Parkinsons/Psychosis

Question 1

How much neuron loss usually occurs before Parkinsons symptoms show?

Answer 1

80%

Question 2

What is the direct pathway of the basal ganglia?

Answer 2

Thalamus -> association cortex -> striatum -> D1 direct to globus pallidus internal + substantia nigra reticulata -> VA/VL of thalamus -> premotor cortex

Question 3

What is the indirect pathway of the basal ganglia?

Answer 3

frontal cortex-> striatum -> GPe -> STN

Question 4

Which basal ganglia pathway predominates in Parksinsons disease?

Answer 4

Indirect

Question 5

What is a likely cause of tremor?

Answer 5

Reduced DA resulting in increased Ach excitation

Question 6

What are the 5 DA pathways of the brain?

Answer 6

Nigrostriatal
Mesolimbic
Mesocortical
Median eminence
Chemoreceptor trigger zone

Question 7

What are the two enzymes which may break down DA?

Answer 7

monoamine oxidase and Catechol-O-methyltransferase

Question 8

What is the effect of carbidopa?

Answer 8

inhibit peripheral metabolism of levodopa, allow more L-dopa to cross BBB

Question 9

Which enzyme does carbidopa inhibit?

Answer 9

DOPA decarboxylase

Question 10

What is selegiline?

Answer 10

selective irreversible MAO-B inhibitor

Question 11

What determines if a cell is noradrenalinergic or dopaminergic?

Answer 11

Presence of dopamine beta hydroxylase converts DA to NA and it is therefore a NA cell

Question 12

Which drug blocks the Catechol-O-methyltransferase dopamine pathway?

Answer 12

Entacapone

Question 13

How can Parkinsons treatment be monitored?

Answer 13

Plasma levels of prolactin are easy to monitor

Question 14

When and why does successful Parkinsons treatment stop working?

Answer 14

After 2-10 years, probably because of huge neuronal death

Question 15

Why is postural hypotension a side effect of LDOPA?

Answer 15

Extra DA is made in NA neurons, so NA levels may be reduced therefore blood pressure reduces

Question 16

Where and what is the chemoreceptor trigger zone?

Answer 16

An area of medulla oblongata that receives inputs from blood-borne drugs or hormones, and communicates with other structures in the vomiting center to initiate vomiting.

Question 17

What is the effect of high LDOPA in the peripheral blood?

Answer 17

Activation of the CTZ and nausea

Question 18

What is the word for a drug designed to counteract side effects?

Answer 18

adjunct

Question 19

Does carbidopa cross the BBB?

Answer 19

No

Question 20

What drug can be used to block nauseous effects of Parkinsons treatment?

Answer 20

Domperidone (D2 R antagonis)

It does not cross BBB, so blocks DA action only outside CNS eg at CTZ to reduce DA nauseous effects

Question 21

When is Benzhexol used?

Answer 21

This can be used to stop tremor in parkinsons, as a muscarinic Ach antagonist (atropine like effects)
This is only prescribed for drug-induced Parkinsons (younger) because ACh block in brain can increase dementia risk

Question 22

What is Risperidone?

Answer 22

antipsychotic partial agonist of 5HT 1A, antagonist of 5HT 2A and D2

Question 23

What is EPS?

Answer 23

extrapyramidal symptoms eg dystonia, parkinsonia