Acetaldehyde-reinforcing effects: differences in low-alcohol-drinking (UChA) and high-alcohol-drinking (UChB) rats.

It has been suggested that acetaldehyde has a biphasic effect on voluntary alcohol consumption. At low brain concentration, it might exert reinforcing effects, whereas high acetaldehyde levels would be predominantly aversive. The objective of the current study was to compare the effect of an intraperitoneal dose of acetaldehyde (50 mg/kg) in high-alcohol-drinking (UChB) and low-alcohol-drinking (UChA) rat lines, which differ in the activity of the brain mitochondrial class 2 aldehyde dehydrogenase (ALDH2) as a consequence of differences in their ALDH2 genotypes. A classical place-conditioning procedure was used to determine the reinforcing or aversive (or both) effects of acetaldehyde in ethanol-naive UChB and UChA rats. Environmental cues were paired with an intraperitoneal 50-mg/kg injection of acetaldehyde. On 10 consecutive days, each rat received one place conditioning per day; the acetaldehyde-pairing was alternated with saline-pairing. Results showed that conditioning with the 50-mg/kg dose of acetaldehyde induced place preference in UChB rats and place aversion in UChA rats. In a second experiment, UChB and UChA rats, pretested for ethanol preference, were injected with one 50-mg/kg dose of acetaldehyde or saline and tested for their voluntary ethanol consumption during 4 weeks. Results showed that the acetaldehyde dose induced a persistent and long-lasting enhancement of ethanol intake in UChB rats, but not in UChA rats. These results, together with the finding that after administration of a 50-mg/kg dose of acetaldehyde cerebral venous blood acetaldehyde levels in UChA rats were consistently higher than levels in UChB rats, support the suggestion that differential acetaldehyde levels, differential brain ALDH2 activity, or both were responsible for the different effects of acetaldehyde in the two rat lines.     

Receptors for morphine and opioids.

Two points concerning enzymatic systems acting on disposal of morphine are discussed, namely the multiplicity of glucuronyltransferase and the effect of nalorphine on N-demethylation of morphine. Evidences of the presence of at least two different glucuronyltransferases in microsomes of rat liver, kidney and intestine are presented. These evidences are given by the different distribution of the glucuronizing activity for morphine and rho-nitrophenol in microsomal preparations of these organs; by the different glucuronidation activity for both substrates induced by phenobarbital and 3-methylcholantrene; and finally by the chromatographic separation of fractions with enzymatic glucuronidating activity only for rho-nitrophenol or only for morphine. Nalorphine in concentrations of 1.3 X 10(-3) M and 1.3 X 10(-4) M inhibited in vitro de-N-demethylation of morphine 1.3 X 10(-3) M by the supernatant of rat liver homogenates, while in concentration of 1.3 X 10(-5) M it enhanced this reaction.     

Gene therapy reduces ethanol intake in an animal model of alcohol dependence

Background:  Some gene polymorphisms strongly protect against the development of alcoholism. A large proportion of East Asians carry a protective inactivating mutation in aldehyde dehydrogenase (ALDH2*2). These subjects display high levels of blood acetaldehyde when consuming alcohol, a condition that exerts a 66 to 99% protection against alcohol abuse and alcoholism. Present knowledge allows the incorporation of therapeutic genes that can modify the expression of disease predisposing genes, an effect that can last from months to years. In line with the above, we have tested if inhibiting the expression of the aldehyde dehydrogenase gene ( ALDH2 ) by an anti- Aldh2 antisense gene can curtail the drive of alcohol-dependent animals to consume alcohol.
Methods:  Wistar-derived rats bred as high alcohol drinkers (UChB; Universidad de Chile Bibulous) were rendered alcohol dependent by a 2-month period of voluntary ethanol (10%) intake, subjected to a 3-day withdrawal period and further allowed access to 10% ethanol for only 1 hour each day. This condition results in a high ethanol intake (1.2 g/kg/60 min) which is 10 times higher than that of naïve UChB rats.
Results:  The single intravenous administration of an anti- Aldh2 antisense gene carried by an adenoviral vector reduced liver ALDH2 activity by 85% ( p  < 0.002) and inhibited voluntary ethanol intake by 50% (ANOVA p  < 0.005) for 34 days.
Conclusions:  This proof-of-principle study indicates that gene therapy approaches can be employed to achieve a long-term reduction of alcohol intake in alcohol-dependent animals and suggests that gene vectors may be developed as long-lasting therapeutic adjuncts for the treatment of alcoholism.     

Ethanol induces stronger dopamine release in nucleus accumbens (shell) of alcohol-preferring (bibulous) than in alcohol-avoiding (abstainer) rats

Several studies on the differences between ethanol-preferring versus non-preferring rat lines suggest an innate deficit in the mesolimbic dopaminergic system as an underlying factor for ethanol volition. Rats would try to overcome such deficit by engaging in a drug-seeking behaviour, when available, to drink an ethanol solution over water. Thus, in the present study we compared the effect of a single dose of ethanol (1 g/kg, i.p.) on the extracellular levels of monoamines measured by microdialysis in the shell of nucleus accumbens of University of Chile bibulous (UChB) and University of Chile Abstainer (UChA) rats, bred for 79 and 88 generations to prefer or reject ethanol, respectively. It is reported that under basal conditions extracellular dopamine levels are lower in the bibulous than in the abstainer rats, while ethanol induced a 2-fold greater increase of dopamine release in bibulous than in abstainer rats. The greater effect of ethanol in bibulous rats was not associated to differences in blood ethanol levels, since the concentration and elimination of ethanol were virtually identical in both rat lines, indicating that bibulous rats are more sensitive to the stimulation of dopamine release by ethanol than abstainer rats. No differences were observed in 5-hydroxytryptamine or metabolites measured simultaneously under basal or ethanol-stimulating conditions in bibulous and abstainer rats. Overall, the present results suggest that a low dopaminergic tone and a strong mesolimbic dopamine response to ethanol are concerted neurochemical features associated to an ethanol-seeking behaviour in rats.     

Differences in sensitivity to the aversive effects of ethanol in low-alcohol drinking (UChA) and high-alcohol drinking (UChB) rats.

A conditioned taste aversion paradigm was used to determine whether aversion to the pharmacological effects of ethanol, apart from orosensory cues, can contribute to differences in voluntary ethanol consumption in rats of the low-alcohol drinking (UChA) and the high-alcohol drinking (UChB) strains. "Alcohol-naive" UChA and UChB rats were injected intraperitoneally with ethanol (0.5, 1.0, 1.5, or 2.0 g/kg) or saline, paired with consumption of a banana-flavored solution during five conditioning trials. Repeated pairings of banana-flavored solution and ethanol at a dose of 1.5 g/kg produced aversion to the banana-flavored solution in UChA rats, but not in UChB rats, at comparable blood ethanol levels. In addition, the highest dose of ethanol tested (2.0 g/kg) produced stronger aversion to the banana-flavored solution in UChA rats, compared with findings in UChB rats. From these results it is suggested that rats of the UChA strain find the postingestional effects of high-dose ethanol more aversive than do UChB rats. Differences in voluntary ethanol consumption seem to be associated with differences in sensitivity to the aversive effects of ethanol.     

Effect of 3-amino-1,2,4-triazole pretreatment on ethanol blood levels after intraperitoneal administration

Aminotriazole (1 g/kg IP) pretreatment resulted in higher ethanol blood levels during the first hour after 90 mmole/kg IP ethanol administration and at 1 hour after when rats received 60 mmole/kg IP, than the respective controls receiving the same doses of ethanol. No difference in the blood levels at time higher than 1 hour were observed, in spite of the fact that the inhibitory effect of aminotriazole lasted more than 7 hours. These results are consistent with the idea that hepatic catalase may play a significant role in liver first pass effect when portal blood levels are expected to be rather high, but not when distribution balance is established.     

The effects of alpha-methyl-p-tyrosine pretreatment on ethanol-induced narcosis and hypothermia, as well as in the development of tolerance to these effects in UChA and UChB rats

We have previously reported that UChA rats (genetically low ethanol consumer) develop tolerance to narcosis time easier than UChB rats (genetically high ethanol consumer). We also have reported that UChA rats develop tolerance to the hypothermic effect of ethanol, while in UChB rats the repeated administration of ethanol induces sensitization towards this effect. In the present paper the effects of alpha-methyl-p-tyrosine (AMPT)--a competitive inhibitor of norepinephrine synthesis--on ethanol-induced narcosis and hypothermia, as well as in the development of tolerance to these effects, were studied in both strains of rats. Results obtained show that AMPT pretreatment induced a significantly higher increase in narcosis time and hypothermia, as well as, greater susceptibility to ethanol toxicity in UChB than UChA rats. Furthermore, the simultaneous treatment with AMPT and ethanol did not change the development of tolerance to narcosis time in both strains and to hypothermia and sensitization in UChA and UChB rats respectively.     

Absence of effect of 3-amino-1,2,4-triazole pretreatment on blood ethanol levels after oral administration, in rats

Blood ethanol levels registered in rats receiving 90 mmole/kg by gavage were not different in rats pretreated with aminotriazole (1 g/kg IP) 1 hour before, than in untreated controls. Results are consistent with the idea that no measurable gastrointestinal catalase first pass effect is present in rats.