How can an anti-wrinkle treatment help patients suffering from an overactive bladder?

TeachableMedicalNews article 12262020

Teachable moment in classrooms:

1. muscular tissue chapter – neurotransmitter release at the neuromuscular junction
2. autonomic nervous system chapter –  parasympathetic division and its neurotransmitters
3. urinary system chapter – role of detrusor muscle in emptying of the bladder
4. microbiology – Clostridium botulinum and its toxin

The news item:  Recently an unusual report appeared about the anti-wrinkle treatment, Botox:

https://westnewsmagazine.com/2019/11/13/117802/beyond-wrinkles-botox-offers-effective-treatment-for-common-bladder-condition

The article states that people suffering from an overactive bladder may find help for their symptoms from twice-a-year Botox injection.

So, Why Do I Care??  There are about 50 million people in the US suffering from overactive bladder symptoms. While this affliction is not life threatening, everyday life, ability to hold down a job are disrupted by it. There are several medical interventions to help patients, so Botox is the latest to join the remedies.

Plain English, Please!!!  First, let’s talk about the mechanics of urination. For urination to happen the muscle (called detrusor) inside the wall of the urinary bladder has to contract when nerve impulses come to it through parasympathetic nerves. The meeting point of the nerve and the muscle is called the neuromuscular junction; that is where the parasympathetic nerve endings release the neurotransmitter acetylcholine intended to reach the muscle which responds by contraction. The contraction of the detrusor muscle increases pressure in the bladder, and that squeezing action empties urine from the bladder.

Second, let’s talk about the overactive bladder. The sudden urge to urinate happens when the detrusor muscle receives unwanted nerve impulses, contracts unexpectedly, and that suddenly increases the pressure in the bladder.  These nerve impulses initiate sudden urination even when the bladder is still part empty.

Third, let’s talk about the mechanics of neurotransmitter release.  The acetylcholine is packed into microscopic bubbles (synaptic vesicles) inside the nerve ending, and those vesicles must open up to release the acetylcholine. Imagine the end of the axon as a cul-de-sac right in front of a school (the muscle tissue). The acetylcholine molecules (the students) are packed inside synaptic vesicles (the school buses), and those vesicles stop at the edge of the cul-de-sac.  For the students to reach the school, the bus doors need to open.  The same way the synaptic vesicles have to open up to allow acetylcholine to stream to the muscle, and to make it contract.

Fourth, let’s talk about how Botox acts on the overactive bladder. The bacterium Clostridium botulinum makes a toxin, and the man-made version of that toxin is called Botox. Botox prevents the opening of the synaptic vesicles at the neuromuscular junction.  Using our metaphor, Botox prevents the opening of the doors of the school bus. After Botox treatment, acetylcholine is not released from the vesicles, and without acetylcholine the detrusor muscle remains relaxed. Therefore, the sudden urge to urinate is eliminated or moderated.