Synaptic abnormalities of mice lacking toll-like receptor (TLR)-9

Area of Science:

• Neuroscience
• Immunology
• Cell Biology

Background:

• Toll-like receptor 9 (TLR9) knock-out (KO) mice exhibit motor, sensory, and autonomic abnormalities.
• The physiological role of TLR9 within the nervous system remains largely uncharacterized.
• Altered synaptic transmission is a potential cause of neurological deficits.

Purpose of the Study:

• To investigate the function and morphology of the neuromuscular junction (NMJ) in TLR9 KO mice.
• To determine if TLR9 deficiency impacts synaptic transmission at the NMJ.
• To elucidate the role of TLR9 in NMJ development and function.

Main Methods:

• Dissection of triangularis sterni nerve-muscle preparations from TLR9 KO and control mice.
• Two-electrode voltage clamp recordings of motor endplate currents (mEPCs and EPCs).
• Quantification of quantal content (m) and analysis of mEPC amplitude distribution.
• Rhodamine α-bungarotoxin staining to assess endplate size.

Main Results:

• TLR9 KO NMJs showed significantly increased amplitude and frequency of miniature end plate currents (mEPCs).
• Quantal content (m) was reduced in TLR9 KO NMJs and declined more rapidly during high-frequency stimulation.
• A rightward shift in mEPC amplitude distribution suggested larger acetylcholine (ACh) vesicle content.
• Endplate size was significantly reduced in TLR9 KO mice, potentially due to ACh-induced downregulation of acetylcholine receptors (AChRs).

Conclusions:

• TLR9 influences neuromuscular junction development and function.
• Deficiency in TLR9 leads to altered spontaneous and evoked neurotransmission at the NMJ.
• Increased spontaneous ACh release in TLR9 KO mice may contribute to retrograde suppression of excitation-secretion coupling.
• These findings suggest a novel role for TLR9 in synaptic plasticity and NMJ homeostasis.