EFFECTS OF CHRONIC ALCOHOL-CONSUMPTION AND OF DEHYDRATION ON THE SUPRAOPTIC NUCLEUS OF ADULT MALE AND FEMALE RATS

Ethanol ingestion affects the hypothalamo-neurohypophysial system resu lting in increased diuresis, dehydration and hyperosmolality. We studi ed the supraoptic nucleus, of the hypothalamus, in ethanol-treated rat s, to determine if ethanol alone and/or the associated disturbances of water metabolism lead to structural alterations in a nucleus known to play a central role in fluid homeostasis. Groups of male and female r ats were ethanol-treated until 12 and 18 months of age and compared wi th age-matched pair-fed controls. Twelve and 18-month-old control grou ps and 12-month-old water control groups (rats submitted to chronic de hydration) were also included in this study in an attempt to different iate between the effects of undernutrition and dehydration/hyperosmola lity, and the specific neurotoxic effects of ethanol. We estimated the volume of the supraoptic nucleus and the numerical density of its neu rons and calculated the total number of supraoptic neurons. The volume of both supraoptic neurons and neuropil were also estimated. In immun ostained material the ratio of vasopressin to oxytocin neurons and the cross-sectional areas of the two neuronal types were evaluated. There was marked neuronal loss in alcohol-treated rats, but the volume of t he supraoptic nucleus was increased. The increase in the volume of the supraoptic nucleus correlated with and was due to increases in the vo lume of its remaining neuronal cell bodies and in the volume of its ne uropil. The increase in cell body volume was particularly marked for v asopressin neurons. No significant differences were found between cont rols and pair-fed controls in any of the parameters investigated. In w ater control rats, the volume of the supraoptic nucleus and of the sup raoptic neurons and neuropil was also greater than in pair-fed control s. However, the variations found were not as marked as in ethanol-trea ted rats and there was no cell loss. These findings reveal, for the fi rst time, that chronic ethanol consumption affects the morphology of s upraoptic neurons and neuropil and, consequently, the structure of the entire supraoptic nucleus. Moreover, this study supports the view tha t ethanol has direct neurotoxic effects on supraoptic neurons because the alterations that occur are not mimicked in animals in which water metabolism alone is disturbed.