Human cortical circuit assembly is critical to neurodevelopment, but our understanding of this
process in Down Syndrome (DS) remains incomplete. Previously, a model for studying DS neurodevelopment
was created by xenotransplanting induced pluripotent stem cell (iPSC) derived
neurons, made from DS individual fibroblasts, into the somatosensory cortex of an immunodeficient
mouse. The transplanted graft cells were then imaged longitudinally using multiphoton
microscopy. In this thesis, I develop an alternate graft type within the framework of the previous
model, in order to study synaptic structural stability and spontaneous and oscillatory
calcium activity in a model of the early DS brain. In addition to utilizing cells derived from
an individual whose genetics have not been studied using this model-type, I have also demonstrated
the ability to utilize this model for extended long-term imaging, with a pilot study of
animals imaged at 8 months post-transplantation. In this study, 2-photon images were taken
of axonal en passant boutons (EPB) and of somatic calcium signals over time. EPB turnover
rate (TOR) and EPB size (strength) changes were quantified using EPBscore software. Calcium
imaging was analyzed via MATLAB/Fiji scripts to determine event frequency, integral,
and amplitude. I found no significant difference in EPB TOR, EPB strength, spontaneous
somatic calcium activity, or oscillatory calcium activity between DS and isogenic control grafts.
Therefore, differences in synaptic stability and somatic activity outcomes have been normalized
across genotypes. Correlative analysis was used to determine whether normalization of
SATB2+ and GFAP+ cell levels contributed to this rescue. GFAP+ cell numbers significantly
correlate with synaptic stability outcomes, but no others. Overall, this study concludes that
trisomy 21-related dysregulation in this graft is not sufficient to alter axonal bouton stability
and neuronal activity compared to control neural networks of similar scale and cellular composition.
I hypothesize that the lack of effect on synaptic structural stability and spontaneous
and oscillatory activity may be correlated to an increased rate of astrogliogenesis in my grafts.
As such, this graft model of DS neurodevelopment provides a foundation upon which to study
the mechanisms behind early fetal changes in DS neurodevelopment, specifically related to the
role of astrocytes in DS. Additionally, this model could be used as an excellent in vivo astrocyte
research model, in WT or diseased cells, due to the high volume of developed astrocytes. Future
research will include comparative transcriptomic analysis of this DS graft type to identify
mechanisms of early DS neurodevelopmental dysfunction.