Non-canonical role for Lpar1-EGFP subplate neurons in early postnatal mouse somatosensory cortex

Abstract

Subplate neurons (SPNs) are thought to play a role in nascent sensory processing in neocortex. To better understand how heterogeneity within this population relates to emergent function, we investigated the synaptic connectivity of Lpar1-EGFP SPNs through the first postnatal week in whisker somatosensory cortex (S1BF). These SPNs comprise of two morphological subtypes: fusiform SPNs with local axons, and pyramidal SPNs with axons that extend through the marginal zone. The former receive translaminar synaptic input up until the emergence of the whisker barrels; a timepoint coincident with significant cell death. In contrast, pyramidal SPNs receive local input from the subplate at early ages but then – during the later time window, acquire input from overlying cortex. Combined electrical and optogenetic activation of thalamic afferents identified that Lpar1-EGFP SPNs receive sparse thalamic innervation. These data reveal components of the postnatal network that interpret sparse thalamic input to direct the emergent columnar structure of S1BF.

Transient Coupling between Infragranular and Subplate Layers to Layer 1 Neurons Before Ear Opening and throughout the Critical Period Depends on Peripheral Activity

“…Auditory cortex shows sound-evoked responses at the end of the first postnatal week, and circuits to subplate neurons are affected by sensory experience in the first postnatal week (Meng et al, 2021). Thus, because subplate neurons send axonal projections across cortical layers including L1 (Friauf et al, 1990;Clancy and Cauller, 1999;Viswanathan et al, 2017;Ghezzi et al, 2021) and the deep input to L1 are most affected in OTOF-KO, we speculate that a large fraction of sensory information might be relayed to L1 via subplate neurons, although subplate is not the dominant input to L1. Thus, early peripheral activity even before ear opening has the ability to shape the intracortical organization of multiple layers in auditory cortex.…”

“…These axons can potentially target dendrites of many neurons present in L1. Moreover, axonal terminals from subplate neurons (SP) are also present in L1 during development (Friauf et al, 1990;Viswanathan et al, 2017;Ghezzi et al, 2021), and stimulation of subplate neurons results in inhibitory responses in Cajal-Retzius cells in L1 (Myakhar et al, 2011), suggesting that subplate neurons can directly influence L1 neurons. However, the precise intracortical innervation of L1 neurons and the development of the functional excitatory and inhibitory circuits to L1 neurons is unknown.…”

Chrna5 and lynx prototoxins identify acetylcholine super-responder subplate neurons

“…Chrna5+ neurons showed distinctive expression of several marker genes, Ctgf, Cplx3, Kcnab1, and Lpar1 ( Figures 3 B and 3C) associated with subplate neurons. 32 , 51 Subplate neurons are early born and vital for brain development, leaving L6b neurons as descendants in adulthood. 33 , 34 , 52 Notably, the highest fold enrichment among all differentially expressed genes in Chrna5+ neurons was found for subplate markers Ctgf (fold change, 5.69) and Cplx3 (3.81) ( Table 1 ).…”

Chrna5 and lynx prototoxins identify acetylcholine super-responder subplate neurons

“…We further examined the expression of marker genes in these respective groups to validate our cell-classification. Chrna5+ neurons showed distinctive expression of several marker genes, Ctgf, Cplx3, Kcnab1 , and Lpar1 (Fig 3B,C) associated with subplate neurons 35,52 . Subplate neurons are early-born and vital for brain development, leaving L6b neurons as descendants in adulthood 36,37,53 .…”

“…We examined the expression of marker genes in these respective groups to validate our cell-classification. To our surprise, Chrna5+ neurons showed distinctive expression of several marker genes-Ctgf, Cplx3, Kcnab1, Lpar1 (Fig 3B,C) associated with subplate neurons (35,58). Subplate neurons are vital for early brain development and L6b neurons are considered descendants of this early-born population (36,37,59).…”