Divergent ethanol-drinking behavior in rats selectively bred for high- or low-ethanol-drinking behavior could be related to differences in the sensitivity of the CNS to ethanol. In the current study, we examined the effects of acute (i.e., single injection) ethanol administration on local cerebral glucose utilization (LCGU) within selected brain regions of high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) rats. Adult, male, HAD and LAD rats from replicate line 2 were injected intraperitoneally with saline, or ethanol, at doses of 0.25 g/kg or 1.0 g/kg, during their dark cycle; 10 min later, [14C]-2-deoxyglucose ([14C]-2-DG; 125 μCi/kg) was injected into the femoral vein. Timed arterial blood samples were collected over 45 min and assayed for plasma glucose, ethanol, and [14C]-2-DG levels. Rats were then decapitated, and their brains were quickly extracted and frozen in isopentane at –50°C. Coronal brain sections were prepared and apposed to x-ray film for 2 days, and image densities were determined by using quantitative autoradiography. Data were collected from several key limbic (nucleus accumbens, ventral tegmental area, olfactory tubercle, amygdala, hippocampus, ventral pallidum, and septum), basal ganglia, cortical (medial prefrontal, frontal, parietal, temporal, occipital, entorhinal, piriform, and cingulate), and subcortical (thalamus, habenula, and superior colliculus) structures. After administration of both low (0.25 g/kg) and moderate (1.0 g/kg) doses of ethanol, LCGU values were lower, relative to those for saline controls, in several CNS regions (lateral septum; posterior cingulate, frontal, parietal, and temporal cortices; dorsomedial striatum; and dorsomedial thalamus) of LAD but not HAD rats. These findings may indicate that certain CNS regions of LAD-2 rats are more sensitive than regions of HAD-2 rats to the effects of low-to-intermediate doses of ethanol.

The [14C]-2-deoxyglucose ([14C]-2-DG) quantitative autoradiographic technique was used to determine rates of local cerebral glucose utilization (LCGU) in discrete brain regions of adult, male alcohol-preferring (P) rats after 2 weeks of ethanol deprivation (E-D), 3 and 14 days of ethanol-relapse drinking (E-R3; E-R14), and in P rats, which were chronically drinking ethanol (E-C) for 8 weeks during daily 3-h scheduled-access sessions to 15% (vol./vol.) ethanol and water, or were ethanol-naive (E-N). The hypothesis to be tested was that ethanol-relapse drinking is initiated to restore changes in functional activity back to their chronic ethanol–exposed state. The LCGU rates were measured 1 h before the scheduled-access session. Mean ethanol intake did not differ among the groups. The LCGU rates were decreased in 41 of 57 regions or subregions examined in E-C rats compared with findings for E-N rats, including subregions of the cerebral cortex, hippocampus, and structures in the mesocorticolimbic and nigrostriatal systems. After 2 weeks of deprivation, LCGU values tended to return toward control values (E-N) in most CNS regions and did not differ significantly from control values in 12 regions or subregions (e.g., parts of the limbic system, cerebral cortex). Compared with LCGU values that recovered toward control levels in the E-D group, ethanol-relapse drinking was associated with decreased LCGU values in (1) 4 of 10 limbic structures, (2) all 6 cerebral cortical regions, (3) 1 of 4 basal ganglia regions, (4) 2 of 7 hippocampus subregions, and (5) 1 of 6 thalamic nuclei. The present results indicate that ethanol-relapse drinking was associated with reduced LCGU rates in most CNS regions that recovered toward control values and suggested to us that ethanol-relapse drinking may be initiated to restore neuronal function to its prior chronic ethanol–exposure state.

BACKGROUND:The present study compared baseline local cerebral glucose utilization (LCGU) values within reward-relevant brain regions in alcohol-naïve, adult male high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) rats from replicate lines 1 and 2.METHODS:2-[14C]Deoxyglucose ([14C]2-DG) was injected (125 microCi/kg) intravenously during the rats' dark cycle. Timed arterial blood samples were collected over 45 min and assayed for glucose as well as [14C]2-DG content. Rats were then decapitated; their brains quickly removed and frozen in isopentane at -50 degrees C. Coronal sections from each brain were apposed to film and exposed for 2 days. Image densities were analyzed using quantitative autoradiography.RESULTS:Data were collected from several key limbic (nucleus accumbens, ventral tegmental area, olfactory tubercle, amygdala, hippocampus, ventral pallidum, and septum), basal ganglia, cortical (medial prefrontal, frontal, parietal, temporal, occipital, entorhinal, pyriform, and cingulate), and subcortical (thalamus, habenula, and superior colliculus) structures. Because there were no significant differences between the replicates within each drinking line, data from the two replicates were combined to determine drinking line differences. When both replicate lines were combined, there were trends toward higher (approximately 15%) LCGU rates in HAD (n = 15) versus LAD (n = 16) rats within the parietal and occipital cortices, but neither of these line differences reached statistical significance (p < 0.01).CONCLUSIONS:The findings suggested that, within the HAD and LAD replicate rat lines, the selection for alcohol preference did not lead to differences in functional brain activity, as measured with the 2-DG method.

BACKGROUND:The present study determined local cerebral glucose utilization (LCGU) rates in alcohol-naïve alcohol-preferring (P), alcohol nonpreferring (NP), and outbred Wistar rats to test the hypothesis that innate differences in functional neuronal activity are present in limbic regions as a result of selective breeding for high-alcohol drinking behavior.METHODS:All procedures were conducted during the dark cycle. 2-[14C]deoxyglucose ([14C]2-DG; 125 microCi/kg) was injected intravenously and timed arterial blood samples were collected during the following 45 min and assayed for glucose and [14C]2-DG content. Rats were then decapitated, the brains removed and frozen to -70 degrees C, and 20 microm coronal sections were prepared for quantitative autoradiographic analysis.RESULTS:Rates of LCGU were determined in 55 regions and subregions, including limbic, cortical, and subcortical structures. LCGU rates were significantly (p < 0.01) higher in several limbic (e.g., ventral tegmental area, nucleus accumbens shell, olfactory tubercle, medial prefrontal cortex, and lateral hypothalamus), cortical (e.g., parietal, temporal, occipital, cingulate, piriform, and entorhinal), and subcortical (e.g., thalamus, habenula, preoptic area, and striatum) regions in P rats, compared with NP and Wistar rats, whereas rates in Wistar rats were higher in a few regions (e.g., CA1 and CA3 regions of the posterior hippocampus) than NP rats.CONCLUSIONS:The data suggest that selective breeding for high-alcohol drinking produces intrinsically higher functional neuronal activity in the central nervous system regions of the high-alcohol consuming P line compared with low-alcohol drinking NP or Wistar rats, although these differences may not generalize to other rat lines selectively bred for divergent alcohol drinking.

The 2-[C-14]deoxyglucose (2-DG) quantitative autoradiography technique was used to determine rates of local cerebral glucose utilization (LCGU) in discrete brain regions in alcohol-chronic (A-C), alcohol-deprived (A-D) and alcohol-naive (A-N) adult, male alcohol-preferring (P) rats. The hypothesis to be tested is that neuronal alterations occur as a result of chronic alcohol drinking and some of these alterations persist for long periods in the absence of alcohol. Following 6 weeks of daily 4-h scheduled access sessions to 15% (v/v) ethanol and water, group A-D received only water during the sessions over the next 2 weeks, whereas groups A-C and A-N continued to receive ethanol-water and water-water, respectively. On the 14th day of the deprivation interval, LCGU rates were measured 1 h prior to the scheduled access period. Mean ethanol intake for the A-D and A-C groups was 1.5 +/- 0.1 g ethanol/kg body weight per 4 h. LCGU rates were significantly decreased in 49 of 57 regions or subregions examined in the A-C group compared to the A-N group, including subregions of the cerebral cortex, hippocampus and structures in the mesocorticolimbic and nigrostriatal systems. Following alcohol deprivation, LCGU values in the A-D group were partially or completely returned to A-N levels in many, but not all, regions. In several limbic regions (e.g., ventral tegmental area, olfactory tubercle, medial prefrontal cortex, ventral pallidum and lateral septum), no recovery of LCGU rates was observed after 2 weeks of alcohol deprivation. This study demonstrates that chronic alcohol consumption produces significant reductions in functional neuronal activity in P rats, some of which persist in the absence of ethanol. The extent to which LCGU rates returned to normal levels following 2 weeks of alcohol deprivation varied among brain regions, suggesting that there are imbalanced interactions among and within several CNS sites, which do not reflect either the alcohol-naive or chronic alcohol-exposed state. Such neuronal imbalances may underlie relapse of alcohol drinking following prolonged abstinence. (C) 2001 Elsevier Science Inc. All rights reserved.

BACKGROUND:The binding of [3H]DAMGO to mu-opioid sites was measured in the CNS of selectively bred high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) rats to test the hypothesis that high alcohol preference is associated with higher densities of mu-opioid receptors.METHODS:Adult, alcohol-naïve male HAD and LAD rats from replicate line 1 were decapitated and their brains frozen in isopentane. Brain sections were incubated with 5 nM [3H]DAMGO, and nonspecific binding was determined in the presence of unlabeled DAMGO. Films were exposed for 60 days, then analyzed using quantitative autoradiography.RESULTS:The densities of [3H]DAMGO binding sites were measured within subregions of neocortex, limbic system, basal ganglia, diencephalon, and brainstem. LAD rats had significantly higher [3H]DAMGO binding (10-30%) than HAD rats within the anterior dorsal hippocampus (CA2), posterior hippocampus (dorsal CA1, and ventral CA1, CA3, and dentate gyrus), thalamus (medial dorsal, lateral, medial dorsal, central, ventral lateral, ventral medial, and ventral medial geniculate nuclei), habenula, and amygdala. No significant interline differences were found in the prefrontal, cingulate, frontal, parietal, temporal, occipital or entorhinal cortices, olfactory tubercle, nucleus accumbens, lateral septum, ventral tegmental area, hypothalamus, caudate-putamen, substantia nigra, claustrum, central gray, or superior colliculus.CONCLUSIONS:The present findings with the HAD and LAD lines do not support the hypothesis that high alcohol preference is associated with higher densities of CNS mu-opioid receptors. Instead, the present results, in combination with previously published findings, suggest that the mu-opioid system may play a complex role in regulating high-alcohol-drinking behavior.