Drugs Affecting Central Nervous System
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Questions and Answers

Which of the following is NOT a cause of neuronal damage in neurodegenerative diseases?

  • Increased neuronal regeneration (correct)
  • Excessive excitotoxicity
  • Apoptosis
  • Oxidative stress

Dopaminergic neurons can regenerate after damage in the central nervous system.

False (B)

Name one neurodegenerative disease mentioned.

Parkinson's disease

The nigrostriatal tract plays a key role in regulating _____ by releasing dopamine.

<p>movement</p> Signup and view all the answers

Match the following dopaminergic pathways with their primary functions:

<p>Nigrostriatal tract = Regulates movement Mesolimbic-mesocortical tract = Regulates cognitive functions Tuberoinfundibular pathway = Decreases prolactin secretion</p> Signup and view all the answers

What is the primary reason large doses of L-dopa are required?

<p>Over 90% is decarboxylated to dopamine in the periphery (A)</p> Signup and view all the answers

Carbidopa and Benserazide are unable to cross the blood-brain barrier.

<p>True (A)</p> Signup and view all the answers

What is the effect of combining L-dopa with Carbidopa?

<p>Increased availability of L-dopa to the CNS</p> Signup and view all the answers

The enzyme that breaks down L-dopa in the periphery is called ______.

<p>Dopa decarboxylase</p> Signup and view all the answers

Match the following drugs with their functions:

<p>Carbidopa = Inhibits peripheral dopa decarboxylase Benserazide = Selectively reduces peripheral dopamine formation Entacapone = COMT inhibitor used alongside L-dopa Tolcapone = Causes potential hepatotoxicity</p> Signup and view all the answers

Which metabolite is produced when L-dopa is broken down by COMT?

<p>3-O-methyldopa (A)</p> Signup and view all the answers

The effectiveness of the L-dopa/Carbidopa combination does not decline over time.

<p>False (B)</p> Signup and view all the answers

What is the primary purpose of using carbidopa in combination with L-dopa?

<p>To inhibit peripheral dopa decarboxylase (D)</p> Signup and view all the answers

Entacapone is a central COMT inhibitor.

<p>False (B)</p> Signup and view all the answers

What phenomenon describes the fluctuations in motor response due to short half-life of L-dopa?

<p>on-off phenomenon</p> Signup and view all the answers

The combination treatment of L-dopa + Carbidopa + ________ is commonly used for Parkinson's disease.

<p>Entacapone</p> Signup and view all the answers

Match the following treatments with their mechanism:

<p>Carbidopa = Inhibits peripheral dopa decarboxylase Entacapone = Inhibits peripheral COMT Tolcapone = Inhibits central and peripheral COMT Direct dopamine agonist = Stimulates dopamine receptors directly</p> Signup and view all the answers

What is a significant side effect of Tolcapone?

<p>Hepatotoxicity (D)</p> Signup and view all the answers

Increasing the frequency of L-dopa doses can help manage the wear-off phenomenon.

<p>True (A)</p> Signup and view all the answers

What happens with chronic use of L-dopa regarding the dopaminergic neurons?

<p>Most dopaminergic neurons degenerate.</p> Signup and view all the answers

The gradual fading of improvement gained from a dose of levodopa is known as the __________ phenomenon.

<p>wear-off</p> Signup and view all the answers

What is the effect of high doses of catecholamines on the pupil?

<p>Mydriasis (C)</p> Signup and view all the answers

Levodopa is effective in patients who have not responded to dopamine receptor agonists.

<p>False (B)</p> Signup and view all the answers

What is the primary concern with administering nonselective MAO inhibitors while on levodopa?

<p>Hypertensive crisis</p> Signup and view all the answers

Bromocriptine is derived from _______.

<p>Ergotamine</p> Signup and view all the answers

Match the drug to its effect:

<p>Levodopa = Increases dopamine levels Dopamine agonists = Stimulate D2 receptors Bromocriptine = Risk of pulmonary fibrosis Nonselective MAO inhibitors = Can cause hypertensive crisis</p> Signup and view all the answers

Which of the following is an adverse effect common to both levodopa and dopamine agonists?

<p>Nausea and vomiting (B)</p> Signup and view all the answers

Dopamine receptor agonists are known to significantly reduce motor fluctuations in advanced Parkinson's disease without the need for L-dopa.

<p>True (A)</p> Signup and view all the answers

What is the main advantage of dopamine agonists over levodopa?

<p>Do not result in significant motor fluctuations or dyskinesias</p> Signup and view all the answers

Prolonged use of _______ may cause mental conditions to worsen in psychiatric patients.

<p>Bromocriptine and l-dopa</p> Signup and view all the answers

Flashcards

What is the nigrostriatal tract?

The nigrostriatal tract is a pathway in the brain that involves the release of dopamine from the substantia nigra to the striatum. This release regulates movement by inhibiting GABA-ergic and cholinergic neurons.

What is dopamine's role in the brain?

Dopamine is a neurotransmitter in the brain that plays an essential role in various functions, including movement, cognition, and emotions. It is released from specific pathways, including the nigrostriatal tract involved in movement regulation.

What are neurodegenerative diseases?

Neurodegenerative diseases are characterized by progressive damage to neurons in certain brain areas. This damage can result from various factors like excessive excitotoxicity, stroke, oxidative stress, or apoptosis.

What are antiparkinsonian drugs?

Antiparkinsonian drugs are medications used to manage Parkinson's disease by targeting the dopamine pathway and alleviating symptoms. They increase dopamine levels or mimic its effects to improve movement.

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Why are neurodegenerative diseases difficult to treat?

Because damaged neurons in the central nervous system (CNS) cannot regenerate, treatment for neurodegenerative diseases focuses on managing symptoms rather than curing the disease.

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What is L-dopa?

L-dopa is the main precursor of dopamine and is used to treat Parkinson's disease.

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What does Dopa decarboxylase do?

Dopa decarboxylase is an enzyme that converts L-dopa into dopamine, but it acts outside the brain, leading to unwanted side effects.

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How do Carbidopa and Benserazide work?

Carbidopa and benserazide are drugs that block dopa decarboxylase in the periphery (outside the brain), allowing more L-dopa to reach the brain.

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What is COMT?

COMT is an enzyme that can also break down L-dopa, but it's a minor pathway.

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What do Entacapone and Tolcapone do?

Entacapone and Tolcapone are drugs that inhibit COMT, decreasing the breakdown of L-dopa.

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Why are high doses of L-dopa needed?

Large doses of L-dopa are needed because most of it is broken down in the periphery before reaching the brain.

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What is the most common treatment for Parkinson's?

Levodopa/Carbidopa combination therapy is the most effective treatment for Parkinson's, but its effectiveness declines over time.

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What is Carbidopa?

A drug that inhibits the enzyme dopamine decarboxylase, preventing the conversion of L-dopa to dopamine in the periphery.

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What is Entacapone?

A drug that inhibits the enzyme catechol-O-methyltransferase (COMT), reducing the breakdown of L-dopa in the periphery.

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What is Stalevo?

A combination therapy for Parkinson's disease that includes L-dopa, Carbidopa, and Entacapone.

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What is the "on-off" phenomenon?

A phenomenon in Parkinson's disease where patients experience alternating periods of good mobility (ON) and severe symptoms (OFF).

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What is the "wear-off" phenomenon?

Gradual worsening of motor function that occurs towards the end of the L-dopa dose, even with regular doses.

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How can we manage the "on-off" phenomenon?

Strategies to manage the "on-off" phenomenon by increasing the duration of L-dopa's effectiveness.

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What causes L-dopa degradation?

The breakdown of L-dopa by the enzyme COMT, which reduces its effectiveness.

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How does L-dopa reach the brain?

The process of L-dopa crossing the blood-brain barrier to reach the brain.

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Why does L-dopa's effectiveness diminish over time?

The effectiveness of L-dopa in treating Parkinson's decreases over time, as more dopaminergic neurons die.

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Dopamine's role in Parkinson's disease

Dopamine is a neurotransmitter involved in movement, mood, and reward. In Parkinson's disease, dopamine-producing neurons in the substantia nigra degenerate, leading to motor symptoms.

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How does Levodopa work?

Levodopa is a precursor to dopamine that can cross the blood-brain barrier. It is converted to dopamine in the brain, increasing dopamine levels and improving motor function.

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What do MAO inhibitors do?

MAO inhibitors prevent the breakdown of dopamine, leading to increased dopamine levels and improved motor symptoms. However, they can interact with other drugs, increasing blood pressure.

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How do dopamine agonists work?

Dopamine receptor agonists mimic the effects of dopamine by directly activating dopamine receptors in the brain. They have a longer duration of action than levodopa, reducing fluctuations in motor function.

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What are the side effects of Levodopa?

Levodopa can be converted to dopamine outside the brain, leading to side effects like nausea, vomiting, and hypotension.

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Bromocriptine: A dopamine agonist

Bromocriptine is a dopamine agonist with a longer duration of action than levodopa, reducing motor fluctuations and improving motor function.

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Side effects of Bromocriptine

Bromocriptine can worsen peripheral vascular disease due to vasoconstriction. It can also cause cardiac problems in patients with a history of myocardial infarction.

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Antipsychotics and Parkinson's

Antipsychotics block dopamine receptors, which can worsen Parkinson's symptoms by reducing the effectiveness of levodopa.

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Vitamin B6 and Levodopa

Vitamin B6 (pyridoxine) increases the conversion of levodopa to dopamine outside the brain, reducing its effectiveness in treating Parkinson's.

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Study Notes

Drugs Affecting the Central Nervous System

  • Neurodegenerative diseases involve neuronal damage in specific brain regions.
  • Causes include excessive excitotoxicity (excess glutamate), stroke, head trauma, oxidative stress (increased reactive oxygen species), and apoptosis (programmed cell death).
  • Neurodegenerative diseases are difficult to treat as CNS neurons cannot regenerate once damaged. Treatment is therefore symptomatic.
  • Examples of neurodegenerative diseases: Parkinson's, Alzheimer's, Huntington's, and Multiple sclerosis.

Dopaminergic Pathways

  • Dopamine (DA) is a precursor to norepinephrine (NE) in noradrenergic pathways.
  • It's a neurotransmitter in:
    • Nigrostriatal tract: DA-releasing neurons project to the striatum, regulating movement by inhibiting GABA-ergic and cholinergic neurons.
    • Mesolimbic-mesocortical tracts: DA-releasing neurons projecting to limbic and cortical structures regulate cognitive functions.
    • Tuberoinfundibular tract: DA-releasing neurons from the hypothalamus regulate prolactin levels in the anterior pituitary.
    • Chemoreceptor trigger zone: DA receptor activation in the medulla increases vomiting.

Parkinson's Disease

  • Parkinson's is a progressive neurological disorder of movement, second only to Alzheimer's disease in frequency.
  • Characterized by four cardinal motor features: resting tremors, muscular rigidity, bradykinesia (slow movement), and abnormal gait.
  • Occurs primarily in individuals over 65.
  • Etiology involves neurodegeneration in inhibitory dopaminergic neurons relative to excitatory cholinergic neurons in the nigrostriatal tract.
  • Imbalance between these causes the symptoms in Parkinson's disease.

Parkinson's Disease Classification

  • Primary (idiopathic): More than 80% dopaminergic neuron degeneration in the substantia nigra leading to dopamine deficiency and increased acetylcholine.
  • Secondary (atypical): Often due to imbalances between acetylcholine and dopamine, including:
    • Vascular Parkinsonism (Small vessel cerebral ischemia)
    • Post-traumatic
    • Toxin-induced
    • Infectious
    • Drug-induced (e.g., antipsychotics)

Treatment of Parkinson's Disease

  • Goal: Restoring the balance between acetylcholine and dopamine in the basal ganglia.
  • Treatment is symptomatic (temporary relief) and does not prevent disease progression.
  • Dopaminergic drugs: Levodopa (L-dopa) is the most common, converting to dopamine in the brain. Peripheral decarboxylase inhibitors (e.g., carbidopa) decrease peripheral dopamine, increasing levodopa reaching the brain.
  • Dopamine receptor agonists: Mimic dopamine's function, used in early stages or along with levodopa.
  • COMT inhibitors: (e.g. Entacapone) Prevent the breakdown of levodopa.
  • Anticholinergic drugs: Help reduce acetylcholine overstimulation, though not as effective as levodopa.

Additional Details

  • On-off phenomenon: Fluctuations in levodopa's effect, causing periods of improved and impaired movement.
  • Dyskinesias: Involuntary movements, often a long-term consequence of levodopa therapy.
  • Adverse Effects: Levodopa may cause nausea, vomiting, dyskinesia, postural hypotension, and confusion.

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Description

This quiz explores the impact of drugs on central nervous system functions, focusing on neurodegenerative diseases and dopaminergic pathways. Participants will learn about causes of neuronal damage, examples of diseases, and the role of dopamine in regulating movement and cognition.

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