Expression of serotonin transporter protein in developing rat brain

Area of Science:

• Neuroscience
• Developmental Biology
• Molecular Biology

Background:

• The serotonin transporter (5-HTT) is crucial for regulating serotonin levels in the adult brain.
• In adults, 5-HTT is found on both synaptic terminals and axons.

Purpose of the Study:

• To investigate the developmental timeline and expression patterns of 5-HTT in the embryonic and early postnatal brain.
• To understand the relationship between 5-HTT and serotonin (5-HT) neurons during development.

Main Methods:

• Utilized established antibodies for 5-HTT and 5-HT to perform immunostaining on embryonic and early postnatal brain tissue.
• Examined the spatiotemporal expression of 5-HTT and 5-HT in various brain regions, including raphe nuclei, thalamus, cortex, and striatum.

Main Results:

• Both 5-HTT and 5-HT immunostaining appear in rostral raphe nuclei (RRN) at embryonic day 12 (E12), with 5-HTT highly expressed on axons.
• 5-HTT-expressing axons from RRN project to various brain regions by E18-20, and transient 5-HTT expression is observed in non-serotonergic systems.
• Early 5-HTT expression on axons precedes synaptic site formation, indicating potential extrasynaptic transmission.

Conclusions:

• 5-HTT is preferentially associated with 5-HT neurons and temporally co-expressed with 5-HT during development.
• Early axonal expression of 5-HTT suggests a role in volumic transmission and influences the development of connected neuronal systems.
• The early appearance of 5-HTT may render developing 5-HT, thalamic, and cortical neurons vulnerable to 5-HTT targeting drugs.