Sensitivity to ethanol hypnosis and modulation of chloride channels does not cosegregate with pentobarbital sensitivity in HS mice

Mutant mice lacking the gamma isoform of protein kinase C show decreased behavioral actions of ethanol and altered function of gamma-aminobutyrate type A receptors

Calcium/phospholipid-dependent protein kinase (protein kinase C, PKC) has been suggested to play a role in the sensitivity of gamma-aminobutyrate type A (GABAA) receptors to ethanol. We tested a line of null mutant mice that lacks the gamma isoform of PKC (PKC gamma) to determine the role of this brain-specific isoenzyme in ethanol sensitivity. We found that the mutation reduced the amount of PKC gamma immunoreactivity in cerebellum to undetectable levels without altering the levels of the alpha, beta I, or beta II isoforms of PKC. The mutant mice display reduced sensitivity to the effects of ethanol on loss of righting reflex and hypothermia but show normal responses to flunitrazepam or pentobarbital. Likewise, GABAA receptor function of isolated brain membranes showed that the mutation abolished the action of ethanol but did not alter actions of flunitrazepam or pentobarbital. These studies show the unique interactions of ethanol with GABAA receptors and suggest protein kinase isoenzymes as possible determinants of genetic differences in response to ethanol.

Interaction of pregnanolone and pregnenolone sulfate with ethanol and pentobarbital

3-alpha-Hydroxy-5-beta-pregnan-20-one [pregnanolone (PA)] and 3-beta-hydroxy-5-pregnen-20-one 3-sulfate [pregnenolone sulfate (PS)] are steroids that have been shown in biochemical studies to be active at the GABA-benzodiazepine-chloride receptor complex, Pa as a "barbiturate-like" agonist and PS as a "picrotoxin-like" antagonist. Since other compounds that are active at this site interact with the effects of pentobarbital and ethanol, the behavioral effects of these steroids alone and in combination with pentobarbital and ethanol were tested. Pa blocks the convulsions caused by pentylenetetrazole (PTZ) and increases motor activity when given alone in low doses. In combination with either pentobarbital or ethanol, it enhances the depression in motor activity, hypothermia, and hypnosis. In contrast, PS has no effect on PTZ convulsions and depresses motor activity by itself. With pentobarbital, PS enhances the depression in motor activity but has no effect on hypothermia or hypnosis. With ethanol, PS enhances the hypothermia but does not affect motor activity or hypnosis. Therefore, Pa and PS show different but not opposite effects in interacting with compounds active at the GABA-benzodiazepine-chloride receptor complex.

Classical Genetic Analyses of Responses to Sedative-Hypnotic Drugs in Crosses Derived from Long-Sleep and Short-Sleep Mice

A classical (Mendelian) genetic analysis of responses to eight sedative-hypnotic compounds (ethanol, urethane, trifluoroethanol, chloral hydrate, barbital, paraldehyde, methyprylon, pentobarbital) was conducted in crosses derived from mouse lines that were selectively bred for differential duration of anesthesia following ethanol. The sleep-time responses of these mice, the long-sleep (LS) and short-sleep (SS) mouse lines, as well as the F1, F2 and backcross (F1 x LS, F1 x SS) generations were measured. Generally, differences in responses among the generations were greater for water soluble compounds than were differences for more lipid soluble compounds. Also, the inheritance of responses to water soluble compounds could be explained primarily by additive effects of alleles while the inheritance patterns for more lipid soluble compounds were more complex. Genetic correlation with ethanol response decreased with increasing lipophilicity. These results suggest that the selection of the LS-SS mouse lines was specific for water soluble anesthetic agents. Because several of these agents are known to act at GABA receptors, examination of the interactions of compounds which differ in lipid solubility at GABA receptors from LS and SS mice may prove useful in elucidating the mechanism of the anesthetic actions of ethanol and other drugs.

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

Selective breeding of rats for sensitivity to the anesthetic effects of ethanol is being carried out with rats derived from the genetically heterogeneous N/Nih stock. Thirteen generations of within family selection have been achieved with replicate high (HAS), low (LAS) and control alcohol sensitive (CAS) lines. Significant separation between lines on sleep time and blood ethanol concentration (BEC) at awakening following ethanol administration has been achieved. In general, the results obtained so far replicate the findings with short (SS) and long (LS) sleep mice. One exception is that the high alcohol sensitivity rats (HAS) also appear more sensitive to pentobarbital relative to LAS rats. This finding is opposite to that which occurs with SS and LS mice where the low ethanol sensitive SS mice appear more sensitive to pentobarbital than the LS mice.

Mammalian genetics in the study of alcohol and anesthetic actions

Rodent lines differing in genetic sensitivity to ethanol have been selected using a variety of behavioral end points to assess ethanol action. The use, albeit limited, of these lines to study anesthetic action is presented. In addition, one pair of lines has been selected for differences in sensitivity to nitrous oxide anesthesia, and studies with these lines are reviewed. Several of these selected lines of rodents have been used to study neurochemical mechanisms of ethanol action, and the importance of combining classical and molecular genetic approaches is discussed. Genetic studies support the concept of multiple mechanisms of action of ethanol and indicate that these mechanisms are not necessarily the same for ethanol, barbiturates, or gaseous anesthetics.

gamma-Aminobutyric acid-activated chloride channels in rats selectively bred for differential acute sensitivity to alcohol

Effects of various sedative hypnotic agents on GABA-mediated chloride flux were evaluated in whole brain membrane vesicles (microsacs) prepared from rats selectively bred for high (HAS) and low sensitivity (LAS) to an acute hypnotic dose of alcohol. The HAS rats were more sensitive to the effects of pentobarbital, phenobarbital, flunitrazepam, and ethanol on GABA-mediated chloride flux compared with the LAS rats. No differences between the lines in GABA-stimulated chloride flux were observed. Modulation of 1-[3H]-phenyl-4-butyl-2,6,7-trioxabicyclo(2.2.2)octane ([3H]-TBOB) and [3H]-diazepam binding also was measured. The lines did not differ in inhibition of [3H]-TBOB binding by pentobarbital, phenobarbital, muscimol or picrotoxin. Although the lines displayed almost identical KD and Bmax for [3H]-diazepam binding, the GABA agonist, muscimol, was a more potent stimulator of [3H]-diazepam binding in membranes prepared from HAS rats than from LAS rats. These findings are discussed in light of previous work using other selected lines.