Many patients will experience nausea and vomiting associated with their migraines. The migraine itself may produce these feelings, and there are many other causes such as medication, fear, motion sickness, ear infection, the list goes on!
To explain what gives us these unpleasant symptoms, requires understanding this essential defense mechanism. In healthy people the brain is surrounded by a protective liquid called cerebrospinal fluid (CSF), it acts in multiple ways to protect the brain from harm. It provides mechanical protection, chemical protection, and helps eliminate harmful substances. Any significant changes to the CSF are very bad news, and its properties are tightly controlled.
The Chemoreceptor Trigger Zone (CTZ) is the part of the brain sensitive to chemical changes in the CSF. Its job is to spot problems and fire urgent messages to the Vomiting Center. This part of the brain is aptly named and is responsible for coordinating nausea (the feeling of being about to vomit) and vomiting (the physical action).
The balance mechanisms in the ears, pain sensors in the body, our higher functioning and thinking centers in the brain, and other parts of our nervous system all send messages to the Vomiting Center. It is an important protective mechanism that makes us stop whatever we are doing! Unfortunately this mechanism often kicks into action when we are not in imminent danger.
Anti-sickness medications (also known as antiemetic medications), act upon the Vomiting Center, the Chemoreceptor Trigger Zone, or sensors elsewhere in the body that contribute to nausea and vomiting. Metoclopramide blocks sensors in the CTZ called dopamine receptors, and other sensors in the brain, gut and peripheries called Serotonin (5-HT3) receptors. It also acts to speed up the emptying of the stomach, and is hence called a prokinetic medication.
The combination of blocking these receptors, and accelerating stomach emptying reduces the likelihood of vomiting, and thereby relieves symptoms.
