Hello and welcome to Sotten Brain Hub. My name's Charlotte and I'm going to be talking about dopamine pathways in the context of antipsychotic drugs. By learning a bit about these pathways, it makes it so much easier to understand how antipsychotics work to control the symptoms of schizophrenia and also why they cause the side effects that they do.
So this is dopamine. It's the primary neurotransmitter that is targeted by antipsychotics. Antipsychotics are generally dopamine antagonists, so they act to reduce the levels of dopamine. There are four dopaminergic pathways in the brain that are affected by these drugs.
Firstly, the mesolimbic pathway. This pathway transmits dopamine from the midbrain to the ventral striatum. It includes the nucleus accumbens, which is associated with motivations, emotions and rewards. Overactivation of the mesolimbic pathway is thought to be responsible for the positive symptoms of schizophrenia, which include hallucinations, delusions and thought disorder.
By reducing dopamine in the mesolimbic pathway, antipsychotics act to reduce the positive symptoms of schizophrenia. So here we have the mesolimbic pathway in blue, which you can see running from the midbrain, specifically the ventral tegmental area, to the ventral striatum. Next is the mesocortical pathway.
This transmits dopamine from the midbrain to the prefrontal cortex. Unlike the mesolimbic pathway, hypo function, so reduced firing, of the mesocortical pathway is thought to be responsible for the negative symptoms in schizophrenia. These negative symptoms include apathy, low motivation, social withdrawal and self-neglect. And here we can see the mesocortical pathway in green running from the midbrain, again from the ventral tegmental area to the prefrontal cortex. Next is the nigrostriatal pathway, which transmits 80% of the brain's dopamine.
It runs from the pars compacta of the substantia nigra to the chordate nucleus and putamen. As antipsychotics generally act to reduce dopamine, inhibition of this pathway can result in extrapyramidal side effects, especially with your typical first-generation antipsychotics. These side effects can include dystonia, akathisia, Parkinsonism and tardive dyskinesia. Here in yellow we can see the nigrostriatal pathway running from the pars compacta of the substantia nigra to the caudate nucleus and putamen.
Finally we have the tuberoinfundibular pathway. This transmits dopamine from the hypothalamus to the pituitary gland. Dopamine in this pathway acts to inhibit prolactin. Therefore, blocking dopamine in this pathway results in hyperprolactinemia.
This can result in side effects including breast enlargement, galacteria, reduced libido, and erectile dysfunction. And here our picture is complete with the tubero-infundibular pathway in red running from the hypothalamus to the pituitary gland. So that was our overview of dopamine pathways in the context of antipsychotic drugs for schizophrenia.
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