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.
Highlights
The emergence of function in the developing mammalian cerebral cortex is dependent on a diverse range of genetic and physiological processes that sculpt emergent network architecture
We demonstrated that Lpar1-EGFP subplate neurons (SPNs) represent two distinct subtypes: (1) transient (
Lpar1-EGFP SPNs form a layer of 2-3 cells deep adjacent to the white matter tract in neonatal S1BF (Figure 1a)
Summary
The emergence of function in the developing mammalian cerebral cortex is dependent on a diverse range of genetic and physiological processes that sculpt emergent network architecture. The subplate is a transient layer in the developing neocortex located between the emergent cortical plate and the underlying white matter 5, 6. It contains a diverse population of neuronal subtypes that differ in term of molecular markers 7, morphology 8, neurotransmitter identity[9], and connectivity[10]. Electrophysiological studies performed in primary sensory areas suggest that SPNs are relatively mature when compared to cortical neurons in the more superficial cortical plate early in development 8, 11. As such they are regarded as key mediators of early spontaneous and sensory-evoked activity[4], and direct circuit maturation[1].
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