Effects of continuous versus intermittent ethanol exposure on rat sympathetic neurons

Background: Binge ethanol exposure is known to induce degeneration of centr al nervous system (CNS) neurons. Sympathetic hyperactivity has been related to ethanol withdrawal symptoms, but the effects of repeated withdrawals on peripheral sympathetic neurons have not been studied previously. Methods: The effects of continuous versus intermittent ethanol consumption on sympathetic neurons of the superior cervical ganglion (SCG) were studied in male Wistar rats. Two-month-old rats were divided into three groups: on e group with ethanol (10% v/v) as the drinking fluid throughout the 51/2-mo nth experiment (continuous, n = 9), one group drinking ethanol on 4 days/we ek and water on 3 days/week (intermittent, n = 9), and a control group (n = 9) with water as the only available fluid. Al groups had food ad libitum. SCG volume, neuron density, and total number of neurons were measured by us ing unbiased morphometric methods. Results: As the mean daily ethanol consumption did not differ between the t wo ethanol-exposed groups (continuous 5.7 g/kg/day versus intermittent 5.8 g/kg/day), the total dose of ethanol consumed was 42% smaller in the interm ittent group. The total number of SCG neurons decreased by 28%, and neuron density by 23%, in the intermittent group compared with the control group, whereas no significant neuron loss was observed in the continuous group. Th e volume of the SCG was similar in all study groups. The results suggest th at repeated ethanol withdrawals, rather than ethanol exposure per se, are d eleterious to sympathetic neurons. Conclusions: Ethanol-induced degeneration of neurons is not only related to the amount of ethanol consumed, but also to the patterns of drinking.