Acetaldehyde: a positive reinforcer mediating ethanol consumption

Characterizing the scent and chemical composition of Panthera leo marking fluid using solid-phase microextraction and multidimensional gas chromatography-mass spectrometry-olfactometry

Lions (Panthera leo) use chemical signaling to indicate health, reproductive status, and territorial ownership. To date, no study has reported on both scent and composition of marking fluid (MF) from P. leo. The objectives of this study were to: 1) develop a novel method for simultaneous chemical and scent identification of lion MF in its totality (urine + MF), 2) identify characteristic odorants responsible for the overall scent of MF as perceived by human panelists, and 3) compare the existing library of known odorous compounds characterized as eliciting behaviors in animals in order to understand potential functionality in lion behavior. Solid-phase microextraction and simultaneous chemical-sensory analyses with multidimensional gas-chromatography-mass spectrometry-olfactometry improved separating, isolating, and identifying mixed (MF, urine) compounds versus solvent-based extraction and chemical analyses. 2,5-Dimethylpyrazine, 4-methylphenol, and 3-methylcyclopentanone were isolated and identified as the compounds responsible for the characteristic odor of lion MF. Twenty-eight volatile organic compounds (VOCs) emitted from MF were identified, adding a new list of compounds previously unidentified in lion urine. New chemicals were identified in nine compound groups: ketones, aldehydes, amines, alcohols, aromatics, sulfur-containing compounds, phenyls, phenols, and volatile fatty acids. Twenty-three VOCs are known semiochemicals that are implicated in attraction, reproduction, and alarm-signaling behaviors in other species.

Motor stimulant effects of ethanol and acetaldehyde injected into the posterior ventral tegmental area of rats: role of opioid receptors

RATIONALE

A recently published study has shown that microinjections of ethanol, or its metabolite, acetaldehyde into the substantia nigra pars reticulata, are able to produce behavioral activation in rats. Another brain site that could participate in such effects is the ventral tegmental area (VTA).

OBJECTIVES

We have investigated the locomotor-activating effects of local microinjections of ethanol and acetaldehyde into the posterior VTA of rats and the role of opioid receptors in such effects.

MATERIALS

Cannulae were placed into the posterior VTA to perform microinjections of ethanol (75 or 150 nmol) or acetaldehyde (25 or 250 nmol) in animals not previously microinjected or microinjected with either the nonselective opioid antagonist naltrexone (13.2 nmol) or the irreversible antagonist of the micro-opioid receptors beta-funaltrexamine (beta-FNA; 2.5 nmol). After injections, spontaneous activity was monitored for 60 min.

RESULTS

Injections of ethanol or acetaldehyde into the VTA increased the locomotor activity of rats with maximal effects at doses of 150 nmol for ethanol and 250 nmol for acetaldehyde. These locomotor-activating effects were reduced by previously administering naltrexone (13.2 nmol) or beta-FNA (2.5 nmol) into the VTA.

CONCLUSIONS

The posterior VTA is another brain region involved in the locomotor activation after the intracerebroventricular administration of ethanol or acetaldehyde. Our data indicate that opioid receptors, particularly the micro-opioid receptors, could be the target of the actions of these compounds in the VTA. These results are consistent with the hypothesis that acetaldehyde could be a mediator of some ethanol effects.

Central vs. peripheral administration of ethanol, acetaldehyde and acetate in rats: effects on lever pressing and response initiation

The metabolites of ethanol, acetaldehyde and acetate, are biologically active, and different effects may be produced depending upon the particular metabolite and the route of administration. These studies characterized the effects of intraperitoneal (IP) vs. intraventricular (ICV) administration of ethanol, acetaldehyde, and acetate administered to male Sprague-Dawley rats. Operant behavior was assessed by conducting a detailed temporal analysis of lever pressing with rats responding on a fixed ratio 5 schedule of food reinforcement. IP administration of all three drugs produced a rate-decreasing effect on the total number of responses. Acetaldehyde and acetate were much more potent than ethanol at reducing lever pressing. The interresponse time (IRT) distribution also was more potently altered by IP administration of ethanol metabolites than by ethanol itself. The total lever pressing and IRT distributions of ethanol- and acetaldehyde- treated rats were not significantly affected when these drugs were administered ICV, while acetate produced a marked suppression of fast responses and an increase in pausing. The metabolites of ethanol are more potent than ethanol itself in terms of altering patterns of lever pressing. Thus, the effects of ethanol administration could in part be due to the actions of its biologically active metabolites.

Higher correlation of ethanol consumption with brain than liver aldehyde dehydrogenase in three strains of rats

Voluntary ethanol consumption and high Km (mM range) brain and liver aldehyde dehydrogenase (ALDH) activity were measured in male rats of the Long-Evans, Wistar and Sprague-Dawley strains. The total amounts of ethanol consumed by the three strains did not differ significantly, nor did the levels of cerebral ALDH activity. Levels of brain ALDH did not differ as a function of ethanol exposure and across strains. Levels of ethanol consumption correlated better with levels of brain than liver aldehyde-oxidizing capacity, which were tested separately for each strain and also combining all the animals. Inherent variation in brain ALDH may be a biochemical counterpart of observed differences in voluntary ethanol intake within strains.

Voluntary ethanol consumption after ethanol and acetaldehyde treatment in alcohol-preferring C57BL mice

C57BL mice normally show a preference for alcohol solutions compared with water. The effect of chronic ethanol treatment sufficient to produce behavioural tolerance on the voluntary ethanol consumption of C57BL mice was compared with the effect of acute ethanol and acute and chronic administration of acetaldehyde. Chronic treatment with ethanol caused a loss of preference which lasted more than 12 weeks after withdrawal from the treatment. The acute ethanol treatment and the acute and chronic acetaldehyde treatments only produced a transient loss of preference which returned to normal within 1 week of cessation of treatment. The effect of these drugs on liver alcohol dehydrogenase (LAdH) was also examined. Changes in LAdH activity did not correlate with alcohol preference. Possible reasons for the different effects of the drug treatments on alcohol preference are discussed.