Effects of ethanol on mature offspring of mice given ethanol during pregnancy

Developmental Ethanol Exposure Causes Reduced Feeding and Reveals a Critical Role for Neuropeptide F in Survival

Food intake is necessary for survival, and natural reward circuitry has evolved to help ensure that animals ingest sufficient food to maintain development, growth, and survival. Drugs of abuse, including alcohol, co-opt the natural reward circuitry in the brain, and this is a major factor in the reinforcement of drug behaviors leading to addiction. At the junction of these two aspects of reward are alterations in feeding behavior due to alcohol consumption. In particular, developmental alcohol exposure (DAE) results in a collection of physical and neurobehavioral disorders collectively referred to as Fetal Alcohol Spectrum Disorder (FASD). The deleterious effects of DAE include intellectual disabilities and other neurobehavioral changes, including altered feeding behaviors. Here we use Drosophila melanogaster as a genetic model organism to study the effects of DAE on feeding behavior and the expression and function of Neuropeptide F. We show that addition of a defined concentration of ethanol to food leads to reduced feeding at all stages of development. Further, genetic conditions that reduce or eliminate NPF signaling combine with ethanol exposure to further reduce feeding, and the distribution of NPF is altered in the brains of ethanol-supplemented larvae. Most strikingly, we find that the vast majority of flies with a null mutation in the NPF receptor die early in larval development when reared in ethanol, and provide evidence that this lethality is due to voluntary starvation. Collectively, we find a critical role for NPF signaling in protecting against altered feeding behavior induced by developmental ethanol exposure.

A Drosophila model for fetal alcohol syndrome disorders: role for the insulin pathway

Prenatal exposure to ethanol in humans results in a wide range of developmental abnormalities, including growth deficiency, developmental delay, reduced brain size, permanent neurobehavioral abnormalities and fetal death. Here we describe the use of Drosophila melanogaster as a model for exploring the effects of ethanol exposure on development and behavior. We show that developmental ethanol exposure causes reduced viability, developmental delay and reduced adult body size. We find that flies reared on ethanol-containing food have smaller brains and imaginal discs, which is due to reduced cell division rather than increased apoptosis. Additionally, we show that, as in mammals, flies reared on ethanol have altered responses to ethanol vapor exposure as adults, including increased locomotor activation, resistance to the sedating effects of the drug and reduced tolerance development upon repeated ethanol exposure. We have found that the developmental and behavioral defects are largely due to the effects of ethanol on insulin signaling; specifically, a reduction in Drosophila insulin-like peptide (Dilp) and insulin receptor expression. Transgenic expression of Dilp proteins in the larval brain suppressed both the developmental and behavioral abnormalities displayed by ethanol-reared adult flies. Our results thus establish Drosophila as a useful model system to uncover the complex etiology of fetal alcohol syndrome.

Peptidergic agonists of activity-dependent neurotrophic factor protect against prenatal alcohol-induced neural tube defects and serotonin neuron loss

INTRODUCTION

Prenatal alcohol exposure via maternal liquid diet consumption by C57BL/6 (B6) mice causes conspicuous midline neural tube deficit (dysraphia) and disruption of genesis and development of serotonin (5-HT) neurons in the raphe nuclei, together with brain growth retardation. The current study tested the hypothesis that concurrent treatment with either an activity-dependent neurotrophic factor (ADNF) agonist peptide [SALLRSIPA, (SAL)] or an activity-dependent neurotrophic protein (ADNP) agonist peptide [NAPVSIPQ, (NAP)] would protect against these alcohol-induced deficits in brain development.

METHODS

Timed-pregnant B6 dams consumed alcohol from embryonic day 7 (E7, before the onset of neurulation) until E15. Fetuses were obtained on E15 and brain sections processed for 5-HT immunocytochemistry, for evaluation of morphologic development of the brainstem raphe and its 5-HT neurons. Additional groups were treated either with SAL or NAP daily from E7 to E15 to assess the potential protective effects of these peptides. Measures of incomplete occlusion of the ventral canal and the frequency and extent of the openings in the rhombencephalon were obtained to assess fetal dysraphia. Counts of 5-HT-immunostained neurons were also obtained in the rostral and caudal raphe.

RESULTS

Prenatal alcohol exposure resulted in abnormal openings along the midline and delayed closure of ventral canal in the brainstem. This dysraphia was associated with reductions in the number of 5-HT neurons both in the rostral raphe nuclei (that gives rise to ascending 5-HT projections) and in the caudal raphe (that gives rise to the descending 5-HT projections). Concurrent treatment of the alcohol-consuming dams with SAL prevented dysraphia and protected against the alcohol-induced reductions in 5-HT neurons in both the rostral and caudal raphe. NAP was less effective in protecting against dysraphia and did not protect against 5-HT loss in the rostral raphe, but did protect against loss in the caudal raphe.

CONCLUSIONS

These findings further support the potential usefulness of these peptides for therapeutic interventions in pregnancies at risk for alcohol-induced developmental deficits. Notably, the ascending 5-HT projections of the rostral raphe have profound effects in regulating forebrain development and function, and the descending 5-HT projections of the caudal raphe are critical for regulating respiration. Protection of the rostral 5-HT-system may help prevent structural and functional deficits linked to abnormal forebrain development, and protection of the caudal systems may also reduce the increased risk for sudden infant death syndrome associated with prenatal alcohol exposure.

Fetal Alcohol Exposure Reduces Serotonin Innervation and Compromises Development of the Forebrain Along the Serotonergic Pathway

BACKGROUND

We reported previously that a moderate level of fetal alcohol treatment reduces the birth, maturation, and migration of serotonin (5-HT) neurons at embryonic days 11 to 15 (E11-E15). Because 5-HT is known as a differentiation signal for forebrain development, we investigated whether alcohol affects 5-HT innervation to the developing brain and how the target brain areas grow as they receive 5-HT innervation between E15 and E18.

METHODS

Pregnant dams were divided into three groups and treated from E7 to E15 or E18 with one of the following conditions: (1) liquid diet that contained 25% ethanol-derived calories (ALC), (2) isocaloric liquid diet pair-fed (PF), or (3) chow fed (Chow). The 5-HT immunostained (5-HT-IM) fibers and size of brain areas were examined as an index of growth along the ascending 5-HT pathway.

RESULT

We found that 5-HT-IM fibers innervate the brain regions specifically under active differentiation and that there were three sets of correlated dysmorphology in the ALC group as compared with those of the PF and Chow groups. The three sets are as follows: (1) fewer 5-HT-IM fibers in the medial forebrain bundle and along the projecting pathway through the hypothalamus, septal nucleus, frontal and parietal cortices, and subiculum/hippocampus; (2) underdevelopment of the brain regions along 5-HT fiber projections; and (3) underdevelopment of somatosensory thalamocortical projections, which are known to transiently express 5-HT transporters and to be regulated by 5-HT. No such differences were found between the PF and Chow groups.

CONCLUSION

We found that fewer 5-HT fibers grew in the embryos that were exposed to alcohol. As forebrain regions differentiated along the 5-HT projection, we found two reductions: (1) the growth of brain regions along 5-HT projection and (2) the growth of the thalamocortical sensory projection regulated by 5-HT. The reduced 5-HT innervation is in agreement with our previous observation of fewer 5-HT neurons. The subsequent retardation of forebrain growth and sensory thalamocortical fibers along the pathway of reduced 5-HT projection is consistent with the role of 5-HT as a signal for forebrain differentiation.

Differential Neurosensitivity to the Discriminative Stimulus Properties of Ethanol in C57BL/6J and C3H/He Mice

BACKGROUND

A large body of evidence suggests that the interoceptive cue associated with ethanol intoxication is complex and dependent on a number of environmental and biological factors. Despite the fact that mice have been widely used to study genetic influences on sensitivity to various actions of ethanol, few studies have used mice to examine sensitivity to the discriminative stimulus effects of ethanol. The purpose of this study was to compare sensitivity to the discriminative stimulus effects of ethanol in two inbred mouse strains, namely C57BL/6J and C3H/He mice.

METHODS

Adult male C57BL/6J and C3H/He mice were trained to discriminate between ethanol and saline using a two-lever food reinforcement operant procedure. Once criterion discrimination performance was achieved, dose-response functions were determined from generalization tests. Additional experiments were conducted to determine whether differences in discrimination performance were related to differential blood/brain ethanol levels in the two mouse strains.

RESULTS

A greater proportion of C57BL/6J mice acquired the discrimination and required fewer trials to achieve criterion performance compared with C3H/He mice with a 1.0 g/kg ethanol training dose. This deficit in acquisition was overcome when the training dose was increased to 2.0 g/kg for C3H/He mice. In a second experiment, a 1.5 g/kg training dose of ethanol was used for both strains. Again, a greater proportion of C57BL/6J mice acquired the discrimination and required fewer training trials to achieve criterion performance compared with C3H/He mice. Blood ethanol levels did not differ between the strains after administration of the 1.5 g/kg training dose. However, blood and brain ethanol levels did differ between the strains after doses of ethanol were administered that produced equivalent discrimination performance.

CONCLUSIONS

Results indicate that ethanol discrimination was more readily acquired and maintained in C57BL/6J mice than C3H/He mice. Ethanol dose-response functions generated from generalization tests also clearly demonstrated greater sensitivity to the discriminative stimulus properties of ethanol in C57BL/6J mice compared with the C3H/He strain. This differential sensitivity to the interoceptive cue produced by ethanol does not seem to be related to learning or pharmacokinetic differences between the two inbred strains.

Chronic Ethanol Consumption by C57BL/6 Mice Promotes Tolerance to Its Interoceptive Cues and Increases Extracellular Dopamine, an Effect Blocked by Naltrexone

BACKGROUND

C57BL/6 (B6) mice voluntarily consume ethanol. Although preingestive factors might be accountable, the fact that B6 mice voluntarily consume sufficient ethanol to set the conditions for an ethanol-deprivation effect suggest that post-ingestive pharmacological induced changes also occur. In this study, we determined the amounts of ethanol voluntarily consumed by B6 mice and associated blood ethanol levels (BEL), the effects of this consumption on extracellular dopamine (DA) and how this was altered by naltrexone, as well as on its interoceptive discriminative cues.

METHODS

In experiment 1, the amounts of 12% ethanol consumed at 2, 4, and 6 hr into the active phase of the circadian cycle and associated BEL were determined. In experiment 2, dialysate samples were collected for 1 hr to establish basal DA levels. Mice were then injected with saline or naltrexone (6 mg/kg) and given access to water and 12% ethanol or to water only, and samples were collected at 20-min intervals for the next 2 hr. In experiment 3, mice were trained to discriminate ethanol's interoceptive cues via operant techniques, and half were given 3 weeks access to ethanol and water, the other half water only. Ethanol-consuming and water control mice were again tested for their ability to discriminate the drug's interoceptive cues.

RESULTS

Mice ingested nearly 6 g/kg of ethanol and attained BEL near 100 mg/100 mL by 6 hr into the active phase. Ethanol intake at 2-hr into the dark phase was approximately 2.5 g/kg, and increased DA to approximately 100% above basal levels. Naltrexone reduced ethanol consumption and blocked the DA increase. Ethanol consumption for 3 weeks attenuated its discriminative cues.

CONCLUSIONS

B6 mice voluntarily consume sufficient ethanol (1) to produce intoxicating BEL; (2) to increase DA levels in nucleus accumbens, an effect blocked by naltrexone; and (3) to attenuate its discriminative cues.

Second generation effects of maternal alcohol consumption during pregnancy in rats

1. Previous studies have shown that when female rats are administered alcohol during pregnancy there are adverse effects on their progeny, including decreased birth weight and delayed neuromotor development. Evidence from several sources suggests alcohol exposure may contribute to cytogenetic abnormalities, suggesting the possibility of cross generational effects from prenatal exposure. 2. On day 1 of gestation female rats were randomly allocated to the Alcohol group, which received a liquid diet containing 5% (v/v) ethanol solution until parturition, the Sucrose control group, which received an identical diet, except that sucrose had been isocalorically substituted for ethanol, or the Chow control, which received standard laboratory chow. 3. When the offspring of these rats reached adulthood they were mated with drug-free rats and the development of their offspring was monitored. 4. In comparison with female pups whose sires had been exposed to alcohol in utero, the weight of pups descended from fetally-exposed dams increased more slowly from day 1 to day 7. 5. At five days of age, significant differences favouring the two control groups were found in latency to right for pups descended from fetally-exposed dams. 6. These data suggest that the effects of prenatal exposure to alcohol are more pervasive than previously thought and affect female pups to a greater extent than males.

Delta-opioid and 5-HT3 receptor antagonist effects on ethanol reward and discrimination in C57BL/6 mice

The effects of the receptor antagonists MDL 72222 (MDL, 5-HT3) and naltrindole (delta-opioid) on ethanol reward and its discrimination were examined in ethanol-preferring C57BL/6 (C57) mice. MDL attenuated lever responding for 12% ethanol delivered on a fixed-ratio 8 reinforcement schedule at a dose that did not influence responding for water reward, thus confirming a previous report that ICS 205-930 reduced ethanol reward for Long-Evans rats. Our study in combination with the reduced ethanol consumption reported for C57 mice injected with odansetron indicates that 5-HT3 receptor systems are involved in mediating behavior directed toward obtaining ethanol as well as its consumption. By attenuating the rewarding effects of ethanol or of ethanol conditioned cues (e.g., the operant environment), 5-HT3 antagonists may be useful in the treatment of alcohol abuse. The 5-HT3 antagonist effects in this study are comparable with the effects of naltrexone on ethanol reward in C57 mice, although higher doses were required to reduce operant responding for ethanol reward. In contrast to the 5-HT3 antagonist and naltrexone effects, naltrindole, an antagonist with greater specificity for the delta-opioid receptor, was without effect on ethanol reward. This result and recent reports for rats and monkeys suggests that the general antagonists might be more efficacious in attenuating ethanol reward. Both MDL and naltrindole produced only slight reductions in the ethanol discriminative cue, suggesting that the rewarding and discriminative effects of ethanol are not likely mediated by identical neural mechanisms as previously suggested.

The discrimination and durability of an ethanol cue in young and mid-aged female mice

Young adult (6 months) and mid-aged (12 months) C57BL/6 mice both learned to discriminate ethanol (ETOH, 1.0 g/kg) although criterion performance occurred later for mid-aged mice. ETOH discrimination improved with increasing dose (0.25-1.0 g/kg) and the dose-response function was unaffected by age. The ETOH cue had declined by 40 min postinjection for young mice not unlike a previous report for young rats. In contrast, the ETOH cue remained discriminable at 40 min for mid-aged mice, an effect perhaps due to their slower rate of ETOH metabolism and accountable for the previously reported reduction in ethanol consumption by mid-aged mice. Retention tests and reacquisition training both indicated that the ETOH cue can be retained by both age groups for at least 60 days without discrimination training or food deprivation. The present study suggests that the ethanol discriminative cue in mid-aged mice does not differ from that in young adult mice in potency but is more long lasting, the latter perhaps being related to their reduced ethanol consumption. Of significance from a therapeutic perspective, is that the ETOH cue remained discriminable for 2 months in both age groups (i.e., approximately 1/12 of their total life span).

Teratogenic actions of ethanol in the mouse: a minireview

The deleterious effects of prenatal ethanol exposure have been extensively documented in clinical and experimental studies. This paper provides an overview of work conducted with mice to examine the myriad of adverse consequences that result from embryonic/fetal exposure to ethanol. All of the hallmark features of the clinical fetal alcohol syndrome have been demonstrated in mice, including prenatal and postnatal growth retardation, structural malformations and behavioral abnormalities associated with central nervous system dysfunction. As expected, the severity and profile of effects is related to both dosage level and timing of exposure. In addition, these effects have been demonstrated following acute and chronic exposure, with a variety of routes of administration employed. Furthermore, a number of strains have been used in these studies and the variant response (susceptibility) to the teratogenic actions of ethanol exhibited among different mouse strains support the notion that genetic factors govern, at least in part, vulnerability to these effects of ethanol. More recent studies using mouse models have focused on examining potential mechanisms underlying the full spectrum of ethanol's teratogenic actions.

Reduced sensitivity to the effects of clonidine on ethanol-stimulated locomotor activity in adult mouse offspring prenatally exposed to ethanol

Prenatal exposure to ethanol (EtOH) alters developing catecholamine (CA) systems and acute sensitivity to the locomotor stimulant effects of EtOH. As an extension of previous work involving CA agents, this study addressed whether prenatal EtOH exposure influences central norepinephrine (NE) systems by examining the motoric effects of the direct alpha 2 adrenoreceptor agonist clonidine given alone and in combination with a low-dose stimulant challenge of EtOH. Standard lab chow or liquid diets containing either 25% EtOH-derived calories (EDC), or 0% EDC (pair-fed group) were given to pregnant C3H/He mice on gestation days 6-18. At 90 days of age, male offspring from each prenatal treatment group were monitored for 10 minutes in an open field following IP injections of clonidine (0, 0.0125, 0.025, or 0.05 mg/kg) and either EtOH (1.5 g/kg) or saline. In control offspring, clonidine suppressed locomotor activity and attenuated the stimulant response to EtOH in a dose-dependent fashion. In contrast, clonidine given alone did not suppress, but appeared to stimulate, activity in prenatal EtOH-exposed offspring. Furthermore, the ability of clonidine to attenuate the locomotor stimulant properties of EtOH was greatly reduced in prenatal EtOH-exposed animals. Taken together, these results indicate a shift to the right in the dose-response function for clonidine in prenatal EtOH-exposed offspring relative to control mice. Further, the results suggest that prenatal exposure to EtOH may result in long-lasting alterations in developing central NE systems, particularly presynaptic alpha 2 adrenoreceptor sensitivity.

Responsiveness to cocaine challenge in adult rats following prenatal exposure to cocaine

Adult rats that were gestationally exposed to cocaine and control offspring were examined for their sensitivity to challenge doses of cocaine. Offspring were derived from Sprague-Dawley dams that had received subcutaneous injections of 40 mg/kg per 3 cc cocaine hydrochloride daily on gestational days 8-20, pair-fed dams that were injected with saline, and nontreated control dams. In order to investigate the sensitivity to challenge doses of cocaine, offspring were assessed in adulthood for locomotor activity, cocaine drug discrimination, and the time course of cocaine in brain tissue following acute cocaine challenge. Adult offspring prenatally exposed to cocaine were observed to exhibit a reduced sensitivity to the discriminative stimulus effects of cocaine as evidenced by a significant shift to the right in the dose-response curve of cocaine discrimination. No prenatal treatment effects were observed in terms of the temporal patterns of cocaine discrimination or with regard to brain levels of cocaine. In addition, baseline locomotor activity and locomotor responses to challenge doses of cocaine were comparable across the prenatal treatment groups. Thus, prenatal cocaine exposure reduced sensitivity of offspring to the discriminative stimulus properties of cocaine without altering either the distribution of cocaine to the brain or the sensitivity of the offspring to the locomotor stimulant effects of cocaine.

Prenatal ethanol effects and dopamine systems of adult C57 male mice

Behavioral, pharmacological, and neurochemical studies indicate that prenatal ethanol exposure can alter dopamine (DA) systems of developing rats. In addition, some of the behavioral changes described for prenatal-ethanol-exposed rats and mice (e.g., reduced responding for food and other rewards) as well as their response to various psychoactive drugs (e.g., amphetamines, methylphenidate, haloperidol) suggest that the DA system changes might extend into adulthood. Neurochemical studies on the effects of prenatal ethanol on DA systems of adults have not been reported for either species. The present study provides a neurochemical assessment of prenatal ethanol effects on DA systems of fully mature mice. Compared to chow and sucrose controls, adult offspring of mice fed a diet containing 25% ethanol derived calories had preadolescent growth deficits as observed in previous studies which also showed long-term behavioral deficits. Prenatal ethanol exposure in the present study, however, did not alter the concentration of DA or dihydroxyphenylacetic acid (DOPAC) nor the progressive decline in the concentration of these compounds in either striatum or nucleus accumbens of mature mice at intervals after synthesis inhibition by alpha-methyl-DL-p-tyrosine. Thus, the present study provides no neurochemical confirmation of altered DA systems resulting from prenatal ethanol exposure under conditions previously observed to alter adult behavior.

Effects of prenatal ethanol exposure on later sensitivity to the low-dose stimulant actions of ethanol in mouse offspring: possible role of catecholamines

The purpose of this study was to examine whether prenatal ethanol (EtOH) exposure alters later sensitivity to the low-dose stimulant effects of EtOH. Because the locomotor stimulant effects of EtOH are thought to be mediated, at least in part, by activation of brain monoamine systems, and because prenatal EtOH exposure has been shown to alter brain monoamine activity, it was hypothesized that prenatal EtOH exposure may alter sensitivity to the stimulant actions of EtOH. To test this hypothesis, sensitivity to the locomotor stimulant effects of various challenge doses of EtOH was examined in male and female offspring from prenatal alcohol (A), pair-fed (PF), and lab chow (LC) groups at different ages. In addition, to address the hypothesis further, sensitivity to the catecholamine synthesis inhibitor alpha-methyl-p-tyrosine (AMPT) was examined in these offspring, as well. Results indicated that male offspring prenatally exposed to EtOH exhibited reduced baseline activity and a blunted stimulant response to all challenge doses of EtOH (0.75-1.5 g/kg) in comparison with control offspring at 30 days of age, but these effects appeared to "normalize" at 70 days of age. Female EtOH-exposed offspring also exhibited a reduced baseline level of activity relative to control offspring, as well as a blunted stimulant response to the lowest challenge dose of EtOH (0.75 g/kg) at 30 days of age, and these effects persisted into adulthood. The stimulant response to higher doses of EtOH did not significantly differ among prenatal treatment groups in young or adult female offspring. However, because baseline activity was significantly lower in female EtOH-exposed offspring than control offspring, the stimulant response to these doses of EtOH (1.125 and 1.5 g/kg) was relatively greater than that for PF and LC offspring. Importantly, none of the differences in performance among the prenatal treatment groups could be attributed to an alteration in EtOH pharmacokinetics, because blood EtOH levels measured immediately following the 10-min test session were similar for all prenatal treatment groups across all of the EtOH test doses. Further, a similar response profile as that observed following EtOH challenge at 70 days of age was obtained following phenobarbital challenge (10-40 mg/kg). Finally, whereas AMPT (50-400 mg/kg) dose-dependently antagonized the stimulant effects of EtOH in all prenatal treatment groups, this effect of AMPT was significantly greater in mice prenatally exposed to EtOH in comparison with control offspring.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of in utero administration of alcohol on alcohol sensitivity in adult rats

In utero exposure to alcohol has been associated with many physical deficits and behavioral abnormalities. The purpose of these studies was to determine the effects of in utero administration of alcohol on behaviors related to tolerance and sensitivity to alcohol in adult rats. Pregnant rats were maintained on a liquid diet containing alcohol [35% ethanol-derived calories (EDC)] throughout pregnancy. Offspring manifested physical characteristics of Fetal Alcohol Syndrome. The 35% EDC group was able to stay on a wooden dowel longer and at higher blood alcohol concentrations than were pair-fed controls. Following a hypnotic dose of alcohol, rats in the 35% EDC group slept longer than pair-fed controls. A greater alcohol-induced hypothermic effect was seen in females in the 35% EDC group than in controls. Treatment did not affect rate of metabolism of alcohol. These studies suggest that in utero administration of alcohol may be a factor in determining an individual's sensitivity and tolerance to alcohol and possibly their preference for alcohol.

Comparative effects of ethanol on motor activity and operant behavior

Ethanol effects on two types of motor activity and on lever responding for food delivered on a fixed-ratio 20 (FR 20) reinforcement schedule were compared using C57BL/6 (C57) mice. Low doses of ethanol (1-2 g/kg) transiently elevated horizontal activity and high doses (2.5 and 3.0 g/kg) reduced this behavior throughout testing with a slight recovery toward the end of a 16-min test period. In contrast, similar ethanol doses produced a monotonic reduction in both vertical activity and lever responding for food under the FR 20 schedule. The ethanol-induced reduction in FR 20 lever responding was less prolonged than the reduction in vertical activity but was more prolonged than the reduction in horizontal activity. Because vertical activity and lever responding for food delivered on the FR 20 schedule were never elevated, were reduced at ethanol doses that either stimulated or depressed horizontal activity, and were unaffected by low ethanol doses that did not affect horizontal activity, it is unlikely that either are sensitive to the stimulatory effects of ethanol. Accountable mechanisms for the different effects of ethanol on the three behaviors are unknown; however, the present study eliminates ethanol dose, postinjection time, testing time, and food deprivation condition as possible reasons for the differences.