Let's talk about the effects of increasing dopamine. So there
are several tracks in the brain that are going to be relevant
here. I'm going to go through all of them because going through
all of them now will help you understand how side effects occur
with these medications and also how we treat Parkinson's
disease in a later lecture. First, let's talk about the pink
nigrostriatal tract. This is where extrapyramidal function is
housed and increasing dopamine will cause an improvement in
Parkinsonian symptoms. In the mesocortical and mesolimbic
tracts, the mesocortical tracts determine apathy and lack
of emotion when you increase dopamine levels, and the
mesolimbic tracts cause hallucination and delusion.
This is where psychosis comes from. The tuberoinfundibular
tract is responsible for prolactin release. You can see that
TI tract goes down into the hypothalamus. Hyperprolactinemia
results from increased dopamine levels. This is why increasing
dopamine with medications can cause hyperprolactinemia. And
finally the chemoreceptor trigger zone. Increasing dopamine levels
will actually cause more anorexia, more nausea and more
vomiting because it houses the vomiting center of the brain.
What about decreasing dopamine? If we decrease dopamine we
are blocking these tracts. So that means that the nigrostriatal
tract worsening parkinsonian symptoms. So antipsychotic
medications can make Parkinson's symptoms worse. In the ML and
MC tracts you have improvement in symptoms and in social
function in patients who have diseases like schizophrenia.
In the TI tract, decreasing dopamine increases prolactine
secretion. So in the case of a breastfeeding mum, they can't
produce milk. And in the CTZ, vomiting center of the brain,
you know that decreasing dopamine has very important
anti-emetic properties and in fact some of the drugs that we
use for mood disorders can be used for nausea and vomiting.