Don’t let botox go to your head…or should we?
The botulinum toxin (botox) is a neurotoxin found in soil and produced by the bacterium Clostridium botulinum. The botulinum toxin is toxic because it inhibits the release of the neurotransmitter acetylcholine. In the peripheral nervous system, acetylcholine is released by nerves to activate muscles. When the secretion of acetylcholine from nerves is disrupted by botulinum toxin, the muscles become weak and unable to contract.
Botulinum toxin as medicine
The medicinal use of botulinum toxin is possible because of its effect on our peripheral nervous system and is used to treat spasticity, headaches, migraines, excessive sweating (hyperhidrosis) and abnormal muscle twitching such as in the eyelid (blepharospasms) and face (hemifacialspasms).
Peripheral nervous system + central nervous system
Given that botulinum toxin affects the peripheral nervous system, could it possibly be affecting the central nervous system too?
A recent study at NeuRA investigated the effect of peripheral injections of botulinum toxin on activity within the cortex – the part of the human brain responsible for movement, learning, memory and sensory processing. The study involved chronic stroke patients suffering from disabling limb spasticity and used paired-pulse transcranial magnetic stimulation to measure electrical activity and patterns in the cortex before and after the injection of botulinum toxin in muscles in the arms or legs.
Weaken a muscle, change the brain
The study showed that prior to the injection of botulinum toxin, chronic stroke patients with significant spasticity in their limbs had altered brain activity compared to healthy people. The study also demonstrated that using botulinum toxin in the affected muscles improved limb spasticity and normalised brain activity. However, just as the effects of botulinum toxin on muscles wear off, changes in electrical activity in the cortex also reverted over time.
This study suggests that the clinical benefits of botulinum toxin in treating spasticity from stroke are related to its effects on the peripheral and central nervous systems. The early use of botulinum toxin in stroke patients at risk of developing disabling spasticity will now be studied.
Ben Bravery is a science communicator and writer at NeuRA.