE-induced diminished responses to the disruptive effects of ethanol on attention, impulsivity and cognitive flexibility may lead to increased alcohol drinking and other maladaptive behaviors in adulthood.

Two-choice reaction time performance in Sprague-Dawley rats exposed to alcohol during adolescence or adulthood

Adolescent alcohol abusers display subtle attention impairments. This study used a two-choice reaction time task to examine the effects of ethanol on sustained attention following adult or adolescent exposure. Sprague-Dawley rats were exposed to ethanol vapor for 14 days starting on postnatal day 30 (adolescence) or 60-64 (adulthood) and were then trained to perform the two-choice reaction time task. Ethanol exposure resulted in blood ethanol levels averaging 215 mg/dl. Behavior following adult ethanol exposure was characterized by increased accuracy and omissions during the two-choice reaction time task, reduced fixed ratio lever pressing, and reductions in the highest fixed ratio completed on a progressive ratio schedule. Adolescent ethanol exposure transiently increased two-choice reaction time accuracy and slightly reduced fixed ratio lever presses. Improved accuracy was unexpected, but might be related to ethanol-induced increases in central nervous system arousal and/or mild behavioral perseveration. Increased omissions, reduced lever pressing, and reductions in the highest fixed ratios completed most likely reflect decreased 'motivation to work' and index generalized anhedonia. This study is the first to demonstrate that rats exposed to ethanol during adulthood are more sensitive to the effects of ethanol on sustained attention than rats exposed to ethanol during adolescence and to ethanol-induced anhedonia, as indexed by two-choice reaction time performance.

Impaired cued delayed alternation behavior in adult rat offspring following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin on gestation day 15

This investigation used random ratio (RR) and cued delayed alternation procedures to examine the operant behavior of adult male and female rats following prenatal 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Offspring were exposed to a single maternal dose of 0.0, 0.06, 0.18 or 0.54 microg/kg po of TCDD on gestation day (GD) 15. For RR, adult subjects were trained to respond on one lever in a two-lever chamber for food reinforcement. The response requirement was increased across sessions. Male offspring responded at higher rates than females regardless of RR value and prenatal exposure history. For delayed alternation, animals were required to alternate responses on both apparatus levers and to inhibit responding during randomly interpolated delay intervals. The performance of male and female offspring exposed to 0.18-microg/kg TCDD was significantly less accurate and this group committed more errors by responding during the delay intervals than the other exposure groups. A similar trend was observed in the 0.54- microg/kg group. Overall, response accuracy during the delayed alternation procedure was inversely related to delay length and tended to improve with experience. Interpretations of these outcomes include the possibility that TCDD interfered with the development of attentional processes, impaired response inhibition or promoted response perseveration despite the presence of cues, indicating changes in reinforcement contingencies.

Prenatal ethanol exposure, generalized learning impairment, and medial prefrontal cortical deficits in rats

Prenatal ethanol exposure may cause neurological damage and subsequent mental retardation in humans, with learning deficits similar to those following damage to the prefrontal cortex. This study examined cognitive dysfunction and cortical damage after prenatal exposure to ethanol using a chronic administration model. Pregnant Sprague-Dawley rats received one of three diets during gestation: a liquid diet containing 35% ethanol-derived calories (ETOH), an isocaloric liquid diet (ISO), or standard chow (CHOW). Subjects were obtained from ETOH dams with blood alcohol concentrations (BACs) above 90 mg/dl and corresponding ISO and CHOW controls (one male pup/litter; n=6 pups/group). At approximately 90 days of age, subjects began training on a series of unique auditory discrimination problems using a successive go/no-go procedure. A criterion of 85% accuracy determined when a rat continued to the next problem. Subjects completed a varying number of problems within a 30-session limit, after which all rats were tested on a tone/click discrimination and reversal. Subjects were then sacrificed and neuronal number in the medial prefrontal cortex (mPFC) was estimated by the optical fractionator method. Prenatal ethanol exposure induced significant cell loss in the mPFC, which was associated with significantly impaired reversal learning. Poor performance by ETOH subjects on the tone/click reversal indicates a transfer of training deficit that may reflect failures of inhibitory control.

Spatial learning in rats exposed to acute ethanol intoxication on gestational day 8

Pregnant Wistar rats were treated on gestational day 8 (GD 8) with two IP injections of either ethanol (2.9 g/kg in 24% v/v saline solution) or saline. Offspring were tested in the water-maze task at 45 or 90 days of age. The escape latencies of rats trained with a submerged escape platform at a fixed location were similar between control and experimental rats. Analyses of responses on a probe trial carried out 10 days after the training period, revealed that 90-day-old females prenatally exposed to alcohol were less likely to swim in the target region. No differences were observed in this free-swim trial in 45- and 90-day-old male, and 45-day-old female animals. Binding studies of low-affinity GABAA sites in the hippocampus showed an increase in affinity of [3H]GABAA for their binding sites in 90-day-old female offspring prenatally intoxicated with ethanol. Our results demonstrate that acute intoxication with ethanol on GD 8 did not modify acquisition but impaired the retention of spatial learning only in adult female rats. It is possible that the impaired retention will be consequence of higher GABAA receptor affinity.

Prenatal ethanol exposure in rats: long-lasting effects on learning

Pregnant Sprague-Dawley rats were fed a liquid diet containing either 0% (group C), 18% (group L), or 36% (group H) ethanol-derived calories (EDC) from gestational day 1 to 20. Male offspring were assessed under a conditioned taste aversion paradigm (PND 35-45), in a complex maze (PND 68-80), and for operant behavior (temporal response differentiation and motivation to work for food, PND 140-198). Although conditioned taste aversion was fully acquired by all groups, retention of the conditioned taste aversion response was impaired in group H animals. Importantly, deficits in the acquisition of timing behavior were found in group H (group L not tested), confirming that this operant task is quite sensitive in detecting prenatal drug effects and demonstrating that neurological effects of prenatal ethanol exposure persist into late adulthood.

Augmented memory loss in aging mice after one embryonic exposure to alcohol

Prenatal exposure to alcohol can produce behavioral and cognitive deficits even in the absence of dysmorphic facial features. In a mouse model, we tested whether embryonic exposure to alcohol could exacerbate functional loss as animals age. Normal-appearing offspring were selected from litters produced by C57Bl/6J mice that had been gavaged with one teratogenic dose (5.8 g/kg) of ethyl alcohol during organogenesis on the 9th day of gestation. In adulthood, the offspring suffered a deficit in long-term retention, but not acquisition, of a place learning task. Although barely detectable in young adults, the retention deficit was severe in aging mice. These findings demonstrate that the functional deficits resulting from embryonic exposure to alcohol can interact with those of aging.

Effect of acute ethanol exposure during pregnancy on dentate gyrus synaptic plasticity in 45-day-old rats

Pregnant Wistar rats were treated during the eighth day of gestation (GD8) with two IP injections, spaced by an interval of 4 h, of either ethanol (2.9 g/kg in saline solution) or saline. At 45 days of age, rats prenatally exposed to alcohol showed an improved hippocampal synaptic plasticity in granule cells layer of dentate gyrus. This was assessed measuring the threshold to generate long-term potentiation (LTP) on hippocampal slices. We propose that this result might account for the good performance in some learning tasks observed in animals prenatally exposed to alcohol during short periods.