Modulating neuromuscular junction density changes in botulinum toxin-treated orbicularis oculi muscle

Area of Science:

• Neuroscience
• Pharmacology
• Ophthalmology

Background:

• Botulinum toxin A is a primary treatment for focal dystonias like blepharospasm and hemifacial spasm.
• A key limitation of botulinum toxin A therapy is its transient duration of effect.
• Muscle function recovery after botulinum toxin treatment is linked to neuromuscular junction (NMJ) plasticity.

Purpose of the Study:

• To investigate the potential of corticotropin releasing factor (CRF) and anti-insulin growth factor I-receptor (anti-IGFIR) antibody to mitigate NMJ upregulation.
• To determine if CRF or anti-IGFIR can prolong the therapeutic effects of botulinum toxin A by targeting NMJ changes.

Main Methods:

• Adult rabbits received localized eyelid injections of botulinum toxin A.
• Subsequent injections of either CRF or anti-IGFIR were administered to assess their impact on NMJ density.
• Orbicularis oculi muscles were histologically analyzed at one, two, and four weeks post-treatment to quantify NMJ density.

Main Results:

• Botulinum toxin A treatment significantly increased NMJ density at one and two weeks, with a further increase by four weeks.
• Co-administration of CRF or anti-IGFIR with botulinum toxin A completely inhibited the observed increase in NMJ density.
• These findings indicate that CRF and anti-IGFIR can prevent the adaptive changes at the NMJ following botulinum toxin-induced paralysis.

Conclusions:

• The return of muscle function post-botulinum toxin treatment is mediated by terminal sprouting and the formation of new NMJs.
• CRF and anti-IGFIR treatments effectively block this sprouting process, suggesting a mechanism to extend botulinum toxin efficacy.
• Prolonging the duration of botulinum toxin A's effects could reduce treatment frequency, minimize side effects, and mitigate long-term drug resistance.