Development of physical dependence on midazolam by oral self-administration

Groups of rats drank either a solution of the ultrashort-acting benzodiazepine midazolam or water under schedule-induced polydipsia conditions in chronic, daily, 3-hr sessions. In Experiment 1, the physical dependence status of animals was tested after 9 months by the precipitated withdrawal method using the benzodiazepine-blocking agent Ro 15-1788 and by exposure to a brief audio stimulus at 1.5, 12 and 24 hr following drug withdrawal. Ro 15-1788 failed to produce withdrawal signs, while the audio stimulus plus withdrawal did. In Experiment 2, similar groups were periodically tested for susceptibility to audiogenically-induced seizures at 3, 6, 12, 15, 18, 21, 24 and 26 weeks 90 minutes after their drug or vehicle intake sessions. In the midazolam-drinking group, physical dependence developed at about 12 weeks and increased in severity over the course of the study. Serum measures confirmed that continuous elevation of drug and active metabolite levels are not necessary for the development of physical dependence. A chronic, daily, single elevation of a few hr was sufficient.

Ethanol polydipsic choice: effects of alternative fluid polydipsic history

Two groups of rats drinking either 5% ethanol or 0.9% NaCl solution under a fixed-time 1-min schedule of food pellet delivery became polydipsic during daily 3-hr sessions. When both fluids were made available to animals during sessions, strong side preferences typically developed so that neither fluid was preferred in spite of the fact that one group had a mild-to-moderate physical dependence on ethanol. The group that drank 0.9% NaCl solution initially failed to acquire a strong 5% ethanol polydipsia when this became the sole available fluid, and special procedures were required to induce an ethanol polydipsia comparable to that of the other group. Hence, a history of 0.9% NaCl solution polydipsia interfered with the institution of chronic, ethanol overdrinking in this group. Equal ethanol intakes were maintained in the groups when a compound solution consisting of 5% ethanol plus 0.9% NaCl solution was available along with a 5% ethanol choice. Whenever a 0.9% NaCl solution was presented in competition with either 5% ethanol or the compound 5% ethanol plus 0.9% NaCl solution, ethanol intake was reduced. Implications for the prevention and amelioration of human ethanol overdrinking are discussed.

The separation of lymphocyte subpopulations with lectins

Wistaria floribunda agglutinin (WFA), Sophora japonica agglutinin (SJA) and Maclura pomifera lectin (MPL) were employed as immunofluorescent and leucoagglutinating reagents to study murine lymphocytes. WFA, which labels 90% of thymocytes, binds to only 57% of the splenocyte population. The latter subset corresponds to surface immunoglobulin bearing cells. Differential agglutination of splenocytes with this lectin results in the isolation of a WFA negative population which exhibits T-lymphocyte surface markers. The agglutinable splenocytes bind only 2.5 times more WFA than non-agglutinable cells suggesting that the preferential agglutination of B-splenocytes is due to a combination of reduced cell surface negative charge and increased number of lectin binding sites on these cells as compared to T-lymphocytes. Forty percent of splenocytes are positive for SJA and differential agglutination of splenocytes yields a population of SJA non-agglutinable cells that are not labeled by this lectin. The two populations fractionated by SJA are unrelated to T- and B-lymphocyte subsets. Differential agglutination of thymocytes by SJA yields a non-agglutinable group representing 42% of total thymocytes. Although the nature of the two thymocyte subsets discriminated by SJA remains unknown, this lectin appears useful in identifying and separating unique thymocyte and splenocyte populations.

Chronic alcohol dependence and water-electrolyte status

Altered water-electrolyte status resulting from chronic alcohol dependence has been reported, although the nature of any such derangement is controversial. To illuminate this problem, four groups of rats were exposed chronically to schedule-induced polydipsia conditions with a single fluid available: 5% ethanol, 0.9% NaCl solution of 5% ethanol, 0.9% NaCl solution, or distilled water. An ad lib control group was also used. The water-electrolyte status of these groups was evaluated in two ways. First, the diuretic response to hydrochlorothiazide doses (8-12 mg/kg) was measured after 3.5 months of chronic polydipsia. Second, after approximately two additional months of polydipsia, extracellular fluid volume, as well as plasma volume and electrolytes were measured. Both alcohol-intake groups drank approximately 11.5 g ethanol/kg/day over the course of the experiment. Urinary volume response to the diuretic agent did not reveal that chronic ethanol led to either water retention or dehydration, even when extra NaCl intake was imposed chronically (NaCl-EtoH group). Animals that were overdrinking either water or the 0.9% NaCl solution had extracellular fluid volumes that were greater than the NaCl-EtOH-polydipsic group, but they were not significantly larger than ad lib controls. There were no significant differences with respect to serum electrolyte concentration measures among the groups. In conclusion, animals that drank ethanol chronically in a pattern known to produce physical dependence revealed no altered water-electrolyte status when evaluated by acute responses to a diuretic agent, a chronically-imposed extra NaCl load, or body fluid compartment and electrolyte concentration measures.

Schedule-induced ethanol dependence and phenobarbital preference

Rats exposed to a daily 3-hr session of intermittent food delivery ingested physical-dependence-produced levels of 5% ethanol solution. Although this schedule induced a chronic, voluntary, daily overindulgence, this had no effect on 21-hr home-cage phenobarbital preference. The substitution of water for 5% ethanol during the daily 3-hr binge session did not change home-cage phenobarbital preference, which remained stable and similar to that of a control group of non-binging animals. This experiment and others indicate that physical dependence on ethanol does not play a major role in the maintenance of ethanol abuse or cross-abuse of the barbiturates.

Midazolam oral self-administration

The technique of chronic schedule-induced drug solution intake was used to determine the possible addiction liability of the short-acting benzodiazepine midazolam. Schedule-induction produces polydipsia over a wide range of fluids as a function of the imposed schedule of food availability. The inducing schedule used presented food pellets automatically once per minute, fixed time (FT) 1-min, for 3 h daily. Two groups of rats, drinking either water or 0.05 mg/ml midazolam solution, were exposed to schedule-induction sessions for approx. 2 months. Then, other FT-values (0, 0.5, 3 and 5 min) were instituted on occasion for single sessions. Each of these 'probe' session determinations was done twice. Although midazolam concentration had been adjusted so that the mean group intakes were equal at FT 1-min, probe values greater than 1 min revealed a greater acceptance of midazolam compared to water. This technique produced session midazolam intakes as great as 25 mg/kg. In the next phase, the entire experiment was repeated except both groups were offered a choice between water and midazolam solution during sessions. Only at FT 0 and FT 5-min was there an indication that midazolam was preferred over water. Two additional groups of animals were exposed to the same schedule-induced polydipsia regimen, drinking water and midazolam solution, respectively. Pre-session administration of doses of Ro 15-1788, CGS 8216 (benzodiazepine antagonists) or midazolam had no effects on either water or midazolam intakes, although the higher dose of midazolam (2 mg/kg, s.c) had a moderately suppressive effect on the non-tolerant water-polydipsic group. All groups were tested on occasion for physical dependence on midazolam with an auditory stimulus as the precipitator and midazolam polydipsic groups were found to have a mild to moderate dependence (clonic seizures, running fits).

Midazolam-induced increase in NaCl solution ingestion: differential effect of the benzodiazepine antagonists Ro 15-1788 and CGS 8216

After adaptation to a 23-hr water deprivation regimen, under which rats were allowed a daily 1-hr water rehydration session, they were injected (SC) with 1 or 2 drugs presession and given 1.5% NaCl solution to drink in place of water. Midazolam (0.5-1.0 mg/kg) increased the intake of 1.5% NaCl solution as did Ro 15-1788 (2.5-10.0 mg/kg). This confirmed a previously noted agonist effect of midazolam and partial agonist action of Ro 15-1788. When injected in combination with midazolam, Ro 15-1788 (2.5-10.0 mg/kg) antagonized the effect of midazolam. CGS 8216 (2.5-20.0 mg/kg) revealed no partial agonist action on the NaCl solution ingestion procedure nor did it block the effect of midazolam.

Chlordiazepoxide injection elevates the NaCl solution acceptance-rejection function

Injection (SC) of chlordiazepoxide (2-8 mg/kg) increased the intake of NaCl solution (0.5-3.0% NaCl) as well as water in water-deprived rats when these fluids were made available singly during daily 1-hr rehydration periods. The marked enhancement of this drug effect when NaCl solution was the available fluid does not appear to be due to the induction of a sodium appetite or the mimicking of an increase in water deprivation. The exaggeration of the drug effect when an NaCl solution is the drinking fluid, as opposed to water, may be useful as a sensitive index of action for punishment-attenuating (anxiolytic) drugs.

Quantification of adducts formed in DNA treated with N-acetoxy-2-acetylaminofluorene or N-hydroxy-2-aminofluorene: comparison of trifluoroacetic acid and enzymatic degradation

We have examined two methods of preparation of DNA adducts from phi X174 RF DNA modified by [3H]N-acetoxy-2-acetylaminofluorene ([3H]NA-AAF) or N-hydroxy-2-aminofluorene ([3H]N-OH-AF). Hydrolysis by enzymes (DNase I, snake venom phosphodiesterase and alkaline or acid phosphatase) and subsequent reverse phase h.p.l.c. of phi X174 RF DNA treated with [3H]NA-AAF yielded 73% N-(deoxyguanosin-8-yl)-2-acetylaminofluorene (dG-C8-AAF), 7% 3-(deoxyguanosin-N2-yl)-2-acetylaminofluorene (dG-N2-AAF), and a peak of unidentified radioactivity (13%). When [3H]N-OH-AF modified phi X174 DNA was analyzed, both N-(deoxyguanosin-8-yl)-2-aminofluorene (dG-C8-AF) and a large percentage of the imidazole ring-opened derivative and unidentified products were found. In contrast, when anhydrous trifluoroacetic acid (TFA) was used to degrade these DNAs, we found for the [3H]NA-AAF modified DNA 86% N-(guanin-8-yl)-2-acetylaminofluorene (G-C8-AAF) and 6% 3-(guanin-N2-yl)-2-acetylaminofluorene (G-N2-AAF), while for [3H]N-OH-AF modified DNA only the N-(guanin-8-yl)-2-aminofluorene (G-C8-AF) was found. When DNA was prepared from human fibroblasts treated with [3H]NA-AAF, only the G-C8-AF product was obtained. Thus, anhydrous TFA solvolysis followed by reverse phase h.p.l.c. is a rapid and convenient method to obtain quantitative yields of DNA adducts formed with acetylaminofluorene and related compounds: quantification by this method prevents loss of G-N2-AAF adducts, the conversion of AAF adducts to AF adducts, and the production of ring opened products in guanine residue.

Production of physical dependence on ethanol by a short drinking episode each day

A 3-hr schedule-induced ethanol polydipsia regimen was used in rats to elevate blood alcohol concentration to a single intoxicating peak each day. After 3 weeks, and again after 3.5 months, animals were tested for the presence of physical dependence by exposure to a brief auditory stimulus (key shaking) at 7 and 11 hr after ethanol polydipsia. Withdrawal signs were observed only at 11 hr when blood ethanol levels had returned to zero. No such signs were observed when animals were made water polydipsic. While sufficient, continuous elevation of blood ethanol concentration is not necessary for the development of a demonstrable physical dependence. A limited daily ethanol binge was sufficient.

Agonistic action of a benzodiazepine antagonist: effects of Ro 15-1788 and midazolam on hypertonic NaCl intake

Rats adapted to a 23-hr water deprivation regimen were allowed a daily 1-hr water rehydration session. On test days the session drinking fluid was 1.5% NaCl solution rather than water. One group was injected (SC) with the benzodiazepine antagonist Ro 15-1788 (2.5-10 mg/kg) and another group with the agonist agent midazolam (0.13-2.0 mg/kg) every 5-6 days at 10 and 15 min before a test session, respectively. Both Ro 15-1788 and midazolam increased 1.5% NaCl solution intake in a dose-related manner. In this study and in previous research, benzodiazepines and barbiturates were shown to increase the intake of hypertonic NaCl solutions. The present results reveal a similar effect for Ro 15-1788, indicating an agonistic dimension to the spectrum of action of this specific receptor antagonist.

Diazepam-induced NaCl solution intake: independence from renal factors

Rehydrating rats injected with diazepam (8 mg/kg, SC) increased their intake of 2.0% NaCl solution. Neither bilateral nephrectomy nor bilateral ureter ligation interfered with the increased NaCl solution ingestion produced by diazepam. It is concluded that the increased intake of the NaCl solution is not secondary to renal water-electrolyte losses nor dependent upon intact renal benzodiazepine receptors.

Complete reversal of chronic ethanol polydipsia by schedule withdrawal

Rats exposed to daily 3-hr intermittent food delivery sessions (binging) chronically ingested excessive amounts of either H2O or 5% EtOH (mean 7.1 g/kg/3-hr). Withdrawing the intermittency of the feeding schedule once every 10 days (single-ration probe session) resulted in reduction of fluid intakes (both H2O and EtOH) to the level of animals always given daily single-ration sessions. This complete dependence of elevated fluid intake levels on the intermittent feeding schedule was unaffected by either the number of probes previously administered (0 to 11) or the duration the feeding schedule was maintained before introduction of the first probe session (29 or 109 days). The results of the probe sessions demonstrated that a history of ethanol overindulgence was not a sufficient condition for the maintenance of overdrinking. Continued overindulgence required the continued presence of the original inducing conditions. Ethanol-polydipsic animals exposed to periodic probe sessions also developed a slow rise in binge session intake. No such increase was observed in the water-polydipsic animals.

Cross-tolerance to phenobarbital following chronic ethanol polydipsia

Using contingent food pellet delivery, rats were trained on a discriminative motor control task requiring that a force transducer be held steadily within a force band. Motor performance following pre-task doses of phenobarbital (40, 60 or 80 mg/kg) both before and after 4 months fo chronic ethanol polydipsia (mean intake = 11.1 g/kg/kay)indicated the development of cross-tolerance from ethanol to phenobarbital. Days on which saline control injections were given in place of phenobarbital injections (on injection days ethanol was withdrawn 5 hr pre-injection) revealed the development of a mild physical dependence on ethanol at this level of ethanol polydipsia. Chronic ethanol polydipsia did not alter the time course of phenobarbital elimination from the serum, indicating that the cross-tolerance probably was due to central nervous system changes.

Barbiturate dependence and drug preference

Rats exposed to a daily 3-hr session of intermittent food delivery ingested physical-dependent levels of a 1 mg/ml sodium phenobarbital solution. This chronic, voluntary, high level of session phenobarbital intake had no effect on 21-hr home cage barbiturate preference. Substitution of water for phenobarbital during the session after 7.5 weeks precipitated various spontaneous withdrawal signs in some of the animals by the 24th hr of drug withdrawal but no change was found in home-cage barbiturate preference at any time. Physical dependence alone does not seem to play a crucial role in the maintenance of drug intake behavior.

Schedule induction and overindulgence

An animal model of human alcoholism is presented in which animals maintain chronic overdrinking to the extent that they develop severe physical dependence. They can be induced to overdrink ethanol in situations where an alternative fluid is present as well, so that the overindulgence is elective. The environmental conditions that produce this result also can induce the overingestion of other substances, aggression, and hyperactivity. It would appear, then, that many kinds of seemingly excessive, maladaptive behavior in animals and humans can have similar environmental sources. Alcoholism may be viewed within a context of environmental conditions that can produce a variety of excesses.

Ethanol withdrawal and discriminative motor control: effect of chronic intake level

Rats drinking a low concentration (2.5%) of ethanol in a chronic, schedule-induced polydipsia situation failed to show withdrawal signs as measured by a discriminative motor control task. When the concentration was raised to 5% ethanol, withdrawal signs were evident, confirming a previous study.

Micro-sample gas-chromatographic technique for the analysis of barbiturates

A procedure for determining barbiturate levels in micro-samples is described. The method takes advantage of a newly available, sensitive nitrogen-phosphorus detector thereby permitting a simplified analytic procedure.

Serum phenobarbital and barbital concentrations in rats on a limited food regimen

Serum barbiturate levels were tracked for several hours in food deprived rats given 40, 60 or 80 mg/kg (SC) of either phenobarbital or barbital. All 3 phenobarbital doses produced peak serum drug levels at 1.5 hr postinjection. Serum barbital concentrations peaked 3 hr after both 60 and 80 mg/kg barbital doses while the 40 mg/kg dose produced a stable low drug level throughout the 4 postinjection hours. For both barbiturates administered, 40 mg/kg doses produced lower serum drug levels than either 60 or 80 mg/kg. The differences in serum drug concentrations between the latter two dose levels were inconsistent over time.

Ethanol dependence as a determinant of fluid preference

Rats made dependent on ethanol by a schedule-induced polydipsia procedure preferred 5% ethanol to an increasing concentration of dextrose solution to a greater extent than animals on a non-dependent, non-polydipsic procedure which allowed an equivalent opportunity to drink ethanol, confirming a previous study. Two corresponding groups of animals drinking isotonic (0.9%) NaCl rather than 5% ethanol behaved similarly to the latter group, changing to a dextrose preference at a lower dextrose concentration than the ethanol polydipsic group. Therefore, neither the intermittent food regimen (polydipsia-generating procedure) in itself, nor a history of isotonic saline polydipsia biased fluid preference against dextrose solution choices. The enhanced preference for ethanol over dextrose solutions shown by the ethanol polydipsic group can be attributed to physical dependence rather than regiment produced artifacts.