Effects of maternal strain on ethanol responses in reciprocal F1 C57BL/6J and DBA/2J hybrid mice

Rodent models of mental illness in polycystic ovary syndrome: the potential role of hypothalamic-pituitary-adrenal dysregulation and lessons for behavioral researchers

Polycystic ovary syndrome (PCOS) is the most commonly diagnosed endocrine disorder in women of reproductive age, with phenotypes including ovarian and metabolic dysfunctions. Women with PCOS also show increased rates of mental illness, dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, and altered responsiveness to stressors that may contribute to the higher rates of mental illness, specifically depression and anxiety. Animal models of PCOS have provided insight into the ovarian and metabolic mechanisms that underlie the syndrome, and several models have been used to study the behavioral consequences associated with PCOS in the laboratory. Several studies in rodent models of PCOS demonstrate changes in anxiety-like behavior, but researchers often neglect to report procedural details or behavioral data crucial to interpreting the differences observed in those studies. Additionally, the impact of potential HPA dysregulation in animal models of PCOS may influence behavioral findings, although only three studies to date have examined this. As such, researchers should consider and report stress-associated variables (e.g., time of day, light/dark cycle, light intensity, housing, and procedures to control experimenter and litter effects) that may influence depression- and anxiety-like behaviors in rodents. This review will summarize the behavioral and HPA-related studies in women with PCOS and rodent models of the disease, and provide considerations for future studies.

Effects of multi-modal cues on conditioned place preference in C57BL/6J and DBA/2J mice

RATIONALE

Previous work has shown that some mouse strains (e.g., DBA/2J [D2]) readily develop robust ethanol-induced conditioned place preference (CPP) while others (e.g., C57BL/6J [B6]) do not. Though commonly interpreted as a difference between strains in sensitivity to ethanol reward, other explanations for this finding are possible.

OBJECTIVES

To explore the hypothesis that variation in sensitivity to contextual cues underlies CPP differences, the present work investigated ethanol-induced CPP in D2 and B6 mice trained with a standard tactile (floor) cue procedure compared to mice trained with tactile plus visual-spatial cues.

METHODS

In an unbiased CPP procedure, mice were assigned to either a single element cue (one-compartment apparatus with tactile cue presented in the dark) or multi-modal cues (two-compartment apparatus with distinct tactile floors and lights on). To track CPP development, mice received preference tests during training in addition to a final test.

RESULTS

Adding visual-spatial cues accelerated CPP acquisition in both D2 and B6 mice. However, this enhancement was observed after just one ethanol-conditioning trial in D2 mice, but was observed only after four ethanol-conditioning trials in B6 mice. Differences between groups trained with single or multi-modal cues disappeared as conditioning reached asymptote, with D2 mice showing a more rapid loss of the effect and a higher maximum CPP.

CONCLUSIONS

Although multi-modal cues produce more rapid conditioning, their inability to reduce or eliminate strain differences in CPP supports the interpretation that these strains differ in their sensitivity to ethanol reward.

Effects of sex on ethanol conditioned place preference, activity and variability in C57BL/6J and DBA/2J mice

Previous studies of ethanol drinking in rodents have shown greater intake in females than in males, but the reasons behind this difference are unknown. To address one possible interpretation of the drinking difference, these studies tested the hypothesis that female and male mice differ in sensitivity to the rewarding effects of ethanol using the conditioned place preference (CPP) procedure. To increase the generalizability of the results, sex differences were examined in two inbred mouse strains known to differ in their sensitivity to ethanol reward: C57BL/6J (B6) and DBA/2J (D2). Mice were conditioned in an unbiased CPP procedure using either 1 or 2 g/kg ethanol. To detect possible differences in learning rate, they were tested once at the midpoint of conditioning and again after conditioning ended. As expected, CPP was stronger with 2 g/kg than with 1 g/kg, and D2 mice generally showed stronger CPP than B6 mice. However, there were no sex differences in the rate of CPP acquisition or in CPP magnitude, suggesting no sex difference in ethanol reward sensitivity as indexed by CPP. Nevertheless, there were sex differences in locomotor activity. B6 females were generally more active than B6 males during CPP acquisition whereas D2 females were slightly less active than D2 males during both CPP acquisition and preference testing. Unexpectedly, female mice showed more variability than males in the behavioral measures recorded in these studies, encouraging greater attention to variability in the design, analysis and interpretation of future studies of sex differences in mice.

Paternal preconception alcohol exposure imparts intergenerational alcohol-related behaviors to male offspring on a pure C57BL/6J background

While alcohol use disorder (AUD) is a highly heritable condition, the basis of AUD in families with a history of alcoholism is difficult to explain by genetic variation alone. Emerging evidence suggests that parental experience prior to conception can affect inheritance of complex behaviors in offspring via non-genomic (epigenetic) mechanisms. For instance, male C57BL/6J (B6) mice exposed to chronic intermittent vapor ethanol (CIE) prior to mating with Strain 129S1/SvImJ ethanol-naïve females produce male offspring with reduced ethanol-drinking preference, increased ethanol sensitivity, and increased brain-derived neurotrophic factor (BDNF) expression in the ventral tegmental area (VTA). In the present study, we tested the hypothesis that these intergenerational effects of paternal CIE are reproducible in male offspring on an inbred B6 background. To this end, B6 males were exposed to 6 weeks of CIE (or room air as a control) before mating with ethanol-naïve B6 females to produce ethanol (E)-sired and control (C)-sired male and female offspring. We observed a sex-specific effect, as E-sired males exhibited decreased two-bottle free-choice ethanol-drinking preference, increased sensitivity to the anxiolytic effects of ethanol, and increased VTA BDNF expression; no differences were observed in female offspring. These findings confirm and extend our previous results by demonstrating that the effects of paternal preconception ethanol are reproducible using genetically identical, inbred B6 animals.

G Protein-Gated Inwardly Rectifying Potassium Channel Subunit 3 Knock-Out Mice Show Enhanced Ethanol Reward

BACKGROUND

G protein-gated inwardly rectifying potassium (GIRK) channels contribute to the effects of a number of drugs of abuse, including ethanol. However, the roles of individual subunits in the rewarding effects of ethanol are poorly understood.

METHODS

We compare conditioned place preference (CPP) in GIRK3 subunit knock-out (GIRK3(-/-)), heterozygote (GIRK3(+/-)), and wild-type (WT) mice. In addition, the development of locomotor tolerance/sensitization and the effects of EtOH intoxication on associative learning (fear conditioning) are also assessed.

RESULTS

Our data show significant EtOH CPP in GIRK3(-/-) and GIRK3(+/-) mice, but not in the WT littermates. In addition, we demonstrate that these effects are not due to differences in EtOH metabolism, the development of EtOH tolerance/sensitivity, or associative learning abilities. While there were no consistent genotype differences in the fear conditioning assay, our data do show a selective sensitization of the impairing effects of EtOH intoxication on contextual learning, but no effect on cued learning.

CONCLUSIONS

These findings suggest that GIRK3 plays a role in EtOH reward. Furthermore, the selectivity of this effect suggests that GIRK channels could be an effective therapeutic target for the prevention and/or treatment of alcoholism.

Effects of cross-fostering on alcohol preference and correlated responses to selection in high- and low-alcohol-preferring mice

BACKGROUND

Selectively bred rodent lines are valuable tools for investigating gene × environment interactions related to risk for alcoholism in humans. Early maternal environment is one particular factor known for critically influencing neural, hormonal, and behavioral outcomes in adulthood. Cross-fostering is a procedure that may be used to explore the role of genotype-dependent maternal influences on phenotypic variability in adulthood. The purpose of these experiments was to examine the effects of cross-fostering on free-choice alcohol drinking and correlated responses to selection for alcohol preference in mice selectively bred for high (HAP2) and low (LAP2) alcohol preference.

METHODS

Mice were assigned to one of the following treatments: SHAM (pups that were fostered to their original biological mother), IN (pups that were fostered to a different mother of the same line), and CROSS (pups that were fostered to a mother of a different line). Mice were tested in adulthood for (i) free 24-hour access to alcohol for a period of 28 days; (ii) the expression of the acoustic startle response and fear-potentiated startle (FPS); and (iii) handling-induced convulsions (HICs) during acute alcohol withdrawal.

RESULTS

Overall, the expression of the alcohol preference selection phenotype was robust in all groups (HAP2 > LAP2). Cross-fostering produced a moderate but significant reduction in g/kg alcohol drinking and preference scores in HAP2 mice (CROSS < SHAM) but had no effect in LAP2 mice. Cross-fostering did not affect the expression of correlated responses to selection: acoustic startle response (HAP2 > LAP2), FPS (HAP2 > LAP2), HICs (LAP2 > HAP2).

CONCLUSIONS

It appears that maternal environment can modify the expression of the high-alcohol-preference phenotype in HAP2 selectively bred mice. These results suggest a gene × environment interaction with respect to the expression of the high-alcohol-preference selection phenotype but not correlated responses to selection.

Using monosodium glutamate to initiate ethanol self-administration in inbred mouse strains

Voluntary oral ethanol consumption in rodents is generally limited by strong taste-aversion in these species. Historically, this has been overcome by combining ethanol with a sweetener, typically sucrose or saccharine, and then slowly 'fading' away the sweetener. While useful in most instances, this approach has not proven as successful for some inbred strains of mice (e.g. DBA/2J) despite consistent evidence in the literature that these same strains express strong conditioned place preference for intraperitoneal- or intragastric-administered ethanol. Importantly, DBA/2J mice express a polymorphism in a 'sweet' taste receptor subunit gene that reduces the potency of sweet substances in these mice. We hypothesized that the presence of this polymorphism might help explain the contrasting behavioral findings of weak voluntary oral ethanol consumption following sucrose-fade yet robust conditioned place preference for ethanol in this strain. To test this, we compared ethanol consumption initiated by either a 'traditional' sucrose-fade or a fade from an alternative tastant, monosodium glutamate (MSG). We found that in both C57BL/6J and DBA/2J mice, the MSG-fade produced robust increases in home cage ethanol consumption relative to the traditional sucrose-fade. This increased ethanol intake following MSG-fade was evident across a range of ethanol concentrations. Our findings suggest the potential utility of the MSG-fade to establish stable voluntary oral ethanol consumption in mice, particularly ethanol 'non-preferring' strains such as DBA/2J and lend additional support to the notion that ethanol consumption in DBA/2J mice is limited by pronounced taste aversion.

Parent-of-origin and trans-generational germline influences on behavioral development: the interacting roles of mothers, fathers, and grandparents

Mothers and fathers do not contribute equally to the development of their offspring. In addition to the differential investment of mothers versus fathers in the rearing of offspring, there are also a number of germline factors that are transmitted unequally from one parent or the other that contribute significantly to offspring development. This article shall review four major sources of such parent-of-origin effects. Firstly, there is increasing evidence that genes inherited on the sex chromosomes including the nonpseudoautosomal part of the Y chromosome that is only inherited from fathers to sons, contribute to brain development and behavior independently of the organizing effects of sex hormones. Secondly, recent work has demonstrated that mitochondrial DNA that is primarily inherited only from mothers may play a much greater than anticipated role in neurobehavioral development. Thirdly, there exists a class of genes known as imprinted genes that are epigenetically silenced when passed on in a parent-of-origin specific manner and have been shown to regulate brain development and a variety of behaviors. Finally, there is converging evidence from several disciplines that environmental variations experienced by mothers and fathers may lead to plasticity in the development and behavior of offspring and that this phenotypic inheritance can be solely transmitted through the germline. Mechanistically, this may be achieved through altered programming within germ cells of the epigenetic status of particular genes such as retrotransposons and imprinted genes or potentially through altered expression of RNAs within gametes.

Endogenous kappa-opioid mediation of stress-induced potentiation of ethanol-conditioned place preference and self-administration

RATIONALE

Exposure to inescapable stressors increases both the rewarding properties and self-administration of cocaine through the signaling of the kappa-opioid receptor (KOR), but the effect of this signaling on other reinforcing agents remains unclear.

OBJECTIVE

The objective of this study is to test the hypothesis that signaling of the KOR mediates the forced swim stress (FSS)-induced potentiation of ethanol reward and self-administration.

METHODS

Male C57Bl/6J mice were tested in a biased ethanol-conditioned place preference (CPP) procedure, and both C57Bl/6J and prodynorphin gene-disrupted (Dyn -/-) mice were used in two-bottle free choice (TBC) assays, with or without exposure to FSS. To determine the role of the KOR in the resulting behaviors, the KOR agonist U50,488 (10 mg/kg) and antagonist nor-binaltorphimine (nor-BNI, 10 mg/kg) were administered prior to parallel testing.

RESULTS

C57Bl/6J mice exposed to repeated FSS 5 min prior to daily place conditioning with ethanol (0.8 g/kg) demonstrated a 4.4-fold potentiation of ethanol-CPP compared to unstressed mice that was prevented by nor-BNI pretreatment. Likewise, pretreatment with U50,488 90 min prior to daily ethanol place conditioning resulted in a 2.8-fold potentiation of ethanol-CPP. In the TBC assay, exposure to FSS significantly increased the consumption of 10% (v/v) ethanol by 19.3% in a nor-BNI-sensitive manner. Notably, Dyn -/- mice consumed a similar volume of ethanol as wild-type littermates and C57Bl/6J mice, but did not demonstrate significant stress-induced increases in consumption.

CONCLUSIONS

These data demonstrated a stress-induced potentiation of the rewarding effects and self-administration of ethanol mediated by KOR signaling.

Hybrid mice as genetic models of high alcohol consumption

We showed that F1 hybrid genotypes may provide a broader variety of ethanol drinking phenotypes than the inbred progenitor strains used to create the hybrids (Blednov et al. in Alcohol Clin Exp Res 29:1949-1958, 2005). To extend this work, we characterized alcohol consumption as well as intake of other tastants (saccharin, quinine and sodium chloride) in five inbred strains of mice (FVB, SJL, B6, BUB, NZB) and in their reciprocal F1 hybrids with B6 (FVBxB6; B6xFVB; NZBxB6; B6xNZB; BUBxB6; B6xBUB; SJLxB6; B6xSJL). We also compared ethanol intake in these mice for several concentrations before and after two periods of abstinence. F1 hybrid mice derived from the crosses of B6 and FVB and also B6 and SJL drank higher levels of ethanol than their progenitor strains, demonstrating overdominance for two-bottle choice drinking test. The B6 and NZB hybrid showed additivity in two-bottle choice drinking, whereas the hybrid of B6 and BUB demonstrated full or complete dominance. Genealogical origin, as well as non-alcohol taste preferences (sodium chloride), predicted ethanol consumption. Mice derived from the crosses of B6 and FVB showed high sustained alcohol preference and the B6 and NZB hybrids showed reduced alcohol preference after periods of abstinence. These new genetic models offer some advantages over inbred strains because they provide high, sustained, alcohol intake, and should allow mapping of loci important for the genetic architecture of these traits.

A method for mapping intralocus interactions influencing excessive alcohol drinking

Excessive alcohol (ethanol) consumption is the hallmark of alcohol use disorders. The F1 hybrid cross between the C57BL/6J (B6) and FVB/NJ (FVB) inbred mouse strains consumes more ethanol than either progenitor strain. The purpose of this study was to utilize ethanol-drinking data and genetic information to map genes that result in overdominant (or heterotic) ethanol drinking. About 600 B6 x FVB F2 mice, half of each sex, were tested for ethanol intake and preference in a 24-h, two-bottle water versus ethanol choice procedure, with ascending ethanol concentrations. They were then tested for ethanol intake in a Drinking in the Dark (DID) procedure, first when there was no water choice and then when ethanol was offered versus water. DNA samples were obtained and genome-wide QTL analyses were performed to search for single QTLs (both additive and dominance effects) and interactions between pairs of QTLs, or epistasis. On average, F2 mice consumed excessive amounts of ethanol in the 24-h choice procedure, consistent with high levels of consumption seen in the F1 cross. Consumption in the DID procedure was similar or higher than amounts reported previously for the B6 progenitor. QTLs resulting in heightened consumption in heterozygous compared to homozygous animals were found on Chrs 11, 15, and 16 for 24-h choice 30% ethanol consumption, and on Chr 11 for DID. No evidence was found for epistasis between any pair of significant or suggestive QTLs. This indicates that the hybrid overdominance is due to intralocus interactions at the level of individual QTL.