PSYC 4309 Ch. 5 Catecholamines

Catecholamines

Group of neurotransmitters and hormones characterized by two chemical similarities: a core structure of catechol and a nitrogen-containing amine. They belong to a wider group of transmitters called monoamines or biogenic amines.

Monoamine

Refers to a compound or transmitter that contains a single amine group.

Biogenic amine

A transmitter that is made by a living organism and contains at least one amine group.

Dopamine (DA)

Neurotransmitter, related to NE and EPI, that belongs to a group called catecholamines.

Dopaminergic

Adjectival form of DA.

Noradrenergic

Adjectival form of noradrenaline (norepinephrine).

Adrenergic

Adjectival form of adrenaline, also called epinephrine (EPI). May be used broadly to include both NE- and EPI-related features.

Tyrosine

Amino acid characterized by a phenol group. It is a precursor for the synthesis of the catecholamine neurotransmitters.

Tyrosine hydroxylase

Enzyme that catalyzes the first step of catecholamine synthesis in neurons, the conversion of tyrosine to DOPA.

AADC (aromatic amino acid decarboxylase)

Enzyme that catalyzes the removal of a carboxyl group from certain amino acids. It is responsible for the conversion of DOPA to DA in catecholaminergic neurons and the conversion of 5-HTP to 5-HT in serotonergic neurons.

Dopamine beta-hydroxylase (DBH)

Enzyme that catalyzes the third step of NE synthesis in neurons, the conversion of DA to NE.

Vesicular monoamine transporter (VMAT)

Vesicle membrane protein that transports monoamines (i.e., catecholamines and 5-HT) into synaptic vesicles. Monoamine neurons express a particular form of _________ called _________2, whereas the epinephrine- and norepinephrine-secreting chromaffin cells of the adrenal medulla express a different form called _________1.

Reserpine

It inhibits vesicular monoamine uptake by VMAT, thereby reducing monoamine levels in the central and peripheral nervous system.

Amphetamine

Psychostimulant that acts by increasing catecholamine release in nerve cells.

albuterol

Drug that selectively stimulates the β-adrenoceptor. It is used in asthma treatments.

AMPT (alpha-methyl-para-tyrosine)

Drug that inhibits TH activity, thereby reducing catecholamine synthesis.

apomorphine

Drug that is a D1 and D2 receptor agonist and causes behavioral activation. It may also be used to treat erectile dysfunction by acting through DA receptors in the brain to increase penile blood flow.

atomoxetine

Selective norepinephrine uptake inhibitor used in the treatment of ADHD.

behavioral supersensitivity

An increased response to a drug treatment as a direct result of previous drug history or drug intake.

catalepsy

State characterized by a lack of spontaneous movement. It is usually associated with D2 receptor blockers (a DA receptor subtype), but can also be induced with a D1 blocker.

Catechol-O-methyltransferase (COMT)

One of the enzymes responsible for metabolic breakdown of catecholamines.

clonidine

An α2-adrenergic agonist that stimulates autoreceptors and inhibits noradrenergic cell firing. It is used to reduce symptoms of opioid withdrawal.

coacaine

Stimulant drug that blocks reuptake of DA, NE, and 5-HT by neurons, thereby increasing their concentration in the synaptic cleft.

DA transporter (DAT)

Protein in the membrane of dopaminergic neurons that is responsible for DA uptake from the synaptic cleft.

dexmedetomidine (Precedex)

Drug that stimulates α2-receptors, characterized by its sedative, anxiolytic, and analgesic effects. It is used to treat surgical patients in intensive care.

entacapone (Comtan)

COMT inhibitor used in conjunction with l-DOPA to treat Parkinson's disease.

guanfacine (Intuniv)

α2A-adrenergic agonist prescribed for the treatment of ADHD. is believed to improve attention and memory by stimulating α2A-adrenergic receptors in the prefrontal cortex.

haloperidol (haldol)

A D2 receptor blocker that can induce catalepsy in animals when administered in high doses. It is used clinically as an antipsychotic agent.

Homovanillic acid (HVA)

Major metabolite formed in the breakdown of DA.

6-hydroxydopamine (6-OHDA)

Neurotoxin similar in structure to DA that damages catecholaminergic nerve terminals and is used to study catecholamine pathways.

isoproterenol

An agonist at β-adrenergic receptors.

L- DOPA

Precursor necessary for the synthesis of DA. L-DOPA is formed by the addition of a hydroxyl group to tyrosine by the enzyme TH. It is used to treat Parkinson's disease by increasing DA formation.

Locus coeruleus (LC)

Collection of noradrenergic neurons in the reticular formation of the pons that supplies most of the NE to the cortex, limbic system, thalamus, and hypothalamus. These cells cause arousal and increased attention when active.

MAO inhibitors (MAOIs)

Class of drugs that inhibit monoamine oxidase (MAO), thereby causing an accumulation of catecholamines and serotonin in the brain. They are often used to treat clinical depression.

mesocortical dopamine pathway

Group of dopaminergic axons that originates in the VTA and travels to the cerebral cortex, including the prefrontal, cingulated, and entorhinal cortices.

Mesolimbic dopamine pathway

Group of dopaminergic axons that originates in the VTA and travels to structures of the limbic system, including the nucleus accumbens, septum, amygdala, and hippocampus. It may also be called the mesolimbic tract.

metabolites

Byproducts of biochemical pathways, such as those involved in neurotransmitter or drug inactivation.

methamphetamine

Psychostimulant that acts by increasing catecholamine release from nerve terminals. It can also cause neurotoxicity at high doses.

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

Dopamine neurotoxin sometimes used to produce an animal model of Parkinson's disease.

3-methoxy-4-hydroxy-phenylglycol (MHPG)

A metabolite of NE, formed primarily as a result of NE breakdown in the brain.

Metoprolol

Drug that selectively blocks the β1-receptor, limiting contraction of the heart muscles. It is useful for treating hypertension.

monoamine oxidase (MAO)

Enzyme responsible for metabolic breakdown of catecholamines and serotonin.

ligands

Molecule that selectively binds to a receptor.

neurotoxin

Chemical that damages or kills nerve cells.

nigrostriatal tract

Dopaminergic nerve tract originating at the substantia nigra and terminating in the stratum. It is important for regulation of movement and is severely damaged in Parkinson's disease.

passive avoidance learning

Type of learning task in rats and mice in which the animal is trained to avoid a location that it would normally enter (e.g., going into a dark compartment from one that is brightly lit) by administeration of a brief electric footshock when it enters the location. The word "passive" in the name of the task reflects the fact that the animal must withhold its usual response of moving into the dark compartment.

Phenelzine (Nardil)

MAO inhibitor used to treat clinical depression.

phenylephrine

α1-receptor agonist that causes behavioral stimulation.

prazosin (minipress)

α1-receptor antagonist that causes dilation of blood vessels and is useful for treating hypertension.

propranolol (inderal)

β-receptor antagonist. It is useful for treating hypertension due to its ability to block β-receptors in the heart, thereby limiting contraction of the heart muscles.

rate-limiting enzyme

Enzyme that catalyzes the slowest step in a biochemical pathway. It determines the overall rate of product formation.

reboxetine

Antidepressant that selectively blocks the NE transporter, thereby increasing NE concentration in the synaptic cleft.

receptor up-regulation

Increase in the number of receptors produced and maintained in a target cell.

SCH 23390

D1 receptor antagonist that may induce catalepsy when administered in high doses.

stereotyped behaviors

Repeated, relatively invariant behaviors associated with a particular situation or drug treatment. They often occur following a high dose of a psychostimulant such as cocaine or amphetamine.

substantia nigra

Collection of dopaminergic cell bodies within the tegmentum of the mesencephalon that innervate the striatum by way of the nigrostriatal tract. Damage to cells in this region leads to Parkinson's disease.

Tolcapone (Tasmar)

COMT inhibitor used in conjunction with l-DOPA to treat Parkinson's disease.

tranylcypromine (Parnate)

MAO inhibitor used to treat clinical depression.

tricyclic antidepressants

Class of antidepressants characterized by a three-ring structure. They block reuptake of NE and 5-HT, thereby increasing their concentration in the synaptic cleft.

tuberohypophyseal dopamine pathway

Pathway that controls the secretion of the hormone prolactin by the pituitary gland.

vanillymandelic acid (VMA)

Metabolite of NE, formed primarily by NE breakdown in the peripheral nervous system.

Ventral tegmental area (VTA)

Region containing dopaminergic cell bodies within the tegmentum of the mesencephalon (midbrain) that form the mesolimbic and mesocortical tracts.

yohimbine

α2-antagonist that blocks autoreceptors and increases noradrenergic cell firing. It enhances symptoms of opioid withdrawal.