Neurodegenerative Disorders Flashcards
At what age is Parkinsons disease most common and what is the rate between men and women having it
Parkinsons is most common in patients in their 80s or older and the rate in men is around 1.5x higher than in women
What are 7 factors that INCREASE the risk of developing PD
Male gender, Age, Hispanic heritage, Head trauma, Rural living, Genetics, Melanoma
What are 7 factors that DECREASE the risk of developing PD
Smoking, Caffeine use, High serum urate, Female gender, Physical activity, NSAID use, urban living
What changes can we see in the brain that provide evidence for PD
Clear loss of Dopaminergic neurons from a specific brain region, the substantia nigra pars compacta (SNpc).
What is the substantia nigra and what happens to it during PD
It is a black substance that appears in normal brains as a dark streak. In the brains of PD patients, the dark areas are lost. However, it may require loss of 50-70% of the SNpc dopaminergic neurons before the motor symptoms of PD become apparent.
What bodies begin to appear when PD patients brains change
Lewy bodies
What are Lewy bodies and what protein do they mainly consist of?
They are intracellular inclusions mostly consisting of protein a-synuclein.
Which protein is important in Proteasome and Mitochondrial function
Parkin
What happens if A-synuclein misfolds
It forms oligomers
How are ‘Proteasome’s not functioning’ linked to Parkinsons
- Proteasome’s usually remove oligomers but if they are not functioning properly then you may get oligomers forming LEWY bodies.
How do Lewy bodies kill cells?
Lewy bodies kill cells via Neuroinflammation or mitochondrial dysfunction (cells wont have enough energy and will die)
PRKN, PINK1, PARK7 are all genes effected causing mitochondrial dysfunction
Is PD a homogenous disorder - why/why not? (3 reasons)
No - lots of ways to get it, lots of genes to make you high risk, and lots of environmental toxins that could lead to its development
What is MPTP
Its a uniquely selective toxin - its a prodrug
What are prodrugs
Prodrugs are medications that turn into an active form once they enter the body
Where is MPTP metabolised and what does it interfere with?
Metabolised in glial cells to MPP and then taken up by neurons where it interferes with mitochondrial electron transport.
What is MPTP used as
Its used in modern day to produce animal models of parkinsons
What animals are used for parkinsons models and why?
non human primates as rodents are immune to MPTP
What 4 features of PD define the disease?
- Bradykinesia
- Resting tremor
- Rigidity
- Postural instability
Whats Bradykinesia
Slowed movement - main defining feature of PD and is a major cause of disability.
What are examples of Bradykinesia (4)
- Slowed walking
- Reduced facial expressions
- Decreased voice volume
- Micrographia (reduction in writing size)
Whats the most visible sign of PD and what does it consist of?
Resting tremor - can consist of repetitive movements with their thumb and forefinger, mainly seen in the hands.
What is Rigidity and what are the 2 types?
Stiffness in mainly arms, legs, back and neck. 2 types: Lead pipe and cogwheel.
What is the difference between lead pipe rigidity and cogwheel rigidity?
- Lead pipe is smooth resistance to movement
- Cogwheel is resistance that momentarily gives way.
What is postural instability and how is treating it different from lots of other symptoms?
- Its the loss of postural reflexes and having problems with balance.
- Its different because its symptoms are not primarily due to loss of dopaminergic neurons in the substania nigra
- So therapies that are based around this do very little for this symptom.
Why is postural instability particularly dangerous
It can lead to falling which is extremely dangerous even in healthy elderly people.
What are the main non-motor symptoms of PD (8 examples)
- Depression
- Apathy
- Cognitive dysfunction (inc dementia)
- Anxiety
- Psychosis
- Loss of sense of smell
- Sleep disorders
- Autonomic dysfunction
What Percentage of PD is idiopathic?
Around 85%
What Percentage of PD is familial?
Around 15%
This normally includes early onset
What is PINK1 and what does it do?
- One of the 20 proteins involved in PD
- Is PTEN induced putative kinase 1
- Is important in mitochondrial function
What is PARK7 and what does it do?
- Is one of the 20 proteins involved in PD
- DJ-1 protein
- Protects against oxidative stress
What is seeding?
Where oligomers cause other copies of the a-synuclein to misfold
What are 4 main structures the the Basal Ganglia consists of?
- Striatum
- Globus Pallidus
- Substantia nigra
- Sub-thalamic nucleus
What are the 4 major roles of the basal ganglia?
- Motor
- Learning
- Mood/emotion
- Links cerebral cortex back to the cerebral cortex through the thalamus
What is the classic motor loop?
- Cerebral cortex
- Cerebellum
- through thalamus
- Back to cerebral cortex
Which dopiminergic pathway is the primary focus of the basal ganglia?
Nigostriatal pathway
What are the two components of the dorsal striatum?
- Putamen
- Caudate nucleus
What is the globus palidus subdivided into?
- Globus palidus externa
- Globus palidus interna
What is the motor cortical-basal ganglia circuit?
- Cortex
- Striatum (putamen)
- Globus palidus
- Thalamus
What is the hyperdirect route of the basal ganglia?
Bypasses the striatum and the globus palidus externa
Goes straight to the STN (sub-thalamic nucleus) and then to the globus palidus interna- to the thalamus
(therefore it will be inhibitory)
What is the indirect pathway of the basal ganglia?
- Excitatory input to striatum
- Sends out inhibitory input to the globus palidus externa
- Globus palidus externa sends a weak inhibitory input to the globus palidus interna and the STN
- STN sends large excitatory signal to the globus palidus interna which then inhibits the thalamo-cortical drive
- This inhibits movement
What is the direct pathway of the basal ganglia?
- Excitatory output from the cortex to the striatum
- Striatum sends an inhibitory signal to the globus palidus interna
- Thr globus palidus interna synapses with an inhibitory interneuron and fires a weak inhibitory signal to the thalamus
- This will excite the thalamo-cortical drive and therefore cause movement
What are the neurons in the striatum which first synapse with the cortex?
Medium spiny neurons (GABAergic)
What do the GABAergic neurons do?
- The substantia nigra neurons are forming synapses with the necks of the dendritic spines
- These have the potential to regulte the output from the cortex
What are the different populations of medium spiny neurons and what do they do?
- Some have dopamine D1 and others D2 receptors
- These have different influences on the dendritic dopamine substantia nigra spine
Which dopamine receptors are associated with the direct pathway?
- Dopamine D1 receptors on medium spiny neurons
- They are excitatory and facilitate the activation of neurons
Which dopamine receptors are associated with the indirect pathway?
- Dopamine D2 receptors on medium spiny neurons
- They are inhibitory, therefore if we inhibit this we will promote movement
How does less dopamine lead to less movement?
- Dopamine promotes movement through the direct pathway
- Therefore less dopamine means less promotion of movement
- Dopamine also inhibits the indirect pathway
- This means less activation of D2 receptors means the inhibition of movement will be strenghtened
What is the current hypothesis of how PD disrupts the cortical plan for movement?
- There is no constant level of activity which is necessary for the basal ganglia to plan activity
- Instead, there are bursts of high activity and periods of quiet
- The change in pattern and frequency of activity may be what disrupts the cortical function as it is hard to interpret this activity
- In turn disrupting the cortical plan
What is L-DOPA?
- Substrate for DOPA decarboxylase
- Can increase CNS dopamine levels
- Metabolised in the periphery (side effects)
- Can cross the blood brain barrier
What are 2 drugs used in conjunction with L-DOPA?
- Carbidopa
- Benserazide
Why are Carbidopa and benserazide used in co-combination therapies with L-DOPA?
- 2 peripheral inhibitors of DOPA decarboxylase
- Cannot cross the BBB
- They reduce the side-effects of L-DOPA and increase CNS levels of L-DOPA
How is L-DOPA degraded in the periphery?
- Can be catalysed by COMT
- Catalysed by DOPA decarboxylase
Why do we want to prevent the amount of COMT degredation of L-DOPA?
COMT converts L-DOPA into 3-O-methyldopa not dopamine (unuseful in the treatment of PD)
Ca use a COMPT inhibitor
How is dopamine degraded in the CNS?
- COMT
- Monoamine oxidase A and B
How do we preserve dopamine in the CNS?
- Block COMT using inhibitor: Tolcapone
- Block monoamine oxidase using inhibitor: selegiline, rasagiline
What are some unwanted effects of L-DOPA treatment?
- Dyskinesia (upregulation of RASGRP1 protein)
- Rapid changes in clinical status (wearing off- hypokinesia followed by dyskinesia)
- Nausea
- Postural hypotension
- Psychiatric effects (schizophrenia like, confusion, insomnia and nightmares in 20% of patients)
What is a benefit of dopamine agonists?
- Don’t rely on DA neurons
- So don’t have the L-DOPA on-off effect
Why are dopamine agonists use limited?
- Due to side effects
- Compulsive behaviour
- Peripheral DA effects (cardiovascular)
What are Bromocriptine, pergolideand apomorphine?
- Less selective dopamine agonists
- Use limited by side effects (nausea/vomiting, lung fibrosis)
- Can be co-administered with doperidone (cannot cross BBB)