Neurotransmitters and Drugs of Abuse (Kaufman Ch 21)
Summarized by Dean Beebe
Dopamine
Synthesis and Metabolism
Phenylalanine 
Tyrosine

DOPA

Dopamine (DA)
Anatomy
 Synthesized mainly in neurons located in the ventral midbrain (substantia nigra pars compacta & ventral
tegmental area)
 Three projection systems:
o nigrostriatal pathway: substantia nigra to caudate and putamen (implicated in Parkinson’s)
o mesolimbic pathway: midbrain to limbic structures (implicated in positive sx of psychosis)
o mesocortical pathway: midbrain to prefrontal cortex (implicated in working memory and other
executive skills and cognitive deficits and negative symptoms of Schizophrenia)
Conditions Due to Deficits in Dopamine Synthesis
 Phenylketonuria (PKU)
o Inherited disorder of enzyme that breaks down phenylalanine into tryrosine
o Result: excessive phenylalanine (excreted in urine) and dopamine depletion
o If not put on very low phenylalanine diet, will develop MR. Even on diet, executive fxn deficits occur.
 Parkinson’s Disease
o Deficit in conversion of precursors into DOPA, which results in diminished DA
o Involuntary movement disorder with both “positive symptoms” (e.g., tremor, especially when on LDopa), and “negative symptoms” (e.g., bradyphrenia, bradykinesia)
o Treated with L-Dopa (which boosts DOPA levels), drugs that reduce L-Dopa metabolism outside of the
CNS (which allows for lower L-Dopa doses and fewer systemic side effects), or DA agonists
Conditions Due to Excessive Dopamine Activity
 Synthetic Causes: Excessive L-dopa, Cocaine, Amphetamines
 Endogenous Causes: tardive dyskinesia (probable increased DA sensitivity due to antipsychotics)
 Result: Visual hallucinations, psychosis, hyperkinetic movement disorders (e.g., dystonia, chorea)
Norepinephrine (also called noradrenaline or NA) and Epinephrine
Synthesis and Metabolism
Dopamine
 Norepinephrine

Epinephrine
Anatomy
 NA synthesized primarily in locus curuleus (located near fourth ventricle in the rostral/dorsal pons)
 Projects to the entire forebrain through the thalamus
 Ascending norepinephrine projection system implicated in modulation of attention, sleep-wake states, mood
 Epinephrine synthesized in adrenal gland
 Outside CNS, major neurotransmitters in the sympathetic nervous system
Related Disorders
 ADHD: psychostimulant or SNRI (Strattera) tx enhances noradrenergic transmission and/or reduces reuptake
 Neuronal depletion of locus curuleus in Parkinson’s can lead to depression and sleep disorders
 noradrenergic transmission also seems to be important in mood disorders including depression and bipolar and
anxiety disorders
 NA depletion can result in orthostatic hypotension and other symptoms of reduced sympathic n. system activity
 Excessive NA causes tremor, sympathetic nervous system overactivity (e.g., bronchodilation, arterial dilation)
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study notes make no promises as to the complete accuracy of the material, and invite you to suggest changes.
Serotonin
Synthesis and Metabolism
Tryptophan  5-Hydrotryptophan  Serotonin (5-Hydrotryptamine or 5-HT)
Anatomy
 Synthesized in dorsal raphe nuclei of the midbrain and pons
 Projects to entire forebrain including cortex, thalamus, and basal ganglia
 Many different receptor types result in a variety of symptoms/behaviors associated with 5-HT disorders
Related Disorders
 Low 5-HT  depression, anxiety, OCD. Also found in Parkinson’s (esp. if depressed) and Alzheimer’s
 Excessive 5-HT  LSD and Ecstacy are serotonin agonists that cause psychosis and hallucinations
Acetylcholine
Synthesis and Metabolism
Acetyl CoA + Choline  Acetylcholine (ACh)
Anatomy
 Synthesized mainly in nucleus basalis of Meynert and adjacent nuclei in the basal forebrain
 Two kinds of receptors
o Nicotinic: involved almost exclusively at neuromuscular junction
o Muscarinic: involved in cerebral cortex (especially in arousal and memory functioning)
Related Disorders
 Alzheimer’s Disease: Deterioration of nucleus basalis of Meynert implicated in memory dysfunction.
Anticholinesterases (e.g., Cognex, Aricept) show some effectiveness in slowing progression a bit
 Botox inhibits Ach release from presynaptic neuron, resulting in localized loss of muscle tone
 Neuroleptics can cause anticholinergic side effects (e.g., confusion, drowsiness, dry mouth); those that tend to
produce the least extrapyramidal symptoms (see DA, above) tend to have more anticholinergic side effects
Glutamate
Synthesis and Metabolism
Glutamine  Glutamate
Anatomy
 Major excitatory amino acid; NMDA receptor modulates Calcium channel flow
 Projects throughout CNS
Related Disorders
 Excessive Glutamate causes excitotoxicity, a probable cause of cell death in TBI, stroke, other disorders
Gamma-Aminobutyric Acid (GABA)
Synthesis and Metabolism
Glutamate  GABA
Anatomy
 Major inhibitory transmitter; opens Chloride (Cl-) channels and closes Calcium channels, hyperpolarizing cells
 Widespread in entire CNS, but highest in striatum, hypothalamus, spinal cord, temporal lobes
Related Disorders
 GABA deficiency implicated in epilepsy and, sometimes, chorea
 Many antiepileptic medications increase GABA activity
THE FINE PRINT: Caveat emptor! These study materials have helped many people who have successfully completed the ABCN board certification process,
but there is no guarantee that they will work for you. The notes’ authors, web site host, and everyone else involved in the creation and distribution of these
study notes make no promises as to the complete accuracy of the material, and invite you to suggest changes.
Several Drugs of Abuse (not including alcohol)
Cocaine
Pharmacology
 CNS Stimulant
 Blocks re-uptake of DA, NA, and serotonin, while also causing release of DA into synaptic cleft
Desired Effects: Euphoria, Increased vigilance
Overdose
 Agitation, paranoia, delusions, hallucinations
 Strokes (or heart attacks) and seizures
 Long-term use: involuntary movement disorders (e.g., “crack dancing”: inability to stand still)
Withdrawal
 Emotional “crash”: dysphoria, anhedonia, strong craving for drug
 Rebound of REM sleep (which was suppressed while on drug), resulting in vivid, disturbing dreams
Amphetamine
Pharmacology
 CNS Stimulant, lasting much longer than cocaine
 Blocks re-uptake of DA while also causing release of DA into synaptic cleft
Desired Effects: Euphoria, Increased vigilance (many ADHD drugs are amphetamines or amphetamine-like)
Overdose
 Paranoia, delusions, hallucinations
 Strokes (or heart attacks) and seizures
 Long-term use: involuntary movement disorders
Withdrawal
 Emotional “crash”: dysphoria, anhedonia, strong craving for drug
 Rebound of REM sleep (which was suppressed while on drug), resulting in vivid, disturbing dreams
Opioids
Pharmacology
 Can affect DA and other neurotransmitters, but primary effect at opiate receptors
Desired Effects: Pain reduction, anxiety reduction, sleepiness
Overdose
 Coma, “pin-point pupils” (miosis), and respiratory depression
 Cerebral hypoxia
 Rarely associated with seizures or cerebral hemorrhages
Withdrawal
 Strong craving for drug
 Dysphoria, autonomic hyperactivity
PCP (Phencyclidine)
Pharmacology
 Central analgesic, depressant, and hallucinogen
 Blocks re-uptake of DA, NA, and serotonin, prevents glutamate from activating NMDA receptor
Desired Effects: Low doses like alcohol use, higher doses cause both positive and negative sx of schizophrenia
Overdose
 Muscle rigidity, vertical nystagmus, stereotypies, blank stare, unresponsiveness
 Seizures that can lead to status epilepticus
 Violent, psychotic behavior
Marijuana (especially the THC in it)
Pharmacology: Affects THC receptors in cortex, basal ganglia, hippocampus, and cerebellum
Desired effects: calming, reduced nausea or vomiting, mood elevation
Negative effects: slowed mentation; sedation; sometimes hallucinations at high doses; sometimes lasting
inattention, fluency problems, or impaired executive functioning