An examination of the synergistic interaction of ethanol and thiamine deficiency in the development of neurological signs and long-term cognitive and memory impairments.
BACKGROUND
The prolonged and heavy consumption of ethanol has been associated with thiamine deficiency and a wide range of cognitive and memory impairments. The present study was undertaken to test the hypothesis that ethanol and thiamine deficiency act synergistically, producing more severe clinical neurological disturbances and cognitive and memory impairments than either thiamine deficiency or chronic ethanol alone.


METHODS
The acute neurological and long-term behavioral consequences of combined chronic (32 weeks) ethanol consumption (20% v/v in drinking water) and three separate 4-week long episodes of dietary thiamine deficiency (ET/TD) versus ethanol (ET) or thiamine deficiency (TD) treatments alone were examined in male Sprague Dawley rats aged 12 weeks at the start of treatment.


RESULTS
The ET/TD group lost less weight than the TD group during each episode of thiamine deficiency. Contrary to expectations, the progression and severity of ataxia, impaired righting reflexes, and opisthotonic posturing were similar in the ET/TD and TD groups. None of the ET animals displayed any neurological or behavioral symptoms during treatment. After withdrawal from ethanol and a 7-week recovery period, none of the groups differed in spontaneous activity. On subsequent testing, the ET group displayed a significant increase in perseverative responding in a spontaneous alternation task. A small but significant proportion of ET/TD (23%), ET (17%), and TD (8%) animals were unable to reach criterion on an initial nonmatching-to-position task (NMTP) or in two subsequent reversals of the matching and NMTP tasks, which indicated persistent learning impairments. A large proportion of animals in each of the three groups demonstrated significantly reduced accuracy compared with controls at longer delays of matching-to-position tasks (MTP), but only the ET group was consistently impaired at the shorter delays. There were no significant correlations between blood ethanol concentration and any of the learning and memory measures.


CONCLUSIONS
These results indicate that the interaction of chronic ethanol consumption and bouts of TD is both domain specific and not always synergistic. Learning and reference memory appear to be sensitive to a synergistic interaction of ET and TD, whereas short-term working memory disturbances are most affected by ET and neurological symptoms are most associated with TD. Furthermore, neither the presence of neurological symptoms nor blood ethanol concentrations appear to be good predictors of learning and memory deficits.