Long-sleep Mice Research Articles

Differential regulation of cocaine-induced locomotor activity in inbred long-sleep and short-sleep mice by dopamine and serotonin systems

Acute injection of cocaine increases locomotor activity of inbred long-sleep (ILS) mice to a greater extent than inbred short-sleep (ISS) mice. Strain differences in dopamine and/or serotonin (5-HT) neurotransmission could underlie these behavioral differences. Here, we found that dopamine D1, 5-HT 2A and 5-HT 3 receptor antagonists reduced cocaine-stimulated activity selectively in ILS mice. In contrast, 5-HT transporter (SERT) or 5-HT 1A receptor antagonists potentiated cocaine-stimulated activity in ISS, but not in ILS, mice; this potentiation in ISS mice was abolished by dopamine D1 receptor blockade. Thus, in ILS mice, cocaine-induced activation of D1, 5-HT 2A or 5-HT 3 receptors is sufficient to produce locomotor stimulation. In contrast, ISS mice require pharmacologically increased 5-HT levels, which appear to result in increased dopamine neurotransmission, for cocaine-induced activation. Our results demonstrate strain differences in dopamine/5-HT receptor subtypes and their interactions that contribute to the differential behavioral responsiveness of ILS and ISS mice to cocaine.

Locomotor Activity Induced by Noncompetitive NMDA Receptor Antagonists Versus Dopamine Transporter Inhibitors: Opposite Strain Differences in Inbred Long-Sleep and Short-Sleep Mice

Locomotor Activity Induced by Noncompetitive NMDA Receptor Antagonists Versus Dopamine Transporter Inhibitors: Opposite Strain Differences in Inbred Long-Sleep and Short-Sleep Mice

Locomotor Activity Induced by Noncompetitive NMDA Receptor Antagonists Versus Dopamine Transporter Inhibitors: Opposite Strain Differences in Inbred Long‐Sleep and Short‐Sleep Mice

The actions of ethanol in the brain involve multiple neuroreceptor systems, including glutamatergic N-methyl-D-aspartate receptor (NMDAR) channels. In a novel environment, both ethanol and the noncompetitive NMDAR antagonist MK-801 stimulate locomotor activity to a lesser extent in inbred long-sleep (ILS) mice compared with inbred short-sleep (ISS) mice. The behaviorally activating effects of noncompetitive NMDAR antagonists are thought to involve increased monoamine neurotransmission. Thus, in this study, we sought to determine whether: (1) habituation to the behavioral environment alters the differential locomotor-stimulant effects of noncompetitive NMDAR antagonists in ILS and ISS mice and (2) the differential behavioral sensitivity of ILS and ISS mice to noncompetitive NMDAR antagonists is mediated through direct inhibition of the dopamine transporter (DAT). Open field locomotor activity was measured following acute systemic injection of saline or drug. [3H]DA uptake parameters were determined in striatal synaptosomes prepared from drug-naïve mice. Habituation to the testing environment abolished the strain differences in saline-induced locomotor activity. However, ethanol- as well as MK-801-treated ILS mice still exhibited reduced locomotor activity compared with ISS mice, suggesting that a drug-environment interaction is not the primary explanation for the strain differences. The noncompetitive NMDAR antagonists phencyclidine and ketamine also induced significantly lower locomotor activity in ILS than in ISS mice. In contrast, the DAT inhibitors cocaine and GBR 12909 and the DA releaser amphetamine induced greater locomotor activity in ILS than in ISS mice, a strain difference opposite that of the noncompetitive NMDAR antagonists. Furthermore, the differential behavioral effect found with DAT inhibitors was not mediated by differences in the affinity nor number of striatal DATs between ILS and ISS mice. Our results support the conclusion that the differential locomotor-stimulant effects of ethanol and noncompetitive NMDAR antagonists in ILS and ISS mice are not mediated through direct inhibition of DAT.

Alcohol differentially affects c-Fos expression in the supraoptic nucleus of long-sleep and short-sleep mice

Ethanol administration in long-sleep (LS) and short-sleep (SS) mice results in a large number of Fos-IR neurons in the supraoptic nucleus (SON) in LS, and almost no Fos-IR neurons in the same nucleus in SS mice. In contrast, isotonic saline, hypertonic saline, with or without ethanol, resulted in a similar pattern of Fos-IR in both strains. These data indicate a differential effect of ethanol on c-Fos signaling specifically in the SON. Since the LS and SS mice were specifically selected for differential sensitivity to the sedative/hypnotic effects of ethanol, this differential in c-Fos activity may be causally implicated in their differential sensitivity to ethanol.

Pressure-sensitive and -insensitive coupling in gamma-aminobutyric acid(A) receptors.

Previous behavioral and biochemical studies suggest that allosteric coupling processes initiated by benzodiazepines, barbiturates and neuroactive steroids can be sub-categorized on the basis of their sensitivities to antagonism by increased atmospheric pressure. However, biochemical evidence supporting this hypothesis was limited to single concentration studies in long sleep (LS) mice. The present paper addresses these issues by extending biochemical investigation of pressure effects on allosteric modulators across a range of concentrations that allosterically enhance gamma-aminobutyric acid (GABA)A receptor function and alter behavior using two mouse genotypes. In addition, the effects of pressure on ligand binding were explored to further investigate the mechanism of pressure antagonism of allosteric modulation. The effects of 12 times normal atmospheric pressure (ATA) of helium-oxygen gas (heliox) on allosteric modulation of GABA(A) receptor function and [3H]flunitrazepam binding was tested in LS and C57BL mouse brain membranes (microsacs) using chloride flux and high-affinity binding assays. In both genotypes, exposure to 12 ATA heliox antagonized the allosteric enhancement of GABA(A) receptor function by flunitrazepam (0.1-10 microM) and pentobarbital (0.1-50 microM) but did not affect allosteric modulation by 3alpha-hydroxy-5beta-pregnan-20-one (0.1-1 microM). Pressure did not affect benzodiazepine receptor affinity (Kd) or the number of benzodiazepine receptors (Bmax). (1) confirm that there are differences in sensitivity to pressure antagonism of allosteric coupling among GABA(A) allosteric modulators; (2) demonstrate that these differences are not concentration or genotype dependent; (3) add evidence that pressure antagonizes allosteric modulation by uncoupling the receptor and (4) support the hypothesis that allosteric modulation of receptor function can be sub-categorized on the basis of sensitivity to pressure antagonism.

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.

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

This article uses a direct ethanol antagonist, increased atmospheric pressure, to further test the causative link between ethanol potentiation of gamma-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. 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. 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, < or =25 mM; SS, >50 mM). Pressure antagonized ethanol's anticonvulsant effect in SS mice. The results add important direct evidence supporting the hypothesis that ethanol potentiation of GABA(A) receptor function is an initial action of ethanol causing its behavioral effects. These findings also provide insight into possible effects of selective breeding on GABA(A) receptor function.

Relationship of Brain Ethanol Metabolism to the Hypnotic Effect of Ethanol. II: Studies in Selectively Bred Rats and Mice

To clarify the role of brain acetaldehyde in the hypnotic effect of ethanol, we compared the ethanol-oxidizing capacity (rate of acetaldehyde accumulation) and catalase and aldehyde dehydrogenase activity in the brains of animals genetically selected for different sensitivities to the hypnotic effect of ethanol. We used high, low, or control alcohol-sensitive rats (HAS, LAS, and CAS) and short- and long-sleep mice (SS and LS), as well as SS x LS recombinant inbred mice with known strain differences in mean duration of ethanol-induced sleep. We studied the rate of accumulation of acetaldehyde from ethanol in brain homogenates of these animals and correlated those values with their hypnotic sensitivity to ethanol. Acetaldehyde accumulation from ethanol was significantly higher in the brain homogenates from HAS rats and LS mice with high sensitivity to the hypnotic effect of ethanol in vivo, compared with LAS rats and SS mice with low sensitivity to ethanol. A correlation was found between the duration of ethanol-induced sleep and the in vitro rate of accumulation of ethanol-derived acetaldehyde in the brains of recombinant SS x LS mice strains. There was no correlation of sleep time with brain catalase levels. There were no line differences in brain catalase or aldehyde dehydrogenase or in alcohol or aldehyde dehydrogenase activity in livers of LAS, CAS, and HAS rats or in SS and LS mice. A correlation between the brain acetaldehyde accumulation, but not catalase levels, and the central effect of ethanol was demonstrated in animals genetically differing in initial sensitivity to the hypnotic effect of ethanol.

N‐methyl‐d‐aspartate Receptor Responses Are Differentially Modulated by Noncompetitive Receptor Antagonists and Ethanol in Inbred Long‐Sleep and Short‐Sleep Mice: Behavior and Electrophysiology

Short-sleep (SS) mice exhibit higher locomotor activity than do long-sleep (LS) mice when injected with low doses of ethanol or the noncompetitive N-methyl-D-aspartate receptor (NMDAR) antagonist MK-801 (dizocilpine). SS mice also have higher densities of brain NMDARs. However, two strains of LS X SS recombinant inbred (RI) mice also show differential activation to ethanol and MK-801, but have similar numbers of NMDARs. Here we used inbred LS (ILS) and SS (ISS) mice to investigate further the relationship between NMDARs and sensitivity to the stimulant effects of low doses of ethanol. Open field activity and spontaneous alternations were measured after saline or drug injection. [3H]MK-801 binding parameters were determined in hippocampus, cortex, striatum, and nucleus accumbens. Extracellular field excitatory postsynaptic potentials (fEPSPs) were recorded in the CA1 region of hippocampal slices. Systemic injection of either ethanol or MK-801 increased locomotor activity to a greater extent in ISS mice than in ILS mice. The competitive NMDAR antagonist 2-carboxypiperazin-4-yl-propyl-1-lphosphonic acid (+/- CPP) depressed activity of ILS, but not ISS, mice. No strain differences were observed in spontaneous alternations or in the number or affinity of NMDARs in the brain regions examined. Likewise, the magnitudes of hippocampal NMDAR-mediated fEPSPs were similar in ILS and ISS mice and were inhibited to the same extent by a competitive NMDAR antagonist. However, both ethanol and the NMDAR NR2B receptor antagonist ifenprodil inhibited the late component of hippocampal NMDAR fEPSPs to a greater extent in ISS, than in ILS, mice. Differential ethanol- and MK-801-induced behavioral activation in ILS and ISS mice was not associated with differences in NMDAR number. Nonetheless, pharmacological differences in hippocampal NMDAR responsiveness suggest that ISS mice express NMDARs that have a greater sensitivity to noncompetitive, but not competitive, NMDAR antagonists. These differences, which may reflect differences in NMDAR subunit composition, could underlie the differential responsiveness to low doses of ethanol in ILS and ISS mice.

N-methyl-d-aspartate Receptor Responses Are Differentially Modulated by Noncompetitive Receptor Antagonists and Ethanol in Inbred Long-Sleep and Short-Sleep Mice: Behavior and Electrophysiology

N-methyl-d-aspartate Receptor Responses Are Differentially Modulated by Noncompetitive Receptor Antagonists and Ethanol in Inbred Long-Sleep and Short-Sleep Mice: Behavior and Electrophysiology

MK‐801‐Induced Locomotor Activity in Long‐Sleep × Short‐Sleep Recombinant Inbred Mouse Strains: Correlational Analysis With Low‐Dose Ethanol and Provisional Quantitative Trait Loci

Low doses of the N-methyl-D-aspartate receptor (NMDAR) antagonist MK-801 (dizocilpine) or ethanol increase locomotor activity to a lesser extent in long-sleep (LS), than in short-sleep (SS), mice. LS mice also have fewer brain [3H]MK-801 binding sites than SS mice. In this study, LSXSS recombinant inbred (RI) mice were used to investigate whether different NMDAR densities contribute to differential MK-801 activation and whether common genes are involved in initial sensitivity to MK-801-and ethanol-induced activation. Locomotor activity was measured for 90 min after saline or MK-801 injection. Quantitative autoradiographic analysis of [3H]MK-801 binding was used to measure densities of NMDARs in seven brain regions. The ethanol (1-2 g/kg) activation scores from Erwin and colleagues (1997) were used for correlational analysis, as was their method for quantitative trait loci (QTL) analysis. Both saline and MK-801 (0.3 mg/kg, given intraperitoneally) induced a continuum of locomotor responses across the LSXSS RI strains. There was a 4-fold range of MK-801 difference scores (MK-801 score-saline baseline), with the RI 9 and RI 4 strains representing low and high responders, respectively. Dose-response experiments with these two strains confirmed that 0.3 mg/kg MK-801 produced significant activation, similar to previous results with LS and SS mice. However, unlike previous LS/SS results, lower densities of NMDARs were not observed in the RI 9 than in the RI 4 mouse brains. No significant genetic correlations were observed between MK-801-induced and ethanol-induced responses in the LSXSS RI mice. Two provisional MK-801 activation QTLs were identified (p < 0.01) on chromosomes 11 and 19, neither in common with those mapped for ethanol activation. Different densities of brain NMDARs are unlikely to account for the differential activation of LSXSS RI mice by MK-801. Additionally, in the RI mice either separate sets of genes regulate low dose MK-801- and ethanol-induced locomotor responses or the overlapping subset of genes controlling these two behaviors is small (< or =10%).

Differences in NMDA Receptor Antagonist‐Induced Locomotor Activity and [3H]MK‐801 Binding Sites in Short‐Sleep and Long‐Sleep Mice

Short-Sleep (SS) and Long-Sleep (LS) mice differ in initial sensitivity to ethanol. Ethanol acts as an antagonist at N-methyl D-aspartate receptors (NMDARs). Therefore, we tested whether SS and LS mice also differ in initial sensitivity to NMDAR antagonists. Systemic injection (intraperitoneal) of either the noncompetitive NMDAR antagonist MK-801 (dizocilpine) or the competitive NMDAR antagonist 2-carboxypiperazin-4-yl-propyl-1-phosphonic acid (CPP) produced similar results. At lower drug doses, SS mice showed greater locomotor activation than LS mice; and at higher doses, SS mice continued to be activated whereas LS mice became sedated. Brain levels of [3H]MK-801 were 40% higher in SS, compared with LS, mice. However, blood levels of [3H]MK-801 and [3H]CPP and brain levels of [3H]CPP were similar in the two lines. NMDARs were measured using quantitative autoradiographic analysis of in vitro [3H]MK-801 binding to SS and LS mouse brains. Significantly higher (20 to 30%) receptor densities were observed in the hippocampus and cerebral cortex of SS mice. Our results support the hypothesis that SS and LS mice differ in initial sensitivity to NMDAR antagonists and suggest that the line differences in the dose-response relationships for MK-801- and CPP-induced locomotor activity are qualitatively similar to those reported for ethanol. Differences in pharmacokinetics and number of NMDARs may contribute to, but are unlikely to entirely account for, the differential behavioral responsiveness of SS and LS mice to MK-801 and CPP.

Differences in NMDA Receptor Antagonist-Induced Locomotor Activity and [H]MK-801 Binding Sites in Short-Sleep and Long-Sleep Mice

Differences in NMDA Receptor Antagonist-Induced Locomotor Activity and [H]MK-801 Binding Sites in Short-Sleep and Long-Sleep Mice

Acute tolerance to the ataxic effects of ethanol in short-sleep (SS) and long-sleep (LS) mice.

The objective of this series of studies was to examine the relationship between alcohol sensitivity and the development of very rapid acute tolerance to alcohol in mice. In order to measure acute tolerance to alcohol, a behavioral test was developed using a rotorod. In the first study, mice selectively bred for resistance (short sleep, SS) or sensitivity (long sleep, LS) to the acute hypnotic effects of ethanol were used, as well as mice from the base population (heterogeneous stock, HS). Mice were trained to run on the rotorod at a speed of 14 rpm to a criterion of 200 s, in four daily training sessions. On the test day, baseline measurements of rotorod performance were taken and mice were injected i.p. with alcohol in doses from 0 to 2.5 g/kg. Animals were tested at 1-min intervals for the first 5 min following injection, then at 5-min intervals for a total of 30 min. The results demonstrated that SS and HS mice developed tolerance within 10 min following the alcohol injections. LS mice did develop some acute tolerance, but at a much slower rate than the SS or HS mice. In the second study, the effects of intoxicated practice on the rates of acute tolerance development were examined in the SS, HS and LS mice at a dose of 2.0 g/kg alcohol. A total of ten groups of each strain were given a different number of practice trials (ranging from one to ten) on the rotorod prior to a final test session at 30 min post-injection. The results provide evidence that SS and HS mice are capable of developing acute tolerance independent of practice. That is, the group of animals injected at 0 time and tested ten times up to 30 min were no better at the 30-min time point than the group injected at 0 time and tested only once at 30 min. On the other hand, the LS mice showed a modest practice effect, developing additional tolerance to the ataxic effects of alcohol with increasing intoxicated practice. Overall, these studies demonstrated that mice can develop acute tolerance within minutes following alcohol exposure, and that this ability is correlated with the initial sensitivity to alcohol.

Fine structure of hippocampal dendrites in the dentate fascia of LS/SS-mice after chronic ethanol treatment

1. 1. The effect of ethanol and its withdrawal on the dendritic microtubules in the dentate fascia of male mice was studied in the ethanol-sensitive, long-sleep (LS) line and the ethanol-insensitive, short-sleep (SS) line. 2. 2. Both mouse lines were treated with a liquid ethanol diet. Dendrites in the dentate molecular layer (DML) of the right hippocampus were examined. 3. 3. They revealed marked changes in microtubule density as compared with the controls. While the microtubule density in LS mice was significantly reduced by 15% and 18% in the middle and distal third of the DML, respectively, in SS mice the reduction (by 12%) took place in the distal third only. During withdrawal a recovery of the microtubule density has been observed in both lines.

Effect of Exogenous GM1 on Ethanol Sensitivity in Selectively Bred Mouse Lines

Ethanol sensitive long-sleep (LS) and ethanol resistant short-sleep (SS) mice are lines that have been genetically selected for differential central nervous system sensitivities to the hypnotic effect of ethanol. Because they were genetically selected only for differences in sensitivity to ethanol hypnosis, biochemical and physiological differences between them are likely related to their differential ethanol sensitivity. The synaptosomal and whole brain concentration of GM1 ganglioside was previously shown to differ significantly between the lines. Further, GM1 alters membrane responses to ethanol, including a differential effect on LS and SS synaptosomal membrane disordering. Therefore, GM1 was administered intracerebroventricularly (i.c.v.) with micro-osmotic pumps, to partially bypass the blood-brain barrier and to test its effect on CNS sensitivity to ethanol hypnosis in LS and SS mice. In the first experiment, 3 days' infusion of GM1 (20 micrograms/microliters, 24 microliters/day), saline control and treated LS and SS mice were tested for both regaining of the righting reflex and waking brain ethanol concentration. Incorporation of 3H-GM1 into brain membranes was verified by scintillation spectroscopy. GM1 did not alter ethanol sensitivity or brain ethanol concentration at time of waking in LS mice. Conversely, SS mice treated with GM1 were significantly more sensitive to ethanol hypnosis than saline controls as measured by the time to regain the righting reflex ("sleep time") and waking brain ethanol concentrations. In the second experiment, GM1-treated SS mice were again significantly more sensitive to ethanol hypnosis than saline controls. GM1 incorporation into the contralateral and ipsilateral cerebral hemispheres was determined by high-performance liquid chromatography.

Glycine receptors from long-sleep and short-sleep mice: genetic differences in drug sensitivity

The long-sleep (LS) and short-sleep (SS) mice were selected for differences in sensitivity to ethanol but also differ in response to propofol and some neurosteroids. To determine the role of strychnine-sensitive glycine receptors in genetic differences between these mice, effects of propofol, ethanol and pregnenolone sulfate on glycine responses were compared in Xenopus oocytes expressing mRNA extracted from spinal cord of LS and SS mice. The two lines of mice did not differ in sensitivity to glycine, ethanol or pregnenolone sulfate. However, receptors expressed from LS mRNA were more sensitive to the potentiation induced by propofol than those from SS. Binding of [3H]strychnine to spinal cord membranes demonstrated a similar affinity and density of receptors in LS and SS. These results suggest that glycine receptor function could account for differences in propofol sensitivity between LS and SS mice, but may not be responsible for the differences in behavioral sensitivity to ethanol or steroids previously reported.

Actions of long chain alcohols on GABAA and glutamate receptors: relation to in vivo effects.

1. The effects of n-alcohols on GABAA and glutamate receptor systems were examined, and in vitro effectiveness was compared with in vivo effects in mice and tadpoles. We expressed GABAA, NMDA, AMPA, or kainate receptors in Xenopus oocytes and examined the actions of n-alcohols on receptor function using two-electrode voltage clamp recording. 2. The function of GABAA receptors composed of alpha 1 beta 1 or alpha 1 beta 1 gamma 2L subunits was potentiated by all of the n-alcohols studied (butanol-dodecanol). 3. In contrast to GABAA receptors, glutamate receptors expressed from mouse cortical mRNA or from cRNAs encoding AMPA (GluR3)- or kainate (GluR6)-selective subunits were much less sensitive to longer chain alcohols. In general, octanol and decanol were either without effect or high concentrations were required to produce inhibition. 4. In contrast to the lack of behavioural effects by long chain alcohols reported previously, decanol produced loss of righting reflex in short- and long-sleep mice, indicating that the in vivo effects of decanol may be due in part to actions at GABAA receptors. Furthermore, butanol, hexanol, octanol, and decanol produce similar potentiation of GABAA receptor function at concentrations required to cause loss of righting reflex in tadpoles, an in vivo model where alcohol distribution is not a compromising factor. 5. Thus, the in vivo effects of long chain alcohols are not likely to be due to their actions on NMDA, AMPA, or kainate receptors, but may be due instead to potentiation of GABAA receptor function.

Quantitative Trait Locus Analyses of Sleep‐Times Induced by Sedative‐Hypnotics in LSXSS Recombinant Inbred Strains of Mice

The long-sleep (LS) and short-sleep (SS) selected lines of mice show highly significant differences in sleep-time for many sedative-hypnotic drugs, and the quantitative genetic nature of these differences has been well-established. Using an interval-mapping approach, quantitative trait locus (QTL) analyses of LSXSS recombinant inbred (RI) strains have been applied to sleep-time responses for various classes of sedative-hypnotic drugs: alcohols (ethanol, n-propanol, and n-butanol), the atypical anesthetic chloral hydrate, barbiturates (pentobarbital and secobarbital), and benzodiazepines (chlordiazepoxide and flurazepam). Several provisional QTLs were mapped to similar locations within and between drug classes, suggesting that some common loci are involved in sleep-times elicited by these drugs. Consistent with correlations of strain mean sleep-times between drugs tested in the LSXSS recombinant inbred strains, the number of provisional QTLs mapping to the locations of highest significance for ethanol decreases when the lipid solubility of a particular drug becomes less similar to that of ethanol. Provisional QTLs mapped for the benzodiazepines, however, revealed considerable overlap with those mapped for ethanol, although these drugs represented the most lipid-soluble category of sedative-hypnotics tested. Provisional QTLs for pentobarbital and secobarbital differed from most of those mapped for the alcohols, which supports the hypothesis that alcohols and barbiturates exert their effects mainly through different biological mechanisms in the LS and SS lines. Blood ethanol concentrations at regaining the righting reflex also mapped to several provisional QTLs corresponding to ethanol-induced sleep-times that support the contention that sleep-time is a reasonable index of the observed differences in central nervous system sensitivities to ethanol between LS and SS mice.

Different levels of [ 3H]MK-801 binding in long-sleep and short-sleep lines of mice

The long-sleep (LS) and short-sleep (SS) lines of mice were selectively bred for differential sensitivity to the hypnotic effects of ethanol. Several studies suggest that excitatory amino acid receptor systems are involved in these genetically determined differences in sensitivity to ethanol. The experiments described in this article examine further the potential role of NMDA excitatory amino acid receptors in genetically determined differences in hypnotic sensitivity to ethanol by measuring [ 3H]MK-801 binding in eight brain regions of LS and SS lines of mice. Significantly greater levels of binding were found in SS hippocampus and striatum. Binding levels in the remaining brain regions revealed no significant between-line differences. Affinity differences between regions were seen but no between-line differences in affinity were found in any brain region. These findings lend support to the hypothesis that differences in NMDA receptor systems are part of the genetically determined biochemistry that produces differential hypnotic sensitivity to ethanol in LS and SS mice.