Neurotrophins, but not depolarization, regulate substance P expression in the developing optic tectum

Area of Science:

• Neuroscience
• Developmental Biology
• Cell Biology

Background:

• Neurotransmitter expression is modulated by neural activity and neurotrophins in vitro.
• The in vivo regulation of substance P-like immunoreactive (SP-ir) cells in the developing frog optic tectum by optic nerve input is not fully understood.
• Previous studies indicated different regulatory mechanisms in adult versus developing systems.

Purpose of the Study:

• To investigate whether neural activity or neurotrophins regulate SP-ir cell populations in the developing frog optic tectum in vivo.
• To compare regulatory mechanisms in the developing tectum with those in the adult system.

Main Methods:

• Pharmacological blockade of glutamate receptors using 6-cyano-7-nitroquinoxaline-2,3 dione (CNQX) and d-(-)-2-amino-5-phosphonovaleric acid (d-AP-5).
• Chronic administration of brain-derived neurotrophic factor (BDNF), neurotrophin-4/5 (NT-4/5), and nerve growth factor (NGF).
• Assessment of SP-ir cell populations and visual map topography in normal and deafferented optic tecta of tadpoles.

Main Results:

• Glutamate receptor blockade with CNQX or d-AP-5 did not alter the percentage of SP-ir cells but disrupted visual map topography.
• Chronic treatment with BDNF and NT-4/5 increased SP-ir cells, with NT-4/5 showing a significant effect.
• BDNF and NT-4/5 prevented the reduction of SP-ir cells in deafferented tectal lobes, while NGF had no effect on SP expression or map formation.

Conclusions:

• Different mechanisms regulate SP expression in the developing and adult frog optic tectum.
• Neurotrophins, particularly NT-4/5, play a crucial role in regulating SP-ir cell populations in the developing optic tectum.
• Neurotrophin levels may selectively control specific neuropeptide-expressing cells during development.