patho - notebooklm

1. Predict the likely effects of drugs that decrease DA vs drugs that increase DA, and hypothesize clinical uses and ADEs

• Pro-dopaminergic drugs (Increase DA activity):

  • Likely Effects & Clinical Uses: Increase movement (used in Parkinson’s disease), increase mood/reward/focus (used in ADHD/depression), inhibit gastric motility, and decrease prolactin secretion.

  • Adverse Effects (MGPA Mnemonic):

    • M (Motor): Dyskinesias ("weaving" dyskinesias from excessive motor D2 stimulation).

    • G (GI): Nausea, vomiting, anorexia, constipation.

    • P (Psychiatric): Psychosis, vivid dreams, impulse control disorders.

    • A (Autonomic): Orthostatic hypotension, tachycardia, sleepiness.

• Anti-dopaminergic drugs (Decrease DA activity):

  • Likely Effects & Clinical Uses: Anti-psychosis (used in schizophrenia/psychosis), anti-nausea/anti-emetic (e.g., metoclopramide, promethazine), and increased gastric motility.

  • Adverse Effects: Depression/dysphoria, impaired movement, Extrapyramidal Symptoms (EPS), Tardive dyskinesia (due to excessive antagonism at motor D2 receptors), and increased prolactin levels.

2. Identify the drugs with NMDA antagonism listed in the slide set

The specific drugs listed in the slide set with NMDA receptor antagonism are:

1. Amantadine (and Amantadine ER: Gocovri, Osmolex) — used in PD as an antidyskinetic.

2. Memantine

3. Dextromethorphan

4. Ketamine

5. Methadone

3. Molecular targets at the DA synapse & predicted synaptic effects

1. Precursor / Central LAADC (L-amino acid decarboxylase):

   • Target: Intracellular enzyme converting L-DOPA to DA inside live presynaptic neurons.

   • Synaptic Effect: Increases DA synthesis and vesicular loading, boosting global synaptic DA release.

2. Peripheral LAADC (Gut/Blood):

   • Target: Peripheral decarboxylase enzyme.

   • Synaptic Effect: Inhibition by Carbidopa prevents peripheral breakdown of L-DOPA to DA, reducing GI toxicity and allowing more L-DOPA to cross the BBB.

3. COMT (Catechol-O-methyltransferase):

   • Target: Peripheral and post-synaptic enzyme breaking down L-DOPA and DA.

   • Synaptic Effect: Inhibition by Entacapone/Tolcapone/Opicapone blocks degradation, extending L-DOPA plasma half-life and increasing synaptic DA duration.

4. MAO-B (Monoamine Oxidase B):

   • Target: Intracellular mitochondrial enzyme breaking down DA7.

   • Synaptic Effect: Inhibition by Selegiline/Rasagiline/Safinamide prevents intracellular DA clearance, raising synaptic DA levels.

5. Post-synaptic DA Receptors (D2/D1):

   • Target: D2-like and D1-like GPCRs on striatal neurons.

   • Synaptic Effect: Direct Agonists (Ropinirole, Pramipexole, Rotigotine, Apomorphine) directly stimulate post-synaptic receptors, bypassing dead presynaptic neurons.

6. DAT (Dopamine Transporter):

   • Target: Presynaptic reuptake transporter.

   • Synaptic Effect: Inhibition blocks reuptake back into the presynaptic terminal, keeping DA in the synaptic cleft longer.

4. Symptoms of Parkinson’s Disease (PD)

Motor Symptoms (TRAP Mnemonic):

• T – Tremor (resting tremor)

• R – Rigidity (muscle stiffness)

• A – Akinesia / Bradykinesia (slowness of voluntary movement)

• P – Postural instability / gait disturbances

Non-motor Symptoms:

• Cognitive/Psychiatric: Cognitive decline, memory loss, depression, anxiety, psychosis, sleep dysfunction.

• Autonomic: Orthostatic hypotension, GI dysfunction (constipation).

• Sensory/Other: Loss of smell (anosmia), pain, fatigue.

5. Change in dopaminergic neurons and DA levels in PD

• Pathophysiology: PD is a neurodegenerative disorder marked by physical degeneration and death of dopaminergic neurons whose cell bodies originate in the Substantia Nigra (SN). It is pathologically defined by intracellular Lewy bodies (misfolded -synuclein aggregates).

• DA Level Changes: Degeneration of SN neurons decreases dopamine delivery to the striatum along the nigrostriatal motor pathway. This causes a marked reduction in actual DA levels in the striatum.

6. Striatal Circuitry & L-DOPA Clinical Barriers / Mitigation

A. Circuitry & Neurotransmitter Balance:

• Glutamate (Glu): Glutamatergic inputs provide the primary excitatory drive onto GABAergic target neurons in the striatum.

• Balance Modulators: Dopamine (D2), Acetylcholine (Muscarinic M1), and Adenosine (A2A) modulate this Glutamate drive.

  • Normal State (DA=ACh/Adenosine): Balanced inputs yield controlled movements.

  • Parkinson’s State (DAACh/Adenosine): Death of DA neurons leaves unopposed ACh/Adenosine excitation, causing blocked movement, rigidity, and tremor.

  • Excess Dopamine (DAACh/Adenosine): Causes drug-induced dyskinesia28.

B. L-DOPA Kinetics & Peripheral Barriers:

1. Dopamine itself cannot cross the blood-brain barrier (BBB), but its precursor L-DOPA crosses the BBB.

2. When oral L-DOPA is given alone:

   • It encounters extensive peripheral metabolism by LAADC and COMT in the GI tract and blood.

   • Only 1–2% of an oral dose reaches the brain intact.

   • Peripheral conversion to DA causes severe GI side effects (nausea and vomiting) and a very short duration of action.

C. How LAADC & COMT Inhibitors Mitigate These Barriers:

• LAADC Inhibitor (Carbidopa): Inhibits peripheral LAADC in the gut and blood. Because Carbidopa does not cross the BBB, it prevents peripheral conversion of L-DOPA to DA without blocking central brain conversion. This eliminates severe peripheral nausea/vomiting and boosts brain bioavailability of L-DOPA to ~10%.

• COMT Inhibitors (Entacapone, Tolcapone, Opicapone): When LAADC is blocked, L-DOPA is redirected toward peripheral COMT degradation. COMT inhibitors block this pathway, extending L-DOPA’s plasma half-life, smoothing out motor fluctuations ("off" time), and further increasing brain entry. (Note: Tolcapone also crosses the BBB to inhibit central COMT).

7. Complete Drug Table: Classes, MOA, and Key Differences

Drug Class	Generic Names (Brand Names)	Mechanism of Action (MOA)	Key Differences & Characteristics
DA Precursor	Levodopa / L-DOPA (Inbrija)	Precursor converted to DA centrally by LAADC	Crosses BBB; requires surviving presynaptic neurons for conversion.
LAADC Inhibitor	Carbidopa (generic)	Inhibits peripheral LAADC enzyme	Does NOT cross BBB; given strictly as an adjunct to L-DOPA to stop GI conversion.
COMT Inhibitors	Entacapone (Comtan), Tolcapone (Tasmar), Opicapone (Ongentys)	Inhibits COMT breakdown of L-DOPA/DA	Entacapone/Opicapone act peripherally; Tolcapone crosses the BBB.
L-DOPA Formulations	Carbidopa/Levodopa (Sinemet), Carbidopa/Levodopa/Entacapone (Stalevo), Gel pump (Duopa), Prodrugs (Vyalev)	Combined precursor + metabolic inhibitors / long-acting forms	Bypasses kinetic swings; Stalevo is a triple combination pill.
Direct D2 Agonists	Ropinirole (Requip), Pramipexole (Mirapex), Rotigotine (Neupro), Apomorphine (Apokyn)	Directly stimulates post-synaptic D2 receptors	Bypasses damaged presynaptic DA neurons17. Rotigotine is a patch; Apomorphine is non-selective D1/D2.
MAO-B Inhibitors	Selegiline (Deprenyl, Zelapar), Rasagiline (Azilect), Safinamide (Xadago)	Irreversibly/selectively inhibits MAO-B	Low doses are MAO-B selective (avoids NE/5HT interactions).
Antidyskinetic (DA Misc)	Amantadine, Amantadine ER (Gocovri, Osmolex)	Dual MOA: Increases DA release/synthesis + NMDA receptor antagonist	Treats motor symptoms AND reduces L-DOPA-induced dyskinesias via NMDA blockade.
Antimuscarinics	Benztropine (Cogentin), Trihexyphenidyl (Artane)	Muscarinic receptor antagonists	Does NOT affect DA levels; restores balance by blocking excess cholinergic drive.
Adenosine A2A Antagonist	Istradefylline (Nourianz)	Selective Adenosine A2A receptor antagonist	Does NOT affect DA levels; counterbalances loss of DA via adenosine blockade.

8. Dopaminergic Agents Across Previous IST Lectures

1. Parkinson’s Disease (Pro-dopaminergic): L-DOPA, Carbidopa, Entacapone, Selegiline, Ropinirole, Pramipexole, Amantadine.

2. Antipsychotics (Anti-dopaminergic):

• First-Generation (e.g., Haloperidol): Potent motor D2 receptor antagonists used in schizophrenia. Danger: Severely exacerbates Parkinson's motor symptoms.

• Second-Generation: Dual D2/5-HT2A antagonists.

3. GI Motility & Anti-emetics (Anti-dopaminergic):

• Agents (e.g., Metoclopramide, Promethazine): D2 antagonists in the CTZ and gut that inhibit nausea/vomiting and increase GI motility.

4. Antidepressants & ADHD (Pro-dopaminergic):

• NDRIs (Bupropion): DAT and NET reuptake inhibitors.

• Stimulants (Amphetamines/Methylphenidate): DAT inhibitors and DA release facilitators.

• MAOIs: Non-selective block of monoamine breakdown.

5. Cardiovascular & Lactation Agents:

• D2 Agonists (Bromocriptine, Cabergoline): Inhibit prolactin release from the pituitary gland.

• Dopamine IV Infusion: Inotropic and vasopressor support.