Synaptic plasticity in human thalamocortical assembloids
Synaptic plasticities, such as long-term potentiation (LTP) and depression (LTD), tune synaptic efficacy and are essential for learning and memory. Current studies of synaptic plasticity in humans are limited by a lack of adequate human models. Here, we modeled the thalamocortical system by fusing human induced pluripotent stem cell-derived thalamic and cortical organoids. Single-nucleus RNA-sequencing revealed that most cells in mature thalamic organoids were glutamatergic neurons. When fused to form thalamocortical assembloids, thalamic and cortical organoids formed reciprocal long-range axonal projections and reciprocal synapses detectable by light and electron microscopy, respectively. Using whole-cell patch-clamp electrophysiology and two-photon imaging, we characterized glutamatergic synaptic transmission. Thalamocortical and corticothalamic synapses displayed short-term plasticity analogous to that in animal models. LTP and LTD were reliably induced at both synapses; however, their mechanisms differed from those previously described in rodents. Thus, thalamocortical assembloids provide a model system for exploring synaptic plasticity in human circuits. HighlightsO_LIHuman thalamic organoids consist of mostly glutamatergic projection neurons. C_LIO_LIThalamocortical assembloids form reciprocal glutamatergic synapses. C_LIO_LISynapses are functional and undergo short-term plasticity resembling animal models. C_LIO_LILong-term potentiation and depression reveal mechanisms distinct from rodents. C_LI eTOCHuman organoids are often used to model diseases with synaptic pathology; however, few studies have examined synaptic function via single-cell or single-synapse recordings. Patton et al. fused human thalamic and cortical organoids into assembloids to examine synaptic transmission and short- and long-term synaptic plasticity in human thalamocortical and corticothalamic circuits. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=199 HEIGHT=200 SRC="FIGDIR/small/578421v2_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@21546org.highwire.dtl.DTLVardef@c2ba28org.highwire.dtl.DTLVardef@4bc28aorg.highwire.dtl.DTLVardef@1d12a98_HPS_FORMAT_FIGEXP M_FIG C_FIG