Effects Of Selective Breeding Research Articles

Assessment of selective breeding effects and selection signatures in Qingyuan partridge chicken and its strains

Qingyuan partridge chicken (QYM) is a highly regarded native breed in China, highly esteemed for its exceptional breeding characteristics. However, the investigation into the selection signatures and its strains remains largely unexplored. In this study, blood sampling, DNA extracting, and high-depth resequencing were performed in 27 QYMs. Integrating the genomic data of 14 chicken (70 individuals) breeds from other researches, to analyze the genetic structure, selection signatures, and effects of selective breeding within QYM and its 3 strains (QYMA, QYMB, and QYMC). Population structure analysis revealed an independent QYM cluster, which exhibited distinct from other breeds, with each of its 3 strains displaying distinct clustering patterns. Linkage disequilibrium analysis highlighted QYMB's notably slower decay rate, potentially influenced by selection pressure from various production indicators. Examination of selection signatures uncovered genes and genetic mechanisms associated with genomic changes resulting from extensive selective breeding within the QYM and its strains. Intriguingly, diacylglycerol kinase beta (DGKB) and catenin alpha 2 (CTNNA2) were identified as commonly selected genes across the 3 QYM strains, linked to energy metabolism, muscle development, and fat metabolism. Our research validates the substantial impact of selective breeding on QYM and its strains, concurrently identifying genomic regions and signaling pathways associated with their distinctive characters. This research also establishes a fundamental framework for advancing yellow-feathered broiler breeding strategies.

A revised model of energy transactions and body composition in sheep.

A mechanistic, dynamic model was developed to calculate body composition in growing lambs by calculating heat production (HP) internally from energy transactions within the body. The model has a fat pool (f) and three protein pools: visceral (v), nonvisceral (m), and wool (w). Heat production is calculated as the sum of fasting heat production, heat of product formation (HrE), and heat associated with feeding (HAF). Fasting heat production is represented as a function of visceral and nonvisceral protein mass. Heat associated with feeding (HAF) is calculated as ((1 - km) x MEI), where km is partial efficiency of ME use for maintenance, and MEI = metabolizable energy intake) applies at all levels above and below maintenance. The value of km derived from data where lambs were fed above maintenance was 0.7. Protein change (dp/dt) is the sum of change in the m, v, and w pools, and change in fat is equal to net energy available for gain minus dp/dt. Heat associated with a change in body composition (HrE) is calculated from the change in protein and fat with estimated partial efficiencies of energy use of 0.4 and 0.7 for protein and fat, respectively. The model allows for individuals to gain protein while losing fat or vice versa. When evaluated with independent data, the model performed better than the current Australian feeding standards (Freer etal., 2007) for predicting protein gain in the empty body but did not perform as well as for gain of fat and fleece-free empty body weight. Models performed similarly for predicting clean wool growth. By explicit representation of the major energy using processes in the body, and through simplification of the way body composition is computed in growing animals, the model is more transparent than current feeding systems while achieving similar performance. An advantage of this approach is that the model has the potential for wider applicability across different growth trajectories and can explicitly account for the effects of systematic changes on energy transactions, such as the effects of selective breeding, growth manipulation, or environmental changes.

Identification of Genomic Signatures in Bullmastiff Dogs Using Composite Selection Signals Analysis of 23 Purebred Clades.

Dog breeds represent canine sub-populations with distinctive phenotypic features and limited genetic diversity. We have established a resource to study breed-specific genetic diversity. Utilising genetic resources within our laboratory biobank, public domain genotype data and the phylogenetic framework of 23 breed clades, the primary objective for this study was to identify genomic regions that differentiate the Bullmastiff breed. Through application of a composite index analysis (CSS), genomic signatures were identified in Bullmastiffs when compared to the formative breeds, Mastiffs and Bulldogs, and to 22 other breed groups. Significant regions were identified on 15 chromosomes, with the most differentiated regions found on CFA1, CFA9, and CFA18. These regions may reflect genetic drift following establishment of the breed or the effects of selective breeding during development of the modern Bullmastiff. This was supported by analysis of genes from the identified genomic regions, including 458 genes from the multi-clade analysis, which revealed enriched pathways that may be related to characteristic traits and distinct morphology of the breed. The study demonstrates the utility of the CSS method in breed-specific genome analysis and advances our understanding of genetic diversity in Bullmastiff dogs.

Effects of Selective Breeding, Voluntary Exercise, and Sex on Endocannabinoid Levels in the Mouse Small-Intestinal Epithelium

The endocannabinoid (eCB) system in the gut communicates with the body and brain as part of the homeostatic mechanisms that affect energy balance. Although perhaps best known for its effects on energy intake, the eCB system also regulates voluntary locomotor behavior. Here, we examined gut eCB concentrations in relation to voluntary exercise, specifically in mice selectively bred for high voluntary wheel running behavior. We measured gut eCBs in four replicate non-selected Control (C) lines and four replicate lines of High Runner (HR) mice that had been selectively bred for 74 generations based on the average number of wheel revolutions on days 5 and 6 of a 6-day period of wheel access when young adults. On average, mice from HR lines run voluntarily on wheels ∼3-fold more than C mice on a daily basis. A recent study showed that circulating levels of primary endocannabinoids 2-arachidonoyl-sn-glycerol (2-AG) and anandamide (AEA) are altered by six days of wheel access, by acute wheel running, and differ between HR and C mice in sex-specific ways [1]. We hypothesized that eCBs in the upper small-intestinal epithelium (i.e., proximal jejunum), a region firmly implicated in eCB signaling, would differ between HR and C mice (linetype), between the sexes, between mice housed with vs. without wheels for six days, and would covary with amounts of acute running and/or home-cage activity (during the previous 30 minutes). We used the same 192 mice as in [1] , half males and half females, half HR and half C (all 8 lines), and half either given or not given access to wheels for six days. We assessed the eCBs, 2-AG and AEA, and their analogs docosahexaenoylglycerol (DHG), docosahexaenoylethanolamide (DHEA), and oleoylethanolamide (OEA). Both 2-AG and DHG showed a significant 3-way interaction of linetype, wheel access, and sex. In addition, HR mice had lower concentrations of 2-AG in the small-intestinal epithelium when compared to C mice, which may be functionally related to differences in locomotor activity or to differences in body composition and/or food consumption. Moreover, the amount of home-cage activity during the prior 30 min was a negative predictor of 2-AG and AEA concentrations in jejunum mucosa, particularly in the mice with no wheel access. Lastly, 2-AG, but not AEA, was significantly correlated with 2-AG in plasma in the same mice.

Effects of Selective Breeding, Exercise, and Sex on Endocannabinoid Levels in the Mouse Small Intestine

Only half of adults in the United States get the physical activity they need to help prevent certain chronic diseases. Such diseases as cardiovascular disease and diabetes are metabolism‐related and closely tied to insufficient physical activity. The endocannabinoid (EC) system serves many physiological roles, including in the regulation of voluntary locomotion, energy balance, and food reward. Signaling at the cannabinoid type 1 receptor (CB1) has been specifically implicated in acute and long‐term rodent voluntary exercise on wheels. Plasma levels of endocannabinoids in mice are known to change in association with wheel running, but EC concentrations in the gut have not been studied in the context of exercise. We studied four replicate lines of high runner (HR) mice that had been selectively bred for 74 generations based on the average number of wheel revolutions on days 5 and 6 of a 6‐day period of wheel access. Four additional replicate lines have been bred without regard to wheel running and serve as controls (C). On average, mice from HR lines voluntarily run on wheels ~3 times more than C mice on a daily basis. HR mice have higher home‐cage activity when housed without wheels, reduced body mass and fat, eat more, and their wheel running responds differently to a CB1 agonist & antagonist compared to C mice. A recent study showed that circulating levels (during peak running) of primary endocannabinoids 2‐arachidonoylglycerol (2‐AG) and anandamide (AEA) are altered by wheel running, differ between HR and C mice, and have sex‐specific interactions (Thompson et al. 2017. Physiology & Behavior 170:141–150). The EC system in the gut is of particular interest because consuming dietary fats leads to increased EC content in rodent small‐intestinal epithelium, which in turn, drives overeating. A focus on HR gut endocannabinoids may present novel insights concerning exercise metabolism of fats and gut‐brain reward signaling. We hypothesized that small intestine [EC] would differ between HR and C mice, between the sexes, between mice housed with vs. without wheels for 6 days, and would covary with acute running amounts (during the previous 30 minutes). We used 196 total mice, half males and half females, half HR and half C, and half either given or not given access to wheels for 6 days. Jejunum gut mucosa was collected for lipid extractions and subsequent EC analysis via ultra‐performance liquid chromatography coupled to tandem mass spectrometry (UPLC/MS/MS). 2‐AG, AEA, as well as their analogs docosahexaenoylglycerol (DHG), oleoylethanolamide (OEA) and docosahexaenoylethanolamide (DHEA), were measured. DHG showed a significant 3‐way interaction of linetype, wheel access, and sex, with no consistent effects of any of these factors. A trend also showed HR mice having lower 2‐AG, which suggests that HR mice may have lower rates of production of intestinal ECs and/or faster rates of degradation by monoacylglycerol lipase (MGL). Functionally, lower 2‐AG in HR jejunum might be related to differences from C mice with respect to locomotor activity, body composition, and/or food consumption.

A chicken for every pot: the economics, evolution and ethics of the modern chicken

ABSTRACT Humans began the transformation of wild jungle fowl into modern day chickens over 8,000 years ago. Over the past 70 years, chickens have become an increasingly important economic and dietary stable throughout the world. There are now over 20 billion chickens on farms worldwide. However, research has revealed that chickens are not as simple as humans once believed. They exhibit complex communication, social learning, numeracy and deception, as well as depression-like symptoms. These findings suggest that chickens posses both access and phenomenal consciousness. This raises critical questions about the effects of selective breeding and the impacts that the current housing systems have on these complex animals.

Genetic diversity of the class II major histocompatibility DRA locus in European, Asiatic and African domestic donkeys

The major histocompatibility complex (MHC) genes coding for antigen presenting molecules are the most polymorphic genes in vertebrate genome. The MHC class II DRA gene shows only small variation in many mammalian species, but it exhibits relatively high level of polymorphism in Equidae, especially in donkeys. This extraordinary degree of polymorphism together with signatures of selection in specific amino acids sites makes the donkey DRA gene a suitable model for population diversity studies. The objective of this study was to investigate the DRA gene diversity in three different populations of donkeys under infectious pressure of protozoan parasites, Theileria equi and Babesia caballi. Three populations of domestic donkeys from Italy ( N = 68), Jordan ( N = 43), and Kenya ( N = 78) were studied. A method of the donkey MHC DRA genotyping based on PCR-RFLP and sequencing was designed. In addition to the DRA gene, 12 polymorphic microsatellite loci were genotyped. The presence of Theileria equi and Babesia caballi parasites in peripheral blood was investigated by PCR. Allele and genotype frequencies, observed and expected heterozygosities and F IS values were computed as parameters of genetic diversity for all loci genotyped. Genetic distances between the three populations were estimated based on F ST values. Statistical associations between parasite infection and genetic polymorphisms were sought. Extensive DRA locus variation characteristic for Equids was found. The results showed differences between populations both in terms of numbers of alleles and their frequencies as well as variation in expected heterozygosity values. Based on comparisons with neutral microsatellite loci, population sub-structure characteristics and association analysis, convincing evidence of pathogen-driven selection at the population level was not provided. It seems that genetic diversity observed in the three populations reflects mostly effects of selective breeding and their different genetic origins.

Selection decisions among reindeer herders in Finland

Selection of breeding animals is a tool to improve the revenues in animal production. Information about selection practices and criteria are essential in assessing the possibilities for systematic selection schemes. Attitudes of reindeer herders towards use of selection in improving production were investigated by means of interviews. We interviewed the managers of reindeer herding cooperatives concerning their selection decisions. Fortyfive out of 56 managers answered to the semi-structured questionnaire. Among herding operations, selection of breeding animals was regarded by managers as critical for calf’s autumn weight and survival. The main selection criteria were calf’s health, vigour, body size and muscularity, dam or dam line, and maternal care. Hair quality and hair length were important as well, while such often quoted traits as antler characteristics, e.g. early shedding of antler velvet and thick antler bases, were unimportant. The results show that reindeer herders i) acknowledge the importance and effects of selective breeding, and ii) have empirical knowledge to list the most important selection criteria.

The effects of selective breeding on the architectural properties of the pelvic limb in broiler chickens: a comparative study across modern and ancestral populations.

Intensive artificial selection has led to the production of the modern broiler chicken, which over the last few decades has undergone a dramatic increase in growth rate and noticeable changes in body conformation. Unfortunately, this has been associated with musculoskeletal abnormalities which have altered the walking ability of these birds, raising obvious welfare concerns, as well as causing economic losses. Here we present a comparative study of ancestral and derived muscle anatomy in chickens to begin to tease apart how evolutionary alterations of muscle form in chickens have influenced their locomotor function and perhaps contributed to lameness. We measured the muscle architectural properties of the right pelvic limb in 50 birds, including the Giant Junglefowl, a commercial strain broiler and four pureline commercial broiler breeder lines (from which the broiler populations are derived) to identify which features of the broiler's architectural design have diverged the most from the ancestral condition. We report a decline in pelvic limb muscle mass in the commercial line birds that may compromise their locomotor abilities because they carry a larger body mass. This greater demand on the pelvic limb muscles has mostly led to changes in support at the hip joint, revealing significantly larger abductors and additionally much larger medial rotators in the broiler population. Differences were seen within the commercial line bird populations, which are likely attributed to different selection pressures and may reflect differences in the walking ability of these birds. In addition, Junglefowl seem to have both greater force-generating capabilities and longer, presumably faster contracting muscles, indicative of superior musculoskeletal/locomotor function. We have provided baseline data for generating hypotheses to investigate in greater depth the specific biomechanical constraints that compromise the modern broiler's walking ability and propose that these factors should be considered in the selection for musculoskeletal health in the chickens of the future. Our new anatomical data for a wide range of domestic and wild-type chickens is useful in a comparative context and for deeper functional analysis including computer modelling/simulation of limb mechanics.

Breast is not always best: The effects of selective breeding on aspects of chicken/broiler locomotor design

Breast is not always best: The effects of selective breeding on aspects of chicken/broiler locomotor design

The effects of selective breeding against scrapie susceptibility on the genetic variability of the Latxa Black-Faced sheep breed

Breeding sheep populations for scrapie resistance could result in a loss of genetic variability. In this study, the effect on genetic variability of selection for increasing the ARR allele frequency was estimated in the Latxa breed. Two sources of information were used, pedigree and genetic polymorphisms (fifteen microsatellites). The results based on the genealogical information were conditioned by a low pedigree completeness level that revealed the interest of also using the information provided by the molecular markers. The overall results suggest that no great negative effect on genetic variability can be expected in the short time in the population analysed by selection of only ARR/ARR males. The estimated average relationship of ARR/ARR males with reproductive females was similar to that of all available males whatever its genotype: 0.010 vs. 0.012 for a genealogical relationship and 0.257 vs. 0.296 for molecular coancestry, respectively. However, selection of only ARR/ARR males implied important losses in founder animals (87 percent) and low frequency alleles (30 percent) in the ram population. The evaluation of mild selection strategies against scrapie susceptibility based on the use of some ARR heterozygous males was difficult because the genetic relationships estimated among animals differed when pedigree or molecular information was used, and the use of more molecular markers should be evaluated.

The effects of selective breeding against scrapie susceptibility on the genetic variability of the Latxa Black-Faced sheep breed

Breeding sheep populations for scrapie resistance could result in a loss of genetic variability. In this study, the effect on genetic variability of selection for increasing the ARR allele frequency was estimated in the Latxa breed. Two sources of information were used, pedigree and genetic polymorphisms (fifteen microsatellites). The results based on the genealogical information were conditioned by a low pedigree completeness level that revealed the interest of also using the information provided by the molecular markers. The overall results suggest that no great negative effect on genetic variability can be expected in the short time in the population analysed by selection of only ARR/ARR males. The estimated average relationship of ARR/ARR males with reproductive females was similar to that of all available males whatever its genotype: 0.010 vs. 0.012 for a genealogical relationship and 0.257 vs. 0.296 for molecular coancestry, respectively. However, selection of only ARR/ARR males implied important losses in founder animals (87 percent) and low frequency alleles (30 percent) in the ram population. The evaluation of mild selection strategies against scrapie susceptibility based on the use of some ARR heterozygous males was difficult because the genetic relationships estimated among animals differed when pedigree or molecular information was used, and the use of more molecular markers should be evaluated.

THE EVOLUTION OF AGING AND AGE-RELATED PHYSICAL DECLINE IN MIC SELECTIVELY BRED FOR HIGH VOLUNTARY EXERCISE

We tested whether selective breeding for early-age high voluntary exercise behavior over 16 generations caused the evolution of lifelong exercise behavior, life expectancy, and age-specific mortality in house mice (Mus domesticus). Sixteenth-generation mice from four replicate selection lines and four replicate random-bred control lines were individually housed from weaning through death and divided between two activity treatments (either with or without running wheels). Thus, there were four treatment groups: selection versus control crossed with active versus sedentary. The effects of selective breeding on life expectancy and age-specific mortality differed between females and males. In females, sedentary selection mice had early and high initial adult mortality and thus the lowest increases in mortality with age. Active selection females had the lowest early adult mortality, had limited mortality during midlife, and exhibited rapid increases in mortality rates at the very end of life; thus, they had deferred senescence. Median life expectancy was greater for both groups of selection females than for the two complementary groups of control females. Like females, sedentary selection males had the highest early adult mortality, and slow but steadily increasing mortality over the entire lifetime. Unlike the active selection females, active control males had the lowest mortality across the lifespan (until the end of life). Interestingly, the males with the lowest median life expectancy were those in the active selection treatment group. In both sexes, running (km/week) decreased over the lifetime to very low and virtually equivalent levels at the end of life in control and selection mice. Overall, these results demonstrate an evolutionary cost of selective breeding for males, regardless of exercise level, but a benefit for females when they have an outlet for the up-selected behavior. We conclude that correlated evolution of senescence occurs in mice selectively bred for high voluntary wheel running; exercise per se is beneficial for control mice of both sexes, but the impact on the effect of selection depends on sex; and the behavioral effect of exercise selection at an early age declines throughout the life span, which demonstrates decreasing genetic correlations over age for the genes involved in increased exercise.

The effects of selective breeding on the genetic structure of shrimp Fenneropenaeus chinensis populations

Seven AFLP primer sets were used to investigate the genetic structure of a wild base population and three generations of marine shrimp Fenneropenaeus chinensis selected for fast growth (F5–F7). More than 500 bands were generated in total. On average, each primer set detected 33.7 polymorphic markers. The expected average heterozygosity ranged from 0.085 to 0.097. As time under selection increased, genetic diversity tended to reduce, the differentiation between generations became less, and the variation of genetic structure of the populations became smaller.

THE EVOLUTION OF AGING AND AGE-RELATED PHYSICAL DECLINE IN MICE SELECTIVELY BRED FOR HIGH VOLUNTARY EXERCISE

We tested whether selective breeding for early-age high voluntary exercise behavior over 16 generations caused the evolution of lifelong exercise behavior, life expectancy, and age-specific mortality in house mice (Mus domesticus). Sixteenth-generation mice from four replicate selection lines and four replicate random-bred control lines were individually housed from weaning through death and divided between two activity treatments (either with or without running wheels). Thus, there were four treatment groups: selection versus control crossed with active versus sedentary. The effects of selective breeding on life expectancy and age-specific mortality differed between females and males. In females, sedentary selection mice had early and high initial adult mortality and thus the lowest increases in mortality with age. Active selection females had the lowest early adult mortality, had limited mortality during midlife, and exhibited rapid increases in mortality rates at the very end of life; thus, they had deferred senescence. Median life expectancy was greater for both groups of selection females than for the two complementary groups of control females. Like females, sedentary selection males had the highest early adult mortality, and slow but steadily increasing mortality over the entire lifetime. Unlike the active selection females, active control males had the lowest mortality across the lifespan (until the end of life). Interestingly, the males with the lowest median life expectancy were those in the active selection treatment group. In both sexes, running (km/week) decreased over the lifetime to very low and virtually equivalent levels at the end of life in control and selection mice. Overall, these results demonstrate an evolutionary cost of selective breeding for males, regardless of exercise level, but a benefit for females when they have an outlet for the up-selected behavior. We conclude that correlated evolution of senescence occurs in mice selectively bred for high voluntary wheel running; exercise per se is beneficial for control mice of both sexes, but the impact on the effect of selection depends on sex; and the behavioral effect of exercise selection at an early age declines throughout the life span, which demonstrates decreasing genetic correlations over age for the genes involved in increased exercise.

Phytosterol composition of hybrid Hibiscus seed oils.

The seed oils from fifteen hybrid Hibiscus varieties were analyzed for desmethyl sterol content to identify bioactive compounds that could promote the use of these oils for edible applications. Hibiscusis being developed as a new crop with edible and nutraceutical applications for the component tissues and tissue extracts. Previously, hybrid varieties were developed for ornamental purposes on the basis of flower morphology and color. Currently, the effects of selective breeding on seed oil components are of interest as these represent potential natural products with bioactive properties. In the present study, sterol structures were identified as the corresponding trimethyl silyl ether derivatives obtained from the unsaponifiable fraction of the seed oils. This material contained an average of 32 wt % sterols and exhibited a relative composition of sitosterol, 76.3%; campesterol, 10.3%; stigmasterol, 7.3%; 5-avenasterol, 4.4%; and cholesterol, 0.6%. The content of 5-avenasterol showed statistically significant variation among the hybrid varieties with a range of 1.2-5.8%.

Understanding behaviour: the relevance of ethological approaches in laboratory animal science

Applied ethology has traditionally focused on farm animal species, whereas there has been much less research directed at understanding the behaviour of laboratory animals in relation to their use as models in research. In this paper, we identify four areas in which ethological approaches could help improve the welfare of laboratory rodents while at the same time enhancing the validity of research based on them. These areas are: (1) the effects of selective breeding and gene manipulations on the animals’ ability to cope with the laboratory environment; (2) the effects of barren housing conditions on behaviour and the mechanisms underlying normal control of behaviour; (3) the sensory perception of the laboratory environment by the animals; and (4) the applicability of standard behavioural tests and the potential for improving them by taking animals’ species-specific characteristics into account. Given the current increase in the use of rodents in the life sciences, these four areas represent promising areas of future research in applied animal behaviour science.

Effects of selective breeding for infant rat ultrasonic vocalization on cardiac responses to isolation.

Heart rates (HR) and autonomic control of heart period (HP) during maternal separation and isolation were measured at postnatal days (P) 10 and 18 in rat pups selectively bred for high, low, and random rates of infant ultrasonic vocalization. P10 pups displayed no significant line differences in HRs, strong tonic basal sympathetic control of HP and little sympathetic reactivity to isolation, and no evidence of tonic baseline or phasic parasympathetic responses to isolation. At P18, during isolation and recovery, Low HRs were significantly higher compared with Random and High pups. High HRs were significantly higher compared with the Random line in the last third of isolation and through recovery. The higher HRs of Low pups during stress were due to greater parasympathetic withdrawal, but greater sympathetic activation could not be ruled out. Higher HRs in High pups were due to increased sympathetic activation. Thus, increases in HR responses in the selected lines are due to different underlying autonomic processes.

Effects of selective breeding for infant rat ultrasonic vocalization on cardiac responses to isolation.

Effects of selective breeding for infant rat ultrasonic vocalization on cardiac responses to isolation.

Direct Evidence for a Cause-Effect Link Between Ethanol Potentiation of GABAA Receptor Function and Intoxication From Hyperbaric Studies in C57, LS, and SS Mice

Background: This article uses a direct ethanol antagonist, increased atmospheric pressure, to further test the causative link between ethanol potentiation of γ-aminobutyric acid (GABA) type A receptor function and ethanol's behavioral effects. This was done by determining whether initial biochemical findings in long-sleep (LS) mice extended to other genotypes and whether the previously reported insensitivity of short-sleep (SS) mice to pressure antagonism of ethanol-induced loss of righting reflex extended to a nonselected ethanol-induced behavior. Methods: The effects of 12 times normal atmospheric pressure of helium-oxygen gas (heliox) versus ethanol (25–200 mM) potentiation of GABA-activated Cl− uptake in brain membranes (microsacs) from C57, LS, and SS mice were tested by using a 36Cl− flux assay. The effects of pressure versus ethanol's (2 g/kg) anticonvulsant effect in SS mice were tested by using time to onset of isoniazid-induced myoclonic seizures. Results: Exposure to 12 times normal atmospheric pressure heliox antagonized ethanol potentiation of GABA-activated Cl− uptake in all three genotypes across a range of ethanol concentrations that cause ethanol's behavioral and anesthetic effects. Pressure did not affect baseline receptor function. The threshold for initiating ethanol potentiation differed between genotypes in accordance with their behavioral sensitivities to ethanol (C57 and LS, ≤25 mM; SS, >50 mM). Pressure antagonized ethanol's anticonvulsant effect in SS mice. Conclusions: The results add important direct evidence supporting the hypothesis that ethanol potentiation of GABAA receptor function is an initial action of ethanol causing its behavioral effects. These findings also provide insight into possible effects of selective breeding on GABAA receptor function.