Another area that relates to basal ganglia disorders would be Huntington’s disease. Huntington’s disease
is going to alter the direct pathway as well as the indirect pathway. So here we see the direct pathway.
What happens here is in the direct pathway, you’ll have a loss of GABAergic striatal neurons in this pathway.
These are the neurons coming in through here. As a result of that loss, you have a loss of inhibitory
influence on the globus pallidus. This then will inhibit the thalamus. If the thalamus is inhibited, the cortex
will be understimulated. If you think about the math again, we’ve lost a color. But again, this was a
minus one inhibitory. This was a minus one inhibitory. And this is a plus one. Well here, we’ve lost this first
inhibitory influencer of the pathway, of the circuit and have this inhibitor and this as being an excitor.
So minus one times a plus one gives you a minus one and so, that then gives you this under excitation.
Huntington’s disease also has an influence on the indirect pathway. Here again, loss of the GABAergic
striatal neurons will impact the processing or the circuitry here. As a result, there’ll be a loss of inhibitory
influence of the indirect pathway. So, if you lose your inhibitory influence then now, you can over excite
your motor cortex. Individuals with Huntington’s will execute motor programs with actually having no
control over that execution. Again, this all relates to math. As you may recall, we had more negative
influencers by one over positive influencers in this pathway. So if you lose one of those influencers
and you had the same number of negative influencers and positive influencers, you then still end up
with a positive or excitatory effect on the cerebral cortex. Here we’re looking at a table that’s going to
identify some of the symptoms of Huntington’s disease as well as structural changes and causes.
Let’s take a look at some of the symptoms that are associated with Huntington’s disease. The first is
chorea. Athetosis is another symptom. Individuals manifest or exhibit personality changes.
Individuals with Huntington’s disease demonstrate dementia. Structural changes: loss of GABAergic
neurons. These are going to be medium sized, spiny neurons from the striatum. Those are the ones
that are impacted or lost. The ventricles will enlarge or expand. This is a genetic disorder that’s
autosomal dominant. What we see genetically is there’s an excessive repeat of three nucleotides: C, G, and A.