Parkinson's Disease Flashcards
What was parkinson’s disease first described as?
“shaking palsy”
1817
by British physician, James Parkinson
Parkinsonism
- progressively deteriorating neurological disorder
- hypokinetic or akinetic disease
- the clinical syndrome that arises from the degeneration of the basal ganglia
- the damage is to the substantial nigra (aka MAY NOT be b/c of loss of DA)
- PD=IPD; secondary parkinsonism
Parkinson’s Disease
- the most common cause of parkinsonism
- idiopathic neurodegenerative condition caused by loss of dopaminergic neutrons in the substantial nigra
What is PD characterized by
- asymmetrical resting tremor
- bradykinesia (brady means slow and kinesis means movement)
- rigidity
- postural instability (shuffling along, bent over)
secondary parkinsonism
- secondary to a known cause
- similar to Parkinson disease, but the symptoms are caused by certain medicines, a different nervous system disorder, or another illness
Akinesia
- slowness or loss of normal motor function, resulting in impaired muscle movement
- literally “without movement” or without much movement
Epidemiology
- estimated 4 million people living world wide with PD
- affects 1 in 100 over 65 (more than combined incidence of MS, muscular dystrophy and Lou Gehrig’s disease)
- incidence increase as people age with average age of onset being around 60
- affects males to females 2:1
- development of IPD is inversely correlated with cigarette smoking and caffeine consumption
tyrosine
- its an important aa that gets taken up from blood into surrounding fluids that our brain is exposed to (CNS)-> BRAIN
- in this terminal, tyrosine gets taken up
what happens to tyrosine once it gets taken up by the substantial nigra neuron
-once taken up it is hydroxylated to L-dopa, then decarboxylated into DA
What happens to DA once it has been formed
- it gets packed into vesicles
- within the ion channels there is an influx of Ca/Na into the nerve channels-> inside becomes positive-> dumping of DA vesicles into the synaptic cleft
- on the post synaptic side, it binds to the D1 and D2 receptors on the putamen neurons
What happens when DA binds to the D1/D2 receptor on the putamen neuron (general)
- the pudamen neurons are located on the striatum
- this ends up increasing the amount of GABA, which actually ends up reducing the putamen activity
- this decrease in putamen activity ends up increasing activity of the ventrolateral thalamus, which controls movement
synaptic transmission (general)
- APs are produced via depolarization of the neuronal membrane due to an influx of Na through Na voltage-gated channels
- the produced AP propagates down the axon towards the pre–synaptic terminal
- arrival of the AP at the pre-synaptic terminal opens Ca channels in the PM
- the influx of Ca triggers the exocytosis of vesicles containing NT
- the NT enters the synaptic cleft and binds to receptors on the post-synaptic membrane
- following binding, the NT is cleaved and taken back up into the pre-synaptic terminal where it is recycled and stored in vesicles
DA synthesis
- tyrosine is taken up form the blood to the brain’s ECF then into dopaminergic substantial nigra neurons via specific enzyme transporters
- it becomes hydroxylated to form L-DOPA, the DA precursor
- L-DOPA is then decarboxylated to make DA
Important anatomical structures involved
-basal ganglia
-substantia nigra
-striatum
-ventrolateral thalamus (VLT)
-motor cortex
(-subthalamic nucleus)
basal ganglia
-controls complex movement s and has a part in motor learning-located at the base of the forebrain and composed of substantia nigra, striatum, sub-thalamic nucleus (and palladum)
substantia nigra
located in the midbrain with an important role in reward, addiction and movement
-input form all over the bran relayed via dopaminergic neurons to striatum
striatum
- composed of putamen and caudate nucleus and located below the cortex of the cerebrum
- major input site of the basal ganglia system-putamen neurons have both D1 and D2 receptors
Ventrolateral thalamus
- integration centre for basal-ganglionic and cerebellar impulses
- brought to the corticospinal system
- sends fibers to the percentile and supplementary motor cortices to initiate body movement
Motor cortex
- input signals are changed to output which leads to movement
- located in the frontal cortex of the brain
- ultimate highest order that needs to be stimulated in order to move (but if the VLT is stimulated, so will the motor cortex)
what NT is overstimulated in any addiction?
DA
What functions is DA involved in?
- reward (motivation)
- pleasure, euphoria
- motor function (fine tuning)
- compulsion
- preservation
What functions is serotonin involved in?
- mood
- memory
- processing
- sleep
- cognition
What are the 3 NT’s all involved in Parkinson’s disease?
- DA
- Ach
- GABA
What do these 3 NT’s control?
movement
Dopamine
- important in many brain fxns: motivation, cognition, learning, mood, attention, reward, sleep, & voluntary movement
- works via the direct/indirect path within the basal ganglia to initiate movement
- insufficient DA biosynthesis causes parkinson’s where a person loses the ability to execute smooth controlled movement
How much DA function must be lost before it manifests as Parkinson’s?
80%
Where are certain areas where problems could lead to DA loss and therefore Parkinson’s?
- presynaptic production
- postsynaptic effect (receptors)
- synaptic cleft effect (destruction)
aka:
- lack of DA (from an inability to be produced or inability to be secreted)
- lack of receptors/ inability of DA to bind to receptors
- over-producing amount of enzyme that chews up all the DA therefore isn’t allowed to work
What is the relationship between Ach and DA?
-antagonistic NTs (Ach excitatory, while DA is inhibitory)
What happens to Ach when there is less than normal DA
-if dopaminergic cells are destroyed, no DA released to compete and Ach runs out of check
What does too much Ach cause?
- it causes over activity of cholinergic neurons
- leading muscles to contract but as there is excess Ach, muscles cant repolarize and will remain contracted
What is the main inhibitory NT?
GABA
In normal motor systems, what is GABA’s release regulated by?
-by binding of DA to receptors
What happens to the relationship between GABA and DA during Parkinsons
- in Parkinson’s disease, release of GABA will increase and decrease in the incorrect portions of the Nigro-Striatal pathway
- a reduction in DA causes an increase GABA resulting the individual to be partially or fully paralyzed
Normal movement
- info from different parts of the brain is sent to the substantia nigra to stimulate DA synthesis
- DA is released from the substantia nigra neurons where it binds to D1 and D2 receptors on the putamen neurons in the striatum
DA upon release binds to:
- D1 DIRECT path
- D2 INDIRECT path (not required to know this path)
Direct path D1 receptors
-DA binds to the D1 receptor of Substance P producing putamen neurons in the striatum
-DA binding causes an increase in GABA levels which inhibits the firing of D1 putamen neurons
(increase in Sub P increases GABA)
-therefore they shut down (GABA shuts them down)
-by decreasing putamen activity, VLT activity increases
(TO MOVE YOU NEED THE PUTAMEN NEURONS TO BE SHUT DOWN)
-results in less inhibition to the VLT
-this allows VLT to send signal to the pre-motor and motor cortices of the brain which leads to bodily movement
(slide 19)
How do both the direct and indirect pathways produce movement?
-in normal movement they produce movement by decreasing inhibition of the VLT
control of GABA in normal movement
-GABA is either up or down regulated to facilitate necessary inhibition to propel the pathways
Pathophysiology of the direct path
-in PD, DA becomes deficient due to problems with synaptic transmission or death of neurons that produce it
-DA doesn’t activate D1 receptors (due to a complete or partial reduction in DA levels)
-no Sub P will be released, leading to decrease in GABA
-firing of D neurons will increase in the putamen as they are not inhibited by GABA that would normally be present
-D1 neurons release GABA upon firing to the VLT inhibiting the VLT from transmitting the signal to the motor cortex (VLT inhibited in both paths by an excess of GABA reaching it)
(slide 22)
net inhibition occurs in the system which stops the motor cortex from being activated resulting in no movement
idiopathic parkinson’s disease
- aka primary parkinsonism
- degeneration of pigmented Dopaminergic neurons in the substantia nigra-> results in loss of DA
- remaining dopaminergic neurons contain Lewy bodies
- this is what michael J fox has
Lewy bodies
- abnormal aggregates of protein that develop inside nerve cells (DA neurons)
- cytoplasmic inclusions
- eosinophilic, contain ubiquitin and alpha-synuclein
is the true etiology of IPD known?
no
etiology of IPD; possible factors:
- genetic factors (alpha-synuclein and parkin genes)-> if IPD develops before 50; over 12 gene mutations are implicated in parkinson’s; only constitute a small % of IPD cases
- oxidative stress
- excitotoxicity
explain the theory of oxidative stress behind the etiology of IPD
-substantia nigra is a region characterized by high levels of oxidative stress
-free radicals generated from DA metabolism
-healthy indivs have several anti-ox molecules in the SN to limit damage
IPD: free radical attack damages neurons b/c anti-ox defences not present
true or false: as a pharmacist it is important/ helpful to recommend antioxidants to people with IPD
true (i.e. Vitamin C or E)
explain the theory of excitotoxicity behind the etiology of IPD
-pathological process where nerve cells are damaged or killed from excess glutamate
IPD: inhibitory effects of DA not present, resulting in excessive glutaminergic stimulation
-> glutamate levels too high in comparison to DA
what is the main excitatory NT in the nigrostriatal pathway?
glutamine
Causes of secondary parkinsonism
Casual factors:
- drugs
- toxins
- infections
- head trauma
drug induced secondary parkinsonism
- DA antagonists block DA receptors and output by the SN cells
- cause parkinsonian signs such as rigidity, hypokinesia, and resting tremor
- onset is abrupt, symptoms symmetrical
- symptoms tend to disappear after use of the drug is discontinued
what are some drugs that causes drug induced secondary parkinsonism;
what are they doing to cause this?
- antipsychotics
- calcium channel blockers
- in both of these you are preventing DA from being released into the synaptic cleft