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Botox

What is the mechanism of action of botulinum toxin?

Muscle contraction is achieved through the transmission of signals from the nerve to the muscle within a structure called the neuromuscular junction. The final part of the nerve (axon) contains vesicles that continuously recharge a neurotransmitter.

Once the body detects activity at the neuromuscular junction, acetylcholine is released, facilitated by the docking of vesicles via a protein complex called SNARE, which acts like a "zipper" to fuse the vesicles with the nerve membrane. Botulinum toxin blocks this docking by cleaving one of the key proteins, SNAP-25. While the body has local recycling mechanisms for these proteins, when SNAP-25 is cleaved by the toxin, the body must synthesize it again in the neuron's nucleus and transport it to the axon, a process that can take months.

Each unit of Botox contains proteases capable of cleaving multiple SNAP-25 proteins. The parameter used to define a Botox unit is LD50, which is the minimum dose required to paralyze muscles in 50% of injected mice under controlled laboratory conditions. One unit of Botox may contain 20 picograms of botulinum toxin, sufficient to affect several cubic millimeters around the injection site. Each nerve terminal can contain between 100 and 200 vesicles ready to release neurotransmitters, though the body has thousands in reserve. Botox binds to cells within the first 4 hours after application.

THE STEPS OF BOTOX ACTION

Muscle blockage and recovery involve several steps:

  1. Toxin internalization into the cell through receptor-specific uptake in the heavy chains of the protein (Botox).
  2. Once inside the cell, the vesicle matures and changes its pH, allowing the light chain of the toxin, containing the proteases, to act in the axon’s cytoplasm.
  3. The light chain of Botox cleaves SNARE complexes in the cytoplasm, depleting preformed reserves within a few days.
  4. Botulinum toxin and unused neurotransmitters are metabolized by the body, although neurotransmitter production continues, as vesicle reloading depends on calcium signals.
  5. The normal muscle contraction cycle resumes once the SNARE complex is restored.

BOTOX ACTION TIME

Generally, the longer it takes for the effect to appear, the shorter the duration of the result, either due to insufficient dosage or incorrect technique. Muscle activity recovers within 4 to 6 months, which is the time the body needs to synthesize new SNARE complexes to reconnect the vesicles to the muscle. In areas where more than 5 units are applied, complete recovery usually takes more than 4 months.

BOTOX APPLICATION IN FACIAL REJUVENATION TREATMENTS

The goal of Botox application is to paralyze the most tense muscles, generating compensatory tone in the non-blocked muscles. In the upper third of the face, the eyebrows are a key point. Their position is influenced by the Botox injection technique, and the eyebrow level may rise if areas are left untreated, generating a compensatory tonic contraction. In the lower third of the forehead, the frontalis muscle is the main elevator of the eyebrows, and its function is affected by the amount of toxin injected into the glabella and upper eyelids. At lower doses and in specific concentrations, more superficial results can be achieved, avoiding the complete blocking of the frontalis muscle fibers.

Botox is also used to treat a gummy smile, smooth upper lip wrinkles, lift the corners of the mouth, reduce chin wrinkles, and diminish expressions of disdain. Additionally, it can be applied to improve cheek appearance by isolating the platysma muscle insertions or to reduce bruxism by softening the bite strength.

The use of botulinum toxin, or Botox, in aesthetic medicine is primarily aimed at relaxing specific muscles to smooth expression lines, reduce the appearance of dynamic wrinkles, and improve facial symmetry.

The most commonly sought effects include the reduction of wrinkles in areas such as the forehead, crow’s feet, and glabella, as well as neck rejuvenation and jawline definition, such as in the Nefertiti lift.

Additionally, in therapeutic procedures, it is used to relieve muscle hyperactivity, such as in bruxism or spasticity.

However, the actual results achieved with Botox depend on the technique applied, the dosage administered, and the individual characteristics of the patient. Precision in the injection points is key to avoid undesired effects such as excessive muscle weakness or temporary asymmetry.

Photographic documentation plays a crucial role in monitoring botulinum toxin treatments, as it provides an objective visual comparison of the patient’s condition before and after the procedures.

This documentation is essential for evaluating treatment effectiveness, tracking the progression of results, and detecting any early complications, such as asymmetry or unwanted effects.

Moreover, photographs allow for adjustments in future applications based on previous outcomes, improving treatment accuracy and helping to personalize doses and injection points according to the patient’s individual responses.

 

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