Sedative-hypnotic anomalies related to dose of pentobarbital in long-sleep and short-sleep selectively-bred mice

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.

Hypothermic effect of ethanol in mice selected for differential sleep-time response to pentobarbital

The hypothermic action of ethanol was investigated in genetically distinct lines of mice selected for sleep-time response to pentobarbital for six generations. Ethanol (3 g/kg, intraperitoneally) was administered to alcohol-naive males and females from each of the unselected control, long-, and short-sleep mouse lines. Rectal temperatures were measured immediately before, and at 15, 30, 60, 90, 120, and 240 min after ethanol injection. Eight female and eight male mice from each line were sacrificed at each time point, and trunk blood was collected for plasma ethanol analysis. The results show that short-sleep mice were less hypothermic (p < 0.05) compared to long-sleep mice at 15 and 30 min after ethanol administration. However, plasma ethanol concentrations were not significantly different between the mouse lines at any time point. Therefore, the line-dependent differential ethanol-induced hypothermia observed may be a result of differences in "brain sensitivity" rather than in the rates of ethanol metabolism among the mouse lines.

Interferon induces sleep and other CNS responses in mice recovering from hexobarbital anesthesia

Immediately after recovery from hexobarbital anesthesia, mice were injected intraperitoneally with one of the following interferons: natural mouse alpha/beta, recombinant mouse (rmouse gamma IFN-A) or human alpha A, alpha D, alpha AD interferon (rHu alpha IFN-A, rHu alpha IFN-D, rHu alpha IFN-AD). All of these interferons, except rHu alpha IFN-A induced unconsciousness ("sleep"); all produced stimulatory effects that mimicked those produced by morphine in the mouse. Quantification of the duration of sleep, induced by rmouse gamma IFN, was investigated and found to be dose-related. Only 3 of the 5 interferons (mouse alpha/beta IFN; rmouse gamma IFN, rHu alpha IFN-AD) possesses antiviral activity and depresses the cytochrome P-450 system in the mouse, yet all 5 of the interferons produced CNS effects. This partition of effects, together with the very short latency of the interferon-induced CNS effects, shows that the CNS effects were mechanistically independent of the anti-viral and anti-cytochrome P-450 effects. This disparity of the actions of the interferons suggests the possibility that selected morphine antagonists could be used to counter some of the dose-limiting CNS effects of the large doses of interferons used in clinical situations.

A recombinant inbred strain analysis of sleep-time responses to several sedative-hypnotics

The results of previous studies suggested that the sleep-time differential between long-sleep (LS) and short-sleep (SS) mice decreases for a series of sedative-hypnotic drugs as lipid solubility increases. Using the LS x SS recombinant inbred (RI) strains, we have tested whether this relationship arises because of common genetic influences on the sleep-time responses or was simply a fortuitous difference between LS and SS mice. Mice were sleep-time tested after intraperitoneal injections of a variety of sedative-hypnotic drugs that vary in lipid solubility including alcohols, barbiturates, chloral hydrate, and urethane. Sleep-time values from each of these drugs were compared with ethanol-induced sleep times in the LS x SS RI strains. Significant genetic correlations were observed between ethanol-induced sleep time and those responses elicited by butanol, propanol, and chloral hydrate, but not by pentobarbital or secobarbital. When the partition coefficient (log P) values were compared with the genetic correlations, a significant relationship (r = -0.85) was observed. These data suggest that common genes mediate sedative-hypnotic reactions to ethanol and some drugs resembling it in log P value, and that anesthetic agents with low lipid solubility may be working through different mechanisms than drugs with greater lipid solubilities.

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.

Correlation of sedative effects with brain levels of barbiturates in LS and SS mice

Long-sleep (LS) and short-sleep (SS) mice, genetically selected for their differential CNS sensitivity to ethanol, have also been shown to differ in their response to other sedative-hypnotics, including the barbiturates. We have applied a gas-chromatographic method of analysis of brain barbiturate concentrations following IP administration of either the water-soluble barbiturate diethylbarbital (DB) or the lipid-soluble barbiturate secobarbital (SB). Brain barbiturate levels were assessed at loss of righting response, and at regaining righting response (waking). In addition, latency to loss of righting response and duration of loss of righting response were measured following IP barbiturate administration. We have observed a differential sensitivity of LS and SS mice to the sedative effects of DB, with LS mice having greater sensitivity compared to SS. This differential sensitivity to DB, as measured by a lower concentration of DB which caused loss of righting in LS, was accompanied by an equal rate of water-soluble barbiturate brain distribution and elimination in the two lines. With the lipid-soluble barbiturate SB, LS and SS mice did not differ in brain SB concentration at loss of righting response or at waking. However, sleep time was much longer in SS mice than LS due to slower brain clearance of the barbiturate in SS. Therefore, duration of loss of righting (sleep time) did not adequately reflect central sensitivity to the lipid-soluble barbiturate. These data suggest the importance of quantifying brain concentrations at loss of righting reflex when assessing central sensitivity to sedative-hypnotic agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Central and peripheral benzodiazepine receptors: involvement in an organism's response to physical and psychological stress

The present review discusses the current knowledge of the molecular pharmacology and neuroanatomical and subcellular localization of both the central benzodiazepine/GABA-chloride ionophore receptor complex and the peripheral benzodiazepine receptor. It then reviews all of the literature to date on how these two receptor sites are modulated by environmental stress. The possible role of these sites in learning and memory is also discussed. Finally, a theoretical model is presented which examines the differential, and perhaps complementary, alterations of these two sites in an organism's response to stress.

t-[35S]butylbicyclophosphorothionate binding under equilibrium and nonequilibrium conditions: differential effects of barbiturates and gamma-aminobutyric acid in the long-sleep and short-sleep selected mouse lines

Significant differences were demonstrated between the long-sleep (LS) and short-sleep (SS) selected mouse lines in the abilities of barbiturates and gamma-aminobutyric acid (GABA) to inhibit t-[35S]butylbicyclophosphorothionate [( 35S]TBPS) binding to well-washed cerebral cortical membranes. Thus, using phenobarbital to initiate the dissociation of [35S]TBPS, the extent of inhibition was significantly greater in LS mice (but not SS mice) than would be predicted using equilibrium conditions. Pentobarbital had the opposite effect, causing [35S]TBPS to dissociate to a greater extent in SS than LS membranes. [35S]TBPS binding was dissociated from LS and SS membranes by GABA to a greater and lesser extent, respectively, than would be predicted from equilibrium studies. Because no line differences in the potencies of these drugs to inhibit [35S]TBPS binding were found using equilibrium conditions, these results indicate that the association rates of barbiturates and GABA may be different between these lines. These findings are consistent with neurochemical studies indicating differences in the benzodiazepine/GABA receptor-chloride channel complex in these selected lines and may explain their differential sensitivities to certain agents acting through this supramolecular complex.

Selected mouse lines, alcohol and behavior

The technique of selective breeding has been employed to develop a number of mouse lines differing in genetic sensitivity to specific effects of ethanol. Genetic animal models for sensitivity to the hypnotic, thermoregulatory, excitatory, and dependence-producing effects of alcohol have been developed. These genetic animal models have been utilized in numerous studies to assess the bases for those genetic differences, and to determine the specific neurochemical and neurophysiological bases for ethanol's actions. Work with these lines has challenged some long-held beliefs about ethanol's mechanisms of action. For example, lines genetically sensitive to one effect of ethanol are not necessarily sensitive to others, which demonstrates that no single set of genes modulates all ethanol effects. LS mice, selected for sensitivity to ethanol anesthesia, are not similarly sensitive to all anesthetic drugs, which demonstrates that all such drugs cannot have a common mechanism of action. On the other hand, WSP mice, genetically susceptible to the development of severe ethanol withdrawal, show a similar predisposition to diazepam and phenobarbital withdrawal, which suggests that there may be a common set of genes underlying drug dependencies. Studies with these models have also revealed important new directions for future mechanism-oriented research. Several studies implicate brain gamma-aminobutyric acid and dopamine systems as potentially important mediators of susceptibility to alcohol intoxication. The stability of the genetic animal models across laboratories and generations will continue to increase their power as analytic tools.

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

Several findings suggest that barbiturates and alcohol produce their sedative effects through a common neural and possibly a common genetic mechanism. We tested this hypothesis by examining the correlation between ethanol and pentobarbital sedative effects in individual animals from a genetically heterogeneous population. The duration of pentobarbital-induced hypnosis (sleep-time) was unrelated to the sleep-time produced by ethanol in heterogeneous stock (HS) mice. Therefore, the present study also examined the effect of ethanol, pentobarbital, and flunitrazepam on muscimol-stimulated chloride flux into brain membranes prepared from HS mice selected for differences in pentobarbital- and ethanol-induced sleep-time. Brain membranes from mice selected for differences in ethanol sleep-time were differentially responsive to ethanol- and flunitrazepam-, but not to pentobarbital-induced augmentation of muscimol-stimulated chloride flux. No differences in augmentation of chloride flux by ethanol, pentobarbital, or flunitrazepam were found in membranes prepared from mice differentially sensitive to pentobarbital hypnosis. The ability of muscimol to stimulate chloride uptake was not related to ethanol or pentobarbital sensitivity. These findings suggest that sensitivity to ethanol is not likely to be genetically linked to pentobarbital sensitivity.

Patterns of convulsive susceptibility in the long-sleep and short-sleep selected mouse lines

It has been hypothesized that the Long-Sleep and Short-Sleep mouse lines were bidirectionally selected for high and low brain excitability, and further, that these differences are mediated by the benzodiazepine/gamma-aminobutyric acid (GABA) receptor-chloride channel complex. Hence, mice from both lines were administered seven convulsants (bicuculline, pentylenetetrazol, 3-carbomethoxy-beta-carboline, picrotoxin, caffeine, flurothyl and strychnine) and myoclonic and clonic seizure latencies recorded. Supporting the original hypothesis, the results show that the two lines were differentiated by all of the convulsants and that in response to the drugs, three distinct convulsive patterns were found. Nevertheless, a simple genetic model accounting for these results was not evident. To further clarify these susceptibility patterns, a convulsant representing each of these patterns (bicuculline, pentylenetetrazol or caffeine) was administered in conjunction with the anticonvulsant-barbiturate phenobarbital or the benzodiazepine antagonist Ro 15-1788. Irrespective of the convulsant given, phenobarbital attenuated both myoclonus and clonus subsequent to all convulsants, while Ro 15-1788 had a more discrete anticonvulsant profile.

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.

Differential convulsive susceptibility of high-activity and low-activity selected mice in response to GABA antagonists

Lines of mice selectively-bred for High and Low-Activity in an open-field maze were tested for seizure susceptibility to three analeptics: flurothyl, pentylenetetrazol and bicuculline. The major finding was that two replicate High-Activity lines were more susceptible to myoclonic convulsions but less susceptible to clonic convulsions than their respective replicate Low-Activity lines. The major exception to this finding was that the High and Low-Activity lines did not differ for bicuculline-induced clonus although females tended to conform to the general pattern. These results are interesting because they demonstrate that diametrically opposite susceptibility to myoclonus and clonus is not an isolated phenomenon. Similar seizure susceptibility patterns and activity differences have also been reported for the Long-Sleep and Short-Sleep selectively-bred mouse lines. Further, since the progenitor population of the High-Activity and Low-Activity lines were developed from strains that were also part of the progenitor population of the Long-Sleep and Short-Sleep lines, it is hypothesized that some of the same alleles underwent selection in both selective-breeding programs.

GABAergic drugs can enhance or attenuate chlordiazepoxide-induced sleep time in a heterogeneous strain of mice

Evidence supports the notion that differences between the Long-Sleep and Short-Sleep selectively-bred lines of mice are attributable to differences in brain excitability and that these differences are mediated by activity of the GABAergic system. The general applicability of this hypothesis to other populations of mice was tested by using an outbred strain of mice. Specifically, a heterogeneous strain of mice was administered several doses of the hypnotic chlordiazepoxide. Additionally, the indirect GABA agonist AOAA, and the GABA antagonists bicuculline, picrotoxin and pentylenetetrazol were administered to independent groups in conjunction with chlordiazepoxide. The results clearly demonstrate that chlordiazepoxide dose-dependently increased hypnosis, while AOAA enhanced, and the antagonists attenuated sleep time. These findings can be used to support the contention that GABA mediates the bidirectional response of Long-Sleep and Short-Sleep mice to CNS hypnotic-depressants; and, further, show that GABA mediation of sleep time in mice is a general phenomenon.