New Publications from Dr. Juan Pascual’s Team

Hello Glut1 Deficiency community!

Welcome to our blog!

In this month’s edition of Science with Sandra I would like to highlight a couple of recent publications from researchers and clinicians in our community.

The first publication is “Isolation of the murine genetic glucose transporter 1 deficient thalamocortical circuit: wavelet characterization and reverse glucose dependence of low and gamma frequency oscillations”. This project was developed by Dr. Juan Pascual in collaboration with researchers from UT Southwestern and UT Dallas.

This publication is a follow-up for another publication from Dr. Pascual published last year “ Metabolic modulation of synaptic failure and thalamocortical hypersynchronization with preserved consciousness in Glut1 deficiency”. Here you can find a brief summary of that and other publications. That publication concluded that seizures experienced by Glut1 Deficiency patients are associated with aberrant thalamocortical oscillations. Their mouse data indicated that the inhibitory neurons in the thalamocortical area are not working properly, therefore allowing the excitatory neurons in the area to be hyperactive and cause seizures.

The purpose of the current project was to develop a neural circuit testbed to characterize the mechanisms of thalamocortical synchronization and the effects of known or novel interventions. 

The method used in this project was to use brain slices from the thalamocortical area that were attached to a glass slide that contained an electrode grid to test different components and their effect on neural activity in that area.

The researchers used Glut1 deficient mice that have a reduction in brain Glut1 protein and have symptoms such as seizures and ataxia.

The prepared slides were under a bath of glucose at a near physiological concentration and were used to characterize low frequency oscillations (indicative of seizures) and gamma – high frequency oscillations (indicative of inhibitory neuronal activity). The reasoning behind using a glucose bath to test the slides, was that previous studies by the team with mice and humans with Glut1 Deficiency had shown that there were neurophysiological changes upon administration of metabolic fuel. The team postulated that there could be a decrease in the occurrence of low frequency oscillations with the addition of glucose to the slices, reflected by a change in high frequency oscillations.

The results of this study show that the thalamocortical connections in the brain slices used are preserved. The recordings of oscillations in brain slices confirmed that there is a robust presence of low frequency oscillations in the thalamocortical area.

As expected, the team found that addition of high glucose concentration for 30 minutes decreased the low frequency oscillations and increased the high frequency oscillations.

The authors discussed how this work using the thalamocortical slice model has shown that low frequency oscillations respond to glucose administration; which is similar to what they have seen in patients with Glut1 Deficiency. The team also mentioned that this work helps expand their understanding of the relationship between Glut1 deficits and how this impacts neurotransmission and electrophysiology.

Dr. Pascual and his team explained how the decrease in low frequency oscillations and the increase in high frequency oscillations after administration of glucose may be due to the enhanced sensitivity of inhibitory GABAergic neurons.  GABAergic neurons are the main inhibitory neurons in the central nervous system, and they play a critical role in many pathophysiological processes including modulation of cortical and hippocampal neural circuitry and activity.

The model and the protocol used for recording the oscillations has proved useful but it has some limitations such as that the recording area of the oscillations is limited just to a specific layer in the cortex.

They authors concluded that they have developed a thalamocortical slice recording and analysis approach that can quantify potential oscillations related with seizures in a mouse model of Glut1 Deficiency.

In addition, they concluded that their findings corroborate that in Glut1 Deficiency, at the level of the thalamocortical circuit, there is a reduction in the inhibition dependent of the metabolism and that it leads to the oscillations in this area. This model enables the possibility to use it as a way to characterize metabolic fuels and medicines that could potentially be used to treat Glut1 Deficiency. 

Finally, this model could also be adapted to study abnormal thalamocortical oscillations that are present in other genetic epilepsies.

Dr. Pascual and his team have published two more manuscripts, one that I briefly mentioned in our summer post “Maintenance of pig brain function under extracorporeal pulsatile circulatory control (EPCC)”. This publication talks about the use of the pig model and how they were able to separate the brain circulation from the rest of the body. This approach enabled them to study neural activity and its circulatory system independently of most of the rest of the organism. Their aim is to be able to establish a pig model to study Glut1 Deficiency due to the similarities between the brain of pigs and humans.

The last publication is “Impoverished Conceptions of Gene Causation and Therapy in Developmental Neurology”. This manuscript talks about the use of gene therapy to treat developmental neurological disorders. The authors analyzed recent examples of unusual or unexpected issues that occurred in the course of treatment of developmental neurological disorders. 

My take home message is that in an organism, changes in the DNA do not necessarily lead to a genetic disorder. If changes in the DNA lead to a defect on a protein and the protein-protein interactions are affected as well, this could possibly lead to a disorder. When thinking about gene therapy it’s important to think about all the other possible things that could be playing a role in a disease. Other things implicated could be other genes, proteins produced by those genes, how proteins interact with each other, how genes and proteins interact with each other and even how environmental factors can influence the expression of genes or the interactions.

At the end of the publication the authors offer a list of questions which answers could help to guide and determine the feasibility to establish gene therapy for developmental neurological disorders.We thank Dr. Pascual, his team and his collaborators for all the hard work and insightful publications, and for helping our community in so many ways!