Sex differences in mesolimbic dopamine responses to ethanol and relationship to ethanol intake in rats.

Sex differences in ethanol intake in rats suggest that there may be sex differences in brain dopamine systems believed to mediate ethanol's reinforcing properties. To test this hypothesis, we used in vivo microdialysis to examine changes in nucleus accumbens and striatal dopamine, DOPAC and HVA following acute administration of several doses of ethanol in male and female Long-Evans rats. Following dialysis, rats were trained to bar press for oral ethanol reinforcement. In nucleus accumbens, females showed greater increases in dopamine than males at low to intermediate doses. In striatum, both sexes showed increased dopamine at the low to intermediate doses. In addition to showing increased responsiveness to ethanol-induced mesolimbic dopamine stimulation, females consumed more ethanol than males during behavioral testing. Correlations between neurochemical measures and subsequent ethanol consumption indicated that among males, both basal and peak ethanol-induced nucleus accumbens dopamine levels were inversely related to later ethanol intake. No such relationship was observed for females. Striatal neurochemical measures were not significantly related to ethanol intake. These findings supported the hypothesis of sex differences in mesolimbic responses to ethanol and suggested that the relationship of those responses to subsequent ethanol intake may differ for males and females.

Prenatal ethanol exposure: effects on androgen and nonandrogen dependent behaviors and on gonadal development in male rats.

Prenatal exposure to alcohol may impair gonadal and behavioral development in male rats, possibly via reduction of perinatal androgenization. We examined locomotor activity on postnatal day 18 (PND 18), which is not influenced by perinatal androgens and juvenile play and testicular development (testes weight), which are dependent on perinatal androgen exposure, in rats whose dams consumed ethanol during pregnancy. Male offspring of pair-fed and lab chow-fed dams served as controls. Despite reduced anogenital distance at birth, indicating compromised perinatal androgenization, fetal ethanol-exposed males did not exhibit demasculinization of play behavior. Hyperactivity in fetal ethanol-exposed males indicated that the treatment regimen was sufficient to produce behavioral deficits. Testes weight was reduced in both ethanol-exposed and pair-fed offspring, indicating that nutritional deficits associated with maternal ethanol intake may impair normal gonadal development in male rats. The findings suggest that fetal ethanol exposure may influence gonadal development but not necessarily affect a gonadal hormone-dependent behavior.

Sex differences in ethanol-induced dopamine release in nucleus accumbens and in ethanol consumption in rats.

In vivo microdialysis was used to examine changes in nucleus accumbens and striatal dopamine, dihydrophenylacetic acid (DOPAC), and homovanillic acid (HVA) following acute administration of ethanol (0.0, 0.25, 0.5, 1.0, or 2.0 g/kg) in male and female Long-Evans rats. Following dialysis, rats were trained to bar-press for oral ethanol reinforcement. In nucleus accumbens, females showed significant increases in extracellular dopamine following 0.25 or 0.5 g/kg ethanol, but did not show significant increases over baseline at the higher doses. Males showed slight increases in dopamine at the lower doses and decreased dopamine at 2.0 g/kg. In striatum, both sexes showed increased dopamine at the lower doses and decreased dopamine at 2.0 g/kg. There were slight increases in nucleus accumbens DOPAC and HVA at some doses in both sexes, but no changes in striatal metabolite levels. In addition to showing increased responsiveness to ethanol-induced mesolimbic dopamine stimulation, females consumed more ethanol than males during behavioral testing. The pattern of both greater ethanol-induced nucleus accumbens dopamine release and greater ethanol consumption in females supports the hypothesis that ethanol reward is mediated, at least in part, by the mesolimbic dopamine system.

Prenatal ethanol exposure alters ethanol-induced dopamine release in nucleus accumbens and striatum in male and female rats.

Using in vivo microdialysis, ethanol-induced dopamine release in nucleus accumbens and striatum was examined in adult male and female Long-Evans rats exposed prenatally to ethanol and in controls. Following dialysis, ethanol intake was measured in an operant paradigm. Control rats showed increased dopamine release in nucleus accumbens and striatum in response to 0.5 g/kg ethanol, but not to 1.0 g/kg. Fetal ethanol-exposed rats showed no dopamine response at 0.5 g/kg. At 1.0 g/kg, fetal ethanol-exposed males showed increased dopamine release in both structures. Prenatally exposed females showed no change in accumbens, and decreased release in striatum. Fetal ethanol exposure did not significantly influence ethanol intake. The findings suggest that prenatal ethanol exposure influences subsequent neurochemical responses to ethanol; however, how these neurochemical measures are related to ethanol intake could not be determined in the present study. Data are discussed in terms of sex-specific shifts in the dose-response function for ethanol-induced dopamine release resulting from prenatal ethanol exposure.

Hyperactivity and altered amphetamine sensitivity in premature juvenile rats.

'Premature' rats that were delivered by cesarean section on day 21 of gestation and 'normal' rats that were delivered spontaneously on day 22 of gestation were tested for basal locomotor activity and locomotor stimulation in response to D-amphetamine at 19-21 days of age. Compared to normal rats, premature rats had increased basal levels of locomotor activity and showed enhanced sensitivity to the locomotor stimulant effects of D-amphetamine. Cesarean-delivered premature rats may be a useful animal model for investigating mechanisms of neurobehavioral deficits associated with premature birth in humans.

Apomorphine-induced motor behavior in rats exposed prenatally to alcohol.

We psychopharmacologically examined dopamine function in rats exposed to ethanol prenatally. Pregnant rats received liquid diets of 35% or 0% ethanol-derived calories (EDC), or ad lib lab chow (LC). Twenty-eight-day-old offspring received systemic doses of apomorphine chosen to stimulate predominantly presynaptic (0.02 or 0.1 mg/kg) or postsynaptic dopamine receptors (2.0 or 5.0 mg/kg). Behavior was scored automatically for 60 min in an "open field." For males, prenatal ethanol exposure resulted in a dose-response shift to the left for locomotor activity. Females exposed to the liquid diet, with or without ethanol, showed less of an increase in locomotor activity following the 5.0 mg/kg dose of apomorphine than did LC controls. There were no effects of prenatal treatment on repetitious motor behavior in the automated "open field" or on stereotypy scored by direct observation in separate groups of rats. The results are consistent with an hypothesis that prenatal ethanol exposure alters the sensitivity of postsynaptic (perhaps mesolimbic) dopamine systems important to locomotor activity in young male rats.

Absence of differential motoric and thermic responses to clonidine in young rats exposed prenatally to alcohol.

We studied the involvement of altered noradrenergic function in the behavioral consequences of fetal ethanol exposure. Pregnant rats were fed a liquid diet containing 35% Ethanol-Derived Calories (EDC), pair-fed a 0% EDC diet with sucrose substituted isocalorically for ethanol, or fed ad lib lab chow. In Experiment 1, offspring from these prenatal treatment groups were injected with the alpha-adrenergic agonist clonidine (0.5 or 2.0 mg/kg) at 10 or 42 days of age and showed age-characteristic, dose-dependent increases in locomotor activity, exploration, forelimb treading, and catalepsy. In Experiment 2, offspring were injected with clonidine (0.25 or 1.0 mg/kg) at 10, 14, or 18 days of age, and locomotor activity and wall-climbing were observed in a warm chamber (33 degrees C). Catalepsy and rectal temperature were also scored. There were no significant differential effects of clonidine on any prenatal treatment group at any age for any measure of activity or rectal temperature. The results do not support the hypothesis that fetal ethanol exposure alters noradrenergic systems in behaviorally significant ways.

Commentary: psychopharmacological assessment in neurobehavioral teratology.

Pharmacological agents can be teratogenic but they can also be valuable tools in behavioral teratology. In this paper we describe some considerations we believe to be important in the use of psychopharmacology to assess the neurological underpinnings of behavioral deficits resulting from teratogenic exposure. Pharmacological challenges of animals exposed in utero to teratogenic agents can increase the sensitivity of behavioral tests and the specificity of the assessment of neural dysfunction. We discuss also some general guidelines for the conduct and interpretation of psychopharmacological experiments with teratogen-exposed animals.

Effects of physostigmine on shuttle avoidance in rats exposed prenatally to ethanol.

Shuttle avoidance performance following pretreatment with physostigmine was assessed in 85- to 100-day-old rats whose mothers consumed a liquid diet consisting of 35% ethanol-derived calories (EDC) during pregnancy. Offspring of pair-fed (0% EDC) and ad lib lab chow (LC) dams served as controls. Animals received either 0, 0.1 or 0.2 mg/kg physostigmine sulfate prior to acquisition training in a shuttle avoidance apparatus. Training consisted of 50 trials/day for 4 days. Thirty-five percent EDC rats made fewer avoidances than controls during acquisition training. Treatment with physostigmine reduced the number of avoidances made, and did so similarly for all prenatal treatment groups. Escape latencies were not affected by prenatal treatment, although they were increased by physostigmine administration prior to training. Neither prenatal treatment nor physostigmine treatment affected activity as measured by the number of intertrial crossings while in the apparatus. These data indicate that alcohol-exposed animals did not respond differentially to physostigmine relative to controls, suggesting that cholinergic dysfunction may not underlie the prenatal alcohol-induced deficit in active avoidance.

Deficits on a spatial navigation task following prenatal exposure to ethanol.

Performance on a Morris water task was examined in young rats whose mothers consumed a liquid diet consisting of 35% ethanol-derived calories (EDC) during pregnancy. Offspring of pair-fed (0% EDC) and ad lib lab chow (LC) dams served as controls. Rats were required to find a platform submerged below the surface in a pool of opaque water. A trial ended when the rat remained on the platform for 15 sec, or had been in the tank for 180 sec without reaching the platform. Subjects received 5 trials daily for 3 consecutive days, followed by reversal training on Day 4. Groups did not differ in swimming ability. On Day 1 there were no group differences among females in latency to reach the platform or in distance traveled, but male 35% EDC and 0% EDC animals had shorter latencies than LC controls. On Day 2, latencies and distance traveled of LC and 0% EDC controls decreased while 35% EDC animals showed no change from Day 1, so that alcohol-exposed rats took longer to reach the platform and traveled a greater distance than controls. On Day 3, 35% EDC females took longer than controls to reach the platform, and 35% EDC animals of both sexes traveled a greater distance than controls. Search patterns on the first reversal trial on Day 4 suggest the differences are in spatial processing and not learning per se, but more so in alcohol-exposed males than females. The impaired performance on this task suggests that prenatal alcohol exposure alters the ability to process spatial information.

Amphetamine-induced activity after fetal alcohol exposure and undernutrition in rats.

Behavioral responses to amphetamine were examined in 28- and 42-day-old rats whose mothers consumed a liquid diet consisting of 35% ethanol-derived calories (EDC) during pregnancy. Offspring of pair-fed (0% EDC) and ad lib chow (LC) dams were included as controls. Animals received 0.0, 0.5, 1.0, or 2.0 mg/kg/ml d-amphetamine prior to single 2-hr tests in automated activity monitors. At 28 days of age, when there were no differences in activity after saline injection, 35% EDC males were more active (measured by distance traveled) than LC and 0% EDC males following treatment with 2.0 mg/kg amphetamine. Thirty-five percent EDC females exhibited brief reductions in activity relative to LC females but were not different from 0% EDC females at 28 days of age following 2.0 mg/kg amphetamine. When treated with 1.0 mg/kg amphetamine, 28-day-old 0% EDC males were less active than LC and 35% EDC males, who did not differ from each other at this dose. At 42 days of age, animals from both liquid diet groups were less active than LC controls following 2 mg/kg amphetamine. These results suggest that both prenatal alcohol exposure and undernutrition may influence the postnatal functional status of catecholamine systems but that the nature of those functional changes varies with type of prenatal insult, sex and age of the animal at testing.

Altered grooming responses to stress in rats exposed prenatally to ethanol.

The effects of prenatal alcohol exposure on grooming, locomotion, and rearing in response to stress were examined in adult rats whose mothers consumed a liquid diet containing 35% ethanol-derived calories (EDC). Offspring of both pair-fed 0% EDC mothers and ad libitum chow-fed mothers were included as controls. In Experiment 1, females groomed more than males following placement into a novel test chamber, but no differences due to prenatal treatment were observed. Ethanol-exposed animals groomed more than controls following the stress of a forced 1-min swim (Experiment 2), but when rats tested in Experiment 1 were observed again after forced swim stress (Experiment 3), no differences due to prenatal treatment or sex were observed. Experiment 4 examined the effects of pretreatment with 1 mg/kg naloxone on novelty-induced grooming and as in Experiment 1 prenatal treatment did not affect grooming responses. Females again groomed significantly more than males and naloxone reduced grooming equally for all groups. The results suggest that novelty-induced grooming is a sex-influenced behavior, with females grooming more than males, and that animals exposed prenatally to alcohol and tested as adults may have altered responses to certain stressors (i.e., forced swim) under specific conditions. The altered grooming response of alcohol-exposed rats to swim stress can be eliminated by preexposing them to novelty stress.