Anti-PD drugs & Neuroleptics Flashcards
Summarise the synthesis pathway of dopamine in the presynaptic cell, stating the enzymes involved.
Step 1: L-tyrosine => L-DOPA
Step 2: L-DOPA => Dopamine (DA)
This process utilises the enzymes: Tyrosine hydroxylase (Step 1) DOPA decarboxylase (Step 2)
Summarise the metabolism of dopamine after it has had its effects on the post-synaptic cell
DA removed from synaptic cleft by dopamine transporter (DAT) & noradrenaline transporter (NET) found on the pre-synaptic cell and glial cell membrane.
Three enzymes metabolise DA:
- MAO-A metabolises DA, NE & 5-HT
- MAO-B: metabolises DA
- Catechol-O-methyl transferase (COMT): wide distribution, metabolises all catecholamines
*MAO-A/B are mitochondrial
What are the four dopaminergic pathways in the brain?
Nigrostriatal pathway
Mesolimbic pathway
Mesocortical pathway
Tuberoinfundibular pathway
For each of the four dopaminergic pathways in the brain, state the brain regions that are connected. Give details on what each pathway is important for.
Nigrostriatal pathway - susbstantia nigra pars compacta (SNc) to the striatum
Mesolimbic pathway - ventral tegmental area (VTA) to the Nucleus Accumbens (NAcc) = brain reward pathway.
Mesocortical pathway - VTA to the cerebrum. Important in executive functions & complex behavioural patterns.
Tuberoinfundibular pathway - arcuate nucleus to the median eminence (inhibition results in hyperprolactinaemia)
Describe the epidemiology of Parkinson’s disease;
- major risk factor
- hereditary aspect
Major risk factor is age
Around 5% of cases are due to mutations in certain genes
Identify the main cause of Parkinson’s disease.
Severe loss of dopaminergic projection cells in SNc
What is also seen in the brains of patients with Parkinson’s disease? What do they consist of specifically and where in the neurone are they each found?
Lewy bodies found within neuronal cell bodies
Lewy neurites found within neuronal cell axons
Consist of abnormally phosphorylated neurofilaments, ubiquitin & 𝛼-synuclein
Clinical presentation of PD; motor symptoms (cardinal symptoms)
resting tremor
bradykinesia
rigidity
postural instability
What other non-motor symptoms are associated with PD? Why are these symptoms important to detect for the treatment of PD?
Autonomic nervous system effects;
- olfactory deficits
- orthostatic hypotension
- constipation
Neuropsychiatric;
- sleep disorders, memory deficits, depression, irritability
These symptoms usually appear early in the disease progression (before any motor symptoms) and so early treatment for PD = better prognosis.
State the rate limiting enzyme in the dopamine synthesis pathway.
Tyrosine hydroxylase (TH)
State the first form of treatment for PD
Dopamine replacement by administering L-DOPA aka Levodopa
Explain why L-DOPA is administered instead of dopamine directly
Levodopa can cross blood-brain barrier and be rapidly converted to dopamine by DOPA-D.
Dopamine when administered directly, will not be able to get into the CNS where it is required.
What are the long-term side effects of Levodopa use?
- Dyskinesias (abnormal movements)
- ‘on-off’ effects (fluctuations in clinical state)
- Improves quality of life but doesn’t prolong life
Peripheral breakdown of Levodopa by DOPA-D causes what negative symptoms?
Nausea & Vomiting
What adjuncts may be used to prevent peripheral breakdown of Levodopa? Explain why
DOPA decarboxylase inhibitors = Carbidopa & Benserazide
that importantly do not cross the BBB (remember that Levodopa CAN)
Therefore they prevent peripheral, and not central, breakdown of levodopa
=> Reduces required levodopa dosage and reduce the acute side effects
What the adjuncts may be co-administered with Levodopa? State the effect of this
COMT inhibitors = Entacapone & Tolcapone
They increase the amount of levodopa in the brain => long-lasting effect
Classify the different dopamine receptor agonists used in the treatment of PD
Ergot derivatives (from natural. sources): Bromocriptine & Pergolide
Non-ergot derivatives: Ropinirole & Rotigotine
Ergot derivatives;
- potent agonists for which receptor type
- associated with what negative side-effect
Act as potent agonists of D2 receptors
Associated with cardiac fibrosis
Non-ergot derivatives;
- method of administration
Ropinirole also available as extended-release formulation
Rotigotine also available as a patch
Name two monoamine oxidase B (MAOB) inhibitors used in treatment of PD.
Explain their usage.
Selegiline & Rasagiline
- Reduce the dosage of L-DOPA required
- Can increase the amount of time before levodopa treatment is required
Describe the epidemiology of Schizophrenia;
- % of population affected
- genetic influence?
- higher incidences in which people
- life expectancy
Affects approx. 1% of population & has genetic influence
Onset of symptoms is between 15-35 years
Higher incidence in ethnic minorities (e.g. Afro-Caribbean immigrants)
Significantly reduced life expectancy
List and explain the positive symptoms of schizophrenia
Hallucinations
Delusions and Paranoia
Thought disorder: Denial about oneself
Caused by increased mesolimbic dopaminergic activity
List and explain the negative symptoms of schizophrenia
Affective flattening: lack of emotion
Alogia: lack of speech
Avolition/apathy: loss of motivation
Caused by increased mesocortical dopaminergic activity
State the two first generation/typical anti-psychotics (used to treat schizophrenia)
Chlorpromazine
Haloperidol
State the primary mechanism of action of Chlorpromazine.
What are the high/low incidence side effects?
Primary mechanism of action – possibly D2 receptor antagonism
Side effects:
anti-cholinergic, especially sedation (high incidence)
Extrapyramidal side-effects (EPS) (low incidence)
Haloperidol;
- type of drug
- when do therapeutic effects develop
- side-effect
Very potent D2 antagonist (~50x more potent than chlorpromazine)
Therapeutic effects develop over 6-8 weeks
Side effect:
EPS (high incidence)
State a second generation/atypical antipsychotic? What is special about it?
Clozapine (most effective anti-psychotic even in treatment resistant schizophrenia)
Mechanism of action of clozapine?
Very potent antagonist of 5-HT2A receptors
Side effects of Clozapine
Can cause potentially fatal neutropenia, agranulocytosis, myocarditis & weight gain
Name two other Second generation antipsychotics.
State the mechanism of action for each.
Risperidone = Very potent antagonist of 5-HT2A & D2 receptors
Quetiapine = Very potent antagonist of H1 receptors
Side effects of Risperidone
More EPS & hyperprolactinaemia than other atypical antipsychotics
Side effects of Quetiapine
Lower incidence of EPS than other antipsychotics
State the mechanism of action of aripiprazole.
Partial agonist of D2 & 5-HT1A receptors
No more efficacious than typical antipsychotics
How does the side-effect profile of aripiprazole compare with the other anti-psychotics?
Reduced incidences of hyperprolactinaemia & weight gain than other antipsychotics
