Electrophysiological correlates of ethanol-induced sedation in differentially sensitive lines of mice

Differences in the biophysical properties of the benzodiazepine/gamma-aminobutyric acid receptor chloride channel complex in the long-sleep and short-sleep mouse lines

Significant differences in the thermal stability of benzodiazepine receptors were found in cerebral cortical membranes prepared from the long-sleep (LS) and short-sleep (SS) selected mouse lines. Thus, benzodiazepine receptors from LS mice were heat inactivated (55 degrees C) at a significantly faster rate than those from SS mice. Although gamma-aminobutyric acid (GABA) reduced the rate of heat inactivation in both lines, the more rapid rate of inactivation in the LS line was maintained. Furthermore, the potency of GABA to enhance [3H]flunitrazepam binding decreased threefold in membranes from LS mice as the incubation temperature was increased from 0 degrees to 37 degrees C, but was unaltered in membranes from SS mice. These differences in the biophysical properties of the benzodiazepine/GABA receptor chloride channel complex ("supramolecular complex"), together with a higher KD for t-[35S]butylbicyclophosphorothionate in membranes from LS compared to SS mice, suggest that the supramolecular complex may modulate the differential sensitivity to some depressants and convulsants in these lines.

Further studies on the neurochemical mechanisms mediating differences in ethanol sensitivity in LS and SS mice

Long-sleep (LS) and short-sleep (SS) lines of mice were selectively bred for differences in CNS sensitivity to ethanol with LS mice exhibiting much greater sensitivity to hypnotic doses of ethanol (4.0-4.5 g/kg) than SS mice. The influence of peripheral and central catecholamine neuronal systems on ethanol sensitivity (sleep time) in LS and SS mice was examined following administration of reserpine, alpha-methyl-p-tyrosine and 6-hydroxydopamine. Ten days after a single dose of reserpine, tyrosine hydroxylase activity was increased in the brain and adrenal gland of LS mice but only in the brain of SS mice relative to untreated mice. Brain catecholamine levels in the reserpine-treated mice were 25-50% lower in both LS and SS mice compared to levels in untreated mice. These changes were associated with a 41% reduction in LS sleep time, but a 90% increase in SS sleep time. SS mice were also more susceptible to the lethal effects of reserpine. The increased mortality of SS mice may relate to a greater degree of reserpine-induced hypothermia and a slower rate of recovery of brain catecholamine levels. Neonatal LS and SS mice treated with 6-hydroxydopamine exhibited increased levels of catecholamines in the locus ceruleus, decreased levels in the cerebellum and unchanged levels in the hypothalamus at 60 days of age. These changes were associated with a modest decrease (10%) in LS sleep time and a marked increase (200%) in SS sleep time. alpha-Methyl-p-tyrosine decreased brain catecholamine levels of both lines by 30-50% while LS sleep times were unchanged and SS sleep times were increased by 45%.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular markers for linkage of genetic loci contributing to alcoholism

Specific locus and random locus linkage approaches to identify markers for genes whose allelic variants predispose to alcoholism or for genes controlling relevant physiological and behavioral phenotypes are discussed. Sib-pair analysis is superior for the direct analysis of complex genetic traits such as alcoholism, but classic family analysis will be useful for transmission and linkage analysis for marker traits whose genetics is less complex. In mice, a large number of inbred strains, recombinant inbred and congenic strains, and specifically selected outbred strains are available. In the human, an intriguing linkage result has emerged between a brain protein variant and alcoholism accompanied by suicide. In the mouse, preliminary linkages have been established to loci controlling ethanol preference and also activation after ethanol. Large panels of random DNA and protein genetic probes and of probes for specific loci will in the future increase the probability of establishing linkage in both species.

Genetic correlation of ethanol-induced ataxia and cerebellar Purkinje neuron depression among inbred strains and selected lines of rats

In the present study, we compared phenotypic differences in behavioral and neurophysiological responses to acute ethanol administration among six inbred rat strains. Genetic variation was found both for ataxia, as measured by loss of righting response (sleep time) after a hypnotic dose of ethanol, and for the depressant action of ethanol on the spontaneous discharge of cerebellar Purkinje neurons. Results from an analysis of covariance of these phenotypes, measured among the inbred strains, provided strong evidence for a high genetic correlation between sleep time and inhibition of cerebellar Purkinje neuron discharge in response to acute ethanol administration. However, ethanol metabolism was also found to correlate with the behavioral sensitivity of rats to ethanol. Preliminary data from the third generation of replicate lines of rats currently being selectively bred for high and low acute sensitivity to ethanol shows a trend toward divergence of both ethanol sleep time and neuronal sensitivity to acute ethanol. The conclusion from these data supports the hypothesis that the cerebellum is an important locus of ethanol action, and suggests that neuronal sensitivity to ethanol will continue to diverge between these rat lines as selection for the sleep time phenotype progresses.

Calcium differentially alters behavioral and electrophysiological responses to ethanol in selectively bred mouse lines

Sensitivity to the hypnotic action of ethanol has been found to increase in SS/Ibg (SS) but not in LS/Ibg (LS) mice after intracerebroventricular (icv) administration of calcium. In the present investigation, a correlation was found between calcium-induced changes in behavioral sensitivity and in the sensitivity of cerebellar Purkinje neurons to the depressant effects of locally applied ethanol. Cerebellar Purkinje neuron sensitivity was measured as the dose of ethanol pressure ejected from a multibarreled micropipette required to produce a 50% depression of spontaneous firing rate of single neurons. Administration of 0.2-0.4 mumol calcium chloride into the lateral ventricle of the brain increased the sensitivity of SS but not LS mice to the hypnotic behavioral effect of systemically administered ethanol. Similarly, Purkinje neuron sensitivity to locally applied ethanol was also enhanced in SS but not in LS mice 15 min following administration of calcium (0.25 mumol) icv. Furthermore, locally applied ethanol was more effective in depressing spontaneous Purkinje neuron discharge in SS mice when a 1 mM calcium solution was concomitantly pressure ejected with ethanol from the micropipette. Magnesium chloride did not mimic the effects of calcium on either behavioral or electrophysiological effects of ethanol, suggesting that the action of calcium is not a nonspecific effect of divalent cations. These data suggest that calcium-dependent processes may be involved in behavioral and electrophysiological effects associated with ethanol intoxication. Further research will be required to determine if the genetically selected difference in ethanol sensitivity expressed in LS and SS mice is regulated by calcium mechanisms.

Effect of ethanol on motor performance and hippocampal population spikes in some standard and selectively outbred rat strains

Ethanol sensitivity of Wistar and Long-Evans rats was compared in vivo and in vitro. Ethanol was more effective in reducing motor performance in Long-Evans than in Wistar rats, as determined by the tilting plane test. In addition, ethanol produced a greater reduction in the population spikes recorded from hippocampal slices (in vitro) of Long-Evans rats compared to Wistar rats. When rats from the Wistar, Long-Evans, and Sprague-Dawley strains were crossbred and then selectively outbred for high (ANT) and low (AT) sensitivity to ethanol-induced impairment of motor performance, no differences were observed in the ethanol sensitivity of the hippocampal population spike between these two strains. These data suggest that differences in ethanol sensitivity may exist among standard laboratory rodent strains. Selective outbreeding may reduce or eliminate the differences in ethanol sensitivity of brain regions or neurons other than those directly involved in producing the selected behavior. Therefore, it may be incorrect to assume a general difference in ethanol sensitivity when these traits are not coselected during outbreeding, thus indicating different neuronal pools in terms of sensitivity to ethanol.

Mapping of a putative genetic locus determining ethanol intake in the mouse

In the mouse, there is evidence that a single genetic locus is a major determinant of differences in ethanol intake between some preferring and non-preferring inbred strains. In this report, we present evidence from two independent experiments indicating that this locus maps to chromosome 1 and that its expressed product is the abundant protein LTW-4 (a 28 kDa, pI 5.6 protein expressed in brain, liver and kidney). The genetic association was found using a panel of 14 polypeptides of mouse brain which were visualized by two-dimensional electrophoresis and which exhibit genetic variation in isoelectric point. Fifteen BXD recombinant inbred strains and the two parental strains were typed for these loci and also tested for ethanol acceptance. Strains exhibiting the basic allele showed significantly higher ethanol acceptance. When 19 distantly related inbred mouse strains were tested for ethanol acceptance and typed for LTW-4, it was again found that strains exhibiting the basic allele showed significantly higher ethanol acceptance.

Variations in membrane sensitivity of brain region synaptosomes to the effects of ethanol in vitro and chronic in vivo treatment

The effects of chronic ethanol treatment on the membrane order of synaptosomes from the cerebral cortex, striatum, cerebellum, brainstem, and hippocampus of rats were determined by measuring the fluorescence polarization of diphenylhexatriene (DPH) that had been incorporated into the synaptosomal membranes. Fischer-344 rats either were fed a nutritionally complete ethanol-containing liquid diet for 5 months or pair-fed with a diet that contained sucrose substituted isocalorically for ethanol. Polarization values for synaptosomes from all the brain regions studied were similar except for those from cerebral cortical synaptosomal membranes, which were significantly less ordered. Ethanol in vitro (30-500 mM) decreased the polarization values in synaptosomes from sucrose-control rats for all brain regions, although the sensitivity of cerebellar synaptosomes to the membrane disordering effects of ethanol in vitro was significantly greater that of synaptosomes from other brain regions. Chronic ethanol treatment did not alter baseline polarization for any brain region. Cerebellar and brainstem synaptosomes from the ethanol-fed rats were significantly less susceptible to the membrane disordering effects of ethanol in vitro compared to their sucrose controls, suggesting that chronic ethanol administration results in tolerance to ethanol's membrane effects. Striatal synaptosomes exhibited intermediate tolerance, whereas the sensitivities of cortical and hippocampal synaptosomes to membrane disordering by ethanol in vitro were not significantly affected by the chronic ethanol treatment. These results suggest that synaptosomal membranes have different membrane order requirements depending on the brain region from which they are prepared. Variations in brain regional neuronal membrane sensitivity to ethanol and differential tolerance development may contribute to some of the acute and chronic behavioral effects of ethanol.

Electrophysiological effects of monoamine-derived aldehydes on single neurons in neocortex and cerebellum in rats

The electrophysiological effects of aldehydes derived from several monoamines were studied on single neurons in the cerebellum and neocortex of rats. The aldehydes derived from dopamine (3,4-dihydroxyphenylacetaldehyde) and serotonin (5-hydroxy-3-acetaldehyde) were prepared as stable disulfite complexes, from which free aldehydes were extracted. Serotonin and 5-hydroxy-3-acetaldehyde caused pronounced depression of firing rates both of cerebellar Purkinje neurons and neurons in prefrontal cortex. When locally applied from multibarrel micropipettes by pressure ejection, 5-hydroxy-3-acetaldehyde was twice as potent in the neocortex as in the cerebellum, and was equipotent with serotonin in both brain areas. The aldehyde of tryptamine also caused depressions of neuronal activity in cerebellum, but only at 5-fold higher doses than were effective for 5-hydroxy-3-acetaldehyde. 3,4-Dihydroxyphenylacetaldehyde was without effect in prefrontal cortex, but had mixed responses in the cerebellum. The results show that monoamine-derived aldehydes are physiologically active. It is possible that changes in the steady state level of these aldehydes caused by drugs such as ethanol and barbiturates might influence the electrophysiological properties of neurons in the central nervous system.

Ethanol increases single unit activity in the inferior olivary nucleus

Single unit recording of rat inferior olivary nucleus neurons reveals significantly elevated discharge after acute intraperitoneal injection of 2 g/kg ethanol. This effect is consistent across 3 different methods of anesthesia and immobilization: local Xylocaine plus intraperitoneal D-tubocurare, intraperitoneal chloral hydrate and halothane vapor. In contrast, under urethane anesthesia acute ethanol produces significant depression of olivary discharge. Since this effect is opposite to that found under the other anesthetic conditions (including topical Xylocaine only), urethane anesthesia may compromise generalizations of electrophysiologic studies of ethanol. Neurons of the inferior olivary nucleus excite cerebellar Purkinje cells through a powerful afferent circuit; our data therefore suggest that ethanol-induced increases in cerebellar Purkinje cell complex (climbing fiber burst) spikes, obtained in our previous studies, are secondary to olivary activation.

Calcium influence on neuronal sensitivity to ethanol in selectively bred mouse lines

Sensitivity to ethanol, as measured by blood ethanol concentration at loss of righting reflex, was increased significantly in SS but not LS mice following intracerebroventricular (ICV) administration of calcium chloride or A23187, a calcium ionophore. Magnesium chloride or lanthanum chloride, ICV, did not alter sensitivity to ethanol in either SS or LS mice, further indicating a specificity for calcium cation. Calcium was without effect on sensitivity to halothane narcosis in LS or SS mice. Endogenous brain calcium content was similar in these mouse lines, and ethanol administration either in vivo or in vitro did not alter brain calcium concentration. These results indicate that differences in brain sensitivity to ethanol are mediated, in part, by genetic differences in calcium-related processes and support the hypothesis that ethanol-induced narcosis may be due to alterations in calcium metabolism in the CNS.

Use of chromosomally mapped and identified mouse brain proteins for behavioral genetic analysis of alcoholism

A logical first place to look in order to identify loci determining behavioral differences between inbred and certain outbred strains of mice is among the proteins expressed in brain. Fourteen mouse brain proteins have been demonstrated to be genetically variant, four of these have been chromosomally mapped and an additional twelve have been identified and can be simultaneously screened by two dimensional electrophoresis. Certain genetic differences in behavior relevant to alcohol consumption and the effects of alcohol occur between inbred, recombinant inbred and selectively outbred strains. Two genetic correlations are reported, one between an isoelectric point variant of A7 (a 71 kd, pI 5.4 abundant protein) and resistance to signs of ethanol withdrawal and the other between A12 (a 28 kd, pI 5.6 protein) and ethanol intake. Though tentative, these findings illustrate the power of this approach for behavioral genetic analysis and may allow the biochemical genetic bases of these traits to be understood.

Genetic brain polypeptide variants in inbred mice and in mouse strains with high and low sensitivity to alcohol

Twelve genetically determined brain polypeptide charge variants were identified by comparing cerebellar vermis of 7 inbred mouse strains and of mice selectively bred from 8 strains closely related to these 7 ancestral strains and one other for acute behavioral sensitivity to the sedative effects of ethanol. The selectively bred ethanol-sensitive (LS, long sleep) and insensitive (SS, short sleep) mice exhibited different allelic variants at 6 of these 12 gene loci expressed in the cerebellum. Variant polypeptide A1 (81 kdalton, pI 5.6) was shown to be associated with the membrane of synaptosomal mitochondria and to exhibit a basic variant in SS mice that is determined by a dominant allele. Other variant polypeptides showed codominant inheritance in F1 crosses. However, the phenotype of no single one of these brain polypeptides consistently correlated with the ethanol behavioral sensitivity of the 7 inbred mouse strains nor of 8 recombinant inbred (B X D, C57BL X DBA) strains. This finding supports the hypothesis that a substantial amount of inbreeding, leading to random fixation of alleles independent of selection for ethanol sensitivity, occurred during the breeding of the SS and LS mice. The present findings of a lack of a strong association between sleep time and a brain polypeptide variant do not preclude the existence of a major gene effect contributing to variation in acute sensitivity to ethanol but are consistent with reports that multiple loci are responsible for the difference in ethanol sensitivity between SS and LS mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol tolerance of cerebellar purkinje neurons from selectively outbred mouse lines: in vivo and in vitro electrophysiological investigations

The electrophysiological activity of cerebellar Purkinje neurons was characterized in long sleep (LS: ethanol sensitive) and short sleep (SS: ethanol insensitive) mice made tolerant to ethanol. After 1 to 4 weeks of feeding on a liquid ethanol diet, mice of both lines were less sensitive to the sedative and ataxic effects of parenteral ethanol than were controls. In addition, cerebellar Purkinje cells in ethanol-fed LS and SS mice were less responsive than the controls to the depressant effects of ethanol applied via bath perfusion in vitro and via local pressure ejection application in vivo. Tolerance to the electrophysiological effects of ethanol were already apparent after 7 to 9 days on the ethanol diet, and the degree of tolerance did not increase significantly in either mouse line fed ethanol for an additional 1-3 weeks. Finally, the differences in ethanol sensitivities of naive mice (LS greater than SS) were maintained following the development of tolerance. We conclude that tolerance to both the cellular and behavioral depressant effects of ethanol can be observed after chronic feeding with ethanol in LS and SS mice, and that there are no significant differences in the degree of tolerance developed by these mice. In addition, our data suggest that the inherited differences in ethanol sensitivity between LS and SS mice, and the changes in ethanol sensitivity which occur in these mice with chronic exposure to this depressant agent, are mediated by different mechanisms.

Language processing in men at risk for alcoholism: an event-related potential study

Event-related potentials (ERPs) were recorded from a group of men with (FH+) and without (FH-) a family history of alcoholism. ERPs were recorded over the left and right cerebral hemispheres and over midline locations while subjects performed a letter rhyming task. The ERPs to the letters displayed major group differences in a negative component with a latency of 430 msec (N430). The amplitude of N430 was significantly smaller in the FH+ as compared to the FH- subjects. These group differences were more pronounced in ERPs recorded from over the right than the left hemisphere. In addition, in the FH+ group only the latency of N430 was linearly related to personal drinking habits. These results suggest that (1) certain brain functions associated with the language processing required in this task are different in men at high and low risk for the development of alcoholism and (2) moderate social use of ethanol may have more pronounced effects on language-relevant brain functions in FH+ than in FH- individuals.

Differential CNS sensitivity to PIA and theophylline in long-sleep and short-sleep mice

Long sleep (LS) and short sleep (SS) mice have a differential sensitivity to the behavioral actions of an adenosine agonist, R-phenylisopropyl-adenosine (PIA) that parallels their differential sensitivity to the soporific effects of ethanol. In addition to being more sensitive to the sedative effects of PIA, LS mice also show a greater excitatory response to an adenosine antagonist, theophylline (1,3-dimethylxanthine). The brain concentrations of both PIA and theophylline following drug administration do not differ in LS and SS mice, suggesting that the central nervous system of the LS mouse is more sensitive to both adenosine receptor agonists and antagonists. However, LS and SS mice made tolerant to ethanol did not show cross-tolerance to PIA. These results suggest that genetic selection for ethanol sensitivity has resulted in a parallel CNS sensitivity to purinergic drugs, but that acute alterations in sensitivity due to the development of ethanol tolerance do not involve changes in purinergic systems.

Reinterpretation of the literature indicates differential sensitivities of long-sleep and short-sleep mice are not specific to alcohol

This paper reviews the findings and conclusions of the literature pertinent to the Long-Sleep and Short-Sleep selectively-bred lines of mice and challenges the widely-held notion that the selective breeding program was successful in separating alleles for specific sensitivities to just alcohol. Rather, it is argued that these lines of mice were selected for differing activity of a more general process. Recent evidence, as well as reevaluated previous evidence, indicates that Long-Sleep mice are more sensitive to the soporific effects of three major classes of CNS depressants (alcohols, barbiturates, and benzodiazepines), as well as many other anesthesia-inducing compounds (adenosine, chloral hydrate, trichloroethanol, paraldehyde, nitrous oxide, enflurane, and isoflurane). Further, much evidence also supports the conclusion that most of these hypnotic-depressants and anesthetics could exert their soporific influence by a potentiation of GABA activity. The other characteristic of interest in this regard is susceptibility to convulsions. Short-Sleep mice have significantly lower thresholds to both flurothyl-induced and bicuculline-induced convulsions, as well as being more likely to suffer from paroxysms during ethanol withdrawal.

Ethanol-induced modulation of the membrane potential and synaptic activity of trigeminal motoneurons during sleep and wakefulness

In the present study we investigated the direct actions of ethanol on the membrane properties and excitatory and inhibitory postsynaptic potentials of trigeminal motoneurons in chronic cats. During states of sleep and wakefulness, extracellular and intracellular recordings were carried out together with juxtacellular (somatic and dendritic) and intracellular pressure injections of 0.05-2.5 M ethanol solutions in femtoliter quantities. Juxtacellularly applied ethanol induced: a sequence of excitatory-inhibitory alterations in firing activity which were accompanied by depolarizing-hyperpolarizing shifts in the resting membrane potential; a decrease in the amplitude of action potentials; and a depression in excitatory and inhibitory postsynaptic potentials. Intracellular ethanol injections resulted in depolarization of the membrane potential and a decrease in the amplitude of action potentials as well as a reduction in the amplitude of excitatory and inhibitory postsynaptic potentials. Both juxtacellularly and intracellularly applied ethanol affected the membrane potential and synaptic activity in a fashion that was not dependent upon the animal's behavioral state of sleep or wakefulness.

Effect of ethanol on tyrosine hydroxylation in brain regions of long and short sleep mice

The effect of ethanol on the in vivo rate of tyrosine hydroxylation in 6 brain regions was examined in two lines of mice selectively bred for a differential sensitivity to ethanol. The mice are designated long-sleep (LS) and short-sleep (SS) and lose their righting reflex for a duration of 100 minutes (LS) and 13 minutes (SS) following an intraperitoneal dose of ethanol of 4.0 g/kg. DOPA accumulation after NSD-1015 administration was measured in the absence and presence of ethanol (4.0 g/kg, IP) in the periods 5-35 minutes and 85-115 minutes after saline or ethanol. There were no differences between the lines in either basal catecholamine levels or basal tyrosine hydroxylation rates (as measured by DOPA accumulation) in any brain region except the cerebellum, where the norepinephrine content in the SS mice is 33% greater and the tyrosine hydroxylation rate is 25% higher than that in the LS mice. In the presence of ethanol, there was a differential effect on the in vivo tyrosine hydroxylation rate. In the cerebellum of both LS and SS mice there was a decreased rate of tyrosine hydroxylation in the early period after ethanol, but the rate in the cerebellum of SS mice returned to the control value at 85-115 min. At that time, the rate in LS mice is still decreased. In the locus ceruleus, hypothalamus and frontal cortex, ethanol has no effect on the rate of tyrosine hydroxylation in either LS or SS mice during the early period, but ethanol decreases the rate during the later period in the LS mice only.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacogenetic strategies for studying alcohol dependence

The importance of genotypic differences in the determination of sensitivity to ethanol, tolerance development and physical dependence susceptibility is achieving ever greater recognition. It is now generally accepted by investigators studying the biochemical and physiological bases for alcoholism that genotype can influence all these different aspects of sensitivity to the effects of ethanol. Although there is convincing evidence that susceptibility to alcoholism is inherited in man, we have no idea what it is that is inherited [2, 7, 19, 24, 31]. By examining a family history for a particular individual, we can identify individuals at familial risk for developing problems with alcohol abuse. However, environmental as well as genetic factors are important in determining who does and who does not become an alcoholic [4]. Thus, one critical need is for a genetic marker for alcoholism. Since the search for such markers in human research is both expensive and time-consuming, this has led to the use of animal models for alcoholism. Animal models are particularly helpful for genetic research since their genetics are well understood and can be specifically tooled to the task at hand. The goal of this paper is to illustrate the principal genetic methodologies that have been employed to study the human and animal pharmacogenetics of alcohol, and to identify future directions in this area.

Effects of ethanol: I. Acute metabolic tolerance and ethnic differences

Forty-five young men were given an initial dose of ethanol calculated to achieve a blood alcohol concentration (BAC) of 100 mg of ethanol/100 ml of blood. Using breath analysis, the rates of ethanol clearance were calculated over a period of a few hours. When each individual reached a BAC level exactly one-half (about 50 mg%) that seen at his peak BAC, he was given a second dose of ethanol amounting to 45% of his initial dose, and the clearance rate was again determined. Estimates of absorption time, peak BAC, volume of distribution, clearance rate, and other metabolic parameters were made separately following each dose of ethanol. As intended, there was no significant difference between peak 1 and peak 2; however, there was a significant increase in clearance rate (beta 60) after dose 2. We term this phenomenon acute metabolic tolerance to ethanol ( AMTE ). When the sample was stratified by ethnicity, there was a trend for men of Oriental ancestry to clear the drug at a faster rate than was the case for men of Caucasian or Polynesian ancestry. The data also indicated that prior drinking history may have had an effect on clearance rate, though this differed by ethnicity. Two different methods for estimating volume of distribution (V) were used. The correlation between the separate estimates obtained was poor, and is probably an indication of the need for development of more accurate methods for estimating V.

Neonatal cerebellectomy alters ethanol-induced sleep time of short sleep but not long sleep mice

The effects of neonatal cerebellectomy on ethanol-induced sleep times in long sleep (LS) and short sleep (SS) mice were investigated. Cerebellectomy did not alter the ethanol sensitivity of LS animals for loss of righting reflex. In contrast, SS mice became more sensitive to alcohol after cerebellectomy. Even so, large differences were still observed between the alcohol-induced sleep times of cerebellectomized LS and SS mice. The data indicate that, while the cerebellum must have a prominant influence on alcohol sleep time in SS animals, this brain structure is not solely responsible for the observed differences in righting reflex sensitivity to ethanol in these two mouse lines. We postulate the existence of noncerebellar central neurons with differential sensitivities to the depressant effects of ethanol in LS and SS mice.

Genetic selection for ethanol withdrawal severity: differences in replicate mouse lines

We report an ongoing within-family selective breeding project for the severity of handling-induced withdrawal seizures in mice made physically dependent on ethanol by inhalation. Two Withdrawal Seizure Prone (WSP) and two Withdrawal Seizure Resistant (WSR) lines have been subjected to five generations of selection, and two control (WSC) lines are maintained. Each WSP line had more severe and each WSR line had less severe withdrawal convulsions than its respective WSC line. Differences relative to control lines were more pronounced in the WSP lines and were not due to differences in effective dose of ethanol. Heritabilities were higher in the WSP lines than in the WSR lines. These lines will be useful for studying physiological determinants of ethanol dependence and withdrawal.

Differential sensitivity of cerebellar purkinje neurons to ethanol in selectively outbred lines of mice: maintenance in vitro independent of synaptic transmission

The effects of ethanol on spontaneous firing of cerebellar Purkinje neurons were examined in outbred lines of mice (short-sleep, SS; and long-sleep, LS) which exhibit differential behavioral sensitivity to ethanol. In order to determine whether the differences in Purkinje cell ethanol sensitivity which are observed in situ reflect differences in intrinsic properties of Purkinje neurons, we developed an isolated in vitro preparation of mouse cerebellum. Even when synaptic transmission was largely inhibited by elevating Mg2+ and decreasing Ca2+ concentrations, Purkinje cells demonstrated stable long-term firing rates quite similar to those observed in vivo. Purkinje cells responded to superfusion of ethanol with both increases and decreases in firing rate. Inhibition of rate was more commonly observed, and was the only response which was demonstrably dose-dependent. The differential sensitivity to ethanol which we have previously reported in vivo was maintained even under under these conditions, with the LS mice being approximately 5 times more sensitive to the depressant effects of ethanol. In addition, it was shown that ethanol, at the concentrations used in these experiments, decreased the amplitude and increased the duration of single action potentials. Thus, taken together, these results suggest that the differential sensitivity of outbred lines to the soporific effects of ethanol are paralleled by differences in the sensitivity of Purkinje neurons in vitro to superfusion with ethanol. Because these differences can be observed even when synaptic transmission is largely suppressed, it would appear that these differences are intrinsic to the purkinje neurons themselves.

Cerebellar role in the differential ethanol sensitivity of long sleep and short sleep mice

Two lines of mice have been selectively bred for differential sleep time responses to ethanol. Long sleep (LS) mice sleep over an order of magnitude longer than short sleep (SS) mice. We have found that these behavioral sensitivities are also reflected in the responsiveness of cerebellar Purkinje neurons in those two mouse lines in situ and in intraocular cerebellar brain grafts. The differential sensitivity of Purkinje cells to the depressant effects of ethanol appears to be an intrinsic property of the cerebellum and shows a high genetic correlation with the hypnotic effects of this drug as measured by sleep time. Sleep time studies of neonatally cerebellectomized LS and SS mice indicate that the cerebellum is not the primary determinant of the sensitivity of these mice to the soporific effects of ethanol. The sleep time of SS, but not LS mice, was altered by cerebellectomy suggesting that the cerebellum has different influences on the ethanol-induced loss of righting reflex in these two mouse lines.

Pharmacogenetic approaches to the neuropharmacology of ethanol

The literature cited in this review clearly demonstrates that many of the behavioral and pharmacological responses to either acute or chronic actions of alcohol are indeed heritable. This conclusion is supported by data derived from several different animal models that have been genetically manipulated to display a wide variety of alcohol-related responses. It is doubtful if any one specific animal model will be developed that will serve as a prototype for human alcoholism. When one considers the amount of knowledge resulting from the pharmacogenetic studies reviewed here, it is more likely that major advances in our understanding of alcohol's complex actions will be derived from several different animal models.

Event-related brain potentials are different in individuals at high and low risk for developing alcoholism

Event-related brain potentials (ERPs) from normal drinkers with and without a family history of alcoholism were compared. Three separate groups of 10 subjects each (5 with and 5 without a family history of alcoholism) ingested either a placebo or ethanol at 0.56 or 0.94 g/kg. In each comparison, ERP components elicited in conjunction with subjects' decisions about task-relevant stimuli were of significantly reduced amplitude in individuals with a family history of alcoholism. Additionally, both the latency of the positive component and reaction times to correctly detected targets were significantly later in individuals with a positive history of alcoholism than in those without such a history. These group differences were apparent both with and without a challenge of alcohol. The data suggest that brain functions are different in individuals at high and low risk for the development of alcoholism (i.e., those with and without a family history of alcoholism, respectively).

Evidence for genetic correlation of hypnotic effects and cerebellar Purkinje neuron depression in response to ethanol in mice

In the present study, we compared phenotypic differences in behavioral and neurophysiological responses to acute ethanol administration among eight inbred strains of mice. Genetic variation for behavioral sedation, as measured by loss of the righting reflex (sleep time) after a hypnotic dose of ethanol, was shown to be present among the inbred strain population. In addition, a large genetic component of variation in the depressant action of ethanol on the spontaneous discharge of cerebellar Purkinje neurons was found. Results from an analysis of covariance of the behavioral and electrophysiological phenotypes, measured on each mouse among the inbred strains, provided strong evidence for a high genetic correlation between sleep time and inhibition of cerebellar Purkinje neuron discharge in response to acute ethanol administration. Taken together with our previously reported data on ethanol-induced electrophysiological changes in selectively bred lines, the results described here strongly support the hypothesis that the cerebellar Purkinje neuron is one important locus for the acute soporific effects of alcohol.

Stereoselectivity of opiate antagonists in rat hippocampus and neocortex: responses to (+) and (-) isomers of naloxone

The relative potencies of the (+) and (-) isomers of naloxone in antagonizing electrophysiological responses to D-alanine2-methionine enkephalinamide were compared in rat frontal cortex and hippocampus. In the in vitro hippocampus, the (-) isomer was found to be at least a 100 times more potent than the (+) isomer in antagonizing opiate-induced changes in field potentials. Similar stereoselectivity was observed in vivo in both frontal cortex and hippocampus in terms of the antagonism of enkephalin-induced changes in spontaneous cell firing. The direct effects of (+) and (-)-naloxone were examined as well. In hippocampus both in vivo and in vitro, no differential effect was observed, whereas in the neocortex (-)-naloxone was considerably more potent than the (+) isomer in eliciting depressions of spontaneous activity. These direct effects of naloxone in the cortex do not appear to be due to an antagonism of the effects of endogenously released opioids. These results demonstrate that the stereoselectivity of naloxone isomers in antagonizing electrophysiological responses to opiates in the cortex and hippocampus parallels that previously observed in other brain regions and in other tissues. In addition, they suggest that naloxone may have interactions with other unknown opiate (or possibly non-opiate) receptors which are of physiological significance.

Arginine vasopressin deficient Brattleboro rats fail to develop tolerance to the hypothermic effects of ethanol

We have tested the hypothesis that animals with reduced levels of arginine vasopressin (AVP) would show reduced tolerance to ethanol. Brattleboro rats either heterozygous or homozygous for the diabetes insipidus (DI) trait and normal Sprague-Dawley rats were exposed to ethanol vapor for 21 days. Two days later, tolerance was evaluated by monitoring body temperature reductions after intraperitoneal injection of 2 g/kg (20% w/v) ethanol. Under the same conditions of chronic ethanol exposure, Sprague-Dawley rats, but not Brattleboro rats, displayed tolerance to the hypothermic effects of intraperitoneal ethanol. This phenomenon did not appear to be related to differences in ethanol metabolism or blood alcohol levels in Brattleboro rats. These data support a possible role for AVP in the development or maintenance of tolerance.

Acute ethanol effects on blood pH, PCO2, and PO2 in LS and SS mice

The effects of ethanol on blood pH, PCO2, and PO2 were measured in LS and SS mice in an attempt to ascertain whether these lines of mice, which differ in CNS sensitivity to the behavioral effects of ethanol, also differ in sensitivity to physiological effects of this drug. Long-sleep (LS) female mice were injected intraperitoneally with 1.8, 2.5, 3.3, or 3.8 g/kg ethanol; short-sleep (SS) female mice were administered 2.5, 3.3, 4.1, or 4.7 g/kg. Blood pH, PCO2, and PO2 were assessed at 15, 30, 60, 120, or 180 min after injection of the 2.5 and 4.1 g/kg doses or at 60 min after injection of the 1.8, 2.5, 3.3, 3.8, 4.1, and 4.7 g/kg doses. Opposite effects on blood pH and PCO2 over time were obtained in LS and SS mice at the 2.5 g/kg dose. Acidosis characterized the LS line, whereas alkalosis characterized the SS. The results obtained with SS mice at 4.1 g/kg dose were similar to those obtained with LS mice at the 2.5 g/kg dose. The dose-response curve for the SS mice generated at 60 min post-injection lies to the right of that for the LS mice. The effects of high ethanol doses on SS mice resemble the effects of low doses on LS animals. Thus, the two lines of mice differ in response to the effects of ethanol on these parameters related to respiration. The difference in sensitivity to the respiratory depressant effects of ethanol may contribute to the differences in behavioral sensitivity between the two lines.

Hippocampal noradrenergic responses in vivo and in vitro. Characterization of alpha and beta components

Pressure ejection of l-norepinephrine (NE) in the in vivo rat hippocampus generally produced depression of pyramidal cell spontaneous activity. In addition, both excitation and biphasic responses were observed. NE-induced inhibition of firing rate was effectively antagonized by concurrent administration of the alpha antagonist phentolamine, but was largely unaltered by the beta antagonist timolol. On the other hand, NE-induced elevation in spontaneous firing rate was effectively blocked by timolol, and largely unaffected by phentolamine. Another beta antagonist, sotalol, did not selectively antagonize either NE-induced inhibition or NE-induced excitation. The beta agonist 2-fluoro-NE produced increases in pyramidal cell firing rates in most cells studied, while the alpha agonist 6-fluoro-NE inhibited the majority of cells examined. The effects of sotalol were also examined on alpha and beta receptor-mediated field responses in the in vitro hippocampal slice. Sotalol was shown to be a selective beta antagonist in this system, blocking excitation evoked by the beta agonist isoproterenol while having no effect on inhibition elicited by the alpha agonist clonidine; however, the potency of sotalol (Ki = 3.5 microM) was considerably less than that of timolol (Ki = 50 nM). Taken together, these results suggest that NE-induced depression and elevation in hippocampal pyramidal cell spontaneous discharge in vivo are mediated via alpha and beta adrenoceptors, respectively.

Interactions of a neuroleptic drug (fluphenazine) with catecholamines in hippocampus

The interactions of fluphenazine with the electrophysiological responses to catecholamines were studied in the rat hippocampus and parietal cortex. In the in vitro hippocampal slice, changes in synaptically evoked responses induced by norepinephrine, isoproterenol and dopamine were not altered by superfusion of fluphenazine. Both alpha- and beta- components of adrenergic responses were unaffected by neuroleptic administration in this preparation. Similarly, alterations in the spontaneous firing of single hippocampal pyramidal neurons in situ to adrenergic agonists or dopamine were not affected by local fluphenazine and administration using pressure ejection through multibarreled micropipettes. In contrast, norepinephrine- or isoproterenol-induced inhibitions of parietal cortical neurons in situ were potently antagonized by fluphenazine. A similar interaction was observed from a hippocampal basket neuron. It is concluded that while fluphenazine can antagonize well-defined noradrenergic effects in some brain regions (e. g., cerebellum, cortex), this property is not generalized to all brain regions receiving noradrenergic input.

Ethanol-induced depressions in cerebellar and hippocampal neurons of mice selectively bred for differences in ethanol sensitivity: an electrophysiological study

The recently discovered profound differential sensitivity of cerebellar Purkinje (P) cells in long-sleep (LS) verus short-sleep (SS) mice to the depressant effects of locally applied ethanol was extended in this study. First, the sensitivity of Purkinje neurons from HS mice (an outbred stock of mice from which the LS and SS lines were derived), was found to be almost exactly intermediate between the values for the long-sleep and short-sleep animals. Second, no differential sensitivity in long-sleep versus short-sleep hippocampal pyramidal neurons was observed. This was true using both spontaneous and evoked activity. Third, no differential sensitivity of P cells was seen in long- versus short-sleep mice with local application of halothane. Taken together with previous reports, these data strongly suggest that whatever genetically determined central nervous alterations result in the differential soporific effects of ethanol in the two (LS and SS) mouse lines, such alterations are brain region- and depressant drug-specific rather than generalized.

Differential electrophysiological and behavioral responses to optically active derivatives of phencyclidine

Dextro- and levorotatory isomers of 1-(1-phenylcyclohexyl)-3-methylpiperidine (PCMP) were synthesized. Both isomers inhibited spontaneous cerebellar Purkinje neuron firing when applied locally by pressure ejection. This effect was dose-dependent, with the (+)-isomer about 5--7 times more potent than the (-)-isomer. Both isomers also depressed rotarod performance in mice. Again, the (+)-isomer was about 5 times more potent than the (-)-isomer. Both rotarod performance and Purkinje cells discharge were depressed maximally 10--15 min after i.p. injection of drug. Our results suggest a correlation between behavioral performance and central neuron electrophysiological activity and suggest that the central actions of PCP or its derivatives are probably mediated at one locus, by a stereospecific mechanism.