Oxytocin attenuates tolerance not only to the hypothermic but also to the myorelaxant and akinesic effects of ethanol in mice.

Inhibition of ethanol tolerance by oxytocin has been demonstrated previously using the hypothermic effect only. The purpose of the present experiment was to investigate the effect of oxytocin on the development of tolerance to ethanol-induced hypothermia, myorelaxation and akinesia in mice. Four groups of mice received daily intraperitoneal injections of saline or oxytocin (0.005 mg) plus saline or ethanol (2 g/kg). The peptide was administered 2 hours before ethanol. For five consecutive days, temperature measurements were performed 20 minutes before and after ethanol injection. Myorelaxation and akinesia were evaluated following the second temperature measure. Oxytocin pretreatment, which had no intrinsic effects, resulted in a robust selective attenuation of tolerance to ethanol-induced hypothermia, myorelaxation and akinesia. These results suggest that the mechanisms for peptide modulation are common to these three typical effects of ethanol.     

The role of conditional drug responses in tolerance to the hypothermic effects of ethanol

The role of predrug cues in tolerance to ethanol-induced hypothermia was investigated in two experiments. The results of Experiment 1 demonstrated that tolerance was displayed only when the drug was administered in conjunction with environmental stimuli that had, in the past, accompanied ethanol administration. A conditional hyperthermic response was elicited when a placebo, instead of ethanol, was administered in conjunction with the usual ethanol cues. Results of Experiment 2 suggested that tolerance to ethanol-induced hypothermia can be extinguished by repeated placebo injections. These results indicate that associative processes, previously demonstrated to modulate opiate tolerance, also modulate ethanol tolerance.     

Influence of felbamate on selected central effects of ethanol in experimental animals

Both felbamate and ethanol demonstrate complex action on central nervous system (CNS). There are several data indicating that ethanol influences pharmacokinetics of new generation of antiepileptic drugs. Investigation of CNS interaction of felbamate and ethanol may bring up some suggestions as for adverse reactions of concomitance of these substances and consequences of such reactions are concerned. The influence of felbamate on the action of ethanol in a rota-rod test (1.5 g/kg), the duration of ethanol sleeping time (4 g/kg) as well as on spontaneous locomotor activity (2 g/kg) and ethanol-induced hypothermia (2.5 g/kg) was investigated. Felbamate was administered at a single dose (200 mg/kg i.p.) or as daily injections dose (50 mg/kg for 10 days). At a single dose, felbamate prolonged ethanol-sleeping time, increased ethanol-induced disturbances of motor coordination and ethanol-induced hypothermia as well as prevented increased locomotor activity observed after ethanol intake. Felbamate administered for 10 days reduced ethanol sleeping time, did not effect ethanol on locomotor activity of mice, but augmented ethanol-induced changes in motor coordination and ethanol hypothermia. These interactions may be of pharmacodynamic character, but pharmacokinetic nature cannot be excluded, felbamate and ethanol are substrates for the cytochrome CYP2E1.     

Initial sensitivity versus acquired tolerance to ethanol in rats selectively bred for ethanol sensitivity

Chronic tolerance to ethanol-induced sleep, motor impairment (moving belt test), and hypothermia were examined in two lines of rats that had been selectively bred for their different initial sensitivities to ethanol. In agreement with previous work (Mayer et al. 1982, 1983), the least-affected (LA) rats were found to be less sensitive than their most-affected (MA) counterparts in all three tests. Chronic treatment with ethanol resulted in a more rapid and more marked tolerance development in MA animals than in LA ones. The two lines did not differ in final level of tolerance achieved for either sleep time or hypothermia. However, significant differences were observed with respect to the moving belt test, in that at the end of chronic ethanol treatment the MA animals were more resistant to ethanol than the LA ones. These studies support the existence of a relationship, but not necessarily a direct genetic linkage, between initial sensitivity and acquired tolerance.     

Interaction between central effects of ethanol and tricyclic antidepressants, imipramine and amitriptyline in mice and rats

The effect of a combined treatment with ethanol and imipramine or amitriptyline was tested in mice and rats. The antidepressants were given in one or, in some experiments, in 21 daily doses of 10 mg/kg each. In mice the effect of antidepressants was tested on acute toxicity, disturbances of rota-rod performance, hypothermia and sleeping induced by ethanol, in rats the effect of the antidepressants on the development of tolerance to sleep-inducing and hypothermic action of ethanol was investigated. Amitriptyline showed a tendency to pontentiate the ethanol-induced acute toxicity, while imipramine did not change it. Given in a single dose the antidepressants have a tendency to potentiate the impairment of motor coordination induced by ethanol, but after a prolonged administration did not influence the ethanol effect in the rota-rod test. The antidepressants enhance ethanol-induced hypothermia and prolong the ethanol sleeping time. The development of tolerance to hypnotic effect of ethanol in rats is not affected by amitriptyline and imipramine, but the antidepressants prevent the development of tolerance to hypothermic effect.     

Initial sensitivity and acute tolerance to ethanol in the P and NP lines of rats

We recently reported that selectively bred, alcohol-preferring (P) and alcohol-nonpreferring (NP) rats differ in sensitivity to a single sedative-hypnotic dose of ethanol, as measured by performance in the jump test. The present study examines the contributions of initial sensitivity and acute tolerance development to this difference. Initial sensitivity, assessed by brain alcohol content upon loss of the aerial righting reflex, was not significantly different between P and NP groups given 3 g ethanol/kg body weight intraperitoneally. Acute tolerance was indexed from blood alcohol concentrations (BAC) upon recovery of jumping performance following two successive ethanol doses. Practiced P and NP rats were required to jump 35 cm to a descending platform following the IP injection of 2.0 g ethanol/kg. The NP group took signiificantly longer (74 min) than the P (33 min) group whereupon BAC₁ of NP rats (234 mg%) was significantly lower than that of P rats (250 mg%). A second injection (1.0 g/kg) was given immediately after the animals reached the 35 cm criterion. Again, NP rats took significantly longer (124 min) than P rats (52 min) to jump 35 cm and BAC₂ of NP animals was lower (295 mg%) than that of P rats (343 mg%). The difference between BAC₂ and BAC₁, the measure of tolerance development, was significantly larger for P rats (90 mg%) than for NP rats (61 mg%). No significant differences in blood ethanol elimination weree observed between the groups. The data indicate no difference in initial sensitivity between P and NP animals but that P rats develop acute tolerance more rapidly and/or to a greater degree than do NP rats. The results are consistent with a relationship in these selectively bred lines of rats between alcohol preference and the development of acute tolerance.     

The effect of doxepin on the central action of ethanol.

The effect of combined treatment with doxepin and ethanol was tested in mice, rats and rabbits. Doxepin was given in a single dose (5 or 10 mg/kg) or chronically (10 mg/kg/d for 21 days). Doxepin did not affect ethanol toxicity and ethanol-induced impairment of rota-rod performance, but potentiated ethanol-induced hypothermia (only acutely) and prolonged ethanol-induced sleep in mice. Given acutely it potentiated the inhibitory effect of ethanol on locomotor activity in mice, while given chronically it counteracted the ethanol-induced sedation. Doxepin did not interfere with ethanol-induced EEG effects in rabbits, and prevented the development of tolerance to hypothermic, but not to hypnotic effects of ethanol in rats. In general, the interference of doxepin with ethanol was more pronounced after single doses of the drug than after chronic treatment.     

Chronic ethanol consumption produces genotype-dependent tolerance to ethanol in LS/Ibg and SS/Ibg mice.

It is well known that chronic ethanol administration produces tolerance to the sedative-hypnotic and hypothermic effects as well as low-dose locomotor inhibitory effects of ethanol. We report herein characterization of a convenient method of producing genotype-dependent functional tolerance to ethanol-induced locomotor inhibition. Mice, LS/Ibg (LS) and SS/Ibg (SS), which differ markedly in acute effects of ethanol on locomotor activity, hypothermia, and hypnotic sensitivity, were required to consume solutions of ethanol in water as the sole source of liquid. Mice were provided lab chow ad lib. and the following regimen of ethanol in water, v/v: 10% for 4 days, 15% for 4 days, 20% for 7 days, followed by 15% for periods longer than 2 weeks. Control animals received water only or were pair-fed sucrose (isocaloric with ethanol) solutions plus lab chow; both control and ethanol-consuming (15 g ethanol/kg/24 h) mice maintained similar body weights for up to 4 weeks. Blood ethanol concentrations from 10-200 mg% were obtained during a 12 L:12 D cycle. At 6 h following withdrawal, LS and SS mice showed differential dose-dependent tolerance to locomotor inhibitory effects of ethanol. However, low-dose locomotor activation was unaltered in either line of mice, and results indicate that an apparent sensitization in SS mice is secondary to development of tolerance to locomotor inhibition. Maximum tolerance to locomotor inhibition was observed after 2 weeks of chronic ethanol consumption, with responses returning to control values within 1-2 weeks after withdrawal. Rates of acquisition of tolerance were similar in LS and SS mice.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of ethanol on startle responding in alcohol-preferring and -non-preferring rats

The objectives of the present study were to determine (a) if differences exist between the selectively bred alcohol-preferring (P) and -non-preferring (NP) lines of rats in the acoustic startle response (ASR) and prepulse inhibition (PPI), and (b) the effects of ethanol on these measures. Alcohol-na?ve adult female P and NP rats received a single i.p. injection of saline or ethanol (0.25, 0.5, 1. 0, or 1.5 g/kg) and were placed in the startle apparatus 10 min later. After a 5-min acclimation period, rats received five alternating trials of a startle stimulus alone (SSA) (115-dB white noise) or a PPI trial (90-dB white noise preceding a 115-dB white noise). Analysis of the ASR revealed that P rats exhibited higher startle amplitudes than did NP rats with saline injections. The 0. 5-g/kg ethanol dose reduced the startle amplitude in P, but not NP, rats. The 1.0- and 1.5-g/kg ethanol doses nearly abolished the ASR in the NP line, whereas only the highest ethanol dose had this effect in the P line. Vehicle-treated P and NP rats exhibited comparable PPI levels, but only P rats showed a significant disruption (30%) at the 0.50-g/kg ethanol dose. Neither P nor NP rats were affected by ethanol treatment at the 0.25-g/kg dose. Overall, the results suggest that: (a) the difference in baseline ASR may indicate line differences in the neurocircuitry mediating this response, possibly reflecting higher innate levels of emotional reactivity in the P line; (b) the P line may be more sensitive than the NP line to the effects of ethanol in reducing emotional reactivity; and (c) low-dose ethanol may have a greater disruptive effect on sensorimotor gating mechanisms in the P than NP rat.     

Tolerance to ethanol and cross-tolerance to pentobarbital and barbital

A chronic regimen of ethanol by intubation, which produced clear tolerance to ethanol-induced hypothermia, ataxia and narcosis, produced only a marginal degree of cross-tolerance to these effects of pentobarbital. The lack of appreciable cross-tolerance to pentobarbital-induced hypothermia and ataxia was also observed over a wide range of test doses. However, cross-tolerance to barbital was observed after chronic treatment with ethanol. Increased rate of drug biotransformation did not contribute significantly to the observed tolerance and cross-tolerance. The difference in the extent of cross-tolerance between ethanol and the two barbiturates is consistent with the hypothesis that there is a degree of specificity in the sites of action of ethanol and other sedative-hypnotic drugs.     

Effect of chronic pentobarbital treatment on the development of cross-tolerance to ethanol and barbital

Recently, we reported that a chronic regimen of ethanol by intubation, which produced clear tolerance to ethanol-induced hypothermia, ataxia and sleep, produced only a marginal degree of cross-tolerance to these effects of pentobarbital. The present experiments were designed to test the reverse process by examining cross-tolerance to pentobarbital after chronic pretreatment with ethanol, chronic pentobarbital treatment by gavage conferred clear cross-tolerance to both barbital- and ethanol-induced hypothermia, ataxia and sleep. In a separate experiment, cross-tolerance to barbital- and ethanol-induced hypothermia and ataxia was demonstrated over a wide range of test doses. Determination of ethanol blood levels as well as a complete time course of absorption, distribution and elimination of ethanol suggested that pharmacokinetic alterations may play a role in the development of cross-tolerance to ethanol in pentobarbital-treated subjects. The asymmetry of cross-tolerance raises the possibility that pentobarbital and ethanol invoke tolerance by mechanisms that are not wholly identical. This possibility requires further exploration. Conceivably the actions of ethanol which mediate the measured effects form a subset of a larger range of pentobarbital actions that could provide a stronger stimulus to tolerance development.     

Cross-tolerance between ethanol and morphine with respect to their hypothermic effects

Daily administration of ethanol (10-12 g/kg) to rats in a liquid diet resulted in tolerance to the hypothermic effects of ethanol. The rats also developed cross-tolerance to the hypothermic effect of morphine (15 and 30 mg/kg), whereas no cross-tolerance to the hyperthermic effect of morphine (5 mg/kg) was seen. Administration of morphine (30 mg/kg i.p.) for 3 days resulted in tolerance to morphine hypothermia and also cross-tolerance to ethanol-induced hypothermia. These studies fit with our hypothesis that tolerance and cross-tolerance among drugs develop to drug effects rather than to the drug per se. Therefore drugs sharing a common effect, even by different mechanisms, might show cross-tolerance for that effect.     

Characteristics of ethanol tolerance in alcohol drinking (AA) and alcohol avoiding (ANA) rats

The development of tolerance to ethanol was examined in two rat lines selected for high (AA) and low (ANA) ethanol consumption. In the first experiment, the acquisition of tolerance to the motor-impairment, hypothermic and hypnotic effects of ethanol produced by daily treatment with 5 g/kg ethanol for a period of 24 days was examined. Tolerance to these effects of ethanol was observed in the AA rats while marginal or no tolerance was demonstrated in the ANA rats. In the second experiment the development of rapid tolerance to the hypothermic and hypnotic effects of ethanol was examined. The hypothermic and hypnotic responses to IP injection of 3.5 g/kg ethanol were found to be attenuated in the AA but not the ANA rats by a single equivalent ethanol injection given 24 h earlier. These results suggest some relationship between the capacity to develop tolerance and voluntary ethanol intake.     

Influence of fluoroquinolones on the central action of ethanol.

The influence of ciprofloxacin, ofloxacin and pefloxacin on acute toxicity of ethanol, ethanol-induced hypothermia, ethanol sleeping time was investigated in mice. Moreover, the combined effect of fluoroquinolones and ethanol on spontaneous locomotor activity, motor coordination in mice and ethanol abstinence syndrome in rats was examined. The fluoroquinolones (20 and 80 mg/kg) were injected intraperitoneally. The drugs were given in single or repeated doses for 7 days. In acute experiments, drugs were given 30 min before ethanol administration. In chronic experiments, the last dose of fluoroquinolones was given 18 h prior to ethanol injection. It has been shown that the fluoroquinolones decrease acute toxicity of ethanol, antagonize its hypothermic effect, decrease ethanol inhibitory effect on motor coordination in mice, and increase ethanol-induced hypermotility in mice and audiogenic seizure response in rats during alcohol abstinence syndrome. Ciprofloxacin and ofloxacin administered repeatedly increase the influence of ethanol on duration of ethanol-induced sleep. The influence of fluoroquinolones on ethanol central action depends on the drug used, its dose and route of administration.     

Differences in response to the aversive properties of ethanol in rats selectively bred for oral ethanol preference

A conditioned taste aversion (CTA) paradigm was used to determine whether aversion to the pharmacological effects of ethanol, apart from orosensory cues, can contribute to genetic differences in voluntary ethanol consumption. Four doses of ethanol, administered IP, were paired with the consumption of a 0.1% saccharin solution in rats from the alcohol-preferring (P) and alcohol-nonpreferring (NP) lines. Repeated pairing of saccharin and ethanol in a dose of 1.0 g/kg produced stronger and more prolonged aversion to saccharin in NP rats, compared with P rats, at comparable blood ethanol levels. A low dose of ethanol (0.25 g/kg) produced transient conditioned facilitation of saccharin consumption in P rats, but not in NP rats, at comparable blood ethanol levels. The results suggest that rats of the NP line find the postingestional effects of high-dose ethanol more aversive, and low-dose ethanol less reinforcing, than do rats of the P line. Genetic differences in voluntary ethanol consumption may be due, in part, to differences in aversion to the postingestional effects of ethanol.     

Environment-dependent tolerance to ethanol produced by intracerebroventricular injections in mice

In comparison to other routes of drug administration, an intracerebroventricular (ICV) injection requires the use of a very small amount of ethanol in mice to produce a brief but substantial hypothermic response. By avoiding the longer duration of drug action, use of ICV injections may facilitate the demonstration of the contribution of certain aspects of learning in the expression of tolerance. Therefore, tolerance to ethanol was developed in mice in a Pavlovian conditioning paradigm with eight ICV injections of ethanol delivered at 2-h intervals so that the animals received four injections per day for 2 days. The effect of ethanol in a different environment was tested on the following day. Environment-dependent tolerance to the hypothermic effect of ethanol and a robust conditioned compensatory response were demonstrated when the mice were trained and tested with ICV injections of 2.0 mg ethanol. The environment-dependent tolerance was also evident when the mice were trained with ICV injections and tested with intraperitoneal injections of ethanol. These results demonstrate that ICV injections are a beneficial means of clarifying the role of learning phenomena in the development of tolerance.     

Sensitivity and tolerance to ethanol-induced incoordination and hypothermia in HAFT and LAFT mice

Acute functional tolerance (AFT) manifests as rapid adaptation during a single ethanol exposure, leading to a decrease in the behavioral response to ethanol. In order to investigate the genetic and environmental components of the development of AFT, mice were selectively bred in replicate from HS/Ibg mice. High (HAFT) and low (LAFT) acute functional tolerance selected lines were bred to differ in the rate of development and magnitude of AFT to ethanol's intoxicating effects using a static dowel-balancing task. In the present set of experiments, HAFT and LAFT mice were tested for development of AFT on a fixed-speed rotarod using a protocol similar to that for which they were selected. HAFT mice developed greater AFT to ethanol than did LAFT mice. In a separate experiment, other mice from these lines were tested for initial sensitivity and the development of chronic tolerance to ethanol-induced hypothermia, and ethanol-induced incoordination in the grid test. Previous research has detected possible common genetic control of these phenotypes. No differences between lines were found in initial sensitivity to ethanol or in the development or magnitude of chronic tolerance in either test. These experiments show that genetic factors influencing the development of acute tolerance to ethanol-induced intoxication are at least partially distinct from those influencing initial sensitivity and the development of chronic tolerance to ethanol-induced hypothermia and incoordination. Furthermore, these experiments show that AFT measured by the stationary dowel generalizes to AFT measured by the fixed-speed rotarod.     

Suppression of ethanol tolerance and dependence in rats treated with DSP-4, a noradrenergic neurotoxin

The formation of tolerance to the hypothermic effect of ethanol was inhibited in rats after intraperitoneal injection of the neurotoxin DSP-4 50 mg/kg. The neurotoxin also significantly suppressed the ethanol withdrawal syndrome; hyperlocomotion, audiogenic seizures and spasticity. These behavioural changes were accompanied by a 52% decrease of the brain norepinephrine (NE) content, with no alterations in the dopamine or serotonin levels. The results indicate that intact NE neurons are necessary for the development of tolerance to ethanol-induced hypothermia and are involved in the expression of the ethanol withdrawal syndrome.     

Interaction between des-Glycinamide-[ARG]vasopressin and serotonin on ethanol tolerance

Sham and electrolytic lesions of the dorsal, median, and dorsal+median raphe nuclei were made in different groups of rats. One week later, daily oral treatment with ethanol (5 g/kg p.o. for 25 days) was started. This treatment produced tolerance to the hypothermic and motor impairing (moving belt test) effects of ethanol. On day 26, ethanol was stopped and subcutaneous injection of either 10 μg of des-Gly⁹-[Arg⁸]vasopressin (DGAVP) in saline or saline alone was started. The retention of tolerance to ethanol was measured at 3-day intervals for both hypothermia and motor-impairment. In sham-saline groups, disappearance of tolerance took 3 days for the hypothermic effect, and 9 days for the motor-impairment effect. Tolerance to both effects, however, was still observed after 9 days in DGAVP-treated rats with either sham or dorsal raphe lesions. Peptide treatment, on the other hand, failed to maintain tolerance in rats with median or median+dorsal raphe lesions. These results suggest that an intact mesolimbic serotonin pathway is necessary for the action of DGAVP on the retention of ethanol tolerance.     

Influence of mianserin on some central effects of ethanol.

The interaction of mianserin with ethanol in central nervous system (CNS) was investigated. Mianserin was administered at a single dose of 5 or 20 mgkg(-1) i.p. or as daily injections in a dose of 2.5 mgkg(-1) given for 14 days. The influence of mianserin on acute ethanol toxicity (LD(50)), on ED(50) of ethanol in rota-rod test, on the duration of ethanol sleeping time as well as on spontaneous locomotor activity and ethanol-induced hypothermia was investigated. Moreover, the influence of mianserin administered in a dose of 10 mgkg(-1) i.p. on post-ethanol changes in the bioelectric brain activity (EEG) recordings in rabbits was also investigated. The electrodes were implanted into midbrain reticular formation (MRF), dorsal hippocampus (Hp) and frontal cortex (C).Mianserin administered as a single dose of 5 mgkg(-1) was found to decrease LD(50) of ethanol and its ED(50) in rota-rod test. Mianserin administered as a single dose of 5 or 20 mgkg(-1) prolongs ethanol sleeping time in mice but given daily for 14 days has no influence on this time. Mianserin-induced hypothermia was observed after administration of single dose as well as increase of ethanol-induced hypothermia after administration of higher dose (20 mgkg(-1)). Mianserin administered daily for 14 days had no influence on post-ethanol changes in body temperature. Single dose of mianserin 20 mgkg(-1) decreases locomotor activity in mice while repeated administration has no influence on locomotor activity. In contrast, both single dose and repeated administration of mianserin prevents increased locomotor activity of animals observed after ethanol (2.5 mgkg(-1)).Mianserin administered to rabbits (10 mgkg(-1)) induces increase of share of low frequency 0.5-4 cps and decrease of share of frequencies 4-7 and 7-10 cps in EEG recordings from MRF and Hp. The recordings from frontal cortex show increase of share of frequencies 10-13 cps. Ethanol increases the share of low frequencies in EEG recordings and decreases the share of fast frequencies. Mianserin increases its influence on fast frequencies.