Human Raphe Magnus Nucleus: a morphometric Golgi-Cox study with emphasis on sex differences

Area of Science:

• Neuroscience
• Developmental Biology
• Neuroanatomy

Background:

• The Raphe Magnus Nucleus (RMN) plays a crucial role in various physiological functions, including pain modulation and sleep.
• Understanding the developmental trajectory and sexual dimorphism of neuronal populations within the RMN is essential for comprehending its functional maturation.

Purpose of the Study:

• To investigate and compare the number and proportion of different neuron types and sizes in the RMN of male and female infants.
• To identify potential sex-based differences in RMN neuronal morphology during early development.

Main Methods:

• Comparative analysis of Golgi-Cox and Nissl stained brain tissue from four female/male infant pairs (aged 2–150 days).
• Quantification and classification of neurons based on type (multipolar, fusiform, ovoid) and size (micrometers).

Main Results:

• Females exhibited a higher total number of neurons compared to males.
• Males displayed a greater proportion of large multipolar ( > 40 µm) and fusiform ( > 20 µm) neurons.
• No significant sex difference was observed in the proportion of ovoid neurons ( > 15 µm); differences varied by cell type and infant age.

Conclusions:

• Significant sex-based differences in RMN neuronal populations exist in infants, particularly concerning larger neuron types.
• These findings suggest early-onset sexual dimorphism in specific neuronal populations within the RMN.
• Observed differences partially align with findings in the human Median Raphe Nucleus, indicating potential shared developmental patterns.