Changes In Blood Neurotransmitter And Steroid Levels During Evoked Vertigo

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Hypothesis and Background:Experimental evidence suggests that steroids as well as various neurotransmitters are critically involved in the functioning of the vestibular system in health and disease. Yet there are no pertinent human data. We hypothesized that changes in the serum levels of cortisol and plasma levels of excitatory and inhibitory neurotransmitters may occur during evoked vertigo.Subjects and Methods:Ten healthy volunteers (median age 37, range 21-57) entered the study. Subjects were investigated at rest and at the time of maximal nystagmic reaction during caloric irrigation. The determination of glutamate, aspartate, and γ-aminobutyric acid (GABA) was performed by reverse phase high-performance liquid chromatography, whereas cortisol measurements were performed with an immunoenzymatic assay with fluorescence polarization.Results:During evoked vertigo, cortisol levels increased from a baseline value of 11.86 (±1.272) μg/dl to 14.375 (±2.183) μg/dl (p < 0.01), whereas all neurotransmitter levels decreased significantly. Glutamate levels, for instance, fell from a resting value of 25.99 (±6.30) ng/ml to 17.40 (±5.50) ng/ml (p < 0.001), and aspartate and GABA decreased as well.Conclusion:Evoked vertigo is consistently associated with an increase in steroid serum levels and accompanying decreases in the plasma levels of glutamate, aspartate, and GABA. The possible underlying mechanisms and the functional significance of these findings are discussed.

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