The induction of ethanol dependence and the ethanol withdrawal syndrome: the effects of pyrazole

Mechanical and Heat Hyperalgesia upon Withdrawal From Chronic Intermittent Ethanol Vapor Depends on Sex, Exposure Duration, and Blood Alcohol Concentration in Mice

Approximately half of patients with alcohol use disorder report pain and this can be severe during withdrawal. Many questions remain regarding the importance of biological sex, alcohol exposure paradigm, and stimulus modality to the severity of alcohol withdrawal-induced hyperalgesia. To examine the impact of sex and blood alcohol concentration on the time course of the development of mechanical and heat hyperalgesia, we characterized a mouse model of chronic alcohol withdrawal-induced pain in the presence or absence the alcohol dehydrogenase inhibitor, pyrazole. Male and female C57BL/6J mice underwent chronic intermittent ethanol vapor ± pyrazole exposure for 4 weeks, 4 d/wk to induce ethanol dependence. Hind paw sensitivity to the plantar application of mechanical (von Frey filaments) and radiant heat stimuli were measured during weekly observations at 1, 3, 5, 7, 24, and 48 hours after cessation of ethanol exposure. In the presence of pyrazole, males developed mechanical hyperalgesia after the first week of chronic intermittent ethanol vapor exposure, peaking at 48 hours after cessation of ethanol. By contrast, females did not develop mechanical hyperalgesia until the fourth week; this also required pyrazole and did not peak until 48 hours. Heat hyperalgesia was consistently observed only in females exposed to ethanol and pyrazole; this developed after the first weekly session and peaked at 1 hour. We conclude that Chronic alcohol withdrawal-induced pain develops in a sex-, time-, and blood alcohol concentration-dependent manner in C57BL/6J mice. PERSPECTIVE: Alcohol withdrawal-induced pain is a debilitating condition in individuals with AUD. Our study found mice experience alcohol withdrawal-induced pain in a sex and time course specific manor. These findings will aid in elucidating mechanisms of chronic pain and AUD and will help individuals remain abstinent from alcohol.

Effect of pyrazole, 4-methylpyrazole, 4-bromopyrazole and 4-iodopyrazole on brain noradrenaline levels of mice and rats

Four daily doses of pyrazole (50 mg/kg), caused a reduction in rat brain noradrenaline (NA) of over 20% when determined 24 hrs after the final injection. Neither 4-methylpyrazole (10-50 mg/kg), nor 4-iodopyrazole (10-50 mg/kg) had any effect. In mice treated similarly, pyrazole (50-400 mg/kg) caused a dose-dependent decrease in brain NA. Neither 4-methylpyrazole, 4-bromopyrazole nor 4-iodopyrazole caused any significant change in the levels. However if the brain NA levels were examined 6 hrs after a single dose, then in addition to pyrazole, 4-methylpyrazole showed a dose-dependent ability to lower brain NA. 4-bromopyrazole and 4-iodopyrazole, given acutely, caused a dose-dependent decrease in rectal temperature and exploratory behaviour. 4-methylpyrazole in high doses (200-400 mg/kg) showed similar properties but they did not correlate with the decrease in brain NA. Pyrazole, after acute treatment, showed little ability to change rectal temperature of exploratory behaviour. It is concluded that the NA-depleting effect of pyrazole is not related to inhibition of alcohol dehydrogenase, since other 4-substituted pyrazoles which are more potent inhibitors of the enzyme have little or no effect on brain NA levels.

Serotonin and alcohol intake, abuse, and dependence: findings of animal studies

Despite a relatively large body of literature on the role of the neurotransmitter serotonin (5-hydroxytryptamine, or 5-HT) in the regulation of alcohol intake, the functional significance of serotonergic neurotransmission and its relationship to alcohol intake, abuse, and dependence remains to be fully elucidated. In part two of this review, the experimental (animal) data is summarized along two lines: the effects of serotonergic manipulations on the intake of alcohol, and the effects of acute and chronic alcohol intake, as well as the withdrawal of chronic alcohol, on the serotonergic system. It is concluded that serotonin mediates ethanol intake as a part of its larger role in behavior modulation, such that increases in serotonergic functioning decrease ethanol intake, and decreased serotonergic functioning increases ethanol intake. Ethanol produces transient increases in serotonergic functioning that activate the mesolimbic dopaminergic reward system. The results are discussed in light of recent theories describing the regulatory role of serotonin in general behavior.

Recent Advances in Pharmacological Research on Alcohol

Alcohol dependence is a major public health problem. Studies have shown that a person dependent on alcohol often coabuses other substances, such as cocaine. Cocaine is a powerful stimulant whereas ethanol is generally considered to be a depressant, with some stimulating properties. The subjective effects of these two substances in a dependent individual may often appear to be more similar than they are different. Animals also self-administer both substances. Basically, although both substances have anesthetic properties and both act to functionally increase catecholaminergic function, especially that of dopamine, there are some differences in their actions. Both alcohol and cocaine have various effects on several neurotransmitters and systems, which ultimately interact to produce the feeling of well-being avidly sought by many individuals today. This drive often eventually produces a dependence which has associated social and medical consequences. It seems likely that the neurochemical changes that ensue following abuse of these substances underlie the phenomena of dependence, tolerance, and subsequent withdrawal. The apparent similarities and differences between these two substances will be reviewed in this chapter.

In vivo microdialysis study of brain ethanol concentrations in rats following oral self-administration

Using intracerebral microdialysis, the time-course of ethanol absorption was determined in the striatum of rats after oral self-administration of an ethanol solution. Microdialysis samples were collected every 10 min for 1 hr before and 1 hr after consumption of ethanol over a 5-min period. Substantial levels of ethanol were detected in the brain in the first sample taken after self-administration although these levels did not correlate with the amount of ethanol consumed. Striatal ethanol levels reached maximum or near maximum by the second sample and remained constant for the time points between 20 and 60 min; at these times, brain ethanol levels correlated significantly with the amount consumed. This study demonstrates that oral consumption of ethanol leads to measurable brain levels within a relatively short time. Results suggest that experimental animals may experience the central effects of ethanol during the course of drinking and this could play a role in alcohol preference or avoidance behavior.

Characterization of an automated apparatus for precise control of inhalation chamber ethanol vapor and blood ethanol concentrations

Inhalation chambers with a monitoring and control apparatus for ethanol vapor exposure of small animals were constructed. A thermal conductivity detector was employed for continuous measurement of inhalation chamber ethanol vapor concentration. The concentration was maintained within a very narrow range (+/- 1 mg/liter) by incorporating into the design a feedback loop which controls the ethanol pump. As expected, the blood ethanol concentrations (BEC) of male Sprague-Dawley rats were positively and linearly correlated to the chamber ethanol concentration. When rats were exposed for 24 hr to a chamber ethanol concentration of 17, 25, or 32 mg/liter, correspondingly low, moderate, or high mean blood ethanol levels were obtained. When a large population of this strain of rats (n = 121) was exposed to a constant ethanol vapor concentration for 14 days (25 mg/liter) considerable interindividual variation in blood levels occurred. There was also individual variation over time in the BEC of animals monitored. The mean +/- SD BEC was 189 +/- 90 mg/100 ml for this population and a gaussian-like distribution was obtained with regard to BEC. Behavior characteristic of alcohol withdrawal was observed in rats with BEC greater than 120 mg/100 ml after 3.5, 7, or 14 days of exposure. This apparatus and inhalation paradigm make possible the precise control of chamber ethanol concentration which markedly enhances control over both intra- and intersubject fluctuation in blood ethanol levels during alcohol exposure and the comprehensive examination of relationships between a wide range of blood ethanol concentrations and their physiological and biochemical effects.

Alcohol dependence and withdrawal in the rat. An effective means of induction and assessment

Numerous problems have been associated with previous attempts to develop a suitable method for the induction and assessment of alcohol dependence and withdrawal syndrome in the rat. Using our modification of a common inhalation method for the long-term administration of ethanol, these problems can be eliminated. Adult male rats (Long Evans and Brattleboro) were exposed to ethanol vapor concentrations of 7 to 35 mg/liter of air, which cause rapid development of tolerance and physical dependence. With this inhalation method, it is possible to obtain and easily maintain high levels of ethanol in the blood (150 to 400 mg/dl). When exposure to ethanol is terminated, ethanol is eliminated from the system within 1 to 6 hr. This rapid elimination of ethanol is accompanied by a high susceptibility to withdrawal reactions. The severity of the withdrawal syndrome was assessed within 6 to 24 hr after cessation of the ethanol administration by exposing each rat individually to a 60 to 120-sec period of bell ringing. Convulsive seizures were observed in nearly 90% of the animals tested, with a mortality rate of less than 20%.

Biochemical basis of alcoholism: statements and hypotheses of present research

Experimental results and theoretical considerations on the biology of alcoholism are devoted to the following topics: genetically determined differences in metabolic tolerance; participation of the alternative alcohol metabolizing systems in chronic alcohol intake; genetically determined differences in functional tolerance of the CNS to the hypnotic effect of alcohol; cross tolerance between alcohol and centrally active drugs; dissociation of tolerance and cross tolerance from physical dependence; permanent effect of uncontrolled drinking behavior induced by alkaloid metabolites in the CNS; genetically determined alterations in the function of opiate receptors; and genetic predisposition to addiction due to innate endorphin deficiency. For the purpose of introducing the most important research teams and their main work, statements from selected publications of individual groups have been classified as to subject matter and summarized. Although the number for summary-quotations had to be restricted, the criterion for selection was the relevance to the etiology of alcoholism rather than consequences of alcohol drinking.

Monoamine metabolism in rat brain regions following long term alcohol treatment

Female Wistar rats (150--200 g) were treated with ethanol (15% w/v) for 21 days and compared with control rats given water. Ethanol administration produced a reduction of fluid and food consumption and changes in the metabolism of cerebral monoamines. There was an increase in serotonin (5-HT) turnover statistically significant in the striatum, and a decrease in noradrenaline (NA) turnover in ethanol rats as compared to controls. Endogenous NA levels were significantly increased in the diencephalon and dopamine (DA) levels were increased in the striatum. After inhibition of catecholamine synthesis with alpha-methyltyrosine (alpha-MT), NA depletion was significantly retarded but no changes in DA depletion were noted. DOPA accumulation after decarboxylation inhibition showed no significant change in any brain region studied.

Problems and pitfalls in acetaldehyde determinations

The determination of acetaldehyde in biologic samples is complicated by a variety of formation and disappearance reactions occurring in the present methods of acetaldehyde analyses. The acetaldehyde formation (ethanol oxidation) in deproteinized supernatant of tissue preparations is prevented by the use of thiourea. During deproteinization, however, it is not inhibited by thiourea, and this remains the main problem in blood acetaldehyde determinations. To circumvent this problem, the use of a correction curve is proposed which is generated by adding control blood samples to the deproteinizing agent such that the blood dilution, temperature, and the ethanol concentrations (the main factors affecting the artifactual acetaldehyde formation) in the controls are identical to those of the samples. Disappearance reactions mainly include loss of acetaldehyde due to binding and/or metabolism. The problem seems to be pronounced with human blood samples, and it is recommended that they be rapidly ( less than 5 sec) deproteinized.

Influence of chronic ethanol vapor inhalation on hepatic parenchymal and Kupffer cell function

This report evaluates the influence of chronic ethanol vapor inhalation on various facets of liver function as well as induction of hepatic and pulmonary pathology in rats. Chronic ethanol inhalation is associated with minimal hepatic dysfunction, but pronounced induction of metabolic tolerance.

Acetaldehyde metabolism in vivo during ethanol oxidation

The liver is the primary site for the oxidation of ethanol-derived acetaldehyde (AcH) in the rat. Only a small amount of the total AcH formed in this organ escapes into the rest of the body, but this amount increases with increasing hepatic ethanol concentrations. The bulk of the hepatic AcH output is eliminated extrahepatically, thus drastically changing the AcH level from that initially leaving the liver. Nevertheless, the extrahepatic blood AcH levels can be used as relatively accurate indicators of the corresponding hepatic AcH levels, since they are highly correlated with them. Significant levels of brain AcH occur only at very high arterial blood AcH concentrations.

A comparison of the effects of chronic administration of ethanol and acetaldehyde to mice: evidence for a role of acetaldehyde in ethanol dependence

After chronic exposure to ethanol or acetaldehyde vapour in concentrations which depress locomotor activity, mice show similar behavioural changes during withdrawal, and there is some degree of cross dependence. Mice exposed to acetaldehyde vapour had blood acetaldehyde concentrations similar to those of ethanol-treated mice, but brain acetaldehyde concentrations were apparently lower. There was no accumulation of acetaldehyde in blood or brain in either group during chronic administration. Chronic ethanol or acetaldehyde administration to mice is associated with an increase in the concentrations of the brain monoamines noradrenaline, dopamine and 5-HT. Withdrawal of ethanol or acetaldehyde is associated with a further, rapid, transient rise in the brain catecholamines, noradrenaline and dopamine. These results suggest that acetaldehyde may play a role in some of the biochemical and behavioural changes associated with ethanol dependence.