Diminished Activity-Dependent Brain-Derived Neurotrophic Factor Expression Underlies Cortical Neuron Microcircuit Hypoconnectivity Resulting from Exposure to Mutant Huntingtin Fragments

Although previous studies of Huntington’s disease (HD) have ad-dressed many potential mechanisms of striatal neuron dysfunction and death, it is also known, based on clinical findings, that cortical function is dramatically disrupted in HD. With respect to disease etiology, however, the specific molecular and neuronal circuit bases for the cortical effects ofmutant huntingtin (htt) have remained largely unknown. In the present work, we studied the relationship between the molecular effects of mutant htt fragments in cortical cells and the corresponding behavior of cortical neuron microcircuits by using a novel cellular model of HD. We observed that a transcript-selective diminution in activity-dependent brain-derived neurotrophic factor (BDNF) expression preceded the onset of a synaptic connectivity deficit in ex vivo cortical networks, which manifested as decreased spontaneous collective burst-firing behavior measured by multielec