Selective breeding of rats differing in sensitivity to the effects of acute ethanol administration

A multicomponent ethanol response battery across a cumulative dose ethanol challenge reveals diminished adolescent rat ethanol responsivity relative to adults

Adolescence is a conserved developmental period associated with low alcohol responsivity, which can contribute to heavy drinking and development of an alcohol use disorder (AUD) later in life. To investigate ethanol responsivity between adolescent and adult rats, we developed an ethanol response battery (ERB) to assess acute ethanol responses across cumulative doses of ethanol during the rising phase of the blood ethanol curve. We tested the hypothesis that adolescent male and female rats would exhibit lower ethanol responsivity to a cumulative ethanol challenge relative to adults. Male and female adolescent (postnatal day [P]40) and adult (P85) Wistar rats underwent ERB assessment following consecutive doses of ethanol (i.e., 1.0, 1.0, and 1.0 g/kg) to produce cumulative ethanol doses of 0.0, 1.0, 2.0, and 3.0 g/kg. The ERB consisted of (1) the 6-point behavioral intoxication rating scale, (2) body temperature assessment, (3) tail blood collection, (4) accelerating rotarod assessment, (5) tilting plane assessment, and (6) loss of righting reflex (LORR) assessment. Across cumulative ethanol doses, adolescent and adult rats evidenced progressive changes in ERB measures. On the ERB, adolescent rats of both sexes evidenced (1) lower intoxication rating, (2) blunted hypothermic responses, particularly in females, (3) longer latencies to fall from the accelerating rotarod, and (4) less tilting plane impairment relative to adults despite comparable BECs. All adult rats, regardless of sex, displayed a LORR at the 3.0 g/kg cumulative ethanol dose while among the adolescent rats, only one male rat and no females showed the LORR. These data reveal decreased adolescent ethanol responsivity across body temperature, intoxication, balance, and coordination responses to a cumulative ethanol challenge as assessed using the novel ERB relative to adults. The results of this study suggest that adolescent-specific low ethanol responsivity may contribute to adolescent binge drinking and increased risk for development of an AUD.

Diazepam and ethanol differently modulate neuronal activity in organotypic cortical cultures

Background

The pharmacodynamic results of diazepam and ethanol administration are similar, in that each can mediate amnestic and sedative-hypnotic effects. Although each of these molecules effectively reduce the activity of central neurons, diazepam does so through modulation of a more specific set of receptor targets (GABA_A receptors containing a γ-subunit), while alcohol is less selective in its receptor bioactivity. Our investigation focuses on divergent actions of diazepam and ethanol on the firing patterns of cultured cortical neurons.

Method

We used electrophysiological recordings from organotypic slice cultures derived from Sprague–Dawley rat neocortex. We exposed these cultures to either diazepam (15 and 30 µM, n = 7) or ethanol (30 and 60 mM, n = 11) and recorded the electrical activity at baseline and experimental conditions. For analysis, we extracted the episodes of spontaneous activity, i.e., cortical up-states. After separation of action potential and local field potential (LFP) activity, we looked at differences in the number of action potentials, in the spectral power of the LFP, as well as in the coupling between action potential and LFP phase.

Results

While both substances seem to decrease neocortical action potential firing in a not significantly different (p = 0.659, Mann–Whitney U) fashion, diazepam increases the spectral power of the up-state without significantly impacting the spectral composition, whereas ethanol does not significantly change the spectral power but the oscillatory architecture of the up-state as revealed by the Friedman test with Bonferroni correction (p < 0.05). Further, the action potential to LFP-phase coupling reveals a synchronizing effect of diazepam for a wide frequency range and a narrow-band de-synchronizing effect for ethanol (p < 0.05, Kolmogorov–Smirnov test).

Conclusion

Diazepam and ethanol, induce specific patterns of network depressant actions. Diazepam induces cortical network inhibition and increased synchronicity via gamma subunit containing GABA_A receptors. Ethanol also induces cortical network inhibition, but without an increase in synchronicity via a wider span of molecular targets.

Quantitative trait loci for sensitivity to acute ethanol and ethanol consummatory behaviors in rats

Individuals with a low initial response to alcohol (i.e., ethanol) are at greater risk of developing alcohol abuse or dependence later in life. Similar to humans, individual differences in ethanol sensitivity also can be seen in rats, and several laboratories have used these individual differences to generate selectively bred rats that differ in acute ethanol sensitivity. We have worked with two sets of such rats (Inbred High or Low Alcohol Sensitivity strains, IHAS or ILAS, respectively; Inbred Alcohol Tolerant or Non-Tolerant strains, IAT and IANT, respectively) and have confirmed previously mapped quantitative trait loci (QTL) for these acute differences with the use of recombinant congenic lines; however, the relationship between acute sensitivity and ethanol drinking in these rats has yet to be determined. Thus, here we tested the hypothesis that QTLs underlying variation in initial low sensitivity to ethanol also will modulate variation in ethanol drinking behaviors. Separate groups of selectively inbred parent and congenic rats were tested for the loss of righting response (LORR) and also assessed for ethanol consummatory behavior using either operant self-administration or an intermittent-access two-bottle choice procedure. LORR testing confirmed the presence of a LORR duration QTL in all of the congenics; however, the lack of a corresponding difference in blood ethanol concentration at the regaining of the righting response suggests that these QTLs may be mediating a difference in ethanol metabolism rather than in neuronal sensitivity. IHAS/ILAS-derived congenic rats did not differ from parent rats at any point during operant self-administration. IAT/IANT-derived congenic rats showed small, but significant, increases in ethanol consumption relative to the parent strains only during the initial stages of operant self-administration. In contrast to operant testing, IHAS/ILAS-derived congenic rats showed significantly greater ethanol consumption and preference than parent rats during intermittent-access testing. There were not differences, however, between IAT/IANT congenic and parent rats during intermittent access. These data support the hypothesis that there is a genetic relationship between initial ethanol sensitivity and ethanol consumption, at least for the IHAS/ILAS-derived congenic rats. Our current studies, however, cannot eliminate pharmacokinetic or taste preference factors as contributing to the rats' responses, nor can we eliminate the possibility of a linkage effect because of the fairly large size of the QTL intervals; i.e., distinct genes may be mediating the acute sensitivity and drinking responses.

Chronic nicotine treatment differentially modifies acute nicotine and alcohol actions on GABA(A) and glutamate receptors in hippocampal brain slices

BACKGROUND AND PURPOSE

Tobacco and alcohol are often co-abused producing interactive effects in the brain. Although nicotine enhances memory while ethanol impairs it, variable cognitive changes have been reported from concomitant use. This study was designed to determine how nicotine and alcohol interact at synaptic sites to modulate neuronal processes.

EXPERIMENTAL APPROACH

Acute effects of nicotine, ethanol, and both drugs on synaptic excitatory glutamatergic and inhibitory GABAergic transmission were measured using whole-cell recording in hippocampal CA1 pyramidal neurons from brain slices of mice on control or nicotine-containing diets.

KEY RESULTS

Acute nicotine (50 nM) enhanced both GABAergic and glutamatergic synaptic transmission; potentiated GABA(A) receptor currents via activation of α7* and α4β2* nAChRs, and increased N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor currents through α7* receptors. While ethanol (80 mM) also increased GABA(A) currents, it inhibited NMDA currents. Although ethanol had no effect on AMPA currents, it blocked nicotine-induced increases in NMDA and AMPA currents. Following chronic nicotine treatment, acute nicotine or ethanol did not affect NMDA currents, while the effects of GABAergic responses were not altered.

CONCLUSIONS AND IMPLICATIONS

Acute ethanol ingestion selectively attenuated nicotine enhancement of excitatory glutamatergic NMDA and AMPA receptor function, suggesting an overall reduction in excitatory output from the hippocampus. It also indicated that ethanol could decrease the beneficial effects of nicotine on memory performance. In addition, chronic nicotine treatment produced tolerance to the effects of nicotine and cross-tolerance to the effects of ethanol on glutamatergic activity, leading to a potential increase in the use of these drugs.

Liquid-diet with alcohol alters maternal, fetal and placental weights and the expression of molecules involved in integrin signaling in the fetal cerebral cortex

Maternal alcohol consumption during pregnancy causes wide range of behavioral and structural deficits in children, commonly known as Fetal Alcohol Syndrome (FAS). Children with FAS may suffer behavioral deficits in the absence of obvious malformations. In rodents, the exposure to alcohol during gestation changes brain structures and weights of offspring. The mechanism of FAS is not completely understood. In the present study, an established rat (Long-Evans) model of FAS was used. The litter size and the weights of mothers, fetuses and placentas were examined on gestation days 18 or 20. On gestation day 18, the effects of chronic alcohol on the expression levels of integrin receptor subunits, phospholipase-Cγ and N-cadherin were examined in the fetal cerebral cortices. Presence of alcohol in the liquid-diet reduced the consumption and decreased weights of mothers and fetuses but increased the placental weights. Expression levels of β₁ and α₃ integrin subunits and phospholipase-Cγ₂ were significantly altered in the fetal cerebral cortices of mothers on alcohol containing diet. Results show that alcohol consumption during pregnancy even with protein, mineral and vitamin enriched diet may affect maternal and fetal health, and alter integrin receptor signaling pathways in the fetal cerebral cortex disturbing the development of fetal brains.

A major QTL for acute ethanol sensitivity in the alcohol tolerant and non-tolerant selected rat lines

The Alcohol Tolerant and Alcohol Non-Tolerant rats (AT, ANT) were selectively bred for ethanol-induced ataxia as measured on the inclined plane. Here we report on a quantitative trait locus (QTL) study in an F(2) intercross population derived from inbred AT and ANT (IAT, IANT) and a follow-up study of congenics that were bred to examine one of the mapped QTLs. Over 1200 F(2) offspring were tested for inclined plane sensitivity, acute tolerance on the inclined plane, duration of the loss of righting reflex (LORR) and blood ethanol at regain of the righting reflex (BECRR). F(2) rats that were in the upper and lower 20% for inclined plane sensitivity were genotyped with 78 SSLP markers. Significant QTLs for inclined plane sensitivity were mapped on chromosomes 8 and 20; suggestive QTLs were mapped on chromosomes 1, 2 and 3. Highly significant QTLs for LORR duration (LOD = 12.4) and BECRR (LOD = 5.7) were mapped to the same locus on chromosome 1. Breeding and testing of reciprocal congenic lines confirmed the chromosome 1 LORR/BECRR QTL. A series of recombinant congenic sub-lines were bred to fine-map this QTL. Current results have narrowed the QTL to an interval of between 5 and 20 Mb. We expect to be able to narrow the interval to less than 5 Mb with additional genotyping and continued breeding of recombinant sub-congenic lines.

Short-term selection for acute ethanol tolerance and sensitization from an F2 population derived from the high and low alcohol-sensitive selectively bred rat lines

Previous studies have identified quantitative trait loci (QTL) in the inbred high and low alcohol-sensitive rat (IHAS1 and ILAS1) strains. The original development of the strains involved selection for ethanol sensitivity based on duration of the loss of the righting reflex (LORR) after a standard dose of ethanol. This paper confirms some of these QTL using a short-term selection procedure based on the difference between the blood ethanol level at LORR and regain of the righting response. An F(2) population of rats was developed by a reciprocal cross of IHAS1 and ILAS1 rats. Selection for five generations was carried out using delta-blood ethanol concentration (dBEC) as the selection trait, where dBEC=BECLR (BEC at loss of righting reflex)-BECRR (BEC at regain of righting reflex). The lines were labeled tolerant (TOL) or sensitive (SENS). Approximately one-third of the offspring for each generation in each line were genotyped using DNA markers that had been previously found to be linked to QTL on chromosomes 1, 2, 5, 12, and 13. By the fifth generation of selection, the lines showed a very large difference in dBEC, BECRR, and duration of LORR; BECLR showed little segregation during the selection, and latency to lose the righting reflex showed none. IHAS allele frequency increased in the SENS line for markers on chromosomes 1, 5, 12, and 13 while ILAS allele frequency increased in the TOL line. These results were in good agreement with the two previous QTL studies. On chromosome 2, the selection resulted in an accumulation of ILAS alleles in both lines. This study provides independent confirmation of the location of QTL on chromosomes 1, 5, 12, and 13 for ethanol sensitivity. It also suggests that genetic differences in duration of LORR are mediated primarily by the dBEC phenotype.

Fearfulness in a large N/Nih genetically heterogeneous rat stock: differential profiles of timidity and defensive flight in males and females

Anxiety-related behaviors were evaluated across various tests in a large sample (n=787, both sexes) of genetically heterogeneous (N/Nih-HS) rats, derived from an eight-way cross of inbred strains. These tests either evoke unlearned (black-white box, BWB-; novel-cage activity, NACT-; elevated "zero" maze, ZM-; baseline acoustic startle response, BAS-) or learned (fear-potentiated startle, FPS-; two-way active-shuttle box-avoidance acquisition, SHAV-) anxious/fearful responses. The results showed that, with the exception of fear-potentiated startle, almost all (unlearned and learned) behaviors assessed fit with a pattern of sex effects characterized by male rats as being more fearful than females. We applied factor analyses (oblique rotation) to each sex, with the final two-factor solution showing: (1) a first factor (labelled as "Timidity") comprising BWB, NACT and ZM variables in both sexes, plus SHAV responding in the case of males, and (2) a second factor (called "Defensive Flight") which grouped BAS, FPS, and SHAV responding in both sexes. An additional regression analysis showed significant influences of (unlearned) risk assessment (i.e. stretch-attendance) behavior on SHAV in males, while FPS was the main variable positively influencing SHAV (in the intermediate and advanced phases of acquisition) in females. This indicates, for the first time, that fear-potentiated startle may have a facilitating role in the rat's active responses (at least in females) to the cue in the intermediate to advanced phases (i.e. when the initial "passive avoidance/active avoidance" begins to fade) of shuttle box avoidance acquisition. The results of this first extensive behavioral evaluation of N/Nih-HS rats are discussed in terms of their potential usefulness for present and future neurobehavioral and genetic studies of fearfulness/anxiety.

Confirmation of quantitative trait loci for ethanol sensitivity and neurotensin receptor density in crosses derived from the inbred high and low alcohol sensitive selectively bred rat lines

RATIONALE

Genetically influenced alcohol sensitivity is thought to be an important risk factor for the development of alcoholism. An effective first step for identifying genes that mediate variation in alcohol sensitivity is through quantitative trait loci (QTL) mapping in model organisms.

OBJECTIVE

Fourteen provisional QTLs related to alcohol sensitivity were previously mapped in an F2 derived from the IHAS1 and ILAS1 rat lines. The objective of the current study was to confirm those QTLs in an independently derived F2 and in congenics that were bred for two of the loci.

MATERIALS AND METHODS

IHAS1 X ILAS1 F2 (n=450) were tested for alcohol-induced loss of righting reflex (LORR), blood ethanol concentration at regain of righting reflex (BECRR), sensitivity and acute tolerance on the Rotarod, and neurotensin receptor density (NTR1). Rats were genotyped at the 14 candidate loci and QTL mapping was conducted. Reciprocal congenic strains were bred for loci on chromosomes 2 and 5 and tested for LORR and BECRR.

RESULTS

Four LORR QTLs were mapped at the suggestive or significant level (chromosomes 2, 5, 12, and 13). BECRR was mapped to chromosomes 5, 12, and 13 either in the original or current experiment. Results of the congenic experiment also support QTLs for LORR and BECRR on chromosomes 2 and 5. QTLs for NTR1 density and behavior on the Rotarod were not confirmed.

CONCLUSIONS

QTL mapping in crosses derived from the IHAS1 and ILAS1 has successfully identified loci related to alcohol sensitivity. Recombinant congenics are now being bred to more finely map the confirmed QTLs.

Genetic Dissociation Between Ethanol Sensitivity and Rapid Tolerance in Mouse and Rat Strains Selectively Bred for Differential Ethanol Sensitivity

BACKGROUND

The Inbred Long- and Short-Sleep mice (ILS and ISS) and the Inbred High- and Low-Alcohol-Sensitive rats (IHAS and ILAS) were selectively bred for differential alcohol sensitivity with use of the duration of loss-of-righting-reflex test (LORR), with the IHAS and ILS animals being much more sensitive than the ILAS and ISS animals, respectively. The current study was undertaken to determine whether acute sensitivity in these strains is genetically correlated to a rapid tolerance to alcohol, a form of tolerance that is evident 24 hr after a single alcohol dose.

METHODS

Separate groups of animals were administered a single pretreatment dose of alcohol (0-6 g/kg for the mice; 0-4 g/kg for the rats). Alcohol sensitivity was tested 24 hr later with the LORR test, and blood ethanol concentration was tested at regain of righting (BECRR). Alcohol-induced hypothermia also was determined in the mice. Independently derived replicate rat strains were used for all experiments (IHAS1, ILAS1; IHAS2, ILAS2); no such replicates exist for the ILS and ISS strains.

RESULTS

Alcohol pretreatment caused a dose-dependent decrease in LORR duration accompanied by an increase in BECRR in the ILS strain, but LORR increased in the ISS strain with no effect on BECRR. Both strains became hypothermic during the LORR test on day two, but the only significant effect of alcohol pretreatment was in the ISS strain, in which alcohol-induced hypothermia was enhanced. Alcohol pretreatment caused a significant dose-dependent decrease in LORR duration accompanied by an increase in BECRR in the IHAS1 but not in the IHAS2 strain. In contrast, ILAS1 and ILAS2 strains both showed a significant increase in LORR duration and also a significant increase in BECRR.

CONCLUSIONS

Alcohol pretreatment caused a dose-dependent decrease in LORR duration and an increase in BECRR in the IHAS1 and ILS strain, suggesting the development of functional rapid tolerance. In contrast, LORR duration increased in the ILAS1, ILAS2, and ISS groups, but BECRR either increased (ILAS1, ILAS2) or did not change (ISS). These observations suggest that central nervous system sensitivity was decreased in the ILAS1 and ILAS2 groups (i.e., rapid functional tolerance) or unchanged in the ISS strain, but that some pharmacokinetic property also was altered in these strains. Overall, the results do not support a genetic relation between alcohol sensitivity and the development of rapid tolerance.

Animal models of complex diseases: An initial strategy

We speculated that the rise in atmospheric oxygen from 2 billion years ago was so integral for the evolution of biocomplexity that it must also associate strongly with complex diseases. As a remote test of this idea, we hypothesized that lines contrasting for disease and health would emerge from artificial selection for low and high aerobic treadmill running capacity. Eleven generations of selection in rats produced lines that differed by 347% in running capacity. The low line demonstrated health risk factors including higher visceral adiposity, blood pressure, insulin, and triglycerides. The high line was superior for VO2max, economy of running, heart function, and nitric oxide-induced vascular dilation.

Quantitative trait loci mapping for ethanol sensitivity and neurotensin receptor density in an F2 intercross derived from inbred high and low alcohol sensitivity selectively bred rat lines

BACKGROUND

Genetic variance in initial sensitivity to ethanol has been implicated as a risk factor for the development of alcoholism. Identification of the genes that confer differential initial sensitivity is an important goal for the development of new treatment strategies and for a comprehensive understanding of the mechanism of ethanol's action. Quantitative trait loci (QTL) mapping for initial sensitivity and other ethanol-related behavioral traits in model organisms has become an important first step for the ultimate identification of genes that contribute to variation in ethanol responses.

METHODS

An F(2) intercross was made from the Inbred High and Low Alcohol Sensitivity rat lines (IHAS and ILAS). The F(2) rats were tested for duration of the loss of righting reflex test (LORR); blood ethanol concentration at regain of righting reflex (BECrrr); BEC at the first time to reach criterion on the rotarod after 1.6 g/kg of ethanol (BEC1); acute functional tolerance on the rotarod (AFT); and high-affinity neurotensin receptor (NTR1) density in the nucleus accumbens (NAc), caudate putamen (CP), and ventral midbrain (VMB). A full genome scan with an average marker spacing of 16.8 cM for interval QTL mapping was conducted on the F(2) rats (N = 363).

RESULTS

Seven significant or suggestive QTL were detected for LORR, one for BECrrr, three for BEC1, two for NTR1 binding in the CP, and one for binding in the NAc, but none were mapped for AFT or NTR1 binding density in the VMB. Effect size of the seven LORR QTL, the trait for which the parental strains were selected, ranged from 3 to 4%, with all accounting for approximately 22% of the total phenotypic variation. One of the LORR QTL on chromosome 2 (approximately 87 cM) was significant, and a second QTL on chromosome 5 (approximately 37 cM) was suggestive for both LORR and BECrrr.

CONCLUSIONS

The results indicate that segregating populations derived from the IHAS and ILAS strains can be used for mapping ethanol sensitivity QTL. The chromosome 2 LORR QTL may confer variation in ethanol metabolism, whereas the chromosome 5 LORR/BECrrr QTL likely mediates central nervous system ethanol sensitivity. The small number or absence of QTL for BEC1, AFT, and NTR1 receptor density suggests that genetic variation for these traits is minimal in the IHAS/ILAS strains and/or the effect size of QTL for these traits is too small to be mapped efficiently in this sample of F(2) rats. The ultimate identification of genes underlying these alcohol sensitivity QTL will contribute to our understanding of the actions of alcohol in the central nervous system if not to a deeper understanding of the genetic risk factors for alcoholism.

Phorbol Ester Differentiates the Levels of [3H]MK-801 Binding in Rats Lines Selected for Differential Sensitivity to the Hypnotic Effects of Ethanol

These studies addressed the possible involvement between sensitivity to the hypnotic action of ethanol and function of the NMDA receptor. The studies were carried out using high-alcohol sensitive (HAS) and low-alcohol sensitive (LAS) rats, two rats having differential sensitivity to the acute hypnotic action of ethanol. The animal models were developed by a selective breeding experiment. Using a quantitative autoradiograph technique, it was demonstrated that [3H]MK-801 binding to the NMDA receptor was highest in hippocampus in both HAS and LAS rats, but significant [3H]MK-801 binding was also detected in cortex, caudate-putamen, and thalamus of HAS and LAS rats. The density of [3H]MK-801 binding was lower only in cerebellar granule layers of untreated HAS rats as compared to the same brain area in untreated LAS rats. Activation of protein kinase C (PKC) by 100 nM PDBu, increased [3H]MK-801 binding in cortex, caudate-putamen, thalamus, central gray, and cerebellum of HAS rats but activation of PKC did not influence [3H]MK-801 binding in LAS rats. These activation of PKC differentiates between [3H]MK-801 binding of HAS and LAS rats in frontal cortex (layer II-IV and cingulate), caudate-putamen, and ventral lateral thalamic nuclei. The basal level of PKC-gamma mRNA was higher in HAS rats than that of LAS rats. These results suggest that the activation of PKC potentiates NMDA receptor function of the rat line which is more sensitive to alcohol (HAS) but does not affect [3H]MK-801 binding of alcohol resistant (LAS) rats.

Genetic polymorphisms: Impact on the risk of fetal alcohol spectrum disorders

Clinical reports on monozygotic and dizygotic twins provided the initial evidence for the involvement of genetic factors in risk vulnerability for fetal alcohol spectrum disorders (FASD) including fetal alcohol syndrome (FAS). Research with selectively bred and inbred rodents, genetic crosses of these lines and strains, and embryo culture studies have further clarified the role of both maternal and fetal genetics in the development of FASD. Research to identify specific polymorphisms contributing to FASD is still at an early stage. To date, polymorphisms of only one of the genes for the alcohol dehydrogenase enzyme family, the ADH1B, have been demonstrated to contribute to FASD vulnerability. In comparison with ADH1B*1, both maternal and fetal ADH1B*2 have been shown to reduce risk for FAS in a mixed ancestry South African population. ADH1B*3 appears to afford protection for FASD outcomes in African-American populations. Other candidate genes should be examined with respect to FASD risk, including those for the enzymes of serotonin metabolism, in particular the serotonin transporter. By its very nature, alcohol teratogenesis is the expression of the interaction of genes with environment. The study of genetic factors in FASD falls within the new field of ecogenetics. Understanding of the array of genetic factors in FASD will be enhanced by future genetic investigations, including case-control, family association, and linkage studies.

Ethanol differentially enhances hippocampal GABA A receptor-mediated responses in protein kinase C gamma (PKC gamma) and PKC epsilon null mice

Ethanol intoxication results partly from actions of ethanol at specific ligand-gated ion channels. One such channel is the GABA(A) receptor complex, although ethanol's effects on GABA(A) receptors are variable. For example, we found that hippocampal neurons from selectively bred mice and rats with high hypnotic sensitivity to ethanol have increased GABA(A) receptor-mediated synaptic responses during acute ethanol treatment compared with mice and rats that display low behavioral sensitivity to ethanol. Here we investigate whether specific protein kinase C (PKC) isozymes modulate hypnotic and GABA(A) receptor sensitivity to ethanol. We examined acute effects of ethanol on GABA(A) receptor-mediated inhibitory postsynaptic currents (IPSCs) in mice lacking either PKCgamma (PKCgamma(-/-)) or PKCepsilon (PKCepsilon(-/-)) isozymes and compared the results to those from corresponding wild-type littermates (PKCgamma(+/+) and PKCepsilon(+/+)). GABA(A) receptor-mediated IPSCs were evoked in CA1 pyramidal neurons by electrical stimulation in stratum pyramidale, and the responses were recorded in voltage-clamp mode using whole-cell patch recording techniques. Ethanol (80 mM) enhanced the IPSC response amplitude and area in PKCgamma(+/+) mice, but not in the PKCgamma(-/-) mice. In contrast, ethanol markedly potentiated IPSCs in the PKCepsilon(-/-) mice, but not in PKCepsilon(+/+) littermates. There was a positive correlation between ethanol potentiation of IPSCs and the ethanol-induced loss of righting reflex such that mice with larger ethanol-induced increases in GABA(A) receptor-mediated IPSCs also had higher hypnotic sensitivity to ethanol. These results suggest that PKCgamma and PKCepsilon signaling pathways reciprocally modulate both ethanol enhancement of GABA(A) receptor function and hypnotic sensitivity to ethanol.

Differential vulnerability to motor deficits in second replicate HAS and LAS rats following neonatal alcohol exposure

Children exposed prenatally to alcohol suffer from a variety of behavioral alterations. However, variation exists in the pattern and severity of these alcohol-related neurodevelopmental disorders. We examined the influence of alcohol sensitivity in the etiology of fetal alcohol effects by studying rat lines selectively bred for extremes in alcohol-induced sleep time: high-alcohol-sensitive (HAS) and low-alcohol-sensitive (LAS) rats. Using subjects from the first replicate, we previously reported that HAS rats exposed to alcohol during development were more vulnerable to ethanol-induced hyperactivity and motor deficits compared to LAS rats. To determine if these effects were, in fact, related to the trait for which these subjects were selected, the present study examined the consequences of developmental alcohol exposure in second replicate HAS and LAS rats. Second replicate HAS and LAS rats, as well as Sprague-Dawley rats, were exposed to 6.0 g/kg/day ethanol on Postnatal Days (PD) 4-9, a period of brain development equivalent to the third trimester, via an artificial rearing procedure. Artificially and normally reared controls were included. Activity was measured on PD 18-21 and parallel bar motor coordination on PD 30-32. Ethanol exposure produced hyperactivity in all genetic groups, and there were no differences among HAS and LAS rats. In contrast, consistent with findings from the first replicate, ethanol-exposed HAS rats were more impaired on the motor coordination task compared with LAS rats. These data suggest that genetically mediated responses to alcohol may relate to behavioral vulnerability to motor deficits following developmental alcohol exposure. They also provide evidence that genetic factors play a role in fetal alcohol effects and suggest that phenotypic markers may indicate individuals at high risk for some fetal alcohol effects.

4-hydroxynonenal decreases interleukin-6 expression and protein production in primary rat Kupffer cells by inhibiting nuclear factor-kappaB activation

Kupffer cells have been documented to play an important role in the early events of liver injury and regeneration by releasing biologically active mediators such as interleukin-6 (IL-6). 4-Hydroxy-trans-2-nonenal (4-HNE), a major end product of lipid peroxidation, has multiple cytotoxic effects and is implicated in chemical-induced liver injury. Consequently, the purpose of this study was to evaluate the ability of 4-HNE to modulate IL-6 production in isolated primary rat Kupffer cells. 4-HNE (0.1-10 microM) reduced both lipopolysaccharide (LPS)-induced IL-6 protein production and mRNA levels. The role of nuclear factor-kappaB (NF-kappaB) in IL-6 induction was elucidated using Kupffer cells transduced in vitro with a recombinant adenovirus containing a IkappaBalpha super-repressor resistant to phosphorylation and degradation (Ad5IkappaB). Using this system, LPS-induced IL-6 protein production was inhibited by 65% in Ad5IkappaB-infected cells. The treatment of Kupffer cells for 1 h with 4-HNE followed by stimulation for 1 h with LPS (500 ng/ml) resulted in a concentration-dependent decrease in NF-kappaB activation. Similarly, decreased NF-kappaB activity in these cells paralleled a reduction in IkappaBalpha mRNA levels. Furthermore, upon LPS stimulation, 4-HNE stabilized IkappaBalpha, which corresponded to a decrease in phosphorylated IkappaBalpha. At lower 4-HNE concentrations (0-5 microM), interactions between p65 and IkappaBalpha proteins were maintained as detected by immunoprecipitation-immunoblot analyses. In conclusion, these data suggest that 4-HNE inhibits IL-6 production in rat Kupffer cells by preventing activation of the NF-kappaB pathway and suppressing IkappaBalpha phosphorylation. These results have functional implications in that 4-HNE may interfere with the ability of Kupffer cells to produce cytokines proposed to play an important role in liver regeneration.

Differential taurine responsiveness to ethanol in high- and low-alcohol sensitive rats: a brain microdialysis study

Several microdialysis studies have investigated the effects of acute ethanol on extracellular amino acids in various rat brain regions. However, these studies led to conflicting results, suggesting that individual differences between rat strains and lines may play an important role. In the present study, high-alcohol sensitive (HAS) and low-alcohol sensitive (LAS) rats were used to investigate the possible relationship between ethanol sensitivity and the concentrations of extracellular amino acids in the nucleus accumbens. Several groups of HAS and LAS rats were injected with either saline or ethanol (1.0, 2.0 or 3.0 g/kg, i.p.) and the concentrations of amino acids in the nucleus accumbens microdialysates were assayed by electrochemical detection. Acute ethanol induced a dose-dependent increase in extracellular taurine concentrations. However, this increase was significantly reduced at 2.0 and 3.0 g/kg ethanol in HAS rats relative to LAS rats. Since the biological functions of taurine suggest its implication in the reduction of ethanol adverse effects, a higher increase in taurine concentrations may contribute to the lower ethanol sensitivity of LAS rats. Although 2.0 and 3.0 g/kg ethanol did not affect extracellular glutamate concentrations, a significant increase in glutamate was observed after 1.0 g/kg ethanol to HAS rats but not to LAS rats. Such an effect remains unexplained but suggests that discrepancies between the results of previous microdialysate studies may be related to differences in the ethanol sensitivities of various rat strains.

Sleep-time variation for ethanol and the hypnotic drugs tribromoethanol, urethane, pentobarbital, and propofol within outbred ICR mice

To evaluate the phenotypic variation within a commercial outbred mouse stock, we examined sleep-time (or duration of loss of righting reflex) of outbred ICR mice after i.p. injection of ethanol (4.0 g/kg of body weight), urethane (1.3 g), tribromoethanol (250 mg), and pentobarbital (60 mg), and after i.v. injection of propofol (30 mg). We observed high-grade individual differences in sleep-time that ranged from 0 to 179 min, 83.1 +/- 4.3 (mean and SEM of 100 mice) for ethanol; 0 to 169 min, 64.5 +/- 3.1 for pentobarbital; 0 to 160 min, 36.6 +/- 3.6 for urethane; 0 to 120 min, 21.5 +/- 2.2 for tribromoethanol; and 3 to 20.5 min, 7.1 +/- 0.3 for propofol. This extensive phenotypic variance within the outbred stock was as great as the variation reported among inbred strains or selected lines, and the varied susceptibility within the colony was inherited by Jcl:ICR-derived inbred strains IAI, ICT, IPI, and IQI. The range of sleep-time variance for ethanol, pentobarbital, urethane, tribromoethanol, and propofol within four-way cross hybrid Jcl:MCH(ICR) mice was 86.6%, 63.3%, 124%, 61.0%, and 53.1% that of outbred Jcl:ICR mice, respectively. The present study indicates that phenotypic variance within an outbred Jcl:ICR stock was at high risk for susceptibility to the drugs that depress the central nervous system and that Jcl:ICR-derived inbreds may be an excellent source of animal models for studying the anesthesia gene.

Activation of Kupffer cells during the course of carbon tetrachloride-induced liver injury and fibrosis in rats

Kupffer cells are involved in the pathogenesis of chemically mediated liver injury through release of biologically active mediators that promote the pathogenic process. The purpose of this study was to elucidate specific biochemical and molecular changes occurring in Kupffer cells throughout a time course of carbon tetrachloride (CCl(4))-mediated liver injury and fibrosis. Rats were administered 1 ml/kg of CCl(4) (10% v/v olive oil) twice weekly for up to 6 weeks. Plasma alanine aminotransferase values and hematoxylin-and-eosin- and trichrome-stained liver sections indicated minor liver damage at 2 weeks followed by increased damage and collagen deposition by 4 and 6 weeks. Additionally, mRNA levels in Kupffer cells isolated from CCl(4)-treated rats demonstrated significant increases in tumor necrosis factor alpha (TNF alpha); tumor growth factor beta; interleukin-6 (IL-6); interleukin 1 beta; cyclooxygenase 2; CD14, and I kappa B alpha transcripts after 2 and 4 weeks of treatment. However, the expression of these genes at 6 weeks was similar to that of controls. Increased gene expression of cytokines in Kupffer cells isolated from CCl(4)-treated rats was accompanied by increases in protein production of TNF alpha, IL-6, IL-1 beta, and interleukin 10 following lipopolysaccharide stimulation. Further, liver sections stained for ED2-positive cells demonstrated an increase in the number of resident macrophages at 2 and 4 weeks with a slight decrease in ED2-positive cells by week 6 but still significantly more than control. Analysis of reduced glutathione (GSH) and oxidized glutathione (GSSG) indicated that Kupffer cells from CCl(4)-treated animals exhibited a 50% decrease in GSH at 2 and 4 weeks, whereas no significant changes were observed for GSSG. In conclusion, these data implicate Kupffer cells as a critical mediator of the inflammatory and fibrogenic responses during CCl(4)-mediated liver damage and provide new insight into the temporal molecular and biochemical changes associated with the ability of these resident macrophages to modulate liver injury.

Genetic selection for high and low alcohol consumption in a limited-access paradigm

BACKGROUND

Several rat lines have been bred for their differences in alcohol consumption based on a continuous-access paradigm in which alcohol solution is available 24 hr/day. The limited-access paradigm (LAP), in which access to alcohol solution is restricted to a short period per day, however, has been used extensively to investigate the neurochemical mechanisms underlying alcohol consumption. There is evidence of possible differences in genetic determination of alcohol drinking in a continuous- versus limited-access condition. For these reasons, selective breeding for high- and low-alcohol consumption (HARF and LARF, respectively) based on a LAP was conducted.

METHODS

N/Nih rats were used as the breeding stock. A within-family breeding procedure was used to develop HARF and LARF lines with 10 families per line. Access to alcohol solution was restricted to 20 min/day. Alcohol was provided as 3%, 6% and 12% w/v solutions. Average intake of alcohol during the 12% phase was used as the selection criterion. Inbreeding began in the seventh generation.

RESULTS

After the sixth generation of selection, rats from the HARF line consumed an average of 1.2 g/kg, whereas rats from the LARF line consumed an average of 0.6 g/kg of alcohol during the 20-min access period. Alcohol consumption remained stable over the next eight generations of inbreeding. In the continuous-access-drinking paradigm, the HARF and LARF rats consumed an average of 5.5 to 7.0 g/kg and 1.0 to 2.0 g/kg of alcohol per day respectively. An estimated heritability of 0.25 was obtained.

CONCLUSIONS

These findings indicate that alcohol drinking in the LAP is influenced by genetic factors. Differences in alcohol drinking in the LAP also generalize to continuous access drinking. These rat lines will be very useful for investigations into the genetic and neurochemical mechanisms underlying alcohol drinking.

Developmental alterations of ethanol sensitivity in selectively bred high and low alcohol sensitive rats

Initial sensitivity and acute tolerance to ethanol have been implicated as risk factors in the development of alcoholism in humans. These behaviors were investigated in rats selectively bred for differences in hypnotic sensitivity following their first dose of ethanol in two different experiments. In Experiment 1, developmental profiles of the association between initial sensitivity and acute tolerance induced by a single exposure to ethanol were examined using male and female high, low, and control alcohol sensitive (HAS, LAS, and CAS) rats. Dose-response curves were constructed for duration of the loss of the righting reflex and for blood ethanol concentration (BEC) at the regain of the righting reflex. Animals were tested with a single ethanol dose ranging from 1.5 to 5.0 g/kg at either 15, 25, 40, 70, 120, or 180 days of age (DOA). For each group, acute tolerance to ethanol was estimated by the slope of the regression line using dose of ethanol and mean BEC at regain. In general, all rat lines showed an increase in hypnotic sensitivity to ethanol with age. To a large degree, the lower sensitivity observed in 15 and 25 DOA HAS and LAS rats was associated with an increase in the development of acute ethanol tolerance relative to older rats. Divergence of the LAS and CAS lines was evident by 25 DOA and remained stable with advancing age. However, HAS rats did not differ significantly from CAS rats until 40 DOA, after which the magnitude of the difference continued to increase with age. In Experiment 2, rats were treated with alcohol at 25, 70, or 180 DOA. Rats at 70 or 180 DOA required less ethanol to disrupt their motor coordination on a rotating dowel (rotarod). Blood ethanol levels were determined at the loss and subsequent regain of the ability to negotiate the rotarod. Total duration of inability to negotiate the rotarod also was recorded. HAS rats were less able to remain on a rotarod while under the influence of alcohol relative to LAS and CAS rats regardless of age. However, no evidence of acute tolerance was observed in this experiment and, in fact, there was evidence of reverse tolerance in that all animals had lower BEC values at regain of ability than they did at loss.

Metabolism of 4-Hydroxynonenal by Rat Kupffer Cells

Kupffer cells are known to participate in the early events of liver injury involving lipid peroxidation. 4-Hydroxy-2,3-(E)-nonenal (4-HNE), a major aldehydic product of lipid peroxidation, has been shown to modulate numerous cellular systems and is implicated in the pathogenesis of chemically induced liver damage. The purpose of this study was to characterize the metabolic ability of Kupffer cells to detoxify 4-HNE through oxidative (aldehyde dehydrogenase; ALDH), reductive (alcohol dehydrogenase; ADH), and conjugative (glutathione S-transferase; GST) pathways. Aldehyde dehydrogenase and GST activity was observed, while ADH activity was not detectable in isolated Kupffer cells. Additionally, immunoblots demonstrated that Kupffer cells contain ALDH 1 and ALDH 2 isoforms as well as GST A4-4, P1-1, Ya, and Yb. The cytotoxicity of 4-HNE on Kupffer cells was assessed and the TD50 value of 32.5+/-2.2 microM for 4-HNE was determined. HPLC measurement of 4-HNE metabolism using suspensions of Kupffer cells incubated with 25 microLM 4-HNE indicated a loss of 4-HNE over the 30-min time period. Subsequent production of 4-hydroxy-2-nonenoic acid (HNA) suggested the involvement of the ALDH enzyme system and formation of the 4-HNE-glutathione conjugate implicated GST-mediated catalysis. The basal level of glutathione in Kupffer cells (1.33+/-0.3 nmol of glutathione per 10(6) cells) decreased significantly during incubation with 4-HNE concurrent with formation of the 4-HNE-glutathione conjugate. These data demonstrate that oxidative and conjugative pathways are primarily responsible for the metabolism of 4-HNE in Kupffer cells. However, this cell type is characterized by a relatively low capacity to metabolize 4-HNE in comparison to other liver cell types. Collectively, these data suggest that Kupffer cells are potentially vulnerable to the increased concentrations of 4-HNE occurring during oxidative stress.

Artificial selection for intrinsic aerobic endurance running capacity in rats

Artificial selection for intrinsic aerobic endurance running capacity was started using genetically heterogeneous N:NIH stock of rats as a founder population (n = 168). Selection for low and high capacity was based upon distance run to exhaustion on a motorized treadmill using a velocity-ramped running protocol. The starting velocity was 10 m/min and was increased by 1 m/min every 2 min (slope was constant at 15 degrees ). At each generation, within-family selection was practiced using 13 families for both the low and high lines. A rotational breeding paradigm maintained the coefficient of inbreeding at less than 1% per generation. On average the founder population ran to exhaustion in 355 +/- 11 m. Six generations of selection produced lines that differed in running capacity by 171%, with most of the change occurring in the high line. At generation 6 the low line ran 310 +/- 8 m and the high line 839 +/- 21 m at exhaustion. Selection for running capacity produced changes in body weight as a correlated trait. By generation 6, the low-line females were 20% heavier than the high-line females, and the low-line males were 16% heavier than the high-line males.

The pharmacodynamics of anticonvulsant and subconvulsant effects of ethanol in CBA and C57BL/6 mice

A method of determination of minimal effective doses (MEDs) of bicuculline causing clonic-tonic convulsions (CTC) and tonic extension (TE) was used to investigate ethanol pharmacodynamics in C57BL/6 and CBA mice, differing in levels of alcohol predisposition. It is observed that ethanol produces a powerful anticonvulsant action antagonizing convulsant effects of bicuculline. On a long-term scale, the pharmacological action of alcohol had two phases in both strains of mice: anticonvulsant (in the interval 5 min to 4 h after ethanol administration) and subconvulsant (4-24 h after ethanol administration). C57BL/6 mice were characterized by a more rapid development of the anticonvulsant effect and its faster decay in comparison to CBA strain. A possibility of correct quantitative evaluation of data allows using the method of MED determination as an express model of an acute alcohol abstinence syndrome, as well as for screening of new antialcohol drugs.

Neonatal alcohol exposure produces more severe motor coordination deficits in high alcohol sensitive rats compared to low alcohol sensitive rats

Prenatal exposure to alcohol can produce a number of behavioral alterations, including hyperactivity, learning deficits and motor impairments. However, the severity and nature of behavioral alterations varies markedly among children of women who drink during pregnancy. One important determinant of this variation may be genetic differences in the response to alcohol. Recently, we demonstrated that exposure to alcohol during development produced hyperactivity in rats bred for high alcohol sensitivity (HAS), but not in rats bred for low alcohol sensitivity (LAS). These lines were selectively bred for extremes in alcohol-induced "sleep time." The present study investigated the effects of ethanol exposure during development on motor coordination later in life in both HAS and LAS rats. Using an artificial rearing procedure, neonatal pups from each line were exposed to a binge-like alcohol treatment on postnatal days (PD) 4-9. Within each line, one group was exposed to ethanol (6.0 g/kg/day), one group served as an artificially reared control, and a third served as a normally reared control group. On PD 30, parallel bar motor performance was evaluated. Exposure to ethanol during development severely impaired motor performance in the HAS rats compared to their controls. In LAS rats, early ethanol exposure produced only mild and nonsignificant effects on motor performance. Thus, HAS rats were more vulnerable to ethanol-induced motor deficits compared to the LAS rats. Importantly, there were no differences in peak blood alcohol level between the lines, indicating that vulnerability to ethanol's teratogenic effects was not due to differences in metabolic rate. These results suggest that genetic differences in response to alcohol may serve as a predictor for susceptibility to ethanol's teratogenic effects.

4-Hydroxynonenal and malondialdehyde hepatic protein adducts in rats treated with carbon tetrachloride: immunochemical detection and lobular localization

The metabolism of CCl(4) initiates the peroxidation of polyunsaturated fatty acids producing alpha,beta-unsaturated aldehydes, such as 4-hydroxynonenal (4-HNE) and malondialdehyde (MDA). The facile reactivity of these electrophilic aldehydic products suggests they play a role in the toxicity of compounds like CCl(4). To determine the rate at which CCl(4)-initiated lipid peroxidation results in the formation of 4-HNE and/or MDA hepatic protein adducts, rats were given an intragastric dose of CCl(4) (1.0 ml/kg) and euthanized 0-72 h after administration. Rabbit polyclonal antisera directed toward 4-HNE- or MDA-protein epitopes were employed in immuno-histochemical and immuno-precipitation/Western analyses to detect 4-HNE and MDA-protein adducts in paraffin-embedded liver sections and liver homogenates. As early as 6 h post CCl(4) exposure, 4-HNE and MDA adducts were detected immuno-histochemically in hepatocytes localized to zone 2 of the hepatic acinus. Liver injury was progressive to 24 h as lipid peroxidation and hepatocellular necrosis increased. The hallmark of CCl(4) hepatotoxicity, zone 3 necrosis, was observed 24 h after CCl(4) administration and immuno-positive hepatocytes were observed in zone 2 as well as zone 3. Immuno-positive cells were no longer visible by 36 to 72 h post CCl(4) administration. From 6 to 48 h after CCl(4) administration, at least four adducted proteins were immuno-precipitated from liver homogenates with the anti-MDA or anti-4HNE serum, which corresponded to molecular weights of 80, 150, 205, and greater than 205 kDa. These results demonstrate that 4-HNE and MDA alkylate specific hepatic proteins in a time-dependent manner, which appears to be associated with hepatocellular injury following CCl(4) exposure.

Neonatal alcohol exposure produces hyperactivity in high-alcohol-sensitive but not in low-alcohol-sensitive rats

Children of women who consume high amounts of alcohol during their pregnancies vary greatly in physical and behavioral outcomes. Although many factors, such as dose and timing of exposure, undoubtedly contribute to this variation, one important determinant may be genetic differences in the response to alcohol. The present study examined activity levels in high alcohol sensitivity (HAS) and low alcohol sensitivity (LAS) rats following neonatal alcohol exposure. These lines were selectively bred for extremes in ethanol-induced "sleep times." The HAS and LAS offspring were exposed to alcohol via an artificial rearing procedure using the "pup-in-the-cup" technique. Rat pups were exposed to ethanol (6 g/kg/day) from postnatal day (PD) 4 through 7 and faded to a dose of 3 g/kg/day on PD 8 and 9. An artificially reared gastrostomy control group (GC) and a normally reared suckle control group (SC) were also included. Activity level was measured on PD 18 through PD 21 for 30 min daily in automated activity monitors. Neonatal ethanol exposure produced overactivity in HAS rats, relative to their controls, but the same ethanol treatment had no effect on the LAS rats. Importantly, there were no differences in blood alcohol concentrations (around 420 mg/dl) between the two lines during the treatment period. These data suggest that genetic differences in response to alcohol may be a predictor for some of the behavioral teratogenic effects of alcohol.

Phenobarbital sensitivity in HAS and LAS rats before and after chronic administration of ethanol

Rats selectively bred for high alcohol sensitivity (HAS) or low alcohol sensitivity (LAS) were tested for initial sensitivity to hypnotic doses of ethanol and a locomotor-altering dose of phenobarbital. Following 6 weeks of either a pair-fed control or 33% ethanol-derived calorie diet, animals were tested again for tolerance to ethanol and cross-tolerance to phenobarbital. HAS and LAS rats did not differ in baseline open field or Rotarod activity before chronic ethanol treatment. However, HAS rats were more sensitive to 50 mg/ kg phenobarbital relative to LAS rats. Both control- and ethanol-diet rats appeared to be less sensitive to phenobarbital after the 6-week treatment period. Chronic ethanol-exposed HAS and LAS rats demonstrated tolerance to ethanol and cross-tolerance to phenobarbital, and in particular LAS rats were even more active in the open field following phenobarbital relative to controls. In summary, significant differences in response to phenobarbital were observed between HAS and LAS rats. These observations suggest that initial sensitivity and tolerance to ethanol are associated with differences in phenobarbital sensitivity and are influenced by similar genes.

Taste reactivity in high-alcohol-sensitive and low-alcohol-sensitive rats

High, low, and control alcohol-sensitive (HAS, LAS, CAS, respectively) rats were tested for their perception of the taste of alcohol using the taste reactivity test. Reactivity tests with a single concentration of sucrose and quinine were also done. After initial taste reactivity, all rats were tested for alcohol consumption in a standard two-bottle test (water in the second bottle). Postconsumption taste reactivity tests completed the experiment. Results indicated that HAS, LAS, and CAS rats did not differ significantly in their taste reactivity response to a range of alcohol concentrations (5-40%), nor did they differ significantly in response to sucrose or quinine. Reactivity responses were similar for each group before and after the consumption tests. Despite the lack of line differences in taste reactivity, HAS and LAS rats consumed significantly less alcohol than the CAS rats during the two-bottle access tests. The present results are in contrast to research done with rats selectively bred for alcohol consumption (Alcohol Preferring and Nonpreferring rats, High Alcohol Drinking and Low Alcohol Drinking rats), which exhibit clear line differences in patterns of reactivity changes following alcohol access. The selection phenotype of alcohol sensitivity appears to be independent of rats' behavioral response to the taste of alcohol.

Ethanol intake after chronic intoxication by inhalation of ethanol vapour in rats: behavioural dependence

In Wistar rats, which practically avoid ethanol when naive, it is possible to induce a large ethanol intake in a free-choice situation after chronic intoxication by ethanol vapour. In this study, we evaluated the ethanol intake of chronically intoxicated and control rats. The ethanol intake was increased in intoxicated animals but the intensity of the response varied according to individuals without any clear relation to the level of the intoxication. The results clearly showed in intoxicated animals two kinds of responders: alcohol-nonpreferring (27/95) and alcohol-preferring rats (68/95). In the alcohol-preferring rats, ethanol intoxication had induced an alcohol drinking-dependent behaviour; about 75% of the animals of this group drank more than 7 g/kg b.wt. per day and could be considered as behaviourally dependent on alcohol. Furthermore, this group presents most of the criteria of alcoholism that an animal model should ideally satisfy.

Neurotensin levels and receptors in HAS and LAS rat brains: effects of ethanol

Previous studies of neurotensin (NT) levels and NT receptor densities in specific brain regions of mice selectively bred for differences in sensitivity to ethanol have shown that NTergic processes may mediate some actions of ethanol. In the present study, we have determined the levels of NT and NT receptor densities in specific brain regions of HAS and LAS rats that have been selectively bred for differences in sensitivity to ethanol-induced loss of righting response. Regional differences in NT levels were observed in brains from both HAS and LAS rats and values in hypothalamus, ventral midbrain, and nucleus accumbens from female rats were 25 to 75% higher than levels in corresponding regions from male rats. However, there were no significant line differences in NT-ir levels in corresponding regions from HAS and LAS animals. High-affinity binding (NTH Bmax values), measured by Scatchard analyses, were higher in ventral midbrain from HAS males than from LAS males. NTH receptor densities were higher in HAS males than in HAS females; sex differences were not observed in the LAS line. There were no significant line or sex differences between HAS and LAS in low-affinity (NTL) Bmax values in any brain region. In HAS females, subhypnotic doses of ethanol produced a decrease in NT levels in nucleus accumbens, whereas, hypnotic doses caused an increase in NT levels. Likewise, hypnotic doses elicited increases in NT levels in hypothalamus of female HAS and LAS, but not in ventral midbrain or caudate putamen. These results are consistent with low dose activation of mesolimbic and nigrostriatal dopaminergic neurons in which NT is colocalized with dopamine and with high dose inhibition of these pathways.

Initiation of ethanol self-administration by the sucrose-substitution method with HAS and LAS rats

This study was performed to examine ethanol self-administration in rats bred for different sensitivities to the sedative effects of alcohol [the Colorado High Alcohol Sensitive (HAS) and Low Alcohol Sensitive (LAS) rats]. Four rats from each replicate line of the HAS and LAS rats (n = 16) were obtained from the University of Colorado, and initiation to self-administer ethanol by the sucrose-substitution procedure was attempted. Before the initiation procedure was conducted, home-cage ethanol intake and preference ratio did not differ between LAS and HAS rats. During the initiation procedure, the LAS rats came to self-administer 10% ethanol (v/v) at similar levels as outbred Wistar rats initiated with the same procedure (approximately 0.4 g/kg/session). The HAS rats, however, failed to initiate (approximately 0.08 g/kg/ session after completing the sucrose-substitution procedure) and lever pressing was reduced even more in the HAS rats when the ethanol concentration presented was > 10% (v/v). Three of the eight HAS rats stopped lever pressing completely when the ethanol concentration was raised to 15%. After initiation, home-cage preference ratio differed significantly between the LAS and HAS rats (LAS > HAS, p < 0.03). That the LAS rats did not consume greater amounts of ethanol compared with outbred Long-Evans or Wistar rats is contrary to our hypothesis, based on recent human data suggesting that a lower sensitivity to ethanol could result in increased alcohol intake. The finding that the HAS rats could not be initiated, while selectively bred ethanol nonpreferring rats can, is also contrary to our hypothesis. Further studies related to ethanol self-administration with the HAS line could provide important information related to the genetics of alcohol nonacceptance.

Genetic models in the study of anesthetic drug action

This chapter reviews the use of genetic models in the study of anesthetic drug action. Genetic model systems provide a novel approach to understanding mechanisms of anesthetic drug action. Many models have been derived using selection processes that emphasize differential drug sensitivity, producing animal lines that differ in their CNS drug response. Studies of vertebrate (rodent) and invertebrate (Drosophila, Caenorhabditis elegans) animal model systems are covered. The review discusses studies employing lines derived from spontaneous and induced mutagenic processes, selectively bred lines, and inbred lines possessing inherent differential drug sensitivities. The primary focus of included studies is the general anesthetic drugs that are commonly used in the clinical setting. These are drugs such as the inhalational agents (halothane, enflurane, isoflurane, nitrous oxide) and the intravenous induction agents (propofol and diazepam). Rodent lines with differential sensitivity to opiates are also discussed. Finally, an approach to identifying and isolating the genes that control anesthetic sensitivity is discussed in a section on mapping quantitative trait loci (QTL) in recombinant inbred lines.

Aldehyde dehydrogenase activities in the brains of rats and mice genetically selected for different sensitivity to alcohol

Aldehyde dehydrogenase activity in brain has been studied for many years. However, the question of its role in the actions of ethanol in the brain has not been resolved. We have utilized mice and rats selectively bred for sensitivity or resistance to the initial hypnotic effects of ethanol to gain some insight into the possible involvement of brain aldehyde dehydrogenase in the actions of ethanol. We compared the levels of aldehyde dehydrogenase activity in the brains of these selected lines of rodents by histochemical methods. It was found that, although aldehyde dehydrogenase activity was detected in many areas of the brain, only in the cerebellar Purkinje cells was there a difference between sensitive and resistant lines of mice or rats. The resistant lines (Short Sleep mice and Low Alcohol Sensitive rats) had statistically higher levels of aldehyde dehydrogenase than did the sensitive lines (Long Sleep mice and High Alcohol Sensitive rats). Although this does not prove that aldehyde dehydrogenase or aldehydes are involved in the central actions of ethanol, it provides another piece of evidence in this direction.

Conditioned taste aversions induced by alcohol and lithium in rats selectively bred for ethanol neurosensitivity

Rats that were selectively bred for differences in alcohol-induced sleep time (alcohol neurosensitivity) were tested for differences in formation and extinction of alcohol- and LiCl-induced conditioned taste aversions. Male rats bred for high, control, or low alcohol sensitivity (HAS, CAS, and LAS rats, respectively) were deprived of water and given daily 30 min access to water for a baseline period of 7 days. Rats were then given a novel 0.125% sodium saccharin solution, followed by an intraperitoneal injection of either saline, 2 g/kg of ethanol (at 10% w/v), or 50.9 mg/kg of LiCl (0.15 M) on 3 conditioning days. Each saccharin exposure was followed by a recovery day of access to water. The ethanol-induced saccharin aversion extinguished more rapidly in LAS rats than in CAS or HAS rats (p < 0.05), but LiCl conditioned equivalent aversions in each group. Also, ethanol injection results in large differences in observed resting behavior in these rats (HAS > CAS > LAS), but LiCl injection produced no reliable group differences in resting. The weaker alcohol-induced taste aversion in LAS rats accords with their previously measured higher oral consumption of alcohol (Kulkosky et al., Alcoholism 17:545-551, 1993) and the idea that alcohol intake is limited by an expectancy of postingestive consequences. The weaker ethanol-induced aversion in LAS rats reflects selective breeding of an alcohol-specific trait and not a general difference in aversive conditioning or chemical neurosensitivity.

Behavioral effects and pharmacokinetics of propofol in rats selected for differential ethanol sensitivity

High- and low-alcohol sensitivity (HAS and LAS) rats have been selected for their differences in ethanol-induced sleep time. The rats also differ in sensitivity to pentobarbital, halothane, isoflurane, and enflurane. To determine if this sensitivity extended to propofol, the anesthetic requirements were measured. In this study, the sleep time and the tissue levels of propofol at awakening, as well as the pharmacokinetics, were evaluated. Propofol was administered intravenously. For one group of rats, sleep times were measured; blood and brain samples were taken at awakening. Blood samples were collected in another group of rats at frequent intervals from 0 to 90 min after injection. Propofol concentration of the samples was determined by gas chromatography. The pharmacokinetic analysis was performed using a nonlinear least-squares regression program. Sleep time was not different; however, blood and brain propofol levels at awakening showed a small, but significant difference between HAS and LAS rats. Propofol blood concentration-time curve data were fitted to a three-compartment model. Pharmacokinetic parameters were also not different between the rat lines. However, sleep time was 50% longer in female rats than male rats in both strains (p < 0.0001). The rates of propofol clearance were slower in female rats, because of different rates of disappearance from the second compartment. The observations suggest that the genetic selection for ethanol sensitivity selection for propofol sensitivity was not nearly as intense and presumably involves some different genes. These two central nervous system depressants would seem to differ significantly in their mechanism of action.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential open field reactivity in HAS and LAS rats

To identify potential differences in emotional reactivity in high (HAS) and low (LAS) alcohol-sensitive rats in open field tests, 20 ethanol naive, 19th generation HAS and 20 LAS rats from the University of Colorado's Alcohol Research Center each received three consecutive daily 20-min exposures to a 1-sq m open field. The results of repeated-measures ANOVA and Keuls tests, performed on each of five concurrently recorded behaviors, indicated that, compared to HAS rats, LAS animals exhibited significantly greater latencies to begin ambulation, elevated ambulation, and rearing scores that failed to habituate over 3 days, and an increasing intersession bolus count. In addition, significant positive correlations occurred between days 2 + 3 (but not day 1) ambulation and bolus counts in LAS but not HAS rats, and between day 1 ambulation and (i) rearings and (ii) center square entries in HAS but not LAS rats. Together with other cited data, these results provide support for a hypothesis of relatively greater emotional reactivity in LAS rats and illustrate the need for multiple measures and sessions in evaluating open field behavior.

Ethanol differentially modulates GABAA receptor-mediated chloride currents in hippocampal, cortical, and septal neurons in rat brain slices

Previous electrophysiological studies have reported conflicting results concerning the effects of ethanol on gamma-aminobutyric acid-A (GABAA) receptor-mediated responses in the brain. To examine the variables that might explain these inconsistencies, the present study was designed to determine whether ethanol modulation of synaptically evoked GABA responses is brain region dependent, to identify factors that might regulate ethanol sensitivity, and to investigate the mechanism(s) underlying ethanol modulation of GABA responses. Whole-cell voltage clamp methods were used to examine the effects of ethanol on synaptically evoked GABAA inhibitory postsynaptic currents (IPSCs) recorded from neurons in hippocampus, cerebral cortex, and intermediate lateral and medial septum from rat brain slice preparations. Bicuculline-sensitive IPSCs elicited by local stimulation were pharmacologically isolated by pretreatment with the glutamate specific antagonists, DL-(-)-2-amino-5-phosphonovaleric acid (APV) and 6, 7-dinitroquinoxaline-2, 3-dione (DNQX). Superfused ethanol (80 mM) potentiated evoked GABAA IPSCs in cortical neurons and in intermediate lateral and medial septal neurons but not in CA1 hippocampal neurons. However, the mechanism by which ethanol enhanced GABAA IPSC amplitudes differed between brain regions. In cortex, ethanol induced a hyperpolarizing shift in the GABAA IPSC reversal potential (EIPSC) without modifying the underlying GABAA receptor-mediated conductance (GIPSC). In contrast, ethanol enhanced GABAA IPSC amplitudes differed between brain regions. In cortex, ethanol induced a hyperpolarizing shift in the GABAA IPSC reversal potential (EIPSC) without modifying the underlying GABAA receptor-mediated conductance (GIPSC). In contrast, ethanol enhanced GABAA IPSC amplitudes in lateral and medial septal neurons by increasing the GIPSC without modifying the EIPSC. These results suggest that ethanol differentially modulates responses to endogenous GABA released during synaptic activation and that important differences between various brain regions may reflect multiple mechanisms of ethanol action.

Effect of pentobarbital and gaseous anesthetics on rats selectively bred for ethanol sensitivity

Rats have been genetically selected to have a differential hypnotic response to an acute injection of ethanol. These high alcohol sensitive (HAS) and low alcohol sensitive (LAS) rats were used to investigate commonalities of the mechanism of action of several gaseous anesthetics, pentobarbital and ethanol. Similar studies have been carried out extensively with mouse lines also differentially sensitive to ethanol (short- and long-sleep mice). Like the mice, the rats are also differentially sensitive to the two gaseous anesthetics, enflurane and isoflurane. However, in contrast to results with these mice, we find that the HAS and LAS rats are differentially sensitive to halothane and pentobarbital in the same direction as their sensitivity to ethanol. In other studies, the rats also have been found to be differentially sensitive to phenobarbital as are SS and LS mice. These results show that, by the use of these anesthetics in combination with selectively bred rodent lines, many new opportunities for dissecting the molecular mechanisms of anesthetic agents present themselves.