Neuropharmacology: Catecholamines

Neurochemistry of Catecholamines

Brian J. Piper, Ph.D.

Norepinephrine

Goals• Biosynthesis• Receptors• Neuroanatomy• Diseases• Drugs – L-Dopa– Methylphenidate

Definition

• Catechol + amine (NH2)• Members: – Dopamine– Norepinephrine (Noradrenaline)– Epinephrine (Nopepinephrine)

catechol

Precursor• Tyrosine: amino acid found in many

foods including cheese & dairy products

Biosynthesis

• Rate limiting (TH): controls production, found in axons

Biosynthesis

• L-DOPA: L-3,4-dihydroxyphenylalanine

Parkinson’s Disease

• Progressive neurodegenerative disease• Described by James Parkinson in 1817• Idiopathic (pesticides, genetics)• Prevalence: 3% of 65+ (500,000!)• Symptoms: resting tremor, pill rolling, slowness of

movement• Tx: L-DOPA + peripheral AADC-I

1 min: http://www.youtube.com/watch?v=_L_WF6gv5BI3 min: http://www.youtube.com/watch?v=ZHRT0uUo7Qs

1755-1824

Thanks, home chemists!

• Barry Kidston develops Parkinson’s after synthesizing MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)

• Later cases were described as:– “Three of the four patients were hospitalized with 14 days

to 6 weeks of first use of the drug. Examination in each revealed near total immobility, marked generalized increase in tone, a complete inability to speak intelligibly, marked diminution of blinking, fixed stare, constant drooling”

– Stopping L-DOPA resulted in “complete immobility & rigidity, being only able to move his eyes”

Langston et al. (1983). Science, 219, 979-980.

MPTP= Parkinson’s model

Parkinson’s Disease Normal

Immunocytochemistry for tyrosine hydroylase in rhesusmonkeys

Masilamoni et al. (2011). Brain, 134, 2057-2073.

Dopamine Release

• VMAT2: vesiciular monoamine transporter, packages DA into vesicle

• Dopamine Transporter (DAT): found on cell membrane, recycles dopamine

• Receptor Families:– D1: – D2:

Dopamine Transmission

• VMAT2: vesiciular monoamine transporter, packages DA into vesicle

• DAT: Dopamine Transporter, found on cell membrane, recycles dopamine

• Receptor Families:– D1: D1 & D5

– D2: D2 D3 D4

Dopamine Neuroanatomy 1Mesocortical

• Label: Soma-Axon Location, Mesencephalon-Cortex• Important for Schizophrenia

Dopamine Neuroanatomy 2Mesolimbic

• Limbic: amygdala, hippocampus, nucleus accumbens• Important for Drug-Abuse

Dopamine Neuroanatomy 3Nigrostriatal

• Nigro: substantia nigra• Striatum: caudate and putamen• Important for movement

Embryonic Transplants: An (Overly?)Optimistic Therapy

Dopaminergic DrugsDrug Mechanism

Resperine VMAT inhibitor (irreversible)

AMPT Inhibits tyrosine hydroxylase

6-OHDA Destroys DA (& NE) neurons

SCH 23390 D1 antagonist

Haloperidol D2 antagonist

Cocaine Inhibits reuptake of DA (& NE)

methylphenidate Inhibits reuptake of DA (& NE)

Rauvolfia serpentina(snakeroot)

Tyrosine hydroylase staining following6-OHDA lesion of left-fibers of nigro-striatal pathway.

Norepinephrine Synthesis

Adrenergic Receptors

• α : α1 α2

• β : β1 β2

Functions of Norepinephrine

Catecholamine Inactivation

NET (norepinephrine transporter): membrane boundMAO (monoamine oxidase): found in neurons & gliaCOMT (catechol-O-methyl-transferase): intracellular & extracellular

ADHD Inattention• Symptoms present at school/work and home• 6+ symptoms that have persisted 6+ months

and are inconsistent with developmental level– Often fails to give close attention or makes careless

mistakes at school or at work.– Has difficulty sustaining attention in tasks or play.– Does not listen when spoken to directly.– Often does not follow through on instructions.– Has difficulty organizing activities.– Is easily distracted.– Is often forgetful in daily activities.

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ADHD: Hyperactive-Impulsive• Symptoms present at school/work and home• 6+ symptoms that have persisted 6+ months

and are inconsistent with developmental level– Often fidgets with hands or feet, leaves seat

when staying seated is expected, runs or climbs excessively

– Often blurts answer before ? completed– Has difficulty waiting turn– Often interrupts others

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“Peculiar” Effects of Methylphenidate in Adolescents

• Ritalin (Schedule II) is FDA approved for narcolepsy & ADHD

• Pharmacological MRI was conducted in adolescent (PD35) and adult rats (PD 60+)

Canese et al. (2009). Psychopharm, 203, 143-153.

Summary

• Synthesis (TH, AADC)• Breakdown (DAT/NET, VMAT, MAO, COMT)• Receptors – D1 D2– α β

Is crystal methamphetamine the new crack?

• Q) Is methamphetamine a national epidemic?• Q) Are there similarities between meth &

crack?

http://www.justicetalking.org/ShowPage.aspx?ShowID=5760-29:20

Dopamine Methamphetamine