Neuroimaging tools for monitoring brain functions in neurodevelopmental diseases

The aim of this project was to evaluate the Intrinsic Optical Signal (IOS) response as a possible biomarker for neurodevelopmental diseases, specifically for Creatine Transporter Deficiency (CTD) and Fragile X Syndrome (FXS). The IOS is a technique that measures brain activity by analyzing blood oxygenation levels and hemodynamic flow in the brain. This is done by tracking the light absorbed by the oxygen present in hemoglobin. Both CTD and FXS are characterized by an alteration in the brain metabolism, leading to changes in blood circulation, thus suggesting the possible use of IOS in their study. To test whether this technique could be a proper biomarker, we tested its ability to differentiate of patients based on disease severity and providing a means of monitoring therapeutic responses. Initially we evaluated the amplitude of the IOS signal and its correlation to the genotype of the animal allowed a distinction between WT, heterozygous, and KO mice, with KO having the highest amplitude and heterozygous females presenting an intermediate amplitude between the other two groups. This suggested the ability of the biomarker to evaluate the expression of the SLC6A8 gene encoding for the creatine transporter. Then we evaluated the behavioural performances of KO mice during grip strength, y-maze, and rotarod, observing a correlation between the results obtained in the tests measuring neurological symptoms and the amplitude of the response of the IOS. Finally, we studied the effects of different therapies and hoe they affected KO animals. Intracerebroventricular injection of AAV9-vector containing hSLC6A8 expressed under JeT promoter allowed a decrease in the amplitude of KO mice to levels closer to those of WT animals. Preliminary studies on the effect of intranasal administration of different concentration of dodecyl creatin ester (DCE) didn’t show a significant difference in the amplitude of the different groups. Nevertheless, it was possible to assess an underlying trend showing a decrease in the amplitude with higher DCE concentrations. We also did preliminary studies on Fragile X Syndrome. An evaluation of the IOS amplitude didn’t allow an emergence of a significant difference between WT and KO, but it was still possible to observe a trend showing a decrease in the in the amplitude of KO mice. The we performed behavioural tests. Open field test didn’t show an increase a significant difference between the two groups, but KO animals’ performance suggested an increase of general activity. This trend was also supported by the results obtained in the Y-maze test, in which KO mice showed an increase in the number of total entries in the branches of the maze. The spontaneous alternation measured in the Y-maze test didn’t show any difference between the groups. Moreover, no significant correlation was present between the amplitude of the IOS signal and the animals’ performance during the behavioural tests. The use of the response of the intrinsic optical signal is also supported by its translatability to human patients through the functional Near-Infrared Spectroscopy technique. This technique is able to measure the hemodynamic flow of the brain through the use of near-infrared light. The main advantage of this technique is its low sensibility to movements, allowing the study of patients with behavioural abnormalities and children, without the necessity to sedate them.