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Development and early postnatal maturation of the primary olfactory cortex
1Laboratorio de Neuroanatomía Comparada, Instituto Cajal (CSIC), Madrid, Spain.
Insights
This study traces neuron development in rat olfactory cortex using tritiated thymidine autoradiography. It reveals the origin and migration patterns of neurons in the primary olfactory cortex from embryonic to postnatal stages.
Area of Science:
- Neuroscience
- Developmental Biology
- Neuroanatomy
Background:
- The development of the primary olfactory cortex (POC) involves complex neuronal migration and differentiation.
- Understanding the precise origins and distribution of neurons is crucial for comprehending olfactory system function.
Purpose of the Study:
- To investigate the origin and spatiotemporal distribution of neurons in the rat primary olfactory cortex.
- To identify the developmental trajectory of neuronal populations from embryonic day 12 (E12) through postnatal development.
Main Methods:
- Tritiated thymidine autoradiography was employed to label newly generated neurons at E12.
- Histological analysis of brain tissue from embryonic day 15 (E15) to postnatal day 63 (P63).
- Golgi staining was used to examine cellular morphology from E15 to postnatal day 8 (P8).
Main Results:
- Early-born neurons at E12 populate the ventrolateral telencephalic vesicle.
- These neurons differentiate into cells of the accessory olfactory bulb and the prospective primary olfactory cortex by E16.
- Neuronal populations segregate into distinct cortical layers (Layer I and Layer III) between E18-E20.
- Transient populations of neurons in Layer I, flanking the lateral olfactory tract, were observed but diminished postnatally.
Conclusions:
- The study elucidates the developmental origins and migration pathways of key neuronal populations in the rat olfactory cortex.
- It highlights the dynamic changes in neuronal distribution, particularly the transient nature of cells in Layer I.
- Findings provide a foundational understanding of olfactory cortex neuroarchitecture and development.
Abstract:
Tritiated thymidine autoradiography was used to study the origin and distribution of neurons in the primary olfactory cortex of the rat. The principal interest was devoted to animals injected at embryonic day 12 (E12) and sacrificed at different pre- and postnatal ages. The first generated neurons appearing at E12 were studied from E15 to P63. Animals sacrificed at E15 show a group of heavily labeled cells occupying a large area of the ventro lateral region of the telencephalic vesicle. At E16 this group differentiates into the principal cells of the accessory olfactory bulb and cells of the prospective primary olfactory cortex (POC). At E18-E20 the ventral tip of the cortical plate apparently divides this group into a superficial part corresponding to layer I and a deep part, corresponding to cells located in the adult in layer III. Labeled cells in layer I were found flanking the lateral olfactory tract (TOL), but rarely in the adult suggesting that they disappear or transform postnatally. Golgi observations were carried out from E15 to postnatal day 8. The morphology of different cells were studied. Layer I contains polymorphic cells resembling Cajal-Retzius cells. Among other cell types, layer II includes kinds of pyramidal cells lacking basal dendrites known as semilunar cells and intrinsic neurons. Layer III contains pyramidal cells having more than one apical dendrite ascending to the surface.