Episodic exposure to ethanol during development differentially affects brainstem nuclei in the macaque

Neuronal vulnerability to ethanol may be non-specific, i.e., vulnerability may be conferred by the developmental state of the population or by the site of derivation. To address these issues, the effect of developmental exposure to ethanol on three brainstem nuclei; the trigeminal motor (MoV), facial motor (MoVII) and medial superior olivary (MSO) nuclei was determined. MoVII and MSO are generated at the same time and from the same rhombomere, r4. MoV is generated earlier from r2. Macaca nemestrina were exposed to ethanol or a control solution one day per week for six or 24 weeks of gestation. Brainstems of the mature offspring were sectioned and stained. The number of neurons and volume of each nucleus were determined stereologically. Neuron number was lower in MoV and MSO following exposure to ethanol whereas MoVII appeared unaffected. No significant effects of ethanol exposure were seen on the volume and weight of the brainstem, or the volume of the individual nuclei. These findings show that ethanol differentially affects brainstem nuclei in a targeted, rather than non-specific, manner. Furthermore, they show that serious ethanol-induced neurological deficits can be present without gross morphological changes.