Source : CHU Sainte-Justine Research Centre
MONTREAL, February 16, 2023– Results of a new study led by Roberto Araya, a neuroscientist, biophysicist and researcher at the CHU Sainte-Justine Research Centre, show that in Fragile X syndrome (FXS), the most common cause of autism, sensory signals from the outside world are integrated differently, causing them to be underrepresented by cortical pyramidal neurons in the brain. This phenomenon could provide important clues to the underlying cause of the symptoms of this syndrome. The research team’s work not only provides insight into the mechanism at the cellular level, but also opens the door to new targets for therapeutic strategies.
The study was published on January 3 in the prestigious journal Proceedings of the National Academy of Sciences.
Autism is characterized by a wide range of symptoms that may stem from differences in brain development. With advanced imaging tools and the genetic manipulation of neurons, the team of researchers at the CHU Sainte-Justine Research Center was able to observe the functioning of individual neurons – specifically pyramidal neurons of cortical layer 5 – one of the main information output neurons of the cortex (the thin layer of tissue found on the surface of the brain).
The researchers found a difference in how sensory signals are processed in these neurons. “Previous work has suggested that FXS and autism spectrum disorders are characterized by a hyperexcitable cortex, which is considered to be the main contributor to the hypersensitivity to sensory stimuli observed in autistic individuals,” explains Roberto Araya, also a professor in the Department of Neurosciences at the University of Montreal. “To our surprise, our experimental results challenge this generalized view that there is a global hypersensitivity in the neocortex associated with FXS. They show that the integration of sensory signals in cortical neurons is underrepresented in a murine model of FXS,” says Diana E. Michell, first co-author of the study.
How can this difference be explained?
A protein, FMRP, that is absent in the brains of people with FXS modulates the activity of a type of potassium channel in the brain. According to the research group’s work, it is the absence of this protein that alters the way sensory inputs are combined, causing them to be underrepresented by the signals coming out of the cortical pyramidal neurons in the brain.
Soledad Miranda-Rottmann, also first co-author of the study attempted to rectify the situation with genetic and molecular biology techniques. “Even in the absence of the FMRP protein, which has several functions in the brain, we were able to demonstrate how the representation of sensory signals can be restored in cortical neurons by reducing the expression of a single molecule.”
“This finding opens the door to new strategies to offer support to those with FXS and possibly other autism spectrum disorders to correctly perceive sensory signals from the outside world at the level of pyramidal neurons in the cortex. Even if the over-representation of internal brain signals causing hyperactivity is not addressed, the correct representation of sensory signals may be sufficient to allow better processing of signals from the outside world and of learning that is better suited to decision making and engagement in action, “says Roberto Araya.
About the study
The article « Altered integration of excitatory inputs onto the basal dendrites of layer 5 pyramidal neurons in a mouse model of Fragile X syndrome » by Diana E. Mitchell, Soledad Miranda-Rottmann, Maxime Blanchard and Roberto Araya, was published in Proceedings of the National Academy of Sciences. Funding for the study was provided by the Canadian Institutes of Health Research (CIHR), the Canada Foundation for Innovation (CFI), the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Scottish Rite Charitable Foundation of Canada (SRCFC) research grant. Maxime Blanchard was supported by a Herber Jesper postdoctoral fellowship at Université de Montréal. Diana E. Mitchell was supported by postdoctoral fellowships from the Fonds de recherche du Québec Santé (FRQS) and the Quebec Autism Research Training (QART) Program.
About the CHU Sainte-Justine Research Centre
The CHU Sainte-Justine Research Centre is a leading mother-child research institution affiliated with the Université de Montréal. It brings together 280 research investigators, including over 140 clinician-scientists, as well as more than 550 graduate and postgraduate students focused on finding innovative prevention means, faster and less invasive treatments, as well as personalized approaches to medicine. The centre is an integral part of CHU Sainte-Justine, which is the largest mother-child centre in Canada.
CHU Sainte-Justine Research Centre
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