Dementia and visual hallucinations associated with limbic pathology in Parkinson's disease.

The pathological basis of dementia and visual hallucinations in Parkinson's disease (PD) is not yet fully understood. To investigate this further we have conducted a clinico-pathological study based on 30 post-mortem PD brains. PD cases were stratified into groups according to clinical characteristics as follows: (1) cognitively intact (n=9); (2) cases with severe dementia and visual hallucinations (n=12); (3) cases with severe dementia and no visual hallucinations (n=4); and (4) cases with severe visual hallucinations and no dementia (n=5). The extent of alpha-synuclein (alphaSyn), tau and amyloid beta peptide (Abeta) deposition was then examined in the CA2 sector of the hippocampus and in neocortical and subcortical areas known to subserve cognitive function. We find that dementia in PD is significantly associated with alphaSyn in the anterior cingulate gyrus, superior frontal gyrus, temporal cortex, entorhinal cortex, amygdaloid complex and CA2 sector of the hippocampus. Abeta in the anterior cingulate gyrus, entorhinal cortex, amygdaloid complex and nucleus basalis of Meynert is also associated with dementia as is tau in the CA2 sector of the hippocampus. alphaSyn burden in the amygdala is strongly related to the presence of visual hallucinations but only in those PD cases with concomitant dementia. Statistical analysis revealed that alphaSyn burden in the anterior cingulate gyrus could differentiate demented from non-demented PD cases with high sensitivity and specificity. We conclude that alphaSyn in limbic regions is related to dementia in PD as well as to visual hallucinations when there is an underlying dementia.

An optical ionic-strength sensor based on polyelectrolyte association and fluorescence energy transfer.

The optical ionic-strength sensor is based on an indicator phase consisting of an aqueous solution of fluorescein-labelled dextran and polyethyleneimine labelled with Sulforhodamine 101 (Texas Red), confined behind a dialysis membrane. At low ionic strength the polymers associate and the average distance between the fluorescein and Texas Red is short enough for efficient energy transfer to occur. With increasing ionic strength the polymers dissociate and the efficiency of energy transfer decreases. The measured parameter is the ratio of the emission intensity at 520 nm, where fluorescein fluorescence is maximal, to the intensity at 620 nm, where the Texas Red emission is strong. The increase in the intensity ratio as a function of ionic strength is similar but not quite the same for different ions, suggesting that the mechanism of response involves more than a simple ionic strength effect.