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Association of alleles at the Taq1 A, Taq1 B, intron 6, Taq1 D, exon 7, exon 8, and promoter-141C sites of the D2 dopamine receptor gene with D2 dopamine receptor binding characteristics in the caudate nucleus of Caucasian alcoholic and nonalcoholic subjects was determined. For the Taq1 D, exon 7, exon 8, and promoter- 141C sites there were no significant allelic differences in Bmax (number of binding sites) or Kd (binding affinity) of the D2 dopamine receptors. However, subjects having the minor alleles at the Taq1 A, Taq1 B, and intron 6 sites had significantly lower Bmax than subjects not having them. None of these three polymorphisms had any significant effect on Kd. Highly significant linkage disequilibria were observed among the Taq1 A, Taq1 B, and intron 6 polymorphic sites, but linkage disequilibria between these three sites and each of the Taq1 D, exon 7, exon 8, and promoter-141C sites were of lesser or of no significance. Taken together, these findings suggest that the Taq1 A, Taq1 B, and intron 6 polymorphisms, but not the Taq1 D, exon 7, exon 8, and promoter-141C polymorphisms, are in linkage disequilibrium with a functional allelic variant that affects D2 dopamine receptor expression.

TaqI A D2 dopamine receptor (DRD2) alleles, family stress, and cognitive markers, including visuospatial ability (Benton's Line Orientation) and event-related potentials (P300 amplitude and latency), were obtained in preadolescent boys of alcoholic and nonalcoholic fathers. In the presence of the DRD2 minor allele (A1+), the Family Stress score negatively correlated with the Line Orientation score and P300 amplitude. No significant correlations were found in boys lacking this allele (A1-). The interaction of the A1+ allele and the Family Stress score produced significant regression coefficients for both Line Orientation score (p = .002) and P300 amplitude (p = .04). Together, these two cognitive markers account for 37% of the variance in the Family Stress score of 47 A1 allele boys (p = .0002) but less than 1% in 71 A1- allele boys (p > .9). This provides the first evidence of a specific gene-environment interaction involving human cognitive functioning.

Previous studies suggest a reduced dopaminergic function in subjects with the A1 (minor) allele of the D2 dopamine receptor (DRD2) gene. To explore influences on visuospatial ability as a function of the DRD2 gene, 182 alcohol- and other drug-naive sons (age 10-14) of active alcoholic, recovered alcoholic, and nonalcoholic fathers were administered a visuospatial task (Benton's Judgment of Line Orientation Test) which makes minimal motoric/verbal demands. Visuospatial scores were lower for boys with the A1 allele and for sons of active alcoholics. A1-allele boys made more errors than A2 boys on all 11 of the template lines, with the effect being largest for the rightmost presentations. In contrast, the effect of family history for alcoholism was strongest on both right and left midquadrant presentations. Moreover, separate analyses of the two types of errors produced allele but not family history of alcoholism effects when the two lines were misjudged as farther apart than they actually were and family history but not allele effects where the two lines were misjudged as closer together. These results suggest that polymorphism of the DRD2 gene and family history of alcoholism are dissociable determinants of visuospatial ability and that visuospatial defects previously observed in alcoholics may, in part, be antecedent to their drinking behavior.

Following our initial observation that the Al allele of the D2 dopamine receptor (DRD2) gene was associated with alcoholism, a number of studies, both in the United States and abroad, have attempted to replicate and extend this finding in different Caucasian populations. In nine independent studies containing a total of 491 heterogeneous alcoholics (less severe and severe) and 495 heterogeneous controls (assessed and unassessed for alcoholism), the prevalence of the Al allele was 43.0% in the former group compared to 25.7% in the latter group (odds ratio = 2.18, p < 10(-7)). The prevalence of the Al allele increased to 56.3% in a more homogeneous sample of 158 severe alcoholics (odds ratio = 3.32, p < 10(-8)). Moreover, the Bl allele of the DRD2 gene was also found to be significantly associated with severe alcoholism. Additional data are accruing which also implicate the DRD2 Al and Bl alleles in substance use disorders other than alcoholism. If further studies continue to support the results currently at hand, they would indicate that the DRD2 gene is the most prominent single gene determinant of susceptibility to severe substance abuse. However, the larger role still appears to be played by a combination of environmental factors and as yet unidentified genes.

The effect of ethanol on an enzyme system within an intact functional plasma membrane has been studied using neural cells grown in culture. Rat C6 glioma cells in mono-layer culture were treated acutely or chronically with 100 mM ethanol and the effect of this exposure on the activity of ecto-5'-nucleotidase was determined. Acute exposure led to an increase in enzyme activity with maximum stimulation occurring at concentrations of 100 - 400 mM ethanol. Chronic treatment of cells with 100 mM ethanol for 4 - 8 days also caused an increase in ecto-5'-nucleotidase activity. Both the acute and chronic ethanol-induced stimulation of enzyme activity was completely reversible by removing the ethanol; the acute effects reversed immediately, whereas the chronic effects required several hours. The addition of Concanavalin A demonstrated that the effects on enzyme activity of both chronic and acute exposure to ethanol were blocked by modification of the external cell surface. The effect of chronic exposure to 100 mM ethanol was further localized to an action on the plasma membrane by studies which showed chronic exposure to have no effect on the intracellular 5'-nucleotidase activity. Furthermore, the occurrence of pharmacological tolerance to acute ethanol was observed in this plasma membrane system following chronic treatment of C6 cells with 100 mM ethanol. These findings are consistent with the hypothesis that mammalian neural cells can adapt to the chronic presence of ethanol through changes in their plasma membrane.

The relationships between drinking practices and cognitive functioning were examined in a non-patient sample. Neither the amount of alcohol consumed over a lifetime nor current frequency of drinking occasions was significantly (ps greater than .05) correlated with cognitive test scores. However, the quantity of alcohol consumed per drinking occasion was inversely related to performance on tests of abstraction, adaptive abilities and concept formation. The results suggest that social drinking may have deleterious effects on cognitive processes.

The enzymatic activities in post-mortem rat brain kept at 4 degrees C and at 25 degrees C were determined for a number of enzymes localized in specific cell types in the central nervous system. Choline acetyltransferase (CAT), glycerol-3-phosphate dehydrogenase (GPDH), glutamine synthetase (GS), lactate dehydrogenase (LDH) and 2',3'-cyclic nucleotide phosphohydrolase (CNPase) were found to be very stable at both 4 degrees C and 25 degrees C with only slight, if any, losses of activity being seen even at periods as long as 72 hr. Glutamic acid decarboxylase (GAD) activity was less stable than that of the other enzymes. In brains kept at 4 degrees C GAD activity was stable out to 24 hr after which it began to decline rapidly to 65% of control at 72 hr. In brains kept at 25 degrees C, GAD activity was stable for 6-8 hr and then began to steadily decline to 58% of control at 24 hr and 29% of control at 72 hr. Assuming that these enzymes have similar stabilities in post-mortem human brain, the effect of post-mortem delay in processing tissues may be of lesser significance than other factors with regard to the measured enzyme activities in human brain samples.