Placebo effects in standard human neuropharmacological studies: effects of physiological variations of blood glucose and ammonia concentration on the electrophysiology of the visual system.
The effects on retinal and cortical visual evoked phenomena of the stimulus intensity/spatial frequency and of the spontaneous, physiological blood glucose/ammonia fluctuations were investigated comparatively in a pilot study on young male volunteers. Flash ERG and flash OPs to 5 different stimulus intensities and pattern VECP to 3 spatial frequencies were recorded at 2-hour intervals during a standard acute pharmaco-EEG experimental session (8 h) with administration of placebo; glucose and ammonia blood concentration levels were assessed concomitantly. The effects of the stimulus intensity/spatial frequency were statistically defined for each amplitude/latency measure by nonlinear regression analysis and were removed by computing the residuals from the regression function, which were then tested separately versus the glucose/ammonia concentration by linear regression. Glucose/ammonia statistically significant effects on the visual system were detected at concentration levels within the range of normality and were representative of a nonnegligeable portion of the data overall variance. These effects were selective on retinal/cortical evoked phenomena and it is conceivable that physiological or pathological metabolic changes might account for a still underestimated source of individual variability in human neuropharmacological studies otherwise adequately controlled.
Sannita
W G
WG
Center for Neuropsychoactive Drugs, University, Genova, Italy.
Balestra
V
V
DiBon
G
G
Hassan
K M
KM
Rosadini
G
G
D000328:Adult; D000641:Ammonia / Q000097:blood*; D001786:Blood Glucose / Q000502:physiology*; D001921:Brain / Q000502:physiology; D004569:Electroencephalography; D004596:Electroretinography; D005074:Evoked Potentials, Visual / Q000502:physiology; D006801:Humans; D008297:Male; D010865:Pilot Projects; D015990:Placebo Effect; D017981:Receptors, Neurotransmitter; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D014793:Visual Cortex / Q000187:drug effects / Q000502:physiology*; D014795:Visual Pathways / Q000187:drug effects / Q000502:physiology
D001786:Blood Glucose; D017981:Receptors, Neurotransmitter; D000641:Ammonia