Signature morpho-electric, transcriptomic, and dendritic properties of extratelencephalic-projecting human layer 5 neocortical pyramidal neurons

Abstract

In the neocortex, subcerebral axonal projections originate largely from layer 5 (L5) extratelencephalic-projecting (ET) neurons. The highly distinctive morpho-electric properties of these neurons have mainly been described in rodents, where ET neurons can be labeled by retrograde tracers or transgenic lines. Similar labeling strategies are not possible in the human neocortex, rendering the translational relevance of findings in rodents unclear. We leveraged the recent discovery of a transcriptomically-defined L5 ET neuron type to study the properties of human L5 ET neurons in neocortical brain slices derived from neurosurgeries. Patch-seq recordings, where transcriptome, physiology and morphology are assayed from the same cell, revealed many conserved morpho-electric properties of human and rodent L5 ET neurons. Divergent properties were also apparent but were often smaller than differences between cell types within these two species. These data suggest a conserved function of L5 ET neurons in the neocortical hierarchy, but also highlight marked phenotypic divergence possibly related to functional specialization of human neocortex.

Scaled, high fidelity electrophysiological, morphological, and transcriptomic cell characterization

“…A powerful aspect of the FACS-based transcriptomic studies is the ability to use similar methods to profile and compare neurons from different brain regions or species ( Bakken et al, 2018 ; Hodge et al, 2019 ; Kalmbach et al, 2020 ). With that in mind, we co-developed this protocol in both mouse tissue and tissue from human surgical resections.…”

“…To probe the phenotypic consequences of this differentiation, a platform is required that is robust to these dimensions. We have successfully used the Patch-seq protocol described here to study non-human primate and human excitatory neurons ( Berg et al, 2020 ; Kalmbach et al, 2020 ; Bakken, 2020 ), mouse cortical neurons ( Gouwens et al, 2020 ; Keaveney et al, 2020 ), and hippocampal ( Dudok et al, 2021 ) interneurons. Here, we demonstrate that the key to successfully adapting the protocol to a new system, like the human or non-human primate, is to focus on consistency in a few aspects, including nucleus extraction and maintaining membrane integrity during retraction.…”

Resilience through diversity: Loss of neuronal heterogeneity in epileptogenic human tissue impairs network resilience to sudden changes in synchrony

“…Additionally, we obtained recordings from neurons in non-epileptogenic middle temporal gyrus (MTG) from patients with mesial temporal sclerosis, which is the overlying cortex routinely removed to approach deep temporal structures. The MTG is a well-characterized part of the human brain, representing a common anatomical region from which non-epileptogenic brain tissue has been studied electrophysiologically and transcriptomically [22–25], and thus our primary source of non-epileptogenic neurons.…”

“…Using the IR-DIC microscope, the boundary between layer 1 (L1) and 2 (L2) was easily distinguishable in terms of cell density. Below L2, the sparser area of neurons (L3) was followed by a tight band of densely packed layer 4 (L4) neurons, with a decrease in cell density indicating layer 5 (L5) [22,25].…”

“…The MTG is a well-characterized part of the human brain, representing a common anatomical region from which non-epileptogenic brain tissue has been studied electrophysiologically and transcriptomically [22][23][24][25], and thus our primary source of non-epileptogenic neurons.…”