Pyramidal neurons form active, transient, multilayered circuits perturbed by autism-associated mutations at the inception of neocortex.

Scientists studied how brain cells connect in developing mouse brains before birth. They found that these connections form in two stages and are active much earlier than expected. The brain cells involved strongly use genes linked to autism. When these autism-related genes don't work properly, it disrupts normal brain development patterns. This research helps us understand how early brain development problems might contribute to autism.

This developmental neuroscience study examined how pyramidal neurons form circuits in the embryonic mouse brain. Researchers found that these neurons undergo two distinct phases of circuit assembly between embryonic days 14.5 and 17.5, forming active, multi-layered connections. The study revealed that these embryonic neurons are electrically active and form functional glutamatergic synapses earlier than previously understood. Notably, these developing neurons strongly express autism-associated genes, and when these genes are disrupted, it interferes with the normal transition between circuit formation phases.

This research provides new insights into early brain development and suggests that disruptions in these fundamental developmental processes may contribute to autism pathophysiology.

This research identifies critical early developmental windows where autism-associated genetic disruptions may interfere with normal brain circuit formation. While conducted in mice, it suggests that autism may originate from fundamental disruptions in embryonic brain development rather than later postnatal processes.

This is a mouse model study with unclear sample sizes. The relationship between embryonic circuit disruptions and autism behaviors is not established. Clinical relevance to human autism development requires validation.

Cortical circuits are composed predominantly of pyramidal-to-pyramidal neuron connections, yet their assembly during embryonic development is not well understood. We show that mouse embryonic Rbp4-Cre cortical neurons, transcriptomically closest to layer 5 pyramidal neurons, display two phases of circuit assembly in vivo. At E14.5, they form a multi-layered circuit motif, composed of only embryonic near-projecting-type neurons. By E17.5, this transitions to a second motif involving all three embryonic types, analogous to the three adult layer 5 types.

In vivo patch clamp recordings and two-photon calcium imaging of embryonic Rbp4-Cre neurons reveal active somas and neurites, tetrodotoxin-sensitive voltage-gated conductances, and functional glutamatergic synapses, from E14.5 onwards. Embryonic Rbp4-Cre neurons strongly express autism-associated genes and perturbing these genes interferes with the switch between the two motifs. Hence, pyramidal neurons form active, transient, multi-layered pyramidal-to-pyramidal circuits at the inception of neocortex, and studying these circuits could yield insights into the etiology of autism.