The effect of ethanol and sex on radial arm maze performance in rats

The interaction of genetic sex and prenatal alcohol exposure on health across the lifespan

Prenatal alcohol exposure (PAE) can reprogram the development of cells and tissues, resulting in a spectrum of physical and neurobehavioral teratology. PAE immediately impacts fetal growth, but its effects carry forward post-parturition, into adolescence and adulthood, and can result in a cluster of disabilities, collectively termed Fetal Alcohol Spectrum Disorders. Emerging preclinical and clinical research investigating neurological and behavioral outcomes in exposed offspring point to genetic sex as an important modifier of the effects of PAE. In this review, we discuss the literature on sex differences following PAE, with studies spanning the fetal period through adulthood, and highlight gaps in research where sex differences are likely, but currently under-investigated. Understanding how sex and PAE interact to affect offspring health outcomes across the lifespan is critical for identifying the full complement of PAE-associated secondary conditions, and for refining targeted interventions to improve the quality of life for individuals with PAE.

Reconceptualizing sex, brain and psychopathology: interaction, interaction, interaction

In recent years there has been a growing recognition of the influence of sex on brain structure and function, and in relation, on the susceptibility, prevalence and response to treatment of psychiatric disorders. Most theories and descriptions of the effects of sex on the brain are dominated by an analogy to the current interpretation of the effects of sex on the reproductive system, according to which sex is a divergence system that exerts a unitary, overriding and serial effect on the form of other systems. We shortly summarize different lines of evidence that contradict aspects of this analogy. The new view that emerges from these data is of sex as a complex system whose different components interact with one another and with other systems to affect body and brain. The paradigm shift that this understanding calls for is from thinking of sex in terms of sexual dimorphism and sex differences, to thinking of sex in terms of its interactions with other factors and processes. Our review of data obtained from animal models of psychopathology clearly reveals the need for such a paradigmatic shift, because in the field of animal behaviour whether a sex difference exists and its direction depend on the interaction of many factors including, species, strain, age, specific test employed and a multitude of environmental factors. We conclude by explaining how the new conceptualization can account for sex differences in psychopathology.

The interaction of chronic restraint stress and voluntary alcohol intake: effects on spatial memory in male rats

Alcohol consumption and exposure to stressful life events activate similar neural pathways and thus result in several comparable physiological and behavioral effects. Alcoholics in treatment claim that life stressors are the leading cause of continued drinking or relapse. However, few studies have investigated the interactive effects of stress and alcohol on cognitive behavior. The effects of restraint stress, alcohol, and stress in combination with alcohol were examined on a spatial memory test, the object placement (OP) task. In addition, intake levels were measured to determine if stress altered general consumption of alcohol. Male Sprague-Dawley rats were assigned to one of four conditions: no alcohol/no stress control (CON), stress alone (STR), alcohol alone (ALC), and STR+alcohol (STR+ALC). Following each restraint stress bout, the STR+ALC and the ALC groups were given access to 8% alcohol for 1h using the two-bottle choice limited access paradigm. As predicted, the STR+ALC group significantly increased alcohol consumption, while the ALC group had consistent drinking over the 10-day treatment. On the OP task, STR and ALC groups performed at chance levels, whereas the CON and STR+ALC groups significantly discriminated between objects in the new and old locations. These data show that stress increases alcohol intake and the intake of alcohol is associated with reduction of the stress-induced impairment of spatial memory. The data have important implications for the development of alcohol abuse and its treatment.

The effects of ethanol and silymarin treatment during gestation on spatial working memory

BACKGROUND

Using a rat model we have found that the bioflavonoid silymarin (SY) ameliorates some of the negative consequences of in utero exposure to ethanol (EtOH). In the current study our aim was to determine if spatial working memory (SWM) was impaired in offspring whose mothers were maintained on a liquid diet containing EtOH during different gestational weeks. We also determined if SWM was altered with a concomitant administration of SY with EtOH during specific gestational weeks.

METHODS

We provided pregnant Fischer/344 rats with liquid diets containing 35% EtOH derived calories (EDC) during specific weeks of the gestational period. A silymarin/phospholipid compound containing 29.8% silybin co-administered with EtOH was also administered during specific weeks of the gestational period. We tested SWM of the offspring with a radial arm maze on postnatal day (PND) 60. After testing the rats were sacrificed and their brains perfused for later analysis.

RESULTS

We observed SWM deficits, as well as a significantly lower brain weight in female offspring born of mothers treated with EtOH during the third week of gestation in comparison to mothers treated during either the first or second weeks of gestation. Rats from any group receiving EtOH in co-administration with SY showed no significant deficits in SWM.

CONCLUSION

EtOH treatment during the last week of gestation had the greatest impact on SWM. The addition of SY to the EtOH liquid diet appeared to ameliorate the EtOH-induced learning deficits.

Moderate doses of ethanol partially reverse avoidance learning deficits in high-alcohol-drinking rats

We previously reported that ethanol-naive high-alcohol-drinking (HAD1 and HAD2) rats exhibited selective deficits in active avoidance learning, as compared to low-alcohol-drinking (LAD1 and LAD2) rats, in a signaled bar-pressing task [Alcohol. Clin. Exp. Res. 24 (2000) 1778]. In the current study, we used appetitive and aversive learning tasks to assess whether administration of ethanol influences approach and avoidance learning in HAD and LAD rats. Rats were administered 0.0, 0.5, 1.0, or 1.5 g ethanol/kg body weight during appetitive and aversive conditioning sessions. We found that ethanol impaired acquisition of the appetitive conditioned response in a dose-dependent manner in both HAD and LAD rats, with 1.5 g/kg ethanol producing the greatest deficits. Notably, moderate doses of ethanol (0.5 and 1.0 g/kg) partially reversed avoidance learning deficits in HAD rats, but only when appetitive conditioning preceded aversive conditioning. The highest dose (1.5 g/kg EtOH) abolished avoidance responding altogether in HAD rats. Avoidance responding in LAD rats was not affected by any dose of ethanol. These results are consistent with previous studies suggesting that alcohol preference may be associated with increased fear or anxiety, but the conditions under which ethanol produces a reduction of fear and anxiety in HAD rats appear to be relatively complex.

Immediate and delayed voluntary ethanol effects on motor performance, learning and inhibition in rats

The effects of prolonged voluntary ethanol consumption on psychomotor performance, operant conditioning and inhibition were examined in adult male Wistar rats. Animals were food deprived and alcohol or control solution was available 1 h/day during 15 days, with free water for the rest of the day. Then, rats were tested in a two-bottle paradigm (solution and water available) for 1 h/day during 19 days, and subjects were tested daily for psychomotor performance and operant conditioning immediately or 6 h after (delayed) the solution access. Psychomotor performance was tested in an 80 degrees -inclined screen. Successive conditioning phases were: free shaping (FS), continuous reinforcement (CRF), operant extinction (EXT), successive discrimination (DIS) and two-stimuli test (TST). Alcohol consumption deteriorated psychomotor performance and improved the animal's ability to learn simple associations between stimuli and responses (free shaping and extinction), in immediate and delayed groups. Finally, alcohol deteriorated behavioral inhibition (DIS and TST) tested immediately after drinking. Taken together, results suggest that prolonged voluntary ethanol intake could induce permanent psychomotor impairment and associative learning facilitation, and also an impairment of the inhibition related to the intoxication state.

Learning and memory in rats gestationally and lactationally exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Recently we reported that in utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or coplanar polychlorinated biphenyls (PCBs) resulted in a reduction of errors on a radial arm maze (RAM) working memory task. The effect was more pronounced in males than in females. In this study, we further investigated the effects of in utero and lactational exposure to TCDD on learning and memory by testing male and female TCDD-exposed rats on three different spatial learning and memory tasks: the RAM, the Morris water maze (MWM), and spatial discrimination-reversal learning (RL), as well as on a nonspatial learning task, visual RL. Time-mated Sprague-Dawley rats were gavaged with either TCDD (0.1 microg/kg/day) or corn oil vehicle on gestation days 10-16. Litters were culled to eight on day 2 and weaned on day 21. Beginning on day 80, one male and one female from each litter were tested on the same RAM working memory task used in the previous study. Again, the TCDD-exposed male rats displayed a pronounced decrease in errors relative to control males. Following the RAM testing, the same animals were tested on the MWM, but no differences between the exposed and control rats were observed. Another male and female from each litter were tested on spatial RL on a T-maze. There were no differences between the exposed and control rats on this task. Following spatial RL, the same rats were tested on visual RL on the same maze. The exposed animals did not differ from controls on original learning, but took more trials to reach criterion on the first and second reversals. These results demonstrate a reliable, but task-specific, facilitation of spatial learning and memory in male rats exposed to TCDD during gestation and lactation. In contrast, both male and female TCDD-exposed rats showed a deficit in learning on the visual RL task. This pattern is consistent with that seen in earlier monkey studies. Perinatally TCDD-exposed monkeys were facilitated on certain spatial tasks, but impaired on visual RL tasks.

EtOH self-administration on shuttle box avoidance learning and extinction in rats

The effects of ethanol on the acquisition and extinction of the two-way active avoidance response were examined in adult, male Wistar rats from two treatment groups, oral self-administration of alcohol solution (10% v/v ethanol and 3% w/v glucose in distilled water) and oral self-administration of control solution (3% w/v glucose in distilled water). Alcohol or control solutions were available 1 h per day during 15 days simultaneously with food, with free water for the rest of the day. Blood was drawn in the last day of this phase to evaluate blood ethanol levels (BEL). After this period, rats were tested in a two-bottle paradigm for 1 h per day and placed in a shuttle box immediately afterwards. This phase went lasted for 10 days. Subjects were trained to avoid an electric foot shock in the first 5 days (15 trials per day). Following this, half of the subjects were tested in an "easy extinction with punishment" (EEP) and the other half in a "difficult extinction with punishment" (DEP) of the avoidance response for the last 5 days. Alcohol accelerates the avoidance responding acquisition, and no significant effects of alcohol were seen in the extinction phase. Data are discussed in terms of the specificity of the effects of alcohol on learning.

Losartan improves the performance of ethanol-intoxicated rats in an eight-arm radial maze

Results of previous research demonstrate that angiotensin II (Ang II) inhibits long-term potentiation (LTP) in medial perforant path-dentate gyrus granule cells and that the inhibition is mediated by the AT1 receptor because it can be blocked by losartan, a specific AT1 receptor antagonist. Ang II impairment of retention and ethanol inhibition of LTP can both be blocked by pretreatment with losartan. Because losartan pretreatment also prevents ethanol intoxication measured in terms of the aerial righting reflex, the purpose of the present study was to assess the effects of 2.0 g/kg ethanol administered by gavage on performance in an eight-arm radial maze, and then to determine the effectiveness of losartan in reducing the impairment of the learning and memory process. Results confirmed the general hypothesis that ethanol-induced cognitive deficits are mediated by Ang II and the AT1 receptor and that the impairment can be reduced by pretreatment with losartan.

Context and tone conditioning are selectively impaired by ethanol in the preweanling rat: effects of dose and time of administration

Depending on dose and task requirements, ethanol can have either a facilitative or an impairing influence on learning. Some explanations for this dichotomy have considered ethanol's suppression of behavioral variability and processing of incidental stimuli (e.g., context). The present study examined the effect of ethanol on context and conditioned stimulus (CS) learning in the preweanling rat. To assess state-dependent effects, a drug dissociation design was used. Learning to both context and CS were analyzed within each dose of ethanol (0, 1.2, 1.6, or 2.0 g/kg) and a trend analysis was conducted to determine dose-response relationships as a function of train-test state. The 1.2 g/kg dose of ethanol did not affect conditioning to either the context or the CS. A 1.6 g/kg dose tended to disrupt context, but not CS, conditioning. The influence of 2.0 g/kg ethanol depended on train-test conditions. Ethanol administration prior to training resulted in the stronger impairment of CS learning while context conditioning was most disrupted if ethanol was given only prior to testing. The results suggest that ethanol selectively attenuates processing of stimuli, possibly dependent on relative saliency at the time of testing.

Hippocampal cholinergic alterations and related behavioral deficits after early exposure to ethanol

The present study was designed to ascertain septohippocampal cholinergic alterations and their related behavioral deficits after early exposure to ethanol. Mouse pups were exposed to ethanol, 3 g/kg by daily subcutaneous injection on postnatal days 2-14. At age 50 days, the ethanol-exposed mice had significant reductions from control levels in eight-arm maze performance. For example, on the fourth testing day, the number of correct entries in the ethanol group was 21% below control levels (P < 0.05) and the number of trials needed to enter all arms was 48% above control (P < 0.001). It took the ethanol-exposed mice twice the time to reach criterion than it did control (P < 0.01). A 33% increase from control level in muscarinic receptor number (Bmax) was found in the treated mice of age 22 days and a 64% increase at age 50 days (P < 0.001). However, no differences between control and treated groups could be detected in the presynaptic component of the cholinergic innervation, choline acetyltransferase activity. The results suggest that early ethanol exposure acts on hippocampal function similarly to phenobarbital, probably via alterations in postsynaptic processes in the septohippocampal cholinergic pathways.

Effects of oral ethanol self-administration on the inhibition of the lever-press response in rats

The effects of ethanol on the inhibition of a learned response were examined in adult, male Wistar rats from two treatment groups: oral self-administration of alcoholic solution (10% ethanol and 10% glucose in distilled water) and oral self-administration of sweet solution (10% glucose in distilled water). Subjects were food deprived and alcoholic or control solutions were available 1 h per day during 15 days. After this period, rats were tested in a two-bottle paradigm during 1 h per day and placed in the operant chambers immediately afterward. This phase went on for 19 days. Subjects were trained to lever press for food and were tested in a continuous reinforcement schedule, operant extinction, successive discrimination, and two-stimuli tests. Alcohol impaired the ability to inhibit previously reinforced responses but only in situations indicated by exteroceptive stimuli. Ethanol intake did not impair the lever-press behavior neither in the acquisition of the response nor in the continuous reinforcement schedule. These data suggest that the sedative effects of alcohol at this dose were not apparent in reinforcement situations, in contrast with extinction situations.

Effects of an alcohol diet on locomotor activity and the acquisition of brain self-stimulation in rats

Male rats (n = 45), implanted with stimulating electrodes in the lateral hypothalamus for intracranial self-stimulation (ICSS), were allocated to three groups equalized for body weights. One group was given an alcohol liquid diet (Lieber-DeCarli) diet as the sole source of food; a second group was given a control liquid diet in which carbohydrates were substituted for alcohol; and a third group was maintained on standard laboratory chow and water. After four weeks on these diets, all animals were tested during the fifth week of the diets for locomotor activity in five daily 15-min sessions, and their reactivity to handling was also measured. During the sixth and seventh weeks of the diets, animals were allowed to self-train for ICSS during daily 15-min sessions. In the eighth week blood alcohol levels were measured. There were no differences between groups in locomotor activity or reactivity to handling. However, when tested for the acquisition of ICSS, animals on the diet containing alcohol made fewer responses than did those receiving the two control diets (p less than 0.001). The mean blood level of alcohol in the alcohol-consuming group at the time of day of behavioral testing was 50.6 +/- 5.0 mg/dl. These results suggested that the chronic ingestion of an alcohol-containing diet which resulted in only moderate blood levels of alcohol may not affect simple behavior such as locomotor activity, but may produce decrements in the performance of a more complex task such as lever pressing for ICSS.

Evolution of spatial cognition: sex-specific patterns of spatial behavior predict hippocampal size

In a study of two congeneric rodent species, sex differences in hippocampal size were predicted by sex-specific patterns of spatial cognition. Hippocampal size is known to correlate positively with maze performance in laboratory mouse strains and with selective pressure for spatial memory among passerine bird species. In polygamous vole species (Rodentia: Microtus), males range more widely than females in the field and perform better on laboratory measures of spatial ability; both of these differences are absent in monogamous vole species. Ten females and males were taken from natural populations of two vole species, the polygamous meadow vole, M. pennsylvanicus, and the monogamous pine vole, M. pinetorum. Only in the polygamous species do males have larger hippocampi relative to the entire brain than do females. Two-way analysis of variance shows that the ratio of hippocampal volume to brain volume is differently related to sex in these two species. To our knowledge, no previous studies of hippocampal size have linked both evolutionary and psychometric data to hippocampal dimensions. Our controlled comparison suggests that evolution can produce adaptive sex differences in behavior and its neural substrate.

Contributions of hippocampus and neocortex to the expression of ethanol effects

The distinctive effects of ethanol on behavior suggest that certain parts of the CNS may be especially sensitive to it. One of the primary candidates is the hippocampal formation. Damage to this structure mimics acute ethanol treatment across a wide variety of behavioral tasks and processes. The possibility of a hippocampal basis for ethanol psychopharmacology was examined in the present experiments. Chosen for behavioral analysis were relatively complex eight-arm radial maze tasks which have independently been shown to be sensitive to ethanol administration and hippocampal lesions. Measures included arm selection predictability, vigilance, and retardation of extinction. Bilateral hippocampal lesions or ethanol injection (1.5 g/kg, IP) produced similar effects. However, hippocampectomy did not disrupt ethanol's influence on any task. Comparatively, neocortical ablation, especially prefrontal, was quite effective in this respect. It blocked or reduced two of the drug's three behavioral effects examined here, without any strong influence of its own, and without altering blood alcohol concentration.

Impaired spatial navigation in adult female but not adult male rats exposed to alcohol during the brain growth spurt

Two groups of male and female rats were given the same dose of alcohol using an artificial rearing procedure on postnatal days 4-10. One group received the alcohol in a condensed manner each day which caused cyclic blood alcohol concentrations (BACs) with high peaks. A second group received the alcohol in a uniform manner over each day which resulted in moderate, stable BACs. Two control groups consisted of male and female rats artificially reared but not exposed to alcohol and rats reared normally by dams. All rats were raised to 90 days of age and then tested for spatial navigation ability in the Morris water maze, which involved locating a hidden underwater platform using distal extramaze cues. Neither the alcohol treatments nor the artificial rearing had any effects on performance of adult male rats relative to suckle controls in this task. In contrast, the condensed alcohol exposure but not the uniform alcohol exposure resulted in detrimental performance in the Morris water maze by adult female rats. When the ability to locate and escape onto a visible platform was examined, there were no differences between the female groups given condensed alcohol exposure or artificially reared on milk solution alone. Thus, exposure to high BACs during the brain growth spurt has a lasting and selective detrimental effect on spatial navigation learning in adult female but not adult male rats.

Repeated withdrawal from ethanol on radial arm acquisition in rats

Male rats were treated with ethanol (8.0-12.0 g/kg/day) for four 2 week periods interrupted every 2 weeks by a 2 week period of no drug treatment. Thus they experienced withdrawal from ethanol four times. Other rats were treated with ethanol for 8 weeks with no interruptions, to control for the total dose and duration of drug treatment. Acquisition of an eight-arm radial maze response when daily ethanol treatment was ended, was not affected by either the experience of four withdrawals from ethanol or by 8 weeks of ethanol treatment. The lack of withdrawal-induced impairment can be attributed to a lack of sensitivity in the maze task to possible withdrawal-induced deficits and to an insufficient duration of ethanol dependence.