Developmental Markers Expressed in Neocortical Layers Are Differentially Exhibited in Olfactory Cortex

Area of Science:

• Neuroscience
• Developmental Biology
• Olfactory System Research

Background:

• Cerebral cortex neurons stratify based on developmental origin, axonal targets, and molecular identity.
• Olfactory cortices share features with the neocortex, including lamination and cell types.
• This study investigates molecular markers and developmental patterns in olfactory cortical neurons.

Purpose of the Study:

• To determine if transcription factors found in deep or superficial neocortical neurons are present in olfactory cortical regions.
• To examine the developmental timing of neuronal production in olfactory cortices.
• To investigate the axonal projection targets of olfactory neurons expressing specific molecular markers.

Main Methods:

• Analysis of transcription factor expression (CTIP2, NOR1, DAARP-32, CUX1, CART) in olfactory cortical regions (AONpP, APC, PPC, olfactory tubercle).
• Use of the mitotic marker EDU to assess neuronal production timing.
• Retrograde tracing from the olfactory bulb to identify axonal projection targets of projection neurons.

Main Results:

• Olfactory regions express neocortical deep and superficial neuron markers, with significant regional and intra-regional variations.
• Neuronal production timing in olfactory cortices mirrors the neocortex, with deep-marker neurons produced earlier than superficial-marker neurons.
• Unlike the cerebral cortex, olfactory neurons expressing deep or superficial markers showed no specificity in axonal targets.

Conclusions:

• Olfactory cortices are complex, heterogeneous structures with distinct neuronal compositions.
• These regions are not simple remnants of the primordial forebrain but evolved as varied and independent entities.
• The lack of target specificity in olfactory projection neurons distinguishes them from neocortical organization.