Effects of moderate ethanol sedation on brain regional 2-deoxyglucose uptake in alcohol-sensitive and alcohol-insensitive rat lines

Impact of Alcohol on Glycemic Control and Insulin Action

Alcohol has profound effects on tissue and whole-body fuel metabolism which contribute to the increased morbidity and mortality in individuals with alcohol use disorder. This review focuses on the glucose metabolic effects of alcohol, primarily in the muscle, liver and adipose tissue, under basal postabsorptive conditions and in response to insulin stimulation. While there is a relatively extensive literature in this area, results are often discordant and extrapolating between models and tissues is fraught with uncertainty. Comparisons between data generated in experimental cell and animals systems will be contrasted with that obtained from human subjects as often times results differ. Further, the nutritional status is also an important component of the sometimes divergent findings pertaining to the effects of alcohol on the regulation of insulin and glucose metabolism. This work is relevant as the contribution of alcohol intake to the development or exacerbation of type 2 diabetes remains ill-defined and a multi-systems approach is likely needed as both alcohol and diabetes affect multiple targets within the body.

Reduction of regional brain glucose metabolism following different durations of chronic ethanol consumption in mice: a selective effect on diencephalic structures

The effects of chronic alcohol consumption on regional brain glucose metabolism were examined in Balb/c mice using the [14C]2-deoxyglucose autoradiographic technique. Animals were given a solution of 12% v/v ethanol as their only source of fluid for either 6, 12 or 18 months and compared to control groups receiving either an isocaloric solution or saccharose or tap water. Alterations of cerebral brain glucose metabolism were assessed in mice who were returned to a non-alcoholic diet and allowed to freely explore a T-maze. The results showed that chronic ethanol consumption induced reductions of regional metabolic activity which were functions both of the duration of alcohol treatment and of the structure studied. Whereas a six month period of alcoholization did not induce any significant effects on metabolic activity, 12 months of treatment were necessary to induce the first observable and significant reductions in [14C]2-deoxyglucose labelling. These effects were mainly limited to diencephalic structures such as the lateral mammillary nuclei and the anterodorsal thalamic nuclei. The cerebellum was also affected but to a lesser degree. After 18 months of alcoholization, a generalized spread of the metabolic reduction to the entire mammillary complex (lateral, medial and posterior nuclei) and to the thalamic nuclei was observed. This same duration of treatment was necessary to induce the first detectable decrease of metabolic activity in the hippocampus. In agreement with data from human neuropathology, these findings confirm the particular vulnerability of diencephalic structures to ethanol and suggest that damage limited to diencephalic regions rather than to hippocampal or cortical areas could be primarily responsible for the memory disorders observed in Korsakoff's syndrome.

Ethanol effects on 2-deoxyglucose uptake into tissues obtained from LS and SS mice

The uptake of 2-deoxy-D-[14C]glucose (2-DG) has been used with some success to identify neuronal sites of drug action, and has also been useful in identifying brain regions that are differentially sensitive to ethanol in selectively bred rat lines, the alcohol tolerant (AT) and alcohol nontolerant (ANT) lines. The studies reported here utilized the 2-DG method in an attempt to ascertain whether the LS and SS mouse lines, which were selectively bred for differences in sensitivity to high dose, anesthetic effects of ethanol, do so because of disruption of specific neuronal sites. LS and SS mice were injected with saline or a 4.0-g/kg dose of ethanol 15 min before injection with 2-deoxy-D-[14C]glucose, and uptakes into blood, eight brain regions, the liver, and adrenal tissues were measured 2-60 min afterwards. Ethanol produced statistically significant decreases in 2-DG uptake into every region of the LS mouse brain, but only three brain regions showed significant decreases in uptake in the SS brain. Other SS brain regions showed a trend towards decreased uptake, but these trends were not significant. A comparison of percent decrease in 2-DG uptake across all brain regions showed that ethanol decreased 2-DG uptake approximately twice as much in LS brain regions as in SS brain regions. Since 2-DG uptake into adrenal and hepatic tissue was not affected by ethanol injection in either mouse line, it seems likely that the decreased 2-DG uptake, seen more readily in the LS brain, is due to ethanol-induced central nervous system (CNS) depression.(ABSTRACT TRUNCATED AT 250 WORDS)

Plus-maze behavior and susceptibility to 3-mercaptopropionate-induced seizures in rat lines selected for high and low alcohol sensitivity

Selective outbreeding for high and low acute alcohol sensitivity has produced two rat lines (alcohol-sensitive ANT and alcohol-insensitive AT lines) that also differ in their sensitivity to GABAergic drugs, benzodiazepines and barbiturates. These rats were now compared in two behavioral tests believed to involve central GABAergic mechanisms, in elevated plus-maze test and in 3-mercaptopropionate-induced seizure test. The AT animals spent more time in the open arms of the plus-maze than the ANT rats, suggesting that the AT's behave less anxiously. The ANT's were more susceptible to seizures induced by 3-mercaptopropionate (50 mg/kg, IP) than the AT's, suggesting the ANT's having greater sensitivity to a decrease in brain GABA concentration. At the time of the first seizure signs, there was a tendency, though a nonsignificant one, to greater decreases in brain GABA in the ANT's than AT's. These results suggest that there are differences in GABA-related behaviors between ethanol-naive rats of the lines produced by selective outbreeding for differences in alcohol sensitivity. In theory, these behavioral line differences might physiologically counteract alcohol effects in the ANT's and enhance them in the AT's. In elevated plus-maze test, however, an acute dose of ethanol (1 g/kg, IP) significantly changed the behavior of the ANT animals, but only up to level of the AT rats. The apparent sensitivity to ethanol may thus be dependent on the naive behavior of the alcohol-insensitive AT and alcohol-sensitive ANT rats.

Mechanisms of alcohol intoxication in a rodent model: blunted alcohol-opposing reaction in "alcohol-sensitive" rats

In this paper we describe new data and review some studies on the mechanisms of alcohol-induced motor impairment in rats. Habituation to handling did not affect the naive behavioural differences between the alcohol sensitive and alcohol insensitive rat lines. Nor was there any effect on the differential sensitivities of the lines to the motor impairing and hypnotic effects of alcohol. Peripheral mechanisms may be involved in the differential behaviours of these lines, as the plasma corticosterone response was much weaker in the alcohol sensitive animals, suggesting a limited capacity to react to stress and alcohol. A similar blunted response to acute ethanol exposure was found in the uptake of the benzodiazepine antagonist [3H]Ro 15-1788 in vivo by the cerebellum of alcohol sensitive rats. The finding that these rat lines do not have any general differences in their brain inhibitory GABAergic receptors was extended to the spinal cord inhibitory glycinergic receptors, which showed only a modest line difference in their dissociation constant. The apparent localisation of the two main receptor differences (high-affinity [3H]muscimol binding and diazepam sensitivity of [3H]Ro 15-4513 binding) to the cerebellar granule layer suggests a genetic modification in the granule cells of alcohol-sensitive rats. In conclusion, our studies on acute intoxication by moderate alcohol doses show that several central nervous and peripheral factors may be involved in this behaviour. As many of these factors mitigate the effects of alcohol, alcohol antagonistic treatments should be aimed at activating and supporting multiple adaptive phenomena.

Cerebellar GABAA receptor binding and function in vitro in two rat lines developed for high and low alcohol sensitivity

The Bmax of the [3H]muscimol binding in the cerebellum of ethanol-naive alcohol-sensitive ANT (Alcohol Non-Tolerant) rats was only about 70% of that in the alcohol-insensitive AT (Alcohol Tolerant) rats. There were no line differences in the muscimol binding to cerebrocortical and hippocampal membranes. In the alcohol-sensitive rats, the cerebellar [3H]muscimol binding (5 nM) negatively correlated with the ethanol-induced motor-impairment measured in the tilting plane test. Muscimol stimulated the flux of 36Cl- in cerebellar synaptoneurosomes and non-filtered microsacs to the same extent in both rat lines. Ethanol produced only a small, although statistically significant, enhancement of the muscimol-stimulated chloride flux in both rat lines. The present data confirms our earlier finding of a low level of muscimol binding in the cerebellar membranes of alcohol-sensitive rats as compared to alcohol-insensitive rats. Further studies are needed to determine the relationship between the Cl- flux stimulation by muscimol and the differential muscimol binding in the cerebellum of these rat lines, and its importance for alcohol sensitivity.