Entorhinal layer 6b subplate neurons govern spatial learning and memory

Abstract

The mammalian hippocampal formation (HF) plays a key role in several higher brain functions, such as spatial coding, learning and memory. Its simple circuit architecture is often viewed as a trisynaptic loop, processing input originating from the superficial layers of the entorhinal cortex (EC) in a linear fashion, and sending it back to its deeper layers. Here, we show that contrary to this canonical view, excitatory neurons in the deepest layer of the mouse EC, exhibiting the unique morphology and molecular profile of layer 6b cortical subplate neurons (SPNs), project to all sub-regions comprising the HF, with a preference towards CA3 pyramidal neurons, and receive input from the CA1, thalamus and claustrum. Furthermore, their output is characterized by unique slow-decaying excitatory post-synaptic currents (EPSCs), capable of driving plateau-like potentials in their target cells. Optogenetic inhibition of the EC-6b pathway markedly affects spatial coding in CA1 pyramidal neurons, while cell ablation impairs not only acquisition of new spatial memories, but also degradation of previously acquired ones. Our results provide the first evidence of a functional role for the cortical layer 6b neurons in the adult brain and elucidate a critical novel element determining cortico-hippocampal activity patterns.

Structure and function of neocortical layer 6b

“…structural properties of layer 6b (L6b) neurons have regained interest (Hoerder-Suabedissen and Molnár, 2013;Marx and Feldmeyer, 2013;Marx et al, 2017;Hoerder-Suabedissen et al, 2018;Zolnik et al, 2020;Ben-Simon et al, 2022), and thus this review may be timely.…”

Uncovering brain tissue architecture across scales with super-resolution light microscopy

“…This will make large-scale studies of local connectivity, complete neuronal synaptic input or output fields, and neuron-glia interplay 21 feasible. We furthermore expect CATS to seamlessly integrate with complementary technologies, such as calcium imaging or viral circuit tracing 54,55 , similar to the combined structural and functional characterization demonstrated here with whole-cell patch clamp recordings. CATS will be an important tool to clarify how tissue architecture and synaptic connectivity are remodeled in response to neuronal activity, during development, or in neurodevelopmental or neurodegenerative disease models.…”

Saturated reconstruction of living brain tissue

“…Preparation of AAV and RVdG envA -CVS-N2c vectors has previously been described. 42,54 Briefly, AAV2-CaMKIIa-TVA-2A-N2cG (Addgene #172363) vectors were pseudotyped with the AAVdj capsid protein by co-transfection of HEK293T cells. Three days later, the cells were harvested and lysed, and the viral stock was purified using heparin-agarose affinity binding.…”

“…Preparation of AAV and RVdG envA -CVS-N2c vectors has previously been described 38,53 . Briefly, AAV2-CaMKIIa-TVA-2A-N2cG (Addgene #172363) vectors were pseudotyped with the AAVdj capsid protein by co-transfection of HEK293T cells.…”