Analyses of smooth endoplasmic reticulum of cerebellar parallel fibers in aging, ethanol-fed rats.

The smooth endoplasmic reticulum (SER), a calcium storage organelle, is essential for normal neuronal function. Dilation of the SER is pathologic and a threat to neuronal calcium homeostasis. Dilation of the SER has been reported within the dendrites of cerebellar Purkinje neurons of aging rats after lengthy ethanol treatment. Ethanol-related alterations of parallel fiber SER have not been investigated despite the fact that such dilation may precede and contribute transsynaptically to SER dilation and degeneration in Purkinje neuron dendrites. Male Fischer 344 rats (n = 120; age = 12 months old) were randomly divided into three dietary groups (40 rats per group) and fed rat chow, the AIN-93M liquid control diet, or the AIN-93M liquid ethanol diet (without water) for 5, 10, 20, or 40 weeks (30 rats per time point). Sections from posterior vermal lobules were viewed with the electron microscope. Maximum and minimum diameters of parallel fiber SER profiles were measured. Ethanol-related dilation of parallel fiber SER was not found after 5, 10, 20, or 40 weeks of treatment. Age-related dilation of parallel fiber SER profiles did occur. These findings support the suggestions that (1) parallel fiber SER, unlike the SER in Purkinje neurons, is insensitive to ethanol and (2) the mechanisms by which ethanol and aging alter cerebellar function and structure are different.